PREPARATION OF a-AXIS ORIENTED YBa2Cu3Ox THIN FILMS

The a-axis oriented YBa₂Cu₃O_x(YBCO) thin films could be grown on (100) SrTiO₃(STO) substrates with STO buffer layers by dc and rf magnetron sputtering either by low-ering the deposition temperature, or by using a self-template technique. For the latter, the resistivity of the thin film at 290K along the substrate [001] direction is about four times larger than that in the [010] direction. The zero resistance temperatures T_c0 are 89 K in both directions. So high quality a-axis oriented YBCO thin films can be prepared by the self-template technique. Also the T_c0 increase monotonously with the reduction of the thickness of the YBCO seed layer.     

Thickness dependence of microstructures in La0.9Sr0.1MnO3 thin films grown on exact-cut and miscut SrTiO3 substrates

The thickness dependence of microstructures of La_0.9Sr_0.1MnO₃ (LSMO) thin films grown on exact-cut and miscut SrTiO₃ (STO) substrates, respectively, was investigated by high-angle X-ray diffraction (HXRD), X-ray small-angle reflection (XSAR), X-ray reciprocal space mapping and atomic force microscopy (AFM). Results show that the LSMO films are in pseudocubic structure and are highly epitaxial [0 0 1]-oriented growth on the (0 0 1) STO substrates. The crystalline quality of the LSMO film is improved with thickness. The epitaxial relationship between the LSMO films and the STO substrates is [0 0 1]_LSMO[0 0 1]_EXACT-STO, and the LSMO films have a slight mosaic structure along the q_x direction for the samples grown on the exact-cut STO substrates. However, an oriented angle of about 0.24° exists between [0 0 1]_LSMO and [0 0 1]_MISCUT-STO, and the LSMO films have a mosaic structure along the q_z direction for that grown on the miscut STO substrates. The mosaic structure of both groups of the samples tends to reduce with thickness. The diffraction intensity of the (0 0 4) peaks increases with thickness of the LSMO film. The XSAR and AFM observations show that for both groups, the interface is sharp and the surface is rather smooth. The mechanism was discussed briefly.     

Improved initial epitaxial growth of superconducting YBa2Cu3O7 thin films on Y–ZrO2 substrates with a La1.85Sr0.15CuO4 buffer layer

Epitaxial thin films of YBa₂Cu₃O₇ (YBCO) have been deposited on Y–ZrO₂ (YSZ) substrates by means of the pulse laser deposition technique. It has been found that the initial epitaxy of YBCO thin films grown on YSZ can be significantly improved by using La_1.85Sr_0.15CuO₄ (LSCO) as a buffer layer. X-ray diffraction measurements show that the epitaxial YBCO films have single in-plane orientation with YBCO [100]LSCO [100] and LSCO [100]YSZ [110]. The real-time resistance measurements reveal that with LSCO buffer layers the initial formation of the YBCO ultra-thin films changes from the island growth to the layer-by-layer growth.     

Aspects of “low field” magnetotransport in epitaxial thin films of the ferromagnetic metallic oxide SrRuO3

Epitaxial thin films of the conductive ferromagnetic oxide SrRuO₃ were grown on an (0 0 1) SrTiO₃ (STO) substrate by using DC sputtering technique. The magnetic and magnetoresistive properties of the films were measured by applying the magnetic field both perpendicular (out-of-plane) and parallel (in-plane) to the film plane and ever maintaining the direction of the applied field perpendicular to that of the transport current. The films grown on an (0 0 1) STO substrate showed identical magnetization properties in two orthogonal crystallographic directions of the substrate, [1 0 0]_S and [0 0 1]_S (in-plane and out-of-plane geometry), which suggests the presence of a multi domain structure within the plane of the film. For such samples, no anisotropic field (hard axis) along de [0 0 1]s direction, i.e., perpendicular to the film-plane could be detected. Nevertheless, a distinguishable temperature dependent out-of-plane anisotropic magnetoresistance (MR) along with strong temperature dependent low field hysteretic MR(H) behavior was detected for the studied films. A negative MR ratio MR(T)=[ρ(μ₀H=9 T; T)−ρ( μ₀H=0 T; T)]/ρ( μ₀H=0 T; T) on the order of a few percent, with maximums of 6% and 4% (right at the Curie temperature, T_C 160 K) was calculated for an in-plane and out-of plane measuring geometry, respectively. In addition there is an equally strong MR effect at low temperatures, which might be related to the temperature dependence of the magnetocrystalline anisotropy together with a magnetization rotation. Both the MR(T) behavior and the achieved values (except for T<30 K) are similar to those obtained on SrRuO₃ films grown on 2° miscut (0 0 1) STO substrates with the current parallel to the field and parallel to the direction, which was identified as the easier axis for magnetization.     

插入二氧化铈薄膜提高MOD-YBa2Cu3O7-x厚膜超导性能的研究

YBa₂Cu₃O_7-x(YBCO)膜存在“厚度效应”: 随着厚度增加, YBCO薄膜的临界电流密度下降, 尤其是YBCO薄膜的厚度超过1 μm时, 它的临界电流密度急剧下降. 本文在YBCO薄膜之间引入极薄的二氧化铈(CeO₂)薄膜, 成功制备出结构为YBCO/YBCO/CeO₂/YBCO的超导厚膜. 所制备的厚度为2 μm的YBCO膜临界电流密度为1.36 MA/cm² (77 K, 自场), 其性能比相同厚度的纯YBCO膜有了较大幅度的提升. 研究表明CeO₂薄膜起到了传递织构、松弛应力的作用.     

High critical current density YBa2Cu3O7−δ tapes prepared by the surface-oxidation epitaxy method

YBa₂Cu₃O_7−δ (YBCO) films with high critical current density (J_c) were successfully fabricated on nickel tapes buffered with epitaxial NiO. NiO was prepared on the textured nickel tape by the surface-oxidation epitaxy (SOE) method. We have reported so far a critical temperature (T_c) of 87 K and J_c=4–6×10⁴ A/cm² (77 K, 0 T) for the YBCO films on NiO/Ni tapes. To enhance the superconducting properties of the YBCO films on the SOE-grown NiO, depositions of thin oxide cap layers such as YSZ, CeO₂, and MgO on NiO were investigated. These oxide cap layers were epitaxially grown on NiO and provided the template for the epitaxial growth of YBCO films. Substantially improved data of T_c=88 K and J_c=3×10⁵ A/cm² (77 K, 0 T) and 1×10⁴ A/cm² (77 K, Hc, 4 T) were obtained for YBCO film on NiO, by using a MgO cap layer with a thickness of 50 nm. The method described in this paper is a simple way to produce long YBCO tape conductors with high-J_c values.     

GROWTH MODE OF Cu-RICH PARTICLES ON LASER-ABLATED YBa2Cu3O7 THIN FILMS

The microstructure of the laser-ablated YBa₂Cu₃O₇ (YBCO) thin film deposited on heated (100) SrTiO₃ substrate was examined by transmission electron microscope. The par-ticles on the film mainly consist of CuO and few CuYO₂. Most of these non-superconducting particles nucleate on or near the surface of the film and protrude about 100-400 nm in height, A large amount of a-axis YBCO grains also exist in the film, which nucleate at the substrate surface and grow perpendicularly above the c-axis YBCO film. The YBCO thin film deposited under low oxygen pressure has very different microstructure compared with YBCO thin film deposited under high oxygen pressure.     

Elemental steps in the growth of thin β-Ga2O3 films on CoGa(1 0 0)

The oxidation of CoGa(1 0 0) at 700 K was studied by means of high resolution electron energy loss spectroscopy (EELS), scanning tunneling microscopy, low energy electron diffraction and Auger electron spectroscopy (AES). At 700 K, thin well-ordered β-Ga₂O₃ films grow on CoGa(1 0 0). The EEL spectrum of the Ga-oxide films exhibit Fuchs–Kliewer phonons at 305, 455, 645, and 785 cm⁻¹. For low oxygen exposure (<0.2 L), the growth of oxide-islands starts at step edges and on defects. The oxide films have the shape of long, rectangular islands and are oriented in the [1 0 0] and [0 1 0] directions of the substrate. For higher oxygen exposure, islands of β-Ga₂O₃ are found also on the terraces. After an exposure of 200 L O₂ at 700 K, the CoGa(1 0 0) surface is homogeneously covered with a thin film of β-Ga₂O₃.     

Structural characterization of ultrathin Cr and Sc films for soft X-ray mirrors

The structure of multilayers of ultrathin scandium (Sc) and chromium (Cr) films has been characterized by means of transmission electron microscopy (TEM). Face centered cubic Sc was found both in magnetron sputtered thin Sc layers on Si(0 0 1) and in Cr/Sc multilayers for soft X-ray mirrors. The single Sc and Cr layers are polycrystalline with randomly oriented grains, while Sc and Cr within the Cr/Sc multilayer show a strong [0 0 1] texture in the deposition direction. From high-resolution images the orientation-relationship at the Cr/Sc interfaces could be deduced as: Sc_[110]//Cr_[100] and Sc_[010]//Cr_[110], which was confirmed by image simulations.     

低能离子对高温超导YBa_2Cu_3O_(7-δ)薄膜的表面改性和机理

低能氩离子束轰击并后退火处理的离子束表面改性,会影响高温超导薄膜的表面结构和超导特性,但是其中的深刻微观机理不清楚.本文通过连续改变离子束轰击时间,系统研究了离子束表面改性对于超导膜结构和临界电流密度的影响.通过扫描电子显微镜、X射线衍射、J_(c-scanning)测试表征样品的结构特性和超导特性,并得出内应变、氧空位缺陷等参量.研究表明,经过表面改性的钇钡铜氧(YBa_2Cu_3O_(7-δ),YBCO)薄膜,随轰击时间增加表面形貌会变得更加均匀致密,a轴晶粒消失,并且临界电流密度有了显著的提高.由化学键收缩配对模型分析得出,临界电流密度的提高与薄膜内应变增大和引发的局部YBCO结构中Cu—O键收缩有关.     

Observation of defects and growth orientations of YBa2Cu3Ox thin films with YSZ buffer layers on Si

We have investigated defects and in-plate orientations of YBa₂Cu₃O_x thin films prepared by pulsed laser deposition (PLD) with YSZ as a buffer layer. The films showed c-axis oriented growth with the transition temperature T_co up to 87 K. Several types of defects including thermally induced cracks, grain boundaries and outgrowths were observed by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The grain boundary provided a favorable path for crack propagation. The outgrowths nucleated on the YSZ surface grew with stoichiometric composition. According to X-ray diffraction (XRD) and HRTEM studies the YSZ buffer layer grew with the orientation relationship, YSZ110//Si110 and YSZ(001)//Si(001) up to the YBCO/YSZ interface. The superconducting YBCO films on top grew mainly with YBCO100//Si110 and YBCO(001)//Si(001), with some minor portions of YBCO110//Si110 and YBCO(001)//Si(001).     

掺杂Y2O3和BaCeO3提高MOD-YBCO超导性能的研究

本文通过在前驱液中添加过量钇盐和铈的有机盐,采用三氟乙酸盐-金属有机沉积法(TFA-MOD) 在铝酸镧单晶基体上制备了含有纳米氧化钇和纳米铈酸钡的YBCO薄膜. 与纯YBCO薄膜相比,掺杂Y₂O₃/BaCeO₃的YBCO膜的临界转变温度几乎保持不变,为91 K左右. 而掺杂Y₂O₃/BaCeO₃的YBCO膜的临界电流密度达到5.0 MA/cm² (77 K, 0T), 是纯YBCO膜临界电流密度的1.5倍.薄膜中的Y₂O₃和BaCeO₃可能在YBCO内部起到了 有效的钉扎磁通作用. 关键词： 钇钡铜氧薄膜 2O₃和纳米BaCeO₃')" href="#">纳米Y₂O₃和纳米BaCeO₃ 磁通钉扎 三氟乙酸盐-金属有机沉积     

在金属基片上激光沉积YBCO超导薄膜

介绍了在金属基片上激光沉积缓冲层和ＹＢａ２Ｃｕ３ｏ７－ｘ（ＹＢＣＯ）高温超导薄膜的研究结果。在带ｙｔｔｒｉａ－ｓｔａｂｉｌｉｚｅｄ－ｚｉｒｃｏｎｉａ（ＹＳＺ）缓冲层的ＮｉＣｒ合金基片上,激光原位沉积出ＹＢＣＯ超导薄膜,薄膜的零电阻转变温度度４８Ｋ,７７Ｋ时临界电流密度约为２００Ａ／ｃｍ＾２;缓冲层的取向可以通过选择适当的沉积参数来改善;用扫描隧道电子显微镜对ＹＢＣＯ薄膜的微观结构分析表明：完善的螺     

X-ray diffraction studies of epitaxy in orthorhombic- DyMnO3/Er1Ba2Cu3O7-δ thin film heterostructures on LaAlO3 (100) substrates

The heteroepitaxy in DyMnO₃/Er₁Ba₂Cu₃O_7-δ bilayer thin films on LaAlO₃ (100) substates was characterized by four-circle X-ray diffractometry. The Er₁Ba₂Cu₃O_7-δ thin films on LaAlO₃ (100) substrates were prepared by molecular-beam deposition (MBD) and post-growth annealing in wet and dry O₂ at 880°C, whereas the DyMnO₃ thin films on the Er₁Ba₂Cu₃O_7-δ/LaAlO₃ (100) heterostructure were deposited by MBD and post-growth annealing in dry O₂ at 750°C. The conventional X-ray diffraction (XRD) patterns as well as pole figures (φ-scans) for specific (hkl) reflections were acquired. The Er₁Ba₂Cu₃O_7-δ thin film in the DyMnO₃/Er₁Ba₂Cu₃O_7-δ/LaAlO₃ (100) heterostructure showed [001] oriented epitaxial growth, as expected. The DyMnO₃ thin film on the Er₁Ba₂Cu₃O_7-δ epilayer in the heterostructure grew with (110) epitaxy in its metastable orthorhombic phase (lattice constants: a_o=5.272 Å, b_o=5.795 Å and c_o=7.38 Å). The heteroepitaxial relationships at the orthorhombic-DyMnO O₃ (110) /Er₁Ba₂Cu₃O_7-δ (001) interface was determined as the following: DyMnO₃ (110) Er₁Ba₂Cu₃O_7-δ (001), DyMnO₃ [1 0] ¶r; Er₁Ba₂Cu₃O_7-δ[100] or Er₁Ba₂Cu₃O_7-δ[010], and DyMnO₃ [001] ¶r; Er₁Ba₂Cu₃O _7-δ[010] or Er₁Ba₂Cu₃O_7-δ [100].     

Structural and electrical characterisation of La0.5Ca0.5MnO3 thin films grown by pulsed laser deposition

Thin films of perovskite manganite, with nominal composition La_0.5Ca_0.5MnO₃, have been prepared by pulsed laser deposition on (1 0 0) SrTiO₃, (1 0 0) LaAlO₃, (1 0 0) Si and YSZ/CeO₂-buffered (1 0 0) Si substrates. Structural and electrical characterisation was performed on the films. The magneto-transport properties of all the thin films depart from the bulk behaviour. The LCMO film grown on buffered Si shows an insulator–metallic transition around 130–150 K while the one deposited directly on Si displayed a similar behaviour under a melting field of 1 T. However, that transition is absent in the films grown on LAO and STO. We suggest that appropriate stress values induced by the substrate favour the formation of metallic percolative paths.     

石英衬底上Au缓冲层对ZnO薄膜微结构的影响

采用单源化学气相沉积(SSCVD)法,在石英衬底上以Au为缓冲层,Zn4(OH)2(O2CCH3)6.2H2O为固相源制备ZnO薄膜。SEM和XRD测试ZnO薄膜的微结构,结果表明:相对于SiO2衬底上生长的ZnO薄膜,Au/SiO2衬底上生长的ZnO薄膜具有较好的结晶质量和表面平整度;对制备ZnO薄膜的衬底温度进行了工艺优化,结果表明:500℃时制备的ZnO薄膜颗粒大小均匀,结晶质量较好;通过荧光光谱仪对Au/SiO2衬底上的ZnO薄膜进行光致发光(PL)谱测试,ZnO薄膜在400nm出现紫光发射峰,而没有出现与缺陷相关的深能级发射峰,表明ZnO薄膜具有较好的结晶质量。     

SrTiO3(110) thin films grown directly on different oriented silicon substrates

We have grown (110)-oriented SrTiO₃ (STO) thin films on silicon without any buffer layer, by means of pulsed laser deposition technique. The crystal structures of the grown films were examined by X-ray diffraction analysis including θ–2θ scan and rocking curve as well as Laue diffraction methods. STO films with single (110) out-of-plane orientation were formed on all (100), (110) and (111)-oriented Si substrates. The in-plane alignments for the epitaxial STO films grown directly on Si (100) were found as STO[001]//Si[001] and STO[11̄0]//Si[010]. The results should be of interest for better understanding of the growth of perovskite oxide thin films on silicon wafers. PACS 77.55.+f; 68.55.JK; 81.15Fg     

Vector magnetometer studies of the easy magnetisation direction in epitaxially grown DyFe2 film

A vector vibrating sample magnetometer has been used to determine the direction of easy magnetisation in a thin film of DyFe₂. The 4000 Å thick film, with a [1 1 0] growth direction, was prepared using molecular beam epitaxy. The results show that the direction of easy magnetisation is temperature dependent. At 4 K this direction corresponds to the [0 0 1] type axes. But at 290  the easy axis is close to a direction, but pointing out of the plane of the film at angle of (14±3)°. On the basis of the vector magnetometer results at 290 K we find two easy magnetisation axes close to or (and opposite directions). Finally, it is shown that DyFe₂ films are unique in that the remanent magnetisation can be manipulated to point either in or out of the plane of the film.     

The effect of hydrogen on copper nitride thin films deposited by magnetron sputtering

Copper nitride thin films were deposited on Si (1 0 0) wafers by reactive magnetron sputtering at various H₂/N₂ ratios. X-ray diffraction measurements show that the films are composed of Cu₃N crystallites with anti-ReO₃ structure and exhibit preferred orientation of [1 0 0] direction. Although the relative composition of the films has obviously changes with the H₂/N₂ ratios, the orientations of the films keep almost no changes. However, the grain size, lattice parameter and composition of the films are strongly dependent on the H₂/N₂ ratios. The copper nitride films prepared at 10% H₂/N₂ ratios show poor stability and large weight gain compared to the copper nitride films prepared at 0% H₂/N₂ ratios.     

Morphological and electrical properties of SrTiO_3/TiO_2/SrTiO_3 sandwich structures prepared by plasma sputtering

SrTiO_3(STO) and TiO_2 are insulating materials with large dielectric constants and opposite signs of the quadratic coefficient of voltage(α). Insertion of a TiO_2 thin film between STO layers increases the linearity of the capacitance in response to an applied voltage, to meet the increasing demand of large-capacitance-density dynamic random access memory capacitors. Both STO and TiO_2 suffer from the problem of high leakage current owing to their almost equivalent and low bandgap energies. To overcome this, the thickness of the thin TiO_2 film sandwiched between the STO films was varied. A magnetron sputtering system equipped with radio frequency and direct current power supply was employed for depositing the thin films. Ti N was deposited as the top and bottom metal electrodes to form a metal–insulator metal(MIM) structure,which exhibited a very large linear capacitance density of 21 fF/um~2 that decreased by increasing the thickness of the TiO_2 film. The leakage current decreased with an increase in the thickness of TiO_2, and for a 27-nm-thick film, the measured leakage current was 2.0 × 10~(-10) A. X-ray diffraction and Raman spectroscopy revealed that Ti N, STO, and TiO_2 films are crystalline and TiO_2 has a dominant anatese phase structure.