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。     

LaAlO3/BaTiO3超晶格薄膜的生长及结构分析

采用激光脉冲分子束外延技术,在(100)取向的SrTiO3 单晶基片上成功外延生长了LaAlO3/Ba TiO3 超晶格薄膜。在超晶格薄膜生长过程中,采用高能电子衍射技术(RHEED)对LaAlO3/BaTiO3 超晶格薄膜的生长过程以及平面晶格变化进行了分析。通过对超晶格薄膜中各层RHEED衍射条纹的分析计算发现超晶格薄膜存在一个临界厚度,其值约为 17nm,当超晶格薄膜的厚度小于该临界厚度时,晶格畸变在逐渐增加,当厚度超过该临界厚度时,晶格畸变因弛豫现象的产生而逐渐减小。超晶格薄膜中不同层的RHEED衍射条纹的差别说明了由于不同应力的作用使超晶格薄膜中LAO层和BTO层表面粗糙度不同。     

LaAlO3/BaTiO3超晶格薄膜界面结构分析

通过研究发现,利用激光分子束外延技术生长的LaAlO3/BaTiO3超晶格薄膜具有良好的电学性能,其剩余极化可达到25μc/cm2.性能决定于结构,因此本文分析研究了LaAlO3/BaTiO3超晶格薄膜的界面结构.首先通过高能电子衍射技术在薄膜生长过程中对各层的生长及界面状况进行观测,再通过小角X射线衍射曲线及其计算机拟合曲线进一步确定超晶格薄膜的界面及结构参数,如界面的粗糙度、单层厚度等.通过研究发现,由于晶格之间的差异,LaAlO3/BaTiO3超晶格薄膜中LaAlO3和BaTiO3层的生长过程及微结构存在着一定的差异.     

BaTiO3/SrTiO3超晶格的微结构研究

本实验研究利用激光分子束外延法（L－MBE）研究在SrTiO3(STO)(001)基片上生长的BaTiO3(BTO)/SrTiO3(STO)超晶格的微结构,利用小角X射线衍射光谱（SAXRD）的计算机模拟来获得BaTiO3/Sr-TiO3超晶格的微结构参数,如：总的膜厚度,超晶格周期,表面和界面的均方根粗糙度等。实验结果表明超晶格的表面和界面非常平整,均方根粗糙度大约为0.2nm,原子力显微镜（AFM）的实验研究已经证明了超晶格结构的平滑程度,超晶格的＜001＞方向存在着微弱的关联现象。     

MgO/SrTiO_3(001)生长初期的各向异性晶格畸变

通过原位的反射高能电子衍射,监测并测量了MgO/SrTiO3(001)岛状生长初期过程中的面内、面外晶格常数的演变。薄膜的面内晶格在一开始生长时就发生弛豫,且大多数应变在2 nm厚度左右被释放并几乎保持稳定,而面外的晶格应变弛豫一直持续进行。这种应变的各项异性被认为与薄膜的织构导致的应变能变化有关。     

BaTiO3/CoFe2O4/BaTiO3复合磁电薄膜生长及应力研究

用激光分子束外延（LMBE）设备,在SrTiO3（001）基片上外延生长BaTiO3/CoFe2O4/BaTiO3多层复合磁电薄膜结构。通过反射式高能电子衍射（RHEED）对薄膜生长过程进行原位监测,结果显示,随着CoFe2O4厚度的增加薄膜内应力逐渐被释放,并且应力释放的过程导致了薄膜生长模式的变化。高分辨X射线衍射（XRD）发现,随着CoFe2O4厚度的增加,CoFe2O4对BaTiO3薄膜的张应力逐渐增大,BaTiO3晶胞的c轴晶格常数逐渐变小。理论计算给出了BaTiO3面外晶格常数c随CoFe2O4沉积时间的变化规律。原子力显微镜（AFM）对表面形貌进行表征,进一步证明了复合薄膜生长模式的变化。     

钙钛矿型氧化物SrTiO3/BaTiO3多层膜的激光分子束外延生长研究

用激光分子束外延技术在SrTiO3(001)衬底上外延生长SrTiO3/BaTiO3多层膜,通过反射式高能电子衍射(RHEED)原位实时监测并结合原子力显微镜(AFM),研究了不同基片温度下所生长薄膜的表面平整度,利用X射线衍射(XRD)对外延薄膜进行了结构分析,结果表明薄膜具有二维生长模式,在基片温度为380～470℃之间生长的薄膜具有原子级光滑,并且具有完全C轴取向.同时运用X射线光电子能谱(XPS)研究了薄膜界面的互扩散,结果表明降低制备薄膜时的基片温度有利于减少互扩散.     

低维材料的研究

主要论述了低维材料的制造方法、特异性能及在光电子和微电子器件领域的应用,包括介质超晶格、金属超晶格和一维量子线;介绍了我们分别采用激光分子束外延制备的BaTiO3/SrTiO3介质超晶格及其介电性能、直流磁控溅射法制备的强紫外光反射的Cu/Ti超晶格和宽禁带的一维ZnO量子线;描述了低维材料的发展前景.     

LaAlO3顶层结构对LaAlO3-BaTiO3铁电超晶格薄膜性能的影响

X射线衍射技术分析发现,通过生长一层较厚的LaAlO3顶层结构,可以把LaAlO3-BaTiO3超晶格中界面处的应变有效地控制在薄膜中,从而增加超晶格薄膜的平均面外晶格常数c.电学性能测试证明LaAlO3顶层结构的存在极大地改善了超晶格薄膜的电学性能,使其剩余极化强度增加了40多倍.     

异质外延MgO/SrTiO3薄膜中界面应力研究

本文利用激光分子束外延(LMBE)技术在SrTiO3(100)单晶基片上外延生长MgO薄膜，同时又在MgO(100)单晶基片上外延生长SiO3(STO)薄膜。通过反射高能电子衍射(RHEED)仪原位实时监测薄膜生长，研究薄膜的生长过程。并结合X射线衍射(XRD)仪来分析在不同的生长条件下，不同应力对薄膜外延生长的影响。在压应力情况下，MgO薄膜在STO基片上以单个晶胞叠层的方式生长，即以“Cubicon Cubic”方式进行外延；在张应力情况下，由于膜内位错较多，STO薄膜在MgO基片上以晶胞镶嵌的方式进行生长，即以“Mosaic”结构进行外延；提高生长温度，可以减少膜内位错，提高外延质量，使STO薄膜在MgO基片上以较好的层状方式外延生长。     

Anisotropic lattice strain relaxation of MgO/SrTiO3(001) in a textured island growth mode

The out-of-plane and in-plane lattice parameters were measured by in-situ reflection high-energy electron diffraction (RHEED) at the initial growth stage of MgO thin films on SrTiO₃(001) substrates in the growth mode of islands. The in-plane lattice was found to relax immediately after initiating the film deposition, and the majority of the in-plane strain was relieved at the film thickness of 2 nm. Beyond the thickness, the in-plane lattice almost was kept unchanged, and the out-of-plane lattice continued to relax gradually. The anisotropic strain can be attributed to the change of strain energy due to film texture during the ripening process. The relationship between strain and texture, grain size was discussed from the viewpoint of energy competition.     

Impact of epitaxial strain on the ferromagnetic transition temperature of SrRuO3 thin films

Epitaxially strained SrRuO₃ films were grown on SrTiO₃, DyScO₃, and NdGaO₃ oxide substrates using liquid-delivery metal-organic chemical vapour deposition. Temperature dependent resistivity measurements showed a shift in the Curie temperature (T_C) of the ferromagnetic phase transition which is suggested to be caused by the incorporated elastic lattice strain in the films. T_C increased with tensile and decreased with compressive strain, which was inferred from high resolution x-ray diffraction measurements of the in-plane and out-of-plane lattice parameters.     

BaTiO3/SrTiO3多层膜的制备及其介电性质

采用脉冲激光沉积法在Pt／Ti／SiO2／Si衬底上制备了BaTiO3／SrTiO3(BTO／STO)多层膜。XRD结果表明：多层膜呈现出明显的(110)择优取向,与Ba0.5Sr0．5TiO3单层膜相比,多层膜的相对介电常数得到了明显的增强,而介电损耗仍然保持在较低的水平。室温下频率为10kHz时,BTO／STO(n=6)多层膜的相对介电常数为506,而介电损耗仅为0．033。薄膜的C-V特性研究表明：多层膜呈现出较好的电容调谐度。     

Ion beam assisted texturing of polycrystalline Y2O3 films deposited via electron-beam evaporation

Ion-beam assisted deposition of polycrystalline Y₂O₃ films using e-beam evaporation was investigated. For growth on non-crystalline substrates, low temperature growth yields randomly oriented polycrystalline material. At elevated temperature, surface energy anisotropy yields a (111) uniaxial texture. For film deposition with irradiation from an Ar ion beam, the out-of-plane texture remained (111) in orientation. The incident Ar ion beam induces an in-plane alignment of the Y₂O₃ films that is relatively broad. A six-fold symmetry in the out-of-plane X-ray diffraction phi-scans was observed for the (111) textured Y₂O₃ films, indicating a multi-variant in-plane texture and suggesting anisotropic damage along both the (110) and (100) projections. The lack of a sharp, single variant in-plane texture with ion beam irradiation is consistent with the relatively weak bond strength in Y₂O₃.     

Structure of epitaxial Mn-stabilized ZrO2 layers on yttria-stabilized zirconia single crystals prepared by sputtering

Epitaxial Mn-stabilized zirconia layers on yttria-stabilized ZrO₂ (YSZ) single crystals were prepared by sputtering a Mn_0.32Zr_0.68O₂ target. Substrates with (001), (110) and (111) orientation were used. Transmission electron microscopy cross sections showed a homogeneous thickness of the layers. Layers prepared at a substrate temperature of 600 °C grew epitaxially. X-ray diffraction showed that these layers are not exactly cubic. We found a slightly larger out-of-plane lattice parameter compared to the in-plane lattice parameter. This means the out-of-plane lattice misfit is lower than the in-plane lattice misfit, contrary to behaviour expected for epitaxially grown layers. This effect was largest for layers on YSZ(111) and small for layers on YSZ(001).     

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。     

First principles study of three-component SrTiO<Subscript>3</Subscript>/BaTiO<Subscript>3</Subscript>/PbTiO<Subscript>3</Subscript> ferroelectric superlattices

The geometrical, chemical and ferroelectric properties of a new nanoscale short-period three-component SrTiO₃/BaTiO₃/PbTiO₃ perovskite superlattice are investigated using a first principles density functional approach. The study focuses on varying the thickness of each component in the superlattice and determining the resulting lattice distortion and total polarization. Thicknesses of up to three unit cells in a single component are considered and the in-plane lattice constants normal to the [001] stacking direction are fixed to the bulk SrTiO₃ values to simulate a rigid substrate. It is found that the PbTiO₃ layers play a key role in strain and polarization enhancement. By increasing the amount of PbTiO₃ in the superlattices the strain in the other components increases significantly resulting in an enhanced total polarization of the superlattice relative to bulk BaTiO₃. Increasing the number of BaTiO₃ layers also improves the overall polarization. All the SrTiO₃ layers in each superlattice are found to be highly polarized. Many of the calculated features are similar to those found previously by others for the SrTiO₃/BaTiO₃/CaTiO₃ superlattice, although in the present study significantly greater enhancement factors and polarization values are found. The predicted enhancement of the polarization is mostly attributed to lattice strain due to mismatch of the in-plane lattice constant of the three-component materials.     

Bi5Ti3FeO15薄膜的结构和多铁性研究

采用脉冲激光沉积的方法, 在Pt/Ti/SiO₂/Si衬底上生长Bi₅Ti₃FeO₁₅ (BTFO15)多铁性薄膜, 并对其结构、磁性、铁电性、铁电畴等进行了研究。通过X射线衍射、扫描电镜以及高角环形暗场像-扫描透射电镜测试, 结果表明, 薄膜具有高结晶度和完美层状晶格结构, 两层Bi原子层紧密堆积, 两层Bi₂O₂之间有三层Bi层和三层Ti(Fe)O₆八面体层, 构成三明治结构; 在室温下的磁滞回线和电滞回线证实了弱铁磁性和铁电性的共存; 采用压电响应力显微镜研究了薄膜的畴结构, 在面内和面外分别施加±3 V和±10 V的电压, 观测到了畴反转。这些研究结果对理解多铁性材料的微观结构和宏观特性的相互调制有重要意义。