The authors report that the growth rate of ZnO can be significantly increased by modifying the oxygen plasma conditions in plasma-assisted molecular beam epitaxy. Both the aperture diameter and the distance between th...The authors report that the growth rate of ZnO can be significantly increased by modifying the oxygen plasma conditions in plasma-assisted molecular beam epitaxy. Both the aperture diameter and the distance between the plasma source and the substrate affect the growth rate and the quality of the ZnO films. A short source to substrate distance is essential in achieving higher growth rate, which is explained by reduced chance of oxygen atom collisions to accommodate the short oxygen mean free path at high background pressure. At a shorter source to substrate distance, the growth rate is higher with a larger aperture diameter. The quality of the ZnO thin films grown under different conditions is assessed by x-ray diffraction and room-temperature photoluminescence measurements.展开更多
This paper reports the induced growth of high quality ZnO thin film by crystallized amorphous ZnO. Firstly amorphous ZnO was prepared by solid-state pyrolytic reaction, then by taking crystallized amorphous ZnO as see...This paper reports the induced growth of high quality ZnO thin film by crystallized amorphous ZnO. Firstly amorphous ZnO was prepared by solid-state pyrolytic reaction, then by taking crystallized amorphous ZnO as seeds （buffer layer）, ZnO thin films have been grown in diethyene glycol solution of zinc acetate at 80 ℃. X-ray Diffraction curve indicates that the films were preferentially oriented [001] out-of-plane direction of the ZnO. Atomic force microscopy and scanning electron microscopy were used to evaluate the surface morphology of the ZnO thin film. Photoluminescence spectrum exhibits a strong ultraviolet emission while the visible emission is very weak. The results indicate that high quality ZnO thin film was obtained.展开更多
Single-crystalline ZnO nanowire arrays with different aspect ratios and nanowire densities were prepared by the hydrothermal growing method using polyethyleneimine （PEI） as a surfactant. PEI can only hinder the late...Single-crystalline ZnO nanowire arrays with different aspect ratios and nanowire densities were prepared by the hydrothermal growing method using polyethyleneimine （PEI） as a surfactant. PEI can only hinder the lateral growth of the ZnO nanowires, which is observed by high resolution transmission electron microscopy （HRTEM） analysis. Dye-sensitized solar cells were assembled by the ZnO nanowire arrays with different thicknesses, which can be controlled by the growing time and characterized using photocurrent-voltage measurements. Their photocurrent densities and energy allover conversion efficiencies increased with increasing ZnO nanowire lengths. Short-circuit current density of 4.31 mA.cm-2 and allover energy conversion efficiency of 0.87% were achieved with 12.9-μm-long ZnO nanowire arrays.展开更多
Zinc oxide hexagonal tubular crystals were synthesized by direct microwave heating from ZnO powders within 5 min without any metal catalysts or transport agents. ZnO source materials were evaporated from the high-temp...Zinc oxide hexagonal tubular crystals were synthesized by direct microwave heating from ZnO powders within 5 min without any metal catalysts or transport agents. ZnO source materials were evaporated from the high-temperature zone in an enclosure, and crystals were grown on the self-source substrate in an appropriate condition. The ZnO vapor formed in the high-temperature zone can deposit and grow on the powders located in the low-temperature zone to form crystals. The scanning electron microscopy （SEM） reveals that these products are hexagonal tube crystals with 80 ~rn in diameter and 250 μm in length, having a well faceted end and side surface. A possible growth mechanism and the influence of reaction temperature on the formation of crystalline ZnO hexagonal tubes were presented. The photoluminescence （PL） exhibits strong ultraviolet emission at room temperature, indicating the potential applications in short-wave light-emitting photonic devices.展开更多
Vapor-phase growth of ZnO nanowires based on gold catalyst is usually accompanied with lateral crawling growth on the substrate surface. We present results from our systematic experiments where the growth temperature ...Vapor-phase growth of ZnO nanowires based on gold catalyst is usually accompanied with lateral crawling growth on the substrate surface. We present results from our systematic experiments where the growth temperature and catalyst size are controlled. The data corroborate that it is possible to obtain clean vertical nanowire arrays while avoiding the crawling growth. 0% the other hand, crawling growth can be manipulated to obtain root-interconnected nanowire arrays, which could be useful for certain applications. Our results also imply that the previously suggested growth mechanism for the wire-on-wall hybridstructure might be incorrect. Finally, we show the formation of sub-millimeter long, straight ZnO nanowalls by combining a gold-catalyzed epitaxial growth of vertical nanowires and their mergence due to a confined crawling growth. These unconventional nanostructures might have unique electric or optical transport properties.展开更多
Tetrapod-shaped ZnO microcrystals in forms of whiskers and microrods have been grown in the same crucible by thermal evaporation of Zn/C mixtures at a temperature of 930℃ in air without using any catalyst. The tetrap...Tetrapod-shaped ZnO microcrystals in forms of whiskers and microrods have been grown in the same crucible by thermal evaporation of Zn/C mixtures at a temperature of 930℃ in air without using any catalyst. The tetrapod-shaped ZnO microrods were capped by hexagonal pyramids. It is for the first time observed that the tetrapod-shaped ZnO whiskers and microrods have quite different morphologies, and this is believed to be a result of different growth behaviors associated with these two forms of ZnO microcrystals. The octa-twin model has been used to discuss their growth behaviors. Photoluminescence properties of these two forms of tetrapod-shaped ZnO microcrystals have been investigated using different excitation wavelengths. Both of the two forms of ZnO microcrystals showed strong green emission and weak ultraviolet emission behaviors. The excitation spectrum of the tetrapod-shaped ZnO whiskers showed a strong excitation peak at 395 nm, which was not observed for the tetrapod-shaped ZnO microrods.展开更多
ZnO sub-millimeter crystals were synthesized by microwave heating from ZnO powders without any catalyst or transport agent. Zinc oxide raw materials were evaporated from the high-temperature zone in an enclosure and c...ZnO sub-millimeter crystals were synthesized by microwave heating from ZnO powders without any catalyst or transport agent. Zinc oxide raw materials were evaporated from the high-temperature zone in an enclosure and crystals were grown on the self-source substrate. The thermodynamics analysis method was used to estimate the partial pressure of gases in the chamber, which shows that the pressure of ZnO could be neglected entirely in the range of experiment temperature. The kinetics analysis was employed to estimate the growth rate in different conditions, which shows a remarkable temperature gradient and a high system temperature would enhance the growth rate. Optics photos reveal that these products are hexagon crystals with 0.2-0.3 mm in diameter and 0.5-1 mm in length. A vapor-solid mechanism is proposed to explain the growth process of ZnO crystals. The temperature distribution in microwave oven is mainly determined by properties of electric field and it is different from that of a conventional method.展开更多
Three kinds of tetrapod-like ZnO nanostructures have been synthesized simultaneously via pure Zn chemical vapor deposition on silicon wafers with （111） orientation （Si （111）） at 920 ℃. X-ray diffraction indicat...Three kinds of tetrapod-like ZnO nanostructures have been synthesized simultaneously via pure Zn chemical vapor deposition on silicon wafers with （111） orientation （Si （111）） at 920 ℃. X-ray diffraction indicates that the nanotetrapods are of wurtzite structure. The morphology and the microstructure of the nanotetrapods are investigated by the scanning electron microscopy. Selected area electron diffraction shows the growth direction, and energy dispersive X-ray spectroscopy reveals the atomic composition ratio of Zn/O. The growth process is briefly discussed. The optical property of the products was also recorded by means of photoluminescence spectroscopy.展开更多
A facile one-step method was developed for the fabrication of hierarchical ZnO film on substrate. Neither seed nor catalyst layer is necessary for the growth of hierarchical ZnO film. Three kinds of nucleation process...A facile one-step method was developed for the fabrication of hierarchical ZnO film on substrate. Neither seed nor catalyst layer is necessary for the growth of hierarchical ZnO film. Three kinds of nucleation process were found, and the influences of growth time, growth electrolyte, growth temperature on the morphology of ZnO film were evaluated. Hierarchical ZnO film can absorb more than 97% of incident photons with wavelength shorter than 380 nm. Such hierarchical ZnO film would be a promising scaffold for photoelectrochemical application.展开更多
Different three-dimension （3D） nanotetrapods, containing club-like nanocrystals, nanotetrapods and four-foot-like nanocrystals were synthesized from Zinc sheet via CO2 laser irradiation and coaxially transporting O2...Different three-dimension （3D） nanotetrapods, containing club-like nanocrystals, nanotetrapods and four-foot-like nanocrystals were synthesized from Zinc sheet via CO2 laser irradiation and coaxially transporting O2. Different nanoproducts were fabricated by changing the content of oxygen in the experiment. The morphologies, components, phase structures and optical properties of the products were investigated by a field-emission scanning electron microscopy, an X-ray diffraction, an energy dispersed X-ray spectrometer and a photoluminescence spectroscope. The X-ray diffraction spectra were obtained on a Rigaku D/max 2500PC diffractometer. The experimental results reveal that high quality ZnO nanotetrapods can be fabricated on the special parameters, and growth of ZnO nanotetrapods depends on Vapour-Liquid-Solid（VLS） model, and the content of oxygen in the gas, namely, oxygen partial pressure is one of main factors to control morphologies and optical properties ofZnO nanotetrapods; these advantages above are important for realization of optoelectronic devices.展开更多
Recently, the efforts in solid-state materials include developing technologies capable of producing ZnO wafers in large dimensions and good quality based device applications. High quality bulk crystals are obtained by...Recently, the efforts in solid-state materials include developing technologies capable of producing ZnO wafers in large dimensions and good quality based device applications. High quality bulk crystals are obtained by growing from high purity the melt. However, the thermochemical properties of ZnO (high melting point and high vapor pressure) make the growth of single crystals difficult. The thermodynamic calculations show that ZnO crystals can be grown from the melt if a suitable dynamic atmosphere composition is used. The oxygen requirement with increasing the temperature can be fulfilled by adding the NO-NO2 gases into the CO2 atmosphere. At ZnO melting point, the oxygen partial pressure of gas mixtures containing CO2-NO-CO-NO2 at Pt = 5 atm reaches to PO2 = 0.29 atm. According to this new thermodynamic result, it would be expected that ZnO crystal could be grown from the melt at lower total pressure comparing to pure CO2.展开更多
文摘The authors report that the growth rate of ZnO can be significantly increased by modifying the oxygen plasma conditions in plasma-assisted molecular beam epitaxy. Both the aperture diameter and the distance between the plasma source and the substrate affect the growth rate and the quality of the ZnO films. A short source to substrate distance is essential in achieving higher growth rate, which is explained by reduced chance of oxygen atom collisions to accommodate the short oxygen mean free path at high background pressure. At a shorter source to substrate distance, the growth rate is higher with a larger aperture diameter. The quality of the ZnO thin films grown under different conditions is assessed by x-ray diffraction and room-temperature photoluminescence measurements.
基金Project supported by the ＂863＂ High Technology Research Program in China （Grant No 2001AA311120）, the National Natural Science Foundation of China （Grant No 60278031）, the Innovation Project of Chinese Academy of Sciences, the Jilin Province Science and Technology Development Program Project of China （Grant No 20040564） and the Young Innovation Function of the Changchun Institute of 0ptics, Fine Mechanics and Physics, Chinese Academy of Sciences （Grant No Q03M23Z）.
文摘This paper reports the induced growth of high quality ZnO thin film by crystallized amorphous ZnO. Firstly amorphous ZnO was prepared by solid-state pyrolytic reaction, then by taking crystallized amorphous ZnO as seeds （buffer layer）, ZnO thin films have been grown in diethyene glycol solution of zinc acetate at 80 ℃. X-ray Diffraction curve indicates that the films were preferentially oriented [001] out-of-plane direction of the ZnO. Atomic force microscopy and scanning electron microscopy were used to evaluate the surface morphology of the ZnO thin film. Photoluminescence spectrum exhibits a strong ultraviolet emission while the visible emission is very weak. The results indicate that high quality ZnO thin film was obtained.
基金financially supported by the National Science Foundation of China (Nos.10775096 and 51072112)China Postdoctoral Science Foundation (No.20100480579)+4 种基金Key Subject of Shanghai Municipal Education Commission (No.J50102)Special Research Foundation for Training and Selecting Outstanding Young Teachers of Universities in ShanghaiInnovation Foundation of Shanghai UniversityNature Science Foundation of Shanghai (No.06ZR14035)Shanghai Leading Academic Disciplines (No.T0101)
文摘Single-crystalline ZnO nanowire arrays with different aspect ratios and nanowire densities were prepared by the hydrothermal growing method using polyethyleneimine （PEI） as a surfactant. PEI can only hinder the lateral growth of the ZnO nanowires, which is observed by high resolution transmission electron microscopy （HRTEM） analysis. Dye-sensitized solar cells were assembled by the ZnO nanowire arrays with different thicknesses, which can be controlled by the growing time and characterized using photocurrent-voltage measurements. Their photocurrent densities and energy allover conversion efficiencies increased with increasing ZnO nanowire lengths. Short-circuit current density of 4.31 mA.cm-2 and allover energy conversion efficiency of 0.87% were achieved with 12.9-μm-long ZnO nanowire arrays.
基金supported by the National Natural Science Foundation of China (No.50472043)the Program for New Century Excellent Talents in Chinese Universities (NCET-06-0658)
文摘Zinc oxide hexagonal tubular crystals were synthesized by direct microwave heating from ZnO powders within 5 min without any metal catalysts or transport agents. ZnO source materials were evaporated from the high-temperature zone in an enclosure, and crystals were grown on the self-source substrate in an appropriate condition. The ZnO vapor formed in the high-temperature zone can deposit and grow on the powders located in the low-temperature zone to form crystals. The scanning electron microscopy （SEM） reveals that these products are hexagonal tube crystals with 80 ~rn in diameter and 250 μm in length, having a well faceted end and side surface. A possible growth mechanism and the influence of reaction temperature on the formation of crystalline ZnO hexagonal tubes were presented. The photoluminescence （PL） exhibits strong ultraviolet emission at room temperature, indicating the potential applications in short-wave light-emitting photonic devices.
文摘Vapor-phase growth of ZnO nanowires based on gold catalyst is usually accompanied with lateral crawling growth on the substrate surface. We present results from our systematic experiments where the growth temperature and catalyst size are controlled. The data corroborate that it is possible to obtain clean vertical nanowire arrays while avoiding the crawling growth. 0% the other hand, crawling growth can be manipulated to obtain root-interconnected nanowire arrays, which could be useful for certain applications. Our results also imply that the previously suggested growth mechanism for the wire-on-wall hybridstructure might be incorrect. Finally, we show the formation of sub-millimeter long, straight ZnO nanowalls by combining a gold-catalyzed epitaxial growth of vertical nanowires and their mergence due to a confined crawling growth. These unconventional nanostructures might have unique electric or optical transport properties.
基金supported by the Doctorate Research Plan of Nanchang University (Grant No. 0061)
文摘Tetrapod-shaped ZnO microcrystals in forms of whiskers and microrods have been grown in the same crucible by thermal evaporation of Zn/C mixtures at a temperature of 930℃ in air without using any catalyst. The tetrapod-shaped ZnO microrods were capped by hexagonal pyramids. It is for the first time observed that the tetrapod-shaped ZnO whiskers and microrods have quite different morphologies, and this is believed to be a result of different growth behaviors associated with these two forms of ZnO microcrystals. The octa-twin model has been used to discuss their growth behaviors. Photoluminescence properties of these two forms of tetrapod-shaped ZnO microcrystals have been investigated using different excitation wavelengths. Both of the two forms of ZnO microcrystals showed strong green emission and weak ultraviolet emission behaviors. The excitation spectrum of the tetrapod-shaped ZnO whiskers showed a strong excitation peak at 395 nm, which was not observed for the tetrapod-shaped ZnO microrods.
基金Funded by the National Natural Science Foundation of China (No.50472043)the Program for New Century Excellent Talents in University (No.NCET-06-0658)
文摘ZnO sub-millimeter crystals were synthesized by microwave heating from ZnO powders without any catalyst or transport agent. Zinc oxide raw materials were evaporated from the high-temperature zone in an enclosure and crystals were grown on the self-source substrate. The thermodynamics analysis method was used to estimate the partial pressure of gases in the chamber, which shows that the pressure of ZnO could be neglected entirely in the range of experiment temperature. The kinetics analysis was employed to estimate the growth rate in different conditions, which shows a remarkable temperature gradient and a high system temperature would enhance the growth rate. Optics photos reveal that these products are hexagon crystals with 0.2-0.3 mm in diameter and 0.5-1 mm in length. A vapor-solid mechanism is proposed to explain the growth process of ZnO crystals. The temperature distribution in microwave oven is mainly determined by properties of electric field and it is different from that of a conventional method.
文摘Three kinds of tetrapod-like ZnO nanostructures have been synthesized simultaneously via pure Zn chemical vapor deposition on silicon wafers with （111） orientation （Si （111）） at 920 ℃. X-ray diffraction indicates that the nanotetrapods are of wurtzite structure. The morphology and the microstructure of the nanotetrapods are investigated by the scanning electron microscopy. Selected area electron diffraction shows the growth direction, and energy dispersive X-ray spectroscopy reveals the atomic composition ratio of Zn/O. The growth process is briefly discussed. The optical property of the products was also recorded by means of photoluminescence spectroscopy.
文摘A facile one-step method was developed for the fabrication of hierarchical ZnO film on substrate. Neither seed nor catalyst layer is necessary for the growth of hierarchical ZnO film. Three kinds of nucleation process were found, and the influences of growth time, growth electrolyte, growth temperature on the morphology of ZnO film were evaluated. Hierarchical ZnO film can absorb more than 97% of incident photons with wavelength shorter than 380 nm. Such hierarchical ZnO film would be a promising scaffold for photoelectrochemical application.
基金Funded by the Open Foundation of Jiangsu Provincial Key Laboratory of Photon-manufacture (GZ200708)the 7th Student Research Train Programof Jiangsu University (No. 07A172)
文摘Different three-dimension （3D） nanotetrapods, containing club-like nanocrystals, nanotetrapods and four-foot-like nanocrystals were synthesized from Zinc sheet via CO2 laser irradiation and coaxially transporting O2. Different nanoproducts were fabricated by changing the content of oxygen in the experiment. The morphologies, components, phase structures and optical properties of the products were investigated by a field-emission scanning electron microscopy, an X-ray diffraction, an energy dispersed X-ray spectrometer and a photoluminescence spectroscope. The X-ray diffraction spectra were obtained on a Rigaku D/max 2500PC diffractometer. The experimental results reveal that high quality ZnO nanotetrapods can be fabricated on the special parameters, and growth of ZnO nanotetrapods depends on Vapour-Liquid-Solid（VLS） model, and the content of oxygen in the gas, namely, oxygen partial pressure is one of main factors to control morphologies and optical properties ofZnO nanotetrapods; these advantages above are important for realization of optoelectronic devices.
文摘Recently, the efforts in solid-state materials include developing technologies capable of producing ZnO wafers in large dimensions and good quality based device applications. High quality bulk crystals are obtained by growing from high purity the melt. However, the thermochemical properties of ZnO (high melting point and high vapor pressure) make the growth of single crystals difficult. The thermodynamic calculations show that ZnO crystals can be grown from the melt if a suitable dynamic atmosphere composition is used. The oxygen requirement with increasing the temperature can be fulfilled by adding the NO-NO2 gases into the CO2 atmosphere. At ZnO melting point, the oxygen partial pressure of gas mixtures containing CO2-NO-CO-NO2 at Pt = 5 atm reaches to PO2 = 0.29 atm. According to this new thermodynamic result, it would be expected that ZnO crystal could be grown from the melt at lower total pressure comparing to pure CO2.
