Influences of initial nitridation process on the optical and structural characterization of GaN layer grown on sapphire (0001) by metalorganic chemical vapor deposition

In this paper. we investigate the influences of the initial nitridation of sapphire substrates on the optical and structural characterizations in GaN films. Two GaN samples with and without 3 min nitridation process were investigated by photoluminescence (PL) spectroscopy in the temperature range of 12-300 K and double-crystal X-ray diffraction (XRD). In the 12 K PL spectra of the GaN sample without nitridation, four dominant peaks at 3.476, 3.409 3.362 and 3.308 eV were observed, which were assigned to donor bound exciton, excitons bound to stacking faults and extended structural defects. In the sample with nitridation, three peaks at 3.453, 3.365. and 3.308 eV were observed at 12 K, no peak related to stacking faults. XRD results at different reflections showed that there are more stacking faults in the samples without nitridation.

880 nm LD pumped passive mode-locked TEM00 Nd:YVO4 laser based on SESAM

We report on an 880 nm LD pumped passive mode-locked TEM00 Nd:YVO4 laser based on a semiconductor saturable absorber mirror (SESAM) for the first time. When the incident pump power was 16 W, 4.76 W average output power of continuous-wave mode-locked laser with an optical-to-optical conversion efficiency of 30% was achieved. The repetition rate of mode-locked pulse was 80 MHz with 25 ps pulse width. The maximum pulse energy and peak power were 60 nJ and 2.4 kW, respectively.

黑土稻田CH_4与N_2O排放及减排措施研究

目前国内稻田生物源温室气体CH_4和N_2O排放的研究主要集中在潮土、红壤与水稻土上，黑土上尚未得到CH_4与N_2O排放的相关数据。本文采用封闭式箱法对黑土稻田CH_4和N_2O排放通量进行了观测，为准确估算不同土壤类型稻田生物源温室气体排放量提供了科学依据。研究发现水稻生长季CH_4排放量低于全国其它地区稻田。CH_4和N_2O排放之间存在互为消长关系(r=-0.409, p<0.05）。本试验对不同水分和肥料管理条件下稻田CH_4和N_2O通量进行测定，结果表明，间歇灌溉条件下与长期淹灌相比，CH_4排放平均通量明显减少而N_2O略有增加，其相对综合温室效应减少，水稻产量未受影响，间歇灌溉可用作减少温室气体排放的措施。土壤排放的CH_4和N_2O是微生物的代谢产物，通过对CH_4和N_2O产生相关的微生物菌群（产甲烷菌、甲烷氧化菌、硝化菌、反硝化菌）数量的测定，深入研究它们之间的关系，可以更好的从本质上认识CH_4和N_2O产生及其排放特性。研究结果为，产甲烷菌数与CH_4排放呈显著性正相关(R~2=0.77，P<0. 05),甲烷氧化菌起减少CH_4排放的作用，硝化菌数和反硝化菌数与NZO排放有密切联系。