基于温度场的冻土路基变形数值分析及对比

考虑相变和全球气温升高的影响,利用数值分析方法,对青藏铁路典型路基的变形问题进行了分析和数值模拟。通过建立路基有限元模型,选取适当的边界条件、初始条件及热学计算参数,在计算了典型路基断面温度场变化的前提下,对三年的路基变形场进行了数值分析并与实际测试资料进行了对比分析。分析表明,融化沉降在一年内已基本完成,并逐渐开始回冻,两三年后,除路堤填料和地基的进一步压密外,蠕变效应开始显现。因此,对高温、高含冰量冻土而言,蠕变产生的沉降变形是不可忽略的。     

Correlation Between Oxygen Precipitation and Extended Defects in Czochralski Silicon: Investigation by Means of Scanning Infrared Microscopy

Through an investigation of oxygen precipitation and extended defects in Czochralski silicon (CZ-Si) specimens subjected to different isothermal anneals, by scanning infrared microscopy and preferential etching combined with optical microscopy, the correlation between the sizes of oxygen precipitates and the generation of extended defects is revealed. It is found that extended defects are generated when oxygen precipitates grow. Afterward, the sizes of extended defects increase, while those of oxygen precipitates do not change significantly. For the onset of the generation of extended defects, we define the maximum size of oxygen precipitates as a critical size for the generation of extended defects. Moreover, it is revealed that this critical size decreases for higher annealing temperatures or more oxidizing ambients.     

A Distributed Node Localization Scheme for Wireless Sensor Networks

A distributed node localization scheme for wireless sensor networks (WSNs) is presented in this paper, and it includes three generic phases: (1) determine node-beacon distances, (2) compute node positions, and (3) refine the positions. Different from previous researches, we propose an algorithm combination Min–max + LI for the position derivation and SD method for the refinement in our scheme. Simulation shows that our proposed scheme can perform more robust than some representative distributed node localization schemes presented in previous researches in terms of the trade-off among accuracy, coverage, computation cost, and communication overhead.     

Observation of DC currents induced in MOS capacitors during NBTS aging

A current which is directly related to build-up of positive charge in thermal oxide due to negative bias temperature stress (NBTS) aging in the temperature range from 25°C to 350°C has been observed in MOS capacitors. The current was very noticeable in the MOS capacitors which had been exposed to plasma in a magnetron sputtering system or in a reactive ion etching system. Two extreme situations were observed. One was that most of the holes injected in oxide move a short distance before being captured. Another was that most of the injected holes transport through the entire oxide, arriving at the metal interface and recombining with electrons there. It was found that, during negative weak field thermal stimulation current (TSC) measurement performed on a heavily charged capacitor, the observed current in the external circuit flows in the direction opposite to the external bias field. A mechanism which is responsible for the slow-trapping related current is proposed.     

Investigation of texturization for monocrystalline silicon solar cells with different kinds of alkaline

In this paper, monocrystalline silicon was textured with different kind of etchants for solar cells, respectively. It was found that, only with sodium hydroxide (NaOH) or sodium acetate anhydrous (CH₃COONa) solution, the textural results were very weak, resulting in high reflectance of silicon surface. However, if using the mixture solution of NaOH and CH₃COONa, the reflectance was noticeably decreased. Moreover, the dependence of reflectance on the etching time showed that longer etching time was necessary for texturization in the NaOH+CH₃COONa+H₂O system. And it was also found that the addition of isopropyl alcohol (IPA) to this mixture solution had a detrimental effect on the texturization. All these results suggested that acetate (CH₃COO⁻) plays a similar role as IPA for alkaline texturization, but they cannot coexist. Finally, the mechanisms of texturization with different kinds of etchant were discussed in detail.     

p型微氮直拉硅中氧施主的电学特性

研究了p型含氮以及不含氮直拉(CZ)硅中热施主(TD)以及氮氧(N-O)复合体的电学性质.硅片在350～850℃范围进行不同时间的退火后,利用四探针和通过室温傅里叶红外光谱(FTIR)分别测量其载流子浓度和间隙氧浓度的变化.实验结果表明:p型含氮直拉硅(NCZ)中热施主的电学特性基本与n型NCZ硅相同,但N-O复合体的消除温度明显低于n型NCZ硅,这是由于p型NCZ硅中硼促进了N-O复合体的消除.     

A simple and novel low-temperature hydrothermal synthesis of ZnO nanorods

A new simple low-temperature hydrothermal process without addition of any surfactant or complexing agent was put forward to synthesize uniform ZnO nanorods, in which hydrazine hydrate instead of NaOH was used as mineralizer. X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and UV-vis diffuse reflectance spectroscopy were used to characterize the product, the results of which reveal that uniform ZnO nanorods approximately 70 nm in width and 2 μm in length were formed at 150°C within 8 h. Prior to the hydrothermal process hydrazine hydrate reacted with ZnCl₂ solution to form a complex, and the complex slowly decomposed in the hydrothermal process. All these characteristics were favorable to this additive-free hydrothermal synthesis of ZnO nanorods. The text was submitted by the authors in English.     

原生直拉单晶硅中的铜沉淀规律席珍强

采用红外扫描仪、扫描电镜以及电子束诱生电流仪研究了不同温度和不同冷却速度下原生直拉单晶硅的铜沉淀规律. 红外扫描仪观察发现：只有在热处理温度高于800℃的样品中才能观察到铜沉淀团，表明在原生单晶硅中铜沉淀温度为800℃. 同时，红外扫描仪和电子束诱生电流谱仪照片显示，快冷（30K/s）时，形成高密度的小铜沉淀团；而慢冷（0.3K/s）导致低密度、巨大的星形铜沉淀团的形成. 实验还发现慢冷所形成的星形铜沉淀团对少数载流子具有更强的复合强度. 最后，讨论了原生直拉单晶硅中铜沉淀规律的机理.     

单晶硅太阳电池的表面织构化

一种新型的腐蚀剂 ,磷酸钠 (Na3PO4 ·12H2 O)溶液 ,首次被用来腐蚀单晶硅太阳电池。在 70℃下 ,用 3%的磷酸钠 (Na3PO4 ·12H2 O)溶液腐蚀 2 5min就能在硅片表面形成金字塔大小均匀、覆盖率高的绒面结构 ,并且其表面反射率也很低。通过SEM观察发现 :开始时 ,随着腐蚀时间的增加 ,金字塔的密度越来越大 ,最后达到饱和 ;而且对于不同的浓度 ,温度 ,这种饱和时间不同 ;如果腐蚀时间过长 ,金字塔的顶部就会发生崩塌 ,从而导致表面发射率的升高。虽然异丙醇 (IPA)在氢氧化钠 (NaOH)溶液中会明显地改善织构化的效果 ,但是在磷酸钠 (Na3PO4 ·12H2 O)溶液中却会对织构化有很强的负面效应。最后 ,在实验的基础上对腐蚀机理进行了深入地探讨并认为 :择优腐蚀是金字塔形成的最基本的原因 ,而缺陷、PO3 -4 或HPO2 -4 和异丙醇等仅仅是促进大金字塔形成的原因。这种腐蚀剂的成本很低 ,不易污染工作环境且可重复性好 ,所以有可能用于大规模生产。     

氮化硅薄膜对晶体硅材料和电池的钝化效果研究

利用等离子体增强化学气相沉积技术,在P型直拉单晶硅硅片和铸造多晶硅片以及太阳电池的表面上 沉积了非晶氮化硅(a-SiNx:H)薄膜,并研究了氮化硅薄膜对材料少子寿命和太阳电池性能的影响。研究发现: 氮化硅薄膜显著地提高了晶体硅材料中少子寿命,同时多晶硅太阳电池的开路电压有少量提高,短路电流普遍 提高了1mA/cm2,电池效率提高了2％。实验结果表明:氮化硅薄膜不仅具有表面钝化作用,也有良好的体钝化 作用。