声波在双层非线性介质中传播的二极管现象

假设声波在双层一维非线性系统中传播时线性部分满足波动方程,非线性部分类似于非线性薛定谔方程的非线性部分.对该模型正反两个方向分别入射相同的声波计算透射率发现:一定频率及强度的声波在模型中具有单向透过性,表现出声二极管的行为;随着非线性强度差异的增强,单向导通性显著提高.     

Evolution of native point defects in ZnO bulk probed bypositron annihilation spectroscopy

This paper studies the evolution of native point defects with temperature in ZnO single crystals by positron lifetime and coincidence Doppler broadening (CDB) spectroscopy, combined with the calculated results of positron lifetime and electron momentum distribution. The calculated and experimental results of the positron lifetime in ZnO bulk ensure the presence of zinc monovacancy, and zinc monovacancy concentration begins to decrease above 600℃ annealing treatment. CDB is an effective method to distinguish the elemental species, here we combine this technique with calculated electron momentum distribution to determine the oxygen vacancies, which do not trap positrons due to their positive charge. The CDB spectra show that oxygen vacancies do not appear until 600℃ annealing treatment, and increase with the increase of annealing temperature. This study supports the idea that green luminescence has a close relation with oxygen vacancies.     

碳化气体引入温度对3C-SiC薄膜生长的影响

通过低压化学气相沉积方法,在Si(100)衬底上生长了高度择优取向的3C-SiC(100)薄膜.SiC(200)峰的摇摆曲线表明SiC薄膜的结晶质量随着丙烷气体引入温度(Tgi)的升高而增加.选区电子衍射像表明高Tgi下生长的薄膜比低Tgi下生长的薄膜具有更好的取向.典型的SiC薄膜高分辨像中观察到了孪晶和层错.表面场发射扫描电镜像表明随着Tgi的升高,SiC薄膜的表明形貌发生了改变.