The study presents an investigation of the optical properties of rectangular -shaped aluminum nanoantenna arrays formed on the surface of an emitting GeSiSn/Si heterostructure with multiple quantum wells. The positions of the localized surface plasmon resonance modes excited along the long ( L ) and short ( S ) sides of the examined nanoantennas are determined utilizing the technique of Fourier -transform infrared reflectance anisotropy spectroscopy. Experimental results demonstrate that both L - and S -modes are located in the near -infrared range, and as the lateral dimensions of the nanoantennas increase, the modes' positions shift towards lower energies with an increase in the intensity of the resonance. The S -mode appears in the spectra as an overlay on the more pronounced L -mode with an intensity an order of magnitude lower. The geometry of the nanoantennas arrays with the resonance position near the photoluminescence peak of Ge 0.84 Si 0.076 Sn 0.084 /Si heterostructures ( E approximate to 0.65 eV) is characterized.

Studies of the optical absorption in the near-IR range of GeSn and GeSiSn layers of various compositions with a silicon content of up to 63% and tin up to 14% grown by molecular beam epitaxy are carried out. Two series of samples obtained on a nanostructured faceted surface and on a Si(100) surface were studied. It was found that at a telecommunication wavelength of 1.55 μm, the value of the GeSiSn absorption coefficient exceeds the value for Ge by more than 4 times. The bandgap values of GeSiSn with different compositions are determined. A good quantitative agreement of the calculated and experimental bandgap values and a qualitative agreement of the optical absorption spectra were obtained.

The work demonstrates the use of photomodulation FTIR spectroscopy to study structures containing epitaxial layers of GeSn and GeSiSn in the temperature range of 79-180 K. The photoreflectance method has enabled observation of direct interband transitions, and evaluation of the impact of temperature variation and mechanical strain on their energy values.

The current-voltage (I-V) characteristics and spectral dependences of the photocurrent of p-i-n structures, including GeSiSn/Si multiple quantum wells (MQWs) with the Sn content up to 15%, are studied. It is shown that the increase in the Sn content from 4.5 to 13% leads to a gradual increase in the dark current density from 6x10-6 A/cm2 to 5x10-5 A/cm2 at the reverse bias of 1 V. The further rise in the Sn content to 15% results in the increase of the dark current density to 5x10-4 A/cm2, which is an order of magnitude lower than the known values for GeSn-based photodiodes. The shift of the cutoff wavelength of the photoresponse with the Sn content increase in heterostructures is demonstrated. The photoresponse spectrum of the detector extends up to wavelengths of larger than 2 & mu;m at the Sn content of more than 10%.

Interband photoluminescence was obtained for structures with multiple quantum wells (MQWs) with different content of germanium and tin. Peak position in photoluminescence spectra obtained from the MQW of Ge _0.93-x Si _x Sn _0.07 /Si shifts to the long wavelength region with an increase in the Ge content in the solid solution and is observed in the energy range 0.85-0.68 eV for the germanium content from 30 to 78 % . Thus, the shift of the peak along the wavelength was observed from 1.46 to 1.82 μ m, and the total spectral range of MQW luminescence covered by these structures was 1.3–2.1 μ m. An even more significant shift of the MQW photoluminescence peak to the long-wavelength region was achieved by increasing the tin content. Increasing the fraction of Sn from 7 to 14 % while keeping the 30 % Ge fraction constant led to a shift of the peak from 0.85 to 0.75 eV. A simultaneous increase in the content of both tin and germanium in the solid solution (up to 14 and 79 μ m. A sharp ‘‘red’’ shift in the position of the photoluminescence peak with increasing temperature was discovered and its value reached 50 meV when the sample heating temperature was changed from 11 to 60–80 K. Such a significant shift in the position of the MQW photoluminescence peak is explained within the framework of a model that assumes that at low temperatures, charge carriers are randomly localized on spatial inhomogeneities of the MQW, and as the temperature increases, they are redistributed and transition to a thermodynamically equilibrium state with the lowest energy.

The thermal stability of carbohydrazide, hydrazine nitrate, acetohydroxamic acid in nitric acid solutions has been studied at atmospheric pressure and above atmospheric pressure. The volumes of gaseous products of thermolysis and the maximum rate of gas evolution have been determined at atmospheric pressure. It has been shown that, despite the high rate of gas evolution and large volumes of evolved gases, the conditions for the development of autocatalytic oxidation are not created. Exothermic processes are observed in a closed vessel in the temperature range of 50–250 °C. With an increase in the concentration of nitric acid, the temperatures of the onset of exothermic effects for all mixtures decrease, and the values of the total thermal effects of reactions increase, to the greatest extent for solutions with carbohydrazide.

The growth of multilayer structures with Ge0.3Si0.7-yGey/Si heterojunction at tin content from 0 to 18% was studied. The X-ray diffractometry method shows the presence of strict periodicity of layers and a high level of tin content. It has been established that GeSiSn compounds are thermally stable in the annealing temperature range of 300-550 °C. A photoluminescence signal in the infrared range of about 3 microns is observed from a structure with pseudomorphic GeSiSn layers.

A hybrid material including tin oxides on the top of a Ge0.3Si0.7–ySny/Si multiple quantum well structure has been first obtained. Tin oxides such as SnO and SnO2 were formed as a result of phase transitions during the oxidation of polycrystalline tin films (β-Sn). The photoluminescence was demonstrated with a maximum intensity at about 2.34 eV, which corresponds to the band gap of SnO. The glow at the photogeneration point is seen in green. The photoluminescence from SnO is observed after the annealing in the temperature range of 300-400 °C. An increase in the annealing temperature leads to a sharp quenching of the photoluminescence. It is associated with the phase transition from SnO to SnO2. The growth of Ge0.3Si0.7–ySny/Si multilayer structures is studied at the Sn content from 0 to 18%. It was found that GeSiSn compounds are thermally stable in the annealing temperature range of 300–550°C. In addition to the photoluminescence signal in the visible range from tin oxides, the photoluminescence signal in the infrared range of about 3 μm appears. It is formed from the GeSiSn/Si structure.

The gas evolution from mixtures consisting of 0.2 M solution of N,N,N′,N′-tetra-n-octyldiglycolamide (TODGA) in n-alcohol (n-decanol or n-nonanol) with Isopar-M diluent was investigated during thermal oxidation. The effect of ionizing radiation on their thermal stability has been studied. It has been determined that the volume of gaseous thermolysis products increases by 260% in the case of n-nonanol and 80% in the case of n-decanol compared to non-irradiated solutions. It has been shown that the gas evolution rate and gas volume increase when the irradiated mixture saturated with nitric acid is heated. However, there are no prerequisites for the development of autocatalytic oxidation.

The effect of accelerated electrons on the lower temperature limit of flame propagation in mixtures containing N, N, N ′, N ′-tetra- n -octyldiglycolamide and n -alcohol ( n -decanol and n -nonanol) in various concentrations in Isopar-M was studied. In the extraction mixtures irradiated to a dose of 0.5 MGy, the lower temperature limit of the flame propagation ( T L ) decreases insignificantly: by 2–3°C for the mixtures with 20% n -alcohol and by 6–11°C for those with 6% n -alcohol. The T L values for the extraction mixtures, including irradiated mixtures, are no lower than 64°C.

The hydrodynamic properties of three promising extraction mixtures, 0.05 M solutions of 2,2′-bi-pyridine-6,6′-dicarboxylic acid di( N -ethyl-4-hexylanilide) (DYP-7), 2,6-pyridinedicarboxylic acid di( N -ethyl-4-fluoroanilide) [Et( p FPh)DPA)], and 2,2′-bipyridine-6,6′-dicarboxylic acid di( N -ethyl-4-ethylanilide) (DYP-9) in trifluoromethyl phenyl sulfone (FS-13), were studied. The density, viscosity, surface tension, and settling rates in the steps of nitric acid extraction, stripping, and regeneration with sodium carbonate solutions were determined for these systems before and after the action of ionizing radiation. The concentrations of the extrac-tants in the irradiated samples were determined, and the radiation-chemical yields of their decomposition were calculated. The density and surface tension increase upon irradiation to a dose of 100 kGy but decrease upon further irradiation.

Hydrodynamic properties have been investigated for promising extraction systems: 0.05 mol L-1 solutions of di(N-ethyl-4-ethylanilide) of 2,2'-bipyridine-6,6'-dicarboxylic acid, di(N-ethyl-4-fluoroanilide) of 2,6-pyridinedicarboxylic acid and di(N-ethyl-4-hexylanilide) of 2,2'-bipyridine-6,6'-dicarboxylic acid in meta-nitrobenzotrifluoride (F-3) or trifluoromethylphenyl sulfone (FS-13) diluents. To evaluate the perspectives for their use as extraction mixtures at the final stage of the nuclear fuel cycle, the change in density, viscosity, surface tension, and phase separation rate under irradiation with accelerated electrons was studied. The concentrations of extractants in the irradiated mixtures have been determined and the radiation-chemical yields have been calculated. Irradiation significantly decreases the phase separation rate at the stages of extraction and back extraction for all the studied systems. The viscosity of the DYP-7 solution in FS-13 increase above the values suitable for its use in extraction processes. (C) 2019 Korean Nuclear Society, Published by Elsevier Korea LLC.

The thermal stability of mixtures of TBP and its solutions in diluents with uranyl nitrate (UN) at 150–200°C was evaluated. Exothermic self-accelerating oxidation processes (thermal explosions) arise in mixtures with TBP at 160–170°C. In mixtures of UN with solutions of TBP in diluents, the intensity of the exothermic processes is appreciably lower. The presence of the extractant in UN solutions fed to high-temperature operations gives rise to the hazard of the initiation of intense exothermic processes.

The dynamics of gas evolution in thermal oxidation of solutions of 2,2'-bipyridine-6,6'-dicarboxylic acid di(N-ethyl-4-hexylanilide) (DYP-7), 2,6-pyridinedicarboxylic acid di(N-ethyl-4-fluoroanilide) [Et(pFPh)· DPA], and 2,2'-bipyridine-6,6'-dicarboxylic acid di(N-ethyl-4-ethylanilide) (DYP-9) in m-nitrobenzotrifluoride (F-3) diluent with 14 M HNO3 in open and closed vessels was studied. The effect of preliminary irradiation of the organic phase on the kinetics of thermolysis of the two-phase system was determined. Heating of the irradiated samples in a closed vessel (autoclave) leads to the pressure buildup, with the pressure reached increasing from 18 to 23 atm as the absorbed dose is increased from 0 to 1 MGy. The exothermic processes occurring in the systems caused a 4 to 10°С increase in the sample temperature. The thermal stability of all the irradiated diamide–F-3 diluent extraction systems studied is acceptable for practical use.