Sn掺杂ZnO半导体纳米带的制备、结构和性能

在无催化剂的条件下, 利用碳热还原反应气相沉积法制备出了高产率单晶Sn掺杂ZnO纳米带. XRD和TEM研究表明纳米带为结晶完好的纤锌矿结构, 生长方向沿[0001], EDS分析表明纳米带中Sn元素含量约为1.9%. 室温光致发光谱(PL)显示掺锡氧化锌纳米带存在强的绿光发射峰和较弱的紫外发射峰, 谱峰峰位中心分别位于494.8 nm和398.4 nm处, 并对发光机制进行了分析. 这种掺杂纳米带有望作为理想的结构单元应用于纳米尺度光电器件领域.     

Controlled growth of semiconducting oxides hierarchical nanostructures

Semiconducting ZnO hierarchical nanostructure, where ZnO nanonails were grown on ZnO nanowires, has been fabricated under control experiment with a mixture of ZnO nanopowders and Sn metal powders. Sn nanoparticles are located at or close to the tips of the nanowires and the growth branches, serving as the catalyst for the vapor-liquid-solid growth mechanism. The morphology and microstructure of ZnO nanowire and nanonail were measured by scanning electron microscopy and high-resolution transmission electron microscopy. The long and straight ZnO nanowires grow along [0001] direction. ZnO nanonails are aligned radially with respect to the surface the ZnO nanowire. The long axis direction of nanonails forms an angle of ∼30° to the [0001] direction.     

Sn掺杂ZnO纳米针的结构及其生长机制(英文)

利用包括磁控溅射和热氧化的两步法在Si(111)衬底上制备了Sn掺杂ZnO纳米针.首先用磁控溅射法在Si(111)衬底上制备Sn:Zn薄膜,然后在650℃的Ar气氛中对薄膜进行热氧化,制备出Sn掺杂ZnO纳米针.样品的结构、成分和光学性质采用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)、能量散射X射线(EDX)谱和光致发光(PL)光谱等技术手段进行分析.结果表明,制备的样品为具有六方纤锌矿结构的单晶Sn掺杂ZnO纳米针,Sn掺杂量为2.5%(x,原子比),底部和头部直径分别为200-500 nm和40 nm,长度为1-3μm,结晶质量较高.室温光致发光光谱显示紫外发光峰比纯ZnO的发光峰稍有蓝移,这可归因于能谱分析中探测到的Sn的影响.基于本实验的实际条件,简单探讨了Sn掺杂ZnO纳米针的生长机制.     

Synthesis of single crystal Sn-doped In(2)O(3) nanowires: size-dependent conductive characteristics

Single crystalline Sn doped In(2)O(3) (ITO) NWs (nanowires) were synthesized via an Au-catalyzed VLS (vapor-liquid-solid) method at 600 °C. The different sizes (～20, ～40, ～80 nm) of the Au NPs (nanoparticles) provided the controllable diameters for ITO NWs during growth. Phase and microstructures confirmed by high-resolution transmission electron microscope images (HRTEM) and X-ray diffraction (XRD) spectra indicated that the phase of In(2)O(3) NWs had a growth direction of [100]. X-ray photoelectron spectroscopy (XPS) was employed to obtain the chemical compositions of the ITO NWs as well as the ratio of Sn/In and oxygen concentrations. The findings indicated that low resistivity was found for ITO NWs with smaller diameters due to higher concentrations of oxygen vacancies and less incorporation of Sn atoms inside the NWs. The resistivity of NWs increases with increasing diameter due to more Sn atoms being incorporated into the NW and their reduction of the amount of oxygen vacancies. Low resistivity NWs could be achieved again due to excess Sn atoms doped into the large diameter NWs. Therefore, by optimizing the well-controlled growth of the NW diameter and interface states, we are able to tune the electrical properties of Sn-doped ITO NWs.     

Ga-F共掺杂ZnO导电性和透射率的第一性原理计算

用基于密度泛函理论的第一性原理平面波超软赝势方法,对本征ZnO,Ga、F单掺ZnO和Ga-F共掺ZnO的几何结构进行优化后计算了各体系的相关性质.结果表明各掺杂体系有各自的优缺点,在制作透明导电薄膜时可根据具体要求采取不同的掺杂方案.Ga掺杂ZnO比F掺杂ZnO的晶格畸变小.相同环境下Ga原子比F原子更容易进入ZnO晶格,因此掺杂后结构更加稳定.Ga、F掺杂都改善了ZnO的导电性,掺杂ZnO的载流子浓度比本征ZnO增加了3个数量级,相同浓度的F掺杂比Ga掺杂能产生更多的载流子.Ga-F共掺杂ZnO折中了上述Ga、F单掺杂ZnO的优缺点.另外,掺杂后ZnO的吸收边蓝移,以Ga-F共掺杂ZnO在紫外区域的透射率最大,在280~380 nm范围内其透射率在90%以上.     

Ga-F共掺杂ZnO导电性和透射率的第一性原理计算

采用基于密度泛函理论的第一性原理平面波超软赝势方法,对本征ZnO,Ga、F单掺ZnO和Ga-F共掺ZnO的几何结构进行优化后计算了各体系的相关性质。结果表明各掺杂体系有各自的优缺点,在制作透明导电薄膜时可根据具体要求采取不同的掺杂方案。Ga掺杂ZnO比F掺杂ZnO的晶格畸变小。相同环境下Ga原子比F原子更容易进入ZnO晶格,因此掺杂后结构更加稳定。Ga、F掺杂都改善了ZnO的导电性,掺杂ZnO的载流子浓度比本征ZnO增加了3个数量级,相同浓度的F掺杂比Ga掺杂能产生更多的载流子。Ga-F共掺杂ZnO折中了上述Ga、F单掺杂ZnO的优缺点。另外,掺杂后ZnO的吸收边蓝移,以GaF共掺杂ZnO在紫外区域的透射率最大,在280~380 nm范围内其透射率在90%以上。     

First-principles Studies on Electronic Structures of Ga-doped ZnO and ZnS

First-principles calculations have been performed to clarify the differences of the electronic structures of Ga-doped ZnO and ZnS. Results show the local density approximation and local density approximation+U calculations are in good qualitative agreement with each other. After doping, impurity states appear near the Fermi level in both ZnO and ZnS cases.When ZnO is doped, the impurity states are delocalized in the whole conduction band. On the contrary, when ZnS is doped, though the p state of Ga is also delocalized, the s state is localized near the Fermi level. Partial charge density distributions of the frontier orbital show the same information. After an exchange of the crystal structures of ZnO and ZnS,results remain unchanged. The localized Ga s state accounts for the bad electrical properties of Ga-doped ZnS.     

Sn掺杂MoO_3的制备、表征及气敏性能

以仲钼酸铵和四氯化锡为原料,采用水热法制备了不同Sn掺杂比例的MoO_3;利用X射线衍射(XRD),扫描电子显微镜(SEM)和Brunauer-Emmett Teller(BET)测试等手段对材料进行了物相、形貌结构和孔径表征;测试了其对乙醇、二氯甲烷、甲醇、甲醛、甲酸、四氯化碳、氨气和丙酮等气体的传感性能.结果表明,Sn掺杂未改变MoO_3的结构;290℃为气体传感测试的最佳测试温度;掺杂后的MoO_3对乙醇气体的灵敏度和响应时间均优于纯相MoO_3,Sn掺杂摩尔比为5%时效果最好,500 mg/m~3测试条件下对乙醇的灵敏度为19.64,响应时间为1.1 s.     

Humidity sensing characteristics of Sn doped Zinc oxide based quartz crystal microbalance sensors

The electrical, optical and humidity sensor properties of nanostructured ZnO samples were investigated. The structural properties of Sn doped ZnO samples were characterized by X-ray diffraction and atomic force microscopy. It was found that the all samples have a hexagonal crystal structure. The electrical conductivity of the samples indicates that undoped and Sn doped ZnO samples exhibit the semiconducting behavior. The optical absorption method was used to determine the optical band gaps of the samples. The optical band gap and activation energy values of the ZnO samples were changed with Sn doping. The ZnO based on quartz crystal microbalance humidity sensors were prepared and sensing properties of the sensors were changed with Sn doping. The response time required to reach 70 % is about 13–16 s, while the recovery time from 70 to 30 % RH is about 13–15 s. The fast response of the sensors is due to easy diffusion of water molecules between ZnO nanopowders. The prepared sensors have a high reproducibility and sensitivity for humidity sensing applications.     

Short-period superlattice structure of Sn-doped In(2)O(3)(ZnO)(4) and In(2)O(3)(ZnO)(5) nanowires

Two longitudinal superlattice structures of In(2)O(3)(ZnO)(4) and In(2)O(3)(ZnO)(5) nanowires were exclusively produced by a thermal evaporation method. The diameter is periodically modulated in the range of 50-90 nm. The nanowires consist of one In-O layer and five (or six) layered Zn-O slabs stacked alternately perpendicular to the long axis, with a modulation period of 1.65 (or 1.9) nm. These superlattice nanowires were doped with 6-8% Sn. The X-ray diffraction pattern reveals the structural defects of wurtzite ZnO crystals due to the In/Sn incorporation. The high-resolution X-ray photoelectron spectrum suggests that In and Sn withdraw the electrons from Zn and enhance the number of dangling-bond O 2p states, resulting in the reduction of the band gap. Photoluminescence and cathodoluminescence exhibit the peak shift of near band edge emission to the lower energy and the enhancement of green emission as the In/Sn content increases.     

Co doped ZnO nanowires as visible light photocatalysts

High aspect ratio cobalt doped ZnO nanowires showing strong photocatalytic activity and moderate ferromagnetic behaviour were successfully synthesized using a solvothermal method and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), vibrating sample magnetometry (VSM) and UV–visible absorption spectroscopy. The photocatalytic activities evaluated for visible light driven degradation of an aqueous methylene orange (MO) solution were higher than for Co doped ZnO nanoparticles at the same doping level and synthesized by the same synthesis route. The rate constant for MO visible light photocatalytic degradation was 1.9·10⁻³ min⁻¹ in case of nanoparticles and 4.2·10⁻³ min⁻¹ in case of nanowires. We observe strongly enhanced visible light photocatalytic activity for moderate Co doping levels, with an optimum at a composition of Zn_0.95Co_0.05O. The enhanced photocatalytic activities of Co doped ZnO nanowires were attributed to the combined effects of enhanced visible light absorption at the Co sites in ZnO nanowires, and improved separation efficiency of photogenerated charge carriers at optimal Co doping.     

Vapor-solid growth of Sn nanowires: growth mechanism and superconductivity

A noncatalytic and template-free vapor transport process has been employed to prepare single-crystalline Sn nanowires with diameters of 10-20 nm. The growth of one-dimensional Sn nanowires follows the mechanism similar to the vapor-solid (V-S) mechanism. Two-dimensional square-shaped nanostructures were also found to form in the region of lower deposition temperatures. The rich morphology may be attributed to the competition in growth rate among different crystallographic planes. Structural characterization with high-resolution transmission electron microscopy showed that the nanowires and nanosquares grew in a preferential direction of [200]. The superconducting transition temperatures for Sn nanowires and Sn nanosquares were about 3.7 K, which was very close to that of bulk beta-Sn. Magnetization measurements showed that the critical magnetic fields for both Sn nanowires and Sn nanosquares increased significantly as compared to that of bulk Sn.     

Lasing mechanism of ZnO nanowires/nanobelts at room temperature

ZnO has become the focus of photonics and optoelectronic research. We prepared pure Mn(II) doped ZnO nanowires with a controlled reduction reaction by carbon in an asymmetrical tube. Careful time-resolved photoluminescence experimental study indicates three types of lasing mechanisms: exciton-exciton interaction, bipolaronic exciton condensation, and plasma; these exist in different ZnO nanowires, which can be changed by doping Mn in ZnO nanowire. The transformation between varied mechanisms is discussed in detail with their spectral behaviors. These results are important in the design of future violet-blue luminescence and display devices.     

Synthesis and characterization of indium-doped ZnO nanowires with periodical single-twin structures

In-doped ZnO (IZO) nanowires have been synthesized by a thermal evaporation method. The morphology and microstructure of the IZO nanowires have been extensively investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The products in general contain several kinds of nanowires. In this work, a remarkable type of IZO zigzag nanowire with a periodical twinning structure has been investigated by transmission electron microscopy (TEM). HRTEM observation reveals that this type of IZO nanowire has an uncommonly observed zinc blend crystal structure. These nanowires, with a diameter about 100 nm, grow along the [111] direction with a well-defined twinning relationship and a well-coherent lattice across the boundary. In addition, an IZO nanodendrite structure was also observed in our work. A growth model based on the vapor-liquid-solid mechanism is proposed for interpreting the growth of zigzag nanowires in our work. Due to the heavy doping of In, the emission peak in photoluminescence spectra has red-shifted as well as broadened seriously.     

Synthesis of europium-doped zinc oxide micro- and nanowires

Single crystalline Eu³⁺-doped wurtzite ZnO micro- and nanowires were synthesized by a chemical vapor deposition method (CVD). The nanostructures were grown by autocatalytic mechanism at walls of an alumina boat. The structure and properties of the doped ZnO is fully characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectrometry (EDX), scanning and transmission electron microscopy (SEM and TEM), and photoluminescence (PL) methods. The synthesis was carried out for 10 min giving vertically aligned nanowires with mean diameter of 50–400 nm and with length of up to several microns. The nanowires were grown along ±[0001] direction. The concentration of Eu³⁺ dopant in the synthesized nanowires was varied from 0.7 to 0.9 at %. The crystal structure and microstructures of the doped nanomaterials were discussed and compared with undoped ZnO. The photoluminescence spectra show that emission of doped samples were shifted towards orange-red region (2.02 eV) relative to undoped zinc oxide nanostructures (2.37 eV) due to Eu³⁺ intraionic transitions from ZnO/Eu.     

Temperature-controlled growth of ZnO nanowires and nanoplates in the temperature range 250-300 degrees C

Starting from a mixture of Zn and BiI3, we grew nanowires and nanoplates on an oxidized Si substrate at relatively low temperatures of 250 and 300 degrees C, respectively. The ZnO nanowires had diameters of approximately 40 nm and grew along the [110] direction rather than the conventional [0001] direction. The nanoplates had thicknesses of approximately 40 nm and lateral dimensions of 3-4 microm. The growth of both the nanowires and nanoplates is dominated by the synergy of vapor-liquid-solid (VLS) and direction conducting. Analysis of photoluminescence spectra suggested that the nanoplates contain more oxygen vacancies and have higher surface-to-volume ratios than the nanowires. The present results clearly demonstrate that the shapes of ZnO nanostructures formed by using BiI3 can be controlled by varying the temperature in the range 250-300 degrees C.     

Synthesis and optical properties of S-doped ZnO nanostructures: nanonails and nanowires

S-doped ZnO nanostructures such as nanonails and nanowires have been synthesized via a simple one-step catalyst-free thermal evaporation process on a large scale. The doping concentration of sulfur into ZnO nanonails and nanowire were 2 atm % and 7.5 atm %, respectively. Studies found that the S-doped ZnO nanonails and nanowires were single-crystalline wurtzite structure and grew along the (001) direction. The average diameters of the nanonails and nanowires were 70 and 50 nm, respectively. Low-temperature photoluminescence spectra of ZnO samples showed two luminescence peaks in the UV and green emission region, respectively. As the concentration of sulfur in the ZnO nanostructures increased, the intensity of the UV emission peak decreased dramatically, and it showed a little blue-shift while the intensity of the green emission increased greatly.     

Synthesis and Magnetic Properties of Manganese-Doped GaP Nanowires

We characterized the structure and magnetic properties of Mn-incorporated GaP nanowires synthesized by thermal evaporation of GaP/Mn powders. The nanowires consist of twin-crystalline zinc blende GaP grown with the [111] direction and doped with about 1 at. % Mn. They are often sheathed with the bumpy amorphous outerlayers containing high concentrations of Mn and O. The ferromagnetic hysteresis curves at 5 and 300 K and temperature-dependent magnetization provide evidence for the ferromagnetism with the Curie temperature higher than room temperature. Magnetic properties of individual nanowires have been measured, showing a large negative magnetoresistance equal to about -5% at 5 K. We suggest that the Mn doping of GaP nanowires would form a dilute magnetic semiconductor.     

Sn4+掺杂对TiO2纳米颗粒膜光催化降解苯酚活性的影响

金属离子掺杂能改善TiO2纳米微粒光催化活性,在光降解大气和水污染物的研究中,已引起人们的重视[1,2].实验证明,掺杂物的浓度、掺杂离子的分布、掺杂能级与TiO2能带匹配程度、掺杂离子d电子的组态、电荷的转移和复合等因素对催化剂的光催化活性有直接影响[3].Kamat等[4]曾利用TiO2颗粒与SnO2颗粒混合制膜,使光催化剂活性得到提高.但Sn4+掺杂TiO2用于光催化剂尚少见报道.本文采用等离子体化学气相沉积法(PECVD)[5]制备了Sn4+离子掺杂的TiO2纳米颗粒膜催化剂(TiO2-Sn),考察了其对苯酚的光催化降解活性,讨论了Sn4+离子的掺杂方式及光催化活性提高的机理.     

Band gap tailoring of chemically synthesized lead sulfide thin films by in situ Sn doping

In the present report, undoped and tin (Sn)‐doped lead sulfide thin films were synthesized via chemical bath deposition method. The effects of Sn molar concentration on the optical, structural, and morphological properties were systematically studied. The concentration of Sn in the chemical bath was characterized by the ratio of [Sn⁺²]/[Pb⁺²] and varied from 0 to 15 at.%. Both doped and undoped thin films were polycrystalline in nature with a face‐centered cubic crystal structure; however, the preferred orientations of the crystallites were varied along the (111) and (200) planes with Sn‐doping concentration. The X‐ray powder diffraction results also showed that peak intensities and the crystalline size were decreased with increasing Sn concentration. The lattice constant varied with Sn concentration and found in the range of 6.020 to 5.944 Å. The variation of Sn concentration in PbS:Sn thin films were confirmed by energy dispersive X‐ray analyses study. The scanning electron microscope and atomic force microscopy studies revealed that Sn doping had a critical role on the surface roughness and morphology of the PbS:Sn thin films. The optical band gap study showed that the band gap of PbS:Sn thin films were engineered from 0.676 to 1.345 eV because of incorporation of Sn⁺² ions via cost‐effective chemical route. Room temperature photoluminescence spectra showed a well‐defined peak at 427 nm and shoulders at 405 and 462 nm for all Sn‐doped and undoped PbS samples.