Structure and surface termination of ZnO films grown on (0001)- and (112¯0)-oriented Al2O3

We have studied the surface termination of ZnO(0001¯) films grown on Al₂O₃ substrates with high epitaxial quality. The structural properties of the ZnO films were investigated by X-ray scattering, revealing a predominant (0001¯)ZnO out-of-plane texture with the [112¯0]_ZnO[0001]_Al2O3 and [112¯0]_ZnO[101¯0]_Al2O3 azimuthal orientations for (112¯0)Al₂O₃ and(0001)Al₂O₃ substrates, respectively. The surface termination was determined by X-ray photoemission spectroscopy (XPS) via pyridine (C₅H₅N) adsorption at the ZnO surface. XPS data recorded at different temperatures after exposure to pyridine revealed that for both orientations of the Al₂O₃ substrates the deposited ZnO films were terminated by oxygen atoms, i.e. corresponding to a ZnO (0001¯) surface.     

Al2O3保护层对高温下Pt/ZnO/Al2O3电极导电稳定性的影响

本工作研究了Al₂O₃保护层的厚度对高温下声表面波器件电极导电稳定性的影响, 采用激光分子束外延方法在Pt/ZnO/Al₂O₃电极上制备了不同厚度的Al₂O₃保护层。通过测量样品高温环境中的实时电阻, 发现Al₂O₃缓冲层的厚度对电极在高温下的导电稳定性的影响非常大。结果表明, 没有Al₂O₃保护层时, Pt/ZnO/Al₂O₃电极的电阻升温至800 ℃时开始急剧地增加。当包覆40 nm的Al₂O₃保护层时, 电极在升温至900 ℃以上才出现电阻值剧烈增加的现象。而随着Al₂O₃保护层厚度的增加, 电极的电阻在高温下的导电性能也更加稳定。SEM测试结果表明, 经过1000 ℃、1 h的高温测试后, Al₂O₃保护层越薄的Pt/ZnO/Al₂O₃电极, 结块形成的Pt颗粒越大与不连续的Pt空洞更多。这些结果为制备高温下稳定工作的声表面波器件提供了一条新的思路。     

Magnetic properties of sputtered Co-Ni-Fe-Pd films for thin-filmheads

Magnetic properties of Co-Ni-Fe-M (M=Rh, Ir, Pd, Pt) films prepared by sputtering are investigated. It is found that addition of Pd decreases the magnetostriction constant of the films from 1×10^-5 to around zero. On the other hand, addition of other elements, such as Rh, Ir, and Pt, increases it. However, coercive forces of Co-Ni-Fe-Pd films become more than 10 Oe when the magnetostriction is less than 2×10^-6. Multilayered films are investigated to obtain films with low coercive force. 43Co-27Ni-15Fe-15Pd films of 0.17 μm and Al₂O₃ films of 0.01 μm in thickness are layered time-sequentially. This multilayered film has saturation induction of 1.4 T, ≈0 magnetostriction, and a low coercive force of 1.5 Oe. Furthermore, Co-Ni-Fe-Pd films are ascertained to be as resistant to corrosion as Permalloy films. Recording heads with multilayered Co-Ni-Fe-Pd films with Al₂O₃ interlayers as magnetic cores have been fabricated. Recording characteristics were evaluated. These laminated Co-Ni-Fe-Pd/Al₂O₃ heads exhibit about 6 dB better overwrite than Permalloy heads     

Characterization and properties of r.f.-sputtered thin films of the alumina–titania system

Thin films of the aluminum oxide (Al₂O₃)–titanium oxide (TiO₂) system including Al₂O₃, TiO₂, and Al₂O₃/TiO₂ were prepared by radio-frequency (r.f.) magnetron sputtering using ceramic targets of Al₂O₃, TiO₂, and Al₂O₃/TiO₂ composites with different Al₂O₃/TiO₂ ratio. These films were studied at different substrate temperatures, r.f. powers, and annealing temperatures. Composition, microstructure, thermomechanical property of internal stress, and mechanical property of scratch adhesion, were evaluated. A thin film with a dielectric constant of 62 and a loss tangent of 0.012 was obtained at 500 °C from a 10/90 target. This thin film remained the high dielectric constant of TiO₂, but had an improvement in the dielectric loss tangent. Al₂O₃-containing films had a higher resistivity and breakdown field, which was improved further by annealing. Optical properties, such as refractive index and optical transmittance, were also investigated.     

Epitaxial and polycrystalline BaFe12O19 thin films grown by chemical vapour deposition

Epitaxial and polycrystalline barium hexaferrite BaFe₁₂O₁₉ thin films were prepared by metalorganic chemical vapour deposition (MOCVD). Films were grown by a liquid MOCVD technique which aim is to control precisely the precursor vapour pressures. Two kinds of substrates were used: sapphire (001) and silicon thermally oxidized. On Si/SiO₂ films are polycrystalline and the magnetization is isotropic. On Al₂O₃ (001), structural studies reveal the films to be predominantly single phase, well crystallized without annealing procedure and with the c-axis perpendicular to the film plane; epitaxial relationships between the film and the substrate were determined. The magnetic parameters, deduced from vibrating sample magnetometer measurements, show a high dependence of the magnetization with the orientation of the field with respect to the surface of the film.     

Growth of SrTiO3 thin epitaxial films by aerosol MOCVD

SrTiO₃ thin films were prepared by aerosol metal-organic chemical vapour deposition on (001) MgO, R-plane Al₂O₃ and (001) Si single-crystal substrates. Strontium tetramethyl heptadionate and titanium n-butoxide dissolved in diethyleneglycol dimethyl ether were used as precursors. The structure of the films was investigated by X-ray diffraction and transmission electron microscopy. Epitaxial films with [001] and [111] orientation perpendicular to the substrate surface were obtained on MgO and Al₂O₃, respectively. The epitaxial films on the MgO substrate were found to be in a relaxed state with lattice parameters corresponding to the bulk values. SrTiO₃ films on the Si substrate were grown as highly textured in the [011]direction and randomly oriented in the plane parrallel to the substrate surface.     

New LaCu0.5Mn0.5O3 thin films deposited by the sol-gel process on different substrates

New LaCu_0.5Mn_0.5O₃ thin films deposited by the sol-gel process on ceramic Al₂O₃ and ZrO₂, glass ceramic and 101 single-crystal quartz, using the sol-gel process. It was found in all cases that the films are polycrystalline and single phase without preferred orientation. The morphology of the films depends strongly on the nature of the substrate. The films deposited on Al₂O₃ exhibit morphological characteristics making them suitable as possible sensors and catalysts.     

Growth of calcium carbonate by the atomic layer chemical vapour deposition technique

Thin films of CaCO₃ (calcite) have been grown with the atomic layer chemical vapour deposition (ALCVD) technique, using Ca(thd)₂ (Hthd=2,2,6,6-tetramethylheptan-3,5-dione), CO₂, and ozone as precursors. Pulse parameters for the ALCVD-type growth are found and self-limiting reaction conditions are established between 200 and 400 °C. Calcium carbonate films have been deposited on soda-lime glass, Si(100), -Al₂O₃(001), -Al₂O₃(012), -SiO₂(001), and MgO(100) substrates. The observed textures were: in-plane oriented films with [100](001)CaCO₃ [100](001)Al₂O₃ and [100](001)CaCO₃[110](001)Al₂O₃ on -Al₂O₃(001), amorphous films on -Al₂O₃(012) when grown at 250 °C, and columnar oriented films on soda-lime glass, Si(001), -SiO₂(001), and MgO(100) substrates with (00l) and (104) parallel to the substrate plane at 250 and 350 °C, respectively. The film topography was studied by atomic force microscopy and AC impedance characteristics were measured on as-deposited films at room temperature. The films were found to be insulating with a dielectric constant (_r) typically approximately 8. Thin films of CaO were obtained by heat treatment of the carbonate films at 670 °C in a CO₂-free atmosphere, but the thermal decomposition led to a significant increase in surface roughness.     

纳米Al_2O_3/聚酰亚胺复合薄膜的介电与力学性能

采用原位聚合与热亚胺化的方法,成功制备了一系列不同纳米Al_2O_3粒子质量分数的纳米Al_2O_3/聚酰亚胺(PI)复合薄膜。通过SEM、TEM、XRD、FTIR、LCR数字电桥、高压电源及电子万能材料试验机对纳米Al_2O_3/PI复合薄膜的微观结构、介电性能及力学性能进行了表征和测试。结果表明:纳米Al_2O_3粒子在均匀地分散在PI基体中;当纳米Al_2O_3粒子质量分数为8%时,纳米Al_2O_3/PI复合薄膜的击穿强度和拉伸强度均达到了最大值;纳米Al_2O_3/PI复合薄膜的介电常数随纳米Al_2O_3质量分数的增加而增加。     

Epitaxial aluminum nitride films on sapphire formed by pulsed laser deposition

Highly oriented aluminum nitride thin films were grown on sapphire (0001)-substrate by pulsed laser deposition technique. Characterization was done by X-ray-diffraction, elastic recoil detection analysis and Rutherford backscattering/channeling measurements. The epitaxial properties were studied as function of the substrate temperature and the deposition rate. An epitaxial relation to the sapphire substrate is found to be AlN [0001] || Al₂O₃ [0001] and AlN [11 0] || Al₂O₃ [10 0]. XRD-texture-analysis on films deposited at 850°C shows a full width half maximum Δω of 0.13° (rocking curve) and Δ of 1.1° (in-plane).     

Growth of La2Mo2O9 films on porous Al2O3 substrates by radio frequency magnetron sputtering

Synthesis conditions of La₂Mo₂O₉ thin film by radio frequency (RF) sputtering technique on Al₂O₃ ceramic substrates are studied. It is found that the deposition temperature and oxygen partial pressure are the most important factors for obtaining pure La₂Mo₂O₉ films. Varying both parameters, Mo-rich, stoichiometric, and Mo-deficient films are obtained. With increasing the La:Mo ratio, films become denser. A crust layer is observed on top of the Mo-rich and the Mo-deficient films. The formation of the La₂Mo₂O₉ phase is discussed with respect to the sputtering mechanism.     

MnTe and ZnTe grown on sapphire by molecular beam epitaxy

We report on growth of MnTe layers by molecular beam epitaxy on Al₂O₃ substrates and of ZnTe layers on hybrid MnTe/Al₂O₃ substrates. The aim of our work was to prepare hexagonal phases of epitaxial thin films of these two materials. In the case of MnTe, the hexagonal NiAs-type phase was prepared by depositing the film directly on Al₂O₃ substrates. On the other hand, the crystal structure of ZnTe layers grown on hybrid MnTe/Al₂O₃ substrates was found to depend on the layer thickness: layers thinner than 0.05 μm grew in a metastable hexagonal wurtzite structure, but with further increases of the thickness, the cubic zinc blende phase of ZnTe tended to appear. The structural properties of MnTe and ZnTe layers were characterized by high energy electron and X-ray diffraction methods. Electrical properties of MnTe films were assessed by the Hall effect measurements. The topography and microstructure were analyzed by atomic force microscope. The Néel temperature and magnetic domains structure of antiferromagnetic hexagonal MnTe layers were obtained from neutron experiments.     

Controllable formation of Er–Yb codoped Al2O3 films by the non-aqueous sol–gel method

1 mol%Er³⁺–10 mol%Yb³⁺ codoped Al₂O₃ thin films have been prepared on thermally oxidized SiO₂/Si(110) substrates by a dip-coating process in the non-aqueous sol–gel method from the hydrolysis of aluminum isopropoxide [Al(OC₃H₇)₃] under isopropanol environment. Addition of N,N-dimethylformamide (DMF) as a drying control chemical additive (DCCA) into the sol suppresses formation of the cracks in the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films when the rare-earth ion is doped with a high doping concentration. Homogeneous, smooth and crack-free Er³⁺–Yb³⁺ codoped Al₂O₃ thin films form at the conditions by a molar ratio of 1:1 for DMF:Al(OC₃H₇)₃. A strong photoluminescence spectrum with a broadband extending from 1.400 to 1.700 µm centered at 1.533 µm is obtained for the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films, which is unrelated to the addition of DMF. Controllable formation of the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films may be explained by the fact that the DMF assisted the deprotonation process of Al–OH at the surfaces of gel particles, resulting in enhancement of the degree of polymerization of sols and improvement of the mechanical properties of gel thin films.     

Al2O3/BaZrO3双陶瓷界面微观组织演化及机理

以Al₂O₃为背层(硅溶胶为粘结剂), 电熔BaZrO₃作为面层材料(钇溶胶为粘结剂), 1550℃烧结后制成50 mm×25 mm×5 mm的Al₂O₃/BaZrO₃双陶瓷试样。通过光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和EDS等手段观察了BaZrO₃层和Al₂O₃/BaZrO₃界面的显微结构, 研究了BaZrO₃与Al₂O₃的界面反应。结果表明, 面层由BaZrO₃基体和分布其上的大小10 μm左右的Y稳定的ZrO₂晶粒组成; Al₂O₃/BaZrO₃界面发生反应形成厚约300 μm的过渡层, 界面反应生成物有BaOAl₂O₃、ZrO₂和BaO·Al₂O₃·2SiO₂。界面从单纯的BaZrO₃/Al₂O₃双陶瓷结构演变为BaZrO₃、ZrO₂、BaO·Al₂O₃、BaO·Al₂O₃·2SiO₂和Al₂O₃等多种物相组成的复杂结构。反应过程中Al元素基本不迁移扩散, BaZrO₃中Ba元素向Al₂O₃所在的位置扩散形成BaO·Al₂O₃, 残留物形成一层条状ZrO₂, 而BaO·Al₂O₃·2SiO₂围绕着EC95(Al₂O₃+5%SiO₂)粉体颗粒周围生成。     

Epitaxially grown model catalyst particles of platinum, rhodium, iridium, palladium and rhenium studied by electron microscopy

In order to obtain oriented thin film model catalysts, small particles of Pt, Rh, Ir, Pd and Re (2–20 nm in size) were grown by high vacuum evaporation on NaCl cleavage faces or on in situ deposited NaCl films at 523–673 K. The particles were covered with a supporting film of Al₂O₃ or carbon and removed from the substrate. High resolution electron microscopy, selected area electron diffraction and weak-beam dark-field imaging were applied to determine the particular morphology, microstructure and orientation of the observed particles. Special attention was paid to Rh particles which appear in a variety of shapes. Pt, Ir and Pd model catalysts consist mainly of (001) oriented half octahedra which may exhibit truncations at the corners or on the top. This was also the dominant shape of Rh particles but in addition half tetrahedra in (011) epitaxy and multiply-twinned particles like decahedra in (001), (011) and (111) orientation were evident. These habits provide a definite “initial state” for study of the changes in structure and morphology of the particles during activating heat treatments necessary to induce catalytic activity of the Al₂O₃ supported metal films. Although Re films consisted of irregularly shaped particles, electron diffraction revealed a partial epitaxial alignment of both c.p.h. and f.c.c. Re.     

Characterization of intermetallic phases and oxides formed in annealed Ni/Al multilayer structures

Two different multilayer structures composed of ten alternating Ni and Al thin films were sputter deposited on Si (111) substrates. These multilayers with individual Ni and Al thin film thicknesses of about 25 nm and 38 nm and of 25 nm and 13 nm, respectively, have the average compositions of Ni_0.50Al_0.50 and Ni_0.75Al_0.25. The samples were heat treated in a differential scanning calorimeter instrument with a constant heating rate of 40 °C min ⁻¹ in Ar from room temperature to 550 °C. The compositions of as-deposited and heat-treated samples were studied with high-resolution Auger electron spectroscopy (AES) rotational depth profiling. X-ray photoelectron spectroscopy (XPS) analyses show an excess of Ni in both annealed samples. X-ray diffraction measurements of annealed multilayers show the formation of Ni₂Al₃ and NiAl₃ phases in the Ni_0.50Al_0.50 sample and the presence of Ni₃Al and Ni A1₃ phases with some excess of Ni in the Ni_0.75Al_0.75 sample. AES and XPS investigations of the reacted layers after 15 min annealing in air at 500 °C disclose considerably different surface oxide thin films: on the Ni_0.50Al_0.50 layer the oxide thin film consists of Al₂O₃ with a small amount of NiO, whereas that on the top of the Ni_0.75Al_0.25 layer is thicker and consists of NiO on top and some Al₂O₃ below.     

Chemical analysis of NiAlFe thin films sputter deposited onto sapphire substrates

NiAlFe thin films were prepared onto sapphire single crystals by physical vapour deposition (PVD) and these were analysed by X-ray photoelectron spectroscopy (XPS) in combination with argon ion etching to determine the composition depth profile and interfacial characteristics of the samples. Non-linear least square fitting (NLLSF) analysis of the data was required due to the conflict of several peaks of interest. XPS depth profiles show that, for non-annealed NiAlFe–Al₂O₃, the interface is sharp and oxygen diffusion occurs at different annealing temperatures. Ni remains chemically unaffected by the presence of oxygen while the formation of aluminium oxide compounds occur. Two iron species are present in the film thickness where the low binding energy component is attributed to Fe–Fe or Fe–Al interactions and the higher one to the NiAlFe compound. The reduction-dissolution of the sapphire substrate leads to depletion of oxygen in the sapphire surface layer and the formation of alumina at the NiAlFe–Al₂O₃ interface. Within the film, aluminium and nickel are present as an intermetallic compound. Annealing of the samples induces surface oxidation and the subsequent formation of an Al₂O₃ layer. This type of interphase morphology should lead to optimal fibre/matrix (F–M) adhesion, and therefore optimal load transfer between the matrix and reinforcement.     

Al2O3基多孔隔热材料表面Al2O3/MoSi2涂层的制备及其性能

采用刷涂法在Al₂O₃基多孔隔热材料表面制备Al₂O₃/MoSi₂涂层,涂层以硅溶胶作为粘结剂,纳米Al₂O₃与Al₂O₃纤维作为耐高温组分,MoSi₂为高发射率组分。通过SEM、XRD对Al₂O₃/MoSi₂涂层微观表面结构、物相组成进行分析。研究纳米Al₂O₃与Al₂O₃纤维的质量比和MoSi₂含量对Al₂O₃/MoSi₂涂层耐温性能的影响,并对Al₂O₃/MoSi₂涂层的抗热震性能、发射率进行表征。结果表明,当纳米Al₂O₃与Al₂O₃纤维的质量比小于1∶1时,热考核后Al₂O₃/MoSi₂涂层表面无裂纹产生;当纳米Al₂O₃与Al₂O₃纤维的质量比在1∶2~1∶4之间时,Al₂O₃/MoSi₂涂层中的纤维网络较完整。MoSi₂的含量为20%时,Al₂O₃/MoSi₂涂层抗热震实验循环25次后表面保持完好,热考核后在2.5~25 μm波段的平均发射率在0.85左右,具有较高的发射率。      

pH对水热合成法制备铬渣源复合薄膜性能的影响

以铬渣为基本原料, 采用水热合成法制备了复合薄膜, 对样品进行了SEM、ICP、XRD、FT-IR及薄膜厚度表征分析, 以薄膜的折射率和反射率为对比参数, 研究了水热反应初始pH对薄膜的影响。研究结果表明, 当水热反应初始pH达11以上时, 薄膜表面呈现完美的空间三维立体网状结构; 当水热反应的pH为9、10时, 样品中形成了Al₂O₃、Fe₂O₃、Fe(OH)₃、Cr₂O₃、AlO(OH)和MgO晶体, 且其衍射峰较强; 样品内部纳米颗粒间存在毛细孔水和表面吸附水, 水热体系内的碱性基团促进膜物质与基底间形成化学键力的结合。薄膜越厚, 其折射率越小, 水热反应pH为11时, 薄膜最薄, 折射率最大; 水热反应的初始pH为12时制备的薄膜对紫外光反射率低于玻璃基底, 水热反应的初始pH为11时制备的薄膜对可见光的反射率小于玻璃基底。     

Formation of MgAl2O4 in Al2O3-(Al-4wt.%Mg) composites

The Al₂O₃ particles are introduced into the Al-4wt.%Mg melt by the “vortex” method. After being cast, Al₂O₃-(Al-4wt.%Mg) composites are remelted at 700, 750, 800 and 850°C for different residence times to investigate the formation of MgAl₂O₄ (spinel).

The results show that MgAl₂O₄ is the unique interface of the Al₂O₃-(Al---Mg) composites held at 700–850°C. Fine MgAl₂O₄ crystals grow on the surface of the Al₂O₃ particle but, as the holding temperature and the residence time increase, some spinels will form themselves into pyramidal shape. The MgAl₂O₄ grows not only at the matrix-particle interface but also on the surface of the composite specimens. The formation reactions of interfacial MgAl₂O₄ are as follows: Mg(1) + 2Al(1) + 2O₂(g) = MgAl₂O₄(s)3Mg(1) + 4Al₂O₃(s) = 3MgAl₂O₄(s) + 2Al(1) Both of them are equally important.