HgCdTe quantum wells grown by molecular beam epitaxy

CdxHg₁₋xTe-based (x = 0 – 0.25) quantum wells (QWs) of 8 – 22 nm in thickness were grown on (013) CdTe/ZnTe/GaAs substrates by molecular beam epitaxy. The composition and thickness (d) of wide-gap layers (spacers) were x ∼ 0.7 mol.frac. and d ∼ 35 nm, respectively, at both sides of the quantum well. The thickness and composition of epilayers during the growth were controlled by ellipsometry in situ. It was shown that the accuracy of thickness and composition were ∆x = ± 0.002, ∆d = ± 0.5 nm. The central part of spacers (10 nm thick) was doped by indium up to a carrier concentration of ∼10¹⁵ cm⁻³ . A CdTe cap layer 40 nm in thickness was grown to protect QW. The compositions of the spacer and QWs were determined by measuring the Е₁ and Е₁+∆₁ peaks in reflection spectra using layer-by-layer chemical etching. The galvanomagnetic investigations (the range of magnetic fields was 0 – 13 T) of the grown QW showed the presence of a 2D electron gas in all the samples. The 2D electron mobility µe = (2.4 – 3.5)×10⁵ cm² /(V·s) for the concentrations N = (1.5 – 3)×10¹¹ cm⁻² (x < 0.11) that confirms a high quality of the grown QWs

New limits on nucleon decays into invisible channels with the BOREXINO Counting Test Facility

The results of background measurements with the second version of the BOREXINO Counting Test Facility (CTF-II), installed in the Gran Sasso Underground Laboratory, were used to obtain limits on the instability of nucleons, bounded in nuclei, for decays into invisible channels ($inv$): disappearance, decays to neutrinos, etc. The approach consisted of a search for decays of unstable nuclides resulting from $N$ and $NN$ decays of parents $^{12}$C, $^{13}$C and $^{16}$O nuclei in the liquid scintillator and the water shield of the CTF. Due to the extremely low background and the large mass (4.2 ton) of the CTF detector, the most stringent (or competitive) up-to-date experimental bounds have been established: $\tau(n \to inv) > 1.8 \cdot 10^{25}$ y, $\tau(p \to inv) > 1.1 \cdot 10^{26}$ y, $\tau(nn \to inv) > 4.9 \cdot 10^{25}$ y and $\tau(pp \to inv) > 5.0 \cdot 10^{25}$ y, all at 90% C.L.Comment: 22 pages, 3 figures,submitted to Phys.Lett.

Numerical study of the problem of electromagnetic oscillations of a three-layer spherical resonator filled with a metamaterial

Background. The purpose of the work is to solve the problem of electromagnetic oscillations of a three–layer spherical resonator, the middle layer of which is filled with metamaterial. Materials and methods. The boundary value problem for the Maxwell system of equations is reduced to solving scalar equations for Debye potentials. The dispersion equation is obtained with respect to the spectral parameter – the circular oscillation frequency. Results. The dispersion equation is solved numerically on the complex plane. Approximate resonant frequencies having a negative imaginary part and symmetrically located relative to the real axis are found. Conclusions. A numerical method for finding the resonant frequencies of a three-layer spherical resonator, the middle layer of which is filled with metamaterial, is proposed and implemented

System monitoring of concrete lining for the mining companies of Khibiny

The paper presents the research results on strength characteristics of monolith concrete and shotcrete supports with a non-destructive method, these characteristics reflect the operational state of the mine workings. The comparative assessment of the concrete strength under in-situ and laboratory conditions has been given. The geometrical parameters of the shotcrete support have been presente

Optimization of parameters of multilayer diffraction gratings using needle variations

Background. The purpose of the work is to optimize the diffraction efficiency in the first diffraction order of a multilayer diffraction grating. Material and methods. Needle variations are used to optimize diffraction efficiency. Results. Computational experiments were performed, which showed that the addition of a second line in the grating period significantly increased the diffraction efficiency in the first diffraction order. Conclusions. The use of needle variations is applicable in the design of multilayer diffraction gratings

On the propagation of electromagnetic waves in a dielectric layer coated with graphene

Background. The problem of propagation of electromagnetic waves in a dielectric layer coated on one side with a layer of graphene, which is considered to be infinitely thin, is considered. The main task in describing the process of wave propagation in a waveguide structure is to obtain a dispersion equation for the propagation constants. Materials and methods. Maxwell’s equations are solved in the frequency domain. The conjugation conditions contain the conductivity of graphene. In this work, we neglect the nonlinearity of graphene. Results and conclusions. A dispersion equation for TE waves in the structure is obtained. The results of calculations of propagation constants depending on the parameters of the problem are presented