The tungsten films with ultra microstructure on CuCrZr alloy and China Low Acti- vation Martensitic （CLAM） steel have been prepared by metal organic chemical vapor deposition （MOCVD）. The films were produced by py...The tungsten films with ultra microstructure on CuCrZr alloy and China Low Acti- vation Martensitic （CLAM） steel have been prepared by metal organic chemical vapor deposition （MOCVD）. The films were produced by pyrolysing the tungsten hexacarbonyl at air or argon atmosphere. When formed at or below 400 ℃, they were poorly crystalized and the films showed low quality in thickness, density, bonding performance etc. While above this temperature, the properties of tungsten films have been improved, all the films consist of tungsten in the β-W. And β-W can change into α-W after heat treatment. As in other variations of pyrolysis, oxy- gen and carbon were observed. When filled with argon, the oxygen and carbon content would reduce apparently. Tungsten films prepared by MOCVD have stable chemical composition and microstructure. Besides, the properties of films on CuCrZr alloy are better than that on CLAM steel.展开更多
Tungsten films growing on copper substrates were fabricated by metallorganic chemical vapor deposition （MOCVD）. The chemi-cal purity, crystallographic phase, cross-sectional texture, and resistivity of the deposited...Tungsten films growing on copper substrates were fabricated by metallorganic chemical vapor deposition （MOCVD）. The chemi-cal purity, crystallographic phase, cross-sectional texture, and resistivity of the deposited films both before and after annealing treatment were investigated by X-ray energy-dispersive spectroscopy （EDS）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and four-point probe method. It is found that the films deposited at 460°C are metastable β-W with （211） orientation and can change into α-W when an-nealed in high-purity hydrogen atmosphere at high temperature. There are small amounts of C and O in the films, and the W content of the films increases with increasing deposition temperature and also goes up after annealing in high-purity hydrogen atmosphere. The films have columnar microstructures and the texture evolution during their growth on copper substrates can be divided into three stages. The resistivity of the as-deposited films is in the range of 87-104 μΩ·cm, and low resistivity is obtained after annealing in high-purity hydrogen atmosphere.展开更多
Tungsten oxide thin films were deposited on glass substrates by the magnetron sputtering of WO3 bulk at room temperature. The deposited films were annealed at different temperatures in air. The structural measurements...Tungsten oxide thin films were deposited on glass substrates by the magnetron sputtering of WO3 bulk at room temperature. The deposited films were annealed at different temperatures in air. The structural measurements indicate that the films annealed below 300℃ were amorphous, while the films annealed at 400 ℃ were mixed crystalline with hexagonal and triclinic phases of WO3. It was observed that the crystallization of the annealed films becomes more and more distinct with an increase in the annealing temperature. At 400 ℃, nanorod-like structures were observed on the film surface when the annealing time was increased from 60 min to 180 min. The presence of W=O stretching, W-O-W stretching, W-O-W bending and various lattice vibration modes were observed in Raman measurements. The optical absorption behaviors of the films in the range of 450-800 nm are very different with changing annealing temperatures from the room temperature to 400 ℃. After annealing at 400 ℃, the film becomes almost transparent. Increasing annealing time at 400 ℃ can lead to a small blue shift of the optical gap of the film.展开更多
Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition （PECVD） at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, st...Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition （PECVD） at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, structure and chemical components of the films were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy-dispersive spectrometer （EDS）, respectively. The results show that the film prepared at CH4/WF6 concentration ratio of 20 and at 800℃ is composed of spherical particles with a diameter of 20-35 nm. Electrochemical investigations show that the electrochemical real surface area of electrode of the film is large, and the electrode of the film exhibits higher electro-catalytic activity in the reaction of methanol oxidation. The designated constant current of the film catalyst is 123.6 mA/cm^2 in the mixture solution of H2SO4 and CH3OH at the concentration of 0.5 and 2.0 mol/L at 70℃, and the designated constant potential is only 0.306 V （vs SCE）.展开更多
Tungsten carbide films (W-C films) were fabricated on silicon substrates by using the filtered pulse arc deposition (FPAD) method. Two types of cemented tungsten carbide (WC) were used as cathode, one containing Co an...Tungsten carbide films (W-C films) were fabricated on silicon substrates by using the filtered pulse arc deposition (FPAD) method. Two types of cemented tungsten carbide (WC) were used as cathode, one containing Co and the other Ti, which were used as binders for forming the cathode shape. The films were fabricated by varying the pulse arc current and substrate bias voltage. The discharge, deposition and film properties were investigated under these deposition conditions. The cathode wear amount when using WC-Co (WC cathode containing Co) was found to be smaller than that measured when WC-Ti (WC cathode containing Ti) was used. The W-C film thickness was approximately 30 - 40 nm under all conditions, except when the pulse arc current was 50 A and the film thickness, was approximately 10 nm. Compared to the WC-Ti, the consumption of cathode material is suppressed in the WC-Co, indicating that the efficiency for film preparation of the latter is good. From the X-ray diffraction analysis, the crystalline phase of W-C films fabricated using WC-Co and WC-Ti were observed as W2C and WC1-x, respectively, indicating that different crystalline phases could be fabricated using different cathodes. From the X-ray photoelectron spectroscopy analysis, the oxidation layer formed by air exposure was observed to exclusively exist on the W-C film surface. Moreover, almost all oxygen in the oxidation layer bonded with tungsten.展开更多
Amorphous metals are totally different from crystalline metals in regard to atom arrangement. Amorphous metals do not have grain boundaries and weak spots that crystalline materials contain, making them more resistant...Amorphous metals are totally different from crystalline metals in regard to atom arrangement. Amorphous metals do not have grain boundaries and weak spots that crystalline materials contain, making them more resistant to wear and corrosion. In this study, amorphous Fe-W alloy films were first prepared by an electroplating method and were then made hydrophobic by modification with a water repellent （heptadecafluoro-1,1,2,2-tetradecyl） trimethoxysilane. Hierarchical micro-nano structures can be obtained by slightly oxidizing the as-deposited alloy, accompanied by phase transformation from amorphous to crystalline during heat treatment. The mi-cro-nano structures can trap air to form an extremely thin cushion of air between the water and the film, which is critical to producing hydrophobicity in the film. Results show that the average values of capacitance, roughness factor, and impedance for specific surface areas of a 600°C heat-treated sample are greater than those of a sample treated at 500°C. Importantly, the coating can be fabricated on various metal substrates to act as a corrosion retardant.展开更多
WO3 thin films were sputtered onto alumina substrates by DC facing-target magnetron sputtering. One sample was rapid-thermal-annealed （RTA） at 600 ℃ in a gas mixture of N2：O2 = 4 ： 1, and as a comparison, another...WO3 thin films were sputtered onto alumina substrates by DC facing-target magnetron sputtering. One sample was rapid-thermal-annealed （RTA） at 600 ℃ in a gas mixture of N2：O2 = 4 ： 1, and as a comparison, another was conventionally thermal-annealed at 600 ℃ in air. The morphology of both was investigated by scanning electron microscopy （SEM） and atomic force microscopy （AFM）, and the crystallization structure and phase identification were characterized by X-ray diffraction （XRD）. The NO2-sensing measurements were taken under LED light at room temperature. The sensitivity of the RTA-treated sample was found to be high, up to nearly 100, whereas the sensitivity of the conventionally thermal-annealed sample was about five under the same conditions. From the much better selectivity and response-recovery characteristics, it can be concluded that compared to conventional thermal annealing, RTA has a greater effect on the NO2-sensing properties of WO3 thin films.展开更多
Electrochromic and auto-bleaching processes at the WO2 anodic film in 0. 5 mol/L H2SO4 solution were investigated by cyclic voltammetry, a. c. impedance technique and photocurrent spectrometry. The colouration mechani...Electrochromic and auto-bleaching processes at the WO2 anodic film in 0. 5 mol/L H2SO4 solution were investigated by cyclic voltammetry, a. c. impedance technique and photocurrent spectrometry. The colouration mechanism consists of hydrogen adsorption on the WO2 surface and the transport of H atoms in the WO, lattice. The bleaching process involves at least two steps: transport of interstitial H atoms and hydrogen desorption on the W surface, resulting in interstitial H+ ions; then extration of the H+ ions driven by the external electric field. The auto-bleaching arises from the hydroxylation due to both partial interstitial H atoms and a little of water contained in the film.展开更多
Hydrogen has been recently attracted much attention with respect to high energy-conversion efficiency and low environmental burden. However, hydrogen gas is dangerous due to an explosive gas and a fast combustion rate...Hydrogen has been recently attracted much attention with respect to high energy-conversion efficiency and low environmental burden. However, hydrogen gas is dangerous due to an explosive gas and a fast combustion rate. Therefore, the development of hydrogen sensor with high accuracy and reliability that can detect hydrogen easily is required. Especially, a flexible hydrogen sensor is useful because it has a high degree of freedom with respect to the shape of location in which the sensor is to be located. A flexible hydrogen sensor—namely, a WO3 thin film formed on a PET film by the sol-gel method using photo irradiation—based on gasochromism of WO3 was developed. By irradiating a thin film, which was prepared by using WO3 precursor solution synthesized by the sol-gel method, with ultraviolet rays, a high-purity WO3 film could be prepared on PET at low temperature. The sensor was structured as a polystyrene (PS) film containing palladium (Pd) laminated on a WO3 film. The WO3 layer was porous, so the PS containing Pd atoms solution penetrated the WO3 layer. WO3 reacted with hydrogen gas and instantly turned blue as the transmittance of the WO3 layer changed. The sensor showed high reactivity even for hydrogen concentration below 4% (1%, 0.5%, 0.25%, and 0.1%), which was the lower limit of hydrogen ignition, and a linear relationship between hydrogen concentration and change in transmittance was found. Moreover, the resistance of the WO3 film significantly and instantaneously changed due to hydrogen-gas exposure, and the hydrogen concentration and resistance change showed a linear relationship. It is therefore possible to quantitatively detect low concentrations of hydrogen by using changes in transmittance and resistance as indices. Since these changes occur selectively under hydrogen at room temperature and normal pressure, they form the basis of a highly sensitive hydrogen sensor. Since the developed sensor is flexible, it has a high degree of freedom with respect to the shape of location in which the sensor is to be展开更多
基金supported by the National Magnetic Confinement Fusion Program of China,ITER(No.2010GB109000)
文摘The tungsten films with ultra microstructure on CuCrZr alloy and China Low Acti- vation Martensitic （CLAM） steel have been prepared by metal organic chemical vapor deposition （MOCVD）. The films were produced by pyrolysing the tungsten hexacarbonyl at air or argon atmosphere. When formed at or below 400 ℃, they were poorly crystalized and the films showed low quality in thickness, density, bonding performance etc. While above this temperature, the properties of tungsten films have been improved, all the films consist of tungsten in the β-W. And β-W can change into α-W after heat treatment. As in other variations of pyrolysis, oxy- gen and carbon were observed. When filled with argon, the oxygen and carbon content would reduce apparently. Tungsten films prepared by MOCVD have stable chemical composition and microstructure. Besides, the properties of films on CuCrZr alloy are better than that on CLAM steel.
基金supported by the National High-Tech Research and Development Program of China (No.2009AA03Z116)
文摘Tungsten films growing on copper substrates were fabricated by metallorganic chemical vapor deposition （MOCVD）. The chemi-cal purity, crystallographic phase, cross-sectional texture, and resistivity of the deposited films both before and after annealing treatment were investigated by X-ray energy-dispersive spectroscopy （EDS）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and four-point probe method. It is found that the films deposited at 460°C are metastable β-W with （211） orientation and can change into α-W when an-nealed in high-purity hydrogen atmosphere at high temperature. There are small amounts of C and O in the films, and the W content of the films increases with increasing deposition temperature and also goes up after annealing in high-purity hydrogen atmosphere. The films have columnar microstructures and the texture evolution during their growth on copper substrates can be divided into three stages. The resistivity of the as-deposited films is in the range of 87-104 μΩ·cm, and low resistivity is obtained after annealing in high-purity hydrogen atmosphere.
基金supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant Nos.11104365 and 11104366)the Hubei Key Laboratory of Low Dimensional Optoelectronic Material and Devices,China(Grant No.13XKL02002)
文摘Tungsten oxide thin films were deposited on glass substrates by the magnetron sputtering of WO3 bulk at room temperature. The deposited films were annealed at different temperatures in air. The structural measurements indicate that the films annealed below 300℃ were amorphous, while the films annealed at 400 ℃ were mixed crystalline with hexagonal and triclinic phases of WO3. It was observed that the crystallization of the annealed films becomes more and more distinct with an increase in the annealing temperature. At 400 ℃, nanorod-like structures were observed on the film surface when the annealing time was increased from 60 min to 180 min. The presence of W=O stretching, W-O-W stretching, W-O-W bending and various lattice vibration modes were observed in Raman measurements. The optical absorption behaviors of the films in the range of 450-800 nm are very different with changing annealing temperatures from the room temperature to 400 ℃. After annealing at 400 ℃, the film becomes almost transparent. Increasing annealing time at 400 ℃ can lead to a small blue shift of the optical gap of the film.
基金This work was supported by the National Natural Scmnce Foundation of China(Grant Nos.20276069,20476097)
文摘Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition （PECVD） at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, structure and chemical components of the films were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy-dispersive spectrometer （EDS）, respectively. The results show that the film prepared at CH4/WF6 concentration ratio of 20 and at 800℃ is composed of spherical particles with a diameter of 20-35 nm. Electrochemical investigations show that the electrochemical real surface area of electrode of the film is large, and the electrode of the film exhibits higher electro-catalytic activity in the reaction of methanol oxidation. The designated constant current of the film catalyst is 123.6 mA/cm^2 in the mixture solution of H2SO4 and CH3OH at the concentration of 0.5 and 2.0 mol/L at 70℃, and the designated constant potential is only 0.306 V （vs SCE）.
文摘Tungsten carbide films (W-C films) were fabricated on silicon substrates by using the filtered pulse arc deposition (FPAD) method. Two types of cemented tungsten carbide (WC) were used as cathode, one containing Co and the other Ti, which were used as binders for forming the cathode shape. The films were fabricated by varying the pulse arc current and substrate bias voltage. The discharge, deposition and film properties were investigated under these deposition conditions. The cathode wear amount when using WC-Co (WC cathode containing Co) was found to be smaller than that measured when WC-Ti (WC cathode containing Ti) was used. The W-C film thickness was approximately 30 - 40 nm under all conditions, except when the pulse arc current was 50 A and the film thickness, was approximately 10 nm. Compared to the WC-Ti, the consumption of cathode material is suppressed in the WC-Co, indicating that the efficiency for film preparation of the latter is good. From the X-ray diffraction analysis, the crystalline phase of W-C films fabricated using WC-Co and WC-Ti were observed as W2C and WC1-x, respectively, indicating that different crystalline phases could be fabricated using different cathodes. From the X-ray photoelectron spectroscopy analysis, the oxidation layer formed by air exposure was observed to exclusively exist on the W-C film surface. Moreover, almost all oxygen in the oxidation layer bonded with tungsten.
基金financially supported by the National Magnetic Confinement Fusion Science Program(No.2010GB106003)the National Natural Science Founda-tion of China(No.91023037)
文摘Amorphous metals are totally different from crystalline metals in regard to atom arrangement. Amorphous metals do not have grain boundaries and weak spots that crystalline materials contain, making them more resistant to wear and corrosion. In this study, amorphous Fe-W alloy films were first prepared by an electroplating method and were then made hydrophobic by modification with a water repellent （heptadecafluoro-1,1,2,2-tetradecyl） trimethoxysilane. Hierarchical micro-nano structures can be obtained by slightly oxidizing the as-deposited alloy, accompanied by phase transformation from amorphous to crystalline during heat treatment. The mi-cro-nano structures can trap air to form an extremely thin cushion of air between the water and the film, which is critical to producing hydrophobicity in the film. Results show that the average values of capacitance, roughness factor, and impedance for specific surface areas of a 600°C heat-treated sample are greater than those of a sample treated at 500°C. Importantly, the coating can be fabricated on various metal substrates to act as a corrosion retardant.
基金supported by the National Natural Science Foundation of China (Grant Nos. 62171070,60771019,and 60801018)Tianjin Key Research Program of Application Foundation and Advanced Technology,China (Grant No. 11JCZDJC15300)
文摘WO3 thin films were sputtered onto alumina substrates by DC facing-target magnetron sputtering. One sample was rapid-thermal-annealed （RTA） at 600 ℃ in a gas mixture of N2：O2 = 4 ： 1, and as a comparison, another was conventionally thermal-annealed at 600 ℃ in air. The morphology of both was investigated by scanning electron microscopy （SEM） and atomic force microscopy （AFM）, and the crystallization structure and phase identification were characterized by X-ray diffraction （XRD）. The NO2-sensing measurements were taken under LED light at room temperature. The sensitivity of the RTA-treated sample was found to be high, up to nearly 100, whereas the sensitivity of the conventionally thermal-annealed sample was about five under the same conditions. From the much better selectivity and response-recovery characteristics, it can be concluded that compared to conventional thermal annealing, RTA has a greater effect on the NO2-sensing properties of WO3 thin films.
基金The project Supported by National Natural Science Foundation of China.
文摘Electrochromic and auto-bleaching processes at the WO2 anodic film in 0. 5 mol/L H2SO4 solution were investigated by cyclic voltammetry, a. c. impedance technique and photocurrent spectrometry. The colouration mechanism consists of hydrogen adsorption on the WO2 surface and the transport of H atoms in the WO, lattice. The bleaching process involves at least two steps: transport of interstitial H atoms and hydrogen desorption on the W surface, resulting in interstitial H+ ions; then extration of the H+ ions driven by the external electric field. The auto-bleaching arises from the hydroxylation due to both partial interstitial H atoms and a little of water contained in the film.
文摘Hydrogen has been recently attracted much attention with respect to high energy-conversion efficiency and low environmental burden. However, hydrogen gas is dangerous due to an explosive gas and a fast combustion rate. Therefore, the development of hydrogen sensor with high accuracy and reliability that can detect hydrogen easily is required. Especially, a flexible hydrogen sensor is useful because it has a high degree of freedom with respect to the shape of location in which the sensor is to be located. A flexible hydrogen sensor—namely, a WO3 thin film formed on a PET film by the sol-gel method using photo irradiation—based on gasochromism of WO3 was developed. By irradiating a thin film, which was prepared by using WO3 precursor solution synthesized by the sol-gel method, with ultraviolet rays, a high-purity WO3 film could be prepared on PET at low temperature. The sensor was structured as a polystyrene (PS) film containing palladium (Pd) laminated on a WO3 film. The WO3 layer was porous, so the PS containing Pd atoms solution penetrated the WO3 layer. WO3 reacted with hydrogen gas and instantly turned blue as the transmittance of the WO3 layer changed. The sensor showed high reactivity even for hydrogen concentration below 4% (1%, 0.5%, 0.25%, and 0.1%), which was the lower limit of hydrogen ignition, and a linear relationship between hydrogen concentration and change in transmittance was found. Moreover, the resistance of the WO3 film significantly and instantaneously changed due to hydrogen-gas exposure, and the hydrogen concentration and resistance change showed a linear relationship. It is therefore possible to quantitatively detect low concentrations of hydrogen by using changes in transmittance and resistance as indices. Since these changes occur selectively under hydrogen at room temperature and normal pressure, they form the basis of a highly sensitive hydrogen sensor. Since the developed sensor is flexible, it has a high degree of freedom with respect to the shape of location in which the sensor is to be
