B. Kh. Bairamov

Detection of high-resolution Raman spectra in short oligonucleotides

High-resolution spectra of single-chain short oligonucleotides d(20G, 20T), where d is a deoxyribonucleoside, G is guanine, and T is thymine, have been obtained by the highly sensitive nonresonant Raman scattering method of biomacromolecules. In addition to their own multifunctional significance, short oligonucleotides attract interest as ideal model objects for revealing poorly studied peculiarities of tertiary and quaternary structures of DNA. The detection of narrow spectral lines has allowed determining the characteristic time scale and makes it possible to study the dynamics of fast relaxation processes of vibrational motions of atoms in biomacromolecules. It has been found that the FWHM of the narrowest 1355.4 cm−1 spectral line attributed to the vibrations of the dT methyl group is 14.6 cm−1. The corresponding lifetime is 0.38 ps.

Photosensitivity of ZnO/CdS/Cu(In,Ga)Se2/Mo thin-film solar cells fabricated on various substrates

The results of measuring the first spectra of relative quantum efficiency for photoconversion in thin-film ZnO/CdS/Cu(In,Ga)Se2/Mo solar cells fabricated on rigid (glass) and flexible (polyimide) substrates are reported. The character of interband transitions has been studied and the values of the band gap for direct and indirect transitions in thin Cu(In,Ga)Se2 films are determined. It is found that a shift of the maximal photosensitivity for the obtained solar cells to shorter wavelengths is observed as rigid substrates are replaced by flexible ones. It is concluded that thin-film Cu(In,Ga)Se2 structures can be used as broad-band photoconverters of solar radiation.

Resonant Mandelstam-Brillouin light scattering and Raman scattering in semiconductors with intermediate exciton states belonging to discrete exciton bands and the continuous spectrum

The results of a theoretical and experimental investigation of resonant Mandelstam-Brillouin light scattering by thermal acoustic phonons with k=0 near the direct absorption edge (in the case of ZnSe crystals) are analyzed. The appearance of a new type of resonant increase in the intensity of Raman scattering by optical phonons with k≠0, which corresponds to resonance with the scattered light in the output channel, near the indirect absorption edge (in the case of semi-insulating GaP:N crystals) is also reported. The resonant gain reaches ∼4×103 at frequencies corresponding to overtone scattering assisted by LO(X) and LO(L) phonons. Exciton states belonging to both discrete exciton bands and to the continuous spectrum are considered as the intermediate states involved in the scattering processes in calculations of the resonant scattering tensors. In addition, all the intraband transitions, as well as the interband transitions between the conduction band, the valence bands, and the spin-orbit split-off band are taken into account, and good agreement with the experimental results is obtained.

Selective resonance enhancement of Raman scattering intensity in photoinduced nonradiative charge transfer

This paper reports on the formation of complexes consisting of isolated free-standing crystalline semiconductor quantum dots, for example, nc-Si/SiO2, functionalized by short oligonucleotides, for example, the single-stranded system d(20G, 20T). Here, d are deoxyribonucleotides, G and T are guanine and thymine nucleotides, respectively. It has been found that these complexes are unique objects for the elucidation of the specific features in the manifestation of new quantum-size effects in biomacromolecules. It has been demonstrated that the possibility exists of detecting and recording, in such complexes of biomacromolecules, spectrally selective resonance enhancement of Raman scattering intensity in fluctuations of nucleotide molecules due to coherent nonradiative transfer of a photoexcited electron and a hole at the interface of the complex. This dynamic optical imaging of spectral responses can be of applied interest for the development of nanobiophotonic technologies.

High-resolution Raman scattering in oligonucleotides

High-resolution Raman spectra have been obtained by a high-sensitivity nonresonant scattering technique for short single-strand oligonucleotides synthesized by the solid-state amidophosphite method on an automated synthesizer.

Quasielastic scattering of light by a photoexcited electron-hole plasma induced in a GaAs layer in the presence of InAs quantum dots

The development of a method for registering quasielastic electronic light scattering spectra in the near-IR region, which makes it possible to detect light scattering by a photoexcited electron-hole plasma induced in a GaAs layer in the presence of a self-organized ensemble of InAs quantum dots, is reported. A substantial resonance intensification of such scattering, two orders of magnitude greater than the values established for the bulk material, is observed, and the main mechanism of such scattering is determined.

Resonant raman scattering in complexes of nc-Si/SiO2 quantum dots and oligonucleotides

We report on the functionalization of nanocrystalline nc-Si/SiO2 semiconductor quantum dots (QDs) by short d(20G, 20T) oligonucleotides. The obtained complexes have been studied by Raman spectroscopy techniques with high spectral and spatial resolution. A new phenomenon of multiband resonant light scattering on single oligonucleotide molecules has been discovered, and peculiarities of this effect related to the nonradiative transfer of photoexcitation from nc-Si/SiO2 quantum dots to d(20G, 20T) oligonucleotide molecules have been revealed.

Quasielastic light scattering in the near IR from photoexcited electron-hole plasma created in a GaAs layer with embedded InAs quantum dots

The paper reports the development of a high-sensitivity technique for measurement of inelastic electronic light-scattering spectra in the near-IR region, which are excited by a stable single-mode cw YAG:Nd laser operating at 1064.4-nm. This technique has permitted detection for the first time of quasielastic scattering of light by a photoexcited electron-hole plasma generated in a GaAs layer with an embedded self-organized ensemble of InAs quantum dots. A considerable resonant enhancement of the quasielastic electronic scattering intensity exceeding the level characteristic of the bulk material by two orders of magnitude has been revealed. The main scattering mechanism, involving joint diffusion of electrons and holes, has been elucidated.

Optoelectronic effects in p-CdGeAs2 single crystals and structures based on them

Spectra of inelastic light scattering by optical phonons in p-CdGeAs2 single crystals were obtained for the first time. The observed clear polarization dependence and the absence of any appreciable dependence of the intensity and frequency of the observed lines when the sample is swept in ≈300 µm steps indicates these CdGeAs2 single crystals grown by directional crystallization from a near-stoichiometric flux, are of high quality and homogeneous. The type of symmetry of the observed phonon lines is interpreted and it is shown that the force constants in CdGeAs2 and CdSnP2 crystals differ slightly. Temperature dependences of the electrical conductivity and the Hall constant were studied in oriented homogeneous p-CdGeAs2 single crystals. It was established that the conductivity of these crystals is determined by the deep acceptor level EA=0.175 eV and has the degree of compensation 0.5–0.6. The temperature dependence of the Hall mobility reflects the competition between impurity and lattice mechanisms of hole scattering. The photosensitivity of In/CdGeAs2 surface barrier structures reaches 20 µA/W at T=300 K and remains at this level within the fundamental absorption of CdGeAs2. It is concluded that these structures may be used as wide-band photoconverters for natural light and as selective photoanalyzers for linearly polarized radiation.

Near-IR laser inelastic electronic light scattering spectroscopy on transitions between ground and excited states of acceptor centers in GaAs and InP crystals

We report the development of a method for recording the low-temperature (T=6 K) near-IR inelastic light scattering spectra and the observation of electronic scattering on the transitions 1s3/2(Γ8) → 2s3/2(Γ8) between the ground and excited states of different shallow acceptor centers in a n-type semi-insulating crystal si-GaAs (n=1.0 × 108 cm−3) and in a doped p-InP crystal (p=3.6×1017 cm−3). Moreover, a new line, associated with the transition 1s3/2(Γ 8) → 2p3/2(Γ8) and due to a dielectric local mode, recorded for the first time in the spectra of narrow-gap semiconductors, was found in the residual-frequency band in the p-InP spectrum between TO(Γ) and LO (Γ) phonons.