Al／Al2O3复合材料界面应力场的LACBED研究

界面是影响复合材料性能的重要内容,对复合材料界面的研究一直受到广泛的重视。本文介绍我们利用大角度会聚束电子衍射(LACBED)研究Al基Al_2O_3颗粒增强复合材料界面应力场的初步结果。图1是这种复合材料的明场象,其中不规则形状的是增强体γ-Al_2O_3颗粒。图2是从Al基体中得到的靠近[013]带轴的LACBED花样,其中箭头所指阴影部分是图1中箭头指出的γ-Al_2O_3颗粒的阴影象。图2可以看出γ-Al_2O_3颗粒界面附近的HOLZ线发生明显的弯曲和分裂并变得模糊,这表明界面处Al基体中存在着应力场。应力场的进一步研究可以通过LACBED花样的动力学模拟得到。     

Si1-xGex/Si界面区的会聚束电子衍射研究

会聚束电子衍射(CBED)技术是研究材料中纳米级微小区域结构特征的重要方法,在材料,物理,晶体学等学科有广泛的应用,特别是应变异质材料性能的一种极为重要的研究技术.采用Tanaka大角会聚束衍射(LACBED)方法时,由于入射束不聚焦在试样平面上,可同时得到LACBED衍射花样和被分析区的阴影像,很适用于研究界面及其附近的晶体结构变化.本文介绍在JEOL2000-FX透射电镜上应用Tanaka方法对硅/锗硅薄膜的界面及附近的晶体点阵变化进行LACBED分析的初步结果.     

定量CBED测定准晶结构因子初步研究

定量会聚束电子衍射(CBED)技术应用于晶体结构因子振幅与位相的测定,应用于晶体中电荷密度分布的测定取得了很大的成功。将定量CBED技术用于研究准晶结构,需要进行电子衍射强度的动力学计算,需要知道尽量准确的准晶结构因子的真实值,而仅将少数结构因子的振幅与位相作为可调参数对衍射强度进行拟合。准晶体的会聚束电子衍射中,不可避免地会发生衍射盘交叠的现象。准晶会聚束电子衍射的强度对结构因子的振幅与位相变化的敏感程度如何也是人们关心的问题。1.准晶结构因子的计算准晶体的结构通常在高维空间进行描述。可以用三维超平面去切…     

应变硅PMOSFET中应变的LACBED研究

本文报道了应变硅p型金属氧化物半导体场效应晶体管(PMOSFET)沟道中的局部应变的大角度会聚束电子衍射表征.由于源和漏极区预非晶化锗离子注入工艺在源漏区引入了大量的缺陷,导致在截面电镜样品中存在切应变.利用大角度会聚束电子衍射(LACBED)测量了沟道区的压应变和切应变,并讨论了沟道区产生巨大压应变(2%以上)的原因.     

Pt／Si外延膜界面处Si基体中应力场的LACBED研究

我们利用大角度会聚束电子衍射(简称LACBED)的方法对Pt/Si外延膜界面处Si基体中的应力场进行了研究。Pt/Si外延膜试样是用蒸镀的方法在基体Si片上沿(111)面外延生成金属Pt而成。X-射线分析结果表明Pt沿Si(111)面外延生长很好。图1是Pt/Si界面的明场象。左面为衬底Si,右边为外延生长Pt层。图2是电子束照射在界面附近不同地方的LACBED花样。图中界面在LACBED花样中所处的位置可以清晰地看出。图2(a)可以看出,当界面远离     

会聚束电子衍射法测定MC碳化物的点阵常数

会聚束电子衍射测定晶体的点阵常数是非常有利的,特别是测定微小析出相的点阵常数。使用STEM分析型电镜可将电子束斑聚焦在20A左右的区域上,并且保持严格的对应性。Ecob等人应用计算机模拟高阶劳厄反射与照片拟合的方法区别了CBED(Convergent Beam Electrou Diffraction)图中的微小差别,精确地测定了镍基合金中r~1相的点阵常数。CBED在铁磁材料中的应用还存在一定的困难,而金属工作者研究的许多对象是铁磁材料。有必要开发这方面的应用。     

SiCf/Ti-6Al-4V基复合材料界面晶格常数变化的CBED研究

本实验采用会聚束电子衍射(CBED)方法,研究3种不同状态SiCf/Ti-6Al-4V复合材料界面附近α-Ti晶粒的晶格常数变化.结果表明:在纤维-基体界面区域,靠近界面处晶格常数变化较大,随距界面反应层距离增大,晶格常数的变化趋近缓慢.有C涂层SiC纤维制成的复合材料中晶格常数变化比无C涂层复合材料晶格常数变化小.相比制备态复合材料,热暴露无C涂层SiCf/Ti-6Al-4V复合材料界面处,晶格常数变化较为缓和.     

立方准晶的高阶劳厄带线和菊池线花样的计算机模拟

本文将晶体学中计算会聚束电子衍射(CBED)明场盘内HOLZ线的传统方法进一步发展到立方准晶的情况。本文应用计算机模拟立方准晶的沿几个主要带轴的CBED明场盘内的HOLZ线和在两个取向三角形内的菊池线的极射赤面投影图。     

用低对称性带轴CBED图中holz线测量点阵常数

用会聚束电子衍射中高阶劳厄带效应产生的holz线测定点阵常数时,通常用(111)带轴图中的holz线。本文探讨在高对称性带轴CBED图中不易观察到holz效应的情况下,用低对称性带铀CBED图中holz线测量点阵常数的可能性。对奥氏体不锈钢和纯铝的不同带轴的CBED图中的holz效应进行了观察。CBED在装有普通SAP极靴的JEOL 100C×H上实现.加速电压120kV。由于奥氏体不锈钢的特征温度较高,原子质量较大,热运动所引起的原子的均方位移较小,Debye—Waller因子较大,(111)带轴的holz线清晰可见,而铝的原子质量较小,Debye—Waller因子较小、(111)带轴的holz线很难观察到。     

会聚束电子衍射在矿物研究中的应用

会聚束电子衍射(CBED)可以从10nm区域提取包括高阶劳厄带(HOLZ)的三维衍射信息。用HOLZ线可以准确地测定晶体的点阵参数,点群和空间群[1—4]。CBED是研究层状晶体和平行于样品表面的层错、堆垛错乱等缺陷的有效方法。HOLZ线对应力很敏感,这为研究位错提供了可能性。因此,CBED是鉴定,表征晶体的强有力手段,在矿物研究中很有用处。最近发展的大角度CBED增强和扩大了CBED的应用范围,为研究大晶胞矿物提供了方便[5]。我们用CBED研究了云母,辉钼矿,石墨,黄铁矿,闪锌矿,金红石等矿物。下面通过实例来说明CBED在矿物研究中的应用。     

Convergent-beam electron diffraction

This paper reviews the convergent-beam electron diffraction (CBED) technique. Point- and space-group determination methods of ordinary crystals are described, along with an example of the determination method for Sr?Ru?O?. The symmetry determination of one-dimensionally incommensurate crystals and quasicrystals is explained. The large-angle CBED technique, which is indispensable for lattice defect and lattice strain analysis, is also described. A real procedure for lattice strain analysis is provided, using an example of a multilayer Si?-xGe(x)/Si material. A nanometer-scale crystal structure refinement method and charge density and crystal potential determination method by CBED are briefly described.     

HOLZ line analysis of lattice parameters in magnesium alloys.

A method of refining lattice parameters from deficit higher-order Laue zone (HOLZ) line data from large angle convergent beam electron diffraction (LACBED) data is presented, relying on distances between nearest neighbour intersections alone in order to minimize effects of distortion over the field of view. Use is made of a dynamical correction deltak to the fast electron wavevector k for kinematic analysis. This correction term is shown to depend on the specific HOLZ beam under consideration, as well as the zone axis and eigenvalue associated with the branch index of the relevant dispersion surface. This method is applied to analysis of data from magnesium alloys, where momentum filtering induced by the LACBED method facilitates HOLZ contrast from a relatively low index zone axis (where contrast is not detectable with conventional CBED), and contrast is enhanced at elevated temperatures from a higher index zone axis. Although the accuracy of refined lattice parameters from these sets of data is shown to be no better than 0.1%, it is felt that issues arising out of the analysis may be of some interest, particularly since these are non-ideal specimens. Full eigen-state analysis of the fast electron wavefunction is presented, and issues related to the influence of the dispersion surface on deficit HOLZ line behaviour are discussed.     

Characterization of MOVPE-grown (Al, In, Ga) N heterostructures by quantitative analytical electron microscopy

The low pressure metalorganic vapor phase epitaxy growth of wurzite (Al, In, Ga)N heterostructures on sapphire substrates is investigated by quantitative analytical scanning transmission electron microscopy techniques like atomic number (Z-) contrast imaging and convergent beam electron diffraction (CBED). Especially (In, Ga)N quantum wells of different thicknesses as well as superlattices were analyzed with respect to defects, chemical composition variations, interface abruptness and strain (relaxation) effects. The interfaces in In_0.12Ga_0.88N/GaN quantum wells appear to be asymmetric. Additionally, we found composition variations of Δx_In≥0.03 within the InGaN quantum wells. The application of electron diffraction techniques (CBED) yields quantitative information on strain and relaxation effects. For the case of 17 nm thick InGaN quantum wells, we observed relaxation effects which are not present in the investigated thin quantum wells of 2 nm thickness. The experimentally obtained diffraction patterns were compared to simulations in order to get values for strain within the quantum wells. Additionally, the influence of dislocations on the digression of superlattices is investigated.     

The effect of the signal-to-noise ratio in CBED patterns on the accuracy of lattice parameter determination

A method of higher-order Laue zone line position measurement in convergent-beam electron diffraction (CBED) is proposed based on Hough transformation. A thorough analysis of the errors introduced by this measurement procedure is performed and their influence on the accuracy of lattice parameter determination is estimated. A criterion is derived which enables the accuracy to be predicted before experimental measurements are made and, thus, allows the selection of the best CBED geometry for parameter measurement.     

Strain analysis of arsenic-doped silicon using CBED rocking curves of low-order reflections

Local lattice strains of semiconductor devices have been so far examined using higher order Laue zone (HOLZ) line patterns of convergent-beam electron diffraction (CBED). Recently, strain analyses in highly strained regions near interfaces have been reported using split HOLZ line patterns. In the present paper, it is demonstrated for arsenic-doped silicon that the use of CBED rocking curves of low-order reflections provides a promising new tool for the determination of strain distributions of highly strained specimen areas. That is, the anomalous intensity increase in the CBED rocking curves of low-order reflections is explained using a model structure with a strain gradient in the electron beam direction, which is similar to the models used for the split HOLZ line patterns.     

Lattice parameter determination of a composition controlled Si1-x Gex layer on a Si (001) substrate using convergent-beam electron diffraction

The six lattice parameters (a, b, c, alpha, beta and gamma) of Si(1-x)Ge(x), which was grown epitaxially on a Si (001) substrate with a varying Ge concentration, were determined by convergent-beam electron diffraction (CBED) without any assumption of crystal lattice symmetry. It was revealed that the lattice parameter c of Si(1-x)Ge(x) varies linearly with the Ge concentration and that the lattice symmetry is lowered from cubic to tetragonal, excluding an artifact due to the thinning of the specimen. The effect of strain relaxation that is caused by thinning specimens is discussed. Ge concentrations of examined specimen areas are evaluated using the obtained lattice parameters.     

First-principles study on electronic properties and lattice structures of WZ-ZnO/CdS interface

We theoretically investigated the lattice structure, interface bonding energy, optical absorption properties and electronic properties of WZ-ZnO (1 1 2)/CdS (1 1 0) interface from first-principles calculations. The interface lattice mismatch is less than 4.3%. The atomic bond lengths and atomic positions change slightly on the interface after relaxation. The WZ-ZnO (1 1 2)/CdS (1 1 0) interface has bonding energy about −0.61 J/m², suggesting that this interface can exist stably. Through analysis of the density of states, no interface state is found near the Fermi level. In addition, there are orbital hybridizations between different interfacial atoms, and these orbital hybridizations effectively enhance the bonding of Zn and S atoms, Cd and O atoms on the interface. By analysis of difference density charge and Bader charge, we find that electrons on the interface are largely redistributed and charges transport near the Fermi level which strengthen the adhesion of the interface.     

Effects of finite ground plane on the radiation characteristics ofa circular patch antenna

An analytical technique to determine the effects of finite ground plane on the radiation characteristics of a microstrip antenna is presented. The induced currents on the ground plane and on the upper surface of the patch are determined from the discontinuity of the near field produced by the equivalent magnetic current source on the physical aperture of the patch. The radiated fields contributed by the induced current on the ground plane and the equivalent sources on the physical aperture yield the radiation pattern of the antenna. Radiation patterns of the circular patch with finite ground plane size are computed and compared with the experimental data, and the agreement is found to be good. The radiation pattern, directive gain and input impedance are found to vary widely with the ground plane size     

Strain-induced symmetry breakdown in HOLZ lines from L1(2) titanium tri-aluminides

Energy filtered CBED patterns of the Cr-stabilized L1(2) phase of a titanium tri-aluminide alloy reveal deficit higher order Laue zone (HOLZ) lines in the zeroth order diffraction disk, for which the expected 4-mm symmetry is significantly broken in the <001> projection. This apparent break of symmetry may be explained by the presence of lattice strains of order 10(-3). Effects of strain-induced lattice distortions on HOLZ line symmetries are calculated by an introduction of rhombohedral, tetragonal or monoclinic distortions to the cubic unit cell. It is shown how tensile and shear components of strain affect the overall HOLZ line symmetries in different ways.     

X-Ray diffraction observation of surface damage in chemical-mechanical polished gallium arsenide

Two novel x-ray diffraction techniques with enhanced surface sensitivity, grazing incidence x-ray diffraction (GIXD) and inclined Bragg plane x-ray diffraction (IBXD), have been used to study surface damage in gallium arsenide (GaAs) due to bromine/methanol (Br₂/MeOH) chemical mechanical (CM) polishing. A factorial design was implemented to determine the effects of four polishing variables on the surface structure of GaAs. Precise lattice parameter measurements were made in both the surface regions using GIXD and deeper into subsurface regions using IBXD after the various CM polishing treatments. Bromine concentration was found to primarily affect the surface lattice parameter, while the total polish time influenced both the surface and subsurface lattice parameters in GaAs samples that were heavily damaged prior to CM polishing. The combined effect of polishing pad rotation speed and the force exerted on the sample was found to have a much greater effect on the surface lattice parameter than either variable had alone.