退火对GaAs窗口晶体断裂模数的影响

LEC GaAs晶片经高温退火后，残余应力得以部分释放；从而减小残余应力诱生断裂的可能性，提高了GaAs晶体的断裂模数。原生GaAs晶片加工的样品的断裂模数平均值约为135MPa，经退火的GaAs晶片加工样品的断裂模数平均值更高，约为150MPa，断裂模数最高值达163MPa。     

锗晶体断裂模数的测试

用四点弯曲法测量了锗单晶和多晶样品（３６ｍｍ×４ｍｍ×３ｍｍ）的断裂模数，其结果与美、英、比等国家公布的数据基本相符．实验证明样品表面加工方法是影响测量值的重要因素；机械应力和热应力将导致断裂模数的下降。     

制样方法对IF钢纳米压入测试结果的影响

 对3种不同方法制备的IF钢试样进行了纳米压入表征,分析了制样方法对IF钢中铁素体纳米压入测试结果的影响。结果表明,制样方法对铁素体杨氏模量平均值影响不大,但对硬度平均值影响显著,机械抛光和机械抛光+化学侵蚀状态铁素体的硬度均高于机械抛光+电解抛光状态的铁素体。这主要是因为机械抛光对试样表面造成了明显的加工硬化层,而化学侵蚀处理不能完全去除硬化层,只有电解抛光才能起到有效消除硬化层的作用。机械抛光+电解抛光处理更有利于IF钢的纳米压入表征。     

Observation of Damage Layer on Surface of GaAs Wafer by TEM

用透射电镜、 扫描电镜对GaAs材料加工工艺中的表面损伤层进行了观察和检测。 结果切片损伤层深度≤50 μm、 双面研磨损伤层深度≤15 μm、 机械化学抛光损伤层深度 (腐蚀前) <1.2 μm。 分析了损伤结构及其引入的因素。     

GaAs抛光表面损伤的RBS研究

本文以卢瑟福离子背散射技术（ＲＢＳ）检测了半绝缘ＧａＡｓ（１００）化学机械抛光表面的微损伤状况，并以α台阶仪测量了抛光表面的粗糙度。研究了以胶体ＳｉＯ２和ＮａＯＣｌ溶液的混合液对ＧａＡｓ进行化学机械抛光方法中主要工艺条件对表面质量的影响。把ＲＢＳ法同Ｘ射线双晶衍射法对表面损伤的测量结果进行了比较，二者对应得很好。通过逐层腐蚀与ＲＢＳ相结合测定了抛光过程造成的损伤层的厚度，发现如果抛光条件不适宜，获得的晶片表面尽管目视光洁度很好，也还有一定厚度的损伤层。ＲＢＳ法测得好的非掺半绝缘ＧａＡｓ（１００）（由ＬＥＣ法生长）抛光表面散射粒子最低产额低达３１％，这样的晶片用腐蚀法未发现有损伤层。     

氧离子注入无定形GaAs的形成及其在外延中的应用

用能量为60kev而剂量不同的氧离子注入研究了GaAs无定形层的形成,并从光吸收法测量计算了形成无定形层所需的临界剂量和能量,分别为5×10~(14)O~+/cm~2和每原子38ev。用氧离子注入的GaAs衬底在MO-CVD反应器中进行了GaAs外延生长。发现随着离子注入造成的表面损伤密度的增加,外延单晶过渡到不生长晶核,这就为选择外延获得应用提供了可能性。     

全层TiAl基合金缺口试样原位拉伸卸载试验的研究

通过对TiAl基合金不同类型的缺口试样进行原位拉伸卸载实验和相应的断裂表面观察,研究了TiAl基合金全层组织的断裂机理。研究发现:对于缺口试样,裂纹起裂于缺口根部,其断裂过程主要是主裂纹首先起裂、扩展并最后断裂。在整个断裂过程中断裂是穿层断裂和沿层断裂的混合体,裂纹路径较曲折。在拉伸过程中,试样产生微裂纹导致材料发生损伤,随后卸载再加载时,与先前相比,裂纹更易扩展。预损伤加快了裂纹的产生和扩展,使损伤进一步加重,促使材料抵抗裂纹产生、扩展的能力下降。     

用红外反射法测定1μ左右n-n~ GaAs外延层厚度

本文验证了测量1μ左右n-n~ GaAs外延层厚度的红外反射法,该法能满足非破坏性测量和测准的要求。本文在一些选定的实验条件下,用红外反射法进行了测量1μ左右n-n~ GaAs外延层厚度的一系列实验,取得了一些结果。结果表明,在我们的实验条件下,是可以用红外反射法来取得薄外延层厚度数据的。本文还将所得结果同用显微镜和扫描电镜所作的测量结果进行了对比。对比表明,用三种方法测得的外延层厚度是一致的,但红外反射法的误差最小。     

纳米/微米Al2O3-ZrO2内衬复相陶瓷的自蔓延高温合成

采用SHS重力分离技术制备出内衬Al2O3-ZrO2复相陶瓷.复相陶瓷基体主要由纤维状(Al2O3+ZrO2)共晶体组成,其中共晶体的ZrO2纤维直径达到纳米/微米尺度.经Vickers压痕法测试其断裂韧度为15.96MPa·m1/2,SEM观察和陶瓷材料断裂韧度测试得出裂纹的扩展主要受共晶体中Al2O3-ZrO2纳米/微米相增韧机制控制,迫使裂纹沿共晶体边界或层片共晶体Al2O3-ZrO2相界偏转,从而维持了该复相陶瓷较高的断裂韧度.     

制备GaAs激光窗口材料的一种新型补偿掺杂剂

用氧化铬 (Cr2 O3)作补偿掺杂剂、LEC法生长的GaAs窗口晶体 ,容易满足高阻补偿条件 ,碳、硅两种主要的残余杂质得到有效抑制 ,获得低自由载流子光吸收的优质GaAs红外激光出口材料。补偿掺杂剂氧化铬 (Cr2 O3)剂量为 99 9999%Ga和 99 9999%As量的优选范围是0 0 1%～ 0 0 4% (质量分数 )。室温下的自由载流子浓度低于 5× 10 6 cm- 3,对光吸收系数的贡献可以忽略。轻掺氧化铬高阻GaAs晶体具有良好的红外透射特性 ;10 6μm处激光量热法测量的红外光吸收系数约为 1 4× 10 - 3cm- 1 。     

Effect of Adding Rare Earth Element on Cemented Carbide YT14 by Digital Image

ＥｆｆｅｃｔｏｆＡｄｄｉｎｇＲａｒｅＥａｒｔｈＥｌｅｍｅｎｔｏｎＣｅｍｅｎｔｅｄＣａｒｂｉｄｅＹＴ１４ｂｙＤｉｇｉｔａｌＩｍａｇｅＳｕｎＬｉｈｏｎｇ（孙丽虹）；ＨｅＣｏｎｇｘｕｎ（贺从训）；ＬｉｎＣｈｅｎｇｕａｎｇ（林晨光）；ＷａｎｇＹｏｕｍｉｎｇ（...     

Strain Transfer Coefficient Analyses for Embedded Fiber Bragg Grating Sensors in Different Host Materials

Fiber Bragg grating (FBG) sensors have attracted a considerable amount of interest for their superior characteristics. However, the FBG sensors made on bare fibers are easily damaged. For their safe use in engineering, the glass core of optical fibers is coated with softer low modulus protective coatings. A portion of the host material strain is absorbed by the protective coatings when the strain transfers from the host material to the fiber core, and hence only a segment of structural strain is sensed. By introducing the shear modulus of the host material, a novel analytical model is developed for evaluating the sensing strain of the embedded FBG sensors in composite structures based on the strain in a host material. The average strain transfer ratio is deduced to describe the percentage transferred to the optical fiber core from the host material. It is concluded that the shear modulus of the host material influences strain transmission, especially when it is much lower than the modulus of the fiber core. Then, the strain transfer ratio of an optical fiber sensor embedded in a multilayered structure is developed in a similar way. The factors that affect the efficiency of strain transfer on the optical fiber sensor are deduced and discussed in detail based on the theoretical analysis. Finally, the theoretical results are verified through laboratory experimentation with the FBG sensors.     

Probabilistic Nonlocal Theory for Quasibrittle Fracture Initiation and Size Effect.?I: Theory

The nonlocal generalization of Weibull theory previously developed for structures that are either notched or fail only after the formation of a large crack is extended to predict the probability of failure of unnotched structures that reach the maximum load before a large crack forms, as is typical of the test of modulus of rupture (flexural strength). The probability of material failure at a material point is assumed to be a power function (characterized by the Weibull modulus and scaling parameter) of the average stress in the neighborhood of that point, the size of which is the material characteristic length. This indirectly imposes a spatial correlation. The model describes the deterministic size effect, which is caused by stress redistribution due to strain softening in the boundary layer of cracking with the associated energy release. As a basic check of soundness, it is proposed that for quasibrittle structures much larger than the fracture process zone or the characteristic length of material, the probabilistic model of failure must asymptotically reduce to Weibull theory with the weakest link model. The present theory satisfies this condition, but the classical stochastic finite-element models do not, which renders the use of these models for calculating loads of very small failure probabilities dubious. Numerical applications and comparisons to test results are left for Part II.     

Fabrication of Ormocer Containing Eu3＋ Ion and Their Optical Spectra

Eu3 ions were incorporated in sol and gel by a sol-gel processing using 3-glycidoxypropyltrimethoxysilane(CH2OCHCH2O(CH2)3Si(OCH3)3, GPTMS) and ethyl silicate (TEOS) as precursors. The basic chemical-physical properties such as DTA curve, FF-IR spectra and specific surface area were recorded. The characteristics of their optical spectra were measured and investigated. The results indicate that the emission intensity of Eu3 ion in ormocer is much higher and the global line width is wider than those in SiO2 gel. The relationship between the composition and structure of gels and the fluorescence intensity and width were discussed. The obtained ormocer shows good mechanical strength, which can be cut and polished in machine without broken.     

Histopathology of human coronary atherosclerosis by quantifying its chemical composition with Raman spectroscopy

BACKGROUND: Lesion composition, rather than size or volume, determines whether an atherosclerotic plaque will progress, regress, or rupture, but current techniques cannot provide precise quantitative information about lesion composition. We have developed a technique to assess the pathological state of human coronary artery samples by quantifying their chemical composition with near-infrared Raman spectroscopy. METHODS AND RESULTS: Coronary artery samples (n=165) obtained from explanted recipient hearts were illuminated with 830-nm infrared light. Raman spectra were collected from the tissue and processed to quantify the relative weights of cholesterol, cholesterol esters, triglycerides and phospholipids, and calcium salts in the examined artery location. The artery locations were then classified by a pathologist and grouped as either nonatherosclerotic tissue, noncalcified plaque, or calcified plaque. Nonatherosclerotic tissue, which included normal artery and intimal fibroplasia, contained an average of approximately 4+/-3% cholesterol, whereas noncalcified plaques had approximately 26+/-10% and calcified plaques approximately 19+/-10% cholesterol in the noncalcified regions. The average relative weight of calcium salts was 1+/-2% in noncalcified plaques and 41+/-21% in calcified plaques. To make this quantitative chemical information clinically useful, we developed a diagnostic algorithm, based on a first set of 97 samples, that demonstrated a strong correlation of the relative weights of cholesterol and calcium salts with histological diagnoses of the same locations. This algorithm was then prospectively tested on a second set of 68 samples. The algorithm correctly classified 64 of these new samples, thus demonstrating the accuracy and robustness of the method. CONCLUSIONS: The pathological state of a given human coronary artery may be assessed by quantifying its chemical composition, which can be done rapidly with Raman spectroscopic techniques. When Raman spectra are obtained clinically via optical fibers, Raman spectroscopy may be useful in monitoring the progression and regression of atherosclerosis, predicting plaque rupture, and selecting proper therapeutic intervention.     

Forensic Study of Warranty Project on US82

This forensic study is unique in that it involves a pavement warranty specification. Extensive field and laboratory testing was conducted to determine the cause(s) of longitudinal cracks observed on the surface. Four trenches were cut and removed to allow more testing on top of each pavement layer. The tests found that the stiffness of the foamed asphalt base is higher than that of a typical flexible base. However, the subgrade modulus is low compared with the average subgrade modulus in Texas. Water seeped into two trenches (dug into the road where there were surface cracks) within 20 min of digging. No water was observed in the other two trenches, where there were no surface cracks. The two trenches with surface cracks have lower base density and higher base moisture content than the two with no surface cracks. Based on observations of the trenching and coring operations, the same surface cracks have been detected in the base layer. Cracks up to 150 mm into the base layer have been observed. Although cracks have been observed in the base (and they can be related to lower stiffness and higher falling weight deflectometer deflections), it is difficult to determine if the cause of surface cracks is due to the base layer alone. It is difficult to prove if the layer is responsible for the failure, except by properties listed in the specification. One faulty pavement layer can easily cause the failure of other layers. For warranty purposes, layer-specific failure criteria should be clearly outlined. The base did not meet the gradation specification. The field material was substantially finer than specified. While some specifications may have been violated, there is little evidence to show that the cause of the longitudinal cracking is primarily related to the foamed-asphalt-stabilized base.     

The kinetics of dissolution of sphalerite in ferric chloride solution

The dissolution of sphalerite in acidic ferric chloride solution was investigated in the temperature range 320 to 360 K. Both sized particles from three sources and polished flat surfaces were used as samples. The effect of stirring rate, temperature, ferric and ferrous ion concentration, purity, and particle size on the dissolution rate were determined. During the initial stages of the process chemical reaction at the mineral surface is rate controlling while during the later stages diffusion through the product sulfur layer is rate controlling. Overall the process follows the mixed-control model embodying both chemical reaction and diffusion. The activation energy for the dissolution of sphalerite particles was found to be 46.9 kJ/mol.