Nonradiative recombination centers in Ga(As,N) and their annealing behavior studied by Raman spectroscopy

Nitrogen-related defects in diluted Ga(As,N) have been detected by Raman scattering in resonance with the localized E+ transition. These defects are attributed to local vibrational modes of nitrogen dimers on Ga- and As-lattice sites. Rapid thermal annealing under appropriate conditions is found to be able to remove the nitrogen dimers. The required minimum annealing temperature coincides with the threshold-like onset of strong, near-band-gap photoluminescence. This finding suggests that the nitrogen dimers are connected with nonradiative recombination centers. (C) 2004 American Institute of Physics.

Defects in GaN films grown on Si(111) substrates by metal-organic chemical vapour deposition

We report the transmission-electron microscopy study of the defects in wurtzitic GaN films grown on Si(111) substrates with AIN buffer layers by the metal-organic chemical vapour deposition method. The In0.1Ga0.9N/GaN multiple quantum well (MQW) reduced the dislocation density by obstructing the mixed and screw dislocations passing through the MQW. No evident reduction of the edge dislocations density by the MQW was observed. It was found that dislocations with screw component can be located at the boundaries of sub-grains slightly in-plane misoriented.

Micro-Raman study on hydrogenated protocrystalline silicon films

Good quality hydrogenated protocrystalline silicon films were successfully prepared by radio frequency plasma enhanced chemical vapor deposition (PECVD) with various hydrogen dilution ratios (R = ([H-2]/[SiH4]) from 10 to 100). The photosensitivity of the films is up to 10(6) under the light intensity of 50mW.cm(-2). The microstructure of the films was studied by micro-region Raman scattering spectra at room temperature. The deconvolution of the Raman spectra by Gaussion functions shows that the films deposited under low hydrogen dilution ratios (R < 33) exhibit typical amorphous properties, while the films deposited under high hydrogen dilution ratios (R > 50) possess a diphasic structure, with increasing crystalline volume fraction with R. The size of the crystallites in the diphasic films is about 2.4 mm, which was deduced from the phonon confinement model. The intermediate range order of the silicon film increases with increasing hydrogen dilution ratio.

基于进程行为的异常检测模型

利用系统漏洞实施攻击是目前计算机安全面临的主要威胁.本文提出了一种基于进程行为的异常检测模型.该模型引入了基于向量空间的相似度计算算法和反向进程频率等概念,区分了不同系统调用对定义正常行为的不同作用,提高了正常行为定义的准确性;该模型的检测算法针对入侵造成异常的局部性特点,采用了局部分析算法,降低了误报率.

种子汽泡传热原理与实验研究

两相流动不稳定性是在各种水力学直径通道内所遇到的复杂现象，这些不稳定性对热能系统可能造成有害影响。本文以丙酮为工质，在受热微通道入口处设置微汽泡发生器，采用脉冲电压激励产生可控微汽泡，并以微汽泡为种子尝试对热微通道内沸腾不稳定性及传热的控制。实验研究表明低频种子汽泡热控能够减轻各参数的脉动幅度；高频种子汽泡热控能彻底抑制沸腾不稳定性；种子汽泡技术的优点是能够在各发泡频率下抑制沸腾不稳定性，强化换热。本研究结果为解决微通道内沸腾不稳定性提供了一种崭新有效的手段，大大延长了待冷却芯片的使用寿命。

非线性放大环形镜“8”字腔光纤激光器实验研究

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注入噪声对光纤激光器锁模启动的影响

国家自然科学基金资助课题(60537060)

表面处理对p-GaN欧姆接触的影响

分别用稀盐酸、王水以及(NH_4)_2S溶液处理p-GaN表面,通过测试样品表面Ols的X射线光电子能谱(XPS),比较了这些溶液去除p-GaN表面氧化层的能力;在经不同溶液处理后的样品表面,以相同的条件制作Ni/Au电极,并测试其与p-GaN的比接触电阻,结果表明经稀盐酸处理后的样品表面,由于其氧含量较高,不能与Ni/Au形成良好的欧姆接触,而经王水和(NH_4)_2S溶液处理后的p-GaN表面,能与Ni/Au形成良好的欧姆接触;最后,通过比较样品表面的Ga/N原子浓度比,探讨了王水处理p-GaN表面能够形成良好欧姆接触的原因.

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。

稗草对水稻及稻田土壤微生物的干扰作用

稗草对水稻的干扰一直是水稻生产中的难题，这种干扰不仅包括竞争和化感作用，而且还有土壤理化因子、土壤微生物和一些土壤酶的参与，所以本研究从水稻、稗草和土壤因子三者相互作用的角度探讨稗草对水稻的干扰作用，主要结论如下： 1、田间条件下，水稻和稗草共生土壤的各种养分在水稻根系附近的分布更丰富，稗草对养分的消耗能力强于水稻；共生处理，化感水稻品种PI312777根区养分含量明显升高，而普通水稻品种辽粳9根区土壤养分含量降低。 2、和稗草共生，PI312777和辽粳9根区土壤中微生物生物量C含量均显著下降，稗草受水稻的影响微生物生物量C含量也被抑制。化感水稻PI312777根系周围细菌和自生固氮菌数量显著增加，真菌、氨化细菌的数量明显下降，而放线菌无明显变化；普通水稻根系周围细菌、真菌、放线菌及氨化细菌数量均显著减少，自生固氮菌数量明显增加。 3、从脱氢酶、脲酶、转化酶和多酚氧化酶活性的变化比较两个水稻品种对抗稗草干扰的能力，化感品种PI312777的表现明显优于普通水稻辽粳9，稗草的存在显著诱导促进了PI312777根区土壤脲酶、转化酶和多酚氧化酶的活性。 4、稗草群体的生命活动对土壤主要微生物类群包括细菌、放线菌、自生固氮菌及氨化细菌的生长和繁殖均有促进作用，而对真菌数量表现为显著抑制。适当的稗草群体对土壤养分的活化作用明显，包括土壤中总N、总P和总K，提高了铵态氮、有效P及速效K的含量，而稗草密度过大则会过量消耗土壤养分。稗草群体的生命活动促进了土壤中脱氢酶、脲酶、转化酶和多酚氧化酶的活性。 5、稗草萌发液及稗草的伴生对三叶期化感水稻化感物质有诱导作用，而且稗草萌发液对水稻的萌发和生长均有抑制作用，尤其对普通水稻品种辽粳9，表明稗草萌发液对水稻有抑制作用。 6、稗草萌发液促进土壤细菌和放线菌的数量，随培养时间的延长，高浓度稗草萌发液的促进作用更明显；真菌和自生固氮菌被高浓度稗草萌发液抑制，而自生固氮菌在培养时间7天以后，适当的浓度可以促进其繁殖。