Effect of deposition temperature on structural, surface, optical and magnetic properties of pulsed laser deposited Al-doped CdO thin films

The objective of this work is to study the influence of deposition temperature on structural, surface, optical and magnetic properties of the Al doped CdO thin films prepared by pulsed laser deposition (PLD) technique. KrF excimer laser (λ = 248 nm, τ_l = 20 ns, ν = 10 Hz, ?_l = 2.5 J/cm²) was employed for the deposition of thin films. It is observed by XRD results that films grown at room temperature and 100 °C show preferential growth along (1 1 1) and (2 0 0) directions while high temperatures (200-400 °C) lead to preferential growth along the (2 0 0) direction only. The optical constants (n, k, α, and optical band gap energy) of films measured by spectroscopic ellipsometry show strong dependence upon deposition temperature. M-H loop of films, measured by vibrating sample magnetometer, deposited at 25 °C and 100 °C show paramagnetic nature while films deposited at temperatures (200-400 °C) exhibit ferromagnetic character. Scanning electron micrographs show degraded elongated grains at lower deposition temperatures, while smooth and compact surface is observed for films deposited at higher deposition temperatures.     

Realization of stable p-type ZnO thin films using Li-N dual acceptors

Lithium and nitrogen dual acceptors-doped p-type ZnO thin films have been prepared using spray pyrolysis technique. The influence of dual acceptor (Li, N) doping on the structural, electrical, and optical properties of (Li, N):ZnO films are investigated in detail. The (Li, N):ZnO films exhibit good crystallinity with a preferred c-axis orientation. From AFM studies, it is found that the surface roughness of the thin films increases with the increase of doping percentage. The Hall Effect measurements showed p-type conductivity. The Hall measurements have been performed periodically up to seven months and it is observed that the films show p-type conductivity throughout the period of observation. The samples with Li:N ratio of 8:8 mol% showed the lowest resistivity of 35.78 Ω cm, while sample with Li:N ratio of 6:6 mol% showed highest carrier concentration. The PL spectra of (Li, N):ZnO films show a strong UV emission at room temperature. Furthermore, PL spectra show low intensity in deep level transition, indicating a low density of native defects. This indicates that the formation of intrinsic defects is effectively suppressed by dual acceptor (Li, N) doping in ZnO thin films. The chemical bonding states of N and Li in the films were examined by XPS analysis.     

The effects of vacuum annealing on the structure of VO2 thin films

Noncrystalline VO_x thin films were deposited onto p-doped Si (100) substrates at 400 °C using magnetron sputtering. By vacuum annealing, we obtained polycrystalline VO₂ thin films with two different structures under a variety of annealing conditions. With the annealing temperature increasing and the annealing time developing, structures of the films underwent the following transformation: amorphous structure→metastable VO₂ (B)→VO₂ (B) + VO₂ (M). Vacuum annealing is useful of acquiring VO₂ thin films with high surface quality, but too high annealing temperature (500 °C) and too long time (15 h) are harmful, which make the surface degenerate.     

High temperature dependence of the cubic phase content and optical properties of BN thin films

The temperature dependence of the cubic phase content and optical properties of Boron nitrogen (BN) thin films was studied in this paper. The BN thin films were deposited on fused silica and Si substrates by radio frequency bias magnetron sputtering. The BN film properties before and after annealing were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and UV-visible transmittance and reflection spectra. The results indicate that annealing temperature has a significant effect on the optical absorption edge, optical absorption coefficient α, refractive index n, and optical conductivity σ of BN films. The optical absorption edge shift to the high energy with annealing temperature increase indicates that the film optical band gap E_g becomes large. The change in the optical absorption properties results from the stress relaxation and phase transformation owing to the high temperature annealings. The dependence of α on the photon energy is fitted by the Urbach tail model in order to determine the Urbach energy E₀. In addition, it is found that refractive index n exists clearly different dependences on temperature in visible and ultraviolet regions, and the optical conductivity σ threshold moves to high energy with increasing annealing temperatures in the threshold region.     

The evolution behavior of structures and photoluminescence of K-doped ZnO thin films under different annealing temperatures

In this work, 1 at.% K-doped ZnO thin films were prepared by sol-gel method on Si substrates. The evolution behavior of the structures and photoluminescence of these films under different annealing temperatures was deeply studied. The crystal structures and surface morphology of the samples were analyzed by an X-ray diffractometer and an atomic force microscope, respectively. The photoluminescence spectra were used to study the luminescent behavior of the samples. The results showed that the films had a hexagonal wurtzite structure and were preferentially oriented along the c-axis perpendicular to the substrate surface. All the samples showed a strong ultraviolet emission and a weak blue emission. With the increase of annealing temperature, the ZnO grains gradually grew up; at the same time, the blue emission gradually decreased. The sample annealed at 500 °C showed the best crystalline quality and strongest ultraviolet emission. The authors think that the blue emission in these samples is mainly connected with K interstitial defects. When the 1 at.% K-doped ZnO thin film is annealed at high temperatures (≥600 °C), most of K interstitials move into ZnO lattice sites replacing Zn. As a result, the blue emission resulting from K interstitial defects also decreased.     

Influence of ion-bombardment-energy on thin zirconium oxide films prepared by dual frequency oxygen plasma sputtering

Thin ZrO₂ films were prepared using dual frequency oxygen reactive plasma sputtering for wear-resistance coating of ceramics products. Influences of ion-bombardment-energy E_i were investigated for improvement of film characteristics. The results revealed that the deposition rate and the hardness of the prepared ZrO₂ thin films gradually increased with increasing E_i for E_i < 220-250 eV and then decreased, whereas the water-contact-angle on ZrO₂ thin films was about 90 °, having a good water-repellent nature.     

Influence of ZnO content and annealing temperature on the dielectric properties of ZnO/Al2O3 composite coatings

ZnO/Al₂O₃ coatings were prepared by atmospheric plasma spraying (APS) using ZnO powders and Al₂O₃ powders as starting materials. The dielectric properties of these coatings were discussed. Both the real part of permittivity and the energy loss increase greatly with increasing ZnO content over the frequency range 8.2-12.4 GHz, which can be ascribed to orientation polarization and relaxation polarization due to a higher ZnO content. The frequency-dependent maximum of the loss tangent is found to obey Debye theory. In addition, annealing temperature which leads to the change of ZnO content also plays an important role in the dielectric performance.     

Relationship between the growth rate and Al incorporation of AlGaN by metalorganic chemical vapor deposition

The growth rate and its relationship with growth conditions of AlGaN alloy films by metalorganic chemical vapor deposition (MOCVD) are investigated. It is found that both parasitic reaction and competitive adsorption play important roles in determining the growth rate and Al incorporation in AlGaN. Low reactor pressure can weaken parasitic reactions, thus increasing the Al composition. In addition, a decrease of absolute amount of Ga atoms arriving on the substrate may lead to a lower Ga competitive power, and then a higher Al content in AlGaN film.     

Effect of negative pulsed high-voltage-bias on diamond-like carbon thin film preparation using capacitively coupled radio-frequency plasma chemical vapor deposition

Mechanical properties of diamond-like carbon films by an effective addition of negative pulsed high-voltage-bias have been investigated in capacitively coupled CH₄/Ar radio-frequency plasma. The results revealed that hardness and elastic modulus of the deposited film, estimated from nano-indentation load-displacement curve for about 1 μm-thick films, increase with the increase of the absolute value of high-voltage V_NPHV for V_NPHV < 5 kV and then saturate. Elastic recovery R got the highest value (> 90%) at V_NPHV = 5 kV.     

Crystallographic, optical and electrical properties of low zinc content cadmium zinc sulphide composite thin films for photovoltaic applications

In this paper a screen-printing method has been employed for the deposition of low zinc content cadmium zinc sulphide (Cd_0.9Zn_0.1S) composite thin films on ultra clean glass substrate. Cadmium sulphide, zinc sulphide and cadmium chloride have been used as the basic source material. With these basic source materials, the optimum conditions for preparing good quality screen-printed films have been found. X-ray diffraction studies revealed that the films are polycrystalline in nature, single phase exhibiting wurtzite (hexagonal) structure with strong preferential orientation of grains along the (1 0 1) direction. SEM/EDAX analysis confirms the formation of ternary compound. The optical band gap (E_g) of the films has been studied by using reflection spectra in wavelength range 350-600 nm. The DC conductivity of the films has been measured in vacuum by a two probe technique.     

Influence of bias voltage on morphology and structure of MgO thin films prepared by cathodic vacuum arc deposition

MgO thin films with high optical transmittance were prepared by cathodic vacuum arc deposition technique. Rutherford backscattering spectroscopy, atomic force microscopy and X-ray diffraction were used to investigate the influences of the negative pulse bias voltage on the composition, the morphology and the crystal structure of MgO thin films, respectively. AFM images show that the grain growth is influenced by high energy ions under bias voltage and that the grains deposited at the pulse bias voltage with set value of |V_p| = 600 V stack densely and look the largest as compared to those prepared at different set V_p. The RBS spectra indicate that the Mg/O ratio is about 0.95-1.00 in MgO thin films which is nearly the stoichiometric composition of bulk MgO. The Mg/O ratio increases with set |V_p| until |V_p| is 450 V, and then keeps almost unchanged with set |V_p| up to 750 V. The MgO thin films have a combined orientation of (100) and (110). Below − 150 V, the (100) orientation is predominant and the intensity ratio of I₂₂₀/I₂₀₀ increases with set |V_p|.     

Influence of substrate bias on the composition of SiC thin films fabricated by PECVD and underlying mechanism

The influence of the substrate bias on the composition of SiC thin films synthesized by plasma-enhanced chemical vapor deposition was studied. Our results indicate that the ratio of Si to C in the thin films is almost stoichiometric at a bias of − 300 V, whereas excessive carbon is observed in the films if the bias is lower or higher. Very little oxygen can be detected in the film produced without biasing. The effects of the bias on the composition of the thin films can be attributed to the interaction between the positive ions in the plasma and the surface atoms. The underlying mechanism is also discussed.     

The influence of size effect of conductivity on the microwave absorption properties of thin Al films

采用中频磁控溅射法制备不同厚度的Al膜。利用直线型四探针法测量不同厚度Al膜的电导率,研究薄膜直流电导率随厚度的变化关系（尺寸效应）;并利用网络矢量分析仪测量Al膜与FR4-epoxy环氧树脂玻璃板复合结构微波吸收率,研究电导率尺寸效应对Al膜微波吸收性能的影响。实验结果表明：薄膜厚度对金属Al膜的电导率产生主要影响;在Al膜和FR4-epoxy环氧树脂玻璃板复合结构中,Al膜电导率变化对复合结构的最大吸收峰值以及吸收峰值对应的Al膜厚度会产生显著影响。实验结果利用传输矩阵方法计算得到了验证。     

Development and characterization of single wire-arc-plasma sprayed coatings of nickel on carbon blocks and alumina tube substrates

A single wire-arc-plasma spray torch has been used to develop metal coatings on carbon and alumina substrates under argon atmosphere for various applications. Nickel coatings of around 1 mm thickness have been deposited on selected area (60 mm × 200 mm on each side) of large size carbon blocks by intermittent arc spraying and cooling to reduce thermal stresses and possibility of coating de-lamination from the base substrate. The same process is also used for depositing about 3 mm thick nickel metal coatings (8 mm dia. × 40 mm long) on alumina tubes for developing electrical feed throughs. The nickel coated alumina tubes were tested for the vacuum compatibility of the coated material with the base tube. The coated assemblies could withstand vacuum of the order of 1 × 10^− 6 Torr and the leak rate was found to be less than 1 × 10^− 9 Std. cc/s for Helium gas, indicating excellent bonding of the coated metal with alumina ceramics and no connected open porosity in the coatings. X-ray diffraction studies were conducted for identifying the phases and the optical microscope with image analysis technique was used for studying the microstructure and porosity in the coatings.     

Influence of electrodeposition parameters on the deposition rate and microhardness of nanocrystalline Ni coatings

In this paper, nanocrystalline nickel (nc-Ni) coatings were prepared by a direct current electrodeposition technique. Their microstructure and microhardness were investigated by a high-resolution transmission electron microscopy and a microhardness tester. It is found that the electrodeposition parameters, including content of C₇H₄NO₃SNa?2H₂O, temperature and current density, have significant influences on the electrodeposition rate and microhardness of nc-Ni coatings. The electrodeposition rate increases with the current density stepwise. The largest electrodeposition rate is achieved at 60 °C. It decrease when the temperature is larger than 60 °C. The electrodeposition rate decreases with the increased content of C₇H₄NO₃SNa?2H₂O. The microhardnesses of the nc-Ni coatings are higher on the condition of the larger current density, lower temperature or higher content of C₇H₄NO₃SNa?2H₂O. But, it remains stable when the current density is in the range of 700-1000 A m^− 2. The relationship between the mean grain sizes and microhardness fits for the Hall-Petch function, approximately.     

Structural, optical and hydrophilic properties of nanocrystalline TiO2 ultra-thin films prepared by pulsed dc reactive magnetron sputtering

TiO₂ ultra-thin (15 nm) films were deposited on silicon wafers (100) and glass slides by pulsed dc reactive magnetron sputtering in an ultra-high vacuum (UHV) system. The effects of substrate temperature, from room temperature to 400 °C, on structural, optical, and hydrophilic properties of the obtained films have been investigated. The structure of the films was characterized by grazing-incidence X-ray diffraction, high-resolution transmission electron microscopy, and atomic force microscopy. The optical properties were determined by UV-vis spectrophotometer and spectroscopic ellipsometry. The hydrophilic properties of the films, after exposed to ultraviolet illumination, were analyzed from contact angle measurements. The results suggested that the substrate temperature at 300 °C was critical in the crystalline phase transformation from amorphous to anatase in the TiO₂ films. The obtained films exhibited good qualities in the optical properties, in addition to excellent photo-induced hydrophilic activities.     

The influence of the processing parameters on the formation of iron thin films on alumina balls by mechanical coating technique

Mechanical coating technique (MCT) was used to fabricate Fe thin films on alumina balls. The influence of the processing parameters including the milling atmosphere and the rotation speed of planetary ball mill on the formation of the thin films was investigated. The results of SEM and EDS showed that Fe particles reacted with oxygen in the air atmosphere and the formed ferroferric oxide hindered the formation of the thin films. Rotation speed also had great influence. Continuous Fe thin films with an average thickness of about 10 μm were formed during the milling operation at 300 rpm. However, they could not be formed at 200 and 400 rpm. Furthermore, the evolution of the thin films was also studied and analyzed. An evolution model was proposed to describe it. According to the model, the evolution fell into nucleation, growth of nuclei, formation of thin films and exfoliation. It was considered that mechanical interlocking played an important role in the formation of the thin films.     

Structure and washing fastness of composite fluorocarbon/ZnO films prepared by RF sputtering

Composite fluorocarbon/ZnO films were deposited by RF sputtering, using polytetrafluoroethylene and Zn targets, on polyethylene terephthalate substrates. Argon and oxygen were used as working and reacting gases, respectively, with an oxygen:argon volume ratio of 3:1. The films were characterized by X-ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy and static contact angle measurements. It was found that the deposited films are made up of the four components -CF₃, -CF₂-, -CF- and -C-. The proportions of the four components varied with sputtering conditions. There was a large number of C=C double bonds on the surface of deposited films. The static contact angle of the deposited films was greater than 90°, indicating excellent hydrophobicity. The contact angle of films decreased after washing, and the washing fastness of the composite films were slightly inferior to those of the fluorocarbon films.     

Study on the Si penetration into Fe sheets using PVD method and its application in the fabrication of Fe-6.5 wt.% Si alloys

FeSi (12 wt.% Si) and Si were alternatively deposited on pure iron (Fe) substrates by direct current magnetron sputtering. Subsequent annealing in vacuum at 1150-1190 °C results in penetration of Si into the substrate. Cross-sectional microstructure and Si concentration were investigated by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The penetration mechanism is found to depend greatly on Si amount in the as-deposited films. When FeSi/Si/FeSi/Si/FeSi was deposited on the Fe substrate, the Si penetration is controlled by phase-boundary migration, while a diffusion-controlling penetration is observed in FeSi/Si/FeSi deposited samples. Fe-6.5 wt.% Si sheet with thickness of 0.35 mm is obtained through the deposition of FeSi/Si multilayer on a Fe-3 wt.% Si sheet together with subsequent annealing at 1180 °C for 2 h.     

Composite fluorocarbon/ZnO films prepared by R.F. magnetron sputtering of Zn and PTFE

In this paper, composite fluorocarbon/ZnO films were prepared by R.F. sputtering used polytetrafluoroethylene (PTFE) and Zn target on polyethylene terephthalate (PET) substrate. Argon was used as the working gas and oxygen used as reacting gas. The obtained films were characterized by means of SEM, XPS and UV-visible spectrophotometer. It was found, the surface morphology of composite fluorocarbon/ZnO films vary as the deposited time of ZnO. The growing mode of composite films is the deposition and expansion. The ultraviolet absorbance of composite fluorocarbon/ZnO films is equal to that of fluorocarbon films' when deposited time of ZnO is within 2 min, while distinctively increases when deposited time of ZnO exceeds 5 min, the absorbance value is larger than the ZnOs'. The composite films exhibit multi-enhanced ultraviolet absorption due to π-conjugated molecular structure, nanoparticle-pore reflection and the absorption effect of nanosized ZnO particles.