Quadrupole moment of the 19/2− isomer in115Sb

The quadrupole moment of the 19/2^? isomeric state in¹¹⁵Sb has been measured using the time differential perturbed angular distribution method. From the quadrupole coupling constante ² Qq/h=66(3) MHz atT=370 K in a Bi host the moment ratio is obtained relative to the stable ground state of¹²¹Sb as ¦Q(¹¹⁵Sb, 19/2^?)/Q(¹²¹Sb, 5/2⁺)¦ =1.45(7) resulting in a moment of ¦Q(¹¹⁵Sb, 19/2^?)¦=52(6) fm².     

Static electric quadrupole interaction of Ce and Pb ions in lead titanate

The static electric quadrupole interaction of¹⁴⁰Ce and²⁰⁴Pb has been studied in polycrystalline PbTiO₃ at the lead site with the time-differential perturbed angular correlation (TDPAC) method. The interaction frequencies areω _Q(2083 keV;¹⁴⁰Ce)=2.11 (17) MHz andω _Q(1274keV;²⁰⁴Pb)=3.60(3) MHz. The results are compared with the electric field gradient calculated in a point charge model. Under the assumption that the covalent contributions for Ce and Pb are equal, one can derive the quadrupole moment of the 1274 keV state of²⁰⁴Pb to be ¦Q¦=0.68 b.     

Percolation mechanism of the diffusion of impurity atoms in dense surface layers

The molecular dynamics method is used to study the migration of an impurity atom on an unfilled square lattice. The calculations are performed on a lattice containing 2¹² × 2¹⁴ sites at various values of the ratio p of the frequencies of jumps impurity and lattice atoms and various relative concentrations of vacancies ? _V . In the limit of vanishingly small concentrations of vacancies, ? _V ? 1, the present simulation results are in agreement with our previous analytical results. With increasing ? _V , the diffusion coefficient of impurity atoms predicted by the simulations exceeds the result of the analytical theory, a behavior that can be explained by the growing influence of vacancy clusters, voids on the surface, in which the impurity atom can travel long distances. This is most clearly seen in the case of highly mobile impurity atoms (p ? 1), where within the characteristic time of displacement of impurity atoms, lattice atoms remain practically immobile, and the problem appears to be closely related to the percolation problem. In this case, up to ? _V ≈ 0.3, the diffusion coefficient is independent of p; then, such a dependence appears, and the diffusion coefficient increases sharply with ? _V .     

Influence of Sb doping on crystal structure and electrical property of SnO2 nanoparticles prepared by chemical coprecipitation

Sb doped SnO₂ (ATO) nanoparticles with Sb doping concentrations ranging from 0% to 20% (Sb/Sb+Sn) have been prepared by chemical coprecipitation using metallic Sn and SbCl₃ as raw materials. The influence of Sb doping concentration on crystal structure and electrical property was studied in detail. Results indicated that all ATO nanoparticles possessed the same tetragonal rutile structure as that of bulk SnO₂. The average crystal size of the ATO nanoparticles decreased from 16 to 7 nm by increasing the Sb doping concentration. The unit-cell volume of ATO nanoparticles was either expanded or contracted, strongly depending on the Sb doping concentration. The electrical resistivity decreased sharply from 111 to minimum of 1.05 Ω cm when the Sb doping concentration was increased from 0% to 15% and then increased slightly to 1.42 Ω cm when the Sb doping concentration was increased from 15% to 20%. Finally, high resolution X-ray photoelectron spectroscopy (XPS) measurement was employed to investigate the valence state of Sb in samples with various Sb doping levels.     

Photoluminescence of bulk Eu-doped GaN crystals

A study of the variation of photoluminescence spectra of bulk Eu-doped GaN samples revealed that the dopant can reside in the crystal in various charge states depending on the total defect concentration in the starting semiconductor host matrix. In crystals with the lowest concentration of shallow-level defects, the ion can exist only in one charge state, Eu³⁺. At higher concentrations of such defects, Eu can be observed in two charge states, Eu²⁺ and Eu³⁺. A rare-earth impurity was found to act as a getter of defects in the starting GaN matrix.     

Irradiation-induced compensation of n-type germanium: An optical study of vibrational absorption

n-type germanium crystals doped with As, Sb, P, P + In, P + Ga or As + B have been rendered transparent by high energy e^? or n⁰ irradiation. Localized vibrations of P, [P-In], [P-Ga], B and [B-As] have been observed. It is concluded that the compensation process must occur predominantly by the introduction of defects which act as acceptors and which do not involve the shallow donor impurity atom.     

The vacancy-interstitial pair in electron irradiated germanium

We have studied the influence of the nature and concentration of donor impurity on the 65°K and 35°K stages in electron irradiated n-type germanium. Because the nature of the impurity does not influence the 65°K stage and because this stage is present alone in lightly doped samples, we confirm that it is associated with the annihilation of a vacancy-interstitial pair. Because the 35°K stage is directly connected to the impurity concentration, and not to the free electron concentration, we conclude that it is associated with the annihilation of a vacancy and interstitial-impurity pair. We have shown that the annihilation of the vacancy-interstitial pair occurs through the interstitial mobility at 65°K, 27°K and 4.5°K depending on its charge state, and that the interstitial-impurity mobility occurs at 35°K.

Our model explains easily the radiation annealing, the behavior of irradiated p-type germanium and can be extended to the case of indium antimonide and perhaps of silicon.     

Giant magnetic moments in dilute magnetic semiconductors

The concentration dependence of the specific magnetic moment value at room temperature in dilute semiconductor titanium oxides doped with either Co or Fe has been investigated. This value was found to increase sharply at small concentrations of magnetic impurity. The magnetic moment of 22.9 μ_B per impurity atom has been revealed for TiO₂ doped with 0.15 at% Co, not yet reported in any semiconductor oxide systems. We conclude the observed giant magnetic moments are caused by the crystal lattice polarization at small impurity concentrations. The comparison with published data point to different types of the magnetization concentration dependence for various semiconductor matrixes that is probably related to the dielectric permittivity of the environment.     

Magnetic moment relaxation of a shallow acceptor center in heavily doped silicon

Results of studying the temperature dependence of the residual polarization of negative muons in crystalline silicon with germanium (9×10 ¹⁹ cm ^?3 ) and boron (4.1×10 ¹⁸ , 1.34×10 ¹⁹ , and 4.9×10 ¹⁹ cm ^?3 ) impurities are presented. It is found that, similarly to n-and p-type silicon samples with impurity concentrations up to ～10 ¹⁷ cm ^?3 , the relaxation rate ν of the magnetic moment of a _μ Al acceptor in silicon with a high impurity concentration of germanium (9×10 ¹⁹ cm ^?3 ) depends on temperature as ν～T ^q , q≈3 at T=(5–30) K. An increase in the absolute value of the relaxation rate and a weakening of its temperature dependence are observed in samples of degenerate silicon in the given temperature range. Based on the experimental data obtained, the conclusion is made that the spin-exchange scattering of free charge carriers makes a significant contribution to the magnetic moment relaxation of a shallow acceptor center in degenerate silicon at T?30 K. Estimates are obtained for the effective cross section of the spin-exchange scattering of holes (σ _h ) and electrons (σ _e ) from an Al acceptor center in Si: σ _h ～10^?13 cm² and σ _e ～8×10^?15 cm² at the acceptor (donor) impurity concentration n _a (n _d )～4×10¹⁸ cm^?3.     

在氢和氘中寻找正的单电荷重粒子

在电磁分离器上用测量粒子荷质比的方法,在氢和氘样品中寻找正的单电荷重粒子。实验中用吸收法排除杂质本底。用特制的薄窗正比计数管记录单个粒子,并且测量粒子的能量。实验扫描了质量从65到220质子质量的重质量区域。扫描的结果给出:天然水中正的单电荷重粒子浓度的上限,在质量65到148质子质量范围内及148到220质子质量范围内,分别小于2×10^-17重粒子/氢原子及5×10^-17重粒子/氢原子。     

Quadrupole interaction of8Li and9Li in LiNbO3 and the quadrupole moment of9Li

The quadrupole interaction of nuclear spin polarized⁸Li (I=2) and⁹Li (I=3/2) in LiNbO₃ has been studied at room temperature. The polarization was achieved by optical pumping of a fast atomic beam with circularly polarized laser light. The atoms were implanted into a hexagonal LiNbO₃ single crystal and the quadrupole splitting ofβ-NMR spectra was measured. A ratio of ¦Q(⁹Li)/Q(⁸Li)¦=0.88(4) for the nuclear quadrupole moments was deduced, yielding a new value of ¦Q(⁹Li)¦=25.3 (9) mb for the quadrupole moment of⁹Li.     

Far-infrared recombination radiation from impact-ionized donors in germanium

We studied the far-infrared emission spectrum resulting from recombination of an electron with an ionized impurity of As and Sb in germanium under impact ionization at liquid, helium temperatures. The emission peaks at the position corresponding to the transition from the 2p _± excited state to the ground state. This observation indicates that recombination occurs through the capture by the excited states of the donor impurity, which is consistent with the cascade trap model. The intensity of emission radiation is of the order of 10⁻⁷ watts for the excitation power of about one watt, which implies a dominant process of recombination to be accompanied by phonon emission.     

Space charge analysis in enamelled wires by using thermally stimulated depolarization current (TSDC)

This paper reports on measurements of thermally stimulated depolarization current (TSDC) that is applied to characterize changes in the large motors and generators enamelled wires that have been exposed to aging under steep-front pulse voltage waveforms. The thermoelectrets are prepared at various polarizing fields, E_P, and measurements of TSDC are carried out both as a function of time and temperature over the range of 23–200 °C. In addition, various TSDC parameters such as activation energy, ?_a, characteristic relaxation time, τ and the released charge, Q during the relaxation process have been determined by applying initial rise method. The experimental results for TSDC spectra of wire specimens have shown that the total stored charge in the insulation bulk increases significantly, as the number of insulation layers increases on the wire. The reason for such a higher concentration of trapped charges is more likely due to the presence of a broad distribution of the traps, which are occupied by the injected charges.     

X-ray photoemission studies on InSb clusters

The changes in core-level electronic structure of In_1−xSb_x nano-clusters have been studied using X-ray photoelectron spectroscopy. Though, clusters with mean composition InSb show shallow and deep core-level binding energies similar to those of bulk InSb, the Sb and In rich versions show a negative BE shift for the excess element and a positive shift for the minority element. The observed BE shifts have been explained considering a core and surface shell model for the structure of the clusters and possible surface atom core-level shifts.     

Electromigration of cadmiun in lead

The electromigration of cadmium in lead up to a concentration of 510 at ppm Cd was measured at constant temperatures between 250 and 290°C by the steady state method and also by a somewhat novel transient technique; the latter required shorter running time and also gave additional information, namely the chemical diffusion coefficient, D_ch. From the steady state runs the observed effective charge number was Z¹_ss = + 2.5 ± 0.3 for the lowest concentration. The positive value was apparently the result of the counterflowing of the lead in a vacancy-interstitial pair mechanism. The temperature dependence of Z¹ is described by $\text{Z}{}^1\text{= (0.5 ± 2.4) + (0.9 ± 1.1)}$$\text{10}{}^{\mathrm{?4}}\text{ρ}$ and both the wind force and the electrostatic Z_el appear to be small. The Z¹_ss, appeared to increase slightly with concentration. The transient measurements were in general less precise, but were consistent with the steady state results within their experimental accuracy. The values of $\text{D}{}_{\mathrm{ch}}\text{D}{}^1$ appeared to be unity within the same accuracy for a range of composition up to 510 at ppm Cd. To a standard dissociation model for impurity mobility we have added a rather extended atomic exciton mechanism to help explain the diffusion kinetics.     

Investigation of224Ra in the226Ra(α, α′ 2n) reaction

Positive and negative parity bands have been followed up to 10⁺ (possibly 12⁺) and 11^? in²²⁴Ra and are compared to the corresponding bands in the isotone²²⁶Th. If a constant value of the intrinsic quadrupole moment is assumed for allE2 transitions in²²⁴Ra theE1/E2 branching ratios are consistent with an intrinsic dipole moment of ¦Q₁¦=0.032(3)e·fm. This small value, as compared to ¦Q₁¦=0.30(2)e·fm for²²⁶Th, can be explained by an almost complete cancellation of large positive liquid-drop and negative shell-model contributions.     

Structural and optical properties of metastable SiGe/Si films with a low germanium concentration

The properties of metastable Si_{1 ? x} Ge _x /Si (10% < x < 16%) layers grown by molecular beam epitaxy on Si(100) substrates have been investigated using atomic force microscopy, X-ray diffraction, and low-temperature luminescence spectroscopy. It has been shown that ring-like aggregates are formed on the surface of layers grown at temperatures of 500–700°C. The size and shape of these aggregates suggest that their formation is associated with the diffusion instability arising due to the existence of a relationship between the surface diffusion, stresses, and the wetting potential during the growth of the epitaxial film. The existence of deviations from the homogeneous germanium distribution in the layer plane has been confirmed by a detailed analysis of the X-ray rocking curves and two-dimensional diffraction patterns. The structures with severe surface disturbances are characterized by an abnormal change in the decay times of the emission lines of bulk silicon, which indicate the presence of local electric and/or strain fields in subsurface regions. The perturbations of the flat crystallization front are suppressed as the growth temperature of layers decreases to 350°C. Despite the absence of a coating layer of silicon, the photoluminescence spectra of the layers themselves depend weakly on their thickness and growth temperature and remain sensitive only to the technological concentration of germanium. A slowly decaying luminescence associated presumably with the localization of excitons near the SiGe-Si interface has been observed in one of the samples grown at a temperature of 700°C and containing a dense array of ring-like aggregates.     

Pecularities of EPR spectra of the Gd impurity in the Sn-Rich Pb1−x Sn x Te(Gd) solid solutions

An electron paramagnetic resonance (EPR) experimental study of crystalline and powder p-Pb_1?x?y Sn _y Gd _y Te samples for various matrix compositionx and Gd contenty has been carried out. The study reveals that grinding the crystals into powder as well as their low-temperature annealing turns Gd impurity ions from the EPR-silent Gd²⁺ state to the EPR-active Gd³⁺ state, whereas high-temperature annealing in vacuum quenches EPR signals from Gd³⁺ ions. The experimental results are interpreted in terms of a model assuming that the trivalent charge state of the Gd impurity ions in lead and tin tellurides is a component part of the “substituting Gd impurity-Te vacancy” complex.     

The study of short-lived nuclei in the regionZ=59–68

β ⁺ -ray endpoint energies for mass-separated samples of neutron deficient Rare-Earth isotopes have been measured using an intrinsic germanium detector. Q_EC values have been obtained and new isomeric states have been identified for the first time.     

Interaction between a He atom and a graphite surface

A study is presented of the interaction V(r) between a He atom and a graphite surface. V(r) is assumed equal to a sum of pair interactions U(r ? R_i) between the He and C atoms. None of a set of isotropic potentials (dependent only on the magnitude ¦r ? R_i¦) is consistent with recent scattering data. Anisotropie pair potentials, in contrast, are found to yield good agreement. The origin of this anisotropy is analyzed in terms of the graphite dielectric function and charge density.