Blue luminescence of Au nanoclusters embedded in silica matrix

Photoluminescence study using the 325 nm He-Cd excitation is reported for the Au nanoclusters embedded in SiO2 matrix. Au clusters are grown by ion beam mixing with 100 KeV Ar+ irradiation on Au [40 nm]/SiO2 at various fluences and subsequent annealing at high temperature. The blue bands above ~3 eV match closely with reported values for colloidal Au nanoclusters and supported Au nanoislands. Radiative recombination of sp electrons above Fermi level to occupied d-band holes are assigned for observed luminescence peaks. Peaks at 3.1 eV and 3.4 eV are correlated to energy gaps at the X- and L-symmetry points, respectively, with possible involvement of relaxation mechanism. The blue shift of peak positions at 3.4 eV with decreasing cluster size is reported to be due to the compressive strain in small clusters. A first principle calculation based on density functional theory using the full potential linear augmented plane wave plus local orbitals (FP-LAPW+LO) formalism with generalized gradient approximation (GGA) for the exchange correlation energy is used to estimate the band gaps at the X- and L-symmetry points by calculating the band structures and joint density of states (JDOS) for different strain values in order to explain the blueshift of ~0.1 eV with decreasing cluster size around L-symmetry point.Comment: 13 pages, 7 Figures Only in PDF format; To be published in J. of Chem. Phys. (Tentative issue of publication 8th December 2004

Universal SSE algorithm for Heisenberg model and Bose Hubbard model with interaction

We propose universal SSE method for simulation of Heisenberg model with arbitrary spin and Bose Hubbard model with interaction. We report on the first calculations of soft-core bosons with interaction by the SSE method. Moreover we develop a simple procedure for increase efficiency of the algorithm. From calculation of integrated autocorrelation times we conclude that the method is efficient for both models and essentially eliminates the critical slowing down problem.Comment: 6 pages, 5 figure

Application of Raman spectroscopy to study the inactivation process of bacterial microorganisms

Raman spectroscopy (RS) is one of the promising approaches for structural and functional studies of various biological objects, including bacterial microorganisms. Both traditional biochemical tests and genetic methods which require expensive reagents, consumables and are time-consuming are used for bacterial analysis. Spectroscopic methods are positioned as noninvasive, highly sensitive, and requiring minimal sample preparation. In this work we investigated the possibility of using the RS method using optical sensors based on gold anisotropic nanoparticles. The applicability of the method was demonstrated by studying the effect of a broad-spectrum cephalosporin antibiotic and an extract of Viburnum opulus L (VO) on Escherichia coli (E. Coli) colonies. The studies were performed by Raman spectroscopy using a Virsa spectrometer (Renishaw). Raman signal amplification was carried out using two original optical sensors proposed by the authors. To create sensors, we used a chemical method of depositing gold nanostars on APTES-modified quartz glasses and a physical method for creating sensors based on anodizing titanium surfaces. The results of the study showed the high sensitivity and information content of the proposed method. The possibility of using the RS method for studying the inactivation of bacterial microorganisms is shown. Spectral Raman bands of E. Coli were determined and identified before and after exposure to VO extract and antibiotic as a control. A decrease in the intensity of spectral modes corresponding to amino acids and purine metabolites was found in the average Raman spectrum of E. Coli after exposure to VO extract. For the first time, a study of the antimicrobial effect of an aqueous extract of VO fruits was carried out by the method of Raman scattering. It has been shown that the use of plant extracts, including VO fruit extracts, to inactivate the vital activity of bacterial colonies is a promising approach to the search for new alternative antibacterial agents. The results obtained are in good agreement with the already known scientific studies and confirm the effectiveness of the proposed method

Translated from Pis'ma v Zhurnal Éksperimental'no oe i

The physics of the vortical state demonstrate a high diversity of phase transformations Recently, considerable progress has been achieved in the methods of creating artificial defects (see, e.g., In this work, we present new results of Monte Carlo modeling the vortex system with periodic pinning. It is shown that the magnetization curves have singularities that are caused by the influence of the periodic lattice of pinning centers. The vortex distribution patterns are obtained for different points on the M ( H ) curve. We have found that the vortex system with periodic pinning becomes ordered with an increase in temperature (inverse crystallization effect). Such an unusual behavior rarely occurs in nature. The inverse crystallization was observed in some magnetic materials We consider a three-dimensional bulk HTSC sample having layered structure in the xy plane. The sample has a finite thickness in the x direction and is infinite in the y and z directions. It is placed in a magnetic field aligned with the z axis to eliminate the demagnetization effects. We assume that the interlayer interaction in HTSC is weak and consider only a quasi-two-dimensional xy plate with thickness d to model a superconducting layer; i.e., we "cut out" a layer with thickness d along the z axis and consider it in our calculations. The sample boundaries in the x direction are the vortex sources, and the Meissner currents flow at a penetration depth. The thermodynamic Gibbs potential of the vortex system in the plate has the form (1) It includes the energies U ( r ij ) of pair interaction between vortices, the energies U p ( r i ) of interaction between vortices and pinning centers, the energies U m ( r i ) of interaction between vortices and Meissner currents, the self-energy U self of the vortex system, an