sol-gel法制备纳米碳化硅晶须的研究

采用长链甲基三甲氧基硅烷〔Cn H2 n+ 1 Si(OCH3)〕和正硅酸乙酯 (TEOS)两种有机物为起始原料 ,用溶胶 -凝胶法通过合理控制反应条件 ,制备出β- Si C凝胶粉体 ,然后在 Ar气氛、 90 0～ 130 0℃下热处理 ,制备出了高纯、低氧含量 ,直径 2～ 10 nm,长度 40～ 80 nm的β- Si C纳米晶须。产物纯度达到 99.92 %。利用 X射线粉晶衍射、透射电镜 (TEM)、拉曼光谱等测试方法对制得的晶须进行了结构及颗粒尺寸等研究。讨论了反应条件对β- Si C纳米晶须生长的影响     

凝胶维度对纳米碳化硅晶须形成过程的影响

讨论了纳米碳化硅晶须的制备过程中出现的直径分布不均匀性问题。在制备纳米碳化硅晶须的实验中发现,凝胶呈现体积跃变的现象,并且发生形貌的改变,这又直接影响纳米晶体的形状,其中的原因归之于凝胶体系的局域氢键作用,称之为维度变化。结果发现,凝胶随温度跃变首先膨胀,然后又萎缩。其逆过程同样存在这一现象并呈现体积跃变迟滞。     

超长六角多型纳米碳化硅晶须的光学性质

采用改进的PECVD技术首次制备出六角多型碳化硅纳米晶须。高分辨率电镜观察其直径在2~6 nm之间。长度为0.3 mm~6 mm。拉曼光谱表明它是六角多型(4 H)纳米碳化硅晶须。紫外光激发出现高强度蓝光发射。随着激发强度的增加,在397 nm处的蓝光强度即刻上升,并溢出,其宽度急剧减小,可能是蓝色激光。     

SIMOX材料的TEM研究

在注入能量为１７０ｋｅＶ，注入剂量从０．６×１０１８／ｃｍ２到１．８×１０１８／ｃｍ２范围，改变注入方式，利用ＴＥＭ技术观察了形成ＳＩＭＯＸ的结构．注入剂量为０．６×１０１８／ｃｍ２时，可以获得连续的ＳｉＯ２埋层且顶部硅层基本上无穿通位错产生；注入剂量为１．５×１０１８／ｃｍ２时，采用双重注入可以获得质量很好的ＳＩＭＯＸ结构，顶部硅层仅有较少的穿通位错；注入剂量为１．８×１０１８／ｃｍ２时，三重注入可以获得质量好的ＳＩＭＯＸ结构，顶部硅层穿通位错稍多．     

碳纳米管卷层结构的TEM研究

碳纳米管发现以来,其结构的研究一直是人们普遍关心的课题。至今为止,已有不少有关碳纳米管结构的报道[1]。给出了一些结构模型,其中以Iijima给出的模型最具有代表性,即认为碳纳米管是由碳原子组成的层面卷成筒状后形成的管状纤维。层面内的碳原子之间以sp2键结合,每个碳原子连接二个碳原子形成一系列连续的六边形(以下简称六圆环)。单层碳纳米管即是由一层卷成筒状的碳原子六圆环组成。而多层碳纳米管则是由多个碳原子六圆环组成的圆筒套在一起组成的。而这些圆筒之间的间距与石墨中碳原子层面间距相等,均为0.34nm。此外还认为碳纳米管的…     

掺Ag颗粒BaTiO3薄膜的TEM研究

由于金属小颗粒（如Ag,Au）具有良好的光吸收性能，在光学器件中具有潜在的应用前景，因此引起了人们的广泛兴趣。最近，Charle和Hoevel研究组对镶嵌Ag小颗粒的不同系统的光性能进行了研究；认为此类材料的光学性能与Ag小颗粒的大小，形状、分散度以及与基体之间的界面结构等有很大关系。而对于结构的研究，目前仅集中在材料的结晶状态、颗粒的大小形状、分散度等形貌方面。所以，对其微观结构的进一步研究是非常重要的。     

旋磁介质加载矩形波导中TEM场的研究

本文首次得出了矩形波导中进行旋磁介质加载可以存在均匀 TEM 场区的特性,导出了在两种不同的磁化状态下传播常数所满足的特征方程以及存在 TEM场区时旋磁介质的尺寸、材料参数和频率之间的关系,并对一些有关的特性进行了分析和研究。     

SiC晶须微观结构的电镜研究

ＳｉＣ晶须微观结构的电镜研究薛菁李亚东（苏州大学分析测试中心，苏州２１５００６）ＳｉＣ晶须是共价键化合物，属于高纯度超细单晶体，其取向度高度一致，强度又接近于原子间的结合力。同时，ＳｉＣ晶须还具有极好的热导率和耐腐蚀性，而电强度高、弹性模量大、加工性...     

Carcinogenic properties of silicon carbide whiskers

In experiments with intrapleural injections of silicon carbide whiskers (20 mg X 3, with one month interval) to random-inbred rats their carcinogenic activity close to that of chrysotile B UICC has been established. The pleural mesotheliomas were induced in 47.7 and 34.1% of rats, respectively.     

TEM investigation of silicon carbide wafers with reduced micropipe density

A technique to reduce the micropipe density in SiC substrates by first filling in the defects and then growing an LPE layer on the filled material has been developed by TDI. LPE growth in SiC is known to result in poor surface morphology, namely step-bunching due to the off-axis substrate orientation. Chemical vapor deposition (CVD) growth experiments on SiC substrates with reduced micropipe density using a cold-wall CVD reactor resulted in a significant improvement in the surface morphology. Although preliminary device results are encouraging, the exact nature of the filled micropipes nor the impact of growing CVD epitaxial layers on LPE SiC had not been fully characterized. We have preformed transmission electron microscopy (TEM) measurements to evaluate the crystallographic properties of the CVD/LPE and LPE/substrate interface. It was observed that no new dislocations were nucleated at the LPE/CVD interface. Although a micropipe was not located in the samples characterized, a tilt of 1.5° was observed between the LPE layer and the substrate. In addition, dislocations were observed to propagate through the LPE layer from the substrate which are most likely the 1C close-core screw dislocations common to SiC hexagonal substrates.     

硅中缺陷的透射电镜观察

随着集成电路制造工艺技术的不断进步,器件线宽不断减小,硅材料中缺陷的危害越来越不可忽视.通过TEM观察了硅中氧沉积、工艺诱生缺陷等并对之进行了分析.     

Comparison of the radiation hardness of silicon and silicon carbide

The radiation hardness of silicon carbide and silicon are compared. It is shown that one of the main characteristics of the radiation hardness of a semiconductor, the carrier removal rate V _d , strongly depends on its measurement conditions in the case of wide-gap semiconductors. A conclusion is made that comparison of the values of V _d , obtained at room temperature for SiC and Si, is not fully adequate from the physical standpoint.     

Anisotropy of the solid-state epitaxy of silicon carbide in silicon

A new method for the solid-state synthesis of epitaxial layers is developed, in which a substrate participates in the chemical reaction and the reaction product grows not on the substrate surface, as in traditional epitaxial methods, but inside the substrate. This method offers new opportunities for elastic-energy relaxation due to a mechanism operating only in anisotropic media, specifically, the attraction of point defects formed during the chemical reaction. The attracting point centers of dilatation form relatively stable objects, dilatation dipoles, which significantly reduce the total elastic energy. It is shown that, in crystals with cubic symmetry, the most favorable arrangement of dipoles is the 〈111〉 direction. The theory is tested by growing silicon carbide (SiC) films on Si (111) substrates by chemical reaction with carbon monoxide CO. High-quality single-crystal SiC-4H films with thicknesses of up to 100 nm are grown on Si (111). Ellipsometric analysis showed that the optical constants of the SiC-4H films are significantly anisotropic. This is caused not only by the lattice hexagonality but also by a small amount (about 2–6%) of carbon atoms remaining in the film due to dilatation dipoles. It is shown that the optical constants of the carbon impurity correspond to strongly anisotropic highly oriented pyrolytic graphite.     

Charge-sheet model for silicon carbide inversion layers

The charge-sheet model for metal-oxide-semiconductor (MOS) inversion layers is extended to silicon carbide. The generalized model is based on an analytical solution of the Poisson equation for the case of incomplete ionization of dopant impurities and incorporating Fermi-Dirac statistics. The results are compared with the conventional charge-sheet model which assumes complete impurity ionization and nondegenerate statistics. It is found that, at room temperature and for gate voltages in weak and moderate inversion, the present model predicts higher inversion-layer charge density at a given gate voltage. However, the relationship between the inversion charge and the surface Fermi potential is essentially independent of the degree of impurity ionization. In strong inversion or at temperatures above ~600 K, the differences between the two models are small. A formula is given for the threshold voltage as a function of the impurity ionization energy. The effects of several different interface state energy distributions on inversion charge are investigated. It is found that a slowly-varying interface-state density has an effect on threshold voltage of a MOSFET similar to that of a fixed oxide charge, while an interface-state density that increases at least exponentially with energy has the effect of lowering the field-effect mobility and transconductance     

Amorphous silicon/silicon carbide superlattice avalanchephotodiodes

An a-Si/SiC:H superlattice avalanche photodiode (SAPD) has been successfully fabricated on an ITO/glass substrate by plasma-enhanced chemical vapor deposition. The room-temperature electron and hole impact ionization rates, α and β, have been determined for the a-Si/SiC:H superlattice structure by photocurrent multiplication measurements. The ratio α/β is 6.5 at a maximum electric field of 2.08×10⁵ V/cm. Avalanche multiplications in the superlattice layer yields an optical gain of 184 at a reverse bias V_R=20 V and an incident light power P_in=5 μW. An LED-SAPD photocouple exhibited a switching time of 4.5 μs at a load resistance R-1.8 kΩ     

Compact models for silicon carbide power devices

Compact silicon carbide (SiC) power semiconductor device models for circuit simulation have been developed for power Schottky, merged-PiN-Schottky, PiN diodes, and MOSFETs. In these models, the static and dynamic performance of the power SiC devices requires specific attention to the low-doped, voltage blocking drift region; the channel transconductance in MOS devices; the relatively low-intrinsic carrier concentration; the incomplete ionization of dopants; and the temperature dependent material properties. The modeling techniques required to account for each of these characteristics are described.     

Photoluminescence of anodized silicon carbide

The luminescence of single-crystalline 6H-SiC plates after electrochemical etching has been investigated. The photoluminescence spectrum was found to change strongly after etching; the decay times of separate bands were determined. Just as in the case of silicon, the change in the photoluminescence could be due to the formation of nanostructures. Fiz. Tekh. Poluprovodn. 31, 315–317 (February 1997)