The adsorption and the growth of ZnO on α-Al2O3（0001） surface at various temperatures were theoretically calculated by using a plane wave pseudopotentials （USP） method based on density functional theory.The avera...The adsorption and the growth of ZnO on α-Al2O3（0001） surface at various temperatures were theoretically calculated by using a plane wave pseudopotentials （USP） method based on density functional theory.The average adsorption energy of ZnO at 400, 600 and 800 ℃ is 4.16±0.08, 4.25±0.11 and 4.05±0.23 eV respectively. Temperature has a remarkable effect on the structure of the surface and the interface of ZnO/α-Al2O3（0001）. It is found that the Zn-hexagonal symmetry deflexion does not appear during the adsorption growth of ZnO at 400 ℃, and that the ZnO[10^-10] is parallel with the [10^-10] of the α-Al2O3（0001）, which is favorable for forming ZnO film with the Zn-terminated surface. It is observed from simulation that there are two kinds of surface structures in the adsorption of ZnO at 600 ℃： one is the ZnO surface that has the Zn-terminated structure, and whose [10^-10] parallels the [10^-10] of the substrate surface, and the other is the ZnO[10^-10] //sapphire [11-20] with the O-terminated surface. The energy barrier of the phase transition between these two different surface structures is about 1.6 eV, and the latter is more stable. Therefore,the suitable temperature for the thin film growth of ZnO on sapphire is about 600 ℃, and it facilitates the formation of wurtzite structure containing Zn-O-Zn-O-Zn-O double-layers as a growth unit-cell. At 600 ℃, the average bond length of Zn-O is 0.190±0.01 nm, and the ELF value indicates that the bond of （substrate）-O-Zn-O has a distinct covalent character, whereas the （Zn）O-Al （substrate） shows a clear character of ionic bond. However, at a temperature of 800 ℃, the dissociation of Al and O atoms on the surface of the α-Al2O3（0001） leads to a disordered surface and interface structure. Thus, the Zn-hexagonal symmetry structure of the ZnO film is not observed under this condition.展开更多
We provide a new way to prepare ZnO nanorods pattern from the solution composed of hexamethylenetetramine （HMT） and Zn（NO3）2. The substrate is ITO substrate covered by well ordered Au islands. Since Au and the und...We provide a new way to prepare ZnO nanorods pattern from the solution composed of hexamethylenetetramine （HMT） and Zn（NO3）2. The substrate is ITO substrate covered by well ordered Au islands. Since Au and the underneath ITO substrate have two different nucleation rates in the initial stage of heterogeneous nucleation process, the subsequent ZnO growth on the quick nucleating area takes place under diffusion control and is able to confine the synthesis of ZnO nanorods to specific locations. The concentrations of zinc nitrate and HMT are well adjusted to show the possibility of the new route for the patterning of the ZnO nanorods. Furthermore, the nanorods pattern was characterized by X-ray diffraction and photoluminescence and the performance of field emission property from ZnO nanorod patterns was investigated. The ZnO nanorods pattern with a good alignment also shows a good field enhancement behavior with a high value of the field enhancement factor.展开更多
首先在氟掺杂的氧化锡导电玻璃(FTO)上水热生长一层TiO2纳米棒阵列薄膜,然后通过旋涂法旋涂ZnO籽晶层后水热法生长ZnO纳米棒得到TiO2/ZnO纳米棒阵列薄膜。通过XRD、SEM、PL、UV-Vis和电化学工作站等对单层TiO2纳米棒和TiO2/ZnO纳米棒的...首先在氟掺杂的氧化锡导电玻璃(FTO)上水热生长一层TiO2纳米棒阵列薄膜,然后通过旋涂法旋涂ZnO籽晶层后水热法生长ZnO纳米棒得到TiO2/ZnO纳米棒阵列薄膜。通过XRD、SEM、PL、UV-Vis和电化学工作站等对单层TiO2纳米棒和TiO2/ZnO纳米棒的结构、表面形貌、荧光性能、光吸收强度以及光电化学性质进行表征。结果表明,随着水热生长ZnO时间的增长,ZnO纳米棒密度增加;ZnO纳米棒的生长时间不同使其荧光强度不同,TiO2/Zn O纳米棒的荧光强度与单层TiO2纳米棒相比有着微小的减弱,没有明显的衍射峰;TiO2/ZnO纳米棒复合材料比单层TiO2的光吸收强度高,提高其光学性能,但是吸光区域都在紫外光区域;在标准模拟太阳光照射下,TiO2/Zn O纳米棒的光电流为0. 002 m A,单层TiO2纳米棒的光电流为0. 006 m A,复合薄膜的电流有着明显的变化。展开更多
ZnO bicrystalline nanosheets have been synthesized by using Ax=AU1-x alloy catalyst via the vapor transport and condensation method at 650 ℃. High resolution transmission electron microscopy characterization reveals ...ZnO bicrystalline nanosheets have been synthesized by using Ax=AU1-x alloy catalyst via the vapor transport and condensation method at 650 ℃. High resolution transmission electron microscopy characterization reveals a twin boundary with {01-13} plane existing in the bicrystalline. A series of control experiments show that both AgxAu1-x alloy catalyst and high supersaturation of Zn vapor are prerequisites for the formation of ZnO bicrystalline nanosheet. Moreover, it is found that the density of ZnO bicrytalline nanosheets can be tuned through varying the ratio of Ag to Au in the alloy catalyst. The result demonstrates that new complicated nanostructures can be produced controllably with appropriate alloy catalyst.展开更多
Characterizing the three-dimensional （3D） shape of a nanostructure by con- ventional imaging techniques in scanning electron microscopy and transmission electron microscopy can be limited or complicated by various f...Characterizing the three-dimensional （3D） shape of a nanostructure by con- ventional imaging techniques in scanning electron microscopy and transmission electron microscopy can be limited or complicated by various factors, such as two-dimensional （2D） projection, diffraction contrast and unsure orientation of the nanostructure with respect to the electron beam direction. In this paper, in conjunction with electron diffraction and imaging, the 3D morphologies of ZnO nanowires and nanobelts synthesized via vapor deposition were reconstructed by electron tomography in a scanning transmission electron microscope （STEM）. The cross-sections of these one-dimensional （1D） nanostructures include triangle, hexagonal, and rectangle shapes. By combining the reconstructed shape with the crystalline information supplied by electron diffraction patterns recorded from the same nanowire/nanobelt, the growth direction and its exposed surfaces were uniquely identified. In total, three different growth directions were confirmed. These directions are 〈 0001 〉, 〈21 10 〉 and 〈21 13 〉, corresponding to 〈001〉, 〈100〉 and 〈101〉 orientations in three-index notation. The 〈0001〉 growth nanowires show triangle or hexagonal cross-sections, with exposed {01]-0} side surfaces. The dominant surfaces of the 〈21 10〉 growth nanobelt are _＋（0001） planes. Both hexagonal and rectangle cross-sections were observed in the 〈 2]-13 〉 growth ZnO nanostructures. Their surfaces include the {01]-0}, {]-101} and {2112} planes. The nanobelts with a large aspect ratio of ~10 normally grow along the 〈 21 10 〉 direction, while nanobelts with small aspect ratio grow along 〈21 13 〉 growth direction. The approach and methodology demonstrated here can be extended to any nanostructures that even amorphous. can be crystalline, polycrystalline or展开更多
For the first time we fabricated ZnO membranes with thicknesses of 2.4 nm by a facile one-pot synthesis in aqueous solution.The crystal analysis revealed that the hexagonal ZnO membranes were about 10 atomic layers in...For the first time we fabricated ZnO membranes with thicknesses of 2.4 nm by a facile one-pot synthesis in aqueous solution.The crystal analysis revealed that the hexagonal ZnO membranes were about 10 atomic layers in thickness.The ZnO membranes bent,scrolled,intersected with each other,and self-assembled to particles in micrometre size.The hierarchical assemblies showed sponge-like structures with room inside.In the growth process,a cationic polyelectrolyte was utilized to modulate growth behavior of the ZnO crystals.As a result,the preferred growth direction of ZnO membranes is along 0110,which was perpendicular to[0001]growth direction in a typical hydrothermal synthesis.The growth mechanism of the membranes was also discussed.展开更多
ZnO nanorod arrays were fabricated in aqueous solutions under external voltages.The morphology and length of the nanorods could be readily controlled by varying such parameters as the voltage magnitude,growth time,sol...ZnO nanorod arrays were fabricated in aqueous solutions under external voltages.The morphology and length of the nanorods could be readily controlled by varying such parameters as the voltage magnitude,growth time,solution concentration and substrate type.The external voltage,which made the adsorption of the Zn 2+ cation-containing complexes more possible,modified the growth behavior of the ZnO crystals and played a key role in guaranteeing the orderliness of the arrays.The increase in the nanorod length with the prolonged growth time gradually saturated due to the balance between the growth and the erosion.The ZnO nanorods respectively grown on the Zn and Si substrates differed considerably in both morphology and defect concentration.Field emission was extracted from arrays of nanorods with tapered ends.This field-assisted solution route for fabricating ZnO nanorods featured simplicity in manipulation,inexpensiveness in instrumentation,and effectiveness in controlling the morphology and length.展开更多
A novel photovoltaic phenomenon of internal photoemission was found in a low cost manganite La0.62Ca0.29K0.09MnO3 （LCKMO）/zinc oxide （ZnO） heterojunction bilayers grown on ITO substrate by pulsed laser deposition ...A novel photovoltaic phenomenon of internal photoemission was found in a low cost manganite La0.62Ca0.29K0.09MnO3 （LCKMO）/zinc oxide （ZnO） heterojunction bilayers grown on ITO substrate by pulsed laser deposition （PLD） at relative low growth temperature. The heterostructure ITO/LCKMO/ZnO/A1 exhibits reproducible rectifying characteristics and light cur- rent under continuous laser irradiation of 2 = 325 nm. We report here the influence of LCKMO/ZnO bilayers＇ thickness on the electrical and photoelectric properties of the heterostructure at room temperature. The power conversion efficiency （PCE） is achieved when the LCKMO and ZnO layers are thin enough or the full space charge layer is sufficient. We obtained the maximum value of PCE of 0.0145% when the thicknesses of LCKMO and ZnO layers are 25 and 150 nm, respectively. The open circuit voltage is 0.04 V under this condition due to the internal photoemission.展开更多
文摘The adsorption and the growth of ZnO on α-Al2O3（0001） surface at various temperatures were theoretically calculated by using a plane wave pseudopotentials （USP） method based on density functional theory.The average adsorption energy of ZnO at 400, 600 and 800 ℃ is 4.16±0.08, 4.25±0.11 and 4.05±0.23 eV respectively. Temperature has a remarkable effect on the structure of the surface and the interface of ZnO/α-Al2O3（0001）. It is found that the Zn-hexagonal symmetry deflexion does not appear during the adsorption growth of ZnO at 400 ℃, and that the ZnO[10^-10] is parallel with the [10^-10] of the α-Al2O3（0001）, which is favorable for forming ZnO film with the Zn-terminated surface. It is observed from simulation that there are two kinds of surface structures in the adsorption of ZnO at 600 ℃： one is the ZnO surface that has the Zn-terminated structure, and whose [10^-10] parallels the [10^-10] of the substrate surface, and the other is the ZnO[10^-10] //sapphire [11-20] with the O-terminated surface. The energy barrier of the phase transition between these two different surface structures is about 1.6 eV, and the latter is more stable. Therefore,the suitable temperature for the thin film growth of ZnO on sapphire is about 600 ℃, and it facilitates the formation of wurtzite structure containing Zn-O-Zn-O-Zn-O double-layers as a growth unit-cell. At 600 ℃, the average bond length of Zn-O is 0.190±0.01 nm, and the ELF value indicates that the bond of （substrate）-O-Zn-O has a distinct covalent character, whereas the （Zn）O-Al （substrate） shows a clear character of ionic bond. However, at a temperature of 800 ℃, the dissociation of Al and O atoms on the surface of the α-Al2O3（0001） leads to a disordered surface and interface structure. Thus, the Zn-hexagonal symmetry structure of the ZnO film is not observed under this condition.
文摘We provide a new way to prepare ZnO nanorods pattern from the solution composed of hexamethylenetetramine （HMT） and Zn（NO3）2. The substrate is ITO substrate covered by well ordered Au islands. Since Au and the underneath ITO substrate have two different nucleation rates in the initial stage of heterogeneous nucleation process, the subsequent ZnO growth on the quick nucleating area takes place under diffusion control and is able to confine the synthesis of ZnO nanorods to specific locations. The concentrations of zinc nitrate and HMT are well adjusted to show the possibility of the new route for the patterning of the ZnO nanorods. Furthermore, the nanorods pattern was characterized by X-ray diffraction and photoluminescence and the performance of field emission property from ZnO nanorod patterns was investigated. The ZnO nanorods pattern with a good alignment also shows a good field enhancement behavior with a high value of the field enhancement factor.
文摘首先在氟掺杂的氧化锡导电玻璃(FTO)上水热生长一层TiO2纳米棒阵列薄膜,然后通过旋涂法旋涂ZnO籽晶层后水热法生长ZnO纳米棒得到TiO2/ZnO纳米棒阵列薄膜。通过XRD、SEM、PL、UV-Vis和电化学工作站等对单层TiO2纳米棒和TiO2/ZnO纳米棒的结构、表面形貌、荧光性能、光吸收强度以及光电化学性质进行表征。结果表明,随着水热生长ZnO时间的增长,ZnO纳米棒密度增加;ZnO纳米棒的生长时间不同使其荧光强度不同,TiO2/Zn O纳米棒的荧光强度与单层TiO2纳米棒相比有着微小的减弱,没有明显的衍射峰;TiO2/ZnO纳米棒复合材料比单层TiO2的光吸收强度高,提高其光学性能,但是吸光区域都在紫外光区域;在标准模拟太阳光照射下,TiO2/Zn O纳米棒的光电流为0. 002 m A,单层TiO2纳米棒的光电流为0. 006 m A,复合薄膜的电流有着明显的变化。
基金ACKNOWLEDGMENTS This work was supported by the Ministry of Science and Technology of China of China （No.2011CB921403）, the National Natural Science Foundation of China （No. 11374274 and No. 11074231）, and Chinese Academy of Sciences （No.XDB01020000）.
文摘ZnO bicrystalline nanosheets have been synthesized by using Ax=AU1-x alloy catalyst via the vapor transport and condensation method at 650 ℃. High resolution transmission electron microscopy characterization reveals a twin boundary with {01-13} plane existing in the bicrystalline. A series of control experiments show that both AgxAu1-x alloy catalyst and high supersaturation of Zn vapor are prerequisites for the formation of ZnO bicrystalline nanosheet. Moreover, it is found that the density of ZnO bicrytalline nanosheets can be tuned through varying the ratio of Ag to Au in the alloy catalyst. The result demonstrates that new complicated nanostructures can be produced controllably with appropriate alloy catalyst.
文摘Characterizing the three-dimensional （3D） shape of a nanostructure by con- ventional imaging techniques in scanning electron microscopy and transmission electron microscopy can be limited or complicated by various factors, such as two-dimensional （2D） projection, diffraction contrast and unsure orientation of the nanostructure with respect to the electron beam direction. In this paper, in conjunction with electron diffraction and imaging, the 3D morphologies of ZnO nanowires and nanobelts synthesized via vapor deposition were reconstructed by electron tomography in a scanning transmission electron microscope （STEM）. The cross-sections of these one-dimensional （1D） nanostructures include triangle, hexagonal, and rectangle shapes. By combining the reconstructed shape with the crystalline information supplied by electron diffraction patterns recorded from the same nanowire/nanobelt, the growth direction and its exposed surfaces were uniquely identified. In total, three different growth directions were confirmed. These directions are 〈 0001 〉, 〈21 10 〉 and 〈21 13 〉, corresponding to 〈001〉, 〈100〉 and 〈101〉 orientations in three-index notation. The 〈0001〉 growth nanowires show triangle or hexagonal cross-sections, with exposed {01]-0} side surfaces. The dominant surfaces of the 〈21 10〉 growth nanobelt are _＋（0001） planes. Both hexagonal and rectangle cross-sections were observed in the 〈 2]-13 〉 growth ZnO nanostructures. Their surfaces include the {01]-0}, {]-101} and {2112} planes. The nanobelts with a large aspect ratio of ~10 normally grow along the 〈 21 10 〉 direction, while nanobelts with small aspect ratio grow along 〈21 13 〉 growth direction. The approach and methodology demonstrated here can be extended to any nanostructures that even amorphous. can be crystalline, polycrystalline or
基金supported by the Ministry of Science and Technology of China(Grant Nos.2013CB933604 and 2010CB934203)the National Natural Science Foundation of China(Grant Nos.61171023 and 61076057)
文摘For the first time we fabricated ZnO membranes with thicknesses of 2.4 nm by a facile one-pot synthesis in aqueous solution.The crystal analysis revealed that the hexagonal ZnO membranes were about 10 atomic layers in thickness.The ZnO membranes bent,scrolled,intersected with each other,and self-assembled to particles in micrometre size.The hierarchical assemblies showed sponge-like structures with room inside.In the growth process,a cationic polyelectrolyte was utilized to modulate growth behavior of the ZnO crystals.As a result,the preferred growth direction of ZnO membranes is along 0110,which was perpendicular to[0001]growth direction in a typical hydrothermal synthesis.The growth mechanism of the membranes was also discussed.
基金supported by the National Natural Science Foundation of China (Grant No. 61171023)the National Basic Research Program of China ("973" Project) (Grant No. 2010CB934203)
文摘ZnO nanorod arrays were fabricated in aqueous solutions under external voltages.The morphology and length of the nanorods could be readily controlled by varying such parameters as the voltage magnitude,growth time,solution concentration and substrate type.The external voltage,which made the adsorption of the Zn 2+ cation-containing complexes more possible,modified the growth behavior of the ZnO crystals and played a key role in guaranteeing the orderliness of the arrays.The increase in the nanorod length with the prolonged growth time gradually saturated due to the balance between the growth and the erosion.The ZnO nanorods respectively grown on the Zn and Si substrates differed considerably in both morphology and defect concentration.Field emission was extracted from arrays of nanorods with tapered ends.This field-assisted solution route for fabricating ZnO nanorods featured simplicity in manipulation,inexpensiveness in instrumentation,and effectiveness in controlling the morphology and length.
基金supported by the National Natural Science Foundation of China (No. 90922034 and No. 21131002)Specialized Research Fund for the Doctoral Program of Higher Education (No. 20110061130005)
文摘A novel photovoltaic phenomenon of internal photoemission was found in a low cost manganite La0.62Ca0.29K0.09MnO3 （LCKMO）/zinc oxide （ZnO） heterojunction bilayers grown on ITO substrate by pulsed laser deposition （PLD） at relative low growth temperature. The heterostructure ITO/LCKMO/ZnO/A1 exhibits reproducible rectifying characteristics and light cur- rent under continuous laser irradiation of 2 = 325 nm. We report here the influence of LCKMO/ZnO bilayers＇ thickness on the electrical and photoelectric properties of the heterostructure at room temperature. The power conversion efficiency （PCE） is achieved when the LCKMO and ZnO layers are thin enough or the full space charge layer is sufficient. We obtained the maximum value of PCE of 0.0145% when the thicknesses of LCKMO and ZnO layers are 25 and 150 nm, respectively. The open circuit voltage is 0.04 V under this condition due to the internal photoemission.
