Realistic representation of the frequency dependence of dielectric function of noble metals has a significant impact on the accuracy of description of their optical properties and farther applications in plasmonics, nanoscience, and nanotechnology. Drude-type models successfully used in describing material properties of silver, for gold are known to be not perfect above the threshold energy at 1.8 eV. We give the improved, simple dielectric function for gold which accounts for the frequency dependence of the interband transitions over 1.8 eV and, in addition, for the finite size effects in gold nanoparticles. On that basis, we provide the improved characterization of the spectral performance of gold nanoparticles. Furthermore, we give the direct size dependence of the resonance frequencies and total damping rates of localized surface plasmons of gold nanoparticles (retardation effects are taken into full account) in diverse dielectric environments. The results are compared to the data obtained experimentally for gold monodisperse colloidal nanospheres, as well with the experimental results of other authors.

Alloying is a commonly accepted method to tailor properties of semiconductor materials for specific applications. Only a limited number of semiconductor alloys can be easily synthesized in the full composition range. Such alloys are, in general formed of component elements that are well matched in terms of ionicity, atom size and electronegativity. In contrast there is a broad class of potential semiconductor alloys formed of component materials with distinctly different properties. In most instances these mismatched alloys are immiscible under standard growth conditions. Here we report on the properties of GaN 1-x As x a highly mismatched, immiscible alloy system that was successfuly synthesized in the whole composition range using a non-equilibrium low temperature molecular beam epitaxy technique. The alloys are amorphous in the composition range of 0.170.2, and to the upward movement of the valence band for alloys with x<0.2. The unique features of the band structure offers an opportunity of using GaN 1-x As x alloys for various types of solar power conversion devices. 3 1. The Ga-N-As Alloy system Dilute alloysSemiconductor alloys formed through substitution of atoms with very different electronegativity and/or size have been known as highly mismatched alloys (HMAs).Because of large miscibility gaps, typically HMAs consist of a semiconductor matrix (elemental or compound) with the substitution of a small amount (up to several percents) of distinctly different isovalent atoms. The HMAs show large band gap reduction and their electronic structure is drastically different from their host materials. This is in contrast to conventional semiconductor alloys such as AlGaAs and GaAsP whose physical, electronic and optical properties can be deduced from a linear interpolation between their corresponding end point compounds with only a slight deviation, as predicted by the virtual crystal approximation (VCA). A most notable example of HMAs is the As-rich GaN x As 1-x in which strong band gap reduction by as much as 180 meV per mole percent of N has been observed [1,2,3,4]. The strong dependence of the band gap on the N content has made these diluted III-V nitrides important materials for a variety of applications, including long wavelength optoelectronic devices [5,6] and high efficiency hybrid solar cells [7,8].In contrast to the very extensively studied As-rich GaNAs alloys much less work has been devoted to HMAs on the N-rich side of this alloy system. It was found that GaN doped with As at low, impurity like levels shows a characteristic blue emission at room temperature. At higher As doping levels an abrupt decrease in the band gap of...

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͑͒The authors have succeeded in growing GaN 1−x As x alloys over a large composition range ͑0 Ͻ x Ͻ 0.8͒ by plasma-assisted molecular beam epitaxy. The enhanced incorporation of As was achieved by growing the films with high As 2 flux at low ͑as low as 100°C͒ growth temperatures, which is much below the normal GaN growth temperature range. Using x-ray and transmission electron microscopy, they found that the GaNAs alloys with high As content x Ͼ 0.17 are amorphous. Optical absorption measurements together with x-ray absorption and emission spectroscopy results reveal a continuous gradual decrease in band gap from ϳ3.4 to Ͻ1 eV with increasing As content. The energy gap reaches its minimum of ϳ0.8 eV at x ϳ 0.8. The composition dependence of the band gap of the crystalline GaN 1−x As x alloys follows the prediction of the band anticrossing model ͑BAC͒. However, our measured band gap of amorphous GaN 1−x As x with 0.3Ͻ x Ͻ 0.8 are larger than that predicted by BAC. The results seem to indicate that for this composition range the amorphous GaN 1−x As x alloys have short-range ordering that resembles random crystalline GaN 1−x As x alloys. They have demonstrated the possibility of the growth of amorphous GaN 1−x As x layers with variable As content on glass substrates. ͓͔

The iron crosslinked chitosan (Ch-Fe-CL) and N-carboxylmethyl chitosan (N-CM-Ch-Fe) complexes were studied by complementary techniques: structurally sensitive Mössbauer and X-ray absorption methods, as well as static magnetic measurements. A detailed and consistent description of these complexes including, besides the overall magnetic behavior, the spin ordering and local atomic structure around Fe ions is presented. Fe atoms in the investigated samples are mostly penta-coordinated and appear in a high spin Fe (3+) ionic state. In Ch-Fe-CL, two kinds of Fe near neighbors are equally probable and several Fe atoms are situated in the second coordination sphere. The magnetic interactions between these Fe ions lead to a sperimagnetic-like ordering. In N-CM-Ch-Fe, only one Fe neighborhood was found. Other Fe atoms were identified neither in the first nor in the second coordination sphere, but the third coordination sphere indicates the presence of Fe atoms. The magnetic coupling between these atoms is antiferromagnetic, but the dominant part of Fe in this sample remains in a paramagnetic state.

Changes of the local structure around Mn atoms in (Ga, Mn)As layers after high temperature annealing were determined by x-ray absorption spectroscopy (EXAFS) and high-resolution x-ray diffraction (HRXRD) measurements, and related to their magnetic properties. X-ray absorption is known to be able to detect crystalline structure changes occurring around investigated atoms. The qualitative and quantitative analysis of EXAFS spectra gives unambiguous evidence for the transition from a cubic to a hexagonal phase around Mn atoms as a result of annealing at temperatures of 500 and 600• C. The performed HRXRD investigation indicated a relaxation of the GaAs matrix during annealing, from highly to slightly compressively strained, and finally, after the formation of inclusions of hexagonal MnAs, to slightly tensile strained. The sample with hexagonal MnAs inclusions exhibits ferromagnetic properties up to room temperature with almost all Mn atoms being in a ferromagnetic phase.

A new alloy system, the GaN1‐xAsx alloys in the whole composition range was successfully synthesized using the non‐equilibrium low temperature molecular beam epitaxy method. The alloys are amorphous in the composition range of 0.17 < x < 0.75 and crystalline outside this region. The amorphous films have smooth morphology, homogeneous composition and sharp, well defined optical absorption edges. The bandgap energy varies in a broad energy range from ∼3.4 eV in GaN to∼0.8 eV at x∼0.85. The reduction of the band gap can be attributed primarily to the downward movement of the conduction band for alloys with x > 0.2, and to the upward movement of the valence band for alloys with x < 0.2. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)