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1.
P. Kamiński R. Koz?owski M. Miczuga M. Paw?owski M. Kozubal J. ?elazko 《Opto-Electronics Review》2009,17(1):1-7
Photoinduced transient spectroscopy (PITS) has been applied to study electronic properties of point defects associated with
charge compensation in semi-insulating (SI) 6H-SiC substrates. The photocurrent relaxation waveforms were digitally recorded
in a wide temperature range of 20–800 K and in order to extract the parameters of defect centres, a two-dimensional analysis
of the waveforms as a function of time and temperature has been implemented. As a result, the processes of thermal emission
of charge carriers from defect centres were seen on the spectral surface as the folds, whose ridgelines depicted the temperature
dependences of emission rate for detected defect centres. The new approach was used to compare the defect levels in vanadium-doped
and vanadium-free (undoped) SI 6H-SiC wafers. 相似文献
2.
A. V. Serber 《Radiophysics and Quantum Electronics》1999,42(11):911-927
Population balance equations for the Landau levels in a non-relativistic rarefied plasma are written for arbitrary polarization
of cyclotron modes. Self-consistent evolution of the transverse distribution of electrons interacting, by virtue of the cyclotron
processes, with an isotropic radiation at frequencies near the first harmonic of the electron gyrofrequency is studied. The
spectrum of the relaxation times of the system is found for a fixed radiation intensity. It is shown that the time of cyclotron
relaxation under the action of the first-harmonic radiation with broad angular and frequency spectra is entirely determined
by the rate of spontaneous processes and does not depend on the radiation intensity. Cyclotron radiation transfer coefficients
which account for the process of mode switching at the first harmonic are obtained.
Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh
Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 11, pp. 1035–1053, November, 1999. 相似文献
3.
Experimental investigation of the time and temperature dependences of the process of relaxation of excited silver chloride has been carried out by the method of a photostimulated burst of luminescence. It is found that the relaxation process can be divided into two components, the rates of which differ by an order of magnitude. The activation energies of these processes of 0.03 and 0.06 eV correspond to the thermal ionization energies of electrons from shallow traps. Thermally activated relocalization of charges from shallow to deep traps in the process of relaxation has been revealed. The depth of a corresponding trap appeared equal to 0.17 eV. A model of a crystal phosphor has been suggested that contains five levels in the forbidden band: a hole center of recombination (luminescence), a deep electron trap, two shallow electron traps located at a depth of 0.03 and 0.06 eV from the bottom of the conductivity band, and a hole trap located at a height of 0.17 eV from the valence band top. Within the framework of this model, we can qualitatively explain the time and temperature dependences of stored light sums. We have shown the possibility of applying the method of a photostimulated burst of luminescence to investigation of the processes of relaxation of electron excitations in crystals to establish the relaxation mechanisms. 相似文献
4.
The relaxation kinetics of primary pairs of radiation defects in ionic crystals with a face-centered lattice is investigated using the Monte Carlo method. The dependence of the relaxation kinetics of an F-H pair on the parameters of the interaction potential between the components of the pair is studied. The obtained kinetic dependences are analyzed to determine the factors responsible for the relaxation processes. 相似文献
5.
We report on the results of mass-spectroscopic analysis of the hydrogen yield from metals saturated with hydrogen under the
action of accelerated electrons (with an energy of up to 100 keV and a current density from 3 to 30 μA). It is found that
the desorption rate is determined not only by parameters of the electron bunch, but also by the structure of the oxide film.
It is discovered that the electronic subsystem of hydrogen-enriched metals enhances their ability to absorb the energy of
the external electromagnetic action and to preserve it for a longer time as compared to a pure metal. This facilitates nonequilibrium
migration and yield of hydrogen under the action of radiation in the subthreshold range. A theoretical model is proposed and
analytic dependences are derived for the intensity of hydrogen yield from metals exposed to an electron bunch. The results
of this study can be used for the removal of hydrogen from metals and for obtaining submicrocrystalline materials (e.g., titanium). 相似文献
6.
M. U. Belyi S. G. Nedel’ko O. V. Chukova V. P. Shcherbatskii 《Journal of Applied Spectroscopy》2000,67(2):245-252
Based on the results of temperature studies of spectral and kinetic characteristics, a study is made to determine the influence
of the structure of different types of luminescence centers (LC) formed in chromate crystals on the processes of relaxation
and radiationless deactivation of excitation energy. It is shown that "isolated" LC are characterized by simple temperature
quenching of luminescence above the barrier. It is established that several excited states take part in the radiation of complex
LC. The possibility of radiationless transitions between them with a change in spin is due to spin-lattice relaxation, which,
as calculations showed, is described for different types of LC by the "van Vleck" or "defect" mechanisms.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 182–187, March–April, 2000. 相似文献
7.
A study has been made of the slow relaxation of the dielectric permittivity of deuterated triglycine sulfate (DTGS) initiated
by application of a dc electric field. The field and temperature dependences of the relaxation time associated with domain-wall
motion were obtained. The effect of the internal electric field on relaxation processes is seen in different behavior of the
field and temperature dependences under different orientations of the external field. The existence in DTGS crystals of two
temperature regions of domain-structure rearrangement lying 7–8 and 15–18 °C below the Curie point has been established.
Fiz. Tverd. Tela (St. Petersburg) 40, 1542–1545 (August 1998) 相似文献
8.
The relation between the molecular relaxation processes and the results of tensile experiments has been studied for hard and toughened polyvinyl chloride (PVC). The relaxation spectra have been determined between 10?4 and 10+4 sec by means of stress relaxation, flexural vibration experiments, and tensile tests. Yield stress, yield strain, rupture stress, rupture strain, and rupture energy have been determined at 23° and 50° C as functions of yield time or rupture time, respectively, over a time-range from 10?2 to 10+4 sec approximately. It is shown that the molecular relaxation processes observed in the range of small deformations also influence the behavior in the nonlinear range, especially the elongation at rupture in tensile experiments. In addition, effects of the molecular processes on the yield stress, the rupture stress, and, consequently, the rupture energy have been observed. These effects are due to the time- and temperature-dependent decrease of the macroscopic stress and of the microscopic notch stresses by certain relaxation mechanisms. The most suitable characteristic parameters in tensile experiments are the yield stress and the rupture strain. It is pointed out that the usefulness of a single value of a mechanical property as determined in a standard “one-point” test is very restricted. 相似文献
9.
V. M. Muravev I. V. Andreev I. V. Kukushkin J. H. Smet K. von Klitzing 《JETP Letters》2008,87(10):577-580
Magnetic oscillations of the photovoltage in a two-dimensional electron system with the back gate, exposed to microwave radiation, are studied. The oscillations result from the interference of screened edge magnetoplasmons (EMPs). The mean free path of the EMPs is quantitatively determined by analyzing the dependence of the oscillation amplitude on the electron density. The dependences of the mean free path of the EMPs on the two-dimensional electron density, microwave frequency, electron relaxation time, and the magnetic field are studied. It is found that the dependences agree qualitatively with the known theoretical calculations. 相似文献
10.
A method is presented for determining the relaxation function from experimental frequency-temperature dependences of the dielectric constant on the basis of a general dispersion relation. Three relaxation processes have been detected in a quartz single crystal with the aid of this method. The relaxation times of these processes and their contribution to the relaxation function at elevated temperatures have been determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 76–81, October, 1986.We thank S. V. Kolodieva and her co-workers for supplying the samples of single-crystal quartz, the arrangement for measuring the dielectric parameters, and for discussion of the results of our work. 相似文献
11.
Internal friction studies on gold-doped lead are reported which yield a relaxation time of τ = 10-14.9exp 0.437 eV/kT. The defect producing the relaxation process appears to have 〈100〉 symmetry and a relatively large elastic-dipole strength. Since this activation energy is equal to that measured in diffusion it is suggested that the two processes are identical, presumably from a dumb-bell configuration. 相似文献
12.
Using the results obtained in the first part of the work, we analyze quasi-linear relaxation of an initial monoenergetic quasi-isotropic
electron distribution embedded in a cold plasma. It is shown that in this case the radiation energy density increases due
to synchrotron instability only at the initial stage of relaxation and after that reabsorption emerges. At the stage of reabsorption,
electrons absorb the emitted radiation for the same characteristic time as the time of radiation energy density increase at
the maser stage. We calculate the maximum fraction of initial electron energy which is converted into synchrotron radiation
energy. Analytical expressions are obtained for the amplitude and width of the frequency spectrum at the instant of the maximum
level of synchrotron radiation and for the maximum value and width of the electron distribution over momentum at the end of
relaxation.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radio.zika, Vol. 49, No. 12, pp. 1063–1074, December 2006. 相似文献
13.
B. A. Belyaev N. A. Drokin V. F. Shabanov V. N. Shepov 《Physics of the Solid State》2003,45(3):598-602
The frequency dependences of the longitudinal and transverse permittivities of oriented nematic liquid crystals belonging to the alkylcyanobiphenyl group nCB (n=5–8) are measured in the relaxation region in the meter and decimeter wavelength ranges. It is established that the dispersion of the longitudinal permittivity is well approximated by the sum of two Debye processes with different relaxation times. The frequency dependence of the transverse permittivity is represented by the dispersion relation with a continuous distribution of relaxation times in a specified time range. It is demonstrated that, in the high-frequency range (f>200 MHz), in which the dielectric spectra exhibit a number of weakly pronounced dispersion features, the total dispersion of the permittivity is adequately described by the sum of relaxation and resonance processes. 相似文献
14.
The temporal dependences μe(t) of the dipole moment of n-dimethylaminobenzonitrile excited to different states by quanta with different energies are evaluated based on the experimental correlation functions of the shift of instantaneous spectra. It is found that, upon excitation into the maximum of absorption, the relaxation changes of the spectra are accompanied by an increase in the dipole moment from 9 D in the Franck-Condon state to 16 D in the stationary state. At the same time, the excitation of luminescence at the red absorption edge by radiation at 403 nm leads to a decrease in the range of variation of the dipole moment. In this case, the initial value of the dipole moment amounts to 14 D and, during the lifetime of the excited state, it increases to 17 D. This indicates that the nature of the radiation excited at the wavelength 403 nm is directly related to internal charge transfer states of n-dimethylaminobenzonitrile. 相似文献
15.
Using pulsed spectrometry with nanosecond time resolution, we have studied the characteristics of creation of induced defects
and the relaxation of such defects in the initial stage in ionic crystals, using as examples ten alkali halide crystals with
sc and fcc lattices and an MgF2 crystal in the temperature range 12.5–500 K. We present the transient absorption spectra, the relaxation kinetics for the
induced defects over a broad temperature range, the dependences of the creation and relaxation on the excitation flux density.
The results of our investigations are generalized in tables and, in the form of the most characteristic dependences, in figures.
We describe the model developed for evolution of primary defects, taking into account the main general characteristics observed
experimentally and the results of mathematical modeling based on it, which allowed us to put together a general picture for
the series of processes determining the evolution of primary defects.
Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 5–29, November,
1996. 相似文献
16.
17.
A steel striker impacting the surface of single-crystalline quartz generates strain waves and their related acoustic and electromagnetic
emissions. Simultaneously, microcracks with free excited SiO• radicals at their edges appear in the single crystal. The relaxation
of the electronic excitation causes bursts of fractoluminescence. The intensity of the bursts is proportional to the microcrack
surface area. It is found that the linear sizes of microcracks vary from 15 to 70 μm. Cracking changes the slope of the time
dependences of the acoustic and electromagnetic emission intensities. The microcrack size distribution obeys a power law with
an exponent of about two. 相似文献
18.
T. P. Stepanova G. N. Gubanova A. N. Pogrebnaya V. M. Kapralova 《Physics of the Solid State》2006,48(2):377-383
The dipole moments and dielectric polarization relaxation of a low-molecular liquid-crystal monomer, namely, 4-[ω-(2-propenoyloxy)pentyloxy]-4′-cyanobiphenyl (CBO-5A), are investigated in a mesomorphic phase, an isotropic melt, and a chloroform solution in the absence of external orienting fields. Analysis of the dipole polarization of the CBO-5A monomer in the chloroform solution (x 2 ~ 0.0566 mol/mol) demonstrates that the temperature dependences of the permittivity and the dipole moment measured with decreasing temperature are characteristic of molecular association with the Kirkwood factor g = 0.77. It is found that the Kirkwood factor g for the isotropic melt is 0.55. The values of g < 1 indicate the presence of associates with a tendency toward antiparallel orientation of the CBO-5A molecules in both the solution and the melt. Dielectric absorption of relaxation nature is observed in the chloroform solution at temperatures in the range from ?50 to ?20°C. Two relaxation processes of dipole polarization are observed in the isotropic and liquid-crystal phases of the CBO-5A monomer in the bulk of the material. Examination of the temperature dependences of the dielectric relaxation time revealed that molecules of the CBO-5A liquid-crystal monomer in the bulk can be involved in several types of motion occurring through either the local mechanism or the cooperative mechanism. 相似文献
19.
In dielectrics with high steady leakage of conductivity, the frequency–temperature dependences of the dielectric loss tangent generally allow us to determine the relaxation time and activation energy of relaxation process only when they are strong. With weak relaxation processes, there are no extrema in the frequency dependence of the dielectric loss tangent. In such cases, the parameters of the relaxation processes are initially determined from the frequency behavior of the imaginary parts of the electrical module or impedance. However, the frequency dependences of these quantities when there is electrical conduction can contain three extrema. Identifying the maxima associated with relaxation polarization therefore requires additional research. 相似文献
20.
在电场为3.2 kV/cm, 电流密度为50 mA/cm2条件下对ZnO压敏陶瓷进行了115 h的直流老化, 研究了直流老化对ZnO压敏陶瓷电气性能及缺陷结构的影响. 发现直流老化115 h 后ZnO压敏陶瓷的电位梯度、非线性系数分别从2845 V/cm, 38.3下降到51.6 V/cm, 1.1, 介电损耗中的缺陷松弛峰被增大的直流电导掩盖, 电模量中只观察到一个缺陷松弛峰, 低频区交流电导率急剧增大并且相应的电导活化能从0.84 eV下降到只有0.083 eV. 通过对直流老化后的ZnO压敏陶瓷在800 ℃进行12 h 的热处理, 发现其电气性能和介电性能都得到了良好的恢复并有一定的增强, 电位梯度、非线性系数恢复到3085 V/cm, 50.8, 电导活化能上升到0.88 eV. 另外, 其本征氧空位缺陷松弛峰也得到了一定的抑制. 因此, 认为热处理过程中氧在晶界处的扩散作用对ZnO压敏陶瓷的直流老化恢复起到了关键作用.
关键词:
ZnO压敏陶瓷
介电性能
直流老化
热处理 相似文献