Terahertz radiation generation in multilayer quantum-cascade heterostructures

I–V and radiative characteristics of multilayer quantum-cascade GaAs/AlGaAs heterostructures with a double metal waveguide are investigated. The I–V characteristics typical of the quantum-cascade lasers are seen. The observed threshold-intensity growth and narrow radiation spectrum are characteristic of laser generation. The measured radiation frequency was found to be about 3 THz, which coincides with the calculated value. Thus, fully domestic terahertz quantum-cascade lasers are demonstrated for the first time.     

Mechanisms of Current Transfer in Electrodeposited Layers of Submicron Semiconductor Particles

Technical Physics Letters - Current–voltage (I–V) characteristics of conductance in multigrain layers of submicron particles of silicon, gallium arsenide, indium arsenide, and indium...     

Determination of <Emphasis Type="Italic">P</Emphasis>,<Emphasis Type="Italic">T</Emphasis>-conditions developed at high-temperature shock compression of silicon nitride in planar recovery ampoules

We performed experiments on shock compression up to pressures of 36 and 50 GPa of mixed samples of silicon nitride and potassium bromide, placed between copper plates that serve as walls of a recovery ampoule. For comparison, similar experiments were carried out by the conventional compression of a mixture of silicon nitride and copper powder. The loading of the samples was fulfilled by means of aluminum flyers accelerated by products of explosion to a few kilometers per second. The pressure profiles prior to a shock wave entering the sample and after its runout were measured with the use of manganin sensors. It is found that for the configurations of the experimental assembly used, the pressure in the samples, accumulated by circulating the shock wave, reaches the desired value before unloading. Based on estimates of the rate of heat transfer between the components, it is shown that thermal equilibrium can be set during the existence of high pressure in the mixed samples. Within the framework of the single-temperature medium model, the equations of state of the samples are derived, and the temperatures of their shock compression are calculated. Using these equations, we performed numerical simulations that showed good agreement with the experimental data.     

Direct observation of non-collinear vortex structures induced by twin boundaries in YBa2Cu3Oy single crystals

Using vector magnetic moment measurements, in twinned YBa₂Cu₃O_y single crystals we observe a nearly reversible M_ab component of the magnetisation with sharp peaks in the dependence of M_ab on the magnetic field H and angle between c-axis and magnetic field. The association of these features with twin boundaries is supported by geometrical arguments and by comparison with detwinned samples. For a crystal with a single dominant direction of twin boundaries, the initial slope of the M_ab(H) and M_ab() dependences corresponds closely to ideal shielding of the transverse H component, as expected for the fully-locked vortex state. The peak position, which is related to the locking angle, shows a close to linear H_p ^–1 vs dependence, which corresponds to a fixed value of H_L, the locking field. The influence of twins vanishes above a trapping angle T which shows rather weak temperature and magnetic field dependences; at 60K and 1T these parameters are _oH_L=27mT and _T 10 °.     

A combined work optimization technology under resource constraints with an application to road repair

We propose an approach for solving the task prioritization problem in road surface repair under bounded resources; the idea is to use a combination of defect recognition and classification methods based on statistical analysis and machine learning (random forests) with original methods for solving infinite-dimensional optimization problems (optical-geometric analogy). We show the results of a computational experiment that indicate high performance of the developed algorithms, and the resulting solutions were evaluated highly by experts in road facilities management. Our results may encourage more efficient use of resources to improve the quality of motorways.     

Phase relations in the HgCr2Se4-CdCl2 system

The phase relations in the HgCr₂Se₄-CdCl₂ system have been investigated using differential thermal analysis and x-ray diffraction, and the primary crystallization field of the spinel phase in this system has been located: 560–750°C, 84–97 mol % CdCl₂. By optimizing growth conditions and using CdCl₂ as a flux, single crystals of Hg_1?x Cd_xCr₂Se₄ solid solutions containing up to 5 wt % Cd have been grown.     

Self-assembly routes towards creating superconducting and magnetic arrays

Using self-assembly from colloidal suspensions of polystyrene latex spheres we prepared well-ordered templates. By electrochemical deposition of magnetic and superconducting metals in the pores of such templates highly ordered magnetic and superconducting anti-dot nano-structures with 3D architectures were created. Further developments of this template preparation method allow us to obtain dot arrays and even more complicated structures. In magnetic anti-dot arrays we observe a large increase in coercive field produced by nanoscale (50–1000nm) holes. We also find the coercive field to demonstrate an oscillatory dependence on film thickness. In magnetic dot arrays we have explored the genesis of 3D magnetic vortices and determined the critical dot size. Superconducting Pb anti-dot arrays show pronounced Little-Parks oscillations in T_c and matching effects in magnetization and magnetic susceptibility. The spherical shape of the holes results in significantly reduced pinning strength as compared to standard lithographic samples. Our results demonstrate that self-assembly template methods are emerging as a viable, low cost route to prepare sub-micron structures.     

High-frequency electrical properties of a vertical-cavity surface-emitting laser with a monolithically integrated electro-optical modulator

The high-frequency electrical properties of a vertical-cavity surface-emitting laser with a monolithically integrated electro-optical modulator are studied using small-signal modulation analysis of the electroreflectance. The experimental data obtained are approximated using the suggested equivalent electrical circuit, which accounts for the formation of a nonequilibrium space charge in the carrier-depletion region of the modulator. The bandwidth of the high-frequency electrical-signal transfer to the electro-optical region, determined for the suggested equivalent electrical circuit of the modulator, is shown to be 3GHz.