二氧化锡纳米线的生长机理研究

使用水平石英管式电炉，以二氧化锡和石墨的混合物为原材料、高纯氮气为载气，在850℃温度下用直接热蒸发法制备二氧化锡纳米线．衬底硅片的直径为10mm，其上覆盖一层5nm厚的金催化剂．原材料放在石英舟中，离原材料30mm的下风口处放置硅衬底，原材料和硅衬底都放置在石英管的中部电炉的恒温区内．用扫描电子显微镜（SEM）和透射电子显微镜（TEM）观察到二氧化锡的纳米线结构；X射线衍射（XRD）表明二氧化锡纳米线具有四方金红石结构；选区电子衍射（SAED）照片表明二氧化锡纳米线具有完善的晶体结构．不同生长时间下制备样品的扫描电子显微镜和透射电子显微镜照片再现了二氧化锡纳米线的生长过程，该纳米线的生长符合传统的VLS生长机制．     

Structure and field emission properties of SnO2 nanowires

SnO₂ nanowires were fabricated using a simple and economical method of rapid heating SnO₂ and graphite powders at 850 °C in a flow of high-purity N₂ as carrier gas. Research by using X-ray diffraction (XRD) indicates that SnO₂ nanowires are primitive tetragonal in structure with the lattice constant a = b = 0.443 nm and c = 0.372 nm. Observations by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that SnO₂ is of nanowire structure. The selected area electron diffraction (SAED) shows that the nanowires are perfect single crystal structure. The Fourier transform infrared (FT-IR) exhibits the difference of nanostructure materials and general materials. The field emission (FE) properties had also been studied.     

Rutile structured SnO2 nanowires synthesized with metal catalyst by thermal evaporation method

One-dimensional (1-D) nanostructures such as tubes, rods, wires, and belts have attracted considerable research activities owing to their strong application potential as components for nanosize electronic or optoelectronic devices utilizing superior optical and electrical properties. Characterizing the mechanical properties of nanostructure is of great importance for their applications in electronics, optoelectronics, sensors, actuators. Wide-bandgap SnO2 semiconducting material (Eg = 3.6 eV at room temperature) is one of the attractive candidates for optoelectronic devices operating at room temperature, gas sensors, and transparent conducting electrodes. The synthesis and gas sensing properties of semiconducting SnO2 nanomaterials have became one of important research issues since the first synthesis of SnO2 nanobelts. Considering the important application of SnO2 in sensors, these structures are not only ideal systems for fundamental understanding at the nanoscale level, but they also have potential applications as nanoscale sensors, resonator, and transducers. The structured SnO2 nanorods have been grown on silicon substrates with Au catalytic layer by thermal evporation process over 800 degrees C. The resulting sample is characterized and analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDS). The morphology and structural properties of SnO2 nanowires were measured by scanning electron microscopy and high-resolution transmission electron microscopy. The mean diameter of the SnO2 nanorods grown on Au coated silicon (100) substrate is approximately 80 nm. In addition, X-ray diffraction measurements show that SnO2 nanorods have a rutile structure. The formation of SnO2 nanowires has been attributed to the vapor-liquid-solid (VLS) growth mechanisms depending on the processing conditions. We investigated the growth behavior of the SnO2 nanowires by variation of the growth conditions such as gas partial pressure and temperature.     

Tailoring the surface properties and carrier dynamics in SnO2 nanowires

We report a study of the role of mid-gap defect levels due to surface states in SnO(2) nanowires on carrier trapping. Ultrafast pump-probe spectroscopy provides carrier relaxation time constants that reveal the nature and positions of various defect levels due to the surface states which in turn provide details on how the carriers relax after their injection. The effect of oxygen annealing on carrier concentration is also studied through XPS valence band photoemission spectroscopy, a sensitive non-contact surface characterization technique. These measurements show that charge transfer associated with chemisorption of oxygen in different forms produces an upward band bending and leads to an increase in the depletion layer width by approximately 70 nm, thereby decreasing surface conductivity and forming the basis for the molecular sensing capability of the nanowires.     

氧化锡纳米线的制备及其乙醇气体敏感性能

采用热蒸发法成功制备氧化锡纳米线。用X射线衍射、扫描电子显微镜和透射电子显微镜对所制备纳米线的晶格结构和表面形貌进行表征。所制材料为金红石氧化锡单晶结构,纳米线直径为50~200nm,长度为5~15μm,符合气-液-固生长机制。以氧化锡为气敏材料,制备了旁热式结构气敏元件,测试该元件对浓度范围为25×10^-6 ~500×10^-6 的乙醇气体环境的敏感性能。结果表明,该元件的最佳工作温度约为260℃;在25×10^-6 和500×10^-6 的乙醇气体中,灵敏度分别为7.54和111.01,响应时间为2~20s,恢复时间为5~33s;在测试范围内灵敏度与气体浓度具有良好的线性关系;7天内重复测量误差在5%以内,稳定性较好。     

Sn-catalyzed synthesis of SnO2 nanowires and their optoelectronic characteristics

We report the rational synthesis of one-dimensional SnO(2) nanowires (SnO(2)NWs) via a Sn-catalyzed vapor-liquid-solid (VLS) growth mechanism, in which Sn nanoparticles can direct the oriented growth of SnO(2)NWs at high temperature. I-V measurement of a field effect transistor made of individual SnO(2)NWs exhibits typical n-type semiconducting characteristics with an electron mobility and concentration of 14.36?cm(2)?V( - 1)?s( - 1) and 1.145 × 10(17)?cm( - 3), respectively. The SnO(2)NW-based photodetector shows a high sensitivity to UV light radiation, and a fast light response speed of millisecond rise time/fall time with excellent stability and reproducibility, whereas it is nearly blind to illumination with wavelengths in the visible range. Detailed reasons to account for the detection selectivity and rapid response speed are proposed. The generality of the above results suggests that our SnO(2)NW photodetectors have potential application in nanoscaled optoelectronic devices.     

A novel method for massive synthesis of SnO2 nanowires

This paper reports a simple, inexpensive and fast method to prepare SnO₂ nanowires. A large amount of ultra-long high purity single-crystalline SnO₂ nanowires with rutile structure, that is over hundreds of micrometers in length and 20–100 nm in diameter, have been synthesized through a one-step typical thermite reaction at 200 °C in O₂ atmosphere, with a gas pressure of 0·9 atm. These SnO₂ nanowires do not grow in one direction as those synthesized by other methods do, and are perfect single crystals without any dislocation or point defects detected in TEM images. The optoelectronic properties of these smooth and uniform nanowires have been characterized by means of X-ray photoelectron spectra, laser Raman spectrum and Fourier transform infrared spectrum. The result of X-ray photoelectron spectra analysis shows that some oxygen vacancies exist in these SnO₂ nanowires. In addition, possible growth mechanism of the SnO₂ nanowires has been described in detail by the studies of comparative experiments, which is quite different from that of SnO₂ nanowires synthesized by some other methods.     

Fully transparent thin-film transistor devices based on SnO2 nanowires

We report on studies of field-effect transistor (FET) and transparent thin-film transistor (TFT) devices based on lightly Ta-doped SnO2 nano-wires. The nanowire-based devices exhibit uniform characteristics with average field-effect mobilities exceeding 100 cm2/V x s. Prototype nano-wire-based TFT (NW-TFT) devices on glass substrates showed excellent optical transparency and transistor performance in terms of transconductance, bias voltage range, and on/off ratio. High on-currents and field-effect mobilities were obtained from the NW-TFT devices even at low nanowire coverage. The SnO2 nanowire-based TFT approach offers a number of desirable properties such as low growth cost, high electron mobility, and optical transparency and low operation voltage, and may lead to large-scale applications of transparent electronics on diverse substrates.     

Large-scale SnO2 nanowires synthesized by direct sublimation method and their enhanced dielectric responses

In this paper, we developed a direct sublimation method to synthesize large-scale rutile SnO₂ nanowires on 6H–SiC substrate using SnO₂ nanoparticles as starting material. The structural properties of these straight nanowires were investigated in detail. These nanowires grow along [121], and the average diameter and length of these nanowires are 80 nm and 5 μm, respectively. In addition, the dielectric measurement indicates that the dielectric response of the SnO₂ nanowires is significantly enhanced in the low-frequency range. It is suggested that both the rotation direction polarization (RDP) and the space charge polarization (SCP) process should be responsible for the enhancement of ε_r of these SnO₂ nanowires.     

Improvement in sensing properties of SnO2 nanowires by functionalizing with Pt nanodots synthesized by gamma-ray radiolysis

Selectively-grown networked SnO2 nanowires were functionalized with Pt nanodots by the radiolysis process. NO2 sensing characteristics of Pt-functionalized SnO2 nanowires were compared with those of bare SnO2 nanowires. The results demonstrate that the Pt functionalization greatly enhances the sensitivity and response time in SnO2 nanowire-based gas sensors. The enhancement is likely to be associated with the spillover effect and/or easy dissociation of NO2 into more active chemical species by the catalytic effect of Pt.     

Acoustically driven photon antibunching in nanowires

The oscillating piezoelectric field of a surface acoustic wave (SAW) is employed to transport photoexcited carriers, as well as to spatially control exciton recombination in GaAs-based nanowires (NWs) on a subns time scale. The experiments are carried out in core-shell NWs transferred to a SAW delay line on a LiNbO(3) crystal. Carriers generated in the NW by a focused laser spot are acoustically transferred to a second location, leading to the remote emission of subns light pulses synchronized with the SAW phase. The dynamics of the carrier transport, investigated using spatially and time-resolved photoluminescence, is well-reproduced by computer simulations. The high-frequency contactless manipulation of carriers by SAWs opens new perspectives for applications of NWs in opto-electronic devices operating at gigahertz frequencies. The potential of this approach is demonstrated by the realization of a high-frequency source of antibunched photons based on the acoustic transport of electrons and holes in (In,Ga)As NWs.     

Synthesis of Zn2SnO4 nanowires and their photoluminescence properties

Single-crystalline Zn2SnO4 nanowires were successfully synthesized on a photoresist-coated Si substrate using a facile chemical vapor deposition method. The growth of the nanowires followed a self-catalytic vapor-liquid-solid process. During annealing, the photoresist was carbonized into a complex glassy and graphite carbon structure. The immiscibility between the carbon layer and the in-situ formed Zn2SnO4 was a prime factor in the formation of the one-dimensional Zn2SnO4 nanowires. A broad blue-red emission band centered at 490.4 nm was observed in the photoluminescence spectrum of these nanowires, and it was related to the oxygen vacancies in these nanowires.     

Enhanced gas sensing by individual SnO2 nanowires and nanobelts functionalized with Pd catalyst particles

The sensing ability of individual SnO(2) nanowires and nanobelts configured as gas sensors was measured before and after functionalization with Pd catalyst particles. In situ deposition of Pd in the same reaction chamber in which the sensing measurements were carried out ensured that the observed modification in behavior was due to the Pd functionalization rather than the variation in properties from one nanowire to another. Changes in the conductance in the early stages of metal deposition (i.e., before metal percolation) indicated that the Pd nanoparticles on the nanowire surface created Schottky barrier-type junctions resulting in the formation of electron depletion regions within the nanowire, constricting the effective conduction channel and reducing the conductance. Pd-functionalized nanostructures exhibited a dramatic improvement in sensitivity toward oxygen and hydrogen due to the enhanced catalytic dissociation of the molecular adsorbate on the Pd nanoparticle surfaces and the subsequent diffusion of the resultant atomic species to the oxide surface.     

Growth and lattice dynamics of single-crystalline SnO2 nanowires prepared by annealing a gel precursor

A large amount of ultra-long single-crystalline SnO₂ nanowires were successfully synthesized through a polymeric sol–gel approach followed by a post-annealing in a crucible covered with a lid. The experimental results indicate that the product is composed of tetragonal SnO₂ nanowires, and moreover, their growth mechanism should arise from the self-catalyzed Sn-terminated polar surfaces due to the enrichment of Sn at the growth front of nanowires. In Raman scattering spectrum, in addition to three fundamental vibrational modes, some infrared (IR) active and surface phonon modes (SPM) are also observed due to size and shape confinement effects and surface disorder. Similarly, low frequency non-active IR and surface phonon mode absorptions are also observed in IR spectra.     

Optical properties of zigzag twinned geometry of Zn2SnO4 nanowires

High-density single-crystalline Zn2SnO4 nanowires have been successfully synthesized by using a simple thermal evaporation method by heating a mixture of ZnO and SnO2 nano powders. The products in general contain various geometries of wires, with an average diameter of 80-100 nm. These nanowires are ultra-long, up to 100 microns. The transmission electron microscopy study showed that these nanowires exhibited zigzag twinned geometry, and grow along the (111) direction. Low-temperature photoluminescence properties of the nanowires were measured, showing a strong green emission band at about 515 nm and a weak peak corresponding to UV emission at about 378 nm, which have not been reported before.     

ZnO-Sn:ZnO core-shell nanowires and ZnO-Zn2SnO4 comb-like nanocomposites

Novel single-crystalline ZnO-Sn:ZnO (SZO) core-shell nanowires and ZnO-Zn2SnO4 (ZTO) comb-like nanocomposites were synthesized by thermal chemical vapor deposition at a low temperature of 650 degrees C. Scanning electron microscopy and transmission electron microscopy show the diameters and lengths of the core-shell nanowires are in ranges of 25-60 nm and 300-500 nm, respectively. The atomic ratios of Sn to (Zn + Sn) in the central and shell parts of the nanowire are 0.4 at.% and 6.1 at.%, respectively. The ZnO-ZTO comb-like nanocomposites possess ZnO nanocombs with ZTO nano-layers deposited on both sides of them. The ZnO branches and ZTO layers are single-crystalline wurtzite and spinel structures growing along the [0002] and [111] directions, respectively. Room-temperature cathodoluminescence measurements show the nanocomposites exhibit strong ultraviolet (UV) emissions at 300, 384 nm, and a broad green emission. The novel luminescence shows promising singularity for opto-electronic applications.