Substrate temperature control from RHEED intensity measurements

Substrate temperature is an importance parameter controlling nucleation and growth dynamics during the thin film epitaxy in MBE system. The most covenant methods able to determine the substrate temperature is based on some calibration procedures, where substrate temperature is calculated as a function of electric power dissipated in heater system. This paper presents possibility of substrate temperature control based on reflection high-energy electron diffraction (RHEED) intensity measurements as in situ technique. Temperature dependence of the specularly reflected electron beam intensity versus the substrate temperature is predicted by dynamical theory of electron scattering. The theoretical RHEED intensity dependence versus Si(1 1 1) substrate temperature was obtained from one-dimensional rocking-curve calculation.     

Specular beam intensity and surface morphology of BSCO films grown by MBE

Bi-Sr-Cu-O (BSCO) thin films have been epitaxially grown on cleaned SrTiO₃ (001) substrates by a sequentially shutter-controlled molecular beam epitaxy system using an oxygen radical beam. A spot intensity of specular beam in in-situ reflection high-energy electron diffraction (RHEED) was monitored during the atomic layer epitaxy. Atomic force microscopy (AFM) images of the epitaxial thin films were observed in the atmosphere at some oscillation points of the specular beam intensities. The chemical composition ratios of the films (about 100 Å) were determined from intensities of X-ray photoemission spectroscopy. The crystallinity of the films was measured by X-ray diffraction.

The amount of metal deposition corresponding to a half cycle of the intensity oscillation of the specular spot was found to be appropriate to form the flat surface. Characteristic islands were found at the surfaces covered with excess bismuth or excess copper atoms in the AFM image. The intrinsic modulated structure of the BSCO crystal was observed at the surface after the first copper deposition on Sr/Bi/SrTiO₃ in the RHEED pattern.     

Effect of heat treatment on characteristics of nanocrystalline ZnO films by electron beam evaporation

Zinc oxide thin films have been grown on glass substrate at room temperature by electron beam evaporation and then were annealed in annealing pressure 600 mbar at different temperatures ranging from 250 to 550 °C for 30 min. Electrical, optical and structural properties of thin films such as electrical resistivity, optical transmittance, band gap and grain size have been obtained as a function of annealing temperature. X-ray diffraction has shown that the maximum intensity peak corresponds to the (002) predominant orientation for ZnO films annealed at various temperatures. The full width at half maximum, decreases after annealing treatment which proves the crystal quality improvement. Scanning electron microscopy images show that the grain size becomes larger by increasing annealing temperature and this result agrees with the X-ray diffraction analysis.     

外延薄膜生长的实时监测分析研究

利用反射式高能电子衍射(RHEED)在超高真空中对SrTiO3(100)、LaAlO3(100)、Si(100)单晶基片进行分析,讨论了衍射花样与晶体表面结构的对应关系,计算出表面的晶体学参数,同时采用激光分子束外延技术同质外延生长SrTiO3薄膜，根据RHEED衍射图样及强度振荡曲线实时监控薄膜的生长。     

Study of the growth of supported Pd-Sn bimetallic nanoclusters

Pd-Sn bimetallic thin films were grown by molecular beam epitaxy on KCl (001) single-crystalline substrate. Substrate and deposit crystallographic structures were studied by reflection high-energy electron diffraction (RHEED). Evolution of lattice parameter and cluster size calculated from the RHEED patterns gave information on the formation of bimetallic system. The early stages of the growth in dependence of Pd and/or Sn deposition sequence were studied. The formation of Pd-Sn core-shell structure was observed. It is composed of (001) epitaxialy oriented Pd core clusters surrounded by polycrystalline Sn and/or Pd-Sn shell. The Auger electron spectroscopy (AES) induced by high-energy electron beam and electron energy loss spectroscopy (EELS) were used as auxiliary methods for chemical analysis. Encapsulation of metallic clusters by the material of the substrate was approved by diffraction as well as by electron spectroscopy methods. This phenomenon influenced the formation of Pd-Sn bimetallic system.     

BST类铁电薄膜低温外延层状生长研究

利用激光分子束外延技术(LMBE)在SrTiO₃(100)单晶基片上外延生长SrTiO₃(STO)、BaTiO₃(BTO)、Ba_0.6Sr_0.4TiO₃(BST)铁电薄膜.通过反射高能电子衍射(RHEED)实时监测薄膜生长,并结合原子力显微镜(AFM)分析薄膜的生长模式,根据RHEED衍射强度振荡曲线及衍射图样的变化确定动态和静态控制最低晶化温度,发现STO、BTO、BST三种铁电薄膜可以分别在280、330、340℃的低温下实现外延层状生长.     

A Monte Carlo investigation of growth and characterization of heteroepitaxial thin films

We investigate the growth of mismatched thin films by a kinetic Monte Carlo computer simulation and including a local photoemission model with reflection high-energy electron diffraction (RHEED) intensity for comparison. The strain is introduced through an elastic energy term based on a valence force field approximation. We describe an atomistic mechanism for dislocation nucleation during first stage of GaSb/GaAs (001) growth and in situ variations of photoemission current (PE) and RHEED intensity are reported. We have shown the formation of grooves corresponding to (111) facets, a precursor to the formation of misfit defects. The surface roughening and facetting by creation of grooves explain the absence of photoemission and RHEED oscillations in accordance with experimental observations [J.J. Zinck and D.H. Chow, J. Cryst. Growth, 175/176 (1997) 323, J.J. Zinck and D.H Chow, Appl. Phys. Lett. 66 (1995) 3524].     

Experimentelle Charakterisierung und zweidimensionale Simulation der mikrostrukturbestimmten Ermüdungsrissausbreitung in einer β‐Titanlegierung

In this project the initiation and propagation of short fatigue cracks in the metastable β‐titanium alloy TIMETAL®LCB is investigated. By means of an interferometric strain/displacement gauge system (ISDG) to measure the crack opening displacement (COD) and the electron back scattered diffraction technique (EBSD) to determine the orientation of individual grains the microstructural influence on short crack initiation and growth can be characterized. Finite element calculations show a high influence of the elastic anisotropy on the initiation sites of cracks. Crack propagation takes place transgranulary along slip planes as well as intergranulary along grain boundaries. The crack growth rate depends strongly on the active mechanism at the crack tip which in turn is influenced by crack length, the applied stress and the orientation of the grains involved. The value of the steady state crack closure stress changes from a positive value at low applied stresses (roughness induced) to a negative one at higher applied stresses (due to plastic deformations at the crack tip). The crack growth simulation is realised by a two‐dimensional boundary element technique, which contains the ideas of Navarro und de los Rios. The model includes the sequence of the applied stress amplitude as well as the experimental measured roughness induced crack closure.     

6H-SiC单晶表面ZnO薄膜的制备及其结构表征

利用脉冲激光淀积(PLD)技术在6H-SiC单晶衬底上制备了ZnO薄膜. 利用X射线衍射(XRD), 反射式高能电子衍射(RHEED)和同步辐射掠入射X射线衍射(SRGID)φ扫描等实验技术研究了ZnO薄膜的结构. 结果表明:在单晶6H-SiC衬底上制备的ZnO薄膜已经达到单晶水平, 不同入射角的SRGID结果, 显示了ZnO薄膜内部不同深度处a方向的晶格弛豫是不一致的, 从接近衬底界面处到薄膜的中间部分再到薄膜的表面处, a方向的晶格常数分别为0.3264、0.3272和0.3223nm. 通过计算得到ZnO薄膜的泊松比为0.504, ZnO薄膜与单晶6H-SiC衬底在平行于衬底表面a轴方向的实际晶格失配度为5.84%.     

Growth dynamics of GaAs, AlAs and (Al, Ga)As on GaAs (110) and (111)A substrates during molecular beam epitaxy

The growth dynamics of GaAs, AlAs and (Al, Ga)As films grown by molecular beam epitaxy (MBE) on GaAs(110) and (111)A substrates have been studied using reflection high energy electron diffraction (RHEED) intensity oscillations and scanning tunnelling microscopy (STM). In contrast to growth on (001) oriented substrates, the period of the RHEED intensity oscillation does not in general provide a measure of the growth rate. This is explained by the very different surface chemistry involved, since the short lifetime of arsenic molecules (As₂ or As₄) on non-(001) surfaces results in cation-stable surface conditions, which generate arsenic (anion)- induced intensity oscillations, whereas on (001) surfaces they are cationinduced under all normal growth conditions. The effects of this behaviour on surface morphology are illustrated, as are the relative influences of Ga and Al. STM images obtained during the first few monolayers of growth provide a detailed indication of the growth mode and in particular explain in a simple manner the origin of bilayer period RHEED intensity oscillations obtained during growth on GaAs (110).     

CW-diode laser crystallization of sputtered amorphous silicon on glass, SiNx, and SiO2 intermediate layers

CW-diode laser crystallization of amorphous silicon (a-Si) deposited by sputtering or by electron beam evaporation onto different substrates (glass without or with SiN_x or SiO₂ intermediate layers) is investigated. The resulting grain sizes and orientations are characterized by electron backscatter diffraction, optical microscopy, and x-ray diffraction. We demonstrate that 200 nm thick sputtered a-Si layers can be crystallized on all of the used substrates to result in grains from 1 up to 100 μm in size, depending on the laser irradiation parameters (intensity, exposure time). Electron beam evaporated a-Si films can be crystallized only on sputtered SiN_x intermediate layers to result in grains of 100 μm in size. Similar crystallographic film properties follow from laser treatment if the product of laser peak intensity and square root of exposure time is kept constant, independent of the scan velocity used. A high fraction of preferred (100)-oriented silicon grains can only be observed for samples with crystallites less than 10 μm in size.     

利用模拟衍射线计算X射线应力测定中的误差

利用模拟衍射线计算了X射线应力测定中不同线形衍射线的峰位角和残余应力的误差,讨论了它们与半高宽（HW）、净峰强度（IP）和峰背比（IP／IB）之间的关系。根据分析结果,分别推导出不同线形衍射线的峰位角和残余应力误差的计算公式,并利用实测衍射线考察了该公式的可靠性。     

MBE生长GaAs薄膜表面形貌的RHEED图样研究

本文通过在GaAs(100)单晶衬底上MBE生长GaAs过程中形成的RHEED衍射图样,对GaAs薄膜的表面形貌进行研究。分析GaAs表面粗糙和生长时不发生RHEED强度振荡的原因。讨论在生长GaAs时出现In(Ga)As/GaAs(100)体系的RHEED衍射图样这种异常现象的原因。     

激光分子束外延SrTiO3薄膜退火过程中表面扩散的研究

用激光分子束外延研究了SrTiO3同质外延时原位退火中,反射高能电子衍射(RHEED)强度的恢复--驰豫时间,导出了高真空下表面扩散的活化能为0.31 eV,与低真空下的结果相比要小许多,这反映了粒子达到基片时的能量差.对沉积不同厚度的薄膜退火研究,表明当薄膜厚度增加时,表面恢复情况减弱,而导致随后的沉积时RHEED振荡周期的改变.     

Effect of downscaling nano-copper interconnects on the microstructure revealed by high resolution TEM-orientation-mapping

In this work, a recently developed electron diffraction technique called diffraction scanning transmission electron microscopy (D-STEM) is coupled with precession electron microscopy to obtain quantitative local texture information in damascene copper interconnects (1.8 μm-70 nm in width) with a spatial resolution of less than 5 nm. Misorientation and trace analysis is performed to investigate the grain boundary distribution in these lines. The results reveal strong variations in texture and grain boundary distribution of the copper lines upon downscaling. Lines of width 1.8 μm exhibit a strong <111> normal texture and comprise large micron-size grains. Upon downscaling to 180 nm, a {111}<110> bi-axial texture has been observed. In contrast, narrower lines of widths 120 and 70 nm reveal sidewall growth of {111} grains and a dominant <110> normal texture. The microstructure in these lines comprises clusters of small grains separated by high angle boundaries in the vicinity of large grains. The fraction of coherent twin boundaries also reduces with decreasing line width.     

Deformation behaviour of aluminium macrocrystals in the grain boundary region

Lattice distortions of deformed aluminium macrocrystals were observed by Electron-microprobe-Kossel techniques. Grain boundary effects due to deformation appeared in various ways such as extraordinary separation and branching of Kossel lines, and as intergranular rotation of the grains in pseudo-Kossel X-ray diffraction patterns obtained from the grain boundary regions of the specimens. Such distortions of the patterns peculiar to the grain boundary regions were attributed to the effect of local slipping induced by the active slip systems of the neighbouring crystals. By the interpretation of these patterns and the orientation relationships between neighbouring grains, it was found that the local slipping was induced towards the slip direction of the active slip plane in the neighbouring crystals, or induced by a type of local stress along the slip direction of the active slip planes in the neighbouring crystals. It was also recognised that at an early stage of stressing, deformation bands were produced in the grain boundary region as a result of a grain boundary effect.     

空心阴极电子束对多弧离子镀TiAlN薄膜组织形貌及摩擦学性能的影响

采用空心阴极电子束辅助多弧离子镀的方式在WC基体上制备了TiAlN薄膜,讨论了电子束能量的大小对膜层组织形貌及摩擦学性能的影响。利用X射线衍射仪、扫描电子显微镜、表面轮廓测试仪及材料表面微纳米力学测试系统对薄膜的相组成、微观结构、三维形貌及摩擦学性能进行了检测和分析。结果表明:在未施加空心阴极电子束作用时薄膜具有明显的(112)择优取向,随着空心阴极电流的提高,薄膜逐渐朝着多晶面生长,择优取向减弱。电子束对膜层的形貌及摩擦学性能有显著影响,随着电子束能量的提高,膜层逐渐变得致密、平整,表面粗糙度和摩擦系数均降低,抗磨损性能提高。     

LaAlO3/BaTiO3/SrTiO3三色超晶格的RHEED原位监测

采用激光脉冲分子束外延技术，在（100）取向的STO单晶基片上成功外延生长了LaAlO3／BaTiO3／SrTiO3超晶格。在超晶格薄膜生长过程中采用反射高能电子衍射（RHEED）对LaAlO3／BaTiO3／SrTiO3超晶格的生长过程进行了分析。通过对超晶格中各层RHEED图像分析，发现由于各层面内晶格失配的不同，超晶格各层生长特性有所区别。借助原子力显微镜（AFM）对超晶格表面形貌进行了表征，表明制备的超晶格具有原子级平整的表面。     

A review of crystallographic textures in chemical vapor-deposited diamond films

Diamond is one of the most important functional materials for film applications due to its extreme physical and mechanical properties, many of which depend on the crystallographic texture. The influence of various deposition parameters matters to the texture formation and evolution during chemical vapor deposition (CVD) of diamond films. In this overview, the texture evolutions are presented in terms of both simulations and experimental observations. The crystallographic textures in diamond are simulated based on the van der Drift growth selection mechanism. The film morphology and textures associated with the growth parameters α (proportional to the ratio of the growth rate along the 〈100〉 direction to that along the 〈111〉 direction) are presented and determined by applying the fastest growth directions. Thick films with variations in substrate temperature, methane concentration, film thickness, and nitrogen addition were analyzed using high-resolution electron back-scattering diffraction (HR-EBSD) as well as X-ray diffraction (XRD), and the fraction variations of fiber textures with these deposition parameters were explained. In conjunction with the focused ion beam (FIB) technique for specimen preparation, the grain orientations in the beginning nucleation zones were studied using HR-EBSD (50 nm step size) in another two sets of thin films deposited with variations in methane concentration and substrate material. The microstructures, textures, and grain boundary character were characterized. Based on the combination of an FIB unit for serial sectioning and HR-EBSD, diamond growth dynamics was observed using a 3D EBSD technique, with which individual diamond grains were investigated in 3D. Microscopic defects were observed in the vicinity of the high-angle grain boundaries by using the transmission electron microscopy (TEM) technique, and the advances of TEM orientation microscopy make it possible to identify the grain orientations in nano-crystalline diamond.     

MBE growth of (1 1 0) refractory metals on a-plane sapphire

The initial stages of growth of epitaxial (1 1 0) niobium, tantalum, and molybdenum films on (1 1 2 0) sapphire by molecular beam epitaxy, MBE, are analyzed in situ by reflection high-energy electron diffraction (RHEED), and ex situ by high-resolution electron microscopy (HREM) and X-ray diffraction (XRD) techniques. The RHEED analysis shows that both Nb and Ta initially deposit (for approximately the first two monolayers in the case of Nb and the first four monolayers for Ta) with an hexagonal surface symmetry that is not consistent with the normal bcc structure of these metals, in agreement with the previous result of Oderno et al. [1] for Nb on sapphire. On further deposition, the films are observed to relax into the normal bcc (1 1 0) structure. Intensity oscillations of the RHEED specular beam are observed during both stages of growth. The RHEED oscillations are damped out after approximately 20 monolayers of Nb (30 monolayers of Ta) as a steady-state surface roughness is reached. HREM analysis reveals that the initial hexagonal structure has transformed completely to the normal bcc structure in the thicker films. The epitaxial relationships at each stage of growth are identified and a model is suggested for the development of the initial hexagonal structure based on Nb–O bonding at the interface. As the thickness of the bcc film increases, strain relief is observed by the formation of misfit dislocations. The growth mode of Mo is found to be different from that of Nb and Ta. The initial deposit grows in a three-dimensional mode with poor atomic order; the RHEED patterns are not sufficiently distinct to identify whether the hexagonal structure is formed. However, the surface becomes progressively smoother as growth proceeds and thicker films of Mo are comparable in crystalline quality, as measured by X-ray rocking curves, to Nb and Ta. The different growth mode of Mo is attributed to greater mismatch with the sapphire substrate and possibly different M–O ionic bonding at the substrate interface.