高温超导YBa2Cu3O7-δ-Y2O3多层薄膜的制备及性能表征

采用脉冲激光沉积技术(PLD)在LaAlO3(100)单晶衬底上外延生长YBa2Cu3O7-δ-Y2O3多层薄膜,用X射线衍射技术(XRD)分析薄膜的物相结构和外延特性,通过原子力显微镜(AFM)观察薄膜的表面形貌.本文主要研究了最佳工艺参数下交替生长多层YBCO-Y2O3膜的超导性能.结果表明,YBa2Cu3O7-δ-Y2O3薄膜为纯c轴取向外延生长,临界电流密度Jc(H=0或H//C)均高于纯YBCO薄膜,纳米Y2O3起到磁通钉扎中心作用.     

NiFe2O4外延薄膜的制备及后退火效应研究

本文利用脉冲激光沉积方法制备了NiFe2O4磁性绝缘薄膜.X-射线衍射线性扫描测量表明,在MgO(110)单晶衬底上可以生长出高质量的NiFe2O4外延薄膜,原子力显微镜显示其具有平整的表面形貌.我们还研究了后退火处理对样品结构、表面形貌和磁性的影响.结果表明,后退火后薄膜的结构和表面形貌都发生了明显的改变,样品的磁性得到增强.这些效应可归结为在氧气氛下退火处理导致的氧含量的变化以及退火过程中阳离子分布和价态发生改变.     

制备45°双外延超导结的新工艺

我们使用脉冲激光沉积方法对YBa2Cu3O7-δ(YBCO)薄膜在MgO基片上通过CeO2/YSZ双缓冲层的生长进行了系统的研究,发现MgO单晶基片的表面质量是决定能否得到理想外延薄膜质量的关键因素,通过使用低能离子束对MgO表面进行轰击,以增加其表面粗糙度和去除变质层,得到了具有100%面内45°旋转的YBCO外延膜,其临界电流密度77K时在106A/cm2量级.通过湿法刻蚀得到的双外延Josephson结表现出RSJ特性.     

Fe3O4/MgO(100)薄膜的激光分子束外延与磁电学性能

 采用激光分子束外延方法,以烧结α-Fe₂O₃/为靶材,在MgO（100）基底上制备了Fe₃O₄薄膜。通过反射高能电子衍射原位观察了薄膜生长前后的表面结构,结果表明所生长的Fe₃O₄薄膜表面平整。经显微激光拉曼光谱和X光电子能谱分析证实所得薄膜表面成分为纯相Fe₃O₄。磁电学性能采用多功能物性系统测量,结果表明：当温度降至100 K附近时,薄膜电阻率有较大增加,Verwey相转变的范围变宽而且不明显,说明反向晶粒边界的存在;在7 160 kA·m^-1的磁场下,室温磁电阻达到-6.9%,在80和150 K温度下磁电阻分别达到-10.5%和-16.1%;薄膜的室温饱和磁化强度约为260 kA·m^-1,其矫顽磁场约为202 kA·m^-1。     

TiO薄膜的制备及电输运性质

利用磁控溅射技术,通过改变氧分压在MgO (001)单晶基片上外延生长了一系列TiO薄膜,并对薄膜的结构、价态和电输运性质进行了系统研究. X射线衍射结果表明,所制备的薄膜具有岩盐结构,沿[001]晶向外延生长. X射线光电子能谱结果表明,薄膜中Ti元素主要以二价形式存在.所有样品均具有负的电阻温度系数,高氧分压下制备的薄膜表现出绝缘体的导电性质,低温下电阻与温度的关系遵从变程跳跃导电规律.低氧分压下制备的薄膜具有金属导电性质,并具有超导电性,超导转变温度最高可达3.05 K.所有样品均具有较高的载流子浓度,随着氧分压的降低,薄膜的载流子类型由电子主导转变为空穴主导.氧含量的降低可能加强了TiO中Ti—Ti键的作用,从而使低氧分压下制备的样品显现出与金属Ti相似的电输运性质,薄膜超导转变温度的提升可能与晶体结构或电子结构突变相关联.     

MgO和Si上NbN超薄薄膜的生长研究

我们在单晶MgO(100)、Si(100)和SiOx/Si基片上成功生长了纳米厚度的超薄NbN薄膜,利用现代分析手段:X射线衍射(XRD)、透射电子显微镜(TEM)、原子力显微镜(AFM)等技术分析研究了所制备的超薄NbN薄膜的微观结构、厚度、表面界面情况等物理特性。研究表明,在MgO(100)基片上获得了外延生长的单晶NbN超薄薄膜,在Si(100)和SiOx/Si基片上获得的是多晶NbN超薄薄膜。厚度均约6nm左右。这些超薄薄膜的超导转变温度分别为:MgO上薄膜是14.46K,Si和SiOx上薄膜分别是8.74K和9.01K.     

Fe3O4薄膜的电输运及光诱导特性研究

用脉冲激光沉积法在(111)Si衬底上成功制备了高度择优取向的Fe₃O₄薄膜.电阻-温度关系表明Fe₃O₄薄膜的Verwey转变(T_V)约在122 K,低温段(T_V)输运特征满足Mott变程跳跃模型,高温段(T>T_V)为小极化子输运.激光作用下的光电导实验发现,在整个温区表现为光致电阻率减小,而且低温段的电阻变化率比高温段要大很多.分析认为Fe₃O₄薄膜的光致电阻率变化主要与激光激发t_2g电子的转移有关. 关键词： 3O₄薄膜')" href="#">Fe₃O₄薄膜 小极化子 光诱导特性     

SrRuO3超薄膜制备条件和拓扑霍尔效应的关联

使用激光分子束外延在SrTiO₃(001)衬底上生长SrRuO₃薄膜,并研究激光能量密度、生长温度和靶材表面烧蚀度等生长参数对于SrRuO₃表面形貌、基本磁电性质以及拓扑霍尔效应的影响.当在最优条件下生长SrRuO₃薄膜时,样品表面平整、台阶清晰,具有最低的金属-绝缘体转变温度,电阻率最低,且具有最显著的拓扑霍尔效应;而改变生长参数生长的SrRuO₃薄膜由于存在更多的缺陷,其表面较粗糙,金属-绝缘体转变温度增大,或表现出绝缘体行为,而拓扑霍尔效应会变弱甚至消失.     

无氟PA-MOD法制备SmBa2Cu3O7-x薄膜的热处理研究

采用无氟(PA-MOD)在(00l)取向的LaAlO3单晶基底上制备SmBa2Cu3O7-x(SmBCO)超导薄膜,研究了不同成相热处理温度对薄膜性能的影响.X射线衍射(XRD)分析结果表明,经过高温处理的SmBCO薄膜其晶粒具有良好的c轴生长取向.扫描电镜(SEM)分析表明,790℃成相的SmBCO薄膜的表面更加平整致密.物理性能测试系统(PPMS)测试结果表明SmBCO样品的超导临界温度Tc为89.74K.研究了高温热处理过程中不同熔融温度制备SmBCO薄膜的影响.     

YBa2Cu3O7-δ薄膜微结构的同步辐射三维倒空间扫描研究

高温超导薄膜因其微波表面电阻低,可用于尖端高温超导微波器件的制作.然而由于高温超导材料特殊的二维超导机制和极短的超导相干长度,高温超导材料的微波表面电阻对微结构特别敏感.为了探究高温超导材料微结构和微波电阻的联系,采用脉冲激光沉积(PLD)技术在(001)取向的MgO单晶衬底上生长了不同厚度的YBa₂Cu₃O_7-δ(YBCO)薄膜.电学测量发现不同厚度的样品超导转变温度、常温电阻差别不大,但超导态的微波表面电阻差异很大.同步辐射三维倒空间扫描(3D-RSM)技术对YBCO薄膜微结构的表征表明:CuO₂面平行于表面晶粒(c晶)的多寡、晶粒取向的一致性是造成超导态微波表面电阻差异的主要原因.     

热处理对MgO基片的表面形貌以及对CeO_2和Tl-2212薄膜生长的影响

研究了MgO基片在高温退火时表面形貌和表面结构的变化,以及它对CeO2缓冲层和Tl-2212超导薄膜生长的影响。原子力显微镜(AFM)研究表明,在流动氧环境中1100℃温度下退火,MgO的表面首先由未退火时的皱褶形貌,演化为光滑表面,随着退火时间的延长,表面形貌最终演化为具有光滑基底的独立生长峰结构。XRD测试表明,通过高温热处理可以大幅度提高MgO基片表面结晶的完整性。在1100℃温度下热处理8小时的MgO基片上可以生长出具有高度c轴取向的CeO2(001)缓冲层。然后在此缓冲层上制备了厚度为500nm的外延Tl-2212超导薄膜,其临界转变温度(Tc)达到108.6K,液氮温度下临界电流密度(Jc)为2.8mA/cm2,微波表面电阻Rs(77K,10GHz)约为360.9μΩ。     

‘In-situ’ ink-jet printed Fe-doped MgO thin films with tunable ferromagnetism

Magnetism in wide band gap materials is of great interests for future spintronic device applications. We prepared MgO and Fe-doped MgO films ‘in-situ’ on substrates by inkjet printing, and investigated the ferromagnetism tuned by the doping of Fe, the annealing temperature and the film thickness. It is found that the Fe-doping improves the crystallinity of the films with lattice structure changed by annealing temperature. The saturation magnetization (M_s) of the films enhanced by ~5 times comparing with the pure MgO thin film of similar thickness (~90 nm), because of both the long-range ordering of localized 3d electrons in Fe and the defects induced magnetism. The M_s at 5 K decreases with the film thickness, which is mainly attributed to the interface induced ferromagnetism. The Fe-doped MgO films with ferromagnetism in this work can be used in future spintronic devices.     

双层锰氧化物薄膜的制备及其物理性质

用脉冲激光沉积(PLD)方法成功地制备了双层钙钛矿结构的La2-2xSr1+2xMn2O7(x=032)单相薄膜.这种薄膜生长在具有不同晶格参数的两种衬底上.测量发现，两种衬底上生长的La2-2xSr1+2xMn2O7(x=032)薄膜具有迥然不同的金属-绝缘体转变温度TM-I及其他物性.界面应力的研究表明这是衬底晶格常数不同引起膜内应变的结果.在衬底的压应力下，薄膜的电阻-温度曲线的峰值(TM-I)向高温移动且电阻率(ρ)下降；相反，对于衬底张应力下的薄膜，TM-I下降ρ上升.这些结果可以用双交换模型做很好的解释. 关键词： CMR 双层锰氧化物薄膜 PLD 应力     

Characteristics of Ni films deposited on SiO2/Si(1 0 0) and MgO(0 0 1) by direct current magnetron sputtering system with the oblique target

280 nm-thick Ni films were deposited on SiO₂/Si(1 0 0) and MgO(0 0 1) substrates at 300 K, 513 K and 663 K by a direct current magnetron sputtering system with the oblique target. The films deposited at 300 K mainly have a [1 1 0] crystalline orientation in the film growth direction. The [1 1 0]-orientation weakens and the [1 1 1]- and [1 0 0]-orientations enhance with increasing deposition temperature. The lattice constant of the Ni films is smaller than that of the Ni bulk, except for the film grown on MgO(0 0 1) at 663 K. Furthermore, as the deposition temperature increases, the lattice constant of the films grown on the SiO₂/Si(1 0 0) decreases whereas that of the films grown on the MgO(0 0 1) increases. The films deposited at 300 K and 513 K grow with columnar grains perpendicular to the substrate. For the films deposited at 663 K, however, the columnar grain structure is destroyed, i.e., an about 50 nm-thick layer consisting of granular grains is formed at the interface between the film and the substrate and then large grains grow on the layer. The Ni films deposited at 300 K consist of thin columnar grains and have many voids at the grain boundaries. The grains become thick and the voids decrease with increasing deposition temperature. The resistivity of the film decreases and the saturation magnetization increases with increasing deposition temperature.     

Spin-resolved photoelectron spectroscopy of the MgO/Fe(110) system

The surface structure and electronic properties of ultrathin MgO layers grown on epitaxial Fe(110) films were investigated at room temperature by means of electron diffraction, Auger electron spectroscopy, scanning tunneling microscopy, and spin-resolved photoelectron spectroscopy. The spin polarization at the Fermi level (E_F) of the Fe(110) film decreases sharply with increasing thickness of the MgO layer. This behavior arises from the formation of a thin FeO layer at the MgO(111)/Fe(110) interface, as revealed by structural and spectroscopic investigations. The strong attenuation of the intrinsic spin polarization is qualitatively attributed to the scattering of spin-polarized electrons at the unoccupied d-orbitals of Fe²⁺. PACS 68.35.-p; 68.55.-a; 73.20.r; 75.70.Cn; 79.60.-I     

Epitaxial growth and magnetic exchange anisotropy in Fe3O4<Emphasis Type="Bold">/NiO bilayers grown on MgO(001) and Al</Emphasis>2O3(0001)

Epitaxial Fe3O4/NiO bilayers were epitaxially grown on MgO(001) and Al2O3(0001) substrates to investigate the influence of the fully spin compensated (001) and the non-compensated (111) NiO interface planes between the ferromagnetic (F) and antiferromagnetic (AF) layers on the AF/F exchange coupling. Bilayers of different magnetite thicknesses and constant NiO thickness were investigated. The structural characterizations indicate a perfect epitaxy of the two layers for the both growth directions in the two Fe3O4/NiO/MgO(001) and NiO/Fe3O4/Al2O3(0001) systems. An epitaxial ferrimagnetic (Ni,Fe)Fe2O4 phase is observed at the AF/F interface when the NiO oxide is grown on the top of the Fe3O4 layer while a perfectly flat AF/F interface is observed in the Fe3O4/NiO/MgO(001) system exhibiting only a very slight interdiffusion. Magnetic measurements indicate a relative strong bias at 300 K for the bilayers grown on Al2O3(0001), which decreases with the inverse of the ferrimagnetic layer thickness as theoretically expected. On the contrary, a zero exchange biasing is observed at 300 K for the bilayers grown on MgO(001).     

Growth of thin Fe(0 0 1) films for terahertz emission experiments

The electrical and magnetic properties of thin iron (Fe) films have sparked significant scientific interest. Our interest, however, is in the fundamental interactions between light and matter. We have discovered a novel application for thin Fe films. These films are sources of terahertz (THz) radiation when stimulated by an incident laser pulse. After intense femtosecond pulse excitation by a Ti:sapphire laser, these films emit picosecond, broadband THz frequencies. The terahertz emission provides a direct measure of the induced ultrafast change in magnetization within the Fe film. The THz generation experiments and the growth of appropriate thin Fe films for these experiments are discussed. Several criteria are used to select the substrate and film growth conditions, including that the substrate must permit the epitaxial growth of a continuous, monocrystalline or single crystal film, yet must also be transparent to the emitted THz radiation. An Fe(0 0 1) film grown on the (0 0 1) surface of a magnesium oxide (MgO) substrate makes an ideal sample. The Fe films are grown by physical vapor deposition (PVD) in an ultrahigh vacuum (UHV) system. Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) are used to characterize the Fe(0 0 1) films. Two substrate surface preparation methods are investigated. Fe(0 0 1) films grown on MgO(0 0 1) substrates that are used as-received and films grown on MgO(0 0 1) substrates that have been UV/ozone-cleaned ex vacuo and annealed in vacuo produce the same results in the THz generation experiments. Either substrate preparation method permits the growth of samples suitable for the THz emission experiments.     

Fabrication of YBCO／YSZ and YBCO／MgO thick films using electrophoretic deposition with top-seeded melt growth process

Superconducting thick films were grown on single crystals MgO and YSZ by electrophoretic deposition with Y_2BaCuO_5(Y211) addition. YBCO thick films were then accomplished by sintering the precursor films above the peritectic temperature. Single crystals of MgO (3×3×0.5 mm^3) were used as top-seed to control crystal structure of the thick films. As shown by scanning electron microscopy, the morphologies of YBCO/YSZ and YBCO/MgO thick films are spherulitic texture and platelet type. The critical temperature is ～89 K for the YBCO/YSZ thick film; the onset transition temperature is 86.4 K and the transition width is ～3 K for YBCO/MgO thick film. The critical current densities (as determined by Bean model) are, in A/cm^2, 3870 (77 K) for YBCO/YSZ thick films and 2399 (77 K) for YBCO/MgO thick films, which are comparable to the best J_c reported of the thick films prepared by the same method.     

Research on temperature field characteristics of optical films under 1064 nm short-pulse laser radiation

The 3-D temperature field distribution (TFD) equation of optical films (OFs) was analyzed, based on the film temperature field distribution (FTFD) model irradiated by Gaussian short-pulse laser, and short-pulse laser-induced temperature field distribution of TiO₂/SiO₂ composite membranes on K9 glasses was obtained by means of numerical simulation. The results show that the thermal effect of optical films is very obvious under the Gaussian short-pulse laser. Temperature at the center of the spot rises faster than in other areas, and it decreases along the radius rapidly. It provides theoretical basis for progress analysis of short-pulse laser acting on optical films.