La0.7Ca0.3MnO3薄膜微观结构的HRTEM表征

利用透射电子显微镜研究了衬底温度600～800℃条件下采用脉冲激光法在(001)LaAlO3(LAO)衬底上制备的La0.7Ca0.3MnO3(LCMO)薄膜的微观结构。结果表明薄膜由大量柱状晶组成且与LAO衬底形成良好外延关系。LCMO薄膜与LAO衬底的取向关系可以描述为:(ⅰ)(100)f∥(001)s、[011]f∥[100]s;(ⅱ)(011)f∥(001)s、[100]f∥[100]s。LCMO显示层状畴结构,即在衬底上初始生长的薄膜为(ⅱ)型畴,在此之上生长的薄膜为(ⅰ)类和(ⅱ)类型畴的混合体。薄膜中可观察到一些反向畴与孪晶等缺陷。薄膜与衬底界面少见错配位错,薄膜以Stranski-Krastanov模式生长。     

衬底温度对Si(111)衬底上MBE异质外延3C-SiC薄膜的影响

利用固源分子束外延(SSMBE)技术, 在Si(111)衬底上异质外延生长3C-SiC单晶薄膜, 通过RHEED、XRD、AFM、XPS等实验方法研究了衬底温度对薄膜结构、形貌和化学组分的影响. 研究结果表明, 1000℃生长的样品具有好的结晶质量和单晶性. 在更高的衬底温度下生长, 会导致大的孔洞形成, 衬底和薄膜间大的热失配使降温过程中薄膜内形成更多位错, 从而使晶体质量变差. 在低衬底温度下生长, 由于偏离理想的化学配比也会导致薄膜的晶体质量降低.     

High resolution electron microscopy study of ferromagnet （La0.7 Ca0.3 MnO3 ）/superconductor （YBa2 Cu3 07 ） bi-layer

采用脉冲激光沉积法在LaAlO3（LAO）衬底上生长了YBa2Cu3O7/La0.7Ca0.3MnO3（YBCO/LC-MO）和La0.7Ca0.3MnO3/YBa2Cu3O7（LCMO/YBCO）两种外延薄膜,利用高分辨电子显微镜研究了其微观结构。在YBCO/LCMO/LAO薄膜中,LCMO以层-岛模式生长,并形成层状取向畴结构。YBCO层均由c轴取向晶粒组成,其中含有c/3平移畴界、额外CuO层及Y2O3第二相等缺陷结构。在LCMO/YBCO/LAO薄膜中,LAO衬底上初始生长的YBCO为c轴取向,至一定厚度（几个纳米）转为c与a轴混合生长。LCMO层在YBCO上外延生长并具有[100]m与[011]m混合取向畴结构。在LCMO/YBCO界面未观察到失配位错,因此二者界面属应变型界面。     

铁磁(La0.7Ca0.3MnO3)/高温超导（YBa2Cu3O7）双层薄膜微结构的高分辨电镜研究

采用脉冲激光沉积法在LaAlO3(LAO)衬底上生长了YBa2Cu3O7/La0.7Ca0.3MnO3(YBCO/LC-MO)和La0.7Ca0.3MnO3/YBa2Cu3O7(LCMO/YBCO)两种外延薄膜,利用高分辨电子显微镜研究了其微观结构。在YBCO/LCMO/LAO薄膜中,LCMO以层-岛模式生长,并形成层状取向畴结构。YBCO层均由c轴取向晶粒组成,其中含有c/3平移畴界、额外CuO层及Y2O3第二相等缺陷结构。在LCMO/YBCO/LAO薄膜中,LAO衬底上初始生长的YBCO为c轴取向,至一定厚度(几个纳米)转为c与a轴混合生长。LCMO层在YBCO上外延生长并具有[100]m与[011]m混合取向畴结构。在LCMO/YBCO界面未观察到失配位错,因此二者界面属应变型界面。     

Sr_(0.5)Ba_(0.5)TiO_3/La_(0.5)Sr_(0.5)CoO_3双层薄膜的微观结构

采用脉冲激光沉积法在(001)LaAlO_3衬底上制备了Sr_(0.5)Ba_(0.5)TiO_3/La_(0.5)Sr_(0.5)CoO_3薄膜,利用透射电子显微镜对薄膜的微观结构进行了研究。结果表明,底电极La_(0.5)Sr_(0.5)CoO_3在LaAlO_3衬底上外延生长并形成立方-立方取向关系。不同于块体结构,LSCO薄膜发生了结构转变,形成一种氧缺位有序调制结构。整个薄膜由大量取向畴组成,其中包含一些层错与反相畴界等缺陷。生长温度为500℃时,Sr_(0.5)Ba_(0.5)TiO_3薄膜为柱状多晶结构;当温度升高至820℃时,薄膜为缺陷较少的单晶结构。     

镍基单晶高温合金的反相畴界强化EI

本项研究表明，在一种抗热腐蚀ＤＤ８单晶高温合金中，观察到反相畴界存在三种形成机制：一种是γ＇相内局部有序化原子产生错排；第二种是基体１／２＜１１０＞位错切入γ＇相；第三种是基体位错网诱发。经推导得到如下反相畴界能对单晶合金强度贡献的表达式：     

Si(111)衬底上3C-SiC的固源MBE异质外延生长

国内首次利用固源分子束外延(MBE)技术,在衬底温度为1100℃时,以Si(111)为衬底成功地外延生长出了3C-SiC单晶薄膜。通过X射线衍射(XRD)、拉曼光谱(Raman)以及原位反射高能电子衍射(RHEED)等手段研究了外延薄膜的晶型、结晶质量、外延膜与衬底的外延取向关系,并考察了薄膜制备过程中衬底的碳化对薄膜质量的影响。结果表明,外延膜与衬底晶格取向完全一致;碳化可以减小SiC和衬底Si之间的晶格失配、释放应力、引入成核中心,有利于薄膜单晶质量的提高;碳化温度存在最佳值,这一现象与成核过程有关。     

Ni75Al7.5V17.5合金时效沉淀D022相的孪生相场模拟

为揭示合金固态相变初期新相形成机制,尤其是D022相变孪晶形成机制,利用三元微观相场模型对Ni75Al7.5V17.5合金于1 273 K下等温时效沉淀过程的前3个阶段进行了模拟.计算结果表明,L12结构的Ni3Al有序相首先沿惯析面(100)从母相中共格形核,而后D022结构的Ni3V有序相在先析出的L12相和母相的相界形核.由于{100}的反相畴界上形成较大的共格失配,导致能量较高且不稳定,反相畴界在两相生长中遭到破坏,而晶面{110}的界面能比{100}的反相畴界能低,生长过程中D022的3种变体互相正交排列形成阶梯状结构的{110}孪晶面.     

不同衬底上Ba0.4Sr0.6TiO3铁电薄膜的制备及外延生长的研究

利用脉冲激光沉积( PLD)技术,通过一系列实验成功地制备出了近外延生长的Ba0.4Sr0.6TiO3铁电薄膜.研究了衬底对Ba0.4Sr0.6TiO3铁电薄膜外延质量的影响.从摇摆曲线的半高宽(FWHM)及原子力显微镜(AFM)图谱中可以看出,在铝酸锶钽镧(LAST)衬底上生长的薄膜,外延质量明显比失配度更小的钛酸锶...     

衬底温度对掺锆酸钡高温超导YBCO薄膜结构和超导电性能的影响

高温超导氧化物YBCO外延薄膜在掺入少量锆酸钡(BaZrO3,BZO)后,其超导性能会得到较大幅度的提高.研究了不同衬底温度对掺BZO的YBCO薄膜的外延特性及超导性能的影响.以固相反应法制备了YBCO及BZO原材料,利用固相烧结工艺制备了BZO含量为2%(质量分数)的YBCO-BZO复合靶材,采用脉冲激光沉积技术(PLD)在LaAlO3(100)基片上外延生长YBCO薄膜.以不同的衬底温度制备了YBCO薄膜,用X射线衍射和高分辨透射电子显微技术对所制备的YBCO薄膜的外延特性进行了分析.最后比较了在不同衬底温度下制备的YBCO薄膜的超导性能,得到了最佳衬底温度.     

Structural engineering of Ba0.5Sr0.5TiO3 epitaxial films

Ba_0.5Sr_0.5TiO₃ single-layered and multilayered films were epitaxially grown on a (001) LaAlO₃ substrate using single target and dual target pulsed laser deposition, respectively. Compared to the single-layered films, the multilayered films exhibited broader phase transition and improved thermo-stability. The microstructure of these epitaxial films was investigated using high-resolution transmission electron microscopy in details. Misfit and threading dislocations were observed in the single-layered film, while the threading dislocations were dramatically decreased and no misfit dislocations were found in the multilayered film. It is suspected that the difference in dislocation densities is responsible for the different behaviors of the permittivity with temperature.     

BST/BZT/BST多层薄膜结构与性能研究

利用脉冲激光沉积法在LaNiO3/LaAlO3(001)基片上生长了Ba0.6Sr0.4TiO3(BST)和Ba(Zr0.2Ti0.8)O3(BZT)单层薄膜,以及Ba(Zr0.2Ti0.8)O3/Ba0.6Sr0.4TiO3/Ba(Zr0.2Ti0.8)O3(BZT/BST/BZT)多层薄膜.X射线衍射(XRD)分析发现,BST、BZT和LNO薄膜都具有高度的(00l)取向.原子力显微镜(AFM)显示三种样品表面光滑无裂纹,晶粒尺寸和表面粗糙度相当.电容测试表明,相对BST、BZT单层薄膜,多层薄膜具有最大的品质因数42.07.表明多层薄膜在微波应用中具有很大的潜力.     

Interface effects on highly epitaxial ferroelectric thin films

Interface effects have been found to play a key role in controlling the epitaxial nature and physical properties on the highly epitaxial ferroelectric thin films. Thin film ferroelectrics are dominantly affected by the strains induced by lattice misfits between the films and the substrates, surface step terrace, both step height and terrace dimension, and the surface terminations. The natures of interface induced local strain formations, edge dislocations, and antiphase domain boundaries are reviewed in this article.     

Microstructure of Epitaxial La_(0.7)Ca_(0.3)MnO_3 Thin Films Deposited by Direct Current Magnetron Sputtering on LaAlO_3 Substrate

Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) have been used to study the microstructural properties of La0.7Ca0.3MnO3 films on (001) LaAlO3 substrates prepared by direct current magnetron sputtering technique.The as-grown thin films with different thickness are perfectly coherent with the substrates.The film suffers a tetragonal deformation in the area near the interface between the film and the substrate.With increasing thickness, the film is partially relaxed.It was found that La0.7Ca0.3MnO3 films consist of two types of oriented domains described as: (1) (110)f[001]f||(001)s[100]sand (110)f[001]f||(001)s[100]s and (2) (110)f[001]f||(001)s[010]s and (110)f[001]f//(001)s[010]s.Upon annealing, the film is relaxed by the formation of misfit dislocations.Other than misfit dislocations, two types of threading dislocations with Burgers vector of <100> and <110> were also identified.     

Defect microstructures in epitaxial PbZr0.2Ti0.8O3 films grown on (001) SrTiO3 by pulsed laser deposition

Transmission electron microscopy has been used to investigate the character and distribution of the microstructural features in epitaxial (001) ferroelectric PbZr_0.2Ti_0.8O₃ films grown on (001) SrTiO₃ substrates by pulsed laser deposition. The TEM observations revealed that the films were predominantly c-oriented with embedded a ₁- and a ₂-oriented domains lying on {101} planes. The substrate/film interfaces contained arrays of edge-type misfit dislocations and there were extraordinarily high densities ( ) of threading dislocations in the films. The character and distribution of these features are consistent with the following relaxation sequence. Firstly, the lattice misfit between the phases is accommodated at the growth temperature by the introduction of misfit dislocations at the edges of island nuclei, and some of these dislocations are forced away from the interface to form threading segments upon island coalescence. Next, the film adopts the c-orientation upon cooling through the Curie temperature with a ₁- and a ₂-oriented domains being formed to ameliorate the self-strain of the transformation. Finally, some redistribution of the embedded domains and misfit dislocations occurs in response to stresses caused by expansion coefficient differences. The impact of these defects on the electrical and electromechanical properties of epitaxial ferroelectric properties is discussed.     

Some features of the behavior of misfit dislocations during diffusion

The misfit between one film and another is often accommodated by misfit dislocations. If the crystals are miscible and are allowed to interdiffuse the misfit dislocations become distributed in the alloyed volume. Frequently, some parts of one dislocation move away from the interface into one crystal and other parts move into the other crystal. The parts in one crystal are connected to those in the other by dislocations that thread the diffusion zone. The density of these threading dislocations depends on the misfit between the two crystals, and may be influenced by the Kirkendall effect and by the misfit accommodated by elastic strain. Interaction between misfit dislocations in the diffusion zone often leads to the creation of new grains. These grains are unusual in that their lattices are curved to accommodate misfit between the upper and lower film surfaces. The boundaries to the grains are approximately perpendicular to the original interface and are made up of misfit dislocations that once occupied the material inside the curved grain. As dislocations and grain boundaries enhance diffusion the threading dislocations, and the boundaries to the curved grains, are expected to contribute to mixing of the films.     

A Study on Crystal Defects in Epitaxial GaN Film by High-Order Weak-Beam Electron Microscopy

Various crystal defects in epitaxial GaN film were studied by high-order bright-field and dark-field electron microscopy. The results revealed that the film is composed of small grains in nano-meter scale. Distinct shapes of the grain boundaries and a great number of threading dislocations were shown in the experimental g/3g weak-beam images. Diffraction contrast analysis verified that the majority of threading dislocations is 1/3<11 0> edge dislocation. A unique (11 0) planar defect was observed in the specimen. The defect was identified to have a similar structure to the incipient 1/3[11 0] edge dislocation.     

Use of misfit strain to remove dislocations from epitaxial thin films

Misfit strain can be used to drive threading dislocations out of epitaxial films and thus to improve their perfection. This process is influenced by film thickness, the orientation of the interface, the dimensions of the interface parallel to its plane, and the misfit between film and substrate. A simple theoretical model, and the experimental observations made on deposits of Ga(As, P) on GaAs, suggest that it is desirable for the film thickness to be small. This in turn implies that the misfit should be large. It should not, however, be large enough to cause dislocation nucleation. If the film is face-centered cubic, and the threading dislocations are uniformly distributed over the 〈110〉 {111} slip systems, then the most desirable interface orientations lie near {012} or {013}. If the Burgers vectors of the threading dislocations are not uniformly distributed then other interfaces may become desirable. Multilayers are able to remove threading dislocations more effectively than single films.     

Line defects, planar defects and voids in SrTiO3 films grown on MgO by pulsed laser and pulsed laser interval deposition

Two and three dimensional growth of SrTiO₃ films on (001) MgO substrate was achieved by pulsed laser interval and pulsed laser deposition respectively. The growth mode was monitored by in-situ reflection high energy electron diffraction. Interval deposition forces layer-by-layer growth of materials even with such a large lattice misfit (~ 7.9%). A titanium dioxide buffer monolayer was deposited to allow the film to wet the substrate to encourage two dimensional growth of the strontium titanate. A variety of defects was investigated using transmission electron microscopy and high resolution scanning transmission electron microscopy. Misfit dislocations, steps at the interface, Ti-rich defects and regularly shaped nano-holes connected by anti-phase boundaries were found to be the dominant defects in these films grown layer by layer. The edges of the nano-holes were mainly along [010] and [100] for a [001] growth direction. The large strain between the two crystal systems with large lattice mismatch leads to in-plane tensile stress during the layer-by-layer growth. The stress is relieved in part by the holes. The films with a three dimensional growth mode possess a uniform surface with dislocations as the dominant defects. The individual densities of the various defects, including a Ti-rich phase and misfit and threading dislocations, are determined by the kinetics of the deposition method.