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  • 1
    ISSN: 1435-1536
    Keywords: Scattering ; absorption ; aggregates of spheres ; electrolyte induced aggregation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Scattering and extinction of colloidal systems containing either nonabsorbing or strongly absorbing spherical particles of some nanometers in diameter were examined in the wavelength range from the near UV to the near IR. If aggregation occurs, scattering and extinction are modified with respect to the single sphere systems. The influence of aggregation can best be recognized for absorbing particles when already the single sphere shows resonant extinction. In this case, the resonance of the single sphere splits into many new resonances for the aggregate, most of which are positioned at larger wavelengths than the single sphere resonance. They strongly depend on the size and shape of the aggregate. Looking at the scattering, additional problems arise in systems of absorbing particles caused by reabsorption by neighboring spheres or aggregates. A simple model was developed to interpret the obtained scattering data.
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  • 2
    ISSN: 1434-6036
    Keywords: PACS. 78.66.Vs Microparticles - 61.46.+w Clusters, nanoparticles, and nanocrystalline materials - 81.05.Zx New materials: theory, design, and fabrication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The size and shape of silver nanoparticles which are embedded in a plasma-polymer matrix were obtained by transmission electron microscopy and analyzed with optical image processing. We used a sample in which silver particles were present before and after reshaping caused by thermal annealing in adjacent regions. As most of the particles appeared as elongated rotational ellipsoids, the major and minor half axis were determined for each particle. We adopted the model of Gans in the Rayleigh approximation to calculate for each investigated particle the extinction spectra from to using the data from the image processing. The various spectra for 368 silver particles were added to get total extinction spectra for the sample as deposited and after reshaping, respectively. We found good agreement with the experimental spectra. The blue shift of the plasma-resonance absorption, which occurs due to the reshaping of the silver particles during thermal annealing, was also confirmed by using only changes in the particle sizes and shapes.
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  • 3
    ISSN: 1435-1536
    Keywords: Surface charge ; colloidal particles ; charged clusters ; cluster plasmon ; blue shift ; red shift
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The optical response of colloidal particles depends on a variety of properties of the cluster, e.g., shape, size, size distribution and particle material. Since particles often are charged, also the surface charge may be a parameter which influences their optical properties. In this paper the effect of a surface charge on optical properties of spherical colloidal particles is studied and its magnitude is estimated by extended computations for silver clusters with surface plasmon in aqueous suspension. Two models are presented and discussed. The first model is based on the electrodynamic solution by Bohren and Hunt (Can. J. Phys. 55, 1930 (1977)), where a surface conductivity σS for a free surface charge yield an additional contribution εS to the dielectric constant of the particle material. In the second model, the surface charge contributes to the number density of free electrons in the cluster. Both models lead to a shift of the cluster plasmon peak, while an increase of the plasmon halfwidth could not be derived. The effect is quite small and limited on very small clusters.
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  • 4
    ISSN: 1434-6079
    Keywords: 41.70 ; 78.40 ; 82.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Small particles, produced in usual experiments, commonly form many-particle systems. Interactions of various kinds among the particles influence the properties of such systems. We consider here the optical properties of noble metal particle systems with separated nearly spherical particles and with aggregates formed by induced coagulation of the single particles. In order to describe their optical extinction we apply electrodynamic interaction models on particles and aggregates. We perform a quantitative analysis of the extinction spectrum of one selected sample with the electrodynamic interaction model.
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  • 5
    ISSN: 1434-6079
    Keywords: 36.40 ; 42.20 ; 78.00 ; 81.20 ; 81.40 ; 82.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract First, some general remarks concerning macroscopic “cluster matter” are given. In the second part, three recent, mainly optically and electron-microscopically performed investigations are discussed which deal with special properties of noble metal cluster systems forming the building units of this kind of matter:(1) dressed Au-55 clusters,(2) electromagnetic coupling effects among coagulated clusters,(3) the transition towards compact inhomogeneous matter caused by coalescence of clusters.
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  • 6
    ISSN: 1434-6079
    Keywords: 78.00 ; 82.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Samples are described which consist of coagulated quasi-fractal structures of 20 nm goldparticles embedded in a nonconducting matrix. By varying coagulation into coalescence electrical percolation can be induced while all topological parameters are kept constant. The first steps of percolation were investigated from the optical spectra. From calculations a fundamental limit for the splitting of plasmon modes in coagulation aggregates of arbitrary size and shape was found. In coalescence aggregates this limit is markedly surpassed. The percolation correlation length can be estimated therefrom. In the present case it amounts to about 300 nm.
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  • 7
    ISSN: 1434-6079
    Keywords: 79.60 ; 71.20 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We measured XPS and UPS spectra of gold clusters with 55 atoms, embedded in an electrically isolating phosphine matrix, and of gold-phosphine, from which the clusters were chemically derived. Compared to the spectra of bulk gold the valence band spectrum and the core level spectra of the clusters showed shifts of the peaks and the fermi level to higher binding energies. The shift of the peaks could qualitatively be interpreted by a final state effect. We succeeded in a separation of bulk and surface contributions to the core level spectra and in a reasonable quantitative analysis of the valence band spectrum of the clusters. The Au 4f core level spectrum of gold-phosphine showed two peaks at 1.5 eV higher binding energies than the corresponding peaks of the clusters.
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  • 8
    ISSN: 1434-6079
    Keywords: 41.70 ; 61.55 ; 73.40 ; 82.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Extinction spectra of Agx-Au(1−x)-alloy particles embedded in glass are compared to spectra of gold coated silver clusters and silver coated gold clusters. It is shown, that the optical extinction of alloy particles is described by the Mie theory applying the homogeneous dielectric function $$\hat \varepsilon $$ (ω,R, x) measured by Paquet. The absorption of core-shell clusters was calculated deriving an extension of the Mie theory to spheres with arbitrary numbers of shells of arbitrary materials. Comparison to measured spectra points to s-electron motion in the clusters with only slight scattering at the interior interface. The appearance of two distinct Mie peaks however proves the existence of the sharp Ag-Au interface. The extended Mie formalism was also applied to a multilayer system consisting of sodium and a dielectric substance as an example for a spherical hetero structure.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of cluster science 10 (1999), S. 319-358 
    ISSN: 1572-8862
    Keywords: Optical properties ; cluster aggregates ; extinction ; scattering ; depolarization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The effect of aggregation on the optical properties of nanometer-sized particles is studied. It is shown that for small noble metal clusters as well as for pigments of Fe2O3, TiN, or ZrN, the aggregation leads to changes in the color of the colloidal systems which are caused by electromagnetic coupling among the clusters in the aggregates. The model of interacting particles is shown to be helpful also for interpretation of optical properties of organic dyes with incorporated metal clusters and for interpretation of the reflectance of magnetooptical cluster systems. For soot particles it is shown that scattering and absorption are enhanced over the whole visible spectral region compared to isolated carbonaceous clusters. Finally, it is shown that the model of interacting clusters can also be applied for data interpretation in scanning near-field optical microscopy.
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  • 10
    ISSN: 1432-2242
    Keywords: Correlation ; Genetic gain ; Allele frequency ; Index weight
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The application of the selection index in the case of an additive two-trait model in which the genetic effect on each trait is determined by a finite number of loci is examined. Simulation results indicate that the direction of change in the frequency of favourable alleles is not necessarily in the positive direction at all loci when index selection is used as the basis for truncation selection. When the genetic correlation was positive (or favourable with respect to the economic weights), there was little difference (〈5%) in genetic gain over 20 generations and no difference in the direction of change in allele frequencies or genetic correlation whether or not updated values for the genetic (co)variances were used in constructing the selection index. However, when the genetic correlation was negative or unfavourable, the effect of using genetic parameters which were not updated had unexpected effects on the allele frequencies and genetic correlation and reduced the genetic gain by a greater amount (〈 12%).
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