Pulse measurements of thermostimulated currents in AgCl crystals

The course of thermostimulated currents in AgCl crystals was measured in a temperature region between 200 and 300K. Maxima at 240, 275 and 290K were observed on the curves obtained.     

Theory of thermostimulated currents in layered crystals

A mathematical model is proposed for layered crystals, based on a system of kinetic equations describing the change in charged relaxation oscillators with time. An analytical solution of this system is found and a theory constructed, which allows determination of the type and parameters of relaxation oscillators, as well as the properties of the crystals. A calculation of the thermostimulated depolarization current spectrum is confirmed by experiment.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 68–72, January, 1991.     

Determination of trap parameters by simultaneous measurement of thermostimulated luminescence and thermostimulated conductivity

A method is proposed for processing of thermostimulated luminescence (TSL) curve in the presence of thermostimulated conductivity (TSC) in which no assumption is made as to the smallness of dn_c/dt (n_c is the conduction electron concentration). Results of the theory are applied to study of ZnSAg, Al and ZnSCu single crystals, in which elementary traps are revealed, and their activation energy and the value of the frequency factor determined. For ZnSCu the radiative transition recombination section is calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 94–101, June, 1977.     

Vacancy formation energies from positron trapping measurements

The threshold temperatureT _t at which thermally generated vacancies produce measurable positron trapping is a linear function of the energy of self-diffusionQ. SinceQ is also linearly related to the vacancy formation energyE _1v ^f , a measurement ofT _t leads directly to a determination of the latter. It is possible to make a precise determination ofE _1v ^f without approaching the melting point—a major advantage in dealing with refractories or with metals having a high vapour pressure in the solid state.     

Calculation of quasi-stationary state parameters within the algebraic version of the resonating-group method

The dynamical equations of the algebraic version of the resonatinggroup method are used to determine the positionsE _res,l and the widths _l of quasi-stationary states or, what is equivalent, to find the polesE _l =E _resl –i _l /2 of theS-matrix in the fourth quadrant of thek-plane. Concrete calculations are performed for the -decay of⁸Be. A comparison with the results of other authors and with experiment is made.     

Determination of trapping parameters in n-Ga4Se3S by thermally stimulated current measurements

Thermally stimulated current (TSC) measurements were carried out on as-grown n-Ga₄Se₃S layered crystals in the temperature range 10–300 K. The experimental data were analysed by using different heating rates, initial rise, curve fitting and isothermal decay methods. The results of the analysis showed good agreement with each other. The measurements revealed the presence of one trapping level with activation energy of 23 meV. The corresponding capture cross-section and concentration of traps were found to be 2.2 × 10^?23 cm² and 2.9 × 10¹¹ cm^?3, respectively. TSC experiments showed the presence of an exponential distribution of electron-trapping states in Ga₄Se₃S crystal. The variation of one order of magnitude in the trap density for every 34 meV was obtained.     

Influence of escape from traps on parameters in the positron trapping model

Positron detrapping may explain weak trapping in some metals, and it can affect deduced vacancy formation energies. However, it appears that the recently observed additional temperature dependence of the positron capture rate cannot be attributed to escape from traps.     

Radiation-enhanced and thermostimulated hydrogen release from palladium and zirconium

The results of a mass-spectrometric analysis of hydrogen release from palladium and zirconium samples under the action of accelerated electrons (with an energy of 40 keV and a current density of 3 to 30 μA/cm²) and x-rays (with energies of 40 and 120 keV) are presented. The amount of hydrogen removed from these samples and the residual hydrogen content are monitored via the methods of mass-spectrometry and thermodesorption. The conclusion is made that substantial removal of hydrogen (up to 90% of the initial content) from the analyzed materials can be achieved under the action of electrons and x-rays. It is found that x-ray irradiation can ensure more efficient removal of hydrogen than electron bombardment.     

On the surface trapping parameters of polytetrafluoroethylene block

Surface flashover phenomena under high electric field are closely related to the surface characteristics of a solid insulating material between energized electrodes. Based on measuring the surface potential decaying curve of polytetrafluoroethylene (PTFE) block charged by a needle-plane corona discharge, its surface trapping parameters are calculated with the isothermal current theory, and the correlative curve between the surface trap density and its energy level is obtained. The maximum density of electron traps and hole traps in the surface layer of PTFE presents a similar value of ∼2.7 × 10¹⁷ eV⁻¹ m⁻³, and the energy level of its electron and hole traps is of about 0.85-1.0 eV and 0.80-0.90 eV, respectively. Via the X-ray photoelectron spectroscopy (XPS) technique, the F, C, K and O elements are detected on the surface of PTFE samples, and F shows a remarkable atom proportion of ∼73.3%, quite different from the intrinsic distribution corresponding to its chemical formula. The electron traps are attributed to quantities of F atoms existing on the surface of PTFE due to its molecular chain with C atoms surrounded by F atoms spirally. It is considered that the distortions of chemical and electronic structure on solid surface are responsible for the flashover phenomena occurring at a low applied voltage.     

Band parameters of nickel deduced from optical measurements

The gap Δ between the top of the d↑ band and the Fermi level is deduced from optical measurements on a nickel single crystal and found to be ≈50 meV, in agreement with previous estimates. The interpretation of the optical spectrum also suggests that the spin-splitting ΔE_d ? 0.40 eV and that a spin- splitting still exists at temperatures higher than T_C.     

Microwave measurements of the critical fields and currents in HTS

The technique of magnetically modulated microwave absorption (MMMA) has been used for measuring the critical fields and critical currents of granular high-temperature superconductors (HTS) and for investigating the Josephson/intergrain critical state.     

Determination of trapping–detrapping events,recombination processes and gap-state parameters by modulated photocurrent measurements on amorphous silicon

Analysis of the out-of-phase modulated photocurrent (MPC) signal, the so-called Y signal, is proposed for determining the trapping–detrapping events, recombination processes and gap-state parameters in amorphous silicon. This is demonstrated by analysing experimental Y spectra obtained on this material from different laboratories including our own. Model simulations are also employed in which the amphoteric nature of the dangling bonds and their distribution according to the defect-pool model are taken into account. From the reconstruction of the Y signal, phase shift and MPC amplitude spectra, several contributions resolved from the frequency dependence of the experimental Y spectra are identified. Two electron trapping–detrapping processes are resolved. These are attributed to hydrogen-related positive defects and to transitions involving the D^+/0 level of the normal dangling bonds from the defect-pool distribution. At lower frequencies a residual contribution is resolved that is attributed to a term related to recombination through the D^+/0 and D^0/? levels. Between 300 and 150?K the above recombination contribution is essentially from the D^0/? and dominates the Y signal at lower frequencies. In this region a characteristic phase lead appears, which is attributed to the existence of safe hole traps in the valence band tail. Around 150?K, trapping–detrapping events in the conduction band tail dominate.     

Calculation of the amplification coefficient of stimulated emission from fluorescence measurements

A formula for calculating the amplification coefficient for a four-level system from luminescence data is derived. Measurement of the absolute value of the quantum yield of photoluminescence is described and the amplification coefficient is calculated for four different sorts of glass.This work was performed in the Institute of Physics, Czechoslovak Academy of Sciences, Prague.Discussions on the problem with K. Pátek and preparation of the samples by J. Walter are gratefully acknowledged.     

Magnetoelectrostatic trapping of ground state OH molecules

We report magnetic confinement of neutral, ground state OH at a density of approximately 3 x 10(3) cm(-3) and temperature of approximately 30 mK. An adjustable electric field sufficiently large to polarize the OH is superimposed on the trap in various geometries, making an overall potential arising from both Zeeman and Stark effects. An effective molecular Hamiltonian is constructed, with Monte Carlo simulations accurately modeling the observed single-molecule dynamics in various trap configurations. Magnetic trapping of cold polar molecules under adjustable electric fields may enable study of low energy dipolar interactions.     

Obtaining three surface-film parameters from two ellipsometric measurements

A powerful approximation method for obtaining the thickness, d, and optical constants, n₂ and k₂, of a thin absorbing film on a known opaque substrate is described. The advantages of the method for certain ellipsometer systems are discussed. Instead of requiring a third measurement, for example the reflectance, |r|, as is often done, the effective reflectance, |r_eff|, is calculated in the two-phase approximation from the measured ellipsometric parameters. This provides the third quantity needed to obtain n₂, k₂ and d. Examples worked out for the systems Ag₂S/Ag and CoO/Co illustrate the accuracy and utility of the method. The technique is shown to be applicable to a wide range of films, roughly $\text{n}{}_2\text{? 2.0}$, k₂ ? 1.0 and $\text{d ? 40}\text{A}\text{?}$ on semiconducting and highly reflecting metal substrates and 2.0 ? n₂ ? 2.7, k₂ ≈ 0.5, and $\text{d ? 10}\text{A}\text{?}$ on less highly reflecting metal substrates. The important systems GeO₂/Ge, SiO₂/Si and Al₂O₃/Al are well within these limits. When the method is used in these ranges, the errors resulting from the approximation are less than those that would be introduced by a measurement of reflectance change on most ellipsometer systems.     

Evaluation of Schottky junction parameters from current-voltage characteristics exhibiting large excess currents

A new method is presented to extract the junction parameters from current-voltage characteristics of Schottky junctions exhibiting high leakage or other excess currents at low bias and current levels, for reduction of errors and uncertainity of the evaluation. In contrary to the Richardson plot, using the new method presented here, the Schottky junction parameters are evaluated from the measured experimental points directly instead of the extrapolated values of saturation current. The temperature dependence of forward bias, which is necessary for a given thermionic emission current level, is used. After transformation of the data, a linear plot is obtained, which yields both the barrier height and effective Richardson constant.