Evidence for Irradiation Triggered Nonuniform Defects Distribution in Multiharmonic Magnetic Susceptibility of Neutron Irradiated YBa2Cu3O7?δ

Multiharmonic ac-magnetic susceptibility χ₁, χ₂, χ₃, of neutron irradiated Li-doped YBa₂Cu₃O_{7− x} has revealed a nonmonotonic dependence of all harmonics on the neutron fluence. The irradiation has a strongly depressive influence on the intergrain connection suggesting an increase of the effective thickness of the intergranular Josephson junction at a neutron fluence of 0.98 × 10¹⁷ cm⁻². Less damaged are the intragrain properties. A spectacular enhancement of the superconducting intragranular properties reflected in the characteristics of all harmonics was observed at highest fluence Φ = 9.98 × 10¹⁷ cm⁻². We assume that this effect results from the development of a space inhomogeneous distribution with alternating defectless and defect-rich regions.     

Nitriding of technical-purity titanium in hollow-cathode glow discharge

The process of nitriding at low pressures and temperatures (≤550°C) in hollow-cathode glow discharge plasma was studied for technical-purity titanium of the VT1-0 commercial grade. The diffusion saturation of titanium with nitrogen in plasma with a concentration of n = 10¹⁰–10¹¹ cm⁻³ takes place at an ion current density on the cathode within 1.6–4.0 mA/cm². It is established that a key role in the process of metal saturation is played by atomic nitrogen. The experiments revealed the formation of a layer of gradient structure with a high microhardness (∼14 GPa) on the surface of nitrided titanium.     

Sorption-atomic-absorption determination of platinum,palladium, and rhodium in dead autocatalysts

The conditions for determination and group concentration of platinum metals (PMs) in the presence of matrix components using new S,N-containing complex-forming sorbents in solutions obtained after decomposition of decontaminated autocatalysts are proposed. The technique of atomic-absorption determination of PMs from a solution (n × 10⁻⁴−n × 10⁻²; s _r = 0.15–0.07) and a solid phase (n × 10⁻⁵−n × 10⁻⁴; s _r = 0.20–0.12) is developed.     

Structural and electrical characteristics of epitaxial InP layers on porous substrates and the parameters of related Au-Ti Schottky barriers

The structures comprising three epitaxial InP layers—buffer (n ⁺⁺), active (n), and contact (n ⁺)—were grown by liquid phase epitaxy on porous and compact (control) InP(100) substrates. High quality of the active n-InP layer obtained on a porous substrate (in comparison to the control samples) is confirmed by the values of the halfwidths of the (311) X-ray diffraction reflections (54″ versus 76″), dislocation concentration (5×10²−5×10³ cm⁻² versus 5×10⁴−5×10⁵ cm⁻²), and electron mobility (4000 cm²/V s versus 3000–3500 cm²/V s). Using these homoepitaxial InP structures, Au-Ti Schottky diodes with a working mesastructure area of ∼1.8￠10⁻⁶ cm² were prepared. It was found that diodes based on the porous substrates are characterized by significantly smaller leak currents and higher breakdown voltages as compared to those of the control diodes: 1 nA, 27 V versus 200 nA, 15 V.     

The effect of hydrogenation on the photoconductivity of ion-doped gallium arsenide structures

It was found that the hydrogenation of ion-doped n ⁺-n-n _i -GaAs structures in atomic hydrogen increases the rate of conductivity relaxation in the doped layers, decreases the effect of bias voltage applied to the n ⁺-GaAs layer on the photoconductivity, and improves characteristics of the Schottky barrier transistors and the related integrated circuits. These phenomena are probably due to the formation of hydrogen complexes with electrically active centers in GaAs.     

Defect formation in silicon implanted with ∼1 MeV/nucleon ions

Defect formation processes in silicon implanted with ∼1 MeV/nucleon boron, oxygen, and argon ions have been studied using microhardness and Hall effect measurements. The results indicate that ion implantation increases the surface strength of silicon single crystals owing to the formation of electrically inactive interstitials through the diffusion of self-interstitials from the implantation-damaged layer to the silicon surface. The radiation-induced surface hardening depends significantly on the nature of the ion, its energy, and the implant dose. In the case of low-Z (boron) ion implantation, the effect had a maximum at an implant dose of ∼5 × 10¹⁴ cm⁻², whereas that for O⁺ and Ar⁺ ions showed no saturation even at the highest dose reached, 1 × 10¹⁶ cm⁻². When the ion energy was increased to ∼3 MeV/nucleon (210-MeV Kr⁺ ion implantation), we observed an opposite effect, surface strength loss, due to the predominant generation of vacancy-type defects.     

Photothermoelectric converters of concentrated radiation

Photothermoelectric converters (PTECs) are proposed for the energy supply of low-power-consumption devices. The photoelectric units of PTECs employ high-efficiency solar cells based on the p-Al_xGa_{1− x} As-n-GaAs heterosystem. The thermoelectric units employ a ternary alloy of the n-BiTeSe-p-BiTeSb type. A new PTEC with a two-stage photoelectric unit, which offers a higher efficiency as compared to a device with a single-stage photocell, is developed.     

Evidence for Irradiation Triggered Nonuniform Defects Distribution in Multiharmonic Magnetic Susceptibility of Neutron Irradiated YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−</Subscript><Subscript><Emphasis Type="Italic">δ</Emphasis></Subscript>

Multiharmonic ac-magnetic susceptibilityx ₁,x ₂,x ₃, of neutron irradiated Li-doped YBa₂Cu₃O_7−x has revealed a nonmonotonic dependence of all harmonics on the neutron fluence. The irradiation has a strongly depressive influence on the intergrain connection suggesting an increase of the effective thickness of the intergranular Josephson junction at a neutron fluence of 0.98 × 10¹⁷ cm⁻². Less damaged are the intragrain properties. A spectacular enhancement of the superconducting intragranular properties reflected in the characteristics of all harmonics was observed at highest fluence φ=9.98 × 10¹⁷ cm⁻². We assume that this effect results from the development of a space inhomogeneous distribution with alternating defectless and defect-rich regions.     

Photoluminescence of i-GaxIn1 ? xAs/n-GaAs heterostructures containing a random InAs quantum dot array

i-Ga _x In_{1 − x} As/n-GaAs heterostructures containing InAs quantum dots have been grown by ion beam deposition and their photoluminescence has been studied. The photoluminescence spectrum of the heterostructures contains three characteristic peaks. The peak at 1.1 eV has a large width and is due to the array of InAs quantum dots of different sizes, randomly arranged on the surface of the i-Ga _x In_{1 − x} As layer. From the position of another peak (hν = 0.94 eV), we have evaluated the composition of the Ga _x In_{1 − x} As solid solution: x = 0.64. The third photoluminescence peak corresponds to the intrinsic absorption edge of the n-GaAs substrate. The key features of luminescence photoexcitation in the heterostructures are discussed. We show that the Ga_0.64In_0.36As quantum well may accumulate not only photogenerated electrons but also electrons that come from a thin interfacial n-GaAs layer through ballistic transport.     

Photoelectrochemical reactions on semiconductor materials

The cathodic reduction of Fe³⁺ ions and I₂ on ann-GaAs electrode was studied. The variation in the current density with the concentration of the oxidant has been interpreted as being the result of a reduction mechanism involving interface or surface states, an interpretation that is amply substantiated by experimental data. The effect of the surface modification with SiW₁₂O₄₀ ^4– on the reduction process was studied. Prior to this electrode activation, the rate constant for electrons being transferred from the conduction-band to the interface or surface states,k _S, was observed to be independent of electrode potential, whereas in the case of the modifiedn-GaAs,k _S depends on band-bending. On the other hand, the rate constant for electrons being transferred from the interface or surface states to oxidant species,k _ox, does depend on electrode potential in the case of the unmodifiedn-GaAs, and is independent of band-bending in the case of the modifiedn-GaAs. This change may be attributed to the filling of the active surface or interface states or their redistribution after the electrode surface activation.     

Direct atomic-absorption determination of platinum,palladium, and rhodium in dead ceramic-based autocatalysts

The data on the effect of different concentrations of components of dead automobile catalysts on determination of platinum, palladium, and rhodium using the method of ETAAS are obtained and systematized. The conditions for direct atomic-absorption determination of Pt, Pd, and Rh are optimized. The technique of atomic-absorption determination of PM in secondary raw and technogenic materials is developed (n × 10⁻⁴−n × 10⁻¹ wt %, s _r = 0.12–0.07).     

Study of microhardness and electrical properties of proton irradiated polyethersulfone (PES)

Polyethersulfone (PES) films were irradiated with 3 MeV proton beams in the fluence range 10¹³–10¹⁵ ions/cm². The radiation induced changes in microhardness was investigated by a Vickers’ microhardness tester in the load range 100–1000 mN and electrical properties in the frequency range 100 Hz-1 MHz by an LCR meter. It is observed that microhardness of the film increases significantly as fluence increases up to 10¹⁴ ions/cm². The bulk hardness of the films is obtained at a load of 400 mN. The increase in hardness may be attributed to the cross linking effect. There is an exponential increase in conductivity with log frequency and the effect of irradiation is significant at higher fluences. The dielectric constant/loss is observed to change significantly due to irradiation. It has been found that dielectric response in both pristine and irradiated samples obey the Universal law and is given by ɛ ∝ f ⁿ⁻¹. These results were corroborated with structural changes observed in FTIR spectra of irradiated samples.     

Effect of centrifugation on the crystal structure of barium nitrate

The structure of barium nitrate crystals grown from supersaturated aqueous solutions under normal conditions and during centrifugation at 11.8×10³ g is studied for the first time by a high-precision powder neutron diffraction method. It is established for the first time that centrifuging leads to displacement of the nitrate oxygen atoms in the xy plane (resulting in rotation of the NO₃ trigonal prism about the third-order axis) and to variation of the bond lengths and angles in the coordination polyhedron of Ba atoms. The latter changes result in the appearance of a torsional mode in the phonon spectrum of barium nitrate and in increasing stiffness of the crystal lattice, as evidenced by a significant increase in microhardness of the samples grown in the centrifuge.     

High Dynamic Range SQUID Readout for Frequency-Domain Multiplexers

A 16-SQUID array has been designed and fabricated, which shows 0.12 μΦ ₀ Hz^−1/2 flux noise at 4.2 K. The readout amplifier based on a cryogenic silicon-germanium bipolar transistor employs short-delay negative flux feedback and reaches 7 MHz bandwith for a 1 Φ _0p-p signal. The −1 dB compression is reached approximately at 4.2 Φ _0p-p amplitude when the signal frequency is 1 MHz. In the feedback mode the flux noise is anomalously increased to 0.35 μΦ ₀ Hz^−1/2.      

Microwave-stimulated relaxation of internal strains in GaAs-based device heterostructures

We have studied the effect of microwave radiation (frequency, 2.45 GHz; specific power density, 1.5 W/cm²) on the relaxation of internal mechanical strains in the (i)n-n ⁺-GaAs structures, (ii) Au-Ti-n-n ⁺-GaAs diode structures with Schottky barriers, and (iii) GaAs-based Schottky-barrier field-effect transistors (SFETs). It is shown that exposure of the samples to the microwave radiation for a few seconds leads to relaxation of the internal mechanical strains and improves the quality of the semiconductor surface layer structure. This results in improved parameters of the GaAs-based device structures of both (diode and SFET) types, as manifested by increased Schottky barrier height, reduced ideality factor and back current in the diode structures, and increased gain slope and initial drain current in the SFETs.     

New values of the Ag-<Emphasis Type="Italic">n</Emphasis>-GaP potential barrier

Surface-barrier structures of the Ag-GaP type based on high-quality epitaxial n-GaP layers with n=(0.5–30)×10¹⁶ cm⁻³ were studied. It was found that the potential barrier height depends on the method of surface treatment prior to the metal deposition and correlates with the structural nonideality coefficient and the intermediate layer thickness. For high-quality structures with a reverse current below 10⁻¹⁴ A, the barrier height is ϕ=1.55±0.04 eV. For structures with a relatively thick intermediate layer, the barrier may reach up to ϕ=1.7±0.07 eV. The dependence of the barrier height on the method of the GaP surface treatment is related to the absence of rigid pinning of the Fermi level on the GaP surface.     

The effect of neutron irradiation on the exciton absorption in gallium arsenide

We have studied the effect of neutron irradiation on the exciton absorption in n-GaAs crystals. It is shown that the observed decrease in the absorption coefficient, broadening of the exciton peak, and its shift toward higher energies are caused by the electric and strain (compression) fields generated by the radiation-induced defects.     

Oxidation of carbohydrazide with nitric acid

The kinetics of carbohydrazide oxidation with nitric acid in aqueous solutions was studied. In the range [HNO₃] = 3–7 M, the reaction rate is described by the equation −d[(NH₂NH)₂CO]/dt = k[(NH₂NH)₂CO][HNO₃] ⁿ , where n = 3.6 and 2.9 at 70 and 90°C, respectively. The constant k = (6.65 ± 0.23) × 10⁻⁴ l^2.9 mol^−2.9 h⁻¹ at 90°C, and the activation energy of the reaction in 7 M HNO₃ is 124 kJ mol⁻¹. The Fe(III) and especially Tc(VII) ions considerably accelerate the reaction, whereas the uranyl ions accelerate it insignificantly. The reaction mechanism in which the reactive species oxidizing carbohydrazide is nitronium ion NO₂⁺ was suggested.     

Nonlinear optical characterization and measurement of optical limiting threshold of CdSe quantum dots prepared by a microemulsion technique

CdSe quantum dots prepared by micro emulsion technique shows quantum confinement effect and broad emission at 532 nm. These quantum dots have about 4.35 nm size, and they exhibit good nonlinear effects which are measured using z-scan technique. The samples have a reverse saturation in the nonlinear absorption as nonlinear optical absorption coefficient β is 2.545 × 10⁻¹⁰ W m⁻¹ and nonlinear optical refraction coefficient n ₂ is −1.77 × 10⁻¹⁰ esu. The third-order nonlinear optical susceptibility is found to be 4.646 × 10⁻¹¹ esu and also the figure of merit is 2.01 × 10⁻¹² esu m. The optical limiting threshold which is found to be 0.346 GW/cm² makes it a good candidate for device fabrication.     

Transient optical phenomena in quartz fibers under high-power pulsed reactor irradiation

Measurements of the intensity of emission and induced optical absorption at 400–750 nm in KU-1 quartz fibers were performed under pulsed irradiation in a BARS-6 reactor (pulse duration, 80 μs; dose per pulse, up to 5×10¹² neutrons/cm² (E>0.2 MeV); dose rate, up to 10⁵ Gy/s). The nondelayed emission component is due to the Cerenkov radiation, the weak relaxation component has a relaxation time of ∼150±50 μs, and the radiation-induced optical absorption reaches a value of 2.5×10⁻⁴ cm⁻¹ (relaxation time, 600–1200 μs). A nonlinear dependence of the Cerenkov radiation on the dose rate and the presence of the relaxation emission component and the transient optical absorption may be associated with an optical inhomogeneity of glass induced by the high-power reactor irradiation.