BST类氧化物铁电薄膜的生长研究

利用脉冲激光分子束外延(PLMBE)并结合反射式高能电子衍射(RHEED)方法,针对BST类氧化物铁电薄膜的生长机理进行了较为系统的实验研究。通过生长模式、生长相图、弛豫时间等的变化规律提出氧化物薄膜的原胞生长机理,通过原位实时监测生长过程获得～300℃的最低层状晶化温度,通过界面形成的压应力、张应力调控薄膜表面的形貌结构,通过不对称介质超晶格的设计获得高性能的铁电极化强度,通过过渡层技术在Si基片上实现了铁电薄膜取向生长等。     

拓扑绝缘体Bi2Se3光电性能研究

文章基于分子束外延法(molecular beam epitaxy,MBE)制备高质量的硒化铋(Bi_2Se_3)薄膜,运用反射式高能电子衍射仪(reflection high-energy electron diffraction,RHEED)表征样品的生长质量。在Bi_2Se_3和Ge上将蒸镀铟(In)电极和银(Ag)电极分开,并将其制成肖特基结光电探测器,据此测量了样品在不同波长激光和不同温度下的光响应特性及低温对样品的影响,并通过计算样品的响应度、开关比、探测率等参数分析了拓扑绝缘体在光电探测方面的应用前景。     

反射式高能电子衍射对氧化物薄膜生长的原位监测

反射式高能电子衍射是一种对薄膜表面结构非常敏感的实时监测手段,通过对衍射花样的研究可以获得诸多有益的信息,将其引入薄膜制备装置对高质量薄膜的生长有着积极的指导意义.     

外延Pb-Zr-Ti-O/Y-Ba-Cu-O异质结的制备研究

应用磁控溅射法在SrTiO3(STO)单晶基片上原位制备了Pb(Zr,Ti)O3/YBaCu3O7(PZT/YB-CO)异质结,X射线衍射、透射电镜和选区电子衍射结果表明PZT/YBCO为外延生长,磁化率的测量结果表明YBCO的超导转变温度接近90 K,外延铁电体/超导体异质结的制备为进一步研究铁电性、超导性以及铁电体/超导体复合器件奠定了基础.     

Si在GaP(111)衬底上的分子束外延

在用分子束外延技术制备半导体异质结时,选择晶格常数相匹配的材料是获得高质量外延膜的关键因素之一.Si和GaP这两种材料的晶格失配仅为0.37%,而且它们的热膨胀系数和弹性常数也非常接近,因此Si/GaP系统是一种非常适用于分子束外延生长的结构.本文对这一体系的外延生长特性作了初步的研究. 外延生长是在一台超高真空电子束蒸发装置中进行的,它由相互间可以隔离的生长室、分析室和进样室三部分组成.生长室中配有8kW的电子束蒸发器、石英晶体厚度监视器、高能电子衍射仪(RHEED)、液氮冷屏罩和一个可使样品自转的样品架.生长室的极限真空度可达8×10~(-9)Pa,工作时压强保持在1×10~(-7)Pa.Si的蒸发速率为0.4A/S,     

Pr掺杂对SrTiO3薄膜光学性能的影响

采用金属有机物分解法在石英衬底上制备了Pr掺杂SrTiO3薄膜材料,并对其光学性能进行了研究。Raman谱显示Pr掺杂SrTiO3样品中存在极性纳米微区。另外,所有样品都表现出高的光学透过率,并且Pr的含量对样品的透过率和能隙都有明显影响,这与Pr掺杂造成样品的晶粒大小、晶格常数、结晶度以及氧空位浓度的变化有关。     

应变SrTiO_3/GaAs异质结的整流特性研究

采用脉冲激光沉积法在P型GaAs基片上制备了缺氧的钛SrTiO3薄膜.X射线衍射测量证明SrTiO3薄膜外延生长.I-V曲线测量显示很好的整流性,说明该SrTiO3薄膜与GaAs形成p-n结.该结的电输运机制为应变导致的隧穿电流,且其电输运性质不受光照影响.     

稀土CeO2纳米固溶体粉末晶格常数与成分的关系

氧化物的晶格常数是材料研究和运用的一个重要参数. 从理论上预测氧化物固溶体的晶格常数是物理学家和材料学家从理论上研究物性参数的方法之一. 经研究, 推导出了计算立方CeO₂ 纳米固溶体晶格常数与固溶体成分关系的方程. 将理论计算纳米氧化物固溶体的晶格常数的方程用于CeO₂ - ZrO₂, CeO₂ - Bi₂O₃ , CeO₂ - La₂O₃, CeO₂ - ZrO₂ - ThO₂ 纳米固溶体晶格常数的计算, 发现晶格常数随固溶体成分变化与立方CeO₂纳米固溶体晶格常数实验结果基本一致, 误差不大于0. 3% , 1. 7%, 3. 4%, 0. 4%.     

退火温度对溅射Al膜微结构及光学常数的影响

用直流溅射镀膜工艺在室温Si基片上制备了250nm厚的Al膜,并用X射线衍射及反射式椭偏光谱技术,对薄膜的微结构和光学常数在不同退火温度下的变化进行了测试分析。结构分析表明:退火后的Al膜均呈多晶状态,晶体结构仍为面心立方;随着退火温度由室温20℃左右升高到400℃,薄膜的平均晶粒尺寸由22.8nm增加到25.1nm;平均晶格常数(4.047)略比标准值4.04960小。椭偏光谱测量结果表明:2600～8300光频范围内,退火温度对折射率n影响较小,对吸收系数k的影响较为明显。     

YBaCo4O7及YBaCo4O8.5中六角超结构的电子衍射分析

制备了氧化学剂量样品.YBaCo4O7,通过电子衍射谱分析确定为六角结构,晶格常数a=0.629(5)nm,c=1.023(5)nm;制备的氧非化学剂量样品YBaCo4O8.5中,过量的氧是以超结构的方式存在.通过电子衍射方法确定了其中一种六角超结构相,其晶格参数as=bs=1.090(4)am,cs=1.002(6)...     

等离子体清洗GaAs和Al2O3衬底的RHEED图像分析

针对GaAs和Al2O3作为外延GaN薄膜的主要衬底材料,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-PEMOCVD)工艺对其分别进行纯氢、氢氮等离子体清洗,并配备高能电子衍射仪(RHEED)实时监测清洗过程．CCD的RHEED图像分析表明,在一定条件下用纯氢等离子体对GaAs衬底清洗只需1min左右,即可得到比较平整的清洗表面,但清洗2min以上表面质量开始变坏．若在氢气中加入少量氮气,清洗时间可延长至10min左右．而Al2O3衬底对纯氢等离子体的清洗时间比较敏感,清洗2min左右就能获得平整的清洗表面,若时间延长到4min,表面质量将开始变坏．如果采用氢氮等离子体清洗,约需20min时间,而且在很宽的清洗时间范围(20～30min)内都能获得良好的清洗表面．     

Tuning the magnetic anisotropy in LSMO manganite films through non-magnetic nanoparticles

We report the observation of anomalous magnetic anisotropy driven by nonmagnetic ZrO2 nanoparticles in epitaxial La2/3Sr1/3MnO (LSMO) films grown on LaAlO3 (LAO) substrates. The compressive epitaxial strain imposed by the lattice mismatch of substrate and film is tuned by the density of ZrO2 nanoparticles embedded in the film matrix and affects the magnetic anisotropy as well as the magnetotransport properties. Epitaxial 54 nm thick LSMO thin films with different concentrations of ZrO2 nanoparticles demonstrate anisotropic hysteresis loops concomitant with anisotropic magnetotresistance behavior. The biaxial epitaxial strain, induced by the substrate/film lattice parameter mismatch is partially relaxed by increasing the density of precipitates and they serve as a tuning parameter for the strain state. We interpret our results by a strain-induced interplay of impurity scattering, weak localization and magnetic domain structure.     

La0.7Sr0.3MnO3外延膜厚度引起的电阻率变化

不同厚度的La0.7Sr0.3MnO3(LSMO)外延薄膜被沉积到立方相的LaA lO3(001)单晶衬底上,XRD测试结果显示,LSMO外延膜的结构是单相的,具有与衬底相同的晶格取向;随着膜厚的增加,LSMO外延膜的晶格经历应变到驰豫的变化.电阻测量显示,应变驰豫的薄膜(较厚的薄膜)有较大的电阻率,这与该膜中缺陷浓度增加有关.此外,也对生长在不同单晶衬底上的LSMO外延膜(厚度相同)的结构和电阻进行了对比研究.     

For progress in natural science: Materials international investigations of structural phase transformation and THz properties across metal–insulator transition in VO_2/Al_2O_3 epitaxial films

Vanadium dioxide (VO2) epitaxial thin films on (0001)-oriented Al2O3 substrates were prepared using radio frequency (RF) magnetron sputtering techniques. To study the metal-insulator-transition (MIT) mechanism and extend the applications of VO2 epitaxial films at terahertz (THz) band, temperature-dependent X-ray diffraction (XRD) and THz time domain spectroscopy of the VO2 epitaxial films were performed. Both the lattice constants and THz transmission exhibited a similar and sharp transition that was similar to that observed for the electrical resistance. Consequently, the MIT of the VO2/Al2O3 epitaxial films should be co-triggered by the structural phase transition and electronic transition. Moreover, the very large resistance change (on the order of ~103) and THz response (with a transmission modulation ratio of ~87%) in the VO2/Al2O3 epitaxial heterostructures are promising for electrical switch and electro-optical device applications.     

Structure and magnetic properties of Ni50Mn35In15 thin film

Thin film of Ni50Mn35In15 Heusler alloy was prepared on Mg O(001) substrate by epitaxial growth in an ultra-high vacuum(UHV) chamber by a Pulsed Laser Deposition(PLD) method. The epitaxial growth process was monitored by in situ reflection high energy electron diffraction(RHEED) and the structure of the film was checked by ex situ X-ray diffraction(XRD), which indicates that high quality Ni50Mn35In15 single crystal film with a face-centered-cubic(fcc) structure could be stabilized on Mg O(001). Magnetic property measurement was also conducted at various temperatures by using physical property measurement system(PPMS). A significant exchange bias was observed for Ni50Mn35In15 film,and the strength of the exchange bias field(HEB) increases with the decrease of temperature. Such a behavior can be ascribed to the fact that the interfacial spin interaction between ferromagnetic(FM) and antiferromagnetic(AFM) cluster is enhanced with the decrease of temperature.     

Epitaxial growth of single-crystalline Ni46Co4Mn37In13 thin filmand investigation of its magnetoresistance

Single-crystalline thin film of Ni46Co4Mn37In13alloy grown on MgO(0 0 1) was prepared by Pulsed Laser Deposition(PLD) method. The epitaxial growth process was monitored by in situ Reflection High Energy Electron Diffraction(RHEED). Structure measurements reveal that the single-crystalline Ni46Co4Mn37In13film could be stabilized on MgO(0 0 1) as a face-centered-cubic(fcc) structure. From the evolution of RHEED,it can be deduced from the patterns that Volmer-Weber growth mechanism(3-D) dominates at the initial stage. Then,it becomes layerby-layer growth mechanism(2-D) with the increase of the film thickness. Lastly,growth mechanism converts back to 3-D when the film is thick enough. Both electrical resistance and magnetoresistance(MR) were measured at various temperatures using Physical Property Measurement System(PPMS). The electrical resistance measurement indicates that the film sample does not have martensitic transformation in the measurement temperature range. However,with the temperature increasing,the film sample exhibits a transition from metallic to semiconductorlike properties. Moreover,a small negative magnetoresistance was observed at different temperature,which can be explained by the spindependent scattering of the conduction electrons.     

衬底材料对Bi4Ti3O12薄膜取向度的影响

以正丁醇钛和硝酸铋为原料,用Ｓｏｌ－Ｇｅｌ技术分别在Ｐｔ／Ｔｉ／Ｓｉ、Ｓｉ、Ｙ－ＺｒＯＴｉＯ３（１００）和石英玻璃基片上生长出ｃ轴取向的Ｂｉ４Ｔｉ３Ｏ１２薄膜,研究了衬底材料表面结构对Ｂｉ４Ｔｉ３Ｏ１２薄膜取得度的影响,晶格失配能和Ｂｉ４ＴｉＯ１２晶体的晶面能决定了薄膜的取向程度。     

TiN/Si3N4界面结构对Ti-Si-N纳米晶复合膜力学性能的影响

采用多层膜模拟的方法研究了Ti-Si-N纳米晶复合膜中Si3N4界面相的存在方式,以探讨纳米晶复合膜的超硬机制。研究结果表明：Si3N4层厚对TiN／Si3N4多层膜的微结构和力学性能有重要影响。当Si3N4层厚小于0．7nm时,因TiN晶体的“模板效应”,原为非晶态的Si3N4晶化,并反过来促进TiN的晶体生长,从而使多层膜呈现TiN层和Si3N4层择优取向的共格外延生长。相应地,多层膜产生硬度和弹性模量升高的超硬效应,最高硬度和弹性模量分别为34．0GPa和352GPa．当层厚大于1．3nm后,Si3N4呈现非晶态,多层膜中TiN晶体的生长受到Si3N4非晶层的阻碍而形成纳米晶,薄膜的硬度和弹性模量亦随之下降。由此可得,Ti-Si-N纳米晶复合膜的强化与多层膜中2层不同模量调制层共格外延生长产生的超硬效应相同。     

PLD制备LiMn2O4薄膜及参数对薄膜微观结构的影响

用脉冲激光沉积（PLD）,分别在不锈钢和单晶硅（111）衬底上生长了LiMn2O4薄膜,并对所生长LiMn2O4薄膜的结构进行了研究。结果发现,生长在不锈钢衬底上的薄膜具有粗糙的表面和随机的结晶取向,生长在单晶硅衬底上的薄膜具有相对光滑的表面,并具有明显的（111）方向上的择优取向。还研究了脉冲频率和总脉冲数对薄膜生长的影响,结果显示,在相同的沉积条件下,对于不同衬底,LiMn2O4薄膜的生长率不同;脉冲频率对薄膜生长的影响明显,在相同总脉冲数情况下,脉冲频率大,薄膜生长率明显增大。