Microstructural study of titanium–palladium–nickel base thin film shape memory alloys

A new generation of thin film shape memory alloys has been developed with 1.65 μm thickness for micro-actuator applications. In this work, the microstructure of thin film Titanium–Palladium–Nickel (TiPdNi) shape memory alloys deposited using ion beam assisted deposition from a Ti₅₀Pd₃₀Ni₂₀ target is studied. The TiPdNi thin films were deposited with and without substrate heating during deposition. As-deposited films without substrate heating were found to be amorphous. Deposition on heated substrate produced a dense, columnar crystalline structure. Microstructures of bulk TiPdNi thin films as well as the interfacial region between the film and substrate were characterized by various techniques including transmission electron microscope, scanning transmission electron microscope, scanning electron microscope-energy dispersive X-ray spectroscopy and scanning transmission electron microscope-energy dispersive X-ray spectroscopy. A transition layer with 70 nm thickness is observed at the interface between the bulk film and silicon substrate. It is composed of three layers; two amorphous layers above the silicon substrate and a 50 nm thick twin absent layer, which was identified as B2 austenite phase by Fourier spectra analysis. In the bulk film, nano-scale grains in the range of 80–200 nm were observed. The width of twin band of the film was very narrower in the range of 5 nm.     

Properties of GaAs solar cells coated with diamondlike carbon films

Thin films of amorphous diamondlike carbon (a:DLC) were deposited on GaAs solar cells, with and without antireflecting coating. The films were deposited by decomposition of CH₄ plasma using a r.f. generator (13.56 MHz). The reflected light from these cells, in the visible light, decreased after deposition of a:DLC film thickness (from 33% for t=0 nm to 14% for t=60 nm) which indicates antireflecting properties. The I–V measurements show an increase of the short circuit current (I_sc) with films thickness up to t40–60 nm, where it reaches a maximum and then decreases for higher thickness (t>60 nm). The efficiency (η) of the cells, as a function of the a:DLC thickness, shows a maximum value of 15% for t=50 nm. It was also shown, that the a:DLC films is a useful material as a protecting material for cells for operation in an abrasive environment. In abrasive environment, the efficiency of the coated cell maintains the level of about 12% whereas the efficiency of uncoated cells drop sharply from 15.5% to 6%.     

氧化锌脱膜和激光刻蚀制备亚微米自支撑聚酰亚胺薄膜及其性能

探讨小于1 μm自支撑聚酰亚胺薄膜的制备及其性能。以稀盐酸为腐蚀剂, 对涂于氧化锌衬底上的聚酰胺酸薄膜进行剥离, 经热亚胺转化为聚酰亚胺薄膜, 再用准分子激光对其刻蚀减薄。采用原子力显微镜、傅里叶变换红外光谱仪和分光光度计对薄膜的微观结构和光谱性能进行了表征。结果表明, 以室温下溅射的氧化锌薄膜为脱膜剂, 制备了厚度约950 nm的自支撑薄膜, 而激光刻蚀使聚酰亚胺薄膜厚度减薄至150 nm。厚度分别为950和150 nm薄膜的红外谱中均出现了聚酰亚胺特征吸收峰(1775、1720、1380和725 cm^-1), 且两者在400~2500 nm范围的平均透过率分别为80.3% 和83.5%。     

Aluminum-induced crystallization of amorphous silicon films deposited by hot wire chemical vapor deposition on glass substrates

Aluminum-induced crystallization of amorphous silicon films is discussed. Amorphous Si films were deposited by hot wire chemical vapor deposition onto Al coated glass substrates at 430 °C. Complete crystallization of a-Si films was achieved during a-Si deposition by controlling Al and Si layer thicknesses. The grain structure of the poly-Si films formed on glass substrate was evaluated by optical and electron microscopy. Continuous poly-Si films were obtained using Al layers with a thickness of 500 nm or less. The average grain size was found to be 10-15 μm, corresponding to a grain size/thickness ratio greater than 20.     

XPS characterisations of passive films formed on martensitic stainless steel: qualitative and quantitative investigations

HNO₃ passivation treatments on martensitic stainless steels used for surgical instrumentation were studied. The pitting corrosion resistance was determined by electropotentiodynamic experiments. The composition and the thickness of the passive films were investigated by XPS. The pitting corrosion potential was more noble for HNO₃-passivated sample than for air-passivated sample. The different methods proposed in the literature to estimate the thickness of passive layers were used and compared. Passive films obtained by HNO₃-passivation were thinner (3 nm) than air-passivated films (4–5 nm). The composition of these passive films also differs. HNO₃-passivated films were enriched in oxidised chromium which represent half of the metallic elements in the passive layer.     

柱状晶形貌TiO2膜厚对FTO/TiO2镀膜玻璃光催化活性影响

采用溶胶凝胶法,在FTO(SnO2:F)低辐射镀膜玻璃衬底上制备了柱状晶体结构的TiO2薄膜,获得双层结构FTO/TiO2镀膜玻璃样品.研究了TiO2薄膜厚度对FTO/TiO2镀膜玻璃样品的光催化活性、低辐射性能以及透光性能的影响.结果表明,FTO/TiO2镀膜玻璃样品光催化活性随着TiO2薄膜厚度的增加先升高后下降,在TiO2薄膜厚度为300 nm时光催化活性最佳;低辐射性能随着TiO2薄膜厚度的增加而下降,但TiO2薄膜厚度为300 nm时仍然具备一定的低辐射性能;透光性能与TiO2薄膜膜厚的关系不大,可见光透射比保持在72%左右;表面平均粗糙度约为1 nm,表面光滑,不易沾染油污灰尘.该镀膜玻璃在保证低辐射建筑节能和透光的前提下,兼具光催化自清洁功能,具有很好的应用前景.     

Dip-coating conditions and modifications of lead titanate and lead zirconate titanate films

The modifications of dip-coated lead titanate (PT) and lead zirconate titanate (PZT) films strongly depend on the film thickness and the substrate in addition to the heat-treatment temperature. At 500 to 600 ° C, metastable paraelectric pyrochlore grew on glass plates (amorphous plates) when the thickness of the coated films produced by one coating cycle was below 100 nm, while ferroelectric perovskite formed on crystalline substrates or when thick films were coated on amorphous plates. This tendency is discussed in terms of an inhomogeneous reaction and the epitaxial effect. The perovskite PT films coated on single-crystal SrTiO₃ plate at 700 ° C were strongly oriented to thec-axis.     

Thickness measurement of SiO2 films thinner than 1 nm by X-ray photoelectron spectroscopy

The thickness measurement of ultra-thin SiO₂ films thinner than 1 nm was studied by X-ray photoelectron spectroscopy (XPS). Amorphous SiO₂ thin films were grown on amorphous Si films to avoid the thickness difference due to the crystalline structure of a substrate. SiO₂ thin films were grown by ion beam sputter deposition under oxygen gas flow and the thickness was measured by in situ XPS. The attenuation length was determined experimentally by a SiO₂ film with a known thickness. The straight line fit between the measured thickness using XPS and the nominal thickness showed a good linear relation with a gradient of 0.969 and a small offset of 0.126 nm. The gradient measured at the range of 3.4–0.28 nm was very close to that measured at sub-nanometer range of 1.13–0.28 nm. This result means that the reliable measurement of SiO₂ film thickness below 1 nm is possible by XPS.     

Optical characteristics of thin ZnSe films of different thicknesses

Polycrystalline ZnSe films of thicknesses 54–785 nm deposited on glass substrates by thermal evaporation were investigated. X-ray diffraction analysis was carried out on as-deposited and annealed films to determine their structure. The ZnSe films were polycrystalline of cubic structure with preferred [111] orientation. Transmission and reflection at normal incidence were performed on ZnSe films in the wavelength range 350–2500 nm to determine the optical constants and optical energy gap. The optical gaps of ZnSe films show remarkable dependence on the film thickness. Analysis of the absorption data revealed the existence of two transition processes (with energy gaps at 2.7 and 2.22 eV for the bulk ZnSe).     

Stress variation in epitaxial GaAs films on silicon under thermal treatment

High quality epitaxial GaAs films of 1.8 and 6.3 μm thickness on silicon substrates were examined for lattice distortion, misalignment and curvature by X-ray diffraction (Bond method) at 20–400 °C. These films were deposited by the metal-organic chemical vapour deposition method on the (001) plane of silicon using a buffer layer produced at T_b = 370 or 460 °C. A top layer was then grown at T_t = 560 or 650 °C. The GaAs films contract more strongly on cooling than the substrate, which causes a curvature and a tetragonal distortion below a critical temperature T_c. This temperature varies on thermal treatment at 200–400 °C and approaches T_b, the growth temperature of the buffer layer. The tetragonal distortion can be stabilized, so that T_c approximates T_b, if the GaAs films are annealed for several days at 400 °C.     

Film thickness dependence on the optical properties of sputtered and UHV deposited Ti thin films

Titanium films of different thicknesses were deposited on glass substrates, using planar magnetron sputtering at 313 K substrate temperature. Their optical properties were measured by spectrophotometry in the spectral range of 200-2500 nm. Kramers-Kronig method was used for the analysis of the reflectivity curves of Ti films to obtain the optical constants of the films. In order to compare the influence of thickness of Ti films prepared using two different PVD methods, namely sputtering and electron gun depositions on the optical properties of Ti films, the optical results of Savaloni and Kangarloo (2007) for Ti films produced using electron gun deposition under UHV condition at 313 K substrate temperature are incorporated in this work.The analysis of the residual stress in the sputter deposited films using sin² ψ technique and the nano-strain in the E. Gun deposited films obtained from X-ray diffraction line broadening analysis (Warren-Averbach method) showed consistency with the results obtained for optical functions and agreed well with the predictions of both structural zone model (SZM) and effective medium approximation (EMA) results. Therefore, a direct correlation between the optical properties and the processes involved in the evolution of thin films is established.The optical data, in particular the conductivity results for sputter deposited Ti films show more agreement with those of bulk sample (Lynch et al., 1975), while those of UHV E. Gun deposited films are more consistent with those of thin film sample (Johnson and Christy, 1974).     

The optical properties of CuGa0.5In0.5Se2 thin films

CuGa_0.5In_0.5Se₂ thin films with thickness in the range 50 to 280 nm were deposited by thermal evaporation of prereacted material on glass substrates. The films were found to be polycrystalline with single phase having chalcopyrite structure as that of bulk material. The optical constants of these films were determined by transmittance and reflectance measurements at normal incidence for light in the wavelength range 400 to 1200 nm. Three characteristic energy gaps of 1.30, 1.55 and 2.46 eV were obtained from an analysis of the optical absorption spectrum. The optical constants of the films appear to be independent of the substrate temperature.     

Epitaxial growth of Ni films sputter-deposited on a GaAs(001) surface covered with a MgO film

We studied the epitaxial growth of a Ni film prepared on a GaAs(001) substrate covered with a thin epitaxial MgO buffer film, assuming that this buffer film plays a key role in the epitaxial growth of the Ni film. The MgO and Ni films were deposited by radio-frequency magnetron sputtering of the MgO and Ni targets in pure Ar gas. First, a MgO film of thickness ranging from 78 to 4.4 nm was deposited on the GaAs(001) substrate at a temperature ranging from ambient temperature to 700 °C, and then, a 136-nm-thick Ni film was deposited on the MgO/GaAs substrate at a temperature range 300-500 °C. Using transmission electron microscopy and X-ray diffractometry, we showed that the MgO film grows with the epitaxial relationship MgO(001)[001]//GaAs(001)[001] on GaAs(001) at 500 °C, and that the structure of the Ni film depends on three factors: the MgO/GaAs substrate temperature, the MgO thickness, and the annealing condition of the MgO/GaAs substrate before the Ni deposition. In conclusion, we proved that the Ni film grows with the epitaxial relationship Ni(001)[001]//MgO(001)[001]//GaAs(001)[001] on MgO/GaAs with the 4.4-nm-thick MgO film when the MgO/GaAs substrate is annealed in situ at room temperature before the Ni deposition and maintained at 300 °C during the Ni deposition.     

Heat treatment effects on the formation of lanthanum-modified lead zirconate titanate thin films

The microstructural and compositional properties of lanthanum-modified lead zirconate titanate (PLZT) thin films deposited on platinum coated Si substrates by RF magnetron sputtering have been studied. The heat treatment processes of substrate heating during deposition and post deposition furnace and rapid thermal annealing were compared as processes for obtaining the desired pervoskite phase. PLZT thin films deposited with in-situ substrate heating showed little evidence of micro-cracking. The XRD data obtained showed the formation of pervoskite phase at 550 °C and indicated the suppression of the pyrochlore phase for increasing temperatures. The RBS analysis revealed a film thickness of 140 nm and composition of (Pb_0.91La_0.09)(Zr_0.6Ti_0.4)O₃. Deposition performed with in-situ substrate heating at 650 °C resulted in highly (110) pervoskite orientated thin films with an average grain size around 160 to 200 nm and an RMS roughness of 3 nm.     

Multiple-angle-of-incidence ellipsometry for GaAs\GaPAs superlattices

In this paper we present results of multiple-angle-of-incidence (MAI) ellipsometry for strained GaAs\GaP_xAs_1−x superlattices (SL) with the composition x ≈ 0.4 and with different layer thickness in the range of 8–80 nm. SLs have been grown on the GaAs (100) substrates by chemical vapour deposition. The geometrical parameters of SLs have been determined by X-ray diffraction patterns. From MAI measurements the thickness and optical constants of SL films have been calculated by solving inverse ellipsometric problem. The latter was solved by using Tichonov’s regularization algorithm. The anisotropic film model of SL and capping isotropic layer were taken into account at solving. The optical constants obtained together with the full thickness of SL have been related to the SL microstructure using an effective medium approximation. These results are compared with ones obtained by far-infrared reflection spectroscopy in the ‘‘reststrahlen’’ band region. The quality of SLs in connection with technology of thin films growth are discussed.     

Properties of SnO2 films fabricated using a rectangular filtered vacuum arc plasma source

Transparent and conducting SnO₂ films of 57–200nm thickness were deposited on microscope glass slide substrates, using a rectangular filtered vacuum arc deposition system. The 40 glass slides were equally distributed on a 400 × 420mm substrate carriage, and were exposed to a Sn plasma beam, produced by a rectangular vacuum arc plasma gun with a Sn cathode, and passed through a rectangular magnetic macroparticle filter towards the substrates. The carriage with the substrates was transported past the 94 × 494mm filter outlet. The SnO₂ films were fabricated on the glass substrates at room temperature by maintaining the chamber oxygen background pressure at 0.52Pa. The film composition, and electrical and optical properties were studied as a function of the film thickness. The films were stored under ambient air conditions, and their electrical resistance was measured as a function of storage time over a period of several months.

The average resistivity of films was 10–17mΩ cm for films with thickness (t) less than 100nm, but that of t > 100nm it was 5–9mΩ cm. The resistivity of the films with t > 100nm did not change significantly after 8months of storage in ambient air. The optical transmittance of the films in the visible spectrum was in the range of 75–90%. The optical constants, i.e., the refractive index and the extinction coefficient of the films at wavelength λ = 550nm were in the range of 2.02–2.09 and 0.013–0.023, respectively, and the optical band gap energy was 4.15–4.21eV. Unlike the electrical resistivity, the optical parameters weakly depended on t.     

Photoluminescence study of GaAs thin films and nanowires grown on Si(111)

Mg-doped GaAs nanowires have been grown by molecular beam epitaxy on a partially Au-coated Si(111) substrate by the vapor–liquid–solid mechanism. Outside the coated areas, a thin film of GaAs was grown epitaxially at the same time. The optical properties in both parts of the sample were investigated by photoluminescence spectroscopy, as a function of temperature. A structured emission in the range ～1.25–1.55 eV was observed at 10 K and the resemblances in both cases were identified. The radiative transitions are discussed with relevance to known defect centers in the GaAs thin films and to their possible relation with the zinc-blende and wurtzite phases in the nanowires. The presence of both crystalline phases in the nanowires was confirmed by μ-Raman spectroscopy.     

The nature of stresses in hot-filament chemical vapour deposited diamond thin films on WC substrates

The nature of film stresses in hot-filament chemical vapour deposited (HFCVD) diamond thin films on tungsten carbide substrates, is reported. Commercial WC substrates were subjected to various surface treatments. Subsequently, they were coated with a diamond film and examined for stresses using X-ray diffraction. All but one of the stress measurements indicated various levels of compressive stresses in the film and at the film–substrate interface. These stresses are compared with those obtained by other researchers. Intrinsic film stresses were also computed for diamond films and found to be tensile. WC drills, of 0.125 in. diameter, were also diamond coated and the stress levels measured along drill flanks and flutes. Significant variations were found in these stresses, and the results were analysed from a film–substrate adhesion perspective.     

Photoluminescence studies on ZnSe1?x Te x films

ZnSe_1?x Te _x films were deposited by the electron beam evaporation technique at a substrate temperature of 300 °C on glass and ITO coated GaAs substrates. The films exhibited cubic structure. Photoluminescence (PL) was studied at room temperature using an excitation wavelength of 320 nm. The films deposited on glass substrates exhibited band edge luminescence and self activated luminescence bands at 2.69 and 2.39 eV respectively. Atomic force microscopic studies indicated that the grain size increased with increase of Te content in the ternary. PL studies on the ZnSe_1?x Te _x /GaAs/ITO strucrure was made with an excitation of 265 nm. The films exhibited band edge emission at 2.33 eV which confirms the incorporation of Te in ZnSe. Another peak ar 2.56 eV was also observed.     

Properties of GaAs films deposited by pulse periodic technique

GaAs is a III-V compound possessing high mobility and a direct band gap of 1.43 eV , making it a very suitable candidate for photovoltaic applications. Thin GaAs films were prepared at room temperature by plating an aqueous solution containing GaCl₃ and As₂O₃ at a pH of 2. The current density was kept as 50 mA cm⁻² and the duty cycle was varied in the range 10–50%. The films were deposited on titanium and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. The surface roughness of the films varied from 3 nm to 6 nm as the duty cycle increased. Raman spectra indicated both the LO and TO phonons for the films deposited at duty cycles above 25%. Photoelectrochemical studies indicated that the current and voltage output are higher than earlier reports on thin film electrodes.