The Meyer-Neldel rule in the processes of thermal emission and hole capture in Ge/Si quantum dots

The hole thermal-emission rates and the cross sections for hole capture to the bound states in Ge quantum dots in Si are determined by admittance spectroscopy. The capture cross sections and the activation energies for emission rate are found to be related to each other by the Meyer-Neldel rule with a characteristic energy of 27±3 meV, which does not depend on the quantum-dot size. It is established that the capture cross section changes with temperature following the activation law. The experimental data are evidence of a unified multiphonon mechanism for the activation processes of hole transitions from the Ge quantum dots to the Si valence band and hole capture back into the quantum dots.     

Meson-exchange currents and energetic particle emission from μ− capture

We consider corrections to the impulse approximation calculation of the excitation function generated by muon capture in complex nuclei, in the form of captures on pairs of nucleons induced via meson-exchange currents. Within the Fermi gas model for the nucleus, these multinucleon captures are found to account for 4–8% of the experimental muon capture rates and to produce high excitation energies. The emission of pre-equilibrium protons with energies between 40 and 90 MeV is calculated for several nuclei using the hybrid exciton model. The agreement with experiment on emission spectra and rates is generally good. The emission of neutrons at these energies is also discussed.     

Deep level transient spectroscopy measurement on tin-doped n-indium selenide

Deep level transient spectroscopy measurements in indium selenide samples doped with different amounts of tin are reported. Three tin-related electron traps have been detected with activation energies for emission of 56, 74, and 110 meV. The capture cross-section has also been measured and it is very low and weakly dependent on temperature for the 74 and 110 meV deep levels that are attributed to electron trap states related to ionized acceptor centers. For the 56 meV level the apparent capture cross-section shows an activated temperature dependence with an activation energy of 35 meV, which yields an ionization energy of 21 meV for the related level, which corresponds to the tin-related shallow donor. That behaviour is interpreted through the presence in InSe of stacking-fault-related barriers. When one of these barriers is swept by the depletion zone edge during the emptying or filling pulses, electrons must overcome that barrier in order to be emitted or captured, which results in a reduction of the effective capture and emission rates of shallow donors which thus become observable through capacitance transients.     

A comparative study of thermoluminescence and isothermal destruction of radiation defects in feldspars

Up to four broad thermoluminescence emission bands were observed in X-ray irradiated feldspars of different composition. Slow decrease of emission after X-ray irradiation indicates the presence of shallow traps in most feldspars. The glow curves were also very broad; the method of Hoogenstraaten led to activation energies between 52 and 105 kJ/mol and small frequency factors around 10⁵ s^-1. Simultaneous measurements of isothermal changes in optical absorption and thermoluminescence intensity indicated transition from first to second order decay in most cases in qualitative agreement with the kinetics of defect formation by X-ray irradiation. The glow curves could also be decomposed into two curves with a first order decay preceding the second order process. The activation energies determined by both methods are in fair agreement, differences may be due to distributions of trap depths. Activation energies and the maxima of emission, absorption and photoconductivity were used for construction of energy level schemes for these radiation defects. Common excited states above the conduction band edge are suggested for all defects.     

Absolute cross sections for one electron capture into excited projectile states in collisions between He2+ (15–150 keV) and Li atoms

We have studied the He²⁺-Li collision system at laboratory energies between 15 and 150 keV using optical methods. From the measured emission cross sections we derive state-selective capture cross sections for n = 2,3,4 and n ? 5 states of the He⁺ ions. Our data are consistent with theoretical predictions of Bransden and Ermolaev. The total capture cross sections as evaluated from our emission cross section data, agree very well with the results of McCullough et al. obtained from projectile charge detection measurements. Near 15 keV our emission cross sections for 30.4 nm and 25.6 nm are much larger than those measured previously by Barrett and Leventhal at slightly lower energies.     

核衰变产生的X射线和俄歇电子数据计算

核衰变过程中,内转换电子发射和电子俘获能在原子电子壳层内留下空穴.其他原子电子壳层的电子将填补这些空穴,其原子电子位置将重排,并发射X射线和俄歇电子.X射线和俄歇电子的能量由原子电子结合能计算得到,X射线和俄歇电子的强度分别由内转换电子发射和电子俘获在原子电子壳层内留下的空穴数,X射线荧光产额,和空穴转移系数计算得到.本文简要介绍核衰变产生的X射线和俄歇电子数据的计算方法、计算程序与工作流程,并以核衰变为例说明其具体应用和简要讨论与总结.     

Charge transfer activation energy for alkali atoms on Re and Ta

Ion and atom desorption energies for five alkali metals on Re and Ta were determined using the ion thermal emission noise method. The activation energies for the charge transfer process in the adsorbed state were calculated using a special energetic balance equation, which describes the surface ionization and thermal desorption effect. Energies for desorption of Li, Na, K, Rb and Cs from Re and Ta surfaces were determined by measuring the time autocorrelation function of the ion thermoemission current fluctuations.     

Some Luminescence Properties of the Blue Emission Band of Muscovite

Egyptian muscovite has the main thermoluminescence emission band in the blue region (450–490 nm). The natural band has thermoluminescence peaks at 240, 260 and 270°C. The initial rise method shows that these peaks have thermal activation energies of 1.32, 1.41 and 1.38 eV, respectively. The laboratory-induced peaks at 100, 140, 160 and 240°C have activation energies of 0.55, 0.64, 0.94, and 1.32, respectively. For fired muscovite when exposed to 1 kGy of γ-radiation, followed by annealing at 500°C for 0.5h and cooling in air, the sensitivity increased to be ~36 the original value. The effect of different cooling rates after the heat treatment was also studied. The phase transitions of the crystal are the main reasons for the changes in the thermoluminescence properties.     

恒星能量下核子俘获反应率的晕核效应

恒星能量下俘获截面很难直接测量。¹⁰Be（n，γ）¹¹Be俘获反应涉及到非均匀宇宙大爆炸核合成，无直接测量实验截面数据。利用转移反应¹⁰Be（d，p）¹¹Be的渐近归一化系数（ANC）方法，计算了¹⁰Be（n，γ）¹¹Be俘获反应截面和反应率。¹¹Be是中子晕核。研究表明，在恒星能量下俘获到晕态的截面和反应率显著增大。     

AlGaAs∶Sn中DX中心电子俘获势垒的精细结构

采用定电容电压法,测量了n型Al026Ga074As∶Sn中DX中心电子热俘获瞬态,以及不同俘获时间后的电子热发射瞬态;并对瞬态数据进行数值Laplace变换,得到其Laplace缺陷谱(LDS).通过分析LDS谱,确定了电子热俘获和热发射LDS谱之间的对应关系,从而得到热俘获系数对温度依赖关系,以及与Sn相关的DX中心部分电子热俘获势垒的精细结构;通过第一原理赝势法计算表明,Sn附近的AlGa原子的不同配置是电子热俘获势垒精细结构产生的主要原因     

Electrical properties of crystals of alkali-halide solid solutions in the KCl-KBr system

The dielectric properties of solid solutions in the KCl-KBr system are investigated. By comparing the melting points of the compounds and the activation energies for migration of current carriers a correlation is derived between the melting point of the solid solution and the activation energy. It is shown that the solid solution has a decreased impurity capture coefficient and increased aggregation of single vacancies.     

Cross sections for the photodisintegration of a deuteron and neutron capture by a proton calculated for the case of nonlocal potential

The processes of deuteron photodisintegration by a gamma-quantum and the radiative capture of a neutron by a proton with the emission of a gamma-quantum are considered. Interaction between nucleons is described by a nonlocal potential of the Yamaguchi type but allowing for repulsion due to the nucleon cores. In contrast to other potentials, the Schroedinger equation is solved exactly for the proposed potential. The potential is more exactly defined in comparison with the previously obtained values for the parameters; information on this potential is important in solving certain fundamental problems in nuclear theory. The effective cross sections for photodisintegration of a deuteron and for radiative capture are computed. Calculations show that the proposed potential makes it possible to describe the photodisintegration processes quite accurately for intermediate (up to 20 MeV) energies. The cross section computed for radiative capture is in somewhat better agreement with experiment than is the same cross section determined for other potentials.     

Observation of a donor-acceptor pair recombination in the edge emission of ZnSe crystal by electro-luminescence

An injection type electro-luminescence in ZnSe crystal has been studied by using ZnSe-SnO₂ hetero-junction at 20°K. In the emission peak observed around 2·70 eV, a clear energy shift toward the higher energy side with increasing injection current density has been found at low temperatures, which could be associated with the D-A pair (donor-acceptor pair) recombination process. The energy sum of the donor and acceptor activation is estimated to be larger than 137 meV. In the higher temperature region, this emission line turns out due to the ‘free-to-bound’ recombination, and the related acceptor ionization energy is considered to be ～120 meV. By taking into consideration the energies of bound exciton emission, the exciton localization energies and the related donor and acceptor ionization energies are evaluated.     

Discrepancy in the doubly radiative neutron-proton capture

In the present paper we reinvestigate the theoretical cross-section for the doubly radiative n-p capture at thermal energies. We find the upper limit of the ratio R of the two photon emission cross-section to the one photon emission cross-section to be R ? 10^?7. This limit is 3 orders of magnitudes larger than a previous calculation, however, still four orders of magnitudes too small compared to a recent experiment which thus remains to be explained.     

Energy spectra and asymmetries of neutrons emitted after muon capture

Inclusive energy spectra and the energy dependence of the asymmetry parameter have been measured for neutrons emitted after muon capture in O, Si, Ca and Pb. In addition a neutron-neutron coincidence measurement has been performed for Ca. The results of these measurements confirm the exponential shape of the energy spectra and the positive asymmetry observed by Sundelin and Edelstein. The observation of neutrons with energies above 50 MeV and the observation of simultaneous emission of two high-energy neutrons suggest the importance of short-range nucleonnucleon correlations in this process.     

In0.49Ga0.51P中缺陷的俘获行为

利用深能级瞬态谱（ＤＬＴＳ）和瞬态光电阻率谱（ＴＰＲＳ）研究了利用金属有机物化学汽相沉淀（ＭＯＣＶＤ）生长的未有意掺杂的Ｉｎ０．４９Ｇａ０．５１Ｐ中缺陷对载流子的俘获过程和发射过程．利用ＤＬＴＳ测量观测到了一个激活能为０．３７ｅＶ的缺陷,该缺陷的俘获势垒值介于１８０ｍｅＶ到２４０ｍｅＶ之间．该缺陷的俘获势垒值的大的分布被解释为缺陷周围原子重组的微观波动．在研究中发现研究这些缺陷的俘获过程比发射过程更有效,俘获势垒为０．０６ｅＶ和０．４０ｅＶ的两个缺陷在俘获过程中被观测到,而在发射过程中并没有观测到     

Field emission current fluctuations from clean tungsten field emitters in the built-up state

Field emission flicker noise spectral density functions of the (012), (113) and (111) tungsten region were measured in the built-up state of the emitter. Their dependence on temperature is analysed in terms of the spectral density and knee frequency activation energies. By comparison with FIM single tungsten adatom migration energies and build-up activation energies of the polyhedral tip and by discussion of the shape of the spectra some conclusions are drawn as to the mechanism of the flicker noise. From the given data favourable operating conditions of TF cathodes can be derived according to the requirements on bandwidth and signal-to-noise ratio.     

Charge transfer in H~ H and H~ He~ collisions at intermediate and high energies using an asymptotic two-state atomic expansion method

ＣｈａｒｇｅｔｒａｎｓｆｅｒｉｎＨ＋＋ＨａｎｄＨ＋＋Ｈｅ＋ｃｏｌｉｓｉｏｎｓａｔｉｎｔｅｒｍｅｄｉａｔｅａｎｄｈｉｇｈｅｎｅｒｇｉｅｓｕｓｉｎｇａｎａｓｙｍｐｔｏｔｉｃｔｗｏｓｔａｔｅａｔｏｍｉｃｅｘｐａｎｓｉｏｎｍｅｔｈｏｄ▲ＺｈｏｕＸｉａｏｘｉ...     

双异质结AlxGa1-xAs/GaAs发光管中与氧有关能级的测量

用DLTS和单次脉冲瞬态电容技术研究了液相外延生长的双异质结AlxGa1-xAs/GaAs发光管,掺Si的n-Al0.05Ga0.95As有源层中的深能级。着重分析了一个与氧有关的电子陷阱,其发射激活能为EC-ED=0.29eV。我们发现该电子陷阱随正向注入脉冲宽度tp的增加DLTS峰向低温移动,即在确定的温度下发射率随tp的增加而增加。用DLTS首次测得该能级的俘获瞬态谱,发现俘获峰随反向撤空脉冲宽度tR的增加向低温端移动,即在确定的温度下俘获率随tR的增加而增加,并且俘获激活能从△Eσ=0.28eV变化到0.26eV,用位形坐标图讨论了引起变化的原因。