The Pockels effect in ADP above room temperature

Longitudinal electro-optic studies in paraelectric ADP have revealed an anomalous variation of the Pockels coefficient r₆₃ with temperature above 90°C. This behavior is shown to be part of a more general variation of r₆₃ with surface condition of the specimen.     

The effect of band non-parabolicity of shallow donors

We have studied theoretically the effect of non-parabolicity of conduction band on the binding energies of shallow donors. The calculation is carried out in momentum space. We find that the binding energies are increased by 3 to 5 percent for shallow donors in Hg_1-xCd_xTe, GaAs, and InP. The discrepencies between the measured donor ionization energies in GaAs and the value from hydrogenic model are, in a substantial part, due to the non-parabolicity effect.     

Conduction-electron drift velocity measurement via electron spin resonance

In analogy with NMR, motion induced phase shift of pulsed ESR signals enables in principle the direct detection of electron drift velocity or electronic current, respectively. Overcoming the difficulties with additional magnetic field gradients induced by the current itself, we succeeded in demonstrating the detection of electron flow via ESR. Measuring the electron drift velocity in the organic conductor (fluoranthene)2PF6 the microscopic Ohmic law could be observed in a current range of more than +/-0.25 A.     

Dielectric relaxation of CsHSeO4 above room temperature

Dielectric measurements of CsHSeO₄ show a distinct relaxation at low frequencies at several isotherms (T < 363 K). For example, the relaxation frequency is around 4 kHz at 323 K and increases to higher frequencies (~ 100 kHz) as the temperature increases. The relaxation has an activation energy of 0.8 eV, which is in close agreement with that associated with transport of charge carriers. We suggest that the observed dielectric relaxation could be produced by the H⁺ jump and SeO₄^? 2 reorientation that cause distortion and change the local lattice polarizability, inducing dipoles like HSeO₄^?.     

Low-threshold interband cascade lasers operating above room temperature

Mid-IR type-II interband cascade lasers were demonstrated in pulsed mode at temperatures up to 325 K and in continuous mode up to 200 K. At 80 K, the threshold current density was 8.9 A/cm² and a continuous wave output power of 140 mW/facet was obtained.     

Monte Carlo calculation of hot electron drift velocity in silicon (100)-inversion layer by including three subbands

A Monte Carlo calculation of the drift velocity of hot electrons in quantized silicon inversion layers for (100)-oriented surface has been performed by considering the three lowest subbands. The intersubband and intervalley phonons conform to the surface Brillouin zone structure and are assumed to have bulk values of deformation potential constants. It is found that most of the electrons tend to occupy the E_0′ subband at about 10 kV cm^-1. The effect of surface-oxide-charge scattering is found to be quite important. The calculated curves show a change of slope at about 10 kV cm^-1 and do not show clear saturation. This is in contrast with the experimental curve which shows first a smooth variation and then tends to saturate.     

Origin of dielectric relaxations in KHSeO4 above room temperature

The dispersion curves of the dielectric response for KHSeO₄ were obtained in the radio frequency range at several isotherms below the fast proton conducting phase (T?<?415 K). The results reveal a distinct dielectric relaxation at low frequency, which is about 682 Hz at 320 K, and then, it shifts to higher frequencies (～10 kHz) as the temperature increases. The f _max vs. reciprocal T shows an activated relaxation process with an activation energy of 0.5 eV, which is in close agreement with that associated with transport of charge carriers. We suggest that the observed dielectric relaxation could be attributed to polarization induced by the proton jump and selenate tetrahedral reorientations. The displacement of mobile H⁺ proton accompanied by SeO ₄ ^??2 tetrahedra reorientations creates structural distortion in both sublattices which induce localized dipoles like HSeO ₄ ^? .     

The room temperature oxidation of porous silicon

The room temperature oxidation of porous silicon was studied using isothermal methods. The oxidation was found to depend on the type of the porous silicon. The microcalorimetric signals from the oxidation of the p⁺- and n-type porous silicon in dry air were different. In humid air the signals from the oxidation could not be distinguished from the strong signal due to adsorption of water vapour, but when the samples were placed in water similar differences were observed. The reason for differences in reactions is discussed. The oxidation in different liquids was also studied. The signal from reactions in methanol and ethanol were found to be 100 times higher than in water. In FTIR studies the reaction gas produced by reactions between alcohols and the porous silicon, silane (SiH₄) was found in the gas. Traces of SiOCH₃ and SiOC₂H₅ groups were also found in FTIR spectra indicating Si---O---C_xH_y passivation of the surface.     

Single-phase epitaxial InFeSb layers with a Curie temperature above room temperature

Physics of the Solid State - Epitaxial InFeSb/GaAs heterostructures were obtained by laser deposition in vacuum. Investigations by high-resolution transmission electron microscopy and...     

Dielectric relaxations above room temperature in DMPU derived polyaniline film

Dielectric measurements carried out on drop casted from solution of emeraldine base form of polyaniline films in the temperature range 30–300 °C revealed occurrence of two maxima in the loss tangent as a function of temperature. The activation energies corresponding to these two relaxation processes were found to be ∼0.5 eV and ∼1.5 eV. The occurrence of one relaxation peak in the dispersion curve of the imaginary part of the electric modulus suggests the absence of microphase separation in the film. Thermogravimetric analysis and infrared spectroscopic measurements showed that the films retained its integrity up to 300 °C. The dielectric relaxation at higher temperatures with large activation energy of 1.5 eV is attributed to increase in the barrier potential due to decrease in the polymer conjugation as a result of wide amplitude motion of the chain segments well above the glass transition temperature.     

Dielectric relaxation in NH4HSO4 above room temperature

The dispersion curves of the dielectric response of NH₄HSO₄ show that the corrected imaginary part of permittivity, εʺ, and its real part ε′ versus frequency reveal a dielectric relaxation around 9.1 × 10⁵ Hz at 31 °C, which shifts to higher frequencies (∼ 10⁶ Hz) as the temperatures increases. The relaxation frequency shows an activated relaxation process over the temperature range 31–83 °C with activation energy E_a = 0.14 eV, which is close to that derived from the dc conductivity. We suggest that the observed dielectric relaxation could be produced by the H⁺ jump and SO₄⁻ reorientation that cause distortion and change the local lattice polarizability inducing dipoles like HSO₄⁻.     

强流脉冲电子束二极管等离子体漂移速度的研究

 强流相对论电子束二极管阴阳极等离子体的形成和漂移,是二极管工作状态研究的重要组成部分。根据Child-Langmuir定律和二极管导流系数,结合二极管阴极电子发射面积的变化模型,给出了二极管阴阳极等离子体漂移所导致的阴阳极间隙闭合速度。     

强流脉冲电子束二极管等离子体漂移速度的研究

强流相对论电子束二极管阴阳极等离子体的形成和漂移,是二极管工作状态研究的重要组成部分。根据Child-Langmuir定律和二极管导流系数,结合二极管阴极电子发射面积的变化模型,给出了二极管阴阳极等离子体漂移所导致的阴阳极间隙闭合速度。     

Stationary laser generation of sound in semiconductors at modulation of electron drift velocity

General quadrature expressions for the space-time distribution of the conduction electron density in semiconductors under inhomogeneous laser illumination of the sample and for the time profiling of the electron drift velocity are obtained from the generalized kinetic equation. Generation of sound in an acoustic resonator under these conditions at harmonic modulation of the drift velocity is described.     

Effect of scattering and trapping by ionized centers on the electron drift velocity in CdTe

Electron drift velocity measurements have been performed with the time of flight technique at 300 and 77°K in high resistivity compensated CdTe containing scattering and trapping centers. It is found that coulombic interaction between electrons and ionized centers strongly reduces the measured drift velocity. There is a further reduction if the centers act also as trapping and detrapping centers. The drift velocity is influenced even at high fields where the Gunn effect occurs.     

Investigation of passivation of porous silicon at room temperature

A practical oxidizing technique with ozone has been developed for the passivation of porous silicon (PS) at room temperature. The fundamental role of ozonization may be attributed to the strong oxidizing process for the Si-Hx species and dangling bonds. The subsequent 158 days’ aging effect with the presence of absorbed ozone molecules is very effective for the oxidizing process. At last we achieve a complete replacing Si-Hx coverage with Si-Ox film and Si-alkyl film. The steady increase of photoluminescence (PL) intensity is assigned to the increase in the barrier’s height efficiency and the increase in quantum confinement effect for the silicon nanocrystallites.     

Kinetics of laser-induced oxidation of silicon near room temperature

The growth of ultra-thin (<6 nm) silicon-dioxide films on Si(100):H, Si(111):H, and a-Si:H surfaces in a dry oxygen atmosphere (0.1–10 Pa) at low temperatures (35–200 °C) was investigated. Oxidation was induced by pulsed F₂-laserradiation at 157 nm. The thickness and composition of the growing films were monitored in real time by spectroscopic ellipsometry in the photon energy range of 1.15–4.75 eV. The kinetics of low-temperature oxidation was similar for the Si surfaces investigated and differs from that of high-temperature thermal oxidation (900–1200 °C) that can be described by the Deal–Grove model. To explain the faster growth at the initial stage, it is proposed that oxidation occurs by diffusion of oxygen atoms O and/or ions O^-rather than oxygen molecules. The recombination of diffusive species to oxygen molecules limits their penetration into the bulk. A diffusion model is developed for low-temperature oxidation which takes into account the recombination process of the diffusive species. Good agreement between theory and experiment is found. The activation energy of diffusion of the active species was found to be 0.15 eV, in agreement with previous results and recent calculations for O^- ions. PACS 82.65.+r; 07.60.Fs; 81.65.Mq; 82.50.Hp     

Ferromagnetism above room temperature in bulk sintered gallium phosphide doped with manganese

Evidence for ferromagnetism in bulk sintered gallium phosphide (GaP) doped with 3% manganese, having a Curie temperature of 600 K considerably higher than previous observations, is obtained using ferromagnetic resonance (FMR) and AC magnetization measurements. The field position and line width of the resonance showed a strong temperature dependence characteristic of FMR spectra. A non-resonant derivative signal centered at zero field was also observed starting at 600 K further confirming high temperature ferromagnetism. AC magnetization measurements also show the existence of ferromagnetism at high temperature.     

Superconductivity well above room temperature in compressed MgH6

It has been suggested that hydrogen-rich systems at high pressure may exhibit notably high super-conducting transition temperatures. One of the more interesting theoretical predictions was that hydrogen sulfide can be metallized and the high-temperature superconducting state can be induced. A record critical temperature (203 K) was later confirmed for H₃S in an experiment. In this paper, we investigated, within the framework of the Eliashberg formalism, the properties of compressed MgH₆, which is expected to be a very good candidate for room-temperature superconductivity. This applies particularly to the pressure range from 300 to 400 GPa, where the transition temperature is close to 400 K. Moreover, the estimated thermodynamic properties and the resulting dimensionless ratios exceed the predictions of the Bardeen–Cooper–Schrieffer theory. This behavior is attributed to the strong electron–phonon coupling and retardation effects existing in hydrogen-dominated materials under high pressure.     

基于微波段电子自旋共振测量电磁波的传播速度

当电子自旋共振发生在微波段时,根据微波段电子自旋共振条件,并使用电子顺磁共振谱仪和微波元件(波导管、谐振腔、短路活塞、环行器)等实验仪器测量出微波的波导波长,可以计算出真空中微波的波长.利用特斯拉计测量出共振时的磁感应强度,从而计算出了电磁波的传播速度.