溶胶-凝胶法制备YBa2Cu3O7-x超导薄膜的研究

传统的TFA-MOD法制备YBa2Cu3O7-x薄膜,采用Y、Ba、Cu 3种金属的三氟醋酸盐(TFA)为先驱体,在热分解时,会产生大量的HF气体,即使通过将近20h的缓慢升温过程来对薄膜进行热分解,也难以获得较为光洁的表面,从而无法实现厚膜的制备.本文提出了一种新的含氟溶胶-凝胶工艺,通过减少溶胶中F的含量,并利用二乙醇胺做修饰剂,缩短了热分解时间,提高了薄膜的表面光洁度.利用该方法在(010)LaAlO3衬底上制备了具有良好c轴取向,临界转变温度为89K的YBCO超导薄膜.     

Formation of copper oxide films on fiberglass by adsorption and reaction of cuprous ions

We have used chemical deposition of copper complex solution to prepare CuO thin films on commercial fiberglass. The deposition of copper oxides was done in a beaker using a solution of thiosulfatocuprate (I) as precursor and NaOH as a film conditioner. In order to establish a correlation between experimental conditions and the produced copper species, as well as the film quality, the as deposited and annealed samples were characterized using X-ray diffraction, visible spectrophotometry and atomic force microscopy. The most important result is that a Cu₂O 80-nm film can be obtained directly with a short immersion of fiberglass into the copper solution. The film growth of this copper phase occurred in [111] and [200] directions. Moreover, this phase is converted to CuO by annealing at 375 °C.     

Si(100)衬底上激光分子束外延制备高质量TiN薄膜

采用激光分子束外延(LMBE)技术在Si(100)上制备了高质量的TiN薄膜.对N2分压和激光脉冲能量对TiN薄膜晶体结构、生长模式和表面形貌影响的研究表明,TiN单晶薄膜呈(200)择优取向,在N2分压为10-1 Pa时,薄膜的结晶度高且表面平整致密.随着N2分压的增加,TiN(200)衍射峰向低角度移动.激光脉冲能...     

Growth of stoichiometric TiO2 thin films on Au(100) substrates by molecular beam epitaxy

The present study reports on the growth of thin TiO₂ films onto Au(100) single crystals by Ti evaporation in a reactive O₂ atmosphere at two different substrate temperatures: room temperature (RT) and 300 °C. The growth of the oxide films was monitored by means of X-ray photoemission spectroscopy, while the valence and conduction band electronic structure was investigated by UV and inverse photoemission spectroscopy, respectively.The TiO₂ film grows epitaxially on the Au(100) substrate at 300 °C exhibiting the rutile (100) surface. The evolution of the Ti 2p lineshape with the oxide coverage shows the presence of reduced oxide species (characterized by Ti^3 + ions) at the Au(100) interface. A crystalline and stoichiometric TiO₂ oxide is produced at high substrate temperature, while growth at RT gives a measurable concentration of defects. Post growth annealing in ultra-high vacuum of the RT grown film increases this concentration, while subsequent annealing in O₂ atmosphere restores the sample to the as-grown conditions.     

氧压对脉冲激光沉积LaNiO_3薄膜结构和电学性能的影响

通过改变氧分压,利用脉冲激光沉积方法在Si(100)衬底上制备了系列LaNiO3导电氧化物薄膜;经XRD测试研究发现,通过调控氧压,可获得具有高(100)取向薄膜,且氧压对薄膜结晶性有很大影响,在氧分压为7.5Pa时获得结晶性最好的薄膜。经XRF分析表明,La、Ni元素化学成分计量比随氧压增大而减小。经四探针法测试,薄膜电阻率最小为2.03×10-4Ω.cm,表现出了良好的金属导电性。经SEM和AFM分析表明,薄膜晶粒为柱状晶,排列均匀致密,薄膜表面均匀,粗糙度较小,表明LaNiO3薄膜可以用作一种良好的铁电薄膜底电极材料。     

Galvanostatic electrodeposition and microstructure of copper (I) oxide film

 Polycrystalline copper (I) oxide films were deposited on stainless steel substrate by galvanostatic electrodeposition method and were characterized by X-ray diffraction and scanning electron microscopy. The effect of bath temperature, bath pH and current density on the compositon, grain size, surface texture and surface morphology of the electrodeposited films were investigated. The films deposited at low bath pH (≤7) consisted of copper (I) oxide and metallic copper; while the films deposited at bath pH between 8 and 12 and bath temperature of 60°C were pure copper (I) oxide. The preferred orientation of the copper (I) oxide films depended on the relative growth rate of {111} and {200} faces and could be controlled by adjusting the bath pH and/or the cathodic current density. (100)-oriented copper (I) oxide films could be deposited at pH=9 and current densities in the range of 0.25–1 mA/cm², while (111)-oriented films could be prepared at pH=12 or at pH=9 using the current densities between 1.5–2.5 mA/cm². Computer simulated crystallite shapes showed that the crystal shape changed from octahedral for (100)-oriented film to trucated pyramids and cubs for (111)-oriented film. And they were approved by scanning electron microscopy. Received: 1 December 1997 / Accepted: 13 December 1997     

Characterization of FeS2-pyrite thin films synthesized by sulphuration of amorphous iron oxide films pre-deposited by spray pyrolysis

FeS₂-thin films with good crystallinity were synthesized by a simple method which consists of sulphuration, under vacuum, of amorphous iron oxide thin films pre-deposited by spray pyrolysis of FeCl₃·6H₂O (0.03 M)-based aqueous solution onto glass substrates heated at 350 °C. At optimum sulphuration temperature (450 °C) and duration (6 h), black green layers having granular structure and high absorption coefficient (5.10⁴ cm⁻¹) were obtained. The study of the electrical properties of the as-prepared films vs. the temperature variations showed three temperature domain dependence of the conductivity behaviour. The first one corresponds to the high temperature range (330 K–550 K) for which an Arrhenius plot type was obtained. The activation energy value was estimated at about 61.47 meV. The second domain corresponding to the intermediate temperature range (80 K–330 K) showed a variable activation energy between the grain boundaries. The barrier height, q¯, was estimated to 27±0.5 meV, and the standard deviation, qσ, was evaluated at about 14±0.5 meV. We found that at lower temperatures (20 K–80 K), the conductivity is governed by two conduction types. The density of localised states, was about 2.45×10²⁰ eV⁻¹ cm⁻³.     

紫外激光脉冲沉积法制备高温超导（Bi,Pb）2Sr2CaCu2O8薄膜的研究

用紫外脉冲激光沉积技术在单晶衬底上制备高温超导(Bi,Pb)2Sr2CaCu2O8薄膜,系统研究了不同镀膜参数对薄膜结晶质量的影响,获得了优化的镀膜工艺。并在较低温沉积、高温退火,以及高温沉积两种工艺下均获得了具有c轴取向、无杂相及无挥发(分解)的(Bi,Pb)2Sr2CaCu2O8薄膜。相比于高温沉积,低温沉积、高温退火制备的薄膜结晶质量更好。     

Pb(Hf_(0.3)Ti_(0.7))O_3铁电薄膜的制备与性能研究

采用脉冲激光沉积方法在不同温度下生长Pb(Hf0.3Ti0.7)O3(PHT)铁电薄膜,利用各种表征手段测试并分析薄膜的微观结构和电性能。研究表明,生长温度为400℃沉积的PHT薄膜具有良好的(111)择优取向;PHT薄膜矫顽场(2Ec)为390 kV/cm,剩余极化强度(2Pr)为53.1μC/cm2,经1.5×109次翻转后剩余极化强度保持85%;PHT薄膜绝缘性能良好,相对介电常数约为540。PHT薄膜有望应用于铁电随机存储器。     

Growth and applications of superconducting and nonsuperconducting oxide epitaxial films

Growth and characterization of high-temperature-superconducting YBa₂Cu₃O₇ and several metallic-oxide thin films by pulsed laser deposition is described here. An overview of substrates employed for epitaxial growth of perovskite-related oxides is presented. Ag-doped YBa₂Cu₃O₇ films grown on bare sapphire are shown to giveT _c=90 K, critical current >10⁶ A/cm² at 77 K and surface resistance =450μΩ. Application of epitaxial metallic LaNiO₃ thin films as an electrode for ferroelectric oxide and as a normal metal layer barrier in the superconductor-normal metal-superconductor (SNS) Josephson junction is presented. Observation of giant magnetoresistance (GMR) in the metallic La_0·6Pb_0·4MnO₃ thin films up to 50% is highlighted.     

Use of Nd: YAG laser forin situ growth of thin films of Y1Ba2Cu3O7−δ

As-deposited superconducting films of Y₁Ba₂Cu₃O_7−δ with zero resistance at a temperature of ⋍ 80 K have been successfully grown using a Nd:YAG laser. A substrate temperature in the range 450–550°C was found most appropriate. The use of a Nd:YAG laser instead of an excimer laser is likely to improve the cost effectiveness of the laser ablation technique.     

Conductivity of (NH4)3[CrMo6O24H6]•7H2O Treated by Nd Chemistry-Heated Diffused Permeation

Rare earth co-permeation of (NH4)3[CrMo6O24H6]•7H2O was reported and the conductivity of (NH4)3[CrMo6O24H6] was improved by 6.734×109 times. X-ray fluorescence spectrometry (XRF), thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD) have been used to character (NH4)3[CrMo6 O24H6] •7H2O and permeated sample. Experimental results showed that Nd could be permeated into the body of this sample and the XRD patterns showed great difference between (NH4)3[CrMo6O24H6] •7H2O and permeated sample. The structure of (NH4)3[CrMo6O24H6] •7H2O was destroyed and new compound MoN perhaps formed.     

Growth,magnetic properties and the effect of cobalt addition in metal-organic chemical vapour deposited (MOCVD) gamma iron oxide thin films for magnetic recording applications

The present study aims at investigating MOCVD technique for the deposition of magnetic oxide thin films using volatile metal-organic compounds as source material. A three-step scheme has been described to form γ-Fe₂O₃ phase starting from α-Fe₂O₃ films as-deposited in optically heated atmospheric cold wall CVD reactor. Growth of γ-Fe₂O₃ in a two-step process has been performed by depositing Fe₃O₄ phase directly by resistively heated low-pressure CVD (LPCVD) technique. Role of substrate temperature in controlling the oxidation leading to direct formation of metastable γ-Fe₂O₃ phase (single-step scheme) by atmospheric CVD technique has been described. A new mode of introduction of cobalt in the film, namely heterogeneous dispersion of cobalt in the γ-Fe₂O₃ matrix, has also been described. Crystallographic structure, microstructure and magnetic properties of the films have been studied in detail. Biaxial vector coil and high-temperature magnetic studies were carried out for determining the nature of anisotropy in the γ-Fe₂O₃ film. Growth of γ-Fe₂O₃ films in different schemes have been discussed from the studies of growth kinetics in a cold-and hot-wall-type reactor chambers.     

Preparation of epitaxial YBa2Cu3O7−x films by magnetron sputtering

Thin films of highT _c superconductor YBa₂Cu₃O_7−x were obtained by magnetron sputtering. MgO, YSZ, YSH and Al₂O₃ single crystals were used as substrates. Epitaxial films with tetragonal structure havingT _c 55–60 K grow at substrate temperaturesT _s between 930 K and 980 K. Orientation of the films in thisT _s range was (100) and (001) for (100) MgO substrate, (111) and (001) for (1012) Al₂O₃ and (111) YSH and (113) or (103) on (110) YSZ and (111) YSH. Single crystalline films with orthorhombic structure and (001) orientation were grown on all the substrates whenT _s exceeded 980 K. They haveT _c>80 K.     

Growth and characterization of laser-deposited Ag-doped YBa2Cu3O7−x thin films on bare sapphire

Microstructural and superconducting properties of YBa₂Cu₃O_7−x thin films grownin situ on bare sapphire by pulsed laser deposition using YBa₂Cu₃O_7−x targets doped with 7 and 10 wt% Ag have been studied. Ag-doped films grown at 730°C on sapphire have shown very significant improvement over the undoped YBa₂Cu₃O_7−x films grown under identical condition. A zero resistance temperature of 90 K and a critical current density of 1·2×10⁶ A/cm² at 77 K have been achieved on bare sapphire for the first time. Improved connectivity among grains and reduced reaction rate between the substrate and the film caused due to Ag in the film are suggested to be responsible for this greatly improved transport properties.     

Fabrication of SmBa2Cu3O7 Films on CeO2 Buffered Sapphire

SmBa₂Cu₃O_7−δ (SmBCO) thin films and CeO₂ buffer layers were deposited on γ-cut sapphire by pulsed laser deposition (PLD) and characterized with X-ray diffraction (XRD) and atomic force microscope (AFM). The θ–2θ XRD scans of the SmBCO/CeO₂/sapphire structures revealed that the CeO₂ and SmBCO films were grown with c-axis perpendicular to the substrate. In Φ-scan XRD patterns, four (103) peaks of the SmBCO film were observed and the peak positions were shifted by 45° from (202) peaks of the CeO₂ films. From the peak shifts we could conclude that the [110]_SmBCO crystal axis is parallel to the [100]_CeO2 crystal axis. Moreover, pole figure also confirmed that SmBCO films were grown on the substrates epitaxially along in-plane direction. The SmBCO films show very flat surfaces with root mean square (RMS) about 5 nm. In agreement with this crystalline perfection, SmBCO thin films present excellent superconducting properties: T _c0 > 90 K, transition width 0.4 K, and J _c(77 K) > 2 MA/cm².     

Fish-Tail effect and irreversibility field of (Cu,C)Ba2Ca3Cu4O x -(LiF) y superconductor

Addition of (LiF) _y≤0.15, and of proper amount of (AgO) _z=0.45–0.8 as oxidizing agent, to (Cu,C)Ba₂Ca₃Cu₄ O_10+δ superconductor is useful to control and to shift the doping characteristics (hole density and distribution, and level of disorder) into the region where the irreversible properties, i.e. fish-tail effect (FTE) and irreversibility fieldH _irr are improved. Among notable effects are the development of the second magnetization peak with a higher amplitudeJ _c,max and the enhancement ofH _irr at high temperatures, above a certain valueT* which depends on bothy _LiF andz _AgO. The best results are obtained for the sample withy _LiF=0.1 andz _AgO=0.73. This sample preserves its single phase Cu,C-1234 composition. The influence on the FTE andH _irr of the interplay between doping characteristics, controlled by LiF and AgO content, is discussed.     

Successful fabrication of bicrystal Si substrates for YBa2Cu3O7 − y Josephson junctions

Bicrystal Si(BiSi) substrates for grain boundary (GB) Josephson junctions (GBJJs) have been fabricated by a direct bonding technique using a hot press method. The fracture strength and structure of the bonding interfaces were investigated to obtain substrates suitable for the junctions. It was found that an increase in the pressure of the hot press improves the reproducibility of the GBJJs. YBa₂Cu₃O_{7 − y} GBJJs were successfully fabricated on Bi-Si substrates with a misorientation angle of 15 ° bonded under a pressure of 90 kgf cm⁻² at 1200 °C in a vacuum of ≈10⁻³ Pa. These junctions showed typical I-V curves described by the RSJ model. The Shapiro steps induced by millimetre wave irradiation of 101 GHz were clearly observed in the I-V curves up to 3 mV, corresponding to at least 1.5 THz (, where e is the unit charge, V the voltage and h Planck's constant).