Home – Home – Jornals – Avtometriya 2023 number 6

The paper presents experimental data on phonon and optical properties of (111)-oriented GaAs nanowires on a gold substrate studied by means of Raman scattering and photoluminescence (PL). The structural parameters of the nanowires are determined by atomic force and scanning electron microscopy (AFM and SEM, respectively). In the micro-Raman and micro-PL spectra of a single GaAs nanowire, phonon modes of GaAs and their overtones up to the third order and an exciton photoluminescence band are observed. In the micro-PL spectra, anisotropy of the PL intensity in nanowires is revealed, and the maximum/minimum signal is observed when the polarization vector is directed along/across the wire. Nano-PL maps of a single GaAs nanowire with a spatial resolution of 20 nm are obtained, which is significantly smaller than the diffraction limit. Plasmon enhancement of the near-field exciton nano-PL in the vicinity of the metallized tip of the AFM microscope is detected.

Under ultra-high vacuum conditions, epitaxial and polycrystalline films of iron (Fe), chromium (Cr), and calcium (Ca) silicides of various thicknesses (from 3.2 nm to 380 nm) are grown on silicon and sapphire substrates by three methods (solid phase epitaxy (SPE), reactive epitaxy (RE), and molecular beam epitaxy (MBE)). The crystal structure and matching with the silicon lattice are determined for them using the X-ray diffraction (XRD) method. A comparative analysis of Raman spectra (RS) and far-IR spectroscopy spectra shows that films of semiconductor silicides have the maximum intensity of Raman peaks, and the detected shifts in their positions are caused by distortions in the silicide lattices. It has been established that the intensity of Raman peaks in films of iron and chromium monosilicides at a fixed laser excitation wavelength (λ = 628.3 nm) and a power of 3.4 mW decreases with decreasing film thickness, which leads to their complete disappearance at a thickness below 10 nm. Chromium trisilicide films are grown on single-crystal sapphire, which makes it possible for the first time to detect Raman-active phonons at 214.3 cm^-1 and 273.1 cm^-1 at λ = 488 nm and a power of 0.42 mW. The studied films of transition metal monosilicides are of significant interest from the viewpoint of the prospects for their use as materials for thermoelectronics and spintronics, and systematic information on Raman-active and IR-active phonons will allow rapid determination the phase type formed immediately after film growth.

The spectral characteristics of optically detectable magnetic resonance (ODMR) are investigated for negatively charged nitrogen-vacancy (NV^-) centers in synthetic diamonds and nanopillars on their surface formed by a Ga⁺ focused ion beam (FIB), when lower spin sublevels are populated with the microwave radiation in 0-20 G magnetic fields. Both a significant decrease in the gyromagnetic ratio and the quenching of luminescence from the NV^- centers inclined to the nanopillar axis are revealed due to residual defects and stresses created by them.

Here we propose the use of photopolymer stereolithography to create millifluidic devices for spectroscopic studies. The efficiency of the approach is demonstrated by an example of the development of a millifluid cuvette for studying single mouse oocytes using Raman scattering under conditions of a varying composition of the surrounding solution. It is shown that using the “sandwich” cuvette designallows Raman measurements from samples inside the cuvette, despite the intense signal from the material from which the cuvette is made.

A method is proposed for determining the orientation of the pore direction in metal-organic frameworks from the spectra of polarized Raman scattering. The method uses the sensitivity of the intensity of the Raman lines to the geometry of light propagation in the crystal. The efficiency of the method is demonstrated on DUT-8 (Ni, Co) crystals. The interpretation results are interpreted by analyzing the symmetry and direction of vibrations within the framework of periodic calculations of the electron density functional theory. The joint approach makes it possible to describe the vibrations and find the main orientation of the crystal, which is collinear to the direction of the pores. The knowledge of the pore orientation is necessary for solving adsorption problems and creating complex multicomponent materials based on metal-organic framework compounds.

A new method for generating laser radiation without population inversion in the «red» wing of the D₁ line of alkali metal atoms under resonant absorption of broadband radiation from pump laser diodes at the D₁ transition has been theoretically investigated. The reason for the occurrence of laser generation is the fact that the probability of stimulated emission in the red wing of the spectral line exceeds the probability of absorption if the uniform broadening due to the interaction of active particles with the buffer gas significantly exceeds the natural one (at high pressures of the buffer gas). Analytical formulas that describe the operation of an alkali metal vapor laser under transverse diode pumping are derived. It has been found that the most promising objects for observing laser lasing without population inversion in the red wing of the D₁ line of alkali metal atoms are cesium atoms. In a sufficiently long active medium (the length of the medium is 50 times greater than its width), the conversion efficiency of pump radiation into laser radiation can reach 57% at a buffer gas pressure of 5 atm, a pump diode radiation intensity of 5 kW/cm², and a half-width of its spectrum of 1 cm^-1. The frequency of laser radiation can be tuned by several tens of cm^-1.

Narrow spectral modes comprising the generation spectrum of a random fiber laser near the threshold are of a great interest in both fundamental aspect and possible applications. The narrow bandwidth, stochastic generation nature, and relatively short lifetime lodge significant issues on the experimental equipment and utilized investigation methods. Possible attitudes for experimental registration and characterization of these modes are discussed in the present paper.

The problem of measuring the space-time and energy parameters of acoustic infrasound vibrations in the atmosphere based on the placement of laser and fiber lines in geoecological monitoring zones is considered. The measurements are based on the phenomenon of the acousto-optical transformation at infra-low frequencies associated with the influence of an external acoustic wave field on the characteristics of propagation of laser pulse beams in this field. Background and anthropogenic atmospheric acoustic processes are used as external sources of the field. The measured parameter is the phase (frequency) fluctuation atmospheric optical signal relative to the reference optical fiber signal. The characteristics of the atmospheric fiber laser system and some results of experiments aimed at estimating the statistics of phase fluctuations of atmospheric laser pulses and the parameters of infrasound fields in a given atmospheric monitoring zone are presented.

Solid and porous films of the Si _1-xGe_x alloys with a germanium content of about 40% and a thickness of 3-4 μm, formed on single-crystal silicon by electrochemical deposition of germanium into a porous silicon matrix followed by rapid thermal annealing at a temperature of 950 °C, are studied by Raman spectroscopy, optical spectroscopy, and scanning electron microscopy. Based on the Raman spectra taken in the Stokes and anti-Stokes frequency regions, using Boltzmann statistics and the Fourier thermal conductivity law, the thermal conductivity of the films is determined, which is found to be 7-9 and 3-6 W/(m×K) for a continuous and porous film, respectively. The low thermal conductivity of the porous film is explained by additional phonon scattering from the developed pore surface. The prospect of using such films in thermoelectric converters is ensured by the simplicity and scalability of the method for manufacturing the alloy, as well as its low thermal conductivity.

The method of Raman scattering (RS) is used to study samples of fossil coals from various deposits. An unusual form of the Raman spectrum of coal graphite from the Seregen deposit (Taimyr) is discovered. The spectrum consists of intense narrow bands, which are usually typical for single crystals, in contrast to the standard spectra for fossil coals, i.e., broadened D and G bands and a weakly pronounced second-order Raman spectrum. The studies have shown that there is no direct analogy between the spectra of the Taimyr sample of coal graphite and the Raman spectra of other allotropic forms of carbon. Based on the experiments carried out, it is suggested that there is a possibility of the existence of a new allotropic form of carbon.

The results of changing the parameters of pseudo-MOS-transistors on silicon-on-sapphire mesastructures under irradiation with swift heavy ions (SHI) Xe⁺²⁶ (150 MeV) and Bi⁺⁵¹ (670 MeV) to a fluence of 2´10¹¹cm^-2 are presented. They reveal the accumulation of mechanical stresses and charges in intermediate ferroelectric layers of HfO₂ (HO) films 20 nm thick and Hf_0.5Zr_0.5O₂ (HZO) films, laminated with Al₂O₃ monolayer inserts (HA, HZA) or without them. SOS heterostructures are formed by direct splicing and hydrogen transfer of 500 nm silicon films on HA and HZA nanolayers pre-deposited by plasma-enhanced atomic layer deposition on sapphire. The electrical parameters are determined from the Y-MOSFET drain-gate characteristics ( I_ds - V_g ) with 100 nm thick drain-stock W electrodes deposited by magnetron sputtering on the SOS mesastructures through a lithographic mask. A comparison of these characteristics with Raman scattering data shows that the mechanical compression stresses introduced by BTI irradiation in silicon correspond to the volume ratios of Xe and Bi tracks in HA ferroelectric and sapphire.

In this paper, we propose a technique for processing noisy spectral data, which allows implementing a mathematically sound selection of sharp signal peaks above an unknown smooth background, for which there is no reliable theoretical model. The main idea of the method is to construct an optimizing functional that predicts the most probable parameters of spectral lines. Unlike the Tikhonov regularization method, in which a smooth unknown function is extracted from the noisy signal, here we consider the problem of regularization of the superposition of a smooth background function with sharp peaks. The proposed approach provides an algorithm for processing experimental data that allows us to filter out random noise and determine both the parameters of the peaks and the background function with good accuracy. Finding the optimal regularization parameters is based on a priori assumptions about the smoothness of the background function and statistical properties of the random noise.

Based on the analysis of the main modern trends in the field of hyperspectral equipment construction, it is shown that the use of integrated optoelectronic circuits and optical nodes in planar design is promising when creating small-sized devices of a new generation focused on applications in ground-based surveillance systems. In particular, the expediency of using micro-mirror matrices in scanning systems and planar Mach-Zehnder interferometers in spectral separation systems is noted. This makes it possible to abandon bulky, slow, and not always reliable mechanical components and create devices with rapid registration of hyperspectral images.