Facile synthesis of ultrathin Au nanorods by aging the AuCl(oleylamine) complex with amorphous Fe nanoparticles in chloroform

Despite plenty of reports on the preparation of Au nanorods, it remains challenging to grow uniform Au nanorods with diameters below 5 nm. In this communication, we demonstrate the facile synthesis of ultrathin Au nanorods with a uniform diameter of 2 nm and an average aspect ratio of 30. The synthesis involves the room-temperature aging of a mixture of the [AuCl(oleylamine)] complex with amorphous Fe nanoparticles in chloroform. Analysis of the growth mechanism indicates that Au nanoparticles with a high density of defects were formed at early stages, followed by etching and redeposition process that gradually led to the growth of ultrathin Au nanorods along the 111 direction. This growth mechanism is different from the mechanism recently reported for ultrathin Au nanowires (ref ), where the [AuCl(oleylamine)] complex is assembled into polymer chains followed by reduction to form wires, although the template effect of oleylamine for the formation of ultrathin Au nanorods cannot be completely ruled out.     

Ferromagnetism driven by oxygen vacancies in SnO2 nanowires

Room temperature ferromagnetism has been observed in SnO2 nanowires synthesized by a chemical vapor deposition using Au layers as catalyst. The nanowires are homogeneous and single-crystalline grown along the [101] direction, with diameters ranging from 25 to 100 nm and length greater than 20 microm. The special magnetization reaches 0.114 emu/g for the nanowires with diameter of approximately 25 nm and reduces with increasing diameters. Branched SnO2 nanowires were prepared via a two-step vapor-liquid-solid approach, and an enhanced magnetization was obtained. To the contrary, the nanowires annealed at 1300 degrees C in air were completely transformed into the particles and exhibit weakened magnetization. These results demonstrate that the ferromagnetic properties of the samples depend on the surface-to-volume ratio of nanowires. With a combined study of photoluminescence, our results reveal that the oxygen vacancies at the surface of nanowires contribute to the ferromagnetism of SnO2 nanowires. This argument is further confirmed by a sequential annealing in a rich-oxygen atmosphere, then in a low vacuum condition.     

Fabrication and optical properties of mesoporous SnO2 nanowire arrays

Large-scale SnO2 mesoporous nanowires have been successfully synthesized by an improved sol-gel method within the nanochannels of porous anodic alumina templates. In this method, chloride of stannic and urea are used as precursors, chloride of stannic is acting as source of tin ions, and urea offers a basic medium through its hydrolysis. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction are used to characterize the SnO2 mesoporous nanowires. It is found that the as-prepared nanowires consist of SnO2 nanoparticles and pores. They can be indexed as rutile structures and diameters are about 50-70 nm. The growth mechanism of the mesoporous nanowires is also been discussed. The band gap of the as-prepared mesoporous nanowires is 3.735 eV, determined by UV/visible absorption spectral results. The SnO2 mesoporous nanowires show strong and stable photoluminescence with emission peak centered at 3.730 eV, which has never been reported in nanowires. It could be attributed to the exciton recombination.     

Selective synthesis and superconductivity of In-Sn intermetallic nanowires sheathed in carbon nanotubes

We demonstrate a simple and reproducible technique to synthesize crystalline and superconducting In-Sn intermetallic nanowires sheathed in carbon nanotubes (CNTs). The method is based on the catalytic reaction of C(2)H(2) over a mixture of both SnO(2) and In(2)O(3) particles. Importantly, tetragonal β-In(3)Sn and hexagonal γ-InSn(4) nanowires with diameters of less than 100?nm are selectively synthesized at different SnO(2) to In(2)O(3) weight ratios. CNTs may serve as cylindrical nanocontainers for continuous growth of liquid-phased In(1-x)Sn(x) nanowires during growth process as well as for their solidification into In-Sn intermetallic nanowires during the cooling process. Microscopic and spectroscopic analyses clearly reveal evidence of a core-shell structure of the CNT-sheathed In-Sn intermetallic nanowires. Magnetization measurements show that the superconducting In-Sn nanowires have a critical magnetic field higher than the value of their bulk intermetallic compounds. Our method can be adopted to the nanofabrication of analogous binary and ternary alloys.     

Ultrathin Graphdiyne Nanowires with Diameters below 3 nm: Synthesis,Photoelectric Effect,and Enhanced Raman Sensing

Due to the intrinsic layered structure, graphdiyne (GDY) strongly tends to form 2D materials, therefore, most of the current research are based on GDY 2D structures. Up to now, the synthesis of its ultrathin nanowires with a high aspect ratio has not been reported. Here, the ultrathin GDY nanowires with diameters below 3 nm are reported for the first time by a two-phase interface synthesis method, which has excellent crystallinity and an aspect ratio of more than 2500. Evidence shows that the GDY ultrathin nanowires are formed by the oriented-attachment mechanism of nanoparticles. The GDY ultrathin nanowires exhibit a significant quantum confinement effect, enhanced photoelectric effect, and promising applications in surface-enhanced Raman sensing.     

Gas nanosensor design packages based on tungsten oxide: mesocages, hollow spheres, and nanowires

Achieving proper designs of nanosensors for highly sensitive and selective detection of toxic environmental gases is one of the crucial issues in the field of gas sensor technology, because such designs can lead to the enhancement of gas sensor performance and expansion of their applications. Different geometrical designs of porous tungsten oxide nanostructures, including the mesocages, hollow spheres and nanowires, are synthesized for toxic gas sensor applications. Nanosensor designs with small crystalline size, large specific surface area, and superior physical characteristics enable the highly sensitive and selective detection of low concentration (ppm levels), highly toxic NO(2) among CO, as well as volatile organic compound gases, such as acetone, benzene, and ethanol. The experimental results showed that the sensor response was not only dependent on the specific surface area, but also on the geometries and crystal size of materials. Among the designed nanosensors, the nanowires showed the highest sensitivity, followed by the mesocages and hollow spheres-despite the fact that mesocages had the largest specific surface area of 80.9?m(2)?g( - 1), followed by nanowires (69.4?m(2)?g( - 1)), and hollow spheres (6.5?m(2)?g( - 1)). The nanowire sensors had a moderate specific surface area (69.4?m(2)?g( - 1)) but they exhibited the highest sensitivity because of their small diameter (～5?nm), which approximates the Debye length of WO(3). This led to the depletion of the entire volume of the nanowires upon exposure to NO(2), resulting in an enormous increase in sensor resistance.     

SiO2/SnO2复合凝胶对丙酮和氨气的吸附动力学研究

应用溶胶－凝胶法制备了SiO2/SnO2复合凝胶，测定了红外光谱，采用静态吸附法测定了不同组成的SiO2/SnO2复合凝胶对丙酮气体和氨气的吸附动力学曲线。结果表明，SiO2与SnO2凝胶的复合有利于气体的吸附，在凝胶中含有一定的羟基是吸附性强的根源。数据拟合得到的吸附动力学方程分别为x=c1(1-exp(-c2t)和x=c′1t/(1 c2′t)的形式，说明SiO2/SnO2复合凝胶对丙酮气体和氨气的吸附机理分别具有单活性位和双活性位吸附特征。     

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.     

The structure and photoluminescence properties of Bi2O3-core/SnO2-shell nanowires

Bi2O3-core/SnO2-shell nanowires have been prepared by using a two-step process: thermal evaporation of Bi2O3 powders and sputtering of SnO2. The crystalline nature of the Bi2O3-core/SnO2-shell nanowires has been revealed by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). TEM analysis and X-ray diffraction (XRD) results indicate that the Bi2O3-core/SnO2-shell nanowires consist of pure tetragonal alpha-Bi2O3-phase momocrystalline cores and tetragonal SnO2-phase polycrystalline shells. The photoluminescence (PL) measurements show that Bi2O3 nanowires have a broad emission band centered at around 560 nm in the yellow-green region. On the other hand, the Bi2O3-core/SnO2-shell coaxial nanowires with the sputtering times of 4 and 8 min have a blue emission band centered at around 450 nm. In contrast, those with a sputtering time of 10 min have a broad emission band centered at approximately 550 nm again. The origin of this yellow-green emission from the core/shell nanowires, however, quite differs from that from Bi2O3 nanowires, i.e., it is not from the Bi2O3 cores but from the SnO2 shells.     

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.     

The template-free synthesis of square-shaped SnO(2) nanowires: the temperature effect and acetone gas sensors

Square-shaped single-crystalline SnO(2) nanowires and their sphere-like hierarchical structures were synthesized successfully with a template-free hydrothermal approach. It was found that an intermediate phase-Na(2)Sn(OH)(6)-is first produced because it is slow to dissolve in ethanol/water media. The intermediate phase gradually decomposes and converts into SnO(2) at temperatures higher than 200?°C. The reaction temperature also affects the microstructure of SnO(2) nanomaterials. Uniform square-shaped SnO(2) nanowires, which form sphere-like hierarchical structures in 100% structure yield, can be produced at 285?°C on a large scale. The diameter of the nanowires shows a decrease accompanying the increase of the reaction temperature. The temperature effect could be a result of the faster and oriented growth of SnO(2) nanowires along their [Formula: see text] direction at higher temperature. Chemical sensors constructed with square-shaped SnO(2) nanowires exhibit excellent stability, good sensitivity and selectivity, as well as a quick response and short recovery times under exposure to acetone gas in practical applications.     

Tin-doped rutile titanium dioxide nanowires: luminescence, gas sensor, and field emission properties

Sn-doped rutile TiO2 nanowires were synthesized by a thermal reactive evaporation route. Field emission scanning electron microscopy (FESEM) imaging reveals that the Sn-doped TiO2 nanowires exhibited diameters of 80-150 nm and 2-3 microns in length. High-resolution transmission electron microscopy (HRTEM) imaging makes it possible to observe that Sn-doped TiO2 nanowires show a certain lattices fringe of approximately 0.32 nm, which demonstrates that the nanowires are single crystalline with rutile structure and grow along the [110] axis. Cathodoluminescence (CL) reflected that on the surface of Sn-doped TiO2 nanowires, many oxygen vacancies and defect states were formed during the crystal growth. These defect states raised a broad emission peak around the red-orange band. The ethanol sensing properties of Sn-doped rutile TiO2 nanowires at a temperature of 190 degrees C for the ethanol concentrations of 50, 100, 150, 200, 400, 500, and 600 ppm, correspond to the sensor' sensitivity of 7, 12, 18, 19, 23, and 26%, respectively. The sensitivity increased with an increase in the ethanol concentration. As-synthesized TiO2 nanowires revealed a turn-on field, approximately 5.1 V/microm, at a current density of 1 microAcm(-2).     

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.     

Investigation of substrate influence on tin dioxide nanostructures synthesized using horizontal furnace

SnO2 nanostructures were directly synthesised by chemical vapour transport on different substrates in a horizontal furnace. The influence of substrate on the morphology of these nanostructures was investigated by changing the substrate type, coating, and temperature. The SnO2 nanowires and nanorods were one dimensional (1D) structures with widths and lengths of 50-200 nm and several micrometers respectively. Scanning electron microscope (SEM) images show formation of short nanorods with lengths of less than 1 microm on indium-tin oxide (ITO) substrates. The effect of substrate temperature on growth was studied. SnO2 nanowires were obtained using silicon substrate, and the effect of Au coating on the size and morphology of these structures was proposed. By coating the Si wafer with a thin layer of Au, the size of the nanostructure was reduced and the length increased. The differences in size and morphology are shown by transmission electron microscopy (TEM). X-ray diffraction (XRD) spectra show tetragonal structures for both substrates.     

Fabrication of reliable semiconductor nanowires by controlling crystalline structure

One-dimensional SnO(2) nanomaterials with wide bandgap characteristics are attractive for flexible and/or transparent displays and high-performance nano-electronics. In this study, the crystallinity of SnO(2) nanowires was regulated by controlling their growth temperatures. Moreover, the correlation of the crystallinity of nanowires with optical and electrical characteristics was analyzed. When SnO(2) nanowires were grown at temperatures below 900?°C, they showed various growth directions and abnormal discontinuity in their crystal structures. On the other hand, most nanowires grown at 950?°C exhibited a regular growth trend in the direction of [100]. In addition, the low temperature photoluminescence measurement revealed that the higher growth temperatures of nanowires gradually decreased the 500 nm peak rather than the 620 nm peak. The former peak is derived from the surface defect related to the shallow energy level and affects nanowire surface states. Owing to crystallinity and defects, the threshold voltage range (maximum-minimum) of SnO(2) nanowire transistors was 1.5 V at 850?°C, 1.1 V at 900?°C, and 0.5 V at 950?°C, with dispersion characteristics dramatically decreased. This study successfully demonstrated the effects of nanowire crystallinity on optical and electrical characteristics. It also suggested that the optical and electrical characteristics of nanowire transistors could be regulated by controlling their growth temperatures in the course of producing SnO(2) nanowires.     

Metal Oxide Nanowire and Thin-Film-Based Gas Sensors for Chemical Warfare Simulants Detection

This work concerns with metal oxide (MOX) gas sensors based on nanowires and thin films. We focus on chemical warfare agents (CWAs) detection to compare these materials from the functional point-of-view. We work with different chemicals including simulants for Sarin nerve agents, vescicant gases, cyanide agents, and analytes such as ethanol, acetone, ammonia, and carbon monoxide that can be produced by everyday activities causing false alarms. Explorative data analysis has been used to demonstrate the different sensing performances of nanowires and thin films. Within the chosen application, our analysis reveal that the introduction of nanowires inside the array composed by thin films can improve its sensing capability. Cyanide simulants have been detected at concentrations close to 1 ppm, lower than the Immediately Dangerous for Life and Health (IDLH) value of the respective warfare agent. Higher sensitivity has been obtained to simulants for Sarin and vescicant gases, which have been detected at concentrations close or even lower than 100 ppb. Results demonstrate the suitability of the proposed array to selectively detect CWA simulants with respect to some compounds produced by everyday activities.     

Preparation of SnO2 nanowires by solvent-free method using mesoporous silica template and their gas sensitive properties

In this paper, a facile method was presented to synthesize tin dioxide (SnO2) nanowires by solvent-free method using SnCl2 x 2H2O as precursor and mesoporous silica SBA-15 as the hard template. No solvent was used in the processing. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and N2 adsorption/desorption isotherms. The results indicated that SnO2 nanowires fabricated by this method have a diameter of about 8 nm and a relatively high surface area 73.0 m2/g. The gas sensing properties of SnO2 nanowires were measured. The response and recovery time of this sensor were 6 s and 12 s, respectively. With the concentration of toluene increasing, the response of the sensor doubled increase. Compared with bulk SnO2, SnO2 nanowires showed much higher response to toluene.     

Medical diagnosis with the gradient microarray of the KAMINA

Investigations with human breath and cultures of oral bacteria have been performed to examine the analytical performance of the KAMINA gradient microarray based on a segmented metal oxide layer. Standard microarray chips with 38 segments, one chip equipped with platinum doped SnO/sub 2/ and the other with WO/sub 3/, were inspected. The results show that the gradient microarray is able to detect acetone and methyl-mercaptane as two model gases of medical relevance at lower ppm-levels in the presence of human breath. Even after consumption of smelly nutrition, acetone at lowest concentrations of some 10 ppm could be detected. A principal component analysis (PCA) of the signal patterns showed that both types of microarrays were able to discriminate between the model gases, ethanol and clean air. Moreover, the even more delicate distinction of different oral bacteria grown on an agar substrate proved to be feasible by the signal pattern analysis of their gaseous metabolites. The signal patterns obtained for mixed bacteria cultures even seem to allow assignment to and quantification of the main cultures of a mixture.     

Room temperature Cl(2) sensing using thick nanoporous films of Sb-doped SnO(2)

Thick film resistive Cl(2) sensors were fabricated using SnO(2) doped with Sb. The nanocrystalline powders of Sb-doped SnO(2) synthesized by a sol-gel method were compressed into an 800?μm thick pellet. The fabricated sensors were tested against gases like Cl(2), Br(2), HCl, NO, NO(2), CHCl(3), NH(3) and H(2). The highest response to Cl(2) was achieved in 0.1% Sb doping where an exposure to 3?ppm of Cl(2) gas led to a 500-fold increase in device resistance. The high sensitivity to Cl(2) is accompanied by minor interference due to other gases at room temperature. It was found that the SnO(2) doped with 0.1% Sb exhibited high response, selectivity (>100 in comparison to the gases described above) and short response time (～60?s) to Cl(2) at 3?ppm level at room temperature.     

Synthesis and characterization of single-crystal strontium hexaboride nanowires

Catalyst-assisted growth of single-crystal strontium hexaboride (SrB6) nanowires was achieved by pyrolysis of diborane (B2H6) over SrO powders at 760-800 degrees C and 400 mTorr in a quartz tube furnace. Raman spectra demonstrate that the nanowires are SrB6, and transmission electron microscopy along with selected area diffraction indicate that the nanowires consist of single crystals with a preferred [001] growth direction. Electron energy loss data combined with the TEM images indicate that the nanowires consist of crystalline SrB 6 cores with a thin (1 to 2 nm) amorphous oxide shell. The nanowires have diameters of 10-50 nm and lengths of 1-10 microm.