Growth Of SnO2 Nanowires Research Articles

Effect of pore structure of the metakaolin-based porous substrate on the growth of SnO2 nanowires and their H2S sensing properties

The metakaolin-based porous substrates were used as the growth substrate to synthesize SnO2 nanowires (SNWs) gas sensing materials via the gold-catalyzed vapor-liquid-solid growth mechanism. The porous substrates were fabricated by a pore-forming method with poly methyl methacrylate (PMMA) microspheres as the pore former. The effect of the porous structure of different as-prepared substrates on their product morphologies were characterized using X-ray diffraction and scanning electron microscopy. The resulting structural and morphological properties showed that all SNWs had a tetragonal rutile structure, and the aspect ratio of the SNWs enhanced with the increase in the apparent porosity or total pore area of substrates. The growth mechanism of the SNWs was discussed with respect to the effect of temperature gradient inside and outside the pores. The SNWs synthesized on the porous substrates with the PMMA content of 30 wt% exhibited the highest sensing performance towards 0.5–10 ppm H2S at the operating temperature of 85 °C, accompanying with the SNWs synthesized on a dense substrate and the substrate with the PMMA content of 20 wt% for comparison. It demonstrates that the porous structure of the metakaolin-based substrates significantly improves the aspect ratio and gas sensing properties of the SNWs.

Synthesis of SnO2 nanowires forCO, CH4 and CH3OH gases sensing

Synthesis of one-dimensional nanostructures, such as nanowires, is of vigorous significance for achieving the desired properties and fabricating functional devices. In this work, we report the synthesis of tin oxide (SnO2) nanowires on gold-catalyzed silicon substrate by carbothermal reduction process. SnO2 nanowires were synthesized with SnO2 and graphite powders as the source materials at atmospheric pressure and temperature of 900°C in the ambience of nitrogen (N2) gas. First, the effect of source material ratio SnO2:C on growth of SnO2 nanowires was studied. The structural, morphological and compositional properties of the samples were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The scanning electron microscopy investigation reveals that uniform dense nanowires of SnO2 (diameter ~127 nm and length ~40 µm) were synthesized with vapour–liquid–solid mechanism. Ultraviolet–visible spectra estimate that the optical band gap of the synthesized SnO2 nanowires was 3.72 eV. Second, the gas sensing performance of synthesized SnO2 nanowires was investigated by testing with carbon monoxide (CO), Methane (CH4) and methanol (CH3OH) gases at different operating temperatures and concentrations. Results indicate that the synthesized SnO2 nanowires are highly promising for gas sensing applications.

Thermal chemical vapor deposition of tin oxide nanowires in a hydrogen reduction atmosphere

We fabricated tin oxide nanowires (NWs) on Au/Si3N4/Si(001) substrates using thermal chemical vapor deposition (CVD) in a hydrogen reduction atmosphere. Unlike typical thermal CVD conditions, a mixture of H2 and Ar gas was used as the carrier gas, and a catalyst powder such as graphite was not used. The hydrogen gas maintained the reducing atmosphere and easily vaporized the SnO2 powder without a catalyst, to supply vapors of Sn and O. This process enables vapor-liquid-solid (VLS) growth of SnO2 NWs at temperatures below 600 °C. The formation of a eutectic AuSn alloy that acts as a liquid seed during the VLS process contributes to lowering the growth temperature. X-ray diffraction and transmission electron microscopy analysis show that SnO2 NWs and SnO NWs coexist in the as-prepared sample. The oxygen-deficient atmosphere results in nucleation and growth of SnO NWs.

Effect of Growth Parameters on SnO2 Nanowires Growth by Electron Beam Evaporation Method

Tin oxide (SnO2) nanowires were synthesized via catalyst assisted VLS growth mechanism by the electron beam evaporation method at a growth temperature of 450 °C. The effects of growth parameters such as evaporation rate of Tin, catalyst film thickness, and different types of substrates on the growth of SnO2 nanowires were studied. Nanowires (NWs) growth was completely seized at higher tin evaporation rates due to the inability of the catalyst particle to initiate the NWs growth. Nanowires diameters were able to tune with catalyst film thickness. Nanowires growth was completely absent at higher catalyst film thickness due to agglomeration of the catalyst film. Optimum growth parameters for SnO2 NWs were presented. Nanocomposites such as Zinc oxide - SnO2, Graphene oxide sheets- SnO2 and Graphene nanosheets-SnO2 were able to synthesize at a lower substrate temperature of 450 °C. These nanocompsoites will be useful in enhancing the capacity of Li-ion batteries, the gas sensing response and also useful in increasing the photo catalytic activity.

In-Depth View of the Structure and Growth of SnO2 Nanowires and Nanobrushes.

Strategic application of an array of complementary imaging and diffraction techniques is critical to determine accurate structural information on nanomaterials, especially when also seeking to elucidate structure-property relationships and their effects on gas sensors. In this work, SnO2 nanowires and nanobrushes grown via chemical vapor deposition (CVD) displayed the same tetragonal SnO2 structure as revealed via powder X-ray diffraction bulk crystallinity data. Additional characterization using a range of electron microscopy imaging and diffraction techniques, however, revealed important structure and morphology distinctions between the nanomaterials. Tailoring scanning transmission electron microscopy (STEM) modes combined with transmission electron backscatter diffraction (t-EBSD) techniques afforded a more detailed view of the SnO2 nanostructures. Indeed, upon deeper analysis of individual wires and brushes, we discovered that, despite a similar bulk structure, wires and brushes grew with different crystal faces and lattice spacings. Had we not utilized multiple STEM diffraction modes in conjunction with t-EBSD, differences in orientation related to bristle density would have been overlooked. Thus, it is only through a methodical combination of several structural analysis techniques that precise structural information can be reliably obtained.

Facile Synthesis of Crystalline SnO2 Nanowires on Various Current Collector Substrates

AbstractCrystalline SnO2 nanowires with smooth surface and uniform diameter were readily produced via chemical vapor deposition (CVD) method on various current collectors including carbon paper, stainless steel and copper. The growth followed a vapor‐liquid‐solid (VLS) mechanism employing a gold thin film as the catalyst. Morphology, composition and structure of the SnO2 nanowires on different collectors were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X‐ray spectroscopy (EDS) and X‐ray diffraction (XRD). Morphology results demonstrated that the growth of SnO2 nanowires only occurred in a narrow temperature range, while the structure and composition information unveiled the correlation between the quality of the nanowires and the employed substrates. The unique architecture of SnO2 nanowires directly growing on current collectors are expected to act as building blocks in producing various types of nanodevices, especially as anode materials for Li‐ion batteries.

The template-free synthesis of square-shapedSnO2 nanowires: the temperature effect and acetone gas sensors

Square-shaped single-crystallineSnO2 nanowires and their sphere-like hierarchical structures were synthesized successfullywith a template-free hydrothermal approach. It was found that an intermediatephase—Na2Sn(OH)6—is first produced because it is slow to dissolve in ethanol/watermedia. The intermediate phase gradually decomposes and converts intoSnO2 at temperatureshigher than 200 °C. The reaction temperature also affects the microstructure ofSnO2 nanomaterials.Uniform square-shaped SnO2 nanowires, which form sphere-like hierarchical structures in 100% structure yield, can be producedat 285 °C on a large scale. The diameter of the nanowires shows a decrease accompanying the increase of thereaction temperature. The temperature effect could be a result of the faster and oriented growth ofSnO2 nanowires along their direction at higher temperature. Chemical sensors constructed with square-shapedSnO2 nanowires exhibit excellent stability, good sensitivity and selectivity, as well as a quickresponse and short recovery times under exposure to acetone gas in practicalapplications.

Growth of SnO2 nanowires with uniform branched structures

SnO2 nanowires have been prepared using the active carbon reaction with the fine SnO2 powder at low temperature (700 °C). These nanowires show rectangular cross-section, with their widths ranging from 10 to 50 nm. Branched nanowires with definite included angle are also observed in these products. The morphology and microstructure of the single crystalline SnO2 nanowires and the branched nanowires are characterized by means of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selective area electron diffraction (SAED) and Raman spectrum. In addition, the possible growth mechanism of the SnO2 nanowires and branched nanowires is also discussed.