聚酰亚胺薄膜的电致发光和光致发光

测量了氙灯辐照后聚酰亚胺(PI)薄膜的光致发光(PL)强度、PL谱和氙灯辐照后直流高电场下PI薄膜的电致发光(EL)强度、EL谱、XRD谱和吸收光谱,研究了其EL、PL特性与微观结构的关系.结果表明:PI薄膜的PL强度随测量时间呈指数衰减,EL强度随场强呈指数增长;辐照39 h后,PI的预击穿场强为2.56MV/cm,...     

Measurement of diffusion coefficients in polystyrene using xenon-129 NMR

A sample of polystyrene beads, 18 μm in diameter, has been sealed in an NMR tube under 10 atm of xenon gas. Two dimensional,¹²⁹Xe NMR spectra show cross peaks between the resonances corresponding to xenon in the free gas and the sorbed state, indicating that appreciable exchange occurs during the mixing time of the NMR experiment. Selective saturation of the free gas resonance attenuates the integrated intensity of the sorbed xenon resonance as a function of saturation time, thus allowing the accurate measurement of the exchange rates between the gas and the sorbed states. A model has been developed using a slightly modified form of Crank’s treatment of diffusion in a sphere which allows for the accurate determination of the diffusion coefficient for xenon in the sorbed state. The diffusion coefficient for xenon in polystyrene at 25°C is determined to be 2.9·10^?9 cm²/s.     

Photoluminescence and electroluminescence properties of ZnO films on p-type silicon wafers

A simplified n-ZnO/p-Si heterojunction has been prepared by growing n-type ZnO rods on p-type silicon wafer through the chemical vapour deposition method. The reflectance spectrum of the sample shows an independent absorption peak at 384 nm, which may be originated from the bound states at the junction. In the photoluminescence spectrum a new emission band is shown at 393 nm, besides the bandedge emission at 380 nm. The electroluminescence spectrum of the n-ZnO/p-Si heterojunction shows a stable yellow luminescence band centred at 560 nm,which can be attributed to the emission from trapped states. Another kind of discrete ZnO rod has also been prepared on such silicon wafer and is encapsulated with carbonated polystyrene for electroluminescence detection. This composite structure shows a weak ultraviolet electroluminescence band at 395 nm and a yellow electroluminescence band. These data prove that surface modification which blocks the transverse movement of carriers between neighbouring nanorods plays important roles in the ultraviolet emission of ZnO nanorods. These findings are vital for future display device design.     

Galvanomagnetic and Thermomagnetic Properties of a Nonideal Xenon Plasma at Megabar Pressures in Megagauss Magnetic Fields

A method has been developed for the calculation of tensors of the electrical conductivity, Seebeck coefficient, and thermal conductivity of a nonideal plasma in a magnetic field within a unified approach where the kinetic coefficients are calculated together with the equation of state of the nonideal plasma within a quasichemical model. The calculations have shown that the Seebeck coefficient in xenon reaches 3 mV/K, which is slightly smaller than that in hydrogen or deuterium, and the figure of merit appears to be insignificantly higher in xenon. Consequently, the transition from hydrogen (deuterium) to xenon does not result in the expected noticeable improvement of thermoelectric properties. This is due to lower values of the Seebeck coefficient and electrical conductivity, as well as to a fast increase in the thermal conductivity of neutral xenon with an increase in its density. It has been shown for the first time that there is a density range where all components of the Seebeck tensor in xenon change their sign because of the Ramsauer minimum in the cross section for scattering of electrons on neutral atoms in the region of comparable values of cyclotron and transport frequencies of electrons.     

一种特殊结构的金刚石薄膜电致发光器件

蓝色波段电致发光器件的研究是近年来光电子和材料科学研究领域最引入注目的研究课题之一。文章作者分别利用脉冲激光淀积设备和微波等离子体化学气相沉积设备制备了不同结构的高质量掺杂金刚石薄膜电致发光器件，并对其发光光谱特性，频率特性以及发光强度与杂质浓度及激发电压的依赖关系进行了研究，发现了金旬石薄膜紫外线的发光现象，取得了一系列有价值的结果。     

a-SiC:H/pin势阱结构可见光电注入发光

本文提出一种新的a-SiC:H/pin势阱结构可见光注入式电致发光器件。设计制作了一组势阱结构和势垒结构对比的a-SiC:H/pin发光器件,其测试结果表明这种新的势阱结构器件发光特性较势垒结构器件有明显改进。本文还研究了该类器件在脉冲电流激励下的瞬态发光特性。     

Electron beam effects in auger analysis of physisorbed xenon

Adsorbed xenon on evaporated films of nickel and platinum has been analysed by Auger electron spectroscopy. The primary electron beam is shown to cause some surface heating resulting in a displacement of the isotherms. This temperature effect is the same for both metals and is due to the limiting thermal conductivity of the glass substrate. A further effect, the electron induced desorption (EID) of xenon is evidenced by a distortion of the isotherms at low equilibrium gas pressures. This effect is more clearly observed on platinum because the coverage is higher than on nickel. The EID cross-section for xenon on both metals is found to be 1 × 10^?17cm². The attenuation of the metal Auger peaks by the xenon overlayer is found to be less for platinum than for nickel. This difference is attributed to a lower packing density of xenon on the platinum surface.     

Statistical theory of thermodynamic stability of crystalline phases

The equation of state of a face-centered cubic phase has been quantitatively analyzed in terms of the statistical theory of crystals. It has been shown that, for xenon at room temperature, the pressure equal to 1.5 GPa determines the instability point where the condition of the positive bulk modulus of a face-centered cubic crystal is violated. A “universal line” bounding the thermodynamic stability region of the face-centered cubic phase of van der Waals crystals has been constructed. An analysis of the data available in the literature allows the conclusion that the revealed transition of face-centered cubic xenon to the martensitic phase at a pressure of 1.5 GPa and a temperature of 300 K can be considered a manifestation of the predicted instability. In this respect, it is important to perform detailed experiments on polymorphic transformations of real xenon (and also krypton). Another aspect of the proposed theory is that it provides a means for quantitatively predicting the characteristics of the so-called “cold” (at negative pressures) melting, which recently has become accessible for experimental observation.     

Influence of delta〈Mn〉 doping parameters of the GaAs barrier on circularly polarized luminescence of GaAs/InGaAs heterostructures

The circular polarization of low-temperature electroluminescence of diodes based on heterostructures with an undoped quantum well InGaAs/GaAs and a delta〈Mn〉 layer in the GaAs barrier has been investigated. The possibility of changing the degree of circular polarization of the electroluminescence by varying the main structural parameters of diodes (spacer layer thickness, i.e., the distance between the delta〈Mn〉 layer and the quantum well, atomic concentration in the delta〈Mn〉 layer, and introduction of an additional acceptor delta layer) has been analyzed. It has been revealed that the variation in the spacer layer thickness is the most effective method for controlling the degree of circular polarization of the electroluminescence.     

闪光灯泵浦钛宝石可调谐激光器

为了提高灯泵钛宝石激光器的输出能量和效率，对灯泵钛宝石激光器进行了大量的试验研究工作。对国产氙灯进行了快速放电和寿命试验；测得了在不同放电电流密度情况下的氙灯发光光谱分布；试验采用双灯串接泵浦，双棱镜色散光学谐振腔，平平腔型，调谐范围为７５０～９５０ｎｍ，在中心波长８００ｎｍ处得到激光输出能量为８９３ｍＪ，电光转换效率为０．８９％。该激光器的阈值约为１５Ｊ。     

Short- and long-range ion-beam mixing in Cu:Al

Ion-beam mixing by 500-keV xenon ions has been studied in targets consisting of 2000-Å films of aluminium on a polycrystalline aluminium substrate, onto which has been evaporated a 500-Å overlayer of copper. Both long- and short-range-mixing processes have been identified, by RBS analysis of the irradiated targets, as a deep copper tail in the aluminium and interfacial broadening, respectively. The long-range component varies linearly with xenon fluence, is temperature-independent in the interval 40–500 K, and is not influenced by the presence of an interfacial oxide layer between the copper and aluminium layers. The number of long-range-mixed atoms is in agreement with theoretical estimates of the recoil mixing. The short-range mixing, which is the dominating process, has a squareroot dependence on xenon fluence and is independent of temperature between 40 and 300 K, increasing rapidly at higher temperatures. The broadening attributed to the short-range mixing is explained by interstitial diffusion within the cascade. For small xenon fluences, interfacial oxide layers inhibited both short-range mixing and thermal diffusion. Higher xenon fiuences subdued the inhibition.     

Electroluminescence spectra of an STM-tip-induced quantum dot

We analyze the electroluminescence spectrum of an STM-tip-induced quantum dot in a GaAs surface layer. A flexible model has been developed, that combines analytical and numerical methods and describes the key features of many-particle states in the STM-tip-induced quantum dot. The dot is characterized by its depth and lateral width, which are experimentally controlled by the bias and the tunneling current. We find, in agreement with experiment, that increasing voltage on the STM-tip results in a red shift of the electroluminescence peaks, while the peak positions as a function of the electron tunneling current through the STM-tip reveal a blue shift.     

Interferometric measurement of two-dimensional Xe and electron density distributions in XeCl laser discharges

A near-infrared, interferometric measurement of the density distribution of the electrons and excited xenon atoms has been performed at two discharge pumped, X-ray preionized XeCl lasers. The experimental results of one of these lasers are in good agreement with model calculations for the homogeneous phase. The electrons and excited states of xenon show a different behaviour in their spatial distributions at both lasers. In addition a region of inhomogeneities, which is identified as the hot-spot region, is been found near the cathode. Filamentation of the discharge can occur after a short time. The dimension of the hot-spot region depends on the preionization delay time. The same holds for the filamentation process, which in addition depends on the HCl partial pressure.     

Quenching of vacuum ultraviolet fluorescence emission from electron beam excited quasi-molecular xenon

A pressure dependent quenching of the VUV broad-band fluorescence (bandwidth 15 nm centred at λ 173 nm) from high pressure xenon has been measured for pressures from 25 to 215 p.s.i. The experimental results can be explained by collisional de-excitation of the excited Xe₂ molecules by Xe atoms. A quenching cross section of ≈ 10^-17 cm², and molecular radiative lifetime of 16 nsec have been derived. The implications for the design of VUV molecular xenon lasers are discussed.     

Impact ionizing electroluminescence of a double barrier structure

The impact ionizing electroluminescence model of a unipolar double barrier structure has been developed. The electron density in the quantum well and the hole density generated in the collector region are based on electron current. The electroluminescence results from direct radiative recombination between the electrons and holes in the quantum well. The results show that a light on-off ratio of the electroluminescence can be obtained.     

Sensitivity enhancement by exchange mediated magnetization transfer of the xenon biosensor signal

Hyperpolarized xenon associated with ligand derivatized cryptophane-A cages has been developed as a NMR based biosensor. To optimize the detection sensitivity we describe use of xenon exchange between the caged and bulk dissolved xenon as an effective signal amplifier. This approach, somewhat analogous to 'remote detection' described recently, uses the chemical exchange to repeatedly transfer spectroscopic information from caged to bulk xenon, effectively integrating the caged signal. After an optimized integration period, the signal is read out by observation of the bulk magnetization. The spectrum of the caged xenon is reconstructed through use of a variable evolution period before transfer and Fourier analysis of the bulk signal as a function of the evolution time.     

ZnS中Er3+的正向注入电致发光

已报导的三价稀土离子(RE3+)和二价锰离子发光的电致发光器件,都是激发机理为碰撞激发的高场发光器件[1,2]。我们研究了znS:RE2+的带边激发光谱,由此提出了实现正向注入下三价稀土离子电致发光的发光器件的设想,这种器件的必要条件是在存在三价稀土离子的区域同时注入电子和空穴。在离子注入的ZnS:Er3+发光二极管上观察到了这种发光,实验证明不是碰撞激发,而是正向注入产生的发光。     

Time-dependent behavior of a pulsed high power xenon flashlamp. Application to the Mega-Joule laser pumping

A numerical model has been developed for studying the time-dependent behavior of cylindrical high power xenon flashlamp. The equations of local energy conservation and mass conservation are solved using the finite volume method to give plasma parameters such as radial temperature profiles, instantaneous emission spectra, pressure, velocity, arc conductance, etc. In a first approximation the plasma is described under local thermodynamic equilibrium, LTE. The results are given as a function of time over the pulse and for several nodes in the cross section. Then the detailed spectral and temporal calculations of the output radiation from xenon flashlamp and radiation efficiencies are provided.     

129Xe NMR studies of the dynamics of xenon in siliceous ZSM-12 zeolite

The adsorption of xenon in siliceous zeolite ZSM-12 has been studied by static, magic angle spinning and 2D-EXSY¹²⁹Xe NMR. Anisotropic lines were observed with parameters dependent on the Xe loading and the temperature of the experiment. The observed dependence of the isotropic chemical shift is at variance with the predictions of the mean-free-path model, which casts further doubt on the applicability of this model to the interpretation of Xe NMR data in porous systems. Based on the continuous changes of anisotropic parameters with the loading, we conclude that there are several adsorption sites for xenon in the pores. A qualitative model for the distribution and rapid exchange of the xenon atoms between several sites is discussed. The observed lines arise from a dynamic average of the chemical shift tensors for the different types of site weighted by their populations. 2D-EXSY spectra show two kinds of slow exchange of Xe: (a) particle to particle and, (b) particle to interparticle gas phase.