电场对量子阱中自由载流子光辐射线宽的影响

本文对固体中在较大空间范围运动的粒子采用轨道、动量及波包来描述。根据量子力学测不准关系, 粒子的能量测不准公式被导出。公式表明, 电场强烈地散射载流子, 使载流子所处能级大为展宽。应用该公式到Ｐ－Ｉ－Ｎ结构的ＧａＡｓ／ＧａＡｌＡｓ 多量子阱中, 理论计算的光辐射线宽与光致荧光实验测得的线宽吻合。     

Investigation of the electrical and optical properties of InAs/InGaAs dot in a well solar cell

The electroreflectance (ER) and current–voltage (J–V) of InAs/InGaAs dots in a well (DWELL) solar cell (SC) were measured to examine the optical and electrical properties. To investigate the carrier capturing and escaping effects in the quantum dot (QD) states the above and below optical biases of the GaAs band gap were used. In the reverse bias region of the J–V curve, the tunneling effect in the QD states was observed at low temperature. The ideality factors (n) were calculated from the J–V curves taken from various optical bias intensities (I_ex). The changes in the ideality factor (n) and short circuit current (J_SC) were attributed mainly to carrier capture at low temperature, whereas the carrier escaping effect was dominant at room temperature. ER measurements revealed a decrease in the junction electric field (F_J) due to the photovoltaic effect, which was independent of the optical bias source at the same temperature. At low temperature, the reduction of photovoltaic effect could be explained by the enhancement carrier capturing effect due to the strong carrier confinement in QDs.     

Determination of titanium NMR parameters of ATiO3 compounds: correlations with structural distortion

Solid state ^47,49Ti NMR spectra have been obtained for a number of perovskite and ilmenite ATiO₃ compounds. The ⁴⁹Ti quadrupole coupling constant varies from 2.75 MHz (CaTiO₃) to 15.5 MHz (MgTiO₃) and the electric field gradient at the titanium site was found to correlate well with the shear strain, independent of structure. The chemical shift in the perovskite structures varies by 160 ppm and correlates well with the mean Ti–O distance. The ²⁵Mg and ¹¹³Cd NMR parameters are also reported for the relevant compounds.     

Non perturbative approach for a polar and polarizable linear molecule in an inhomogeneous electric field: Application to molecular beam deviation experiments

A non perturbative approach is used to solve the problem of a rigid linear molecule with both a permanent dipole moment and a static dipole polarizability, in a static electric field. Eigenenergies are obtained and compared to perturbative low field and high field approximations. Analytical expressions for the orientation parameters and for the gradient of the energy are given. This non perturbative approach is applied to the simulation of beam deviation experiments in strong electric field. Results of simulations are given for inhomogeneous alkali dimers. For LiNa, the simulations are compared to experimental data. For LiK, deviation profiles have been simulated in order to prepare future experiments on this molecule. Received 21 July 1999 and Received in final form 22 September 1999     

A novel high-resolution interference spectrometer

A novel precision wavemeter is presented with a resolution of better than 0·01 nm. A Sagnac interferometer with two diffraction gratings forms the basis of the instrument. Using spatial heterodyning techniques and a CCD camera/frame grabber data acquisition system allows fast computer control and power spectrum analysis. The mode structure and mode hopping characteristics of a typical laser diode were examined as a function of diode injection current.     

Nucleon form factors in a relativistic quark model

Electromagnetic form factors of protons and neutrons are investigated based on a relativistic quark model with the inclusion of a pion cloud. Pseudo-scalar π-quark interaction is employed to study the coupling between the nucleon and the π. The results show the important role of the pion cloud for the neutron charge form factor. Moreover, our numerical analysis indicates a difference between the relativistic and the nonrelativistic treatments. Received: 10 March 1999 / Revised version: 14 June 1999     

梯度膜作为高功率激光反射膜的初步研究

 对渐变折射率薄膜替代均匀膜系作为高功率激光反射膜的可行性进行了理论研究。以较容易获得的线性共蒸法制备的光学膜在中心波长为1 064 nm的激光作用为例,分析了薄膜与基体之间波长的匹配、场强分布等问题。提出了通过改变微小单元获得梯度膜匹配厚度的数值方法,将之运用在14个周期结构的梯度膜中,并由膜系计算软件验证了所获得结果。最后通过分析Maxwell方程,计算了梯度膜中与薄膜损伤密切相关的电场强度分布。结果表明：周期性结构梯度高反射膜中的电场分布与传统高反射膜具有相似性,但相对于传统高反射膜容易在界面处出现损伤的情形而言,梯度膜更容易在表面出现损伤,使梯度膜表面反射相移接近π是高功率梯度高反射膜的设计方向。     

Electrical resistivity of the alkaline earth metals Ca,Sr and Ba in the 50–300K temperature region

The computed values of the temperature dependent electrical resistivity is presented for the alkaline earth metals Ca, Sr and Ba. Numerical values of the mean free paths obtained using a finite mean free path approach is also reported. The structure factor has been evaluated using experimental values for the phonon spectra while local model potentials were used for the form factors. Our numerical results compare favourably with experiments.     

Pd/Au纳米结构制备和粒子组分自旋的谱学性能研究

为研究Pd/Au纳米结构制备和电催化性能、控制粒子大小组分和自旋,用油浴热分解方法制备了核/壳纳米结构Pd/Au双金属合金纳米颗粒,采用PVP和多元醇作表面活性剂和稳定剂,依据溶液浓度、颗粒大小、吸附能控制晶相获得了均匀、一致的2层和3层Pd/Au纳米样品,并采用HAADF和HRTEM测试了纳米结构尺寸形貌,用EDS测试了成分分布,试验产物用TEM/XRD进行了表征,结果表明,Pd/Au具有面心立方八面体结构,与Au/Pd核壳不同,纳米Pd/Au具有活性、耐久性、电催化性和稳定性。     

A prototype of a high rating MRPC

Six-gap resistive plate chamber （MRPC） prototypes with semiconductive glass electrodes （bulk resistivity ～ 10^10Ω·cm） were studied for suitability in time-of-flight （TOF） applications at high rates. These studies were performed using a continuous electron beam of 800 MeV at IHEP and an X-ray machine. Time resolutions of about 100 ps and efficiencies larger than 90% were obtained for flux densities up to 28 kHz/cm^2.