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  • 1
    Electronic Resource
    Electronic Resource
    Photolysis experiments on SiC mixed clusters: From silicon carbide clusters to silicon-doped fullerenes (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 6927-6938 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Silicon carbon binary clusters are generated in a laser vaporization source from SixC1−x mixed targets (x=0 to 50%). We have first analyzed stoichiometric (SiC)n (n≤40) clusters grown from a silicon carbide target (x=50%). Both high fluence photoionization of (SiC)n neutral clusters and photofragmentation of size-selected (SiC)n+ natural positive ions show that silicon-doped fullerenes emerge as stable photoproducts through the laser induced annealing of these clusters. They are detected as stable species as soon as a sufficient amount of silicon is eliminated through unimolecular processes involving the sequential losses of Si2C and Si3C neutral molecules in the earliest evaporation steps. This result is in favor of an efficient substitution of silicon atoms (about 12) into stable "cagelike" carbon networks. We will also show that an efficient doping of carbon fullerenes with silicon atoms can be obtained in carbon-rich mixed clusters directly grown as positive ions from nonstoichiometric targets (x〈25%). Mass abundance spectroscopy gives a clear signature of cagelike structures where silicon atoms are substituted for carbon ones. The results on the favored stability of even-numbered C2n−qSiq+ clusters with q=0, 1, 2 are presented here in the size range: 2n=32–80. More largely doped species (q≥3) cannot be evidenced in abundance mass spectroscopy because of unavoidable mass coincidences. A careful analysis of the photofragmentation behavior of selected sizes relative to the laser fluence nevertheless succeeds in indicating the contribution to the photofragmentation spectra of largely doped heterofullerenes C2n−qSiq+ (q=7 at least) that mainly dissociate by the loss of small even-numbered mixed molecules such as Si2,Si3C,... . Both approaches are consistent with the surprising capability of substituting a large number of silicon atoms into fullerenes without destabilizing their cage structure too much. In this respect, a value close to 12 seems to be an upper limit. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478598
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  • 2
    Electronic Resource
    Electronic Resource
    Static dipole polarizability of small mixed sodium–lithium clusters (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 5568-5577 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the static dipole polarizability of Nay−xLix clusters (with y=2, 3, 4, and 8) by molecular beam deflection technique. For a given size, the polarizability of pure lithium clusters is smaller than the polarizability of pure sodium clusters. For mixed clusters, a smooth decrease in the polarizability is observed as the proportion of lithium atoms increases. For the NaLi molecule, both experimental permanent dipole and average polarizability have been obtained. Experimental results are compared to results of density functional theory and configuration interaction single and double (CISD) ab initio calculations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478455
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  • 3
    Electronic Resource
    Electronic Resource
    Direct measurement of the electric polarizability of isolated C60 molecules (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 9771-9772 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the first direct measurement of the electric polarizability of isolated C60 molecules by molecular beam deflection technique. We have obtained a value of 76.5±8.0 Å3 which is consistent with most of the recent calculations and slightly lower than the value of the polarizability of C60 measured in fullerite crystals. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478944
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  • 4
    Electronic Resource
    Electronic Resource
    Diabetes mellitus in patients with infantile cystinosis after renal transplantation (1999)
    Springer
    Pediatric nephrology 13 (1999), S. 524-529 
    Details
    ISSN: 1432-198X
    Keywords: Key words Infantile cystinosis ; Renal transplantation ; Diabetes mellitus ; Impaired glucose tolerance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Diabetes mellitus is a frequent long-term complication of infantile nephropathic cystinosis. We studied 44 cystinotic patients, aged 22.1±5.4 years, transplanted at a mean age of 11.3±2.5 years; 25% were treated with insulin at 20 years of age or 10 years after transplantation, and over half required insulin at latest follow-up. In comparison, diabetes mellitus occurred in only 1% of non-cystinotic transplanted patients. Sequential oral glucose tolerance tests (OGTTs) in these patients showed the progressive deterioration of glucose metabolism. All but 2 patients had an abnormal response at latest follow-up. The high doses of corticosteroid given after transplantation or during rejection episodes were responsible for transient insulin dependency. However, the development of impaired glucose tolerance and diabetes mellitus depended mainly on the cystinotic process, which developed slowly with time. The deterioration of glucose tolerance was correlated with a decreased early phase of insulin secretion, estimated from the plasma insulin level at 30 min of the OGTT, while there was no evidence of insulin resistance. The occurrence of diabetes mellitus correlated with a worsening of the vital prognosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004670050651
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  • 5
    Electronic Resource
    Electronic Resource
    Magnetic nanostructures of mixed cobalt–samarium clusters (1999)
    Springer
    The European physical journal 9 (1999), S. 475-478 
    Details
    ISSN: 1434-6079
    Keywords: PACS: 61.46.+w Clusters, nanoparticles, and nanocrystalline materials – 75.50.Tt Fine-particle systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We synthesized Co-Sm mixed clusters from a SmCo5 solid target mounted in a laser vaporization source. We studied both pure nanostructured SmCo5-cluster-assembled films and the same isolated clusters embedded in a matrix. The supported cluster size distribution centered around 3 nm was determined from transmission electron microscopy observations. Mass spectra obtained on the photoionized clusters in the gas phase and Rutherford backscattering spectrometry analyses performed on 100-nm-thick films confirm the conservation of the compound-target stoicheiometry in both free and deposited clusters. However, X-ray photoemission spectroscopy measurements seem to indicate a segregation of samarium at the cluster surface. This segregation effect could explain the low values of the magnetization and coercive fields obtained from magnetometry measurements with respect to those in the bulk SmCo5 crystallized phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050481
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  • 6
    Electronic Resource
    Electronic Resource
    Properties of silicon–carbon-cluster-assembled films (1999)
    Springer
    The European physical journal 9 (1999), S. 639-642 
    Details
    ISSN: 1434-6079
    Keywords: PACS: 61.46.+w Clusters, nanoparticles, and nanocrystalline materials – 81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We have investigated SiC films, obtained by the low-energy cluster beam deposition (LECBD) technique, and using AFM Raman and XPS spectroscopies. We produce these films at room temperature and in an ultrahigh vacuum environment to protect them from the pollution. The inner morphology of the clusters is close to an amorphous-like structure. However, most of the theoretical models predict an sp 3 hybridization, in disagreement with our experimental results. We find that the films are composed mainly by free components formed by rich silicon, rich carbon, and rich SiC regions, respectively. In our case, the mean hybridization of the rich carbon region is mainly sp n -like with 2〈n〈3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050517
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  • 7
    Electronic Resource
    Electronic Resource
    Production and stability of silicon-doped heterofullerenes (1999)
    Springer
    The European physical journal 9 (1999), S. 49-54 
    Details
    ISSN: 1434-6079
    Keywords: PACS: 36.40.-Qv Stability and fragmentation of clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Silicon–carbon binary clusters with various mean compositions are generated in a laser vaporization source from targets processed as mixtures of graphite and silicon powders. Their size distribution is first analyzed by time-of-flight mass spectroscopy, which shows the stability of carbon fullerenes doped with silicon atoms in substitutional sites. Further investigations on the level of silicon doping are carried out by means of the laser-induced fragmentation of selected sizes. The photoproduct size distributions give evidence for at least nine silicon atoms substituted into still stable fullerene networks. The synthesis of heterofullerenes is mainly assisted by the nucleation mechanisms from Si-C mixed atomic vapors. Just as in the case of externally doped fullerene precursors, the laser-induced annealing of stoichiometric silicon-carbide clusters appears as an alternative route to produce heterofullerenes in the gas phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050398
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  • 8
    Electronic Resource
    Electronic Resource
    Static electric dipole polarizabilities of alkali clusters (1999)
    Springer
    The European physical journal 9 (1999), S. 243-248 
    Details
    ISSN: 1434-6079
    Keywords: PACS: 36.40.-c Atomic and molecular clusters – 32.10.Dk Electric and magnetic moments, polarizability – 31.15.Ew Density functional theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We have measured the static dipole polarizability of lithium and sodium clusters (n=1-22). Values measured for sodium are in agreement with previous experiments. While the polarizability per atom for sodium clusters decreases slowly as a function of the cluster size, a sharp decrease between sizes 1 and 4 is observed for lithium clusters. Experimental values are compared to Density Functional Theory (DFT/PW91) calculations. The size evolutions for sodium and lithium cluster polarizabilities are well reproduced by our calculations. The sharp decrease observed for small lithium clusters is discussed in terms of electronic density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050433
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  • 9
    Electronic Resource
    Electronic Resource
    Angular distributions in photoelectron spectroscopy of small tungsten clusters: competition between direct and thermionic emission (1999)
    Springer
    The European physical journal 9 (1999), S. 21-24 
    Details
    ISSN: 1434-6079
    Keywords: PACS: 36.40.-c Atomic and molecular clusters – 33.60.Cv Ultraviolet and vacuum ultraviolet photoelectron spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Single-photon photodetachment of mass-selected W n - clusters has been studied by velocity map imaging. Photoelectron imaging allows us to measure simultaneously the kinetic energy spectrum and the angular distribution of photoelectrons, providing a clear distinction between the isotropic thermionic emission and the anisotropic direct photoemission. A careful study of threshold electrons shows that the thermal distribution p(ε) cannot be described, even qualitatively, by a simple exponentially decreasing Boltzmann function, as is usually assumed. On the contrary, our results are in excellent agreement with more refined theoretical models. Our results indicate that the transition towards a bulk-like statistical behavior of the internal energy redistribution occurs in very small systems, because of the high density of states in metal clusters. The asymmetry parameter β of the most intense band observed in direct photoemission for each cluster decreases monotonically with size; the direct photoemission of small systems is strongly anisotropic, and becomes isotropic as the size of the system increases. This probably indicates the loss of coherence induced by electron–electron collisions occurring in large systems prior to electron–phonon coupling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050392
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  • 10
    Electronic Resource
    Electronic Resource
    Plasmon-phonon coupling and resonant raman scattering of silver clusters (1999)
    Springer
    The European physical journal 9 (1999), S. 585-589 
    Details
    ISSN: 1434-6079
    Keywords: PACS: 36.40.-c Atomic and molecular clusters – 36.20.Ng Vibrational and rotational structure, infrared and Raman spectra – 63.20.Pw Localized modes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Absorption and low-frequency Raman scattering experiments have been performed on thin films consisting of small silver clusters embedded in a porous alumina matrix. When the Raman excitation wavelength is close to the maximum (≈420 nm) of the Mie band (dipolar surface plasmon resonance) the Raman spectra exhibit a strong band located around 10 cm-1, the maximum of which depends on the mean cluster diameter 〈D〉 in the sample according to the approximate law ωvib∝〈D〉-1. The Raman band corresponds to the excitation of the quadrupolar vibration mode of the clusters. Moreover, the maximum of the Raman band shifts towards lower frequencies when the excitation light is shifted to the red. This feature, as well as the rather large Mie-band width, is thought to reflect the ellipsoidal shape distribution of part of the embedded clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050505
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