Search

The structural and optical properties of thin Ge films deposited onto semiconducting and insulating substrates and modified by pulsed laser radiation are studied. The films are deposited by the sputtering of a Ge target with a low-energy Xe ion beam. Crystallization of the films is conducted by their exposure to nanosecond ruby laser radiation pulses (λ = 0.694 μm) with the energy density W = 0.2−1.4 J cm. During pulsed laser treatment, the irradiated area is probed with quasi-cw (quasi-continuous-wave) laser radiation (λ = 0.532 and 1.064 μm), with the reflectance recorded R( t). Experimental data on the lifetime of the Ge melt are compared with the results of calculation, and good agreement between them is demonstrated. Through the use of a number of techniques, the dependences of the composition of the films, their crystal structure, the level of strains, and the reflectance and transmittance on the conditions of deposition and annealing are established. [ABSTRACT FROM AUTHOR]

The electronic, geometric, and magnetic structure of nanofilms of the β phase of iron disilicide FeSi with the (001), (100), and (010) surfaces have been simulated through density functional calculations. A substantial reconstruction of the (001) surface terminated with silicon atoms has been observed, which was accompanied by an increase in the surface symmetry and appearance of 'squares' of silicon atoms. Analysis of the electron density of states (DOS) and spin DOS projected on the contributions of layers of atoms (LSDOS) indicates that all plates have metallic properties. The main contribution near the Fermi level comes from the surface iron layers and it decreases rapidly with an increase in the distance from the surface of the plate. Analysis of the calculated effective magnetic moments of atoms shows that the surface layers in the plates have a significant magnetic moment, in particular, iron layers on the (001) surface (1.89 μ/atom). The moments of atoms decrease rapidly with an increase in their distance from the surface. The electron and geometric regions of a (001)Si/FeSi interface have been studied. Analysis of the LSDOS shows that the surface conducting state mainly determined by the contribution from the near-surface silicide layers is implemented in this region. The possibility of the formation of the perfect and sharp Si/FeSi interface has been demonstrated. [ABSTRACT FROM AUTHOR]

Ab initio techniques have been used to investigate structural changes in semiconducting Mg 2 Si and Ca 2 Si thin films (from 17 nm down to 0.2 nm corresponding to the 2D structure) along with band-gap variations due to quantum confinement. Cubic Mg 2 Si(111) thin films being dynamically stable at thicknesses ( d ) larger than 0.3 nm displayed an indirect band gap, the reduction of which with increasing d could be reasonably well described by the simple effective mass approximation. Only 2D Mg 2 Si has a unique structure because of the orthorhombic distortion and the direct band gap. Since the surface energy of cubic Ca 2 Si(111) films was lower with respect to any surface of the orthorhombic phase, which is the ground state for the Ca 2 Si bulk, the metastable in-bulk cubic phase in the form of thin films turned out to be preferable in total energy than any orthorhombic Ca 2 Si thin film for d < 3 nm. Sizable structural distortion and the appearance of surface states in the gap region of Ca 2 Si thin films with d < 3 nm could be the reason for an odd dependence of the band-gap variation on d .

Nanocrystalline GaSb films were grown on Si(001) from the stoichiometric Ga⁻Sb mixture using solid-phase epitaxy at temperatures of 200⁻500 °C. Use of the solid-phase epitaxy method allowed the suppression of Ga surface diffusion and prevention of intense Sb desorption. At the annealing temperature of 300 °C, a 14-nm-thick GaSb film aggregates, while a 20-nm-thick GaSb film remains continuous with a roughness of 1.74 nm. A GaSb film with a thickness of 20 nm consists of crystalline grains with a size of 9⁻16 nm. They were compressed by ~2%. For some GaSb grains, new epitaxial relationships have been found: GaSb ( 111 ) ||Si ( 11 1 ¯ ) and GaSb [ 11 2 ¯ ] ||Si [ 1 1 ¯ 0 ] , GaSb ( 113 ) ||Si ( 11 1 ¯ ) and GaSb [ 1 1 ¯ 0 ] ||Si [ 1 1 ¯ 0 ] , and GaSb ( 11 1 ¯ ) ||Si ( 002 ) and GaSb [ 1 1 ¯ 0 ] ||Si [ 1 1 ¯ 0 ] .

Carrageenan:chitosan (CG:CH) polyelectrolyte complexes (PEC) were obtained and the effect of the initial components ratio on formation was studied by dynamic light scattering, atomic force microscopy (AFM) and electrokinetic measurements. Positively charged PEC particles (average ζ-potential 40.2 mV) were formed, provided that the polycation was present in excess in the complex and was stabilized by chitosan amino groups. According to the AFM data, chitosan was located on the surface of the carrageenan fibers. In PEC where carrageenan prevailed, the number of unbound sulfate groups decreased when the chitosan content increased, this resulted in a decrease in the PEC negative surface charge (from -92.4 to -55.6 mV). In this case, AFM showed that chitosan was incorporated into the network structure of carrageenan and breaks it at a CG:CH ratio of 1:0.5 w/w. Complexes with a high content of kappa-CG inhibited biofilm formation by Gram negative and Gram positive microorganisms., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The growth, composition and structure of sandwich structures (Fe-rich layer/Si-rich layer/Fe-rich silicide layer) grown on a Si(111) surface were studied by a few complementary microscopic and spectroscopic techniques with high spatial resolution. Intermixing at the Fe/Si and Si/Fe interfaces is demonstrated. Fe-rich layers grown directly on the Si(111) surface are crystalline and have abrupt but rough interfaces at both sides. The succeeding layers are disordered and their interfaces are fuzzy. The distributions of Fe and Si within the layers are laterally non-uniform. The reproducible fabrication of thin non-magnetic silicide spacers of predetermined thickness is demonstrated. Sandwich structures with such spacers exhibit exchange coupling between ferromagnetic Fe-rich layers.

By using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, a p(+)-Si/p-Si/β-FeSi2 nanocrystallites/n-Si(111) diode structure was fabricated. Transmission electron microscopy data confirmed a well-defined multilayered structure with embedded nanocrystallites of two typical sizes: 3-4 and 15-20 nm, and almost coherent epitaxy of the nanocrystallites with the Si matrix. The diode at zero bias conditions exhibited a current responsivity of 1.7 mA/W, an external quantum efficiency of about 0.2%, and a specific detectivity of 1.2 × 10(9) cm × Hz(1/2)/W at a wavelength of 1300 nm at room temperature. In the avalanche mode, the responsivity reached up to 20 mA/W (2% in terms of efficiency) with a value of avalanche gain equal to 5. The data obtained indicate that embedding of β-FeSi2 nanocrystallites into the depletion region of the Si p-n junction results in expansion of the spectral sensitivity up to 1600 nm and an increase of the photoresponse by more than two orders of magnitude in comparison with a conventional Si p-n junction. Thereby, fabricated structure combines advantage of the silicon photodiode functionality and simplicity with near infrared light detection capability of β-FeSi2.

The complexes of chitosan (Ch) with lipopolysaccharides (LPSs) from Escherichia coli O55:B5 (E-LPS) and Yersinia pseudotuberculosis 1B 598 (Y-LPS) of various weight compositions were investigated using quasi-elastic light scattering, ζ-potential distribution assay and atomic force microscopy. The alteration of ζ-potential of E-LPS-Ch complexes from negative to positive values depending on Ch content was detected. The Y-LPS-Ch complexes had similar positive ζ-potentials regardless of Ch content. The transformation of the supramolecular structure of E-LPS after binding with to Ch was revealed. Screening of E-LPS and Y-LPS particles by Ch in the complexes with high polycation was detected. The ability of LPS-Ch complex to induce biosynthesis of TNF-α and reactive oxygen species in stimulated human mononuclear cells was studied. A significant decrease in activity complexes compared to that of the initial LPS was observed only for E-LPS-Ch complexes., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The soluble polyelectrolyte complexes (PEC) κ-carrageenan (κ-CG):chitosan was obtained. Binding constant value (2.11 × 10(7)mol(-1)) showed high affinity of κ-CG to chitosan. The complex formation of κ-CG:chitosan 1:10 and 10:1 w/w was shown by centrifugation in a Percoll gradient. Using atomic force microscopy we showed that the supramolecular structure of the complexes is different from each other and from the macromolecular structure of the initial polysaccharides. The gastroprotective and anti-ulcerogenic effect of κ-CG, chitosan and their complexes was investigated on the model of stomach ulcers induced by indometacin in rats. PEC κ-CG:chitosan have gastroprotective properties which depend on their composition. Complex κ-CG:chitosan 1:10 w/w possesses higher gastroprotective activity than the complex 10:1 w/w. These results suggest that the gastroprotective effect of complexes can be associated with their protective layer on the surface of the mucous membrane of a stomach, which avoids a direct contact with the ulcerogenic agent., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

In the present article, the atomic force microscopy was applied to investigate macromolecular structures of various carrageenan types including hybrid polysaccharides (κ-, κ/β-, κ/ι-, λ-, and X-carrageenans) depending on polysaccharide concentration. The structures dependence on a polysaccharide concentration also was focused. κ-Carrageenan forms both single and two stranded structures at a low concentration. At high concentrations κ-, κ/β-, and κ/ι-carrageenans form fibrous network-like structures by a side-by-side association type at the same time for κ/ι-carrageenan end-to-end association type also was found. Comparably to κ-carrageenan, κ/β-carrageenan network was more open with coarser fibers while κ/ι-carrageenan structure is characterized with a more flexible network. Honeycombed structures due to end-to-end and side-by-side association types were observed for X-carrageenan, while λ-carrageenan formed honeycombed structures only at high concentrations. In order to investigate topographical parameters of the carrageenans macromolecular structure a new method of the autocorrelation function analysis was used for the first time., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

An explicitly polarizable force field based exclusively on quantum data is applied to calculations of relative binding affinities of ligands to proteins. Five ligands, differing by replacement of an atom or functional group, in complexes with three serine proteases-trypsin, thrombin, and urokinase-type plasminogen activator-with available experimental binding data are used as test systems. A special protocol of thermodynamic integration was developed and used to provide sufficiently low levels of systematic error along with high numerical efficiency and statistical stability. The calculated results are in excellent quantitative (rmsd = 1.0 kcal/mol) and qualitative (R(2) = 0.90) agreement with experimental data. The potential of the methodology to explain the observed differences in the ligand affinities is also demonstrated.

The authors have recently introduced a general, polarizable force field QMPFF fitted solely to high-level quantum mechanical data for simulations of biomolecular systems. Here the authors demonstrate using an advanced version QMPFF3 how the problem of insufficient accuracy of the MP2-based training set for the aromatic carbon atom type can be effectively solved by a simple model correction using state-of-the-art CCSD(T) data. The approach demonstrates excellent transferability, which is confirmed for three phases of matter by accurate calculations of the second virial coefficient for benzene vapor and various properties of liquid benzene and polyaromatic hydrocarbon crystals.

We have recently introduced a quantum mechanical polarizable force field (QMPFF) fitted solely to high-level quantum mechanical data for simulations of biomolecular systems. Here, we present an improved form of the force field, QMPFF2, and apply it to simulations of liquid water. The results of the simulations show excellent agreement with a variety of experimental thermodynamic and structural data, as good or better than that provided by specialized water potentials. In particular, QMPFF2 is the only ab initio force field to accurately reproduce the anomalous temperature dependence of water density to our knowledge. The ability of the same force field to successfully simulate the properties of both organic molecules and water suggests it will be useful for simulations of proteins and protein-ligand interactions in the aqueous environment.

The relationship between heart rate and errors and work quality was studied in the examinees during somatosensory, mathematic, and Lindolt's tests. There was a significantly higher correlation between the time course variations of heart rate, the types of cardiac regulation (central, respiratory, autonomic), and the levels of the achieved. There was a basic difference between the groups of subjects in their responses to testing errors, by reflecting in altered heart rate and work quality.