A. I. Bobrov

Thermal evolution of the morphology, structure, and optical properties of multilayer nanoperiodic systems produced by the vacuum evaporation of SiO and SiO2

The alternate vacuum evaporation of SiO and SiO2 from separate sources is used to produce amorphous a-SiOx/SiO2 multilayer nanoperiodic structures with periods of 5–10 nm and a number of layers of up to 64. The effect of annealing at temperatures Ta = 500–1100°C on the structural and optical properties of the nanostructures is studied. The results of transmission electron microscopy of the samples annealed at 1100°C indicate the annealing-induced formation of vertically ordered quasiperiodic arrays of Si nanocrystals, whose dimensions are comparable to the a-SiOx-layer thickness in the initial nanostructures. The nanostructures annealed at 1100°C exhibit size-dependent photoluminescence in the wavelength range 750–830 nm corresponding to Si nanocrystals. The data on infrared absorption and Raman scattering show that the thermal evolution of structural and phase state of the SiOx layers with increasing annealing temperature proceeds through the formation of amorphous Si nanoinclusions with the subsequent formation and growth of Si nanocrystals.

Impact of growth and annealing conditions on the parameters of Ge/Si(001) relaxed layers grown by molecular beam epitaxy

Influence of the Ge layer thickness and annealing conditions on the parameters of relaxed Ge/Si(001) layers grown by molecular beam epitaxy via two-stage growth is investigated. The dependences of the threading dislocation density and surface roughness on the Ge layer thickness, annealing temperature and time, and the presence of a hydrogen atmosphere are obtained. As a result of optimization of the growth and annealing conditions, relaxed Ge/Si(001) layers which are thinner than 1 μm with a low threading dislocation density on the order of 107 cm–2 and a root mean square roughness of less than 1 nm are obtained.

Forming dense arrays of gold nanoparticles in thin films of yttria stabilized zirconia by magnetron sputtering

Layers of Au nanoparticles (NPs) were formed in films of yttria stabilized zirconia (YSZ) on fusedquartz substrates by layer-by-layer magnetron deposition with subsequent annealing. The obtained structures were studied by applying high-resolution transmission electron microscopy (TEM) to transverse sections and using optical absorption spectroscopy. TEM studies revealed the formation of Au NPs with a diameter of 2?3 nm concentrated in a thin layer within the YSZ film. The optical absorption spectra of the studied samples exhibited peaks of resonance plasmon absorption in Au NPs with a maximum wavelength of ~650 nm. The dependences of geometric and structural parameters of Au NP arrays (size, density, thickness of the Au NP layer, etc.) on the formation conditions were determined, and the regimes of fabrication of dense Au NP arrays that allow for collective plasmon excitations were identified.

Capacitors with nonlinear characteristics based on stabilized zirconia with built-in gold nanoparticles

It is shown that capacitors based on stabilized zirconia with gold nanoparticles exhibit nonlinear properties: the admittance of these capacitors depends on the amplitude of the control voltage, test-signal frequency, and temperature. The nonlinearity is due to electron capture by traps generated during nanoparticle formation. The possibility of determining the trap parameters by measuring the capacitor admittance has been established.

Peculiarities in the formation of gold nanoparticles by ion implantation in stabilized zirconia

The investigation of bulk single crystals and sputter-deposited films of yttria-stabilized zirconia (YSZ) upon irradiation by gold (Au) ions with an average energy of 160 keV followed by postimplantation annealing revealed peculiarities in the formation of nanocrystalline metal (nc-M) particles in this matrix. In the case of irradiation to small doses (∼5 × 1015 cm−2), the optical absorption spectra of samples showed evidence of the formation of nanoclusters of matrix cations (nc-Zr). In these samples, postimplantation annealing at temperatures ∼700°C and above leads to the formation of nc-Au particles. Local elemental analysis of individual nc-M particles in the YSZ matrix irradiated to a dose of 4 × 1016 cm−2 and annealed at 800°C showed the presence of metal nanoparticles with complex compositions including both implanted Au and matrix Zr atoms.

Application of cobalt in spin light-emitting Schottky diodes with InGaAs/GaAs quantum wells

Spin injection light-emitting diodes based on heterostructures with InGaAs/GaAs quantum wells and a ferromagnetic metal (Co) contact layer are fabricated and studied. The effect of the penetration of cobalt in GaAs is experimentally detected. It is demonstrated that the use of tunnel-thin (1–3 nm) Al2O3 layers as diffusion barriers leads to a decrease in the concentration of cobalt atoms in the semiconductor surface layers. In diodes with the Co/Al2O3/GaAs contact, circularly polarized radiation is detected, which is caused by the injection of spin-polarized holes from the ferromagnetic contact into the semiconductor.

Annealing-induced evolution of the structural and morphological properties of a multilayer nanoperiodic SiOx/ZrO2 system containing Si nanoclusters

The structural and morphological properties of nanoperiodic structures produced by the alternate vacuum evaporation of SiO and ZrO2 followed by annealing at temperatures of 500–1100°C are studied by the transmission electron microscopy of a transverse cross section. Upon annealing at temperatures below 700°C, the layers are amorphous. Upon annealing at 900°C and 1000°C, nanocrystals separated by twinned boundaries or amorphous regions are formed in the ZrO2 layers. The formation of Si nanocrystals in the SiOx layers occurs upon annealing at 1000°C and 1100°C. At 1100°C, because of the reaction between SiOx and ZrO2, spherical SixZryOz-type nanocrystals are formed in place of the ZrO2 layers; the nanocrystal diameters exceed the initial layer thickness. The annealing-induced structural evolution is consistent with the previously considered behavior of the optical and luminescence properties of the system.

Anomalous Hall effect in two-phase semiconductor structures: The role of ferromagnetic inclusions

The Hall effect in InMnAs layers with MnAs inclusions of 20-50 nm in size is studied both theoretically and experimentally. We find that the anomalous Hall effect can be explained by the Lorentz force caused by the magnetic field of ferromagnetic inclusions and by an inhomogeneous distribution of the current density in the layer. The hysteretic dependence of the average magnetization of ferromagnetic inclusions on an external magnetic field results in a hysteretic dependence of RH(Hext). Thus we show the possibility of a hysteretic RH(Hext) dependence (i.e. observation of the anomalous Hall effect) in thin conductive layers with ferromagnetic inclusions in the absence of carriers spin polarization.

Structural studies of a ferromagnetic GaMnSb layer

The crystalline structure and composition of a GaMnSb film is studied. The film is produced on a GaAs (100) substrate by deposition from laser plasma in a hydrogen flux at a temperature of 400°C. The formation of GaMn inclusions in the GaSb:Mn matrix is detected. The stoichiometry ratio of the inclusions corresponds to that of the Ga162.5Mn101.5 compound.

Time and energy reconstruction at the electromagnetic calorimeter of the Belle-II detector

The Belle-II electromagnetic calorimeter inherited crystals and front-end electronics from the Belle detector, however the readout electronics was essentially modified. New electronics provides continuous digitization of the shaped signal followed by the signal wave form analysis with the further reconstruction of both, amplitude and time of the signal. The time information allows one to suppress background essentially. The algorithm, which is implemented in FPGA, is properly simulated. We implemented this algorithm to the simulation software and studied it with the MC background data. The procedure for the calibration of the response function has been developed and tested with the barrel counters using cosmic-ray data.