基于双肖特基接触GaN薄膜特性参数测试新方法

提出了一种GaN薄膜电学参量测试新方法.该方法基于双肖特基结二极管结构,利用非对称的电极图形获取整流特性,从而省去了复杂的欧姆接触形成工艺,可方便地导出电子电导迁移率和肖特基接触理想因子等特征参数.对残留载流子浓度为7×1016 cm-3 的非故意掺杂GaN薄膜进行了试验,新方法得到Ni/Au-GaN肖特基接触的理想因子为2.8,GaN薄膜方块电阻为491Ω和电子电导迁移率为606cm2/(V·s).这些典型参数与利用欧姆接触实验和普通Ni/Au-GaN肖特基二极管测试所得结果较为吻合.该方法为半导体薄膜测试提供了新思路,可推广用于难以形成良好线性欧姆接触或材料特性受欧姆接触工艺影响较大的外延材料及其金半接触的监测研究.

非晶/微晶过渡区域硅薄膜的微区喇曼散射研究

通过改变氢气对硅烷气体的稀释程度，并保持其他的沉积参量不变，用等离子体增强化学气相沉积（PECVD）方法成功地制备出非晶/微晶相变过渡区域的硅薄膜样品。测量了样品的室温光电导和暗电导，样品的光电性能优越，在50 mW·cm~（-2）的白光照射下，光电导和暗电导的比值达到10~6。在室温下用微区喇曼谱研究了薄膜的微结构特性，用高斯函数对喇曼谱进行了拟合分析。结果表明，在我们的样品制备条件下，当H_2和SiH_4的流量比R较小时，样品表现出典型的非晶硅薄膜 的结构特性；随流量比R的增大，薄膜表现出两相结构，其中的微晶成分随氢稀释比的增大逐渐增多；用量子尺寸效应估算了两个高氢稀释样品（R > 50）中微晶粒子的平均尺寸大小为2.4 nm左右；样品的中程有序度随氢稀释程度的增加而增大。

Simulations to design an online motion compensation system for scanned particle beams

Respiration-induced target motion is a major problem in intensity-modulated radiation therapy. Beam segments are delivered serially to form the total dose distribution. In the presence of motion, the spatial relation between dose deposition from different segments will be lost. Usually, this results in over-and underdosage. Besides such interplay effects between target motion and dynamic beam delivery as known from photon therapy, changes in internal density have an impact on delivered dose for intensity-modulated charged particle therapy. In this study, we have analysed interplay effects between raster scanned carbon ion beams and target motion. Furthermore, the potential of an online motion strategy was assessed in several simulations. An extended version of the clinical treatment planning software was used to calculate dose distributions to moving targets with and without motion compensation. For motion compensation, each individual ion pencil beam tracked the planned target position in the lateral aswell as longitudinal direction. Target translations and rotations, including changes in internal density, were simulated. Target motion simulating breathing resulted in severe degradation of delivered dose distributions. For example, for motion amplitudes of +/- 15 mm, only 47% of the target volume received 80% of the planned dose. Unpredictability of resulting dose distributions was demonstrated by varying motion parameters. On the other hand, motion compensation allowed for dose distributions for moving targets comparable to those for static targets. Even limited compensation precision (standard deviation similar to 2 mm), introduced to simulate possible limitations of real-time target tracking, resulted in less than 3% loss in dose homogeneity.

Alpha decay half-lives of new superheavy elements through quasimolecular shapes

The lifetimes of alpha decays of the recently produced isotopes of the elements 112, 114, 116 and the element (294)118 and of some decay products have been calculated theoretically within the Wentzel-Kramers-Brillouin approximation. The alpha decay barriers have been determined in the quasimolecular shape path within a generalized liquid drop model including the proximity effects between nuclei in a neck, the mass and charge asymmetry and the precise nuclear radius. These calculations provide reasonable estimated for the observed alpha decay lifetimes. The calculated results have been compared with the results of the density-dependent M3Y effective interaction and the experimental data. It is indicated that the theoretical foundation of the generalized liquid drop model is as good as that of the microscopic DDM3Y model, at least in the sense of predicting the T-1/2 values as long as one uses a correct alpha decay energy. The half lives of these new nuclei are well tested from the consistence of the macroscopic, the microscopic and the experimental data.

PROJECTILE FRAGMENTATION OF Ar-36,Ar-40 INDUCED REACTIONS

Fragment yields for Z >= 5 from projectile fragmentation using primary beams of Ar-36,Ar-40 at 50 MeV/nucleon on Ni-64 target have been measured in RIBLL fragment separator. We compare the fragment cross sections with the predictions of the empirical EPAX parametrization of fragmentation cross-sections and Statistical Abration-Ablation model (SAA) by considering the RIBLL separator transmission rate. Isotope yield ratios between these two reactions were calculated and isoscaling parameters alpha and beta are extracted, their dependences on fragment atomic number Z and neutron number N were presented.