GaN layers with different polarities prepared by radio frequency molecular beam epitaxy and characterized by Raman scattering

GaN layers with different polarities have been prepared by radio-frequency molecular beam epitaxy (RF-MBE) and characterized by Raman scattering. Polarity control are realized by controlling Al/N flux ratio during high temperature AlN buffer growth. The Raman results illustrate that the N-polarity GaN films have frequency shifts at $A_{1}$(LO) mode because of their high carrier density; the forbidden $A_{1}$(TO) mode occurs for mixed-polarity GaN films due to the destroyed translation symmetry by inversion domain boundaries (IDBS); Raman spectra for Ga-polarity GaN films show that they have neither frequency shifts mode nor forbidden mode. These results indicate that Ga-polarity GaN films have a better quality, and they are in good agreement with the results obtained from the room temperature Hall mobility. The best values of Ga-polarity GaN films are 1042 cm$^{2}$/Vs with a carrier density of 1.0$\times $10$^{17}$~cm$^{ - 3}$.     

PLD制备的籽晶层对ZnO纳米棒形貌及性能的影响

本文研究了脉冲激光沉积法(PLD)制备的不同籽晶层对水热生长ZnO纳米棒的形貌及发光性能的影响,通过比较得出,籽晶层是获得高度取向,排列有序的ZnO纳米棒的基础.电子回旋共振(ECR)氧等离子体参与沉积,有利于获得表面均匀且光滑平整的籽晶层,进而得到形貌及结晶质量较好的ZnO纳米棒.籽晶层的厚度不仅能够改变纳米棒的疏密程度,而且还能够改善纳米棒的取向性.通过调节籽晶层的退火温度可以调节纳米棒直径的大小,恰当的籽晶层退火温度也是获得形貌优良的ZnO纳米棒的一个关键因素.     

cBN/TiC/Al合成PCBN及其性能研究

以cBN, TiC, Al为主要实验原料,利用高温和超高压条件合成聚晶立方氮化硼(PCBN)复合材料。利用X射线衍射(XRD)、扫描电子显微镜(SEM)以及X射线色散能谱(EDS)对复合材料的物相组成、显微结构、表面微裂纹以及各类元素分布情况进行了分析,同时对复合材料的显微硬度和抗弯强度进行了测试。研究表明:在超高压5.5 GPa,高温1 450℃下,PCBN烧结体由BN, TiC, AlB₂和AlN组成;结合剂均匀的分布在cBN颗粒周围,牢固的将cBN颗粒粘结在一起。PCBN的硬度随着cBN含量的增加而显著增加,抗弯强度则是先增大后减小,PCBN的断裂方式是沿晶断裂和穿晶断裂共同作用的结果。     

氢能源技术预测与燃料电池产业发展策略规划

近年由于能源短缺与全球暖化的问题,使得洁净能源的开发逐渐受到重视.针对氢能源科技的相关技术与燃料电池产业,运用专家访谈、专利计量学、成长曲线模型与策略分析等方法,进行技术预测与产业发展策略规划.研究结果显示,产氢技术与储氢技术尚未达到成熟阶段,需要更多的R&D资金以强化技术发展;同时,政府应采取适当的补助措施,以加速其技术发展进程;而燃料电池技术则以PEMFC技术发展最为迅速.