钙钛矿型外延薄膜中两种分解失配位错的HRTEM研究

在（001）LaAlO3上生长钙钛矿型Ba0.3Sr0.7TiO3外延薄膜近界面层,用HRTEM观察到多种新型的分解失配位错,其中两种较复杂的分解失配位错已见报道。本文介绍在该薄膜中观察到的另外两种有趣的分解失配位错。这两种失配位错都分解成两个柏格斯矢量b=（1／2）（110）的不全位错,都与（1／2）（110）层错相伴。这些不全位错对薄膜应变松弛都有贡献,其发生与Ba0.3Sr0.7TiO3薄膜的岛状成核和莫扎克生长有关。     

分子束外延HgCdTe薄膜位错密度的研究

本文报道在晶格失配ＧａＡｓ衬底上分子束外延ＨｇＣｄＴｅ薄膜的位错密度研究结果．用位错腐蚀坑密度（ＥＰＤ）、Ｘ射线双晶衍射以及透射电子显微镜方法,对ＣｄＴｅ缓冲层以及ＨｇＣｄＴｅ薄膜的位错密度、其纵向分布及与工艺条件的相关关系进行了评价、分析．研究发现退火可以有效地降低ＨｇＣｄＴｅ薄膜的位错密度．     

AlSb／GaAs异质外延薄膜应变的HRTEM几何相位分析

用几何相位分析（geometric phasean alysis,GPA）方法研究了AlSb／GaAs畀质外延薄膜的应变。此方法基于高分辨像的傅里叶变换。通过选择傅里叶变换点分辨率以内的某个强衍射,做反傅里叶变换得到晶格条纹的相对的相位分布,进一步得到应变分布。Bragg滤波条纹像确认了60°和90°失配位错的存在。分析讨论了位错核心区域应变分布差异的可能机制。     

高失配半导体薄膜材料的纳米异质外延新技术

纳米异质外延技术是制备高失配半导体薄膜的一种纳米制作技术路线,随着超大规模集成电路纳米图样加工技术的进步,它将在制备无缺陷密度且单晶品质完美的高失配半导体薄膜材料中发挥巨大的作用。详细地综述了纳米异质外延技术的原理,介绍了纳米图样制作技术并展示了运用纳米异质外延技术在Si(111)衬底上实现高失配GaN(失配度为20%)薄膜材料及在Si(100)衬底上实现InP薄膜材料的高品质单晶外延生长。     

在c面蓝宝石上生长的InN外延薄膜中位错与极性的TEM研究

有关GaN和富Ga的InGaN薄膜中的位错和极性已有TEM研究，而InN和富In的InGaN薄膜却少见报道。研究InN薄膜中的缺陷和极性对生长高质量的InN薄膜很有意义。本文用TEM研究在c面蓝宝石上分子束外延生长的InN（760nm）／GaN（245nm）／AlN（14nm）薄膜中的穿透位错和极性。     

异质外延立方氮化硼薄膜的微结构研究

利用离子束辅助沉积技术在金刚石薄膜衬底上制备立方氮化硼薄膜,傅立叶变换红外谱的结果表明,在高度(001)织构金刚石薄膜衬底上沉积的立方氮化硼薄膜是纯的立方相,而在多晶金刚石薄膜衬底上制备的立方氮化硼薄膜中还含少量的六角氮化硼。高分辨透射电镜的分析表明,在金刚石晶粒上异质外延的c-BN直接成核于金刚石衬底,界面没有六角氮化硼过渡层;而在含有大量缺陷的晶粒边界,存在六角氮化硼的成核与生长。     

外延生长的Gd掺杂CeO2薄膜内位错的透射电子显微学表征

利用脉冲激光沉积（ pulsed laser depositon, PLD）方法在YSZ（ Y2 O3 stabilised zirconia）单晶衬底上外延生长了Gd掺杂的CeO2薄膜（gadolinium doped CeO2,GDC）。利用透射电子显微镜（TEM）对GDC／YSZ界面以及GDC薄膜内部的位错结构进行了表征。实验发现,界面处存在周期性分布的失配位错,界面失配主要通过失配位错释放。 GDC薄膜内部存在两种不同的位错,其中一种为纯刃型位错,另外一种为混合型位错。     

在(001)SrRuO_3/(001)SrTiO_3上外延生长c轴取向Bi_(3.15)Nd_(0.85)Ti_3O_(12)铁电薄膜的显微结构研究

用脉冲激光沉积在(001)SrRuO3,(001)SrTiO3上外延生长了c轴取向的Bi3.15Nd0.85Ti3O12(BNdT)铁电薄膜.SrRuO3底电极层厚约117 nm,BNdT薄膜厚～35nm.X射线衍射(XRD)和透射电镜(TEM)观察证实了SrRuO3层和BNdT薄膜的外延生长.通过TEM平面样品观察,在SrRuO3/BNdT界面附近看到了两种村度处于不同高度的失配位错网,位错线沿<110>走向,其柏格斯矢量沿[110]或[110]方向有分量,在[001]方向上可能没有分量.讨论了位错的形成机制.     

钙钛矿氧化物薄膜和异质结的外延生长与物性研究

用激光分子束外延，原子尺度控制的外延生长出多种钙钛矿氧化物薄膜和异质结．原子力显微镜和高分辨透射电镜测量结果表明，薄膜与异质结的表面和界面均达到原子尺度的光滑．制备出在可见光波段透过率大于85％的导电氧化物薄膜；物性研究结果表明，随着含氧量的不同，BaTiO3薄膜具有绝缘体、半导体和导体的不同特性。BaTiO3／SrTiO3超晶格的光学非线性效应比BaTiO3体材增大23倍．首次在La0．9Sr0．1MnO3／SrNb0．01Ti0.99O3(LSMO／SNTO)异质结上，观测到全氧化物p-n结电流和电压的磁调制与正磁电阻效应。在255K条件下，当外加磁场分别为5和1000Oe时，LSMO／SNTO p-n结的磁电阻变化率R／RO达到：46．7％和83．4％；在外加磁场为3T时，在100K条件下，在LSMO／SNTO多层p-n异质结上观测515％的正磁电阻变化率。     

Fabrication and characterization of Ti-Ba-Ca-Cu-O superconducting films on LaAlO3 substrates

A multi-step process is used to fabricate Tl₂Ba₂Ca₁Cu₂O₈ films on (100) LaA10₃ substrates. Submicron thick precursor films of Ba-Ca-Cu-O are rf magnetron sputter deposited from a single target. Film stoichiometry is measured by ion beam backscattering spectroscopy. Deficiencies of the alkaline earths that are found in the precursor films are then compensated for by the addition of appropriate CaF₂ and/or BaF₂ films onto the surface of the precursor film. Post deposition annealing of the films is then done in an atmosphere of thallium oxide and oxygen in order to form the superconducting phases. The annealed films are examined using x-ray diffraction (XRD), an ac inductance technique, and critical current in an external magnetic field. XRD shows the c-axis length of the superconducting phase to increase as the overall film stoichiometry approaches 2212. The transition widths measured by inductive coupling weakly correlate with 77 K critical current measurements. Our best critical current results are 1.5*10⁶ amps/ cm² for a film measured at 4 K in an 8 T magnetic field (parallel to the films' c-axis).     

LaAlO3单晶基片上制备Ba0．5Sr0．5TiO3薄膜的透射电镜研究

铁电钛酸锶钡(Ba1-xSrx)TiO3(BSTO)薄膜材料具有很好的可调性，在微电子工业有广阔的应用前景。本文采用脉冲激光沉积(PLD)技术在(001)LaAlO3单晶基片上外延生长了Ba0.5Sr0.5TiO3薄膜。利用透射电子显微镜对薄膜的截面样品进行了微结构和界面行为的研究。     

Microwave performance-property relationships of YBa2Cu3O7-δ thin films grown on LaAlO3 (001) substrate

We report correlations between growth parameters, structure and microwave performance for YBa₂Cu₃O7-δ (YBCO) thin films. Two series of YBCO thin films were grown byin-situ laser ablation. The first series were deposited at 100 mTorr oxygen pressure with a laser fluence of 2.9 Joule/cm², the second series were deposited at 600 mTorr of oxygen and a higher laser fluence of 5 Joule/cm². Microwave performance of these films was evaluated using a 5.6 GHz resonator. In both series, we found that films with higherT _c , narrower x-ray rocking curve width, and sharper electron channeling pattern tend to have higher microwave resonator Qs. Optimal film growth conditions were infered from this systematic study. Films grown at higher oxygen pressure have smoother surfaces and fewer second phases.     

Oxygen Stoichiometry Effect on Polar Properties of LaAlO3/SrTiO3

Discovery of a ferroelectric‐like behavior of the LaAlO₃/SrTiO₃ (LAO/STO) interfaces provides an attractive platform for the development of nanoelectronic devices with functionality that can be tuned by electrical or mechanical means. However, further progress in this direction critically depends on deeper understanding of the physicochemical mechanism of this phenomenon. In this report, this problem by testing the electronic properties of the LAO/STO heterostructures with oxygen stoichiometry used as a variable is addressed. Local probe measurements in conjunction with interface electrical characterization allow to establish the field‐driven reversible migration of oxygen vacancies as the origin of the ferroelectric‐like behavior in LAO/STO. In addition, it is shown that oxygen deficiency gives rise to the formation of micrometer‐long atomically sharp boundaries with robust piezoelectricity stemming from a significant strain gradient across the boundary region. These boundaries are not ferroelectric but they can modulate the local electronic characteristics at the interface. The obtained results open a possibility to design and engineer electromechanical functionality in a wide variety of nominally nonpolar and non‐piezoelectric complex oxide heterostructures and thin films.     

层状钙钛矿铁电薄膜的层错结构研究

由于铁电薄膜具有工作电压低、读写速度快及较好的耐久性等优点,在非易失存储器(FRAM)方面受到人们的广泛重视。在过去的十年里,研究的重点集中在Pb(Zr,Ti)O3(PZT)系铁电薄膜材料,但由于该系材料存在严重的疲劳现象,限制其在FRAM器件上的应用。近年来,铋系层状钙钛矿结构的铁电薄膜材料在FRAM器件中的应用与日俱增。SrBiTa2O9(SBT)铁电薄膜作为铋系层状钙钛矿结构材料的代表,它具有优良的耐疲劳特性(极化反转次数高达1012次)和较好的保持力特性,成为制备FRAM器件的首选材料[1]。虽然人们对SBT铁电薄膜的制备工艺、电学性能及…     

无卷边单分子层WS2纳米片原子结构的高分辨电子显微术研究

本文利用高分辨电子显微术(HRTEM)确定了无卷边的单分子层WS2纳米片的原子结构像.通过对样品不同区域HRTEM像进行傅里叶变换(FFT)分析,得到了各个区域的WS2纳米片的晶体取向,确定了WS2纳米片分子层数分布.根据电子显微像强度与样品层数的线性关系以及WS2纳米片的单分子层数分布模型,确定不同区域WS2纳米片的分子层数.为了进一步定量分析结果的正确性,通过模拟电子显微像在不同碳膜厚度及不同成像条件下WS2纳米片的HRTEM像,也确定了在像衬度上与实验像很好的匹配.     

(1-x)LaAlO_3-xSrTiO_3陶瓷结构及介电性能研究

采用固相法制备了钙钛矿型(1-x)LaAlO_3-xSrTiO_3介质陶瓷,研究了其烧结特性、显微结构和介电性能。结果表明,随SrTiO_3含量增加,陶瓷主晶相由三方相变化为正交相,再到立方相;相对介电常数εr、谐振频率温度系数τf随SrTiO_3含量增加而增加,介电损耗tanδ与陶瓷相结构转变有关。当x=0.46,且在1 550℃烧结4h,试样晶粒发育良好,结构致密,晶界清晰,可得介电性能εr=35.7,tanδ=3.01×10~(-4),τf=-14.6×10~(-6)/℃。