Investigations on AlN/sapphire piezoelectric bilayer structure for high-temperature SAW applications

This paper explores the possibility of using AlN/sapphire piezoelectric bilayer structures for high-temperature SAW applications. To determine the temperature stability of AlN, homemade AlN/sapphire samples are annealed in air atmosphere for 2 to 20 h at temperatures from 700 to 1000°C. Ex situ X-ray diffraction measurements reveal that the microstructure of the thin film is not affected by temperatures below 1000°C. Ellipsometry and secondary ion mass spectroscopy investigations attest that AlN/sapphire is reliable up to 700°C. Beyond this temperature, both methods indicate ongoing surface oxidation of AlN. Additionally, Pt/Ta and Al interdigital transducers are patterned on the surface of the AlN film. The resulting SAW devices are characterized up to 500°C and 300°C, respectively, showing reliable frequency response and a large, quasi-constant temperature sensitivity, with a first-order temperature coefficient of frequency around -75 ppm/°C. Between room temperature and 300°C, both electromechanical coupling coefficient K(2) and propagation losses increase, so the evolution of delay lines' insertion losses with temperature strongly depends on the length of the propagation path.     

Effect of substrate on processing of multi-gun sputter deposited, near-stoichiometric Ni2MnGa thin films

Near-stoichiometric Ni₂MnGa thin films were sputter deposited with a multi-gun sputter deposition system onto sapphire, silicon dioxide and silicon substrates and exposed to heat treatments in vacuum. The multi-gun setup was proven to be feasible for switching compositions quickly and reliably. Using chemical, morphological, magnetic and structural characterisation methods the effects of the different substrates on the Ni₂MnGa film properties as a function of heat treatment temperature were studied: sapphire and silicon dioxide provided a metallurgically inert substrate for Ni₂MnGa thin films and resulted in films showing room temperature magnetizations of up to  ~ 350 kA/m and austenitic/martensitic structures upon heat treatments at 700 °C. The highest mechanical stability of Ni₂MnGa occurred on sapphire substrates, due to the closest match of the thermal expansion coefficients. Silicon substrates led to silicide formation for heating temperatures of 550 °C and above, leading to the loss of ferromagnetism and the austenite/martensite structure in the films.     

Infrared and raman spectroscopic studies of optically transparent zirconia (ZrO2) films deposited by plasma-assisted reactive pulsed laser deposition

Plasma-assisted pulsed laser deposited zirconia (ZrO(2)) films were studied by Fourier transform infrared (FT-IR) and Raman spectroscopy for structural characterization and thermal stability in combination with optical characterization by spectroscopic ellipsometry and optical transmission measurements. Only the monoclinic ZrO(2) phase was positively identified from the infrared and Raman spectra of the as-deposited ZrO(2) films, which show excellent optical transparency from the ultraviolet to the near infrared as revealed by optical characterization. The as-deposited ZrO(2) films are free of any SiO(x) interfacial layer when deposited on silicon. The prepared ZrO(2) films exhibit good thermal stability in their structural, optical, and interfacial properties up to 900 °C. Upon annealing above 1100 °C, a silicon oxide interfacial layer forms due to the oxidation of the silicon substrate surface by the oxygen diffused from the oxide film to the silicon substrate at high temperatures.     

Laser damage properties of TiO2/Al2O3 thin films grown by atomic layer deposition

Research on thin film deposited by atomic layer deposition (ALD) for laser damage resistance is rare. In this paper, it has been used to deposit TiO(2)/Al(2)O(3) films at 110 °C and 280 °C on fused silica and BK7 substrates. Microstructure of the thin films was investigated by x-ray diffraction. The laser-induced damage threshold (LIDT) of samples was measured by a damage test system. Damage morphology was studied under a Nomarski differential interference contrast microscope and further checked under an atomic force microscope. Multilayers deposited at different temperatures were compared. The results show that the films deposited by ALD had better uniformity and transmission; in this paper, the uniformity is better than 99% over 100 mm Φ samples, and the transmission is more than 99.8% at 1064 nm. Deposition temperature affects the deposition rate and the thin film microstructure and further influences the LIDT of the thin films. As to the TiO(2)/Al(2)O(3) films, the LIDTs were 6.73±0.47 J/cm(2) and 6.5±0.46 J/cm(2) at 110 °C on fused silica and BK7 substrates, respectively. The LIDTs at 11 °C are notably better than 280 °C.     

蓝宝石衬底上制备SiO2薄膜的研究

采用射频磁控反应溅射法,以高纯Si为靶材,高纯O2为反应气体,成功地在蓝宝石基片上制备出了二氧化硅(SiO2)薄膜,并对薄膜的沉积速率、成分、结构及红外光学性能进行了研究.结果表明,制备的SiO2薄膜与蓝宝石衬底结合牢固;和其它镀膜技术相比,射频磁控反应溅射法可以在较低的温度下制备出SiO2薄膜;制备出的SiO2薄膜在3～5μm波段对蓝宝石衬底有明显的增透效果.     

应力对蓝宝石衬底上生长二氧化钒薄膜结构和光电性能的调控

利用脉冲激光沉积技术在蓝宝石衬底上生长不同厚度的VO₂薄膜, 对薄膜的结构、表面形貌和光电性能进行研究。结果表明: 所沉积的VO₂薄膜为具有单晶性能、表面平整的单斜晶相的VO₂薄膜, 相变前后, 方块电阻的变化可达到3~4个数量级, 在波长为2500 nm的透过率变化最高可达56%, 优化的可视透过率(T_lum)和太阳能调节率( ∆T_sol )为43.2%和8.7%。薄膜受到的应力对VO₂薄膜有重要影响, 可以通过调节薄膜的厚度对VO₂薄膜光电性能实现调控。当VO₂薄膜厚度较小时, 薄膜受到拉应力, 拉应力能使相变温度显著降低, 金属-绝缘体转变性能(MIT)不但与载流子浓度的变化相关, 而且还受载流子迁移率变化的影响;当VO₂薄膜厚度较大时, 薄膜受到压应力, VO₂薄膜的相变温度接近块体VO₂的相变温度, MIT转变主要来自于载流子浓度在相变前后的变化, 其载流子迁移率几乎不变。     

Infrared waveguide fabrications with an E-beam evaporated chalcogenide glass film

Chalcogenide glasses have a variety of unique optical properties due to the intrinsic structural flexibility and bonds metastability. They are desirable materials for many applications, such as infrared communication sensors, holographic grating, optical imaging, and ultrafast nonlinear optic devices. Here, we introduce a novel electron-beam evaporation process to deposit the good quality arsenic trisulfide (As₂S₃) films and then the As₂S₃ films were used to fabricate the As₂S₃ waveguides with three approaches. The first method is photoresist lift-off. Because of the restriction of thermal budget of photoresist, the As₂S₃ film must be deposited at the room temperature. The second one is the silicon dioxide lift-off process on sapphire substrates, in which the As₂S₃ film could be evaporated at a high temperature (>180 °C) for better film quality. The third one is the plasma etching process with a metal protective thin layer in the pattern development process.     

Zr/ZrO2 sensors for in situ measurement of pH in high-temperature and -pressure aqueous solutions

The aim of this study is to develop new pH sensors that can be used to test and monitor hydrogen ion activity in hydrothermal conditions. A Zr/ZrO2 oxidation electrode is fabricated for in situ pH measurement of high-temperature aqueous solutions. This sensor responds rapidly and precisely to pH over a wide range of temperature and pressure. The Zr/ZrO2 electrode was made by oxidizing zirconium metal wire with Na2CO3 melt, which produced a thin film of ZrO2 on its surface. Thus, an oxidation-reduction electrode was produced. The Zr/ZrO2 electrode has a good electrochemical stability over a wide range of pH in high-temperature aqueous solutions when used with a Ag/AgCl reference electrode. Measurements of the Zr/ZrO2 sensor potential against a Ag/AgCl reference electrode is shown to vary linearly with pH between temperatures 20 and 200 degrees C. The slope of the potential versus pH at high temperature is slightly below the theoretical value indicated by the Nernst equation; such deviation is attributed to the fact that the sensor is not strictly at equilibrium with the solution to be tested in a short period of time. The Zr/ZrO2 sensor can be calibrated over the conditions that exist in the natural deep-seawater. Our studies showed that the Zr/ZrO2 electrode is a suitable pH sensor for the hydrothermal systems at midocean ridge or other geothermal systems with the high-temperature environment. Yttria-stabilized zirconia sensors have also been used to investigate the pH of hydrothermal fluids in hot springs vents at midocean ridge. These sensors, however, are not sensitive below 200 degrees C. Zr/ZrO2 sensors have wider temperature range and can be severed as good alternative sensors for measuring the pH of hydrothermal fluids.     

Synthesis of nanocrystalline TiO2 thin films by liquid phase deposition technique and its application for photocatalytic degradation studies

A transparent, high purity titanium dioxide thin film composed of densely packed nanometer sized grains has been successfully deposited on a glass substrate at 30°C from an aqueous solution of TiO₂-HF with the addition of boric acid as a scavenger by liquid phase deposition technique. From X-ray diffraction measurement, the deposited film was found to be amorphous and turns crystalline at 500°C. The deposited film showed excellent adherence to the substrate and was characterized by homogeneous flat surface. TiO₂ thin films can be used as a photocatalyst to clean up organohalides, a class of compound in pesticides that pollute the ground water. Photocatalytic degradation experiments show that indanthrene golden orange dye undergoes degradation efficiently in presence of TiO₂ thin films by exposing its aqueous solution to ultraviolet light. The suitable surface structure and porosity increases the photocatalytic activity. It was also observed that hemin doped TiO₂ thin films break up organohalides at a surprisingly high rate under visible light.     

二氧化钒薄膜在α-Al2O3衬底上的外延生长及其金属-半导体相变特性研究

利用ＸＲＤ及ＸＲＤ极图技术表征了用激光剥离技术生长的ＶＯ_２薄膜．结果表明：在衬底温度为５００℃,氧气偏压６．６７Ｐａ的条件下,在Ａｌ_２Ｏ_３（１１２０）衬底上能实现ＶＯ_２的二维外延生长．薄膜的结构除了与沉积工艺有关外,还和衬底的取向密切相关．在Ａｌ_２Ｏ_３（１１２０）衬底上,定向生长的（１００）ＶＯ_２在Ｍｉｌｌａｒ指数＜５时,除了［０１０］以外,不存在其他晶格矢量与衬底相匹配,从而不可能实现三维单晶薄膜的外延生长．电学特性的测试结果显示,在温度为６５℃左右,ＶＯ_２薄膜出现相交,薄膜的电阻率变化达４个数量级．     

ZnO thin films deposited by a CVT technique in closed ampoules

ZnO thin films were prepared on quartz glass, Si (100), and sapphire (001) substrates by a chemical vapour transport (CVT) technique. During the growing processes, the source and substrate temperatures were maintained at 1000 °C and 600 °C, respectively. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements showed that the crystalline qualities of ZnO thin films were sensitively dependent on substrates. ZnO thin film deposited on sapphire substrate exhibited the best morphology with the largest crystallite size of more than 20 μm. Meanwhile, the XRD patterns showed that ZnO thin film deposited on sapphire substrate was strongly c-axis preferred-oriented with high crystalline quality. The optical properties of ZnO thin films were investigated by photoluminescence (PL) spectroscopy at room temperature (RT). The results suggested that the optical properties of ZnO thin films were highly influenced by their crystalline qualities and surface morphologies.     

Material and sensing properties of Pd-deposited WO3 thin films

The physicochemical and electrical properties of Pd-deposited WO3 thin films were investigated as a function of Pd thickness, annealing temperature, and operating temperature for application as a hydrogen gas sensor. WO3 thin films were deposited on an insulating material using a thermal evaporator. X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to evaluate the crystal structure, microstructure, surface roughness, and chemical property of the films, respectively. The deposited films grew into polycrystalline WO3 with a rhombohedral structure after annealing at 500 degrees C. Adding Pd had no effect on the crystallinity, but suppressed the growth of WO3 grains. The Pd was scattered as isolated small spherical particles of PdO2 on the WO3 thin film after annealing at 500 degrees C, while it agglomerated as irregular large particles or diffused into the WO3 after annealing at 600 degrees C. PdO2 reduction under H2 and reoxidation under air were dependent on both the Pd deposition thickness and annealing conditions. The WO3 thin film with a 2-nm-thick Pd deposit showed a good response and recovery to H2 gas at a 250 degrees C operating temperature.     

蓝宝石光纤黑体腔传感器定度技术研究

基于Planck辐射原理和光纤测温技术的溅射高温陶瓷薄膜的蓝宝石光纤黑体腔传感器可进行恶劣环境下瞬态高温的测量。本文介绍了该传感器的结构和用来对其进行定度的系统,将已标定的钨铼热电偶和被定度的瞬态表面高温传感器同时置于乙炔焰热源所形成的高温均热金属熔池,实现了传感器静态定度;采用阶跃上升的高功率CO2激光脉冲对黑体感温腔加热进行动态标定,解决了此类高温传感器在工程应用中的标定问题。实验结果表明该传感器响应时间在10^-2s数量级,标定技术简单实用,利用该传感器首次成功地测量了某导弹发射时的瞬态高温。     

Post treatment of plasma-polymerized SnOx organic-like films with poly ethylene glycol for improving CO gas sensitivity

In this study, a new room temperature type gas sensor device based on plasma deposition of tetramethyltin (TMT) and O2 organically hybridized film followed by post treatment on the deposited film was developed for improving CO gas sensitivity and distinguishing from methane, butane, and carbon monoxide gases in the test environment. Plasma deposited SnOx thin film was first produced from TMT and O2 gas mixtures at room temperature, and then post treatments on the SnOx thin films were carried out by either spin coating with poly ethylene glycol (PEG) or surface grafting with p-styrenesulfonic acid sodium salt (Nass). It was found that the gas sensor spin coating post treated with PEG exhibits linear response to CO gas with the sensitivity not affected by methane and butane gases. For CO concentrations ranging from 30 to 650 ppm, steep change in the sensor resistance can be detected without warming up the sensor.     

Effect of film thickness and annealing on optical properties of TiO2 thin films and electrical characterization of MOS capacitors

Titanium dioxide (TiO₂) thin films were deposited on glass and silicon (100) substrates by the sol–gel method. The influence of film thickness and annealing temperature on optical transmittance/reflectance of TiO₂ films was studied. TiO₂ films were used to fabricate metal–oxide–semiconductor capacitors. The capacitance–voltage (C–V), dissipation–voltage (D–V) and current–voltage (I–V) characteristics were studied at different annealing temperatures and the dielectric constant, current density and resistivity were estimated. The loss tangent (dissipation) increased with increase of annealing temperature.     

Al2O3/silicon nanoISFET with near ideal nernstian response

Nanoscale ISFET (ion sensitive field-effect transistor) pH sensors are presented that produce the well-known sub-nernstian pH-response for silicon dioxide (SiO(2)) surfaces and near ideal nernstian sensitivity for alumina (Al(2)O(3)) surfaces. Titration experiments of SiO(2) surfaces resulted in a varying pH sensitivity ～20 mV/pH for pH near 2 and >45 mV/pH for pH > 5. Measured pH responses from titrations of thin (15 nm) atomic layer deposited (ALD) alumina (Al(2)O(3)) surfaces on the nanoISFETs resulted in near ideal nernstian pH sensitivity of 57.8 ± 1.2 mV/pH (pH range: 2-10; T = 22 °C) and temperature sensitivity of 0.19 mV/pH °C (22 °C ≤ T ≤ 40 °C). A comprehensive analytical model of the nanoISFET sensor, which is based on the combined Gouy-Chapman-Stern and Site-Binding (GCS-SB) model, accompanies the experimental results and an extracted ΔpK ≈ 1.5 from the measured responses further supports the near ideal nernstian pH sensitivity.     

晶粒尺寸对氧化钒薄膜电学与光学相变特性的影响

采用直流对靶磁控溅射方法制备氧化钒薄膜,通过改变热处理温度获得了具有不同晶粒尺寸的相变特性氧化钒薄膜,对氧化钒薄膜相变过程中电阻和红外光透射率随温度的突变性能进行研究.结果表明:经300℃和360℃热处理后,薄膜内二氧化钒原子分数达到40%,氧化钒薄膜具有绝缘体-金属相变特性,薄膜的晶粒尺寸分别为50nm和100nm;...     

Structural and optical characterizations of nitrogen-doped ZnO nanowires grown by MOCVD

One dimensional nitrogen-doped ZnO nanowires were deposited on C-plane sapphire using metal organic chemical vapour deposition. Nanowires have been characterized by scanning electron microscopy, transmission electron microscopy, micro-Raman scattering and micro-photoluminescence spectroscopy. The structural analysis has shown a high crystalline quality. In N-doped ZnO nanowires nitrogen incorporation was emphasized by Raman spectral analysis and reduction of nitrogen concentration along the wire, from the bottom to the top was found by local analysis. Low temperature micro-photoluminescence spectra exhibit donor-acceptor pair transitions.     

Crystallography of epitaxially grown molybdenum on sapphire

Molybdenum thin films were deposited onto (0001), ($\text{1012}$) and (10$\text{12}$) sapphire substrates by electron-beam evaporation in ultrahigh vacuum. The surface morphology and crystallographic orientation of these films were characterized by electron microscope replication and reflection electron diffraction. The effect of the crystallographic plane of the sapphire substrates as well as that of the deposition rate on the crystallographic orientation of the deposited molybdenum films were examined in the temperature range 25°-1000°C. The epitaxial temperature range was 600°-900°C for basal plane substrates and 300°-1000°C for ($\text{1}$012) and (10$\text{1}$2) substrates. The orientation of the deposited film was strongly dependent on that of the sapphire substrate.     

低温制备二氧化钛纳米薄膜研究进展

低温下制备二氧化钛薄膜具有重要的意义.开发纳米晶TiO2薄膜低温制备技术,可以提高太阳能电池光电转化效率及气体传感器的气敏性能,并且对拓展光催化技术的应用领域、降低生产成本尤为重要.本文就低温制备二氧化钛薄膜的进展情况进行了详细的介绍.