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

<正>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°C 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.     

金刚石膜微结构的慢正电子束测量研究

用慢正电子束辅助以拉曼光谱方法对一批较高质量的PECVD金刚石膜的微结构进行测量研究．拉曼光谱实验结果显示,这批金刚石膜中金刚石相含量比较高,正电子湮没实验进一步从微观结构上指出各个金刚石膜之间存在很大差异,并且从缺陷角度发现各样品中缺陷尺寸和缺陷浓度不一样,造成膜质量不同．S-E曲线变化趋势反映出各样品金刚石晶体结构存在明显不同．这表明正电子湮没技术是测量金刚石膜微结构的有力手段．     

金纳米颗粒等离激元对不同形貌氧化锌薄膜发光性能的调控

采用化学气相沉积法制备了纳米棒状的氧化锌纳米结构薄膜和没有纳米棒的氧化锌薄膜,通过直流溅射在所制备的有纳米棒和没有纳米棒的氧化锌薄膜上淀积约3 nm厚的金纳米颗粒薄膜,研究了金纳米颗粒对不同表面形貌氧化锌薄膜的发光特性的影响。实验发现金纳米颗粒的存在使具有纳米棒的氧化锌薄膜的紫外发射增强,但使来自缺陷的可见光发射受到很大的抑制。通过比较有纳米棒和没有纳米棒的氧化锌薄膜在镀金纳米颗粒前后的发光特性,发现金表面等离激元对氧化锌发光的调控取决于氧化锌的表面形貌,纳米棒的存在更有利于金纳米颗粒等离激元调控氧化锌的发光特性。     

Dependence of Intrinsic Defects in ZnO Films on Oxygen Fraction Studied by Positron Annihilation

Defects in ZnO films grown by radio-frequency reactive magnetron sputtering under variable ratios between oxygen and argon gas have been investigated by using the monoenergetie positron beam technique. The dominate intrinsic defects in these ZnO samples are O vacancies （Vo） and Zn interstitials （Zni） when the oxygen fraction in the O2/Ar feed gas does not exceed 70% in the processing chamber. On the other hand, zinc vacancies are preponderant in the ZnO films fabricated in richer oxygen environment. The concentration of zinc vacancies increases with the increasing O2 fraction. For the oxygen fraction 85%, the number of zinc vacancies that could trap positrons will be smaller. It is speculated that some unknown defects could shield zinc vacancies. The concentration of zinc vacancies in the ZnO films varies with the oxygen fraction in the growth chamber, which is in agreement with the results of photolurninescence spectra.