GaAs(001)衬底上分子束外延生长立方和六方GaN薄膜

采用分子束外延方法在GaAs(001)衬底上生长出了03微米厚的GaN薄膜,X射线双晶衍射和室温光荧光测试结果表明,采用GaAs氮化表面作为成核层可获得高纯度立方GaN薄膜而采用AlAs氮化表面作为成核层可获得高纯度六方GaN薄膜.这一研究结果表明在GaAs衬底上生长GaN薄膜的相结构可以通过选择不同的成核层来控制. 关键词：     

C60分子在GaAs(001)表面的外延生长的扫描隧道显微镜研究

利用扫描隧道显微镜（STM）系统地研究了C₆₀薄膜在GaAs（001）表面的异质外延生长．在GaAs（001）2×4-β相表面，观察到C₆₀薄膜以非密排面进行生长，并在生长中有结构相变产生．实验数据表明，薄膜下层面心立方（fcc）的晶格常数比C₆₀晶体的晶格常数要大13%；而薄膜的表层结构则展示了非理想的六角密堆（hcp）结构，其表面为hcp（1100）面，生长过程是非理想的层状生长模式．在GaAs（001）-c（4×4）衬底上，C₆₀薄膜的表面仍然是fcc（111）面，其结构参数与C₆₀晶体一致，但C₆₀薄膜采用了三维模式进行生长 关键词：     

在Pd/Cu(100)表面上外延的超薄Co膜的结构和磁性

利用脉冲激光溅射(PLD)和分子束外延(MBE)方法制备了超薄膜系统 Co/Pd/Cu(100).脉冲激 光溅射生长的单原子Pd层呈现了很好的二维生长模式.在这个Pd表面上，分子束外延生长的C o层直至12个原子层都表现了层-层生长模式.利用俄歇电子谱(AES)和低能电子衍射(LEED)研 究了该系统的表面结构.利用低温磁光克效应(MOKE)研究了系统的磁学性质.结构研究表明， Co层由于面内晶格失配应力而具有一个四方正交结构；与对比样品Co/Cu(100)的比较研究说 明Pd层的存在强烈地改善了Co膜的起始生长模式和结构.磁光克效应测量表明，Pd层的存在 改变了Co层的磁学性质. 关键词： 薄膜的磁性质 组织与形貌 界面磁性     

Cu-Au体系非对称异质外延行为的分子动力学研究

利用分子动力学模拟方法研究了Cu/Au(001)和Au/Cu(001)异质外延岛的演化行为. 研究结果显示：Cu-Au体系的相互外延行为呈现出明显的非对称性. Cu在Au(001)基体表面可以形成完整的外延结构，而Au在Cu(001)基体表面外延将导致失配位错的出现. 导致非对称外延生长行为的根本原因是外延岛的应变状态的差异和外延岛自身性质的不同. 随着外延岛的长大，Cu外延岛与Au(001)基体的微观失配度由最初的接近宏观失配度的9%左右迅速单调下降，并最终趋于晶格匹配；而Au在Cu(001)基体表面外延的微观失配度则呈现出振荡增加趋势. Cu/Au(001)体系的基体形变主要发生在外延岛的边缘，而Au/Cu(001)体系的基体形变主要发生在外延岛内部所对应的区域.     

GaAs/Al_xGa_(1-x)As多量子阱外延结构及其LP-MOCVD生长工艺研究

在低压金属有机化学气相沉积生长工艺中,对用于制作850nm垂直腔面发射激光器件的GaAs/Al_xGa_(1-x)As多量子阱外延结构的生长温度、反应室压力、总载气流量以及生长速度等主要工艺参量进行优化,并进行了完整外延结构的生长.实验结果表明:在700℃条件下,得到多种组分的GaAs/Al_xGa_(1-x)As多量子阱结构,通过光致发光谱对比测试得到的最佳组分x为0.24,同时得到良好的表面形貌,最终确定的最佳生长速度为0.34~0.511nm/s.     

FexMn1-x合金在GaAs(001)表面外延的结构和磁性

报道了对于0≤x≤1的Fe_xMn_1-x合金在GaAs(001)表面上分子束外延的结构与磁性的实验结果,当x>0.8时,Fe_xMn_1-x合金以单晶体心立方结构生长;当x<0.35时,则以单晶面心立方结构生长;对于0.35xMn_1-x生长的结构比较复杂,而正是在这一区域中,该合金发生了从铁磁相到反铁磁相的转变. 关键词：     

Co100-xMnx合金在GaAs(001)表面的生长结构和磁性的实验研究

对Co_100-xMn_x合金在GaAs(001)表面的分子束外延生长、晶体结构和磁学性质进行了研究.结果表明,当0100-xMn_x合金薄膜是体材料中不存在的体心立方(bcc)结构,并且具有较强的铁磁性,当44100-xMn_x合金薄膜最初为bcc结构,随着厚度的增加,逐渐从bcc向面心立方(fcc)结构转化,最后成为完全的fcc结构,薄膜具有较 关键词：     

用N2-H2等离子体氮化GaAs衬底对ECR-PEMOCVD生长立方GaN的影响

我们研究了采用电子回旋共振等离子体增强金属有机化学气相沉积(ECR-PEMOCVE)技术在GaAs(001)衬底上外延生长立方GaN的过程中衬底氮化条件对外延膜生长的影响.发现氮化时在氮等离子体中加入氢等离子体对于立方GaN薄膜生长具有显著影响.和氮化过程中不加入氢等离子体相比,氮化过程中加入氢等离子体生长出的外延膜其X射线衍射(XRD)半高宽(FWHM)可以最高降低40%以上.原子力显微镜(AFM)观察表明:在N2-H2混合等离子中氮化过的衬底上外延的缓冲层表面变得更为平滑,晶粒也变得粗大.最后,我们提出了一个化学模型对上述结果进行了分析和解释..     

液滴外延下生长参数对InAs纳米结构形貌的影响

利用液滴外延法在GaAs(001)衬底表面制备InAs量子点,通过控制变量分别研究沉积速率、沉积量对In液滴在GaAs表面生长过程中的影响.使用原子力显微镜(Atomic Force Microscope, AFM)表征InAs纳米结构形貌,得出结论：(1)沉积速率主要通过影响In液滴成核率来控制液滴的密度,即随着沉积速率的增大,In原子在衬底表面的成核率增加,InAs量子点密度增加,实验符合生长动力学经典成核理论.(2)沉积量的改变主要影响液滴的熟化过程,即随着沉积量的增大,可参与生长的活跃的In原子增加,促进了液滴熟化,使得扩散坍塌的原子数量增加,导致在InAs纳米结构中出现多量子点现象.     

Al/GaAs表面量子阱界面层的原位光调制反射光谱研究

用分子束外延（MBE）方法在GaAs表面量子阱上外延生长不同厚度的Al层，以超高真空下的原位光调制光谱（PR）作为测量手段，研究Al扩散形成的表面势垒层对于GaAs表面量子阱中带间跃迁峰位和峰形的影响.根据跃迁峰的变化，采用有效质量近似理论计算出了Al和GaAs 的互扩散长度为0.5nm，这是半导体工艺中的一个重要常数. 关键词： Al GaAs 原位光调制反射光谱（PR） 分子束外延（MBE）     

Self-propagating high-temperature synthesis in Pt/Co/MgO(001) epitaxial thin films

The self-propagating high-temperature synthesis in the two-layer and multilayer Pt/Co(001) thin films has been investigated. It is shown that the initiation of the synthesis occurs at temperatures of 770–820 K. After the synthesis in the two-layer film samples, the PtCo(001) disordered phase exhibits an epitaxial growth at the interface between cobalt and platinum layers. In the multilayer Pt/Co(001) thin films, the self-propagating high-temperature synthesis also brings about the formation of the PtCo(001) disordered phase on the MgO(001) surface. Further annealing at a temperature of 870 K for 4 h results in the transition of the PtCo(001) disordered phase to the ordered phase. Rapid thermal annealing of the Pt/Co(001) multilayer films at a temperature of 1000 K leads to the formation of the CoPt₃ phase. The magnetic characteristics change in accord with the structural transformations in Pt/Co film samples.     

Long-range chemical interaction in solid-state synthesis: The formation of a CuAu alloy in Au/β-Co(001)/Cu(001) epitaxial film structures

The effect of an inert Co layer (0, 210, 480 nm) on the chemical interaction between Cu and Au in Au/β-Co(001)/Cu(001) epitaxial films has been investigated by X-ray diffraction, nuclear magnetic resonance, photoelectron spectroscopy, and magnetic structure measurements. Mixing at interfaces in Cu/β-Co(001) and Au/β-Co(001) bilayer films has not been revealed up to a temperature of 600°C. The solid-state synthesis of ordered CuAu| and CuAu∥ phases occurs through the Co inert buffer layer in Au/β-Co(001)/Cu(001) trilayer film systems with an increase in the annealing temperature. The initiation temperatures of the CuAu| and CuAu∥ phases increase only slightly with the thickness of the Co buffer layer. The assumption of the long range of the chemical interaction between Cu and Au through the chemically inert Co layer is justified using the performed investigations.     

Magnetic force microscopy of GaAs:Mn ferromagnetic semiconductors

The dependence of magnetic properties of GaAs:Mn and MnAs epitaxial films grown on GaAs (001) by laser ablation of Mn and undoped GaAs in a hydrogen atmosphere under the growth conditions has been studied by magnetic force microscopy (MFM). Magnetic probe calibration for quantitative MFM measurements was performed by scanning across the slit of the magnetic-head of a tape recorder through which controlled direct current was passed. The dipole approximation was used to describe the magnetic properties of the MFM probe. Nonuniformity of the magnetization of GaAs:Mn films related to the formation of MnAs nanoinclusions, which are ferromagnetic at 300 K, has been observed. The typical scales of the spatial nonuniformity of the magnetization of GaAs:Mn films were varied from 270 to 550 nm depending on the film-growth conditions. The MnAs phase was identified by MFM measurements at an elevated temperature (up to 80°N).     

Strain induced epitaxial relationships of Cr on Co/Pd(111)

The growth and structure of Co ultra-thin films on Pd(111) and Cr on Co/Pd(111) have been analyzed by grazing incidence X-ray diffraction and low energy electron diffraction. It is shown that the in-plane lattice constant of the epitaxial Co film depends on the growth temperature. Although the strain decreases as a function of the Co film thickness, it persists for 20 monolayer (ML) films or even thicker. When Cr is deposited at room temperature on a strained Co film (10 to 20 ML thick) a Kurdjumov–Sachs epitaxial relationship is observed, whereas when Cr is deposited on a Co(0001) single-crystal or on a very thick Co film on Pd(111), a Nishyama–Wassermann orientation is obtained.     

Raman study of ultrathin Fe3O4 films on GaAs(001) substrate: stoichiometry,epitaxial orientation and strain

The growth and characterization of high‐quality ultrathin Fe₃O₄ films on semiconductor substrates is a key step for spintronic devices. A stable, single‐crystalline ultrathin Fe₃O₄ film on GaAs(001) substrate is obtained by post‐growth annealing of epitaxial Fe film with thicknesses of 5 and 12 nm in air. Raman spectroscopy shows a high ability to convincingly characterize the stoichiometry, epitaxial orientation and strain of such ultrathin Fe₃O₄ films. Polarized Raman spectroscopy confirms the unit cell of Fe₃O₄ films is rotated by 45° to match that of the Fe (001) layer on GaAs, which results in a built‐in strain of − 3.5% in Fe₃O₄ films. The phonon strain‐shift coefficient(−126 cm⁻¹) of the A_1g mode is proposed to probe strain effect and strain relaxation of thin Fe₃O₄ films on substrates. It can be used to identify whether the Fe layer is fully oxidized to Fe₃O₄ or not. Copyright © 2011 John Wiley & Sons, Ltd.     

Structure and composition of gallium nitride films produced by processing gallium arsenide single crystals in atomic nitrogen

Thin GaN films are grown on (001) single-crystal GaAs substrates processed in an atmosphere of active nitrogen radicals. Auger electron spectroscopy is applied to take the depth profiles of the basic chemical elements that enter into the composition of the epitaxial GaN films and single-crystal GaAs substrates. It is found that the surface composition of the GaN films is characterized by considerable nonstoichiometry (the excess nitrogen achieves ≈9%), which is caused by the presence of atomic nitrogen in the discharge chamber. With a high-resolution X-ray diffraction method, the structural perfection of the epitaxial layers is investigated. It is shown that low-temperature annealing (at temperatures below 700°C) is responsible for the formation of cubic GaN films on the (001) surface of cubic GaAs, whereas higher temperature annealing results in the growth of the hexagonal films.     

Reactive sputtering of (Co,Fe) nitride thin films on TiN-bufferd Si

Epitaxial (Co,Fe) nitride films were prepared on TiN buffered Si(001) substrates by dual-target reactive co-sputtering method. With lower Co content, thin films mainly consist of (Co _x Fe_1?x )₄N phase. With higher Co content, STEM EELS found no N signal in the thin film, and, combined with XRD results, shows that fcc Co is the main phase of the thin films instead of Co₄N. The N₂ atmosphere is helpful to induce the fcc Co phase formation during dual-target reactive co-sputtering deposition. For the films with less Co content, the RT magnetization measurements show similar magnetic properties as epitaxial Fe₄N(001) films, while increasing the Co content, the resulting fcc Co thin films show biaxial anisotropy with the [110] in-plane easy axis.     

Growth of SrTiO3 on Si(001) by hybrid molecular beam epitaxy

We report the heteroepitaxial growth of SrTiO₃ thin films on Si(001) by hybrid molecular beam epitaxy (hMBE). Here, elemental strontium and the metal‐organic precursor titanium tetraisopropoxide (TTIP) were co‐supplied in the absence of additional oxygen. The carbonization of pristine Si surfaces during native oxide removal was avoided by freshly evaporating Sr into the hMBE reactor prior to loading samples. Nucleation, growth and crystallization behavior as well a structural properties and film surfaces were characterized for a series of 46‐nm‐thick SrTiO₃ films grown with varying Sr to TTIP fluxes to study the effect of non‐stoichiometric growth conditions on film lattice parameter and surface morphology. High quality SrTiO₃ thin films with epitaxial relationship (001)SrTiO₃ || (001)Si and [110]SrTiO₃ || [100]Si were demonstrated with an amorphous layer of around 4 nm thickness formed at the SrTiO₃/Si interface. The successful growth of high quality SrTiO₃ thin films with atomically smooth surfaces using a thin film technique with scalable growth rates provides a promising route towards heterogeneous integration of functional oxides on Si. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

亚稳态fcc-Mn薄膜的生长及其同步辐射光电子能谱研究

报道亚稳态fcc-Mn薄膜在衬底温度为400K的GaAs(001)表面成功外延的结果.进而利用同步辐射光电子能谱研究该fcc-Mn薄膜随厚度变化的过程.从实验上得到fcc-Mn占有态的电子态密度分布,比较分析亚稳态的fcc-Mn相与热力学稳定的a-Mn相之间电子结构的显著差别,并给出可能的机制. 关键词：