Temperature dependence of growth-sector-dependent Raman spectra of boron-doped diamonds synthesized at high-pressure high-temperature.

Single crystals of boron-doped diamond (BDD) were synthesized by the temperature gradient method in high-pressure and high-temperature conditions in the Fe-Al-B-C system, and multisectoral diamond plates were extracted. Temperature-dependent (77-600 K) high-resolution Raman spectroscopic studies have been carried out to investigate the behavior of anharmonic phonon decay in the {001}, {113}, and {111} growth sectors of multisectoral diamond plates with different content of boron impurities (⩽80 ppm) and compare with the data for undoped IIa diamond. Micro-Fourier transform infrared spectroscopy was used to estimate the spatial distribution of uncompensated boron impurity[Na-Nd]in BDD plates by analyzing boron-related absorption peaks. The plates were shown to have non-uniform growth-sector-dependent content of uncompensated boron impurity in the range from 1.1 × 1018to 1.4 × 1019cm-3. The effects of anharmonic decay (damping) of optical phonons in BDD are studied by modeling the temperature dependence of phonon frequency and linewidth of the diamond's F2gand boron-induced vibrational modes. The extrapolated zero-temperature optical phonon linewidth and frequency and the anharmonic nature of their linear relationship are determined as a function of the growth sector and boron doping. The predominant mechanisms and parameters of the anharmonic decay of optical phonons are determined, which is of fundamental importance for the thermal conductivity of semiconductor materials. The anharmonic phonon decay remained the predominant process at higher temperatures, irrespective of the doping level.

The effect of 2D tungsten disulfide nanoparticles on Lewis lung carcinoma cells in vitro.

The unique physicochemical properties of modern two-dimensional (2D) nanomaterials with graphene-like structures make them promising candidates for biology and medicine purposes. In this article, we investigate the influence of the two-dimensional tungsten disulfide (2D WS2) water suspension nanoparticles obtained by an improved mechanochemical method from powdered WS2 on morphological and structural characteristics of Lewis lung carcinoma cells using FT-IR, Raman spectroscopy, and confocal microscopy. The characterization of the 2D WS2 nanoparticles by different physical methods is given also. We have highlighted that 2D WS2 does not exert cytotoxic activity in the case of 1 day incubation with tumor cells. Prolongation of the incubation period up to 2 days has caused a statistically significant (p < 0.05) concentration-dependent decrease of the number of viable cells by more than 30% with the maximum cytotoxic effect at concentrations of 2D WS2 close to 2 µg ml-1. In the Raman spectra of 2D WS2 treated cells the bands centered at 354 cm-1 and 419 cm-1, which are assigned to characteristics and modes of WS2 nanoparticles were observed. The obtained data indicate, that the cytotoxic effect of 2D WS2 on tumor cells in the case of long-term incubation is realized particularly through the ability of 2D WS2 to enter tumor cells and/or accumulate on their surface, which gives a rationale to conduct further studies of their antitumor efficacy in vitro and in vivo when combined with chemotherapeutic drugs.

Dispersion of electron-phonon resonances in one-layer graphene and its demonstration in micro-Raman scattering.

In the present work, we used Raman spectroscopy as sensitive tool for characterization of dispersion of electron-phonon resonances in one-layer graphene. We analyzed Stokes and anti-Stokes components of the Raman spectra to investigate the temperature dependence of the graphene G-band on the power of exciting radiation. Appearance and drastic intensity increase of zone-edge D-like modes caused by introduction of structural defects and/or deformations in the graphene layer were observed in the Raman spectra at high powers of excitation. We investigated phonon dispersion of one-layer graphene for iTO phonon branch at K point along K-M direction, which is involved in double-resonance Raman scattering. Raman dispersion slope of D-band is in good agreement with results of theoretical calculations based on the Green's functions approach based on the screened electron-electron interaction. Deviation of the experimental iTO phonon frequency from the linear dependence on excitation energy was observed at excitation E(exc) = 3.81 eV. Self-consistent classification of phonon states according to the symmetry for all dispersion branches of one-layer graphene was carried out.

Low- and high-frequency intermediate modes with step-like dispersion in resonance Raman scattering of carbon nanotubes.

Resonance Raman spectra of mixture of single-wall carbon nanotubes were investigated in details. The diameter distribution of the investigated nanotubes was estimated from the experimental frequencies of radial breathing modes. Two series of two-phonon lines revealing step-like behavior with excitation energy as well as non-dispersive single-phonon lines were registered in the intermediate frequency range 200-1200 cm(-1). Observed Raman lines were analyzed and their assignment to particular phonons was carried out. Step-like dispersive high intermediate-frequency modes in the range of 720-1000 cm(-1) are attributed to resonance two-phonon processes with combinations of optical and acoustical modes Low intermediate-frequency modes in the range of 300-650 cm(-1), also revealing step-like behavior, are attributed to resonance two-phonon processes with combinations of flexural optical and acoustical modes.

Band offsets and photocurrent spectroscopy of Si/Ge heterostructures with quantum dots.

Raman and lateral photoconductivity spectra of self-assembled SiGe nanoislands were studied with a height of ∼2 nm and a base of ∼20 nm formed at a temperature of 500 °C. It was estimated that the value of elastic deformation (ε(xx)) was -0.022 (ε(zz) = 0.017), while the germanium content in the islands (x) was 0.66. The obtained values of x and ε were used to calculate band offsets at the interfaces and the energy of interband transitions of structures under study. It was shown that the minimal energy of photocurrent observation is 0.52 eV, which is below the bandgap of the QDs under study. The first photocurrent component which began to contribute at 0.52 eV and had a peak at 0.68 eV is explained by optical transitions of electrons from the QD HH localized states of the valence band to the conduction band Δ(2) valley of the surrounding silicon matrix in which tensile strains are present. The second component with limiting energy of 0.73 eV can be caused by interband electron transitions from the HH valence band of the QDs to the Δ(4) valley of the QD conduction band.