Electron traps in CdS single crystals obtained by admittance spectroscopy on the hetero- and Schottky junctions

The electron trap parameters in semiconducting CdS single crystals were obtained by admittance spectroscopy on its hetero- and Schottky junctions, and the trap depths obtained were 0.065, 0.09, 0.15 0.20, and 0.40 eV. The capture cross-section of the shallowest trap on the Cd-face of the crystals was about 10⁻¹⁹ cm², one order smaller than that of the bulk crystal. The resolving power of the employed method was about 50 meV to distinguish the two traps with different depths. The results of the computer simulation of this method suggested that the trap can be determined when the trap density is at least one order lower than the donor density. The calculated density of the each trap was 1×10¹⁵ cm⁻³ for the shallowest trap and 2×10¹⁶ cm⁻³ for the remaining traps, respectively.     

低温低剂量率下金属-氧化物-半导体器件的辐照效应

对金属氧化物半导体(MOS)器件在低剂量率γ射线辐照条件下的剂量率效应以及温度效应进行了研究.对不同剂量率、不同温度辐照后MOS器件的阈值电压漂移进行了比较.结果表明,低剂量率辐照下,感生界面态要受到辐照时间的长短以及生成的氢离子数目的影响,辐照时间越长,生成的氢离子越多,感生界面态密度越大;温度对界面态的影响与界面态建立的时间有关,低温辐照时,界面态建立的时间要加长 关键词： 辐照效应 阈值电压漂移 低剂量率 低温 界面态     

Creating Ioffe-Pritchard micro-traps from permanent magnetic film with in-plane magnetization

We present designs for Ioffe-Pritchard type magnetic traps using planar patterns of hard magnetic material. Two samples with different pattern designs were produced by spark erosion of 40 μm thick FePt foil. The pattern on the first sample yields calculated axial and radial trap frequencies of 51 Hz and 6.8 kHz, respectively. For the second sample the calculated frequencies are 34 Hz and 11 kHz. The structures were used successfully as a magneto-optical trap for ⁸⁷Rb and loaded as a magnetic trap. A third design, based on lithographically patterned 250 nm thick FePt film on a Si substrate, yields an array of 19 traps with calculated axial and radial trap frequencies of 1.5 kHz and 110 kHz, respectively.     

Electrical conduction in coevaporated antimony trisulphide films

Antimony trisulphide films were prepared by the three temperature method. The temperature dependence of conductivity for films prepared at different substrate temperatures were measured. The I–V characteristics of the Sb-Sb₂S₃-Sb systems studied showed a space charge limited conduction indicating a I ∝ V² /d³ dependence. The trap density and the trap energy level were determined.     

Influence of oxidation on space charge dynamics in DC aged low-density polyethylene

In this study, low-density polyethylene (LDPE) samples were aged under different oxygen concentration (0, 20%, and 50%). The ageing was implemented with an average external DC electric field of 50 kV/mm at 40 °C for 1000 h. It was found that augmentation of charge accumulation and suppression of charge dissipation were enhanced with increasing of oxygen concentration. The capture capability of trap sites got stronger with higher oxygen contents, which could be attributed to oxidation product newly generated during DC ageing. These trap sites acted as trap centers to capture the injected carrier while it was on the way towards the opposite electrode and decrease the apparent mobility. FTIR absorption spectra showed that new elements between 1680 and 1750 cm^?1 corresponding to ketone and aldehyde occurred due to oxidation. The bipolar charge injection model was implemented to simulate space charge transport in aged LDPE samples. It was shown that more carriers were captured and the traps gradually filled up when the oxygen concentration in the ageing test increased. A higher oxygen concentration seemed to result in a deeper average trap depth, which increased the amount of trapped charge because it was not easy to detrap. These simulation result corresponded to the experimental measurement.     

High-resolution spectroscopy with laser-cooled and trapped calcium atoms

We report on high-resolution spectroscopy with two different samples of calcium atoms, in a laser-cooled and deflected beam and in a magneto-optical trap. The atomic beam was excited by spatially separated laser fields. For spectroscopy with stored atoms in a magneto-optical trap we used a multiple-pulse excitation scheme. The resolution as low as 2.5 kHz was limited by residual frequency fluctuations of our dye-laser spectrometer. The results should allow to establish a frequency standard with a relative uncertainty below 10^–14.     

Trapping of ions from high energy sources into a radiofrequency ion trap

An attempt is described to confine ions, created externally and accelerated to some energy, in an rf quadrupole trap. 4 keV Ba⁺ ions were stopped on a Ni foil, placed in an aperture of one trap electrode. The Ba then was evaporated from the heated foil and ionized by electron impact. At background pressure of about 10^–5 mbar of various light buffer gases (He, H₂, N₂), the trap was filled once with 10⁵ ions, at a minimum primary ion number of 10¹⁰. The storage time was 10 min. From the data obtained the possibility of spectroseopic experiments on rare isotopes, created with accelerators or nuclear reactors, is discussed.     

Generation of compressed sub-poisson Bose condensate by an atom laser

The dynamics of Bose-condensate generation by a cw atom laser with simultaneous stimulated evaporative cooling in a magnetic trap was analyzed using a quantum-mechanical master equation. The model of the atom laser includes irreversible processes of incoherent trap mode pumping and spontaneous atomic transitions due to the interaction of the atomic ensemble with heat reservoirs. The inelastic atomic collisions in the trap and the continual coherent Bose-condensate output coupling from the trap were considered. At certain values of parameters, the Bose condensate created in this laser scheme occurs in a compressed sub-Poisson state. For large Bose condensates with a mean number of atoms ～10⁶, the Fano factor may be as high as ?0.5. The influence of spontaneous transitions from the excited trap modes on the statistics of Bose condensate was analyzed.     

Precise - and -factor measurements of Ba+ isotopes

Laser-microwave double and triple resonance experiments were performed on clouds of Ba⁺ ions confined in a Penning ion trap to induce and detect electronic and nuclear spin flip transitions. Collisions with buffer gas molecules in the trap was used to reduce the lifetime of a long lived metastable state of the ions, in which population trapping might occur, and to cool the ions to the ambient temperature. Loss of ions from the trap by collisions were prevented by coupling the magnetron and reduced cyclotron motions by an additional r.f. field at the sum frequency of the two motions. Electronic Zeeman transitions in ¹³⁸Ba⁺ and ¹³⁵Ba⁺ were observed at a full width of about 3 kHz at a transition frequency of 80 GHz. The uncertainty of the line center was . From the magnetic field calibration by the cyclotron resonance of electrons stored in the same trap the g_J-factor for both isotopes could be determined to . From radiofrequency induced transitions of ¹³⁵Ba⁺ the nuclear g-factor could be determined . Both measurements improve earlier results by about one order of magnitude. Received: 9 July 1998 / Accepted: 14 July 1998     

The thermoluminescence properties of CdS films under nitrogen atmosphere

Chemically deposited cadmium sulphide (CdS) films have been grown on glass at 60 °C and annealed at nitrogen atmosphere at different temperatures. The as-deposited film shows a mix phase of cubic and hexagonal. Once the film subjected to annealing the hexagonal phase becomes dominant and the crystal size increases due to these changes optical band gap energy decreases from 2.44 to 2.28 eV. The electrical conductivity increases depending on temperature and the film annealed at 423 K shows the highest conductivity. Thermoluminescence (TL) intensity of the films was measured after irradiating the films with ⁹⁰Sr/⁹⁰Y β-source and the trap depths were calculated after the TL curves deconvoluted by using the computer glow curve deconvolution (CGCD) method. It is observed that the as-deposited film has three different trap depths, at around 0.257, 0.372, and 0.752 eV corresponding to 383, 473, and 608 K, respectively.     

Photoionization cross-sections of the first excited states of sodium and lithium in a magneto-optical trap

A two element magneto-optical trap (MOT) for Na and ⁷Li or ⁶Li is used to cool and trap each of them separately. A fraction of the cold atoms is maintained in the first ²P_3/2 excited state by the cooling laser. These excited state atoms are ionized by laser light in the near-UV region, giving rise to a smaller number of trapped atoms and to different loading parameters. Photoionization cross-sections were derived out of these data. They are in reasonable agreement with data previously obtained using thermal samples and with theoretical predictions. Received 21 March 2001 and Received in final form 3 August 2001     

Penning trap assisted decay spectroscopy of neutron-rich 115Ru

Exotic, neutron-rich ¹¹¹Mo and ¹¹⁵Ru nuclei, produced in proton-induced fission of ²³⁸U target, were separated with the IGISOL mass separator. The separator was coupled to the JYFLTRAP Penning trap to select the ions of a single, desired element out of the isobaric IGISOL beam. Monoisotopic samples of ¹¹⁵Ru and ¹¹¹Mo ions were observed with a microchannel plate detector after the trap or were implanted on a catcher foil for gamma- and beta-ray coincidence spectroscopy. In spite of short data taking time new gamma transitions were identified in the beta decay of very neutron-rich ¹¹⁵Ru.     

Influence of ion bombardment on the photoluminescence response of embedded CdS nanoparticles

Semiconductor nanoparticles (CdS) were fabricated by an inexpensive chemical route using polyvinyl alcohol (PVA) as the dielectric host matrix. Nano-CdS in PVA were subjected to ion irradiation (using oxygen, chlorine and gold) in the medium energy range (80–100 MeV) and under fluence variation of 10¹¹–10¹³ ions/cm². The nature of light emission was found to be drastically different in each of the three cases. Photoluminescence spectra of oxygen irradiated samples exhibit band edge emission (2.8 eV) as well as trap related emission (1.76 eV) whereas band edge emission is found to be bleached out for chlorine ion irradiated nano-CdS. The intense broad PL peaks, noticeable in the case of gold ion irradiated samples suggest superposition of the two peaks — namely, band edge emission and trap related emission. Furthermore, in the case of gold ion irradiated nano-CdS, energy shift in the PL spectra reveals variation in size distribution caused by the extra pressure effect of heavy gold ion beams. The mechanism of such a difference as a result of ion irradiation-type and ion-fluence is discussed in detail.     

Pulsed polarization gradient cooling in an optical dipole trap with a Laguerre-Gaussian laser beam

We utilized a blue-detuned Laguerre-Gaussian (doughnut) laser beam to trap cold rubidium atoms by optical dipole force. ”Pulsed” polarization gradient cooling was applied to the trapped atoms to suppress the trap loss due to heating caused by random photon scattering of the trapping light. In this trap about 10⁸ atoms were initially captured and the trap lifetime was 1.5 s, which was consistent with losses due to background gas collisions. This trap can readily be applied to atom guiding, compression, and evaporative cooling. Received: 10 July 1997 / Received in final form: 5 January 1998 / Accepted: 16 January 1998     

Measurement of storage time, estimation of ion number and study of absorption line profile in a Paul trap

Europium (Eu⁺) ions were confined in a Paul trap and detected by non-destructive method. Storage time of Eu⁺ ions achieved in vacuum was improved by orders of magnitude employing buffer gas cooling. The experimentally detected signal was fitted to the ion response signal and the total number of ions trapped was estimated. It is found that the peak signal amplitude as well as the product of FWHM and the peak signal amplitude is proportional to the total number of trapped ions. The trapped ion secular frequency was swept at different rates and its effect on the absorption line profile was studied both experimentally and theoretically.     

Luminescence studies on photostimulable phosphor CsBr:Eu2+

Photostimulable phosphor CsBr:Eu²⁺ is prepared through a solid-state reaction. The effect of annealing atmosphere on photoluminescence and photostimulated luminescence was investigated. Optimum luminescence intensity was obtained when samples were prepared at 350°C in air atmosphere. The effect of irradiation of gamma and neutron had resulted in the formation of optically stimulable traps with different trap depths. The role of monovalent and divalent dopants on thermoluminescence dosimetric properties has been discussed.     

聚合物材料空间电荷陷阱模型及参数

采用电声脉冲测量技术研究了直流电场下低密度聚乙烯材料的电荷入陷和脱陷特征. 发现在不同电场周期下样品的电荷衰减呈现不同的特征, 为此提出了一个简单的基于两陷阱水平的入陷和脱陷模型, 并计算了相应的参数, 如陷阱能级和密度. 确定了不含任何添加剂的低密度聚乙烯样品中存在的两种水平的陷阱能级分别为: 较浅陷阱能级0.77–0.81 eV 对应的浅陷阱电荷密度为(1.168–1.553)× 10¹⁹ m^-3; 较深陷阱能级0.96–1.01 eV 对应的深陷阱电荷密度为(1.194–4.615)× 10¹⁸ m^-3. 最后初步验证了材料的深陷阱能级和对应的深陷阱电荷密度随老化而增加, 可考虑将模型中的两能级陷阱参数作为老化诊断特征参量. 关键词： 聚合物 空间电荷 陷阱 老化     

用激光计数放射性氪原子

原子阱痕量分析是一种基于激光的新方法,能够对数微升氪气中丰度低至10^-14的⁸⁵Kr和⁸¹Kr原子进行计数测量．介绍了在合肥建成的痕量放射性氪同位素测量系统,包括ATTA装置、水中溶解气提取和氪气分离提纯的样品处理设备．利用该系统对国内多处大气中⁸⁵Kr浓度的测量结果为1.3～1.6 Bq/m³,与文献中北半球大气本底值相吻合．对华南和华北的几个浅层和深层地下水样品进行了⁸⁵Kr和⁸¹Kr测年,示范了该系统的应用．     

Laser cooling of a small number of Be+ ions in a penning trap

Be⁺ ions stored in a Penning trap were cooled by a laser beam perpendicular to the magnetic field. The cooled ions are strongly coupled and phase transitions of up to 100 ions were observed. In experiments with only a few ions stored in the trap, a stepwise decrease in fluorescence intensity was observed. All steps are of the same size and so every step is attributed to a single ion. The discrete changes in fluorescence occurred more frequently when the background pressure was increased, caused by collisions between stored ions and background neutral molecules.     

Manipulation of ultracold atomic mixtures using microwave techniques

We used microwave radiation to evaporatively cool a mixture of of ¹³³Cs and ⁸⁷Rb atoms in a magnetic trap. A mixture composed of an equal number (around 10⁴) of Rb and Cs atoms in their doubly polarized states at ultracold temperatures was prepared. We also used microwaves to selectively evaporate atoms in different Zeeman states.