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  • 36.40. + d  (51)
  • Springer  (51)
  • 1990-1994  (51)
  • 1945-1949
  • 1930-1934
  • 1991  (51)
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Keywords
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  • Springer  (51)
Years
  • 1990-1994  (51)
  • 1945-1949
  • 1930-1934
Year
  • 1
    Electronic Resource
    Electronic Resource
    Orbital magnetism in finite size systems (1991)
    Springer
    The European physical journal 19 (1991), S. 247-250 
    Details
    ISSN: 1434-6079
    Keywords: 75.20.-g ; 35.20.My ; 36.40. + d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The orbital magnetism in atoms is described in terms of Larmor diamagnetic and van Vleck paramagnetic contributions. The orbital magnetism in metals is described by Landau diamagnetism. Here, a discussion of the intermediate, mesoscopic regime is presented using a simple free-particle-in-a-box approximation. It is argued that, in general, one cannot separate Larmor and van Vleck contributions, and that the total susceptibility is expected to be small. The conclusions are illustrated on some experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448303
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic deflection of neutral metal clusters in a beam (1991)
    Springer
    The European physical journal 19 (1991), S. 251-254 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. + d ; 75.50.Cc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new apparatus for measuring the magnetic properties of metal clusters has been constructed. The technique involves the conventional Stern-Gerlach deflection scheme together with modern pulsed laser vaporization source technology and time of flight mass spectrometry. High field seeking monodirectional deflections have been measured for cobalt clusters containing between 40 and 400 atoms. The measured magnetic moments per atom are found to be lower than the known values for the bulk. Special attention has been given to velocity measurements of the metal clusters and the carrier gas atoms in the beam. The residence time of the particles in the source cavity has been measured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448304
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  • 3
    Electronic Resource
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    Symmetry and ferromagnetic clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 255-257 
    Details
    ISSN: 1434-6079
    Keywords: 31.20. Sy ; 36.40. + d ; 75.60. Jp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Isomers of pure Fe13 and icosahedral Fe12X clusters are studied using the all-electron linear-combination-of-Gaussian-type-orbital (LCGTO) local-density-functional (LDF) methods that allow the spin and geometry of the cluster to be determined self-consistently. The Fe13 ground state is icosahedral. The icosahedral cluster also has the greatest magnetic moment because of increased symmetry-required orbital degeneracy for electrons of different spins. The central atom of the icosahedral iron cluster has been varied to optimize the spin of the cluster keeping the oribital contribution to the magnetic moment quenched. Varying the central atom under this constraint can alter the magnetic moment by more than 20%. Similar studies have begun on 55-atom icosahedral iron clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448305
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  • 4
    Electronic Resource
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    Magnetic properties of 3d-transition-metal alloy clusters: (Fe x Cr1−x ) n (1991)
    Springer
    The European physical journal 19 (1991), S. 263-265 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. + d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present results for the magnetic properties of (Fe x Cr1−x ) n alloy clusters obtained by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. The dependence of the average magnetic moment, local magnetic moments, magnetic order, and cohesive energy on the size and composition of the cluster were determined. In agreement with surface calculations, we find that the average magnetic moment of the alloy is larger than that of the cluster of one element. Forn=15 a transition from ferromagnetic to antiferromagnetic order is obtained forx≈0.4−0.53. We discuss the importance of the overlap interaction in the spin polarized charge distribution of the alloy (e.g., charge transfer, local magnetic moments). The characteristic properties of the mixed clusters are also discussed by comparison with available results for homogeneous clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448307
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  • 5
    Electronic Resource
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    Structure of supported palladium, silver and gold clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 303-306 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. + d ; 61.16.Di
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Clusters nucleated by inert gas aggregation have been studied by HREM. The clusters were supported by amorphous carbon films and by crystalline graphite fibres. Multiply twinned particles with 5-fold axes of symmetry were observed whose structures and orientations are discussed. It is also demonstrated that crystalline graphite substrates can be used to calibrate lattice distances and to improve the image processing. With the help of computer simulations complex structures were resolved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448316
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  • 6
    Electronic Resource
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    Ultra-fine particles of TiN (1991)
    Springer
    The European physical journal 19 (1991), S. 299-301 
    Details
    ISSN: 1434-6079
    Keywords: 61.16D ; 61.50J ; 81.15J ; 36.40. + d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Ultra-fine particles of TiN have been produced by evaporating titanium in an atmosphere of helium and nitrogen. After evaporation titanium is cooled by the helium gas and small particles are formed. These are extremely reactive and react with the nitrogen gas making nitride. The particles were either collected as a powder on a vertical tube cooled by liquid nitrogen, or as a surface coating on some areas of the tungsten crucible. The produced powder was observed to consist of single crystalline particles with sizes ranging from 5 to 20 nm. The only phase observed was the δ-phase (fcc, NaCl-structure), and the dominating particle morphology was cubic with (100)-surfaces. Due to the size of the particles it was not possible to determine the stoichiometry by accurate lattice parameter measurements. However, quantitative electron energy loss spectroscopy (EELS) was applied on single particles and indicated a quite low content of nitrogen (about 33 at%). Some areas of the tungsten evaporation source were covered with a 10 μm thick TiN coating with its typical yellowish colour. The grains had a size of 1–10 μm and a rectangular shape. The grains were heavily stressed and had an amount of nitrogen quite similar to that of the small particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448315
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  • 7
    Electronic Resource
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    Adhesion of small particles of palladium on Al2O3 (1991)
    Springer
    The European physical journal 19 (1991), S. 315-317 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. + d ; 38.65. − i
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The adhesion of small particles of palladium prepared by thermal evaporation onto a substrate of Al2O3 was studied. Al2O3 was obtained by oxidation of a pollycristalline aluminum strip. The deposit of palladium was observed by Transmission Electron Microscopy which allowed to determine the size and the density of particles according to the average deposition thickness. The adhesion of particles was determined by two methods: the study of particle number density, and the study of the particle shapes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448319
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  • 8
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    Growth mechanism of gold particles on Al2O3 substrates (1991)
    Springer
    The European physical journal 19 (1991), S. 311-313 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. + d ; 61.16.D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We investigated the growth of small gold particles on thin alumina substrates obtained by oxidation of aluminum. The particles were vapor deposited in vacuum from a Knudsen cell source with a vapor rate of 1·1013 cm−2·s−1. In our experiments small Au particles on Al2O3 were examined by electron microscopy. From electron micrographs we draw a size histogram of Au particles depending on the mean deposit thickness and the deposition rate. For a mean thickness larger than 1.5 nm the particle size distributions show two peaks. The shapes and the positions of these two peaks allow us to determine the particle growth mechanism and to evidence the importance of the liquid-like coalescence resulting of diffusion and collision of the aggregates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448318
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  • 9
    Electronic Resource
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    Scanning tunneling microscopy of sputtered aluminum particles (1991)
    Springer
    The European physical journal 19 (1991), S. 323-325 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. + d ; 61.16.Di
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The scanning tunneling microscope is an ideal tool to study the local geometric and electronic structure of single supported metal clusters. Our experimental setup consists of an extraction type ion gun combined with a quadrupol mass spectrometer to deposit mass-selected metal cluster. ions. First results showing scanning tunneling microscopy pictures of sputtered aluminum clusters are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448321
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  • 10
    Electronic Resource
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    Silicon clusters: chemistry and structure (1991)
    Springer
    The European physical journal 19 (1991), S. 337-342 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. + d ; 82.20.Pm ; 82.30.Fi
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The chemical reactions of size selected silicon cluster ions (containing up to 70 atoms) have been studied with a number of different reagents using injected ion drift tube techniques. Both kinetic and equilibrium measurements have been performed as a function of temperature, and the influence of cluster annealing on chemical reactivity explored. Unlike metal clusters, where bulk behavior appears to be approached with around 30 atoms, large silicon clusters (n up to 70) are much less reactive than bulk silicon surfaces. These results suggest that the clusters in the size range examined here are not small crystals of bulk silicon, but have compact, high coordination number structures with few dangling bonds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448324
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  • 11
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    Gold clusters: reactions and deuterium uptake (1991)
    Springer
    The European physical journal 19 (1991), S. 353-355 
    Details
    ISSN: 1434-6079
    Keywords: 82.40. − g ; 36.40. + d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have examined the reactivity and saturation of small gold clusters (cations, neutrals and anions) towards several molecules and find that specific small gold clusters exhibit a pronounced variation in their reactivity towards hydrogen, methane and oxygen. The reactivity not only depends strongly on cluster size but also on the cluster charge state. For example, small (n〈15) gold cations react readily with D2, but no evidence of reaction is observed for the anions under our experimental conditions. Similar behavior is seen for methane. With oxygen only even atom (odd electron) anions are reactive, and Au 10 + is the only cation which exhibits evidence of reaction. The global features (small cluster cations reactive towards H2, CH4, but large ones not reactive, odd electron anions reactive towards O2) are qualitatively explained by appealing to a simple frontier orbital picture. The uptake of deuterium and methane on gold clusters also exhibits a pronounced size dependence with D/Au varying from a high of 3 for the dimer to zero for clusters containing more than 15 Au atoms. Comparison of the methane and deuterium saturation behavior leads us to suggest that methane is dissociated and bound as CH3 and H.
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    URL: http://dx.doi.org/10.1007/BF01448327
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  • 12
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    Reactivity and stability of bimetallic clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 357-359 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 35.20. Wg ; 82.65. − i
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using two independent vaporization lasers, bimetallic clusters composed of transition elements and A1 were generated by the laser vaporization method. Reactivity toward hydrogen adsorption of bimetallic clusters was compared with genuine clusters. It was found that A1 which has no reactivity toward hydrogen plays a role of either inhibitor or accelerator of the reaction when A1 is mixed with Nb or Co. Unusual stability of Co12 V1 in contrast to the high reactivity of Co12–13 is attributed to the rigid geometric structure where V occupies the central position.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448328
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  • 13
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    Dissociative chemisorption of D2 on a Ni13 cluster (1991)
    Springer
    The European physical journal 19 (1991), S. 371-373 
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    ISSN: 1434-6079
    Keywords: 34.10. + x ; 36.40. + d ; 82.20.Fd ; 82.20.Wf
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Selected characteristic results of a quasiclassical trajectory study of dissociative adsorption of a D2 molecule on a Ni13 cluster are presented. These include detailed probabilities as functions of the impact parameter and of the relative translational energy of D2, and cross sections as functions of this energy. The roles of the initial rovibrational state of the D2 molecule and of the initial temperature of the cluster are examined. The effect of freezing the cluster into a rigid geometry is tested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448331
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  • 14
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    Two photon states in alkali metal clusters (1991)
    Springer
    The European physical journal 21 (1991), S. 281-283 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. + d ; 33.20.kf
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study the problem of two-photon absorption in alkali metal clusters: a) by using a sum rule approach for double dipole excitation operators to have some insight on the nature of the corresponding excited states; b) by using a simple random phase approximation [RPA] model to develope an harmonic model for the excited states of the system which allows an explicit prediction for the probability to excite states in the vibrational band build on the surface plasma resonance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426386
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  • 15
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    The intrinsic line width of the plasmon resonances in metal microclusters at very low temperatures: quantal surface fluctuations (1991)
    Springer
    The European physical journal 21 (1991), S. 289-292 
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    ISSN: 1434-6079
    Keywords: 73.20.Mf ; 36.40. + d ; 71.45. − d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The line shape of the plasmon resonance in a cold, small sodium cluster (Na8) is calculated taking into account its coupling to the quantal quadrupole fluctuations of the cluster shape. This coupling is found to give rise to a small damping factor (Γ/ħω1∼0.03, where ħω1 denotes the energy centroid and Γ the full width at half maximum of the resonance), and to an asymmetric line shape with Gaussian behaviour in the wings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426388
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  • 16
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    Geometries and binding energies of small beryllium clusters using various levels of approximations for exchange and correlation: a comparative study (1991)
    Springer
    The European physical journal 18 (1991), S. 171-174 
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    ISSN: 1434-6079
    Keywords: 31.20.Di ; 36.40. + d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Electronic structure and geometries of small (n≦4) neutral, singly, and doubly ionized clusters of beryllium atoms have been studied using ab initio quantum chemical and local density techniques. In the quantum chemical method the exchange potential is treated exactly in the Hartree-Fock scheme while the correlation correction is incorporated through perturbative procedure. In the density functional approach the exchange and correlation potentials are treated in the local spin density approximation. To facilitate an unambiguous comparison between these methods we have used the same basis functions and numerical procedures. All the investigations yield nearly identical geometries. However, the binding energies using these methods can vary by as much as 2 eV and this variation is comparable to what one obtains using different basis functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437443
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  • 17
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    Collective excitations in deformed alkali metal clusters (1991)
    Springer
    The European physical journal 18 (1991), S. 193-201 
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    ISSN: 1434-6079
    Keywords: 71.45.-d ; 36.40. + d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A theoretical study of collective excitations in deformed metal clusters is presented. Sum rules are used to study the splittings of the dipole surface plasma resonance originating from the cluster deformation. The vibrating potential model is developed and used to predict the occurrence of a low lying collective mode of orbital magnetic nature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437447
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  • 18
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    Structure of the CO bond on supported Pd particles: influence of size and surface state (1991)
    Springer
    The European physical journal 19 (1991), S. 361-365 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 35.20. Wg ; 82.65. − i
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have investigated the surface of supported palladium particles by static secondary ion mass spectrometry (SSIMS). Pd particles were grown in situ on alumi na (oxide layer and sapphire surfaces) and stabilized by heating treatment. The particle size, density and crystallographic structure were determined in previous studies by transmission electron microscopy and diffraction (TEM and TED). Various ionic species are detected by SSIMS analysis which makes it possible to characterize the CO absorbed layer: Pd n CO+ (n=1, 2) for molecular adsorption and Pd n C+ for CO dissociation. The size dependence of the bonding state of CO (linear, bridge, ...) was monitored by: PdCO+/σ n Pd n CO+ signal ratio over various size particles (mean diameter in the 2–9 nm range). Investigations were performed as a function of CO coverage (adsorption at room temperature) and also under CO dissociation conditions: heating under CO atmosphere or CO+O2 (catalysis). The data analysis shows that on clean Pd particles smaller than 3 nm the CO molecules give rise mainly to PdCO+ species. We have interpreted this result by the adsorption of CO on two palladium atoms, the carbon end being tightly bonded to a low coordination Pd atom and the oxygen end weakly bonded to a neighbour Pd atom. These couples of Pd atoms form the specific sites for CO dissociation, the density of which depends on the roughness of the particle surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448329
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  • 19
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    The structure of small carbon clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 413-418 
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    ISSN: 1434-6079
    Keywords: 36.40. + d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract New non linear isomers of C n forn=4, 5, 6 have been observed using the combination of the laser photodetachment technique and the Coulomb Explosion Imaging method. Electron affinities of these isomers were found to be lower than the corresponding known linear isomers. The structure of low electron affinity C4 isomer was found to be rhombic in accordance with recent theory. Indications for the non linearity of the low electron affinity isomers of C5 and C6 are also presented.
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    URL: http://dx.doi.org/10.1007/BF01448341
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  • 20
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    Photofragmentation and photoabsorption cross sections for mass selected argon cluster ions,n=3 to 108 (1991)
    Springer
    The European physical journal 20 (1991), S. 33-34 
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    ISSN: 1434-6079
    Keywords: 36.40. + d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A tandem time-of-flight mass spectrometer is used to measure photofragmentation mass spectra and optical absorption spectra of mass selected argon cluster ions in then=3 to 108 atoms per cluster range.
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    URL: http://dx.doi.org/10.1007/BF01543931
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  • 21
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    TPEPICO studies near ionization threshold of argon and krypton clusters (1991)
    Springer
    The European physical journal 20 (1991), S. 29-32 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 82.50.Fv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Single photon ionization of argon and krypton clusters has been studied in the region between threshold and the ionization potential of the corresponding atom. Synchrotron radiation from the electron storage ring BESSY is used to ionize the clusters; threshold-photo-electron-photoion-coincidence (TPEPICO)-time-of-flight technique is used to detect ions correlated with the emission of zero-kinetic-energy-electrons. The spectra of the clusters in the range ofn=2 to 15 are discussed in view of the extensive fragmentation taking place in these systems. In order to characterize the properties of the clusters a method using scaling laws is applied. The principles and the deduction of Hagena's scaling parameter Γ* are briefly reviewed. Using Γ* an experimentally derived mean cluster size for molecular beams can be assigned. This allows one to clearly demonstrate the systematic variations of the measured spectra due to cluster fragmentation. As a general feature it is observed that, in the range studied, the peak in the measured ionization rate for a cluster ion (fragment) of a given size shifts to higher photon energies as the mean cluster size is increased.
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    URL: http://dx.doi.org/10.1007/BF01543930
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  • 22
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    Rotationally resolved ultraviolet spectra of benzene-noble gas van der Waals clusters (1991)
    Springer
    The European physical journal 20 (1991), S. 43-46 
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    ISSN: 1434-6079
    Keywords: 33.20.Lg ; 35.20.Pa ; 36.40. + d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Sub-Doppler electronic spectra with hundreds of resolved rotational lines are now available for benzene-Ar dimers and trimers. From their analysis the structure of these clusters is precisely determined. The analysis of two bands, 6 0 1 and 16 0 2 , of C6H6 · Ar is presented in detail. It leads to accurate values of the van der Waals bond length in the electronic ground and excited state. The change in frequency upon clustering is found to be a factor of 17 larger for the overtone of the out-of-plane modev 16 than for the in-plane vibrationv 1. This can be tentatively explained by an interaction of the low frequency out-of-plane motion of the ring with the van-der-Waals motion of the Ar atom.
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    URL: http://dx.doi.org/10.1007/BF01543934
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  • 23
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    Photoabsorption of sulfur dioxide cluster anions (1991)
    Springer
    The European physical journal 20 (1991), S. 57-59 
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    ISSN: 1434-6079
    Keywords: 36.40. + d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Photodissociation and photodetachment of negatively charged sulfur dioxide clusters (SO2) n − ,n=2–11, were investigated in the wavelength range from 458 to 660 nm. Electrons obtained from the interaction of photons with clusters were found to be produced in two photon processes forn≥3. Hence their detachment threshold energy is increased by at least 0.7 eV with respect to the dimer. Wavelength dependent depletion spectra indicate that the clusters are composed of a dimer anion chromophore solvated by neutral molecules. The spectral position of the absorption band is maintained and the shape evolves continuously with cluster size. However, a narrowing of the band with increasing cluster size is observed.
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    URL: http://dx.doi.org/10.1007/BF01543937
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  • 24
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    Surface induced ionization of neutral water clusters (1991)
    Springer
    The European physical journal 20 (1991), S. 61-63 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 79.20.RF
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The paper presents the results of study of a new phenomenon — the formation of cluster ions of both signs in the scattering of neutral water clusters by solid surfaces and the appearance of a current to the target. The experiments were carried out by the nozzle molecular beam technique. The probabilities of the charge removal from the surface were measured in dependence on incident angle, cluster size, and target material. The model of the process has been proposed which incorporates 1) formation of an ion pair during ion dissociation of a vibrationally excited molecule in a water cluster colliding with the surface; 2) asymmetric neutralization of an ion pair by surface; 3) inertial removal of a cluster ion from the surface. However the measured angular and energy distribution of emitted charged particles testify to more complex mechanisms of ionization and scattering because the spatial pattern of ion emission is of rainbow character and in some cases the direction of inertial removal (along the tangential component of initial velocity) does not dominate.
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    URL: http://dx.doi.org/10.1007/BF01543938
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  • 25
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    Experimental and theoretical studies of the structure of alkali halide clusters (1991)
    Springer
    The European physical journal 20 (1991), S. 93-96 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 35.20. Wg ; 79.20.Ds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have investigated the structures and properties of alkali halide cluster ions produced by laser vaporization of solid samples. In many alkali halide cluster ions, we observe the appearances of bulk-like characteristics even at sub-nanometer sizes:fcc crystalline structures (including surface terraces), ionic binding, and a susceptibility to common bulk defects such as F and H color-centers. To understand the origins of cluster structures, we have made calculations of ground state energetics, high-temperature molecular dynamics, and the electronic structure of clusters having excess electrons.
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    URL: http://dx.doi.org/10.1007/BF01543946
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  • 26
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    Fragmentation of doubly charged noble metal clusters (1991)
    Springer
    The European physical journal 20 (1991), S. 101-104 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 35.80. + S
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    Topics: Physics
    Notes: Abstract The dissociation patterns of doubly charged noble metal clusters (M) n ++ to two singly charged clusters, (M) m Emphasis〉1/+ and (M) m Emphasis〉2/+ have been investigated using a double focusing mass spectrometer. They are compared with the dissociation patterns from singly charged clusters. The dissociation probabilities to (M) 3 + and (M) 9 + were large and the odd-even alternations were observed in both patterns.
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    Evaporation rates of hot sodium clusters (1991)
    Springer
    The European physical journal 20 (1991), S. 119-122 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 31.20.Sy ; 65.50. + m ; 63.70. + h
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A scheme based in density functional theory with pseudopotentials is used to obtain the normal modes of vibration of Na n clusters (4 ≤n ≤ 22). The monomer and dimer evaporation rates from thermally excited clusters are obtained in this harmonic approximation. The time evolution of the abundance spectra from an initial uniform mass distribution of hot clusters is studied and its influence in the experimentally observed spectra is discussed.
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    Ejection, excitation and decomposition of large clusters from the surface of group II, III and IV elements by excimer laser excitation (1991)
    Springer
    The European physical journal 20 (1991), S. 137-140 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 79.20.Ds ; 78.47. + P
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    Topics: Physics
    Notes: Abstract Light emission and scattering are analyzed for the plume of vapor produced by laser excitation of the solid target of Group II, III and IV elements. Spectroscopic evidences suggest that the plume consists of microclusters of target elements. The size of microclusters is estimated to be 0.6 nm in diameter.
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    On the stability of Pb n m+ -clusters (1991)
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    The European physical journal 20 (1991), S. 133-135 
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    ISSN: 1434-6079
    Keywords: 36.40. + d
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    Topics: Physics
    Notes: Abstract The stability of multiply charged Pb n m+ -clusters (n ≤ 3;m=0, 1, 2) was studied by solving exactly for the valencep-electrons a many body Hubbard-like Hamiltonian with intra- and interatomic Coulomb interactions. Particularly we obtain that Pb 3 2+ has a metastable ground state, in which Pb 3 2+ has isosceles shape (bond lengthR=3.2 Å, bond angle θ=124°) and a positive binding energyE B =3.4 eV. The activation barrier against dissociation into Pb 2 + + Pb+ is 0.13 eV, yielding a very long lifetime. This is in agreement with recent experiments [1] in which the lifetime of Pb 3 2+ was determined to be at least 10−6 s. Comparison with self consistent Hartree-Fock calculations shows that the metastability of Pb 3 2+ is due to electronic correlations within the paramagnetic ground state.
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    Collisional electron emission at solid surfaces induced by mass selected negative cluster ions (1991)
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    The European physical journal 20 (1991), S. 141-143 
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    ISSN: 1434-6079
    Keywords: 36.40. + d
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    Topics: Physics
    Notes: Abstract Electron emission efficiency induced by the collision of clusters with a solid surface was measured as a function of cluster size. Emitted electron energy distribution for the impact of mass selected negative ion clusters or mass selected neutral clusters was also measured in the energy region of 0–5 eV. The difference in the shape of the electron spectra was observed depending on the size and charge of the clusters.
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    Frequencies of breathing vibrations of nearly spherical Ar clusters calculated by molecular dynamics (1991)
    Springer
    The European physical journal 20 (1991), S. 161-162 
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    ISSN: 1434-6079
    Keywords: 31.20 − d ; 36.40. + d
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    Topics: Physics
    Notes: Abstract The breathing vibration of Ar N cluster,N=13, 20, 25, 30 and 55, was investigated by use of the molecular dynamics method. The average distance $$(\bar r)$$ averaged over the positions of all Ar atoms with respect to the center of mass was calculated as a function of time and its frequency spectrum was derived by the Fourier transform analysis. The $$\bar r$$ value was proved to be a good index of the breathing vibration in comparison with the exact breathing vibration of an Ar dense sphere. The vibrational frequency thus estimated,f MD, was found to increase with the cluster sizen as expected.
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    Metastable decay and binding energies of van der Waals cluster ions (1991)
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    The European physical journal 20 (1991), S. 189-192 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 35.20.Wg ; 35.20.Gs
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    Topics: Physics
    Notes: Abstract In this work the appearance potentials for the metastable decay channel of a series of van der Waals dimer ions are presented. Ionization and metastable dissociation is achieved by resonance-enhanced two-photon absorption in a linear reflection time-of-flight mass spectrometer. From the appearance potentials the binding energy of the neutral dimers is obtained and from the additionally measured ionization potentials binding energies of the dimer cations are achieved. The contribution of charge transfer resonance interaction to the binding in cluster ions is evaluated by investigation of several homo-and heterodimers of aromatic components and the heterodimer benzene/cyclohexane as an example for a dimer consisting of an aromatic and a nonaromatic component.
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    Fragmentation dynamics of ammonia cluster ions after single photon ionisation (1991)
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    The European physical journal 20 (1991), S. 193-196 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 35.20.Wg ; 33.80.Eh
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    Topics: Physics
    Notes: Abstract A reflecting time of flight mass spectrometer (RETOF) is used to study unimolecular and collision induced fragmentation of ammonia cluster ions. Synchrotron radiation from the BESSY electron storage ring is used in a range of photon energies from 9.08 up to 17.7 eV for single photon ionisation of neutral clusters in a supersonic beam. The threshold photoelectron photoion coincidence technique (TPEPICO) is used to define the energy initially deposited into the cluster ions. Metastable unimolecular decay (µs range) is studied using the RETOF's capacity for energy analysis. Under collision free conditions the by far most prominent metastable process is the evaporation of one neutral NH3 monomer from protonated clusters (NH3) n − 2NH 4 + . Abundance of homogeneous vs. protonated cluster ions and of metastable fragments are reported as a function of photon energy and cluster size up ton=10.
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    Metastable dissociation dynamics of molecular cluster ions (1991)
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    The European physical journal 20 (1991), S. 197-200 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 35.80 + s
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    Topics: Physics
    Notes: Abstract Metastable uni-cluster dissociation for several hydrogen-bonded and van der Waals cluster ions are observed via resonance-enhanced two-photon ionization reflectron time-of-flight (TOF) mass spectrometry. All of the cluster ions studied show evaporation of a single molecule from the respective parent cluster ions as dominant metastable decay processes. Furthermore, the averaged metastable evaporation rate constants (k evap) of these cluster ions in a fixed time domain of 0.2–50 µs are obtained by analyzing the relative intensity of metastable ion peaks due to evaporation in the acceleration and the field-free drift regions of the TOF mass spectrometer. An intensity anomaly in some of the observed metastable ion peaks, indicative of magic number stability of the cluster ion, is also presented.
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    Cluster size effect on electron-induced luminescence (1991)
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    The European physical journal 20 (1991), S. 205-208 
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    ISSN: 1434-6079
    Keywords: 36.40. + d
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    Topics: Physics
    Notes: Abstract As a result of combined measurements of radiation intensity, electronically excited particles density and the density of mass-separated ions formed by a collision of electrons with CO2, N2O, H2O molecules and clusters in intersecting beams it has been found that the process of ejection of electronically excited particles from clusters forms a main contribution to electron-induced luminescence in a mass-spectrum of molecular, fragmented and microcluster ions. The value of this contribution depends on the cluster sizeN. The enhancement of electron-induced luminescence by small clusters (N ≲ 15) has been found.
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    Isomer- and “phase”-selective spectroscopy of van der Waals solvent clusters (1991)
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    The European physical journal 20 (1991), S. 209-214 
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    ISSN: 1434-6079
    Keywords: 68.45 Gd ; 33.10.Gx ; 33.80. − b ; 36.40. + d
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    Topics: Physics
    Notes: Abstract At the atomic size level, descriptions of rearrangement of structures and shapes of molecules are couched in chemical terminology (isomerization, racemization, rearrangement, etc.). In bulk solids, structural changes are described on a collective scale as order-disorder transformations and phase transitions (melting). To describe structural changes in atomic and molecular clusters we employ elements of both pictures:(a) local bonding rearrangements in molecules, and(b) collective permutational and/or translational rearrangements in the bulk. Various examples are given of isomerism and collective structural transformations in clusters.
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    Quantum statistical effects in helium clusters (1991)
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    The European physical journal 20 (1991), S. 219-222 
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    Keywords: 36.40. + d ; 67.40. − w
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    Topics: Physics
    Notes: Abstract We discuss ground state and statistical properties of helium clusters with special emphasis to quantum statistical effects. We investigate the density of states of4He and3He clusters, their cooling due to evaporation as well as the role played by surface excitations in the superfluid motion.
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    The photoionization dynamics of Ne clusters (1991)
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    The European physical journal 20 (1991), S. 21-23 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 33.80 ; 33.60 ; 32.80F
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    Topics: Physics
    Notes: Abstract Photoionization experiments have been performed to investigate Ne clusters after absorbing a single photon of known energy. The photon energies used were below the threshold energy of the Ne atom. Masses and initial velocities of the clusters were determined by time-of-flight techniques with a resolution ofm/Δm ≈ 500 (t/Δt ≈ 1000). The mass spectra of Ne clusters differ significantly from those reported for other rare gas clusters. An analysis of the isotopic composition of the clusters showed an enrichment of22Ne, which is attributed to a photo-induced fragmentation process.
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    Temperature jump induction of isomerization dynamics of alkali halide clusters (1991)
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    The European physical journal 20 (1991), S. 227-229 
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    Keywords: 35.20. − i ; 33.80. − b ; 36.40. + d
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    Topics: Physics
    Notes: Abstract The time resolved dynamics of diffusionless cube → ring isomerization of the Na4Cl4 cluster was interrogated by constant energy molecular dynamics simulations, utilizing the first passage time method. The nonreactive isomerization induced by nonselective vibrational excitation is well accounted for in terms of the statistical RRK theory, opening avenues for experimental exploration of time-resolved cluster isomerization dynamics.
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    Microscopic solvation: spectroscopic results vs. Monte Carlo simulations (1991)
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    The European physical journal 20 (1991), S. 247-250 
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    Keywords: 61.20.Ja ; 64.60.Cn ; 36.40. + d ; 33.20.Lg
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    Topics: Physics
    Notes: Abstract Van-der-Waals clusters of carbazole (representing the ‘solute’) with up to 40 nitrogen or methane solvent molecules were characterized using two-color resonant two-photon ionization spectroscopy. Features in these spectra (redshift, homogeneous and heterogeneous broadening, etc.) are interpreted as being caused by various static and dynamic effects of the solvent shell surrounding the aromatic substrate. For a better understanding of such effects, Monte Carlo simulations of the clusters were performed: Statics: Using a Monte Carlo simulated annealing minimization procedure, minimum energy structures (local, probably global) were found for the various cluster species. Using a simple empirical additivity rule, spectral shifts are rationalized from these structures.Dynamics: Starting from these minimum configurations, canonical ensemble simulations were carried out in a temperature range from 0 to 35 K. Severalorder-disorder transitions were identified including: 1 orientational isomerization or ‘melting’ 2 surface isomerization or decoupling 3 rigid → fluxional transitions 4 full cluster ‘melting’ We present some of our experimental results on the systems carbazole · (N2) n and carbazole · (CH4) n together with the corresponding simulation data.
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    Collective excitations of3He clusters (1991)
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    The European physical journal 20 (1991), S. 277-279 
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    Keywords: 36.40. + d ; 67.50. Dg
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    Topics: Physics
    Notes: Abstract Collective excitations of3He clusters are studied by treating the cluster as a quantum liquid drop. We have used the Random-Phase Approximation sum rules technique within a Density Functional Formalism. Results forL=2 to 10 surface modes and theL=0 volume mode are presented.
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    Experimental (LMIS) and theoretical study of Si n Au m p+ and Ge n Au m p+ (1991)
    Springer
    The European physical journal 20 (1991), S. 17-19 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 79.00
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    Topics: Physics
    Notes: Abstract In a first part, we present experimental results on Si n Au m p+ and Ge n Au m /p+ produced by the Liquid Metal Ion Source methods (LMIS). In these experiments the liquid tips are SiAu and GeAu eutectic alloys. We compare our results with LMIS experiments made on pure liquid tips and also with data given in the literature. Among the results, we note that GeAu m + exhibit an interesting alternating behaviour. In a second part, we give a quantum mechanical description of Si m p+ properties. In the range 20≲n≲40 these ions show a Δn=6 periodic behaviour. Such an effect is also observed by LMIS on Ge n Emphasis〉3+ and Sn n + aggregates. Our geometries are fragment of Zintl phase lattices (formula K8Si46 or K8Ge46). In these lattices the elementary cell is a regular array of 5-atom and 6-atom rings and the studied fragments have an integer number of rings.
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    Optical spectra and laser-induced dissociation of supported Na particles (1991)
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    The European physical journal 20 (1991), S. 381-383 
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    Keywords: 32.80. Fb ; 78.40. − q ; 36.40. + d
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    Topics: Physics
    Notes: Abstract This paper reports new results on the optical spectra of Na particles and on laser-induced photodissociation of Na atoms from the surface of these particles. In continuation of our earlier studies we have performed experiments to elucidate the mechanism of thenonthermal dissociation process. Furthermore, theoretical calculations have been carried out with the goal to correlate the wavelength dependence of the photodissociation yield with the optical absorption spectra of the metal particles. In addition, manipulation of the size distribution of metal particles on supports is outlined as an application of the effect. This allows for the preparation of very special surfaces with novel physical and chemical properties.
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    Production of “cold/hot” metal cluster ions: a modified laser vaporization source (1991)
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    The European physical journal 20 (1991), S. 411-412 
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    Keywords: 36.40. + d
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    Topics: Physics
    Notes: Abstract Metal clusters are generated via laser vaporization technique, but in contrast to common designs metal wires are used as target materials. This allowed to simplify the construction of the source dramatically, because buffer gas leakage and hole drilling by the laser beam could easily be prevented. The source producesneutral clusters as well ascharged clusters (negative and positive). Time-of-flight mass spectrometry was used to characterize these three different cluster distributions for two target materials: silver and gold.
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    A new type of cluster and cluster ion source (1991)
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    The European physical journal 20 (1991), S. 413-415 
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    Keywords: 36.40. + d ; 81.15.Ef
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    Topics: Physics
    Notes: Abstract Combining a magnetron gas discharge with the gas aggregation technique an intense source of clusters has been developed. A large part (up to 80%) of the clusters can be generated as ions without using additional electron impact ionisation.
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    Large clusters of cesium from pure vapor expansions (1991)
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    The European physical journal 20 (1991), S. 421-423 
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    Keywords: 36.40. + d
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    Topics: Physics
    Notes: Abstract The generation of cesium clusters with up to 2500 atoms per cluster by nozzle expansion of pure metal vapor without carrier gas is reported. Electron impact is found to lead to positively or negatively charged clusters with comparable probability.
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    The pulsed arc cluster ion source (PACIS) (1991)
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    The European physical journal 20 (1991), S. 417-420 
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    Keywords: 36.40. + d ; 07.77. + p ; 07.75. + h
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    Topics: Physics
    Notes: Abstract A new cluster source, the “PACIS”, has recently been developed [1, 2]: a pulsed high-current arc is fired between two electrically isolated electrodes. In a stream of carrier gas, the nascent metal plasma cools down, thus undergoes significant aggregation. After supersonic expansion into high vacuum, the resulting cluster ions will be subject to investigation. Here, we present the current state of the source development and further technical details. The integral intensity is estimated by film thickness measurements and yields a deposition rate of, e.g., up to 2 Å per shot for lead. About 10% of the emitted material turns out to be charged. Time-of-flight measurements show similar cluster ion mass spectra as they are known from laser vaporization. Already single shot mass spectra display completen-series which can be followed ton ≈ 40. For heavy clusters, a significant velocity slip is estimated from the beam velocities.
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    Cluster generation in expansions of pure water vapour and of mixtures with carbon dioxide (1991)
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    The European physical journal 20 (1991), S. 429-432 
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    Keywords: 36.40. + d
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    Topics: Physics
    Notes: Abstract The condensation of pure superheated water vapour and of a mixture with carbon dioxide in a supersonic jet behind a sonic nozzle has been investigated by the nozzle molecular beam method. The relation of source temperature, pressure, and nozzle diameter necessary for fully developed condensation has been determined for the pure vapour. By using the retarding potential technique, the cluster size distribution function and the dependence of the mean cluster size on the nozzle source conditions have been obtained. Mass-spectrometric measurements of the beam composition in a mixture expansion have revealed the presence of both homogeneous and heterogeneous clusters. The fully developed condensation in CO2-H2O mixture was found to begin at a smaller total source pressure than in pure water vapour or carbon dioxide.
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    Evidence for the direct ejection of clusters from alkali-halides during laser vaporization (1991)
    Springer
    The European physical journal 20 (1991), S. 461-463 
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    Keywords: 36.40. + d ; 35.20.Wg ; 79.20.Ds
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    Topics: Physics
    Notes: Abstract We have studied the formation of clusters of alkali halides during laser vaporization. Measurements of the abundances of cluster ions produced by several different source configurations indicate that clusters are ejected directly from the source sample and do not necessarily grow from an atomic or molecular vapor. Using samples consisting of mixed alkali halide powders, we have found that unalloyed clusters are easily produced in a source that prevents growth from occurring after the clusters leave the sample surface. Melting the sample or encouraging growth after vaporization lead to the production of alloyed cluster species. We also obtain information about the relative binding energies for substituted halogen ions bound to alkali halide clusters.
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    Ab initio spectroscopy and thermochemistry of the BN molecule (1991)
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    The European physical journal 21 (1991), S. 47-55 
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    ISSN: 1434-6079
    Keywords: 05.70.Ce ; 31.20.Tz ; 36.40. + d
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    Topics: Physics
    Notes: Abstract The lowest1Σ+ and3Π states of the BN molecule have been studied using the quadratic configuration interaction method and (spdf) basis sets. The lowest1Σ+ and3Π states lie extremely closely (T e≈100 cm−1) together; it is not clear which is the ground state. The very small separation should form a useful benchmark for basis sets and electron correlation methods. The dissociation energyD 0 is computed to be 103.9±2 kcal/mol. A self-consistent set of spectroscopic constants is derived from a combination of ab initio and experimental data. JANAF-style thermodynamic functions in the range 100–6000 K, including anharmonic, rovibrational coupling, centrifugal stretching, and spin-orbit coupling effects are computed using direct numerical summation over the 25 lowest electronic states. A modified procedure for the latter is outlined that reduces computer time by one or two orders of magnitude without compromise in accuracy.
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    Metastable decay of argon clusters after photoionisation at high excess energies (1991)
    Springer
    The European physical journal 21 (1991), S. 85-87 
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    ISSN: 1434-6079
    Keywords: 36.40. + d ; 34.30. + h
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    Topics: Physics
    Notes: Abstract Recently Märk and collaborators [1, 2] reported the metastable emission of large fractions from argon and neon cluster ions after electron impact ionisation at high excess energies. The decay was interpreted as the result of an intra-cluster excitation of a metastable state by one of the electrons involved in the ionisation process. Here we report the first direct observation of such a correlated two electron process during photoionisation of argon clusters using synchroton radiation and the TPEPICO technique. We observe at least two distinct maxima of the metastable TPEPICO spectrum at around 27 eV and 28.5 eV, the former being consistent with the previously reported energetic threshold for electron impact ionisation [1, 2].
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