Trajectories of return surface magnetostatic waves in a ferrite-dielectric-metal structure magnetized by a nonuniform “ridge” field

Calculations are made of the trajectories of return surface magnetostatic waves (SMSWs) in a ferrite-dielectric-metal structure magnetized by a nonuniform “ridge” field. It is shown that there are four different types of trajectories. Conditions are determined for which the return SMSWs propagate in the direction opposite to the forward SMSWs and in the same direction as the forward SMSWs. Pis’ma Zh. Tekh. Fiz. 25, 61–66 (December 12, 1999)     

Identification of singular interfaces with Δ<Emphasis Type="Bold">g</Emphasis>s and its basis of the O-lattice

This article identifies singular interfaces according to singularity in terms of structural defects, including dislocations and ledges. Defect singularities are defined by the elimination of one or more classes of defects, which must be present in the vicinal interfaces. In addition to the three commonly classified structural interfaces, a new type of interface—the CS-coherent interface—is introduced. Singularities in dislocation and ledge structures have been integrated in the study of orientation relationships (OR). The dislocation structures are determined through the O-lattice theory, originally proposed by Bollmann. The basic concepts of the O-lattice and related formulas from the original theory and extended studies are briefly reviewed. According to the theory, singular interfaces exhibiting singularity in the dislocation structures have been identified. An interface that is singular with respect to the interface orientation must be normal to at least one Δg, a vector connecting two reciprocal points from different lattices. An interface that is singular also with respect to the OR must obey one or more Δg parallelism rules. The selection of proper Δgs for different preferred states of interfaces are explained. Identification of singular interfaces with measurable Δgs provides a convenient and effective approach to the interpretation of the observed facets and ORs. The ambiguity about the selection of the deformation matrix (A) for the O-lattice calculation and the advantage of the O-lattice approach over the approach using the Frank–Bilby equation for the calculation of the interfacial dislocations are clarified. Limitations of the present approach and further study are discussed.     

EXAFS investigations on PbMoO<Subscript>4</Subscript> single crystals grown under different conditions

Extended X-ray absorption fine structure (EXAFS) measurements on PbMoO₄_{\boldsymbol{4}} (LMO) crystals have been performed at the recently-commissioned dispersive EXAFS beamline (BL-8) of INDUS-2 Synchrotron facility at Indore, India. The LMO samples were prepared under three different conditions viz. (i) grown from a stoichiometric starting charge in air ambient, (ii) grown from a stoichiometric starting charge in argon ambient and (iii) grown from PbO-rich starting charge in air ambient. The EXAFS data obtained at both Pb L₃{\boldsymbol{L}}_{\boldsymbol{3}} and Mo K edges of LMO have been analysed to determine Pb–O, Pb–Mo and Mo–O bond lengths in the crystals. The information thus obtained has been used to examine the microscopic defect structures in crystals grown under different conditions.     

AlGaAsSb lasers emitting in the 1.6 μm region

AlGaAsSb lasers with different Al concentrations in the active and confinement regions are fabricated and investigated. The structures lase in the region ∼1.6 μm. The AlGaAsSb solid solution in the active region is a direct-gap material with a small energy separation (∼56 meV) between the direct-gap Γ minimum and the indirect-gap L minimum of the conduction band. The lasers have a single-mode spectrum with a predominant longitudinal mode in the spatial distribution of the emission. The lasers operate at room temperature in a pulsed mode. Pis’ma Zh. Tekh. Fiz. 25, 35–41 (May 26, 1999)     

Influence of local pressure on the current-voltage characteristic of Au-Si〈Ni〉-Sb structures

Results of an investigation of the influence of local pressure on the current-voltage characteristic of Au-Si〈Ni〉-Sb structures are presented for the first time. It is shown that nickel impurities in the silicon increase the total strain sensitivity n-Si〈Ni〉 structures. Pis’ma Zh. Tekh. Fiz. 23, 62–64 (May 12, 1997)     

Hysteresis of the current-voltage characteristics of porous-silicon light-emitting structures

A new hysteresis effect is described in metal-porous-silicon-p-type silicon structures and a new model is proposed to describe current flow in these structures. Pis’ma Zh. Tekh. Fiz. 23, 59–65 (June 12, 1997)     

Efficiency and reliability of metal-insulator-semiconductor radiative structures based on broad-band semiconductors with unipolar conductivity

This paper discusses the possibility of increasing the efficiency and reliability of radiation sources made from semiconductors with unipolar conductivity and operating in strong electric fields. To this end, the active region of the structure is fabricated in the form of alternating layers of different resistance, so that strong-field regions are spatially separated from luminescence-generation regions. The proposed idea is put into practice on M-i-n structures made from gallium nitride. The properties of fabricated LED structures are presented. Pis’ma Zh. Tekh. Fiz. 23, 17–23 (November 12, 1997)     

Long-wavelength uncooled sources of λ=5–6 μ radiation using graded-index InAsSb(P) layers grown by liquid-phase epitaxy

Graded-index p-n InAsSb/InAsSbP/InAs structures capable of emitting at the maximum of the spectral curve up to 5.4 μm with a half-width of ∼26 meV (∼0.6 μm) without cooling have been fabricated and studied. This is the longest-wavelength radiation obtained at room temperature in III–V structures grown by liquid-phase epitaxy and the band is the narrowest obtained for semiconductor spontaneous radiation sources. Pis’ma Zh. Tekh. Fiz. 24, 88–94 (March 26, 1998)     

Influence of pumping uniformity on current tuning of the emission wavelength of InAsSb/InAsSbP diode lasers

An investigation was made of continuous tuning of the emission wavelength in two types of InAsSb/InAsSbP diode heterolasers: three-layer structures with combined electrical and optical confinement and five-layer structures with separate confinement. In three-layer structures the emission wavelength initially decreases by 2–4 Å with increasing current and then increases by 10–15 Å. In five-layer structures the emission wavelength mainly decreases. This difference is attributed to the better flow of carriers in the bulk of the active region in five-layer structures as compared with three-layer ones. Pis’ma Zh. Tekh. Fiz. 24, 77–84 (March 26, 1998)     

Possible use of two-dimensional Bragg structures in an FEL amplifier powered by a sheet electron beam

It is shown that two-dimensional doubly-periodic Bragg structures can be used effectively in the amplification schemes of free electron lasers powered by sheet relativistic electron beams. The presence of such a structure ensures spatial coherence of radiation from different parts of the electron beam when the input signal propagates across the electron flux. Theoretical analysis shows that the gain in the regenerative scheme can reach 50 dB. Pis’ma Zh. Tekh. Fiz. 25, 87–95 (October 12, 1999)     

Polyethylene ionomer-based nano-composite foams prepared by a batch process and MuCell® injection molding

To understand the correlation between foamability and melt rheology of polyethylene-based ionomers having different degrees of the neutralization and corresponding nano-composites, we have conducted the foam processing via a batch process in an autoclave and microcellular foam injection molding (FIM) process using the MuCell^® technology. We have discussed the obtainable morphological properties in both foaming processes. All cellular structures were investigated by using field emission scanning electron microscopy. The competitive phenomenon between the cell nucleation and the cell growth including the coalescence of cell was discussed in light of the interfacial energy and the relaxation rate as revealed by the modified classical nucleation theory and rheological measurement, respectively. The FIM process led to the opposite behavior in the cell growth and coalescence of cell as compared with that of the batch process, where the ionic cross-linked structure has significant contribution to retard the cell growth and coalescence of cell. The mechanical properties of the structural foams obtained by FIM process were discussed.     

(BETS)2[RuX5NO] (X = Cl, Br): An Explanation of Different Conductive Properties Through Structural and Spectroscopic Studies

For the development of new crystal and electronic structures in molecular conductors, dimeric tetrathiafulvalene (TTF) and tetraselenafulvalenes (TSFs)1–3 linked by single or double methyl antimony bridge(s) have been prepared and their neutral crystal structures have been investigated. The donor2 (cis-2) forms a metallic cation radical salt with tetracyanoquinodimethane (TCNQ) containing one-dimensional array interactions.     

Resolution of optically addressed liquid-crystal spatial light modulators

Results are presented of calculations of the modulation transfer function of optically addressed, liquid-crystal, spatial light modulators based on layered photoconductor-liquid crystal structures, including surface-plasmon light modulators. Allowance is made for diffusive spreading of carriers in the photoconductor and the propagation length of surface plasmons in the layered structures. Pis’ma Zh. Tekh. Fiz. 24, 48–53 (July 12, 1998)     

Bolometric properties of silicon thin-film structures fabricated by plasmachemical vapor-phase deposition

A method of fabricating uncooled thermally sensitive sandwich structures based on amorphous hydrated silicon films is discussed and experimental results are reported. The structures have an area of 10⁻⁴ cm², a resistance of ≅10 kΩ, and a temperature coefficient of resistance ≃2%/K. At 30 Hz and a current of ≃1 μA, the excess noise exceeds the thermal resistance noise by a factor of 1.7. Pis’ma Zh. Tekh. Fiz. 23, 63–68 (June 26, 1997)     

Room-temperature lasing in structures with CdSe quantum islands in a ZnMgSSe matrix without external optical confinement

It has been shown that lasing may be achieved in structures with submonolayer CdSe inclusions in a ZnMgSSe matrix at above-room temperatures without additional optical confinement of the active region by thick layers of lower refractive index. The temperature dependence of the excitation density at the lasing threshold is typical of structures with three-dimensional carrier localization. Pis’ma Zh. Tekh. Fiz. 23, 26–30 (April 26, 1997)     

Enhancement of the efficiency of i-n-GaN light-emitting diodes by electrochemical etching

An investigation was made of the electrochemical etching of i-n-GaN light-emitting diode structures in aqueous solutions of KOH and NaOH to remove parasitic low-resistivity layers and inclusions in the structures which shunt the active current flow channels through the structures and lower the electroluminescence intensity. The electroluminescence intensity of the structures increased by two or three orders of magnitude during the etching process. Pis’ma Zh. Tekh. Fiz. 25, 55–60 (January 26, 1999)     

Synthesis and morphology of new functional polyimide/titania nano hybrid materials

The synthesis and full characterization of 3,5-diamino-N-(1-oxo-3-phenyl-1-(phenylamino)propan-2-yl)benzamide (5), as a new diamine monomer containing l-phenylalanine fractions in the structure of pendant group is presented. The stated diamine is employed as a key monomer for the in situ sol–gel fabrication of polyimide/titania nano hybrid thin films containing different titania contents. It is shown that titania particles are created in the size range of 20–80 nm, well-dispersed and enjoy the favorable spherical shapes supposing the constructive organic–inorganic interactions. The superior thermal stabilities of resulted nanocomposite films are confirmed using thermal analysis techniques. Moreover, the UV–Vis spectroscopy has shown the growing up in blocking efficiency along with the increase in titania contents. Predictably, the produced titania nanoparticles have amorphous structures.     

Mechanisms of photocurrent amplification in isotypic n +-GaSb-n 0-GaInAsSb-n +-GaAlAsSb heterostructures

Measurements of the current-voltage characteristics, the photocurrent, and its dependence of the latter on the bias voltage (forward and reverse) and the magnetic field were used to determine the current transport mechanisms in isotypic n⁺-GaSb-n⁰-GaInAsSb-n⁺-GaAlAsSb heterostructures. Two mechanisms of photocurrent amplification were observed. In structures with binary injection in the diffusion approximation amplification is caused by a change in the lifetime with the level of dark carrier injection. In structures with drift transport, amplification is caused by a “transit” effect. In both cases, the trapping levels play an important role. Pis’ma Zh. Tekh. Fiz. 24, 37–42 (May 26, 1998)     

Influence of sulfide treatment of profiled-interface Au-GaAs Schottky diodes on the polariton peak of the photoresponse

We discuss the feasibility of controlling the photosensitivity of metal/thin intrinsic-oxide/semiconductor surface-barrier structures under conditions of excitation of surface polaritons. These structures may be used as polarization-sensitive photodetectors. Pis’ma Zh. Tekh. Fiz. 23, 52–57 (May 12, 1997)     

Modified layered composite with high anisotropy of the piezoconstants e ij* and d ij*

A three-component composite combining features of structures with 2-2 and 3-1 connectivity and characterized by considerable piezoelectric anisotropy e ₃₃*/|e ₃₁|, d ₃₃/|d ₃₁*| is investigated for different volume concentrations of one of the components. An analysis is made of the physical factors influencing the piezoelectric anisotropy of the composite and causing the peculiar distribution of the internal stress and electric fields in this material. Pis’ma Zh. Tekh. Fiz. 24, 65–70 (June 12, 1998)