Humboldt-Universität zu Berlin - Mathematisch-Naturwissenschaftliche Fakultät - Prof. Rademann


165. "Mechanochemical synthesis of cerium(IV)-phosphonates", Wilke M., Akhmetova I., Rademann K., Emmerling F., JOURNAL OF MATERIALS SCIENCE, 2018, Vol 53 (19), 13733 - 13741. 


164. "Synthesis, characterization and in situ monitoring of the mechanochemical reaction in process of two manganese (ii)-phosphonates with N-containing ligands", Akhmetova I., Schutjajew K., Wilke M., Buzanich A., Rademann K., Roth C., Emmerling F., JOURNAL OF MATERIALS SCIENCE, 2018, Vol 53 (19), 13390 - 13399. 


163. "Functionalized Cellulose for Water Purification, Antimicrobial Applications, and Sensors", Bethke K., Palantöken S., Andrei V., Roß M., Raghuwanshi V. S., Kettemann F., Greis K., Ingber T.T.K., Stückrath J. B., Valiyaveettil S., Rademann K., ADVANCED FUNCTIONAL MATERIALS, 2018, Vol 28 (23), art. no. 1800409.    


162. "Eckart Rühl zum 60. Geburtstag", Graf C., Baumgärtel H., Rademann K., ZEITSCHRIFT FÜR PHYSIKALISCHE CHEMIE, 2018.


161. "In Situ Investigations of Mechanochemical One-Pot Syntheses", Kulla H., Haferkamp S., Akhmetova I., Röllig M., Maierhofer C., Rademann K., Emmerling F., ANGEWANDTE CHEMIE - INTERNATIONAL EDITION, 2018, Vol 57 (20), 5930-5933.


160. "Unifying Concepts in Room-Temperature CO Oxidation with Gold Catalysts", Kettemann F., Witte S., Birnbaum A., Paul B., Clavel G., Pinna N., Rademann K., Kraehnert R., Polte J., ACS CATALYSIS, 2017, Vol 7 (12), 8247-8254. 


159. "Crystal structure and in situ investigation of a mechanochemical synthesized 3D zinc N-(phosphormethyl)glycinate", Wilke M., Kabelitz A., Zimathies A., Rademann K., Emmerling F.,  JOURNAL OF MATERIALS SCIENCE, 2017, Vol 52 (20), 12013-12020.


158. "In Situ Complementary Doping, Thermoelectric Improvements, and Strain-Induced Structure within Alternating PEDOT:PSS/PANI Layers", Andrei V., Bethke K., Madzharova F., Bronneberg A.C., Kneipp J., Rademann K., ACS APPLIED MATERIALS AND INTERFACES, 2017, Vol 9 (38), 33308-33316.


157. "Fabrication and Charakterization of Surfaces Modified with Carboxymethylthio Ligands for Chelate-Assisted Trapping of Copper", Adongo J. O., Neubert T.J., Sun G., Janietz S., Lauermann I., Rademann K., Rappich J., ACS APPLIED MATERIALS AND INTERFACES, 2017, Vol 9 (28), 24273-24281. 


156. "Impact Is Important - Systematic Investigation of the Influence of Milling Balls in Mechanochemical Reactions", Fischer F., Fendel N., Greiser S., Rademann K., Emmerling F., ORGANIC PROCESS AND RESEARCH DEVELOPMENT, 2017, Vol 21 (4), 655-659. 


155. "Bringing Catalysis with Gold Nanoparticles in Green Solvents to Graduate Level Students", Raghuwanshi V.S., Wendt R., O'Neill M., Ochmann M., Som T., Fenger R., Rademann K., Hoell A., Mohrmann M., JOURNAL OF CHEMICAL EDUCATION, 2017, Vol 94 (4), 510-514. 


154. "Knowing When to Stop - Trapping Metastable Polymorphs in Mechanochemical Reactions", Kulla H., Greiser S., Benemann S., Rademann K., Emmerling F., CRYSTAL GROWTH AND DESIGN, 2017, Vol 17 (3), 1190-1196.


153. "Quantitative NMR spectroscopy for gas analysis for production of primary reference gas mixtures", Meyer K., Rademann K., Panne U., Maiwald M., JOURNAL OF MAGNETIC RESONANCE, 2017, Vol 275, 1-10.


152. "Control of organic polymorph formation: Crystallization pathways in acoustically levitated droplets", Nguyen T.Y., Roessler E.A., Rademann K., Emmerling F., ZEITSCHRIFT FÜR KRISTALLOGRAPHIE - CRYSTALLINE MATERIALS, 2017, Vol 232 (1-3), 15-24.


151. "Size Dependence of Electrical Conductivity and Thermoelectric Enhancements in Spin-Coated PEDOT:PSS Single and Multiple Layers", Andrei V., Bethke K., Madzharova F., Beeg S., Knop-Gericke A., Kneipp J., Rademann K., ADVANCED ELECTRONIC MATERIALS, 2017, Vol 3 (2), art. no. 1600473.


150. "The effect of the ball to reactant ratio on mechanochemical reaction times studied by: In situ PXRD"; Kulla H., Fischer F., Benemann S., Rademann K., Emmerling F., CRYST ENG COMM, 2017, Vol 19 (28), 3902 - 3907.


149. "Versatile H2=2-driven mixed aerogel synthesis from CdTe and bimetallic noble metal nanoparticles"; Wendt R., Märker B., Dubavik A., Herrmann A.-K., Wollgarten M., Rakovich Y. P., Eychmüller A., Rademann K., Hendel T., JOURNAL OF MATERIALS CHEMISTRY C, 2017, Vol 5 (39), 10251 - 10259.


148. "Quantitative NMR spectroscopy for gas analysis for production of primary reference gas mixtures."; Meyer K., Rademann K., Panne U., Maiwald M., JOURNAL OF MAGNETIC RESONANCE, 2017, Vol 275, 1-10.


147. "Missing piece of the mechanism of the Turkevich method: the critical role of citrate protonation."; Kettemann F., Birnbaum A., Witte S., Wuithschick M., Pinna N., Kraehnert R., Rademann K., Polte J., CHEMISTRY OF MATERIALS, 2016, Vol 28, 4072-4081.


146. "In situ investigation of a self-accelerated cocrystal formation by grinding pyrazinamide with oxalic acid."; Kulla H., Benemann S., Rademann K., Emmerling F.; MOLECULES, 2016, Vol 21.


145. "Quantitative determination of activation energies in mechanochemical reactions"; Fischer F., Wenzel K.-J., Rademann K., Emmerling F.; PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 2016, Vol 18, 23320 - 23325. 


144. "Supply and demand in the ball mill: competitive cocrystal reactions"; Fischer F., Lubjuhn D., Greiser S., Rademann K., Emmerling F.; CRYSTAL GROWTH, 2016, Vol 16, 5843 - 5851.  


143. "Mechanochemical induced conversion of crystalline benzamide polymorphs"; Fischer F., Greiser S.; Pfeifer D., Jager C., Rademann K., Emmerling F.; ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 2016, Vol 55, 14279 - 14283.


142. "The crystallisation of copper(II)phenylphosphonates"; Wilke M., Kabelitz A., Gorelik T., Buzanich A., Reinholz U., Kolb U., Rademann K., Emmerling F.; DALTON TRANSACTIONS, 2016, Vol 45, 17453 - 17463.

141. "The structure and in situ synthesis investigation of isomorphic
mononuclear molecular metal phenylphosphonates"; Wilke, Manuel; Buzanich, Ana Guilherme; Reinholz, Uwe; Rademann, Klaus; Emmerling, Franziska; DALTON TRANSACTIONS, 2016, Vol 45. 

140. "Adjusting the thermoelectric properties of copper(I) oxide-graphite-polymer pastes and the applications of such flexible composites"; Andrei, Virgil; Bethke, Kevin; Rademann, Klaus; PHYSICAL CHEMISTRY CHEMICAL PHYSICS; 2016; Vol 18, 10700 - 10707.

139. "Strong-field photoemission in nanotip near-fields: From quiver to
sub-cycle electron dynamics"; Echternkamp, K. E.; Herink, G.; Yalunin, S. V.; Rademann, K.; Schaefer, S.;  Ropers, C.; APPLIED PHYSICS B-LASERS AND OPTICS; 2016; Vol 122.

138. "Decreasing the effective thermal conductivity in glass supported thermoelectric layers"; Bethke, Kevin; Andrei, Virgil; Rademann, Klaus; PLOS ONE; 2016; Vol 11.

137. "Polymorphism of mechanochemically synthesized cocrystals: A case study"; Fischer, Franziska; Heidrich, Adrian; Greiser, Sebastian; Benemann, Sigrid; Rademann, Klaus; Emmerling, Franziska; CRYSTAL GROWTH & DESIGN, 2016, Vol. 16.

136. "Thermoelectricity in the context  of renewable energy sources: joining forces instead of competing"; Andrei, Virgil; Bethke, Kevin; Rademann, Klaus; ENERGY & ENVIRONMENTAL SCIENCE; 2016, Vol 9, 1528 - 1532.

135. "Cadmium phenylphosphonates: preparation, characterisation and in situ
investigation"; Wilke, Manuel; Batzdorf, Lisa; Fischer, Franziska; Rademann, Klaus; Emmerling,    Franziska;  RSC ADVANCES; 2016, Vol 6, 2046 - 2069.

134. "Fast and efficient synthesis of a host guest system: a mechanochemical
approach"; Wilke, Manuel; Klimakow, Maria; Rademann, Klaus; Emmerling, Franziska; CRYSTENGCOMM, 2016, Vol 18, 1096 - 1100.

133. "Survival of the fittest: Competitive co-crystal reactions in the ball mill", Fischer, Franziska; Joester, Maike; Rademann, Klaus; Emmerling, Franziska;
CHEMISTRY-A EUROPEAN JOURNAL, 2015, Vol 21, 14969 - 14974.

132. "Illustrating the formation of metal nanoparticles with a growth concept based on colloidal stability", Wuithschick, M.; Witte, S., Kettemann, F., Rademann, K., Polte, J., PHYSICAL CHEMISTRY CHEMICAL PHYSICS 2015, Vol 17, 19895-19900


131. "Reliable palladium nanoparticle syntheses in aqueous solution: the importance of understanding precursor chemistry and growth mechanism", Kettemann, Frieder; Wuithschick, Maria; Caputo, Gianvito; Kraehnert, Ralph; Pinna, Nicola; Rademann, Klaus; Polte, Joerg; CRYSTENGCOMM; 2015; Vol 17; 1865 - 1870.


130. "Turkevich in new robes: Key questions answered for the most common gold nanoparticle synthesis"; Wuithschick, Maria; Birnbaum, Alexander; Witte, Steffen; Sztucki, Michael;    Vainio, Ulla; Pinna, Nicola; Rademann, Klaus; Emmerling, Franziska; Kraehnert, Ralph;    Polte, Joerg; ACS NANO, 2015, Vol. 9; 7052 - 7071.

129. "Fragmentation mechanism of the generation of colloidal copper(I) iodide nanoparticles by pulsed laser irradiation in liquids"; Schaumberg, Christian Alexander; Wollgarten, Markus; Rademann, Klaus; PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 2015, Vol. 17; 17934 - 17938.

128. "In situ determination of colloidal gold concentrations with UV-Vis spectroscopy: Limitations and perspectives", Hendel, Thomas; Wuithschick, Maria; Kettemann, Frieder; Birnbaum, Alexander; Rademann, Klaus; Polte, Joerg;  2015; Vol. 87, 5846 - 5847.  

127. "Experimental crystal structure determination"; Fischer, Franziska; Joester, Maike; Rademann, Klaus; Emmerling, Franziska; Cambridge Structural Database, 2015.

126. "Direct evidence of polyamorphism in paracetamol", Yen Nguyen Thi; Rademann, Klaus; Emmerling, Franziska; CRYSTENGCOMM, 2015; Vol 17; 9029 - 9036.

125. "Controlled pore formation on mesoporous single crystalline silicon nanowires: Threshold and mechanisms" Weidemann, Stefan; Kockert, Maximilian; Wallacher, Dirk; Ramsteiner, Manfred; Mogilatenko, Anna; Rademann, Klaus; Fischer, Saskia F.; JOURNAL OF NANOMATERIALS; 2015.

124. "Gold nanoparticles in novel green deep eutectic solvents: Self-limited growth, self-assembly & catalytic implications" O'Neill, Maeve; Raghuwanshi, Vikram Singh; Wendt, Robert; Wollgarten, Markus; Hoell, Armin; Rademann, Klaus; ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS; 2015; VL 229, 221 - 234.

123. "Self-assembly of gold nanoparticles on deep eutectic solvent (DES) surfaces" V. S. Raghuwanshi, M. Ochmann, F. Polzer, A. Hoell, K. Rademann, Chem. Comm. 2014, Vol 50, 8693-8696Self-assembly of gold nanoparticles was obtained by sputter deposition on DES. SAXS and TEM investigations reveal the formation of spherical nanoparticles with a mean diameter of 5 ± 0.5 nm. For extended sputtering times, the number density of AuNPs increases linearly and a very pronounced 1st and 2nd shell ordering is observed.

122. "Deep eutectic solvents for the self-assembly of gold nanoparticles: A SAXS, UV-Vis, and TEM Investigation" V. S. Raghuwanshi, M. Ochmann, A. Hoell, F. Polzer, K. Rademann, Langmuir 2014, Vol 30, 6038-6046In this work, we report the formation and growth mechanisms of gold nanoparticles (AuNPs) in eco-friendly deep eutectic solvents (DES; choline chloride and urea). AuNPs are synthesized on the DES surface via a low-energy sputter deposition method. Detailed small angle X-ray scattering (SAXS), UV–Vis, and cryogenic transmission electron microscopy (cryo-TEM) investigations show the formation of AuNPs of 5 nm diameter. Data analysis reveals that for a prolonged gold-sputtering time there is no change in the size of the particles. Only the concentration of AuNPs increases linearly in time. More surprisingly, the self-assembly of AuNPs into a first and second shell ordered system is observed directly by in situ SAXS for prolonged gold-sputtering times. The self-assembly mechanism is explained by the templating nature of DES combined with the equilibrium between specific physical interaction forces between the AuNPs. A disulfide-based stabilizer, bis((2-mercaptoethyl)trimethylammonium) disulfide dichloride, was applied to suppress the self-assembly. Moreover, the stabilizer even reverses the self-assembled or agglomerated AuNPs back to stable 5 nm individual particles as directly evidenced by UV–Vis. The template behavior of DES is compared to that of nontemplating solvent castor oil. Our results will also pave the way to understand and control the self-assembly of metallic and bimetallic nanoparticles.

121. "Graphene oxide/alpha-Bi2O3 composites for visible-light photocatalysis, chemical catalysis, and solar energy conversion."
T. Som, G. V. Troppenz, R. Wendt, M. Wollgarten, J. Rappich, F. Franziska, K. Rademann, ChemSusChem 2014, Vol 7, 854-865The growing challenges of environmental purification by solar photocatalysis, precious-metal-free catalysis, and photocurrent generation in photovoltaic cells receive the utmost global attention. Here we demonstrate a one-pot, green chemical synthesis of a new stable heterostructured, ecofriendly, multifunctional microcomposite that consists of alpha-Bi2 O3 microneedles intercalated with anchored graphene oxide (GO) microsheets (1.0 wt%) for the above-mentioned applications on a large economical scale. The bare alpha-Bi2 O3 microneedles display two times better photocatalytic activities than commercial TiO2 (Degussa-P25), whereas the GO-hybridized composite exhibits approximately four to six times enhanced photocatalytic activities than the neat TiO2 photocatalyst in the degradation of colored aromatic organic dyes (crystal violet and rhodamine 6G) under visible-light irradiation (300 W tungsten lamp). The highly efficient activity is associated with the strong surface adsorption ability of GO for aromatic dye molecules, the high carrier acceptability, and the efficient electron-hole pair separation in Bi2 O3 by individual adjoining GO sheets. The introduction of Ag nanoparticles (2.0 wt%) further enhances the photocatalytic performance of the composite over eightfold because of a plasmon-induced electron-transfer process from Ag nanoparticles through the GO sheets into the conduction band of Bi2 O3 . The new composites are also catalytically active and catalyze the reduction of 4-nitrophenol to 4-aminophenol in the presence of borohydride ions. Photoanodes assembled from GO/alpha-Bi2 O3 and Ag/GO/alpha-Bi2 O3 composites display an improved photocurrent response (power conversion efficiency 20% higher) over those prepared without GO in dye-sensitized solar cells.

120. "Size-controlled synthesis of colloidal silver nanoparticles based on mechanistic understanding" M. Wuithschick, B. Paul, R. Bienert, A. Sarfraz, U. Vainio, M. Sztucki, R. Kraehnert, P. Strasser, K. Rademann, F. Emmerling, J. Polte, Chem. Mater. 2013, Vol 25, 4679-4689Metal nanoparticles have attracted much attention due to their unique properties. Size control provides an effective key to an accurate adjustment of colloidal properties. The common approach to size control is testing different sets of parameters via trial and error. The actual particle growth mechanisms, and in particular the influences of synthesis parameters on the growth process, remain a black box. As a result, precise size control is rarely achieved for most metal nanoparticles. This contribution presents an approach to size control that is based on mechanistic knowledge. It is exemplified for a common silver nanoparticle synthesis, namely, the reduction of AgClO4 with NaBH4. Conducting this approach allowed a well-directed modification of this synthesis that enables, for the first time, the size-controlled production of silver nanoparticles 4-8 nm in radius without addition of any stabilization agent.

119. "Cascade catalysis of highly active bimetallic Au/Pd nanoclusters: structure-function relationship investigation using anomalous small-angle X-ray scattering and UV-Vis spectroscopy" S. Haas, R. Fenger, E. Fertitta, K. Rademann, J. Appl. Crystallogr. 2013, Vol 46, 1353-1360Recently, a so-called 'crown-jewel' concept of preparation of Au/Pd-based colloidal nanoclusters has been reported [Zhang, Watanabe, Okumura, Haruta & Toshima (2011). Nat. Mater. 11, 49-52]. Here, a different way of preparing highly active Au/Pd-based nanoclusters is presented. The origin of the increased activity of Au/Pd-based colloidal bimetallic nanoclusters was unclear up to now. However, it is, in general, accepted that in the nanometre range (1-100 nm) the cluster size, shape and composition affect the structural characteristics (e. g. lattice symmetry, unit cell), electronic properties (e. g. band gap) and chemical properties (e. g. catalytic activity) of a material. Hence, a detailed study of the relationship between the nanostructure of nanoclusters and their catalytic activity is presented here. The results indicate that a high surface-to-volume ratio of the nanoclusters combined with the presence of 'both' Au and Pd isolated regions at the surface are crucial to achieve a high catalytic activity. A detailed structure elucidation directly leads to a mechanistic proposal, which indeed explains the higher catalytic activity of Au/Pd-based catalysts compared with pure metallic Au or Pd. The mechanism is based on cascade catalysis induced by a single type of nanoparticle with an intermixed surface of Au and Pd.

118. "Nonuniform friction-area dependency for antimony oxide surfaces sliding on graphite" C. Ritter, M. Z. Baykara, B. Stegemann, M. Heyde, K. Rademann, J. Schroers, U. D. Schwarz, Phys. Rev. B 2013, Vol 88, 045422We present frictional measurements involving controlled lateral manipulation of antimony nanoparticles on graphite featuring atomically smooth particle-substrate interfaces via tapping- and contact-mode atomic force microscopy. As expected from earlier studies, the power required for lateral manipulation as well as the frictional forces recorded during the manipulation events exhibit a linear dependence on the contact area over a wide size range from 2000 nm2 to 120 000 nm2 . However, we observe a significant and abrupt increase in frictional force and dissipated power per contact area at a value of about 20 000 nm2, coinciding with a phase transition from amorphous to crystalline within the antimony particles. Our results suggest that variations in the structural arrangement and stoichiometry of antimony oxide at the interface between the particles and the substrate may be responsible for the observed effect.

117. "Crystal growth rates and molecular dynamics of nifedipine"
T. Gnutzmann, R. Kahlau, S. Scheifler, F. Friedrichs, E. A. Rossler, K. Rademann, F. Emmerling CrystEngComm 2013, Vol 15, 4062-4069The unusually fast crystallization of the organic compound nifedipine has been investigated in detail using different solutions as precursors for the formation of the initial glassy nifedipine films. Starting from these amorphous films the crystallization process was investigated by time-resolved light microscopy at different temperatures around Tg of nifedipine. In all studied cases (acetone, acetonitrile, ethyl acetate, dichloromethane, tetrahydrofuran) the measured mean crystallization rates are, on average, 10000 times higher than rates reported in previous studies. Such high rates cannot be explained by a classical diffusional crystal growth mechanism of nifedipine. Instead, nifedipine shows a strong propensity for diffusionless growth. Solvent assisted or solvent induced preordering of the glassy modification is suggested to be the most probable driving force behind these fast crystallization processes. The nifedipine crystallization rates can be controlled not only by specific solvent–molecule interactions but also by temperature. Below 40 °C, the temperature dependence of the rates is generally small. Above 40 °C, a slowing down of the crystallization rates with increasing temperatures indicates a kinetic competition between different polymorphs. The molecular dynamics of nifedipine molecules in the amorphous phase as well as the relaxation times are studied by dielectric measurements. The dielectric data corroborate the inherently strong propensity of nifedipine to crystallize diffusionlessly under all conditions. PDF

116. "Formation mechanism of silver nanoparticles stabilized in glassy matrices"
A. Simo, J. Polte, N. Pfander, U. Vainio, F. Emmerling, K. Rademann, JACS 2012, Vol 134, 18824-18833In any given matrix control over the final particle size distribution requires a constitutive understanding of the mechanisms and kinetics of the particle evolution. In this contribution we report on the formation mechanism of silver nanoparticles embedded in a soda lime silicate glass matrix. For the silver ion exchanged glass it is shown that at temperatures below 410 degrees C only molecular clusters (diameter <1 nm) are forming which are most likely silver dimers. These clusters grow to nanoparticles (diameter >1 nm) by annealing above this threshold temperature of 410 degrees C. It is evidenced that the growth and thus the final silver nanoparticle size are determined by matrix assisted reduction mechanisms. As a consequence, particle growth proceeds after the initial formation of stable clusters by addition Of silver monomers which diffuse from the glass matrix. This is in contrast to the widely accepted concept of particle growth in metal-glass systems in which it is assumed that the nanoparticle formation is predominantly governed by Ostwald ripening processes. PDF

115. "Pulsed supersonic beams with nucleobases" A. Sarfraz, K. Rademann, W. Christen
Anal Bioanal Chem 2012, Vol 404, 2087–2090The dissolution of the primary nucleobases in supercritical fluids has been investigated using pulsed molecular beam mass spectrometry. Due to the low critical temperatures of ethylene and carbon dioxide, their adiabatic jet expansion permits transferring thermally sensitive solutes into the gas phase. This feature is particularly attractive for pharmaceutical and bio- medical applications. In this study, adenine, guanine, cytosine, thymine, and uracil have been dissolved in supercritical ethylene with a few percent of ethanol as cosolvent. At source temperatures of 313 K, these solutions have been expanded from supercritical pressures into high vacuum using a customized pulsed nozzle. A mass spectrometer was used to monitor the relative amounts of solute, solvent, and cosolvent in the super-sonic beam. The results suggest a paramount influence of the cosolvent. PDF

114. "Near-ideal complete coverage of CD3 onto Si(111) surfaces using one-step electrochemical grafting: An IR ellipsometry, synchrotron XPS, and photoluminescence study" F. Yang, K. Roodenko, R. Hunger, K. Hinrichs, K. Rademann, J. Rappich
J. Phys. Chem. C 2012, Vol 116, 18684−18690A one-step electrochemical grafting process using Grignard reagents has been performed to achieve a complete monolayer methyl-terminated Si(111) surfaces. Anodic treatment (0.5 mA/cm(2) for 300 s) has been applied to atomically flat H-terminated Si(111) surfaces in methylmagnesium bromide (CH3MgBr), methylmagnesium iodide (CH3MgI), and methyl-d(3)-magnesium iodide (CD3MgI) to obtain methylated Si(111) surfaces. Infrared spectroscopic ellipsometry (IRSE) clearly reveals a vibrational shift of the symmetric PDF

113. "Quinaldine: Accessing two crystalline polymorphs via the supercooled liquid"
R. Kahlau, T. Gnutzmann, F. Emmerling, K. Rademann, E. A. Rossler
J. Chem. Phys. 2012, Vol 137, 054505Quinaldine (2-methyl quinoline) is a liquid at room temperature, which can be supercooled to reach finally the glassy state. By heating the glass above the glass transition temperature T-g = 180 K the sample performs two subsequent transitions into, likewise, dielectrically active phases. Thus, the reorientational relaxations of these phases as well as the kinetics of the phase transitions can be tracked in a highly resolved way by dielectric spectroscopy. X-ray diffraction analysis clearly shows two structurally different crystalline phases in addition to the supercooled liquid. Calorimetric measurements support the notion of first order phase transitions, occurring irreversibly in the supercooled regime, and suggest that the intermediate crystalline phase is metastable, too. Analyzing the quite distinct dielectric relaxation strengths, we discuss the possible nature of the two crystalline phases. Additionally, a very similar behavior to quinaldine is observed for 3-methyl quinoline, indicating a broad field of polymorphism among the quinoline derivatives. PDF

112. "Formation mechanism of colloidal silver nanoparticles: Analogies and differences to the growth of gold nanoparticles" J. Polte, X. Tuaev, M. Wuithschick, A. Fischer, A. F. Thuenemann, K. Rademann, R. Kraehnert, F. Emmerling
ACS Nano 2012, Vol 6, 5791-5802The formation mechanisms of silver nanoparticles using aqueous silver perchlorate solutions as precursors and sodium borohydride as reducing agent were investigated based on time-resolved in situ experiments. This contribution addresses two important issues in colloidal science: (i) differences and analogies between growth processes of different metals such as gold and silver and (ii) the influence of a steric stabilizing agent on the growth process. The results reveal that a growth due to coalescence is a fundamental growth principle if the monomer-supplying chemical reaction is faster than the actual particle formation. PDF

111. "Bismuth hexagons: Facile mass synthesis, stability and applications"
T. Som, A. Simo, R. Fenger, G. V. Troppenz, R. Bansen, N. Pfänder, F. Emmerling, J. Rappich, T. Boeck, K. Rademann
ChemPhysChem 2012, Vol 13, 2162-2169A unique direct electrodeposition technique involving very high current densities, high voltages and high electrolyte concentrations is applied for highly selective mass synthesis of stable, isolable, surfactant-free, single-crystalline Bi hexagons on a Cu wire at room temperature. A formation mechanism of the hexagons is proposed. The morphology, phase purity, and crystallinity of the material are well characterized by FESEM, AFM, TEM, SAED, EDX, XRD, and Raman spectroscopy. The thermal stability of the material under intense electron beam and intense laser light irradiation is studied. The chemical stability of elemental Bi in nitric acid shows different dissolution rates for different morphologies. This effect enables a second way for the selective fabrication of Bi hexagons. Bi hexagons can be oxidized exclusively to α-Bi2O3 hexagons. The Bi hexagons are found to be promising for thermoelectric applications. They are also catalytically active, inducing the reduction of 4-nitrophenol to 4-aminophenol. This electrodeposition methodology has also been demonstrated to be applicable for synthesis of bismuth-based bimetallic hybrid composites for advanced applications. PDF

110. "Detecting crystalline non-equilibrium phases on the nanometer scale"
T. Gorelik, A. Sarfraz, U. Kolb, F. Emmerling, and K. Rademann
Cryst. Growth. & Design 2012, Vol 12, 3239-3242.The use of automated electron diffraction (ADT) technique is presented as a novel approach for crystallization studies at the nanometer scale for non-equilibrium phases. Here, ADT was applied to elucidate the structural identity of the recently reported hexagonal morphology of caffeine crystals which grow only on specific surfaces. Caffeine was crystallized from solution on a specially treated TEM carbon grid. The analysis of ADT data revealed that the lattice parameters of these hexagons match those of the high temperature α-form of caffeine. Furthermore, it was observed that in this hexagonal morphology, the α-form remained stable for a prolonged period of time. The stabilization of hexagons can be interpreted in terms of enhanced interactions with the supporting surfaces. PDF

109. "Size dependent catalysis with CTAB-stabilized gold nanoparticles"
R. Fenger, E. Fertitta, H. Kirmse, A. F. Thünemann, K. Rademann
PCCP 2012, Vol 14, 9343-9349.CTAB-stabilized gold nanoparticles were synthesized by applying the seeding-growth approach in order to gain information about the size dependence of the catalytic reduction of p-nitrophenol to p-aminophenol with sodium borohydride. Five different colloidal solutions of stabilized gold nanoparticles have been characterized by TEM, AFM, UV-Vis, SAXS, and DLS for their particle size distributions. Gold nanoparticles (mean sizes: 3.5, 10, 13, 28, 56 nm diameter) were tested for their catalytic efficiency. Kinetic data were acquired by UV-Vis spectroscopy at different temperatures between 25 and 45 °C. By studying the p-nitrophenol to p-aminophenol reaction kinetics we determined the nanoparticle size which is needed to gain the fastest conversion under ambient conditions in the liquid phase. Unexpectedly, CTAB-stabilized gold nanoparticles with a diameter of 13 nm are most efficient. PDF

108. "Characterization of mechanochemically synthesized MOFs"
M. Klimakow, P. Klobes, K. Rademann, F. Emmerling, Microporous and Mesoporous Materials 2012, Vol 154, 113-118.The compound MOF-14 (Cu3(BTB)2, BTB = 4,4′,4″-benzenetribenzoate) was synthesized by ball milling and characterized by powder X-ray diffraction (XRD). The raw material was activated using an efficient single washing step to ensure a free pore access. Nitrogen adsorption measurements were carried out to determine the specific areas of the samples before and after activation. To interpret the activation process in terms of blocking effects in the micropore channels, NLDFT evaluations (Nonlocal Density Functional Theory) of the MOF-14 nitrogen isotherms were carried out. In connection with the appearance of additional hysteresis loops in the nitrogen isotherms, calculations of the mesopore size distribution were performed using the method of Barret, Joyner, and Halenda (BJH). The results are compared to those of a structurally analogue MOF, namely HKUST-1 (Cu3(BTC)2, BTC = 1,3,5-benzenetricarboxylate). This comparison showed notable differences regarding the impact of the activation step on the formation of mesopores and their size distribution. PDF

107. "Morphological diversity of caffeine on surfaces: Needles and hexagons"
A. Sarfraz, A. Simo, R. Fenger, W. Christen, K. Rademann, U. Panne, F. Emmerling
Cryst. Growth Des. 2012, Vol 12, 538-588. A systematic crystal morphology study on the pharmaceutical model compound caffeine has been conducted on different surfaces: silicon, silver, soda lime glass, and silver subsurface ion-exchanged soda-lime silicate (SIMO) glasses. The morphology of the solid caffeine deposits has been investigated using environmental scanning electron microscopy (ESEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). Needle-shaped caffeine crystals have been observed by drop-casting and also by applying the rapid expansion of supercritical solutions (RESS) technique using supercritical carbon dioxide. The aspect ratio of the crystalline needles typically vary between 10 and 100, but have been observed as large as 500. The XRD data of the RESS products indicate unambiguously the presence of the thermodynamically most stable polymorph of caffeine known as the β-form. Under defined conditions we observe a unique, surface-mediated morphology for caffeine crystals with nearly perfect hexagonal shape. The relative fraction of the hexagons was seen to strongly increase especially when SIMO glasses were used. These hexagons have a distinct upper size limit depending on the solvent and substrate being used. The size distribution analysis of the hexagons yielded an average perimeter of typically 10 μm. The mechanism of the formation process of this new hexagonal motif is explained in terms of the spinodal dewetting of the thin film of caffeine solution on the surface. PDF

106. "Fast crystallization of organic glass formers", T. Gnutzmann, K. Rademann, F. Emmerling, ChemComm 2012, Vol 48, 1638-1640An unusually fast crystallization of the organic glass former nifedipine has been observed. The crystallization process, starting from an amorphous film to crystalline material, was investigated by time resolved Raman microspectroscopy. The crystallization rates of the initially crystallizing metastable β-form are four orders of magnitude higher than those of previous studies. PDF

105. "Long-term stable silver subsurface ion-exchanged glasses for SERS applications" A. Simo, V. Joseph, R. Fenger, J. Kneipp, K. Rademann
ChemPhysChem 2011, Vol 12 (9), 1683-1688. We report on the formation of silver subsurface ion-exchanged metal oxide (silver SIMO) glasses and their surface-enhanced Raman scattering (SERS) activity. The samples were prepared by a combined thermal and chemical three-step methodology and characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), environmental electron scan-ning microscopy (ESEM), and UV/Vis spectroscopy. This unique method provides SERS substrates with protection against contamination and strong, reliable and reproducible SERS enhancement. The Raman enhancement factors of the long-term stable SIMO glasses were estimated to approximately 10(7). PDF

104. "Quantitative study of (4)He real gas effects using supersonic beams"
W. Christen, K. Rademann, Zschrft. für physk. Chemie 2011, Vol 225 (5), 517-525. The experimental realization of accurately defined source conditions, combined with an undisturbed flight path of precisely known length, permits the generation of supersonic molecular beams with an extremely well characterized axial velocity distribution. This achievement can be used for a quantitative assessment of theoretical models of condensation during the jet expansion, based on high accuracy equations of state. For helium-4, which is commonly put on a level with the ideal gas, we contrast two empirical equations of state with respect to enthalpy changes. These can be validated through a comparison with experimentally determined mean terminal flow velocities. At cryogenic temperatures, strong deviations from the ideal gas behavior are observed. Most notably, even the differences between the predictions of the two fundamental equations are large enough to be distinguished by high-resolution time-of-flight measurements. PDF

103. "Precision velocity measurements of pulsed supersonic jets", W. Christen, T. Krause, B. Kobin, K. Rademann, J. Phys. Chem. A 2011, Vol 115 (25), 6997-7004. We introduce a straightforward experimental approach for determining the mean flow velocity of a supersonic jet with very high precision. While time measurements easily can achieve accuracies of Δt/t ≤ 10−4, typically the absolute flight distances are much less well-defined. This causes significantly increased errors in calculations of the mean flow velocity and mean kinetic energy. The basic concept to improve on this situation is changing the flight distance in vacuo by precisely defined increments employing a linear translation stage. We demonstrate the performance of this method with a flight path that can be varied by approximately 15% with a tolerance of setting of 50 μm. In doing so, an unprecedented accurate value for the mean flow velocity of Δv/v < 3 × 10−4 has been obtained without prior knowledge of the total distance. This very high precision in source pressure, temperature, and particle speed facilitates an improved energetic analysis of condensation processes in supersonic jet expansions. The technique is also of broad interest to other fields employing the strong adiabatic cooling of supersonic beams, in particular, molecular spectroscopy. In the presented case study, a thorough analysis of arrival time spectra of neutral helium implies cluster formation even at elevated temperatures. PDF

102. "X-Ray-assisted formation of gold nanoparticles in soda lime silicate glass: Suppressed Ostwald Ripening", D. Tatchev, A. Hoell, M. Eichelbaum, K. Rademann
Phys. Rev Lett. 2011, Vol 106, 085702. The in situ formation of gold nanoparticles in soda lime silicate glass under constant x-ray irradiation is compared with the ex situ formation in preirradiated glasses. The ASAXS measurements confirm that pure Au particles are formed. The comparison shows that the number of particles nucleated under irradiation is about an order of magnitude higher than of those nucleated with preirradiation. The radius, R, remains slightly below 1 nm under in situ conditions and the Ostwald ripening stage is slowed down. Under ex situ conditions Ostwald ripening is clearly observed and R grows up to 3 nm. PDF

101. "Photoluminescence and surface photovoltage of ethynyl derivative-terminated Si(111) surfaces" F. Yang, R. Hunger, K. Rademann, J. Rappich
PSSC 2010, Vol 2, 161-164. The electrochemical grafting of ethynyl derivatives on Si(111) surfaces has been investigated by means of pulsed photoluminescence (PL) and surface photovoltage (SPV) techniques. Ethynyl derivatives (ethynyl-MgCl, ethynyl-MgBr, propynyl-MgBr, and phenylethynyl-MgBr) from Grignard compounds were used. By SPV, a high surface photovoltage signal, UPh, is observed. The halogene in the Grignard reagents influences strongly the electronic properties and the polymerisation process, i.e. Br in the Grignard compound leads to better electronic properties than Cl. The propynyl-terminated Si surface shows the highest PL intensity and at the same time the weakest UPh signal, i.e. this polymeric layer induces the smallest amount of recombination active defects at the interface but also the smallest change in surface band bending. PDF

100. "Supersonic beams at high particle densities: Model description beyond the ideal gas approximation" W. Christen, K. Rademann, U. Even
J. Phys. Chem. A 2010, Vol 114, 11189-11201. Supersonic molecular beams constitute a very powerful technique in modern chemical physics. They offer several unique features such as a directed, collision-free flow of particles, very high luminosity, and an unsurpassed strong adiabatic cooling during the jet expansion. While it is generally recognized that their maximum flow velocity depends on the molecular weight and the temperature of the working fluid in the stagnation reservoir, not a lot is known on the effects of elevated particle densities. Frequently, the characteristics of supersonic beams are treated in diverse approximations of an ideal gas expansion. In these simplified model descriptions, the real gas character of fluid systems is ignored, although particle associations are responsible for fundamental processes such as the formation of clusters, both in the reservoir at increased densities and during the jet expansion.In this contribution, the various assumptions of ideal gas treatments of supersonic beams and their shortcomings are reviewed. It is shown in detail that a straightforward thermodynamic approach considering the initial and final enthalpy is capable of characterizing the terminal mean beam velocity, even at the liquid-vapor phase boundary and the critical point. Fluid properties are obtained using the most accurate equations of state available at present. This procedure provides the opportunity to naturally include the dramatic effects of nonideal gas behavior for a large variety of fluid systems. Besides the prediction of the terminal flow velocity, thermodynamic models of isentropic jet expansions permit an estimate of the upper limit of the beam temperature and the amount of condensation in the beam. These descriptions can even be extended to include spinodal decomposition processes, thus providing a generally applicable tool for investigating the two-phase region of high supersaturations not easily accessible otherwise. PDF

99. "Mechanochemical synthesis of metal-organic frameworks: A fast and facile approach toward quantitative yields and high specific surface areas", M. Klimakow, P. Klobes, A. Thuenemann, K. Rademann, F. Emmerling
Chemistry of Materials 2010, Vol 22, 5216-5221. The strategy of utilizing mechanochemical synthesis to obtain metal organic frameworks (MOFs) with high surface areas is demonstrated for two model systems. The compounds HKUST-1 (Cu-3( BTC)(2), BTC = 1,3,5-benzenetricarboxylate) and MOF-14 (Cu-3(BTB)(2), BTB = 4,4',4''-benzenetribenzoate) were synthesized by ball milling and characterized by powder X-ray diffraction (XRD), Raman spectroscopy. scanning electron microscopy (SEM) and thermal analysis (DTA/DTG/MS). The specific surface area (SSA) of both compounds was characterized by nitrogen adsorption. To verify these results and to understand how the synthetic conditions influence the pore structure and the surface area, additional small-angle X-ray scattering (SAXS) experiments were carried out. Our investigations confirm that this synthesis approach is a promising alternative method for distinct M Of's. This facile method leads to materials with surface areas of 1713 m(2)/g, which is comparable to the highest given values in the literature for the respective compounds. PDF

98. "Combined synchrotron XRD/Raman Measurements: In situ identification of polymorphic transitions during crystallization processes", M. Klimakow, J. Leiterer, J. Kneipp, E. Rossler, U. Panne, K. Rademann, F. Emmerling
Langmuir 2010, Vol 26, 11233-11237. A combination of two analytical methods, time-resolved X-ray diffraction (XRD) and Raman spectroscopy, is presented as a novel tool for crystallization studies. An acoustic levitator was employed as sample environment. This setup enables the acquisition of X R D and Raman data in situ simultaneously within a 20 s period and hence permits investigation of polymorphic phase transitions during the crystallization process in different solvents (methanol, ethanol, acetone, dichloromethane, acetonitrile). These real time measurements allow the determination of the phase content from the onset of the first crystalline molecular assemblies to the stable system. To evaluate the capability of this approach, the setup was applied to elucidate the crystallization process of the polymorphic compound nifedipine. The results indicate the existence of solvent-dependent transient phases during the crystallization process. The quality of the data allowed the assignment of the lattice constants of the hitherto unknown crystal structure of the beta-polymorph. PDF

97. "Toward novel pseudo-polymorphs of nifedipine: Elucidation of a slow crystallization process", M. Klimakow, K. Rademann, F. Emmerling
Crystal Growth & Design 2010, Vol 10, 2693-2698. The crystallization of nifedipine was studied by means of synchrotron-X-ray diffraction, single-crystal X-ray structural analysis, and Raman spectroscopy. The results of slow evaporation (24 h in minimum) using dimethyl sulfoxide (DMSO) are presented. Since fast crystallization processes (typically minutes) in different solvents always led to the final formation of the thermodynamically most stable a-polymorph of nifedipine, we observed a novel pseudo-polymorph due to slow crystallization from DMSO. The single-crystal X-ray structure of the solvated species nifedipine. DMSO (1:1) is reported for the first time. In addition, the crystallization process on surfaces was followed by means of light microscopy and environmental scanning electron microscopy (ESEM) coupled with energy-dispersive X-ray spectroscopy (EDS) analysis. Different diffractions pattern and Raman spectra were observed for crystals grown from stock solution and those obtained by drying the solution on soda lime silicate surfaces. PDF

96. "Nucleation and growth of gold nanoparticles studied via in situ small angle X-ray scattering at millisecond time resolution", J. Polte, R. Erler, A. F. Thunemann, S. Sokolov, T. T. Ahner, K. Rademann, F. Emmerling, R. Kraehnert
ACS Nano 2010, Vol 4, 1076-1082. Gold nanoparticles (AuNP) were prepared by the homogeneous mixing of continuous flows of an aqueous tetrachloroauric acid solution and a sodium borohydride solution applying a microstructured static mixer. The online characterization and screening of this fast process (similar to 2 s) was enabled by coupling a micromixer operating in continuous-flow mode with a conventional in-house small angle X-ray scattering (SAXS) setup. This online characterization technique enables the time-resolved investigation of the growth process of the nanoparticles from an average radius of ca. 0.8 nm to about 2 nm. To the best of our knowledge, this is the first demonstration of a continuous-flow SAXS setup for time-resolved studies of nanoparticle formation mechanisms that does not require the use of synchrotron facilities. In combination with X-ray absorption near edge structure microscopy, scanning electron microscopy, and UV-vis spectroscopy the obtained data allow the deduction of a two-step mechanism of gold nanoparticle formation. The first step is a rapid conversion of the ionic gold precursor into metallic gold nuclei, followed by particle growth via coalescence of smaller entities. Consequently it could be shown that the studied synthesis serves as a model system for growth driven only by coalescence processes. PDF

95. "Probing free jet expansions of supercritical fluids", W. Christen, K. Rademann
Physica Scripta 2009, Vol 80, 1-7. Attempting to improve the comprehension of supersonic molecular beams at elevated pressures we present a comparative study of thermodynamic descriptions of the terminal flow velocity in free jet expansions. As model system we choose carbon dioxide due to its widespread utilization in supercritical fluid technology. Numerical results for the thermodynamic quantities are obtained using a high accuracy equation of state explicit in the Helmholtz free energy. The influence of pressure and temperature on the beam velocity is investigated for a broad range of stagnation conditions. A consistent physical picture is obtained for calculations employing the initial and final molar enthalpies, while enormous discrepancies are found for descriptions based on the molar isobaric heat capacity or the heat capacity ratio. The deviations are particularly pronounced at the gas-liquid phase transition and in the vicinity of the critical point and can be related to the diverse assumptions of ideal gas behavior. It is shown that computations using real fluid enthalpies permit to assess the fraction of condensation in supersonic jets. PDF

94. "Plasmonic enhancement or energy transfer? On the luminescence of gold-, silver-, and lanthanide-doped silicate glasses and its potential for light-emitting devices", M. Eichelbaum, K. Rademann
Advanced Functional Materials 2009, Vol 19, 2045-2052. With the technique of synchrotron X-ray activation, molecule-like non-plasmonic gold and silver particles in soda-lime silicate glass can be generated. The luminescence energy transfer between these species and lanthanide(III) ions is studied. As a result, a significant lanthanide luminescence enhancement by a factor of up to 250 under non-resonant UV excitation is observed. The absence of a distinct gold and silver plasmon resonance absorption, respectively, the missing nanoparticle signals in previous SAXS and TEM experiments, the unaltered luminescence lifetime of the lanthanide ions compared to the non-enhanced case, and an excitation maximum at 300-350 nm (equivalent to the absorption range of small noble metal particles) indicate unambiguously that the observed enhancement is due to a classical energy transfer between small noble metal particles and lanthanide ions, and not to a plasmonic field enhancement effect. It is proposed that very small, molecule-like noble metal particles (such as dimers, trimers, and tetramers) first absorb the excitation light, undergo a singlet-triplet intersystem crossing, and finally transfer the energy to an excited multiplet state of adjacent lanthanide(III) ions. X-ray lithographic microstructuring and excitation with a commercial UV LED show the potential of the activated glass samples as bright light-emitting devices with tunable emission colors. PDF

93. "Vibrational and electronic characterization of ethynyl derivatives granted onto hydrogenated Si(111) surfaces", F. Yang, R. Hunger, K. Roodenko, K. Hinrichs, K. Rademann, J. Rappich, Langmuir 2009, Vol 25, 9313-9318. Covalent grafting of ethynyl derivatives(-C C-H, -C C-CH3, -C C-aryl) onto H-terminated Si(111) surfaces was performed by a one-step anodic treatment in Grignard electrolytes. The electrochemical grafting Of Such ethynyl derivatives, which tends to form ultrathin polymeric layers, can be controlled by the current and charge flow passing through the Si electrode. The prepared ultrathin layers cover the Si surface and had a thickness up to 20 rim, as investigated by the scanning electron microscopy (SEM) technique. Exchanging Cl for Br in the ethynyl Grignard reagent leads to very thin layers, even under the same electrochemical conditions. However, for all ethynyl derivatives, high-resolution synchrotron X-ray photoelectron spectroscopy (SXPS) investigations reveal the incorporation of halogen atoms in the organic layers obtained. Moreover, it was observed that the larger the end group of the ethynyl derivative, the thinner the thickness of the ultrathin polymeric layers as measured by both SXPS and SEM techniques after low and high current flow respectively. For the first time, these new types of ultrathin organic layers on Si surfaces were investigated using infrared spectroscopic ellipsometry (IRSE). The different possible reaction pathways are discussed. PDF

92. "Transferring pharmaceuticals into the gas phase", W. Christen, T. Krause, K. Rademann, International Journal of Mass Spectrometry 2008, Vol 277, 305-308. The dissolution of molecules of biological interest in supercritical carbon dioxide is investigated using pulsed molecular beam mass spectrometry. Due to the mild processing temperatures of most supercritical fluids, their adiabatic expansion into vacuum permits to transfer even thermally very sensitive substances into the gas phase, which is particularly attractive for pharmaceutical and biomedical applications. In addition, supercritical CO2 constitutes a chemically inert solvent that is compatible with hydrocarbon-free ultrahigh vacuum conditions. Here, we report on the dissolution and pulsed supersonic jet expansion of caffeine (C8H10N4O2), the provitamin menadione (C11H8O2), and the amino acid derivative I-phenylalanine tert-butyl ester hydrochloride (C6H5CH2CH(NH2)COOC(CH3)(3)center dot HCI), into vacuum. An on-axis residual gas analyzer is used to monitor the relative amounts of solute and solvent in the molecular beam as a function of solvent density. The excellent selectivity and sensitivity provided by mass spectrometry permits to probe even trace amounts of solutes. The strong density variation of CO2 close to the critical point results in a pronounced pressure dependence of the relative ion currents of solute and solvent molecules, reflecting a substantial change in solubility. (C) 2008 Elsevier BY. All rights reserved. PDF

91. "Cooling and slowing in high-pressure jet expansions", 
W. Christen, K. Rademann, Physical Review A 2008, Vol 77, 012702. The mathematical term for the mean flow velocity in supersonic beams of ideal gases is extended to include real gas properties. This procedure yields an explicit dependence of the flow velocity on pressure, as observed in recent experiments of free jet expansions. Applied to stagnation conditions slightly above the critical point, the model suggests that seeded high-pressure jet expansions might be suitable for slowing down virtually any molecule with maximum efficiency. Moreover, we discuss the consequence of a pressure-dependent flow velocity v(0) for the speed ratio S=v(0)/Delta v(parallel to) with respect to collisional cooling and suggest to use the velocity spread Delta v(parallel to) as a more nonambiguous measure of translational temperature in high-pressure jet expansions. PDF

90. "SERS and multiphoton-induced luminescence of gold micro- and nanostructures fabricated by NIR femtosecond-laser irradiation", M. Eichelbaum, J. Kneipp, B. E. Schmidt, U. Panne, K. Rademann, Chemphyschem 2008, Vol 9, 2163-2167. PDF

89. "Photoluminescence of atomic gold and silver particles in soda-lime silicate glasses"
M. Eichelbaum, K. Rademann, A. Hoell, D. M. Tatchev, W. Weigel, R. Stößer, G. Pacchioni, Nanotechnology 2008, Vol 19. We report the chemistry and photophysics of atomic gold and silver particles in inorganic glasses. By synchrotron irradiation of gold-doped soda-lime silicate glasses we could create and identify unambiguously the gold dimer as a stable and bright luminescing particle embedded in the glassy matrix. The gold dimer spectra coincide perfectly with rare gas matrix spectra of Au-2. The glass matrix is, however, stable for years, and is hence perfectly suited for various applications. If the irradiated gold-doped sample is annealed at 550 degrees C a bright green luminescence can be recognized. Intense 337 nm excitation induces a decrease of the green luminescence and the reappearance of the 753 nm Au-2 emission, indicating a strong interrelationship between both luminescence centers. Time-dependent density functional theory (TD-DFT) calculations indicate that the green luminescence can be assigned to noble metal dimers bound to silanolate centers. These complexes are recognized as the first stages in the further cluster growth process, which has been investigated with small-angle x-ray scattering (SAXS). In silver-doped glasses, Ag-0 atoms can be identified with electron paramagnetic resonance (EPR) spectroscopy after synchrotron activation. Annealing at 300 degrees C decreases the concentration of Ag-1, but induces an intense white light emission with 337 nm excitation. The white luminescence can be decomposed into bands that are attributed to small silver clusters such as Ag-2, Ag-3 and Ag-4, and an additional band matching the green emission of gold-doped glasses. PDF

88. "Tracing coffee tabletop traces", J. Leiterer, F. Emmerling, U. Panne, W. Christen, K. Rademann, Langmuir 2008, Vol 24, 7970-7978. Crystallization processes under different conditions are of fundamental interest in chemistry, pharmacy, and medicine. Therefore, we have studied the formation of micro- and nanosized crystals using water-caffeine (1,3,7-trimethyl-1H-purine-2,6(3H,7H-dione) solutions under ambient conditions as a relevant model system. When droplets of an aqueous caffeine solution evaporate and eventually dry on surfaces (glass, polystyrene, and polyester), stable >coffee tabletop< rings with a perimeter of typically 3 mm are formed after 20 to 50 min. Using a micro focus X-ray beam available at the BESSY mu Spot-beamline, the fine structure of different caffeine needles can be distinguished. Unexpectedly, both crystal modifications (alpha- and beta-caffeine) are present, but locally separated in these rings. Furthermore, AFM studies reveal the presence of even smaller particles on a nanometer length scale. To eliminate influences of surface irregularities from the crystallization process, acoustic levitation of liquid samples was employed. Such levitated droplets are trapped in a stable position and only surrounded by air. The solvent in an ultrasonically levitated drop evaporates completely, and the resulting crystallization of caffeine was followed in situ by synchrotron X-ray diffraction. In this case, the diffraction pattern is in accordance with pure alpha-caffeine and does not indicate the formation of the room temperature polymorph beta-caffeine. Hence, our investigations open new vistas that may lead to a controlled formation of cocrystals and novel polymorphs of micro- and nanocrystalline materials, which are of relevance for fundamental studies as well as for pharmaceutical and medical applications. PDF

87. "The formation of intermediate oxygen states on Ru(10-10) at high pressures"
R. Blume, W. Christen, H. Niehus, K. Rademann, Journal of Physical Chemistry C 2007, Vol 111, 4774-4779. The reaction of Ru(10-10) with oxygen has been investigated under high-pressure conditions (<= 1 bar) with thermal desorption spectroscopy (TDS), low electron energy diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and measurements of the work function changes Delta Phi, derived from ultraviolet photoelectron spectroscopy (UPS). For oxygen exposures between 0.1 and 1000 L, only chemisorption is observed independent of the sample preparation temperature T-P (425 K < T-P < 750 K). For exposures higher than 1000 L, chemisorption is followed by oxide formation at T-P > 525 K. At exposures larger than 1000 L and temperatures below 525 K, the formation of an intermediate oxygen state as a precursor to the actual oxide is observed with XPS and TDS. It is accompanied by a perturbation of the long-range order of the Ru surface structure. Significant changes of the work function, Delta Phi, indicate that a Ru(10-10) surface exposed to oxygen at T-P < 525 K resembles properties of a defect-rich Ru(0001) surface. The minimum oxygen exposures required for the formation of oxide as well as the intermediate state are found to be approximately 2 orders of magnitude smaller than on Ru(0001). PDF

86. "Precise thermodynamic control of high pressure jet expansions", W. Christen, T. Krause, K. Rademann, Review of Scientific Instruments 2007, Vol 78. We describe an experimental setup for supersonic jet expansions of supercritical fluids. It is characterized by well-defined thermodynamic values to allow systematic investigations of pressure and temperature effects on molecular beam parameters. The design permits stagnation temperatures T-0=225-425 K with a thermal stability Delta T-0 < 30 mK and stagnation pressures p(0)=0.2-12 MPa that are measured with 0.05% precision. For optimum stability, gas reservoir, pressure transducer, and gauge amplifier are temperature-controlled, and a feedback loop permits active pressure stabilization using a pulseless syringe pump. With this approach stagnation pressures can be reproduced and kept constant to Delta p(0)< 2.9 kPa. As a result, flow velocity and kinetic energy of molecular beams can be controlled with maximum accuracy. (c) 2007 American Institute of Physics. PDF

85. "Ultrasonic force microscopy on strained antimony nanoparticles", M. T. Cuberes, B. Stegemann, B. Kaiser, K. Rademann, Ultramicroscopy 2007, Vol 107, 1053-1060. Ultrasonic force microscopy (UFM) is used to resolve the elastic nanostructure of strained antimony (Sb) particles. These nanoparticles were formed by aggregation and spontaneous rapid crystallization of thermally deposited Sb onto the (0 0 0 1) basal planes of highly oriented pyrolytic graphite (HOPG) and molybdenum disulfide (MoS2) UFM reveals clear contrast within individual nanoparticles, which can be attributed to differences in the local stiffness. This interpretation is confirmed by transmission electron microscopy (TEM) images, in which bending contours prove the existence of strained regions within the nanocrystals. (c) 2007 Elsevier B.V. All rights reserved. PDF

84. "Gold-ruby glass in a new light: On the microstructuring of optical glasses with synchrotron radiation", M. Eichelbaum, K. Rademann, W. Weigel, B. Lochel, M. Radtke, R. Muller, Gold Bulletin 2007, Vol 40, 278-282. We describe the microstructuring of gold-ruby glasses with synchrotron radiation. Plasmonic or luminescent microstructures with a lateral width of minimum 5 pm can be written directly into the glasses by implementing X-ray lithography. The technique involves two steps: First, gold containing glass samples are irradiated with synchrotron X-rays through a microstructured mask. And second, subsequent annealing at minimum 500 degrees C induces the growth of,gold nanoparticles. The patterned sites are ruby coloured due to the gold surface plasmon resonance of gold nanoparticles. Furthermore we investigated the photoluminescence of the microstructured glass. After synchrotron irradiation a red photoluminescence is observed under UV light excitation. Subsequent annealing for a few minutes at 300 degrees C induces the quenching of the red luminescence. If the irradiated sample is annealed for 5 minutes at a higher temperature of 500 degrees C a bright green light emission is detected. The green photoluminescence decreases after further annealing and finally vanishes. We assume that the origin of the luminescence are silicate hole centres. The technique of generating gold particles with synchrotron X-ray lithography has potential to produce micro-optical devices like optical storage units, photonic crystals, gratings or sensors. PDF

83. "Three-photon-induced luminescence of gold nanoparticles embedded in and located on the surface of glassy nanolayers", M. Eichelbaum, B. E. Schmidt, H. Ibrahim, K. Rademann, Nanotechnology 2007, Vol 18, 1-8. We report on the multiphoton-induced luminescence of gold nanoparticles embedded in thin glassy silicate-titanate films. The glassy layers doped with gold( III) chloride are synthesized by a sol-gel coating process. Gold nanoparticles are generated by subsequent annealing of the thin films at 300 degrees C. Intensive near-infrared femtosecond laser irradiation also initiates the formation of gold particles, providing the possibility of spatially resolved photoactivation of the film. The reduction of gold ions to gold nanoparticles is monitored by Au L-3-edge x-ray absorption near edge spectroscopy ( XANES), UV-vis absorption spectroscopy, scanning electron microscopy ( SEM) and transmission electron microscopy ( TEM). The particle sizes and shapes can be tuned by changing the metal concentration in the matrix. We demonstrate that the particles exhibit an efficient, long time stable, white luminescence during near-infrared Ti: sapphire femtosecond laser excitation. The laser power-emission intensity law indicates that the luminescence is induced by the absorption of three laser photons. Cross-sectional TEM images show that gold nanoparticles are both embedded in the glassy matrix and located on the film surface. Hence, the particles should be accessible for viable applications, for example as sensor materials, and could therefore become a powerful alternative to organic and semiconducting fluorophores in biological imaging. PDF

82. "Apparatus for reactive cluster-surface studies", W. Christen, K. Rademann
Review of Scientific Instruments 2006, Vol 77. We present a new instrument that has been specifically designed for systematic studies of reactive cluster-surface collisions under well-defined ultrahigh-vacuum conditions. As a key feature, it incorporates a temperature-controlled, high-pressure cluster source with an unsurpassed pulse-to-pulse stability for the generation of weakly bound molecular aggregates. Impact processes can be investigated in two experimental configurations complementing one another: In the first, the exploration of intracluster reactions of accelerated, size-selected, positively or negatively charged cluster ions (1-100 eV/molecule) is accomplished, employing an inert target surface combined with angular-integrated ion detection. This arrangement uses a compact, homebuilt dual time-of-flight mass spectrometer with excellent mass resolution m/Delta m > 2000 and postacceleration capabilities. In the second configuration, the detailed analysis of chemical reactions between neutral clusters and a well-defined single crystal at lower kinetic energies (0.01-1 eV/molecule) is possible. Here, the surface interaction of a seeded supersonic cluster beam is probed with angular-, time-, and velocity-resolved detection of neutral reaction products using a high-performance quadrupole mass spectrometer. PDF

81. "Efficient cooling in supersonic jet expansions of supercritical fluids: CO and CO2"
W. Christen, K. Rademann, U. Even, Journal of Chemical Physics 2006, Vol 125. Pulsed, supersonic beams of pure carbon monoxide and carbon dioxide at stagnation conditions above their critical point have been investigated by time-of-flight measurements as a function of pressure and temperature. Although both molecules form clusters readily in adiabatic expansions, surprisingly large speed ratios (above 100) indicative of very low translational temperatures (below 0.1 K) have been achieved. In particular, the supersonic expansion of CO2 at stagnation temperatures slightly above the phase transition to the supercritical state results in unprecedented cold beams. This efficient cooling is attributed to the large values of the heat capacity ratio of supercritical fluids in close vicinity of their critical point. PDF

80. "Non-destructive investigation of composition, chemical properties and structure of materials by synchrotron radiation", W. Görner, M. Eichelbaum, R. Matschat, K. Rademann, M. Radtke, U. Reinholz, H. Riesemeier, Insight 2006, Vol 48, 540-544. PDF

79. "On the chemistry of gold in silicate glasses: Studies on a nonthermally activated growth of gold nanoparticles", M. Eichelbaum, K. Rademann, R. Muller, M. Radtke, H. Riesemeier, W. Gorner, Angewandte Chemie-International Edition 2005, Vol 44, 7905-7909. Gold in glass: Activating gold silicate glasses with synchrotron X-rays results in the spatial reduction of cationic gold to gold atoms. Subsequent annealing allows the growth of nanoparticles with defined sizes and tailored optical properties (see picture). This opens up new vistas in functionalizing chemically and mechanically stable glasses for integrated nanophotonic applications. PDF


78. "Zur Chemie des Goldes in Silicatgläsern: Untersuchungen zum nicht-thermisch aktivierten Wachstum von Goldclustern", M. Eichelbaum, K. Rademann, R. Muller, M. Radtke, H. Riesemeier, W. Gorner, Angewandte Chemie 2005, Vol 48, 8118-8122. Gold im Glas: Durch eine Aktivierung von Gold-Silicatgläsern mit Synchrotron-Röntgenstrahlung ist es möglich, ortsaufgelöst Goldkationen zu Goldatomen zu reduzieren. Mit einer anschließenden thermischen Behandlung kann man Nanopartikel definierter Größe mit maßgeschneiderten optischen Eigenschaften wachsen lassen und somit chemisch und mechanisch beständige Gläser für integrierte, nanophotonische Anwendungen funktionalisieren. PDF

77. "Contact-area dependence of frictional forces: Moving adsorbed antimony nanoparticles", C. Ritter, M. Heyde, B. Stegemann, K. Rademann, U. D. Schwarz
Physical Review B 2005, Vol 71. Antimony nanoparticles grown on highly oriented pyrolytic graphite and molybdenum disulfide were used as a model system to investigate the contact-area dependence of frictional forces. This system allows one to accurately determine both the interface structure and the effective contact area. Controlled translation of the antimony nanoparticles (areas between 10 000 and 110 000 nm2) was induced by the action of the oscillating tip in a dynamic force microscope. During manipulation, the power dissipated due to tip-sample interactions was recorded. We found that the threshold value of the power dissipation needed for translation depends linearly on the contact area between the antimony particles and the substrate. Assuming a linear relationship between dissipated power and frictional forces implies a direct proportionality between friction and contact area. Particles about 10 000 nm2 in size, however, were found to show dissipation close to zero. To explain the observed behavior, we suggest that structural lubricity might be the reason for the low dissipation in the small particles, while elastic multistabilities might dominate energy dissipation in the larger particles. PDF

76. "Native polarization of pristine P(VDF-TrFE) nanotubes and nanorods"
M. Steinhart, M. Geuss, Y. Luo, P. Goring, K. Rademann, E. Hempel, T. Thurn-Albrecht, U. Gosele, Abstracts of Papers of the American Chemical Society 2005, Vol 230, 269-PMSE. PDF

75. "Pulsed supersonic expansion of nonvolatile solids", W. Christen, S. Geggier, S. Grigorenko, K. Rademann, Review of Scientific Instruments 2004, Vol 75, 5048-5049. A compact apparatus for transferring nonvolatile particles into the gas phase and depositing them on a solid surface has been built and tested successfully. As initial experiment, solid caffeine with a vanishingly low vapor pressure has been dissolved in supercritical carbon dioxide, expanded into vacuum using a pulsed, supersonic molecular beam, and detected using a simple residual gas analyzer. PDF


74. "Crystallization of antimony nanoparticles: Pattern formation and fractal growth"
B. Stegemann, C. Ritter, B. Kaiser, K. Rademann, Journal of Physical Chemistry B 2004, Vol 108, 14292-14297. The spontaneous formation of complex interfacial patterns from thermally deposited Sb-4 clusters on HOPG is controlled by the deposition conditions (i.e., coverage and deposition rate) at constant temperature (300 K) under ultrahigh vacuum conditions. Two main driving forces for the pattern formation in this system have been identified. Initially, the crystallization of compact nanoparticles with spherical shape at a maximum diameter of 120 nm drives the system toward irregular, fingerlike shapes. Second, the ramification of these fingerlike nanoparticles is governed by the deposition rate, as the increase of the deposition rate allows the nanoparticle shape to be continuously tuned from fingerlike to further ramified and eventually fractal forms. On the basis of electron microscopy and atomic force microscopy measurements, these phenomena are quantified with a focus on fractal dimension, particle perimeter, and size of the side branches (tip width). PDF

73. "Characterization of the (0001) cleavage surface of antimony single crystals using scanning probe microscopy: Atomic structure, vacancies, cleavage steps, and twinned interlayers", B. Stegemann, C. Ritter, B. Kaiser, K. Rademann, Physical Review B 2004, Vol 69. Atomically resolved scanning tunneling microscopy images of the unreconstructed hexagonal structure of surface atoms on Sb(0001) are presented. Lateral and vertical lattice parameters have been determined. The interatomic spacing of 4.31 Angstrom (+/-0.05 Angstrom) on the Sb(0001) surface corresponds to the known bulk data. Cleavage has been found to occur always between adjacent double layers, yielding at least diatomic cleavage steps of 3.75 Angstrom (+/-0.10 Angstrom()) height. Different kinds of defect structures on the cleavage plane have been imaged with atomic resolution. Point defects, caused by a single or by three missing surface atoms, have been uncovered. Stable imaging of cleavage steps, which were found to be straight along the atomic rows, has been achieved. Twinned interlayers formed upon cleavage of Sb even at room temperature have been revealed by atomic force microscopy. The mean twinning angle of 2.42degrees (+/-0.20degrees) is quantitatively in accord with the value of 2.45degrees predicted by the model of twinning in Sb crystals. The observed features are discussed with respect to other layered materials and with regard to their relevance for the use of Sb(0001) as a support of nanostructures. PDF

72. "Crystalline structures of Sb4 molecules in antimony thin films", T. M. Bernhardt, B. Stegemann, B. Kaiser, K. Rademann, Angewandte Chemie-International Edition 2003, Vol 42, 199-+. Sb4: The building block of a new solid-state modification of antimony. This is a somewhat provocative description of the fact that nanocrystalline structures of Sb4 tetrahedrons exist on the substrates AuSb2(100) and MoS2(0001). Scanning tunneling microscopy images (see picture, (a) and (b), respectively, each 39×39 Å2) of thin amorphous antimony films show such local well-ordered areas with nearly cubic symmetry. PDF

71. "Controlled translational manipulation of small latex spheres by dynamic force microscopy", C. Ritter, M. Heyde, U.D. Schwarz, K. Rademann
Langmuir 2002, Vol  18 , 7798-7803. We report on the application of a home-built scanning force microscope for translation and in-plane rotation of nanometer-sized latex spheres by dynamic surface modification (DSM). This technique is based on the increment of the amplitude of the oscillating voltage applied at the dither piezo that drives the cantilever vibrations in the dynamic mode of scanning force microscopy. Thus, it is easily possible to switch between the imaging mode and DSM mode, enabling the direct manipulation of nanostructures under ambient conditions with high precision. The main advantage of our technique compared to earlier methods is that it operates with an active feedback loop, allowing a steady manipulation of nanostructures independent of the surface corrugation or sample tilt. Such controlled translations of latex spheres enable us in addition to study their properties regarding friction, adhesion, and cohesion. By translating latex spheres of different sizes (radii between 50 and 110 nm), it was found that the force needed to move a particle depends on its dimensions. Finally, the lateral translation of an intentionally marked sphere gives evidence that sliding is preferred over rolling. PDF

70. "Mass-selected infrared photodissociation spectroscopy of V4O10+"
K. R. Asmis, M. Brummer, C. Kaposta, G. Santambrogio, G. von Helden, G. Meijer, K. Rademann, L. Woste, Physical Chemistry Chemical Physics 2002, Vol 4, 1101-1104. The gas-phase infrared spectroscopy of V4O10+ produced by laser vaporization has been studied in the spectral region from 7 to 16 mum. Mass-selected V4O10+ cations were stored in a helium filled radio frequency hexadecapole ion trap and excited using tunable infrared radiation from a free electron laser. The photodissociation spectrum was recorded by monitoring the V4O8+ yield (O-2 loss) as a function of the excitation wavelength. Two absorption bands at 842 and 1032 cm(-1) are observed, which are assigned to resonant excitation of the antisymmetric V-O-V stretching and V=O stretching vibrations, respectively. Comparison to recent theoretical and experimental studies indicate that the absorbing species consists of a V4O8+ ionic core weakly bound to an oxygen molecule. PDF


69. "Unimolecular decomposition of antimony and bismuth cluster ions studied by surface collision induced dissociation mass spectrometry", T. M. Bernhardt, B. Kaiser, K. Rademann, Physical Chemistry Chemical Physics 2002, Vol 4, 1192-1200. Fragment ion distributions of antimony clusters Sbn+ (n = 3-12) and bismuth clusters Bin+ (n = 3-8) after collision with different solid target surfaces at hyperthermal energies are reported. The measured fragmentation patterns for antimony and bismuth clusters of the same size are similar. Main fragmentation channels identified in our study at impact energies up to 150 eV correspond to the sequential unimolecular dissociation of the colliding clusters with a preferred loss of stable neutral tetrameric and dimeric cluster units. The efficiency of the energy transfer from kinetic energy into internal cluster energy during surface collision was found to be up to 10%. The fragmentation patterns are independent of the employed target surface. In contrast, the integral scattered ion yield strongly depends on the surface type. High scattered ion yields are observed for a silicon oxide surface with high work function, whereas graphite or metallic gold target surfaces result in considerably lower scattered ion yields. For a given surface the integral ion yield also shows strong variations as function of the size of the colliding clusters. PDF

68. "Molybdenum doped bismuth oxide clusters and their reactivity towards ethene: comparison with pure bismuth oxide clusters", A. Fielicke, K. Rademann
Chemical Physics Letters 2002, Vol 359, 360-366. Mixed bismuth-molybdenum oxide clusters containing one or two molybdenum atoms have been produced in a molecular beam. Their compositions can be formulated in terms of (Bi2O3)mBiOMoO3+, (Bi2O3)mBiO(MoO3)2+ (m greater than or equal to 2), (Bi2O3)mOnMoO3+, and (Bi2O3)mOn(MoO3)2+ (m greater than or equal to 3, n = 0, 1). Reactivities of these molybdenum-doped and pure bismuth oxide cluster cations towards ethene have been investigated and rate constants have been calculated, e.g., for Bi6O9+ and Bi6O9MoO3+. Remarkably, the reactivity of the highly active bismuth oxide cluster Bi6O9+ is only slightly 9 varied by addition of one (MoO3) unit, providing evidence for the independence of the different metal oxide centres in the cluster. PDF

67. "Stability and reactivity patterns of medium-sized vanadium oxide cluster cations VxOy+ (4 <= x <= 14)", A. Fielicke, K. Rademann, Physical Chemistry Chemical Physics 2002, Vol 4, 2621-2628. Gas-phase vanadium oxide clusters VxOy+ in the size range 4 less than or equal to x less than or equal to 14 have been produced via laser vaporisation in a continuous flow of He/O2 carrier gas. The cluster distributions were subsequently characterised by their scattering behaviour at low-density gas targets (10-4-2 x 10-3 mbar). The experimental scattering cross sections were used to study differences in the interactions with rare gases, hydrocarbons (alkanes: methane, propane, n-butane and alkenes: ethene, propene, but-1-ene) and also small inorganic molecules (N2, O2, CO, NO, SO2). The compositions of the dominant oxide clusters reveal the predominance of vanadium atoms in the formal oxidation states +4 and +5. The interaction patterns of these oxide clusters with rare gases show no indications for fragmentation at collision energies corresponding to a cluster beam velocity of 900 ms-1. Clusters with a composition of (V2O5)n+ have increased cross sections for the interaction with alkanes and alkenes. Indeed, for the alkenes stable adducts have been detected under the applied scattering conditions. The increased cross sections have been interpreted in terms of a strong reactivity towards hydrocarbons, which is in agreement with previous results on smaller vanadium oxide clusters. PDF

66. "Instabilities and pattern formation during the self-organized growth of nanoparticles on graphite", B. Kaiser, B. Stegemann, H. Kaukel, K. Rademann
Surface Science 2002, Vol 496, L18-L22. Sb-4-clusters have been deposited onto highly oriented pyrolytic graphite (00011), and the formal ion or larger antimony particles has been observed as a function of surface coverage by SEM. The initial morphology of the particles is nearly spherical, according to a Volmer-Weber type growth. At a radius of about 60 nm this geometry becomes unstable, and the particles transform into dendritic and viscous finger-like islands. We suppose that the driving force for this conversion is due to a supercooling of the particles, which itself arises from I size dependent amorphous to crystalline phase transition. PDF

65. "STM investigation of surface alloy formation and thin film growth by Sb4 deposition on Au(111)", B. Stegemann, T. M. Bernhardt, B. Kaiser, K. Rademann
Surface Science 2002, Vol 511, 153-162. The growth of thin antimony films on the Au(1 1 1) surface at room temperature is studied by scanning tunneling microscopy (STM) in ultrahigh vacuum. At coverages up to one monolayer nanometer-sized islands are formed on the Au(1 1 1) terraces. High resolution STM images of these islands allow the distinction of gold and antimony atoms and confirm the formation of a well-ordered surface alloy. Its symmetry and interatomic distances agree well with the unreconstructed (1 0 0) plane of the bulk compound AuSb2. With increasing antimony coverage amorphous layers grow on the alloy support. In the initial stage of the amorphous layer growth ordered regions with cubic lattice structure are found in the overall amorphous films. The measured lattice constants and symmetries of these local structures imply that they consist of undissociated Sb-4 clusters. PDF

64. "Subsequent layer growth of supported nanoparticles by deposition of Sb4 clusters onto MoS2(0001)", B. Stegemann, B. Kaiser, K. Rademann
New Journal of Physics 2002, Vol 4. The surface morphology after deposition of Sb4 clusters onto MoS2 (0001) at 90 K has been studied in detail with scanning tunnelling microscopy in ultrahigh vacuum. It has been found that during the initial stage of growth two-dimensional nanoparticles are formed. With increasing coverage these nanoparticles grow layer by layer and each layer has the height of one monolayer of undissociated Sb4 clusters. The interface width (surface roughness) has been quantitatively determined as a function of total coverage. Ideal three-dimensional layer-by-layer growth has been identified for the single particles according to a Poisson distribution of exposed areas of the layers of the particles. Consequently, antimony grows on MoS2 (0001) without interlayer diffusion which is suppressed by an effective step edge (Schwoebel-Ehrlich) barrier. PDF

63. "Dislocation of antimony clusters on graphite by means of dynamic plowing nanolithography", M. Heyde, B. Cappella, H. Sturm, C. Ritter, K. Rademann
Surface Science 2001, Vol 476, 54-62. Antimony clusters of different shapes and dimensions have been obtained by evaporating antimony on graphite. The dependence of the shape and dimensions of the particles on the evaporation parameters (effective layer thickness, temperature, pressure) is discussed. A characterisation of the different structures is presented. In particular, the decoration of graphite steps is discussed. Clusters have been dislocated by means of dynamic plowing nanolithography, both in vector and in image pattern mode. The dependence of the energy needed to dislocate a cluster on its dimensions and position is discussed. PDF

62. "Dynamic plowing nanolithography on polymethylmethacrylate using an atomic force microscope", M. Heyde, K. Rademann, B. Cappella, M. Geuss, H. Sturm, T. Spangenberg, H. Niehus, Review of Scientific Instruments 2001, Vol 72, 136-141. We present dynamic plowing nanolithography on polymethylmethacrylate films, performed with a scan-linearized atomic force microscope able to scan up to 250 mum with high resolution. Modifications of the surface are obtained by plastically indenting the film surface with a vibrating tip. By changing the oscillation amplitude of the cantilever, i.e., the indentation depth, surfaces can be either imaged or modified. A program devoted to the control of the scanning process is also presented. The software basically converts the gray scale of pixel images into voltages used to control the dither piezo driving cantilever oscillations. The advantages of our experimental setup and the dependence of lithography efficiency on scanning parameters are discussed. Some insights into the process of surface modifications are presented. PDF

61. "Submicrosecond range surface heating and temperature measurement for efficient sensor reactivation", W. Moritz, U. Roth, M. Heyde, K. Rademann, M. Reichling, J. Hartmann, Thin Solid Films 2001, Vol 391, 143-148. A method for submicrosecond heating of sensor surfaces and simultaneous detection of the surface temperature was developed enabling accurate and fast reactivation of a semiconductor based oxygen sensor. High power electrical pulses with current densities of more than 107 A/cm2 were applied to the 60-nm-thick Pt layer of a chemical semiconductor sensor structure resulting in surface temperatures as high as 700 K maintained in the nanosecond to microsecond range. Temperature measurement was carried out using the temperature dependent electrical resistance of the Pt film. Electrical power pulses of defined shape allowed accurate control of the surface temperature with ns time resolution. The high reactivation surface temperatures required high current densities, eventually leading to fatal destruction of the sensor structure. Comparative numerical simulations of the thermal impact as well as photo thermal and scanning force microscopy measurements were performed to optimize the heating process and to investigate the destruction mechanism. PDF

60. "Antimony and bismuth oxide cluster ions", J. Opitz-Coutureau, A. Fielicke, B. Kaiser, K. Rademann, Physical Chemistry Chemical Physics 2001, Vol 3, 3034-3041. The formation of charged antimony and bismuth oxide clusters in a pulsed arc cluster ion source (PACIS) has been studied with time-of-flight mass spectrometric techniques. We compare series of antimony and bismuth oxide cluster anions with their known cationic counterparts. The anionic series (M2O3)nMO2- and (M2O3)nO2- have been predicted proceeding from the known cationic series (M2O3)nMO+ and (M2O3)nO+ by adding O2- and have been experimentally established. All these series contain the metal atoms (M=Sb or Bi) in the formal oxidation state +3. However, only in the case of antimony, oxygen rich oxide clusters appear, that can be explained with a gradual transition in the oxidation number from +3 to +5 of single antimony atoms in the cluster. To estimate the influence of the special oxide formation conditions comparative investigations with the PACIS and a laser vaporisation cluster source have been carried out for bismuth oxide cations. The similar oxide cluster distributions at comparable oxygen availability display clearly that the special thermodynamical stability of the discussed magic clusters is the significant driving force for their formation. PDF

59. "Size dependent evolution of the electronic structure of small rhenium clusters investigated by photoelectron spectroscopy: approaching the bulk"
A. Pramann, K. Rademann, Chemical Physics Letters 2001, Vol 347, 46-50. The size dependent evolution of the electronic structure of isolated gas-phase rhenium clusters Ren (n = 2-40) is measured by photoelectron (PE) spectroscopy at 4.99 and 6.42 eV photon energies. For very small clusters the photodetachment threshold energies show a strong size dependence varying between 1.6 eV (Re2) and 2.6 eV (Re13). As for larger clusters, electron affinities (EA) increase smoothly toward bulk work function (WF). Bulk-like electronic features can already be observed around very small cluster sizes. PDF

58. "Rhenium oxide cluster anions in a molecular beam", A. Pramann, K. Rademann
International Journal of Mass Spectrometry 2001, Vol 209, 1-4. The formation of rhenium oxide cluster anions is studied in a pulsed molecular beam experiment as a function of source conditions and oxygen content (0.1-10%) in the carrier gas. RenOm- clusters are formed directly in plasma reactions in the laser vaporization cluster source. With both increasing oxygen content and stagnation pressure, larger oxide clusters are formed (m greater than or equal ton) and the distribution is dominated by certain mass peaks of high intensity indicating a high stability. At lower pressure and less oxygen content, a large variety of oxides is observed. Most stable clusters contain Re atoms with a formal oxidation state of +7 and oxygen in the -2 oxidation state. Oxygen rich clusters can be attributed to a series (ReO4)(Re2O7)mOn- with 1=0-1, m=0-4, and n=0-1. The results are explained by the nature of the Re-O bond which is important for the alkene metathesis reaction mechanism. PDF

57. "Photoelectron spectroscopy of ReO2- and ReO3-", A. Pramann, K. Rademann
Chemical Physics Letters 2001, Vol 343, 99-104. The photoelectron spectra of ReO2- and ReO3- have been investigated at 4.99 and 6.42 eV photon energies in a pulsed molecular beam experiment using a laser vaporization cluster source (LVS) and a magnetic bottle type time-of-flight (TOF) photoelectron spectrometer (PES). Electron affinities (EAs) and vertical detachment energies (VDEs) have been measured for both oxides. The EA and VDE of ReO2 are 2.5 +/- 0.1 and 2.7 +/- 0.1 eV; those of ReO3 are 3.6 +/- 0.1 and 3.7 +/- 0.1 eV. These values are in good agreement with those recently determined by Andrews and co-workers [J. Phys. Chem. A 104 (2000) 3457] using infrared matrix spectroscopy and density functional calculations. PDF

56. "A new scintillation-type time-of-flight anion detector", A. Pramann, K. Rademann
Review of Scientific Instruments 2001, Vol 72, 3475-3476. A new scintillation-type anion time-of-flight detector of high transmittance is reported. The precursor type of this detector, which is known as the Daly detector, is often used in molecular beam experiments in combination with time-of-flight mass spectrometry. We present an improved and simple design which has several advantages compared to most common anion detectors. PDF

55. "Interaction of bismuth oxide cluster cations with alkenes and molecular oxygen: Bi4O6+, a possible reactive center for alkene oxidation", A. Fielicke, K. Rademann
Journal of Physical Chemistry A 2000, Vol 104, 6979-6982. The activation of molecular oxygen by bismuth oxide cluster cations has been observed in the presence of unsaturated hydrocarbon molecules. Reactivities of gas-phase bismuth oxide cluster cations BixOy+ (x = 3 or 4, y less than or equal to 7) with hydrocarbons have been studied by measuring scattering cross sections and analyzing products formed under multiple collision conditions. The integral cross sections for the scattering of the cations BixOy+ (x = 3 or 4, y I 7) from argon, alkanes (methane, propane, butane), and alkenes (ethene, propene, l-butene, 1,3-butadiene) have been measured. In particular, the cation Bi4O6+ has a significantly increased cross section for the scattering from the alkenes as compared to the other oxides Bi4Oy+. The larger total cross section is explained by assuming an increased cross section for reactive collisions, which could be caused by a specific reactivity of that cation. Products for the reactions of small bismuth oxide cluster cations BixOy+ (x = 3 or 4) with ethene and propene have been investigated by conducting fast-flow reactor experiments. In the series BixOy+ (x = 3 or 4), a simple addition of one or more alkene molecules to the oxide cation has been observed. Only Bi4O6+ is special, because it shows addition of alkene and O2 as shown by the formation of Bi4O8(alkene)+ and Bi4O8(alkene)2+. PDF

54. "New application for the calibration of scanning probe microscopy piezos", M. Heyde, H. Sturm, K. Rademann, Surface and Interface Analysis 1999, Vol 27, 291-295. Scanners for scanning probe microscopy (SPM) are generally built of piezos, which are used to move the sample with respect to the tip in the x-, p- or z-direction or vice versa, Piezoelectric scanners are usually height calibrated by the manufacturer with laser interferometry, with a calibration grid or with the crystallographic or artificial step of a known height standard. Although the displacement depends on the voltage history of the piezoelectric device, SPM data are collected in one lateral direction to minimize the divergence between the adjusted position and the true position. Here we present the utility of a cheap and easy-to-use fibre-optic displacement sensor, The sensor can be employed in measuring static and dynamic displacement of a z-piezo in order to discuss the influence of the static piezo displacement on the dynamic performance that is needed for SPM purposes. The data collected can be used to characterize the non-linearity and hysteresis for slow and fast z-displacements individually, Slow but large z-displacement refers to the sample tilt; fast but small z-displacement refers to topographic features. Our investigations on interfaces and small surface-deposited particles should derive advantage from the improved accuracy achieved, Copyright (C) 1999 John Wiley & Sons, Ltd. PDF

53. "Formation, stability, and structures of antimony oxide cluster ions"
B. Kaiser, T. M. Bernhardt, M. Kinne, K. Rademann, A. Heidenreich
Journal of Chemical Physics 1999, Vol 110, 1437-1449. The formation of positively charged antimony oxide clusters has been investigated as a function of oxygen partial pressure using time of flight mass spectrometry. With increasing oxygen partial pressure magic number patterns are observed, which can be attributed to the clusters of (Sb2O3)(n)(+) and (Sb2O3)(n)(SbO)(+) with 2 less than or equal to n < 7 and 1 less than or equal to n < 7, respectively. Oxygen rich clusters, i.e., clusters formed by the addition of one or more oxygen atoms to the above observed series, gain in intensity with increasing cluster size and increasing oxygen partial pressure. To obtain information about structures and general building principles of these clusters we have performed ab initio quantum chemistry calculations for the series (Sb2O3)(n), (Sb2O3)(n)(+), (Sb2O3)(n)(SbO)(+), (Sb2O3)(n)(SbO2)(+), and (Sb2O3)(n)(SbO3)(+). Except from a defect center in the cationic series, antimony atoms are trivalent and oxygen atoms divalent. For the cationic series (Sb2O3)(n)(SbO)(+), an open valence atone antimony atom is avoided by the formation of an additional Lewis-donor Lewis-acceptor Sb-O bond with a trivalent oxygen atom. Open structures with terminal oxygen atoms or with Sb-Sb bonds are very high in energy, expressing a principle of the formation of a maximum number of Sb-O bonds. In the series (Sb2O3)(n)(SbO2)(+), an excess oxygen valence leads to structures with a central Sb+V O-4 unit (i.e., without terminal oxygen). For n greater than or equal to 3, such structures have a very pronounced energetic stability compared to isomers with a terminal oxygen atom or with an O-O bond. Characteristic building blocks in the neutral and in the cationic series are eight-membered rings, which are also found in the bulk antimony(III)oxide modification senarmonite, as well as Sb4O5 units bridged by oxygen atoms. (C) 1999 American Institute of Physics. [S0021-9606(99)00102-6]. PDF

52. "Bimodal distribution in the fragmentation behavior of small antimony clusters Sb-x(+) (x=3-12) scattered from a highly oriented pyrolitic graphite surface"
B. Kaiser, T. M. Bernhardt, B. Stegemann, J. Opitz, K. Rademann
Physical Review Letters 1999, Vol 83, 2918-2921. The fragment ion-yield curves for the scattering of antimony cluster cations from highly oriented pyrolitic graphite show two clearly separated abundance maxima. On the low-energy side (less than or equal to 150 +/- 30 eV) the interaction is characterized by the unimolecular fragmentation of the clusters and by neutralization as the competing process. The neutralization efficiency reaches a maximum at collision energies of 150 +/- 30 eV. Above this boundary a transition to two different processes is indicated by a change in the fragment ion distribution. These competing processes are hen the shattering and the implantation of the clusters. The threshold for implantation depends significantly on cluster size. PDF

51. "Interaction of mass selected antimony clusters with HOPG", B. Kaiser, T. M. Bernhardt, B. Stegemann, J. Opitz, K. Rademann, Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms 1999, Vol 157, 155-161. We have investigated the interaction of positively charged antimony clusters Sb-n(+) with HOPG as a function of cluster size (2 < n < 13) and cluster kinetic energy (<600 eV) by tandem time of flight mass spectrometry and scanning tunneling microscopy. The processes taking place when the cluster hits the surface can be classified into three main categories according to its kinetic energy. At very low kinetic energies (less than or equal to 13 eV) soft landing should be feasible, i.e. no fragmentation of the cluster is taking place as a result of the impact. With increasing kinetic energy up to about 150-180 eV we find two competing processes. One is the fragmentation of the cluster into the most stable products (unimolecular decay), the other is neutralization. The efficiency of the second process increases with increasing particle energy from about 85% to almost 100% at 150-180 eV kinetic energy. The third category, too, is characterized by two competing processes. At about 150-180 eV collision energy the interaction leads to an ultrafast heating of the projectile. The cluster shatters immediately forming very small fragments. These fragments are ionized in part directly at or near the surface. The second process, namely implantation, starts at about 110 eV for the smallest investigated cluster, and it shows a strong threshold behavior as a function of cluster size. During this process the cluster is presumably strongly deformed and the surface atoms are displaced from their original positions, leaving the impact area in a highly amorphous state. (C) 1999 Elsevier Science B.V. All rights reserved. PDF

50. "Direct observation of platinum etching during the fluorination of a Pt/LaF3/Si structure", A. Nefedov, S. Fanchenko, S. Sbitnev, M. Heyde, K. Rademann, L. Bartholomaus, U. Roth, W. Moritz, Physica Status Solidi a-Applied Research 1999, Vol 176, 943-952. The platinum etching during fluorination of the Pt surface of a Pt/LaF3/Si(111) sandwich structure is investigated by means of X-ray methods, atomic force microscopy (AFM), and quartz crystal microbalance (QCM). XeF2 and F-2 have been used as sources of fluorine atoms. The X-ray triple-crystal rocking curve measurements show a smoothing of the rough Pt surface due to the interaction with fluorine. AFM observations confirm this change in surface roughness. For verification of these data, X-ray theta-2 theta scans have been performed for several samples using a Seeman-Bohlin X-ray diffractometer. The decrease of the integrated Pt peak intensity for a sample that had been fluorinated for about 30 h in XeF2 shows a decrease of the film thickness from initially 40 nm by 25 +/- 5%. QCM measurements showed an initial increase of the total mass followed by a decrease after 80 min. We conclude that the surface smoothing can be explained by the etching of platinum with the formation of a platinum fluoride layer during the first stage of this process followed by decomposition and desorption of this PtFx layer. PDF

49. "Tertiarybutylhydrazine: a new precursor for the MOVPE of Group III-nitrides", 
U. W. Pohl, C. Moller, K. Knorr, W. Richter, J. Gottfriedsen, H. Schumann, K. Rademann, A. Fielicke, Materials Science and Engineering B-Solid State Materials for Advanced Technology 1999, Vol 59, 20-23. Tertiarybutylhydrazine (tBuHy), generated from tBuMy hydrocloride, was found to have a convenient vapor pressure (6.7 mbar at 20 degrees C) for MOVPE applications. Thermolysis of tBuHy, studied by quadrupole mass spectroscopy (QMS), starts at about 220 degrees C by homolytic cleavage into reactive tBuNH and NH, radicals. Almost complete decomposition under QMS conditions is observed above 350 degrees C. Mirror-like GaN epilayers with mixed cubic/hexagonal and hexagonal structure were grown on GaAs and Al2O3 substrates, respectively, at 670 degrees C using tBuHy and Me3Ga or Et,Ga with a V/III ratio of 70. Low carbon incorporation was found in tBuHy-grown layers with respect to layers grown with Me2Hy under the same conditions. PDF

48. "Mass-spectrometric study of formation and stability of manganese and manganese oxide cluster anions", A. Pramann, K. Rademann, International Journal of Mass Spectrometry 1999, Vol 187, 673-683. We present a mass-spectrometric investigation of the reactions of manganese cluster anions Mnx- (in the size range x = 2-12) with molecular oxygen in the gas phase. The manganese and manganese oxide cluster anions are studied in a pulsed supersonic molecular beam experiment and generated in a conventional laser vaporization cluster source with an additional flow tube reactor. Relative reactivities are determined at near room temperature as a function of oxygen partial pressure, cluster size, and composition. We observed for the first time the controlled formation of at least four stable manganese oxide series: MnxO-, MnxO2-, MnxO3-, and MnxO4- (x = 2-12). The reactivities decrease rapidly with cluster size reaching a minimum around Mn, and Mn;. They increase smoothly with further increasing cluster size and show no significant pressure dependence for clusters of x > 5. The adsorption of molecular oxygen on the cluster surface most probably takes place in a dissociative way resulting in the formation of distinct Mn-O bonds. The Mn5- cluster exhibits a special behavior. It has the highest intensity in mass spectra and shows the lowest reactivity towards oxygen. Another interesting feature is the evolution of an intense Mn2O- peak with increasing oxygen pressure. PDF

47. "The use of a fibre-based light sensor for the calibration of Scanning Probe Microscopy piezos", H. Sturm, M. Heyde, K. Rademann, Physica Status Solidi a-Applied Research 1999, Vol 173, 225-234. Scanners for Scanning Probe Microscopes (SPM) are generally built of piezos, which are used to move the sample with respect to the tip in x-, y- or z-direction or vice versa. These piezoelectric scanners are usually calibrated by the manufacturer with laser interferometry, with a calibration grid or with the crystallographic or artificial step of a known height standard. However, the displacement depends on the voltage history of the piezoelectric device. In order to avoid this effect for the x- and y-positions, SPM data are generally collected in one lateral direction to minimize the divergence between commanded position and true position. The aim of this work is to present the usefulness of a cheap and easy-to-use fibre optic displacement sensor. The sensor can be used to measure static and dynamic displacement of a z-piezo in order to find a calibration procedure or at least an error look-up table for open-loop systems. The collected data of two different piezo scanner types can be used to characterize their nonlinearity and hysteresis. PDF

46. "Zinc and cadmium doped rare gas cluster cations", J. Opitz, B. Stegemann, B. Kaiser, K. Rademann, International Symposium on Cluster and Nanostructure Interfaces 1999, Richmond, USA VI, 523-528.

45. "Formation of superperiodic patterns on highly oriented pyrolytic graphite by manipulation of nanosized graphite sheets with the STM tip", T. M. Bernhardt, B. Kaiser, K. Rademann, Surface Science 1998, Vol 408, 86-94. Scanning tunneling microscopy investigations of superperiodic lattices on graphite (0001) are reported. The origin of these superperiodic features is still uncertain. In this investigation particular attention is paid to unusual superstructures with a spatially varying periodicity, because this sort of superstructures refers to the presence of in plane bending forces which affect the topmost graphite layer. We use the tip of the scanning tunneling microscope to manipulate single weakly bound nanometer-sized sheets on the graphite surface in order to directly induce intralayer strain and interlayer mismatch. By this means it has been possible to fold a graphite sheet onto a step or a boundary region and thus create superstructures with hexagonal symmetry. The observed lattice constants in the stressed area varied continuously between 50 and 80 Angstrom. The giant pattern vanished as the topmost layer was forced to break up. These observations also point to the important role of intralayer strain in the formation of the observed superstructures on graphite surfaces and are discussed in terms of the rotational moire pattern hypothesis and a dislocation network model. (C) 1998 Elsevier Science B.V. All rights reserved. PDF

44. "Formation of antimony oxide clusters in a molecular beam", B. Kaiser, T. M. Bernhardt, M. Kinne, K. Rademann, International Journal of Mass Spectrometry 1998, Vol 177, L5-L8. The formation of positively charged antimony oxide clusters has been investigated as a function of oxygen partial pressure. At low oxygen concentration oxide clusters with a large variety of stoichiometries are observed. With increasing oxygen pressure some mass peaks become prominent. The special stability of these antimony oxide clusters can be explained by simple valence bond arguments, all the antimony atoms being in a formal +III and all the oxygen atoms being in a formal -II oxidation state. A further increase in the oxygen partial pressure shifts the distribution to mixed valence oxide clusters with one or more of the antimony atoms in the formal +V oxidation state. According to this model it is possible to predict discrete structures for these clusters. They have no direct Sb-Sb bonds, instead all the Sb-atoms are bridged by O-atoms. Further oxygen can then be added in a terminal position to form the mixed valence oxides. This model is also supported by bulk and gas-phase data of antimony oxides. (Int J Mass Spectrom 177 (1998) L5-L8). (C) 1998 Elsevier Science B.V. PDF

43. "Deposition of size-selected clusters at hyperthermal energies investigated by STM", B. Kaiser, T. M. Bernhardt, K. Rademann, Applied Physics a-Materials Science & Processing 1998, Vol 66, S711-S714. We have studied the interaction of mass-selected antimony clusters (Sb-x(+), x = 3, 4, 8) with the (0001) basal plane of highly oriented pyrolythic graphite (HOPG) in the energy range from 40 eV to 410 eV by STM and STS. A threshold behaviour is observed for cluster implantation, which is dependent on cluster size. Below this threshold the interaction is characterised by neutralisation, adsorption, and diffusion of the incoming particles. STM and STS data suggest that some of these particles are intercalated in the graphite surface. Above this threshold the clusters are implanted into the surface, resulting in a strong distortion of the substrate and cluster structure. PDF

42. "Reactions of selected bismuth oxide cluster cations with propene", M. Kinne, A. Heidenreich, K. Rademann, Angewandte Chemie-International Edition 1998, Vol 37, 2509-2511. PDF

41. "Depletion of bismuth oxide clusters by reaction with propylene", M. Kinne, K. Rademann, Chemical Physics Letters 1998, Vol 284, 363-368. The reaction of bismuth clusters, produced in a gas aggregation source, with pure oxygen resulted in enhanced stable poly oxides following the series BiO+(Bi2O3)(n) up to n = 8. Reactions of these magic clusters with propylene in a scattering cell, under single collision conditions, lead to a significant reduction of the oxide peaks. Unexpectedly this finding is similar to the known catalytic reactions of propylene and solid Bi2O3. In the case of antimony oxide clusters no special reactivity can be found. (C) 1998 Elsevier Science B.V. PDF

40. "Fragmentation of clusters induced by collision with a solid surface: Comparison of antimony and bismuth cluster ions", T. M. Bernhardt, B. Kaiser, K. Rademann,
Zeitschrift für Physik D-Atoms Molecules and Clusters 1997, Vol 40, 327-330. Mass-selected antimony cluster ions Sb-n(+) (n = 3-12) and bismuth cluster ions Bi-n(+) (n = 3-8) are allowed to collide with the surface of highly oriented pyrolytic graphite at energies up to 350 eV. The resulting fragment ions are analysed in a time-of-flight mass spectrometer. Two main fragmentation channels can be identified. At low impact energies both Sb-n(+) and Bi-n(+) cluster ions lose neutral tetramer and dimer units upon collision. Above about 150 eV impact energy Sb-3(+) becomes the predominant fragment ion of all investigated antimony clusters. The enhanced stability of these fragment clusters can be explained in the framework of the polyhedral skeletal electron pair theory. In contrast, Bi-n(+) cluster scattering leads to the formation of Bi-3(+), Bi-2(+) and Bi+ with nearly equal abundances, if the collision energy exceeds 75 eV. The integral scattering yield is substantially higher in this case as compared to Sb-n(+) clusters. PDF

39. "Scattering and deposition of mass-selected antimony clusters", B. Kaiser, T. M. Bernhardt, K. Rademann, Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms 1997, Vol 125, 223-227. Positively charged antimony cluster ions (Sb-n(+): 2 < n < 13) have been scattered from the surface of highly oriented pyrolythic graphite (HOPG) at energies up to 350 eV. Main fragmentation channels for the positively charged clusters are the formation of neutral Sb-2- and Sb-4- and charged Sb-3(+)-, Sb-5(+)- and Sb-7(+)- species. The stability of these products can be understood in the framework of the polyhedral skeletal electron pair theory. STM-images taken after the scattering of a mass selected cluster at a predefined energy from HOPG show the formation of islands with a diameter of about 30 to 40 Angstrom. The islands are assumed to be formed by statistical diffusion of the collision products on the substrate surface. The number density of islands correlates well with the measured scattering efficiencies and the cluster intensity in the beam. PDF

38. "Formation and stability of antimony and bismuth oxide clusters: a mass spectrometric investigation", M. Kinne, T. M. Bernhardt, B. Kaiser, K. Rademann
International Journal of Mass Spectrometry 1997, Vol 167, 161-172. Antimony oxide and bismuth oxide clusters are produced in a gas aggregation source. The pure metal (Sb, Bi) mixed with molecular oxygen as the reaction gas or alternatively the solid metal oxide (Sb2O3, Bi2O3) is vaporised into a Row of cold helium carrier gas. The resulting products are photoionised with a KrF short-pulse excimer laser and detected in a combined Wiley-McLaren/reflectron time-of-flight mass spectrometer. Independently of the used educts, oxides following the general sequence MO(M2O3)(n)(+) (where M is Sb or Bi) become most abundant. The stability of these hitherto unknown cluster ions is explained in terms of minimising the number of the unpaired electrons by the building of metal-oxygen electron pair bonds. (C) 1997 Elsevier Science B.V. PDF

37. "Formation of antimony oxide clusters by gas aggregation", M. Kinne, T. M. Bernhardt, B. Kaiser, K. Rademann, Zeitschrift Fur Physik D-Atoms Molecules and Clusters 1997, Vol 40, 105-107. SbxOy clusters are produced by using a gas aggregation technique. Antimony vapor is mixed with He/O-2 or He/N2O and cooled in a reaction channel. After photoionisation with a KrF (248 nm) or ArF (193 nm) excimer laser the products are mass analyzed in a time of flight mass spectrometer. In the presence of N2O no oxide clusters besides SbO+ can be detected, while with oxygen under similar experimental conditions dramatic changes can be observed. At low oxygen partial pressure the obtained spectra are dominated by the pure Sb-x(+) clusters with low intensity of SbxOy+, whereas at high oxygen partial pressure antimony oxides following the general sequence SbO+(Sb2O3)(n) are most abundant. The same stable species can furthermore be produced via aggregation of vaporised solid antimony oxide (Sb2O3). Within these experiments another new Series of antimony oxides tentatively assigned to (Sb2O3)(n)(+) appeared in the mass spectra. PDF

36. "Fragmentation of charged antimony clusters induced by collision with a solid surface", T. M. Bernhardt, B. Kaiser, K. Rademann, Zeitschrift für Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics 1996, Vol 195, 273-280. The impact energy dependence of the collision of size-selected antimony clusters with the (1000) basal plane of highly oriented pyrolytic graphite has been studied in a new time-of-flight mass spectrometer arrangement. Main fragmentation channels fur positively charged cluster ions Sb-n(+) (5 less than or equal to n less than or equal to 12) are loss of neutral Sb-2 or Sb-4 units and formation of Sb-3(+) and Sb-5(+) fragment ions, which can be explained by the stability of the formed products. In contrast, during impact of Sb-n(-) (3 less than or equal to n less than or equal to 7) no fragment ions are detected, instead an intense electron emission is observed. PDF

35. "Formation of potassium oxide clusters by seeded supersonic expansion"
A. Goldbach, F. Hensel, K. Rademann, International Journal of Mass Spectrometry and Ion Processes 1995, Vol 148, L5-L9. Binary oxygen potassium clusters were generated by seeded supersonic expansion of a gaseous mixture of potassium, argon and molecular oxygen. Clusters of composition KxO (x = 5, 7, 9) and KxO2 (x = 5-7, 9) were detected for the first time. Their ionization potentials are smaller than 3.67 eV. Scattering experiments with H2O as target molecules indicate that K3O and K-4 have much more compact ground state structures than the planar aggregates K-3 and K-4. PDF

34. "Size-dependent trends in the scattering of small potassium clusters by water-molecules", A. Goldbach, F. Hensel, K. Rademann, Zeitschrift Fur Naturforschung Section a-a Journal of Physical Sciences 1994, Vol 49, 1067-1073. Scattering of small potassium clusters by water molecules has been studied in a molecular beam experiment for the first time. In the size range up to eight atoms, trends for cross sections have been obtained by investigating low energy collisions. Significant differences in relative cross sections can be assigned to inelastic collisions. As in case of scattering of sodium clusters by argon (Goerke, A. et al., J. Chem. Phys. 98, 9653 (1993)), rotational excitation of the clusters seems to be the dominating interaction. PDF

33. "Probing the nonmetal metal-transition of divalent elements - Direct experimental-observation of discrete electronic shells in cadmium clusters", M. Ruppel, K. Rademann
1994, 265-273. By measuring size specific photoelectron spectra of neutral cadmium clusters Cd(x) (5 less-than-or-equal-to x less-than-or-equal-to 46) in a molecular beam, we find direct experimental evidence for the existence of discrete electronic shells and subshells. The formation and filling of shells has been observed at 10 eV and 8.3 eV photon energy. The photoionization mass spectra of neutral cadmium clusters also clearly exhibit pronounced electronic shell closings with 20 (Cd10), 40 (Cd20), 70 (Cd35), 92 (Cd46) and 138 (Cd69) electrons. Ionization potential measurements indicate a rapid convergence towards the values expected for clusters with metallic interaction. PDF

32. "New alternative arsenic precursors for the metal organic vapor-phase epitaxy of Iii-V-semiconductors - Insitu formation of as-H functionality by beta elimination of specific metal organic arsenic compounds", P. Gimmnich, A. Greiling, J. Lorberth, C. Thalmann, K. Rademann, G. Zimmermann, H. Protzmann, W. Stolz, E. O. Gobel
Materials Science and Engineering B-Solid State Materials for Advanced Technology 1993, Vol 17, 21-24. In this study we report on the chemical synthesis, thermal decomposition and first metal-organic vapour-phase epitaxy (MOVPE) growth studies for a new class of metal-organic As compounds, designed as substitutes for the highly toxic AsH3. The key feature of these molecules is the in-situ formation of As-H functions only in the hot temperature zone of the MOVPE reactor. Compounds with the principal molecular structure As(R(rad))n(R(beta))3-n (n = 0, 1, 2; R(rad) = alkyl group with radical formation, R(beta) = alkyl group with beta elimination) do not a priori contain the As-H bonds needed for the growth of high quality III-V semiconductors using MOVPE; they are formed in situ in the reactor by thermal decomposition. The postulated beta elimination process has been proven by decomposition studies using an ersatz reactor system with quadrupole mass spectrometry for the potential beta elimination groups isobutyl and tert-butyl. The principal methods of synthesis of high purity arsenic compounds are presented and discussed. In addition we describe experiments for the MOVPE of GaAs epitaxial layers with the model compound diethyl-tert-butylarsine (DETBAs). The residual impurity levels of GaAs epitaxial layers grown in combination with trimethylgallium for different batches of DETBAs are presented and discussed as a function of the MOVPE growth conditions. PDF

31. "Electronic-structures and properties of microclusters - Cadmium and mercury"
K. Rademann, Journal of Non-Crystalline Solids 1993, Vol 156, 794-802. Recently obtained experimental results on the size dependence of ionization potentials (IP), photoelectron spectra, photoionization cross-sections, and optical absorption cross-sections for mercury Hg(x) and cadmium Cd(x) clusters are presented. While small mercury clusters are weakly bound, larger mercury clusters gradually assume with increasing size (between about 13 and 70 atoms) metallic-like properties, as indicated by the trend of IPs, photoelectron spectra, as well as by the appearance of a surface-plasmon resonance excitation at 5.93 eV. A similar, but much more pronounced electronic transition is exhibited by molecular beam isolated clusters of cadmium. For instance, IP(Cd1)-IP(Cd10) = 3.1 eV, compared with the much smaller value IP(Hg1)-IP(Hg10)) = 2.2 eV. Photoelectron spectra of mass specified neutral Cd10-clusters have revealed the existence of discrete electronic shells and subshells. The electronic shell structure in neutral cadmium clusters clearly dominates mass spectrometric Cd+-intensity distributions. Pronounced shell closings are observed for Cd10 (with 20 valence electrons), for Cd20, Cd35, Cd46, and Cd69. PDF

30. "Photoselective processes in cyclooctasulfur layers - Desorption versus polymerization", J. Geyer, H. Stulpnagel, K. Rademann, Angewandte Chemie-International Edition in English 1992, Vol 31, 874-876. Since the desorption rate depends on the light intensity, a purely thermal desorption mechanism for a thin sulfur film at lambda = 225 nm can be rejected. Nonthermal desorption of adsorbed cyclooctasulfur was hitherto unknown. By contrast, at lambda = 328 and 382 nm only a small amount of light-induced desorption was detected. Instead, polymerization of sulfur was observed at these wavelengths to significantly larger extent than at lambda = 255 nm. PDF

29. "Photoelectron-spectroscopy of neutral mercury clusters Hgx (X-Less-Than-or-Equal-to-109) in a molecular-beam", B. Kaiser, K. Rademann, Physical Review Letters 1992, Vol 69, 3204-3207. Vacuum ultraviolet photoelectron spectra are reported for mercury clusters with up to 109 atoms. These spectra yield quantitative information about the evolution of ionization potentials and bandwidths. Further results about partial photoionization cross sections are obtained by varying the photon energy. The photon energy dependence provides direct experimental evidence that large mercury clusters Hg(x) (x greater-than-or-equal-to 60) possess already a high density of p states near E(F). PDF

28. "Direct absorption studies of jet-cooled metal dimers - Magnesium and cesium"
H. Lauterwald, K. Rademann, Berichte Der Bunsen-Gesellschaft-Physical Chemistry Chemical Physics 1992, Vol 96, 1273-1275. Optical absorption of diatomic magnesium and cesium molecules is investigated in a supersonic molecular beam. A vibronic band of Mg2, which is located at 270nm and assigned to a 1PI(u) <-- 1SIGMA(g)+ transition, is found to have remarkable fine structure. The vibrationally resolved spectrum and the spectroscopic constants of the excited state are reported here for the first time. PDF

27. "Evolution of surface-plasmon resonance-absorption in large gas-phase clusters of mercury - Approaching the bulk", K. Rademann, O. Dimopoulourademann, M. Schlauf, U. Even, F. Hensel, Physical Review Letters 1992, Vol 69, 3208-3211. We have advanced a new optical-absorption technique for the study of molecular-beam isolated clusters. For Hg(x) clusters (2 < x < 200), the optical-absorption cross sections have been measured directly between 4.3 and 6.2 eV. With increasing cluster sizes a gradual enhancement of the absorption cross section at 5.93 eV is observed and discussed in terms of a surface plasmon resonance. The spectra of large clusters can be fitted quantitatively either by using the complex dielectric function of the metallic bulk material or by using the Mie-Drude imaginary part of the dynamic polarizability. PDF

26. "Clusters of divalent elements - Electronic-properties of Cdx-aggregates"
K. Rademann, M. Ruppel, B. Kaiser, Berichte Der Bunsen-Gesellschaft-Physical Chemistry Chemical Physics 1992, Vol 96, 1204-1211. We have recently succeeded in generating and detecting neutral cadmium clusters Cd(x) (x < 80) in a seeded supersonic molecular beam. The mass spectrometric abundances of photoionized clusters exhibit remarkable intensity variations. There are large intensity ratios for Cd10/Cd11 as well as Cd20/Cd21 indicating the closing of electronic shells with 20 and 40 electrons. The photoelectron spectra of neutral cadmium clusters show the formation and filling of shells, indeed. Discrete electronic states (2S2) have been observed directly in the photoelectron spectra of mass specified Cd10 clusters. Pronounced electronic shell closings are also clearly observed for clusters with 70 electrons (Cd35), 92 electrons (Cd46), and 138 electrons (Cd69). Furthermore, we have obtained quantitative information on the size dependence of ionization potentials and photoionization cross sections. The ionization potentials (7.7 +/- 0.1 eV for the dimer Cd2 and 5.0 +/- 0.1 eV for Cd46) decrease rapidly but rather smoothly with increasing cluster size. PDF

25. "Abundance distributions and ionization-potentials of neutral cadmium clusters Cd(X)(X-Less-Than-or-Equal-to-50)", M. Ruppel, K. Rademann, Chemical Physics Letters 1992, Vol 197, 280-285. We report the determination of ionization potentials for molecular beam isolated clusters of cadmium by photoionization mass spectrometry. The mass spectra reveal multimodal size distributions indicating particular stabilities for clusters with 20, 40, 70 and 92 electrons, which are shell closings in the electron shell model. A rapid convergence of the ionization potentials towards the values expected for the nonclassical metallic sphere model is observed. Ionization potentials for clusters with up to 30 atoms are reported. PDF

24. "In situ formation of as-H functions by beta-elimination of specific metalorganic arsenic compounds for the move of Iii/V Semiconductors", G. Zimmermann, H. Protzmann, W. Stolz, E. O. Gobel, P. Gimmnich, A. Greiling, J. Lorberth, C. Thalmann, K. Rademann, Journal of Crystal Growth 1992, Vol 124, 136-141. We report on the chemical synthesis, thermal decomposition studies and the first low pressure MOVPE growth experiments for a new class of metalorganic As compounds, designed as substitutes for the highly toxic AsH3. The key feature of these molecules is the in-situ formation of As-H-functions, formed by thermal decomposition under beta-elimination only in the hot temperature zone of the MOVPE reactor. As a model precursor, the As-source diethyl-tertiarybutyl-arsine (DETBAs) has been synthesized. The expected thermal decomposition mechanism of this molecule under beta-elimination, studied in an ersatz reactor system at low pressure, is proved by the detection of the products diethylarsine (DEAsH) and the stable isobutene (C4H8) in the mass spectra as cracking pattern. In first LP-MOVPE growth experiments, DETBAs has been used in combination with the standard group (III) sources TMGa and TMAl to realize GaAs and (AlGa)As bulk layers as well as AlAs/GaAs superlattices. The influence of growth parameters on the structural and electrical quality of the epilayers is presented and discussed by means of high-resolution X-ray diffraction, interference microscopy and Hall investigations. Smooth surface morphologies and narrow X-ray diffraction linewidths are achieved for GaAs (12 PDF

23. "Generation of intense selenium and tellurium cluster beams", J. Becker, K. Rademann, F. Hensel, Zeitschrift für Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics 1991, Vol 173, 21-35. A new high temperature molecular beam source for the generation of intense selenium- and tellurium cluster beams has been developed. The alumina source allows flexible change of nozzles and can be operated at temperatures up to 1200-degrees-C for many hours. At a distance of 112 mm from the nozzle, the doubly skimmed beam contains up to 10(12) chalcogene clusters/cm3. The high density of selenium and tellurium clusters in the seeded supersonic molecular beam allows high intensity time-of-flight mass- or photoelectron spectroscopy. The results of mass spectroscopy are evaluated by the use of a newly developed theoretical approach based on cluster formation probabilities. The evaluation indicates an anomalous behaviour of the Se5-molecules in the cluster formation process. PDF

22. "Electronic and geometrical structure of Se5, Se6, Se7, and Se8", J. Becker, K. Rademann, F. Hensel, Zeitschrift für Naturforschung Section A - A Journal of Physical Sciences 1991, Vol 46, 453-461. The vacuum-UV-photoelectron spectra of Se2, Se5, Se6, Se7, and Se8 have been recorded at a photon energy of hv = 10.0 eV. The isolated molecules are examined in a supersonic molecular beam employing a new photoelectron-photoion coincidence technique. The structure of the photoelectron spectra of selenium molecules with even and odd numbers of atoms differs in a characteristic manner. While the spectra of Se6 and Se8 show one single broad band, three separated bands with different intensities are observed for Se5 and two for Se7. The spectra are compared to molecular orbital energy calculations based on theoretically supposed geometries. The comparison indicates that Se6 and Se8 have D(nd)-symmetrical ring structures, whereas Se5 and Se7 are C1h-symmetrical rings. PDF

21. "Ultraviolet photoelectron studies of the molecules Se5, Se6, Se7 and Se8 with relevance to their geometrical structure", J. Becker, K. Rademann, F. Hensel
Zeitschrift für Physik D-Atoms Molecules and Clusters 1991, Vol 19, 229-231. The vacuum-UV-photoelectron spectra (hv = 10.0 eV) of Se2, Se5, Se6, Se7, and Se8 were measured. The isolated particles were examined in a supersonic molecular beam employing the photoelectron-photocation-coincidence technique. The structures of the photoelectron spectra of selenium molecules with even and odd numbers of atoms differ in a characteristic manner. Whereas the spectra of Se6 and Se8 show one single broad band, three separated bands with different intensities are observed for Se5 and two for Se7. An attempt to connect these experimental observations with the geometrical structure of the molecules shows that the photoelectron spectra are consistent with the C1h-symmetry of the Se5 and Se7 rings proposed in the literature. PDF

20. "Electronic-structure of selenium-clusters and tellurium-clusters", J. Becker, K. Rademann, F. Hensel, Zeitschrift für Physik D-Atoms Molecules and Clusters 1991, Vol 19, 233-235. The vacuum-UV-photoelectron spectra (hv = 10.0 eV or 8.3 eV) of selenium- and tellurium-clusters of different sizes (up to Se25 and Te8) were measured in a molecular beam by a photoion-photoelectron-coincidence experiment. Especially, the photoelectron spectra (4p-pi-electrons) of the selenium-clusters converge with growing cluster size to the well known spectra of amorphous solid selenium by taking into account the dielectric constant of the bulk material. The experimental results indicate the first evidence that larger selenium aggregates are van der Waals clusters of the molecules Se5, Se6, Se7 and Se8 which are contained in the equilibrium vapour. PDF

19. "Partial photoionization cross-sections of large mercury clusters and liquid mercury in the vacuum ultraviolet photon energy region", B. Kaiser, K. Rademann
Zeitschrift für Physik D-Atoms Molecules and Clusters 1991, Vol 19, 227-228. Photoelectron spectra for neutral mercury clusters (up to a size of 109 atoms) and liquid mercury have been recorded for several different photon energies between 7.1 eV and 10.6 eV. For both large mercury clusters (Hg(x), x greater-than-or-equal-to 60) and liquid mercury a strong increase of the partial photoionization cross sections near threshold with decreasing photon energy is observed. This shows clearly that the local electronic structure of large mercury clusters is very similar to the electronic structure of the metallic bulk material. PDF

18. "Photoelectron-spectroscopy and Uv/Vis-photoabsorption spectroscopy of isolated clusters", K. Rademann, Zeitschrift Fur Physik D-Atoms Molecules and Clusters 1991, Vol 19, 161-164. Experimental innovations have allowed for the application of rather conventional spectroscopic molecular beam techniques to the study of electronic properties of molecular beam isolated neutral aggregates. Recent results for mercury clusters obtained by photoelectron spectroscopy and photoabsorption spectroscopy will be discussed. The experimentally available data for mercury clusters indicate a size dependent gradual evolution of metallic bulk properties in the approximate size region between 13 and 70 atoms. PDF

17. "A new coincidence technique for vacuum ultraviolet photoelectron-spectroscopy of neutral clusters in a molecular-beam", K. Rademann, T. Rech, B. Kaiser, U. Even, F. Hensel, Review of Scientific Instruments 1991, Vol 62, 1932-1941. The magnetic bottle photoelectron spectrometer principle has been employed for the study of neutral clusters in a seeded supersonic molecular beam. Mass selectivity is achieved by correlating each detached photoelectron to the cluster cation that is produced simultaneously. The necessary high detection probabilities for both particles, the photoelectron and the cluster ion, are achieved by time-of-flight spectrometers for both channels. The collection efficiency of the magnetic photoelectron spectrometer is increased to almost-equal-to 80% of 4-pi by combining a permanent ring magnet, which produces an inhomogeneous field to parallelize the electron trajectories, with a 730-mm-long coil that guides the electrons by a weak, homogeneous field through the flight tube towards a scintillation detector. An advanced data acquisition electronics is described that is capable of recording and storing simultaneously photoelectron-photoion coincidence spectra of those neutral clusters that have sufficient intensity in the molecular beam. PDF

16. "Metal-nonmetal transition and homogeneous nucleation of mercury-vapor"
H. Uchtmann, K. Rademann, F. Hensel, Annalen Der Physik 1991, Vol 48, 207-214. The paper presents ionization potentials of mercury clusters obtained by photoelectron spectroscopy which provide evidence that a size-dependent gradual transition from van der Waals-type to metallic interaction occurs in Hg(x)-clusters for x > 13. In order to probe the role of this nonmetal to metal transition in the homogeneous nucleation process of supersaturated mercury vapour we have determined the supersaturation necessary for homogeneous condensation of mercury vapour in the temperature range 250 to 320 K. The measurements were made using an upward thermal diffusion cloud chamber. The results demonstrate that none of the current theories for homogeneous nucleation satisfactorily predict the observed critical supersaturations. The measured values are about 3 orders of magnitude lower than the values predicted by the conventional Becker-Doring-Zeldovitch-theory. PDF

15. "Reactivity and electronic-structures of isolated clusters", K. Rademann,
Berichte Der Bunsen-Gesellschaft-Physical Chemistry Chemical Physics 1990, Vol 94, 1295-1304. Some aspects of recent advances in the study of isolated clusters and their size dependent properties are reviewed. Reliable techniques for cluster generation and detection are briefly discussed. Methods for studying physical properties and electronic structures of isolated clusters and cluster ions are addressed in the context of relevant fundamental questions. Progress concerned with the exploration of solvated organic clusters, the interrogation of transition metal cluster reactivities and the investigation of electronic structures of metal clusters is documented by selected examples. In some cases, relations between isolated cluster properties and condensed phase behaviour are indicated. PDF

14. "Photoionization mass-spectrometry and valence photoelectron-photoion coincidence spectroscopy of isolated clusters in a molecular-beam", K. Rademann, Berichte Der Bunsen-Gesellschaft-Physical Chemistry Chemical Physics 1989, Vol 93, 653-670. PDF

13. "Vacuum-Uv photoemission-photoion coincidence spectroscopy of neutral metal atom clusters", K. Rademann, B. Kaiser, T. Rech, F. Hensel, Zeitschrift Fur Physik D-Atoms Molecules and Clusters 1989, Vol 12, 431-434. PDF

12. "Photoelectron-photoion-coincidence spectra of the monomer and dimer of potassium in a seeded molecular-beam", K. Rademann, B. Kaiser, T. Rech, F. Hensel, Zeitschrift für physikalische Chemie Neue Folge 1989, 145-151. PDF

11. "Direct absorption-spectra of jet-cooled Hg2", M. Schlauf, O. Dimopoulourademann, K. Rademann, U. Even, F. Hensel, Journal of Chemical Physics 1989, Vol 90, 4630-4631. PDF

10. "Are leached porous glasses fractal - response", U. Even, K. Rademann, J. Jortner, N. Manor, R. Reisfeld, Physical Review Letters 1987, Vol 58, 285-285. PDF

9. "Size dependence of the gradual transition to metallic properties in isolated mercury clusters", K. Rademann, B. Kaiser, U. Even, F. Hensel, Physical Review Letters 1987, Vol 59, 2319-2321. PDF

8. "Photoisomerization dynamics of alkyl-substituted stilbenes in supersonic jets"
K. Rademann, U. Even, S. Rozen, J. Jortner, Chemical Physics Letters 1986, Vol 125, 5-11. PDF

7. "A mass spectroscopic study on the dissociative photoionization of 1, 1-dichlorodifluoroethene - the adiabatic ionization-potential of gaseous singlet 1a1 dichlorocarbene", K. Rademann, H. W. Jochims, H. Baumgärtel, Journal of Physical Chemistry 1985, Vol 89, 3459-3464. Using monochromatized synchrotron radiation, we have derived the adiabatic ionization potential and the appearance potentials of the most abundant fragment ions of CFZ=CCIZ from their ion yield curves: IPad(C2F2ClZ) 9.64 eV, AP(CCl2+)= 12.91 eV, AP(C2FZCl+) 13.87 eV, AP(CZFCIZ+) 15.26 eV, APfCCl') = 16.13 eV, and AP(CFt) = 17.0 eV. The ionization potential of gaseous CCIZhas been measured directly: IP,d(cc12) = 9.10 0.10 eV. Reliable heat of formation values have been determined for CFZCCl+(AHfoZg8897.0 12.5 kJ/mol) and CCl2+(AHfoZg8 1107.9 f 7.5 kJ/mol). The latter value is about 60 kJ/mol lower than the currently accepted literature value.PDF

6. "A chemical-reaction and charge-transfer in heteroclusters of fluorobenzene"
U. Dimopoulou-Rademann, K. Rademann, P. Bisling, B. Brutschy, H. Baumgärtel
Berichte der Bunsen-Gesellschaft-Physical Chemistry Chemical Physics 1984, Vol 88, 215-217. Heterodimers of fluorobenzene (FB) with 1,4-dioxane and methanol were synthesized in a seeded supersonic beam and studied by resonant two-photon ionization combined with TOF mass spectrometry. The electronic spectra near the origin of the S1(π π*)← S0 transition of FB revealed solvent induced shifts and spectral features due to the excitation of van der Waals modes. In addition, strong dynamic behaviour of the photo-ionized dimers could be observed.

5. "Direct electronic-energy transfer on fractals", U. Even, K. Rademann, J. Jortner, N. Manor, R. Reisfeld, Journal of Luminescence 1984, Vol 31-2, 634-638. The site distribution of a fractal structure was characterized by the interrogation of electronic energy transfer in a porous glass, resulting in the fractal dimension of Image = 1.74±0.12 for this irregular structure. PDF

4. "Electronic-energy transfer on fractals", U. Even, K. Rademann, J. Jortner, N. Manor, R. Reisfeld, Physical Review Letters 1984, Vol 52, 2164-2167. We advance an experimental method for the characterization of the geometric site distribution of a fractal structure, which rests on the interrogation of direct, long-range, singlet-singlet, intermolecular, electronic energy transfer. Time-resolved picosecond spectroscopy was utilized to study energy transfer from rhodamine B to malachite green doped into a porous glass, resulting in a fractal dimension of d̅ =1.74±0.12 for this irregular structure. PDF

3. "Electronic spectroscopy of fluorobenzene Van der Waals molecules by resonant two-photon ionization", O. Dimopoulou-Rademann, K. Rademann, B. Brutschy, H. Baumgärtel, Electronic and Atomic Collisions 1983, XIII ICPEAC, Berlin.

2. "Isotopically selective 2-photon ionization of toluene and fluorobenzene in a supersonic beam", O. Dimopoulou-Rademann, K. Rademann, B. Brutschy, H. Baumgärtel, Chemical Physics Letters 1983, Vol 101, 485-489. Laser-induced resonant two-photon ionization of toluene and fluorobenzene cooled in a seeded supersonic expansion of Ar, combined with time-of-flight mass spectrometry, reveal the isotopic shifts of the vibronic origin of the 1B2 ← 1A1 transition: 13C-toluene: +2.5 cm−1; 13C2-toluene: +5.4 cm−1; 13C-fluorobenzene: +1.9 cm−1. Large separation factors are observed for isotopes containing one and two 13C atoms. PDF

1. "Electronic spectroscopy of fluorobenzene Van-der-Waals molecules by resonant 2-photon ionization", K. Rademann, B. Brutschy, H. Baumgärtel, Chemical Physics 1983, Vol 80, 129-145. Van der Waals (vdW) clusters of fluorobenzene (FB), synthesized in a seeded supersonic rare-gas expansion were studied by laser-induced, resonant two-photon ionization (R2PI) combined with TOF-mass spectrometry. The molecules were excited near the FB monomer's vibronic origin of the S1(ππ*) ← S0 transition (λ00 = 2644 Å). The heterogeneous clusters FB·Arn) (n < 4) showed specific shifts of the 0-0 band relative to λ00 induced by vdW interaction (FB·Ar: −23 cm−1: FB·Ar2: −46 cm−1: FB·Ar3: +4.6 cm−1). Additional satellite bands appeared due to intermolecular photofragmentation. A second band found for FB·Ar at 20 cm−1 was assigned to a vdW vibration (νvdW = 43 cm−1). Similar results were obtained for FB·Kln??? (n < 3). The spectra of the homogeneous clusters FB2 and FB3 were more complex. The dimer spectrum showed two broad spectral features, one blue- the other red-shifted relative to λ00. Each one is probably due to a different isomer. The blue-shifted contained progressions, which were tentatively assigned to a vdW vibration with 20 cm−1 in the ground and 15 cm−1 in the excited state. The trimer spectrum showed a broad blue-shifted absorption maximum with prominent bands at −2.6, −20, −29 and −50 cm−1. From the observed spectra the feasibility of cluster-specific spectroscopy is discussed. PDF




  1. “Verwendung von elementorganischen Verbindungen zur Abscheidung des Elements auf Substraten“
    H. Donath, P. Gimmnich, E. O. Göbel, J. Lorberth, K. Rademann, W. Stolz, C. Thalmann, G. Zimmermann
    Patent P 42 14224.5-45 Erteilungsbeschluß des Dt. Patentamtes vom 17.09.1992
  2. “Method and device for setting the calorific value in fuel gases containing methane“
    M. Goschin, T. Ryll, K. Rademann
    Patent EP2169035 Erteilungsbeschluß des Dt. Patentamtes vom 31.03.2010

Humboldt-Universität zu Berlin - Mathematisch-Naturwissenschaftliche Fakultät - Institut für Chemie - AK Rademann