Self-catalytic formation and characterization of Zn2SnO4 nanowires

Mass production of transparent semiconducting ternary oxide Zn₂SnO₄ nanowires is successfully synthesized by the thermal evaporation method without any catalyst. The as-synthesized products are characterized with field-emission scanning electron microscope (FE-SEM), X-ray powder diffraction (XRD), energy-dispersive spectroscopy (EDS), high-resolution transmission electron microscope (HR-TEM) and selected area electron diffraction (SEAD). A formation of Zn₂SnO₄ nanowires based on a self-catalytic VLS growth mechanism is discussed. The photoluminescence spectrum (PL) of the nanowires shows a broad blue-green emission around the 300-600 nm wavelengths with a maximum center at 580 nm under room temperature.     

ZnO sputter coating on SnO2 nanowires: Effects of thin coating and subsequent thermal annealing

The structural and optical properties of SnO₂–ZnO core–shell nanowires were studied and the effects of thermal annealing were investigated. As-prepared SnO₂–ZnO core–shell nanowires exhibited a smooth and continuous shell layer along the nanowire, with a thickness in the range of 5–10 nm. While the thin ZnO shell layer disappeared after annealing at 800 °C, this did not occur after annealing at 600 °C. The as-fabricated SnO₂–ZnO core–shell nanowires exhibited yellow emission, presumably from the core SnO₂ nanowires. The UV emission from ZnO shell layer was obtained by annealing at 600 °C, whereas it was removed by annealing at 800 °C.     

Low temperature growth of SnO2 nanowires by electron beam evaporation and their application in UV light detection

For the first time, high quality tin oxide (SnO₂) nanowires have been synthesized at a low substrate temperature of 450 °C via vapor–liquid–solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2–4 μm and diameter of 20–60 nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO₂ nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO₂ nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4 × 10⁻⁴ mbar suggested that a temperature equal to or greater than 450 °C was the best condition for phase pure SnO₂ nanowires growth. The SnO₂ nanowires grown on a SiO₂ substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO₂ NWs photo detector (at 10V applied bias) was 12 A/W and 45, respectively, for 12 μW/cm² UV lamp (330 nm) intensity on the photo detector..     

Polycrystalline SnO2 nanowires coated with amorphous carbon nanotube as anode material for lithium ion batteries

One-dimensional (1D) SnO₂ nanowires, coated by in situ formed amorphous carbon nanotubes (a-CNTs) with a mean diameter of ca. 60 nm, were synthesized by annealing the anodic alumina oxide (AAO) filled with a sol of SnO₂. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns revealed that the prepared SnO₂ nanowires exist in polycrystalline rutile structure. The coating of carbon nanotubes has some defects on the wall after the internal SnO₂ nanoparticles were removed. The 1D SnO₂ nanowires present a reversible capacity of 441 mAh/g and an excellent cycling performance as an anode material for lithium ion batteries. This suggests that 1D nanostructured materials have great promise for practical application.     

Influence of SnO2 coating and annealing on the luminescence properties of porous silicon nanowires

Porous silicon (PS)-core/SnO₂-shell nanowires (NWs) were synthesized by a two step process: electrochemical anodization of silicon followed by atomic layer deposition of SnO₂. The photoluminescence spectrum of the PS nanowires showed a broad blue green emission band centered at approximately 510 nm. PL measurement also showed that the blue green emission was enhanced by SnO₂ coating and enhanced further by thermal annealing. It appeared that annealing in a reducing atmosphere was more efficient in increasing the blue green emission intensity than annealing in an oxidizing atmosphere. Energy-dispersive X-ray spectroscopy revealed that the enhancement in the blue green emission by annealing in a reducing atmosphere was attributed to the formation of Sn interstitials in the PS cores due to the dissociation of the SnO₂ shells followed by the diffusion of the Sn atoms, generated as a result of the dissociation of SnO₂, into the PS cores during the annealing process.     

Growth and characterization of thermally evaporated ATO nanowires

The Sb-doped SnO₂ (ATO) nanowires have been synthesized on an alumina substrate using thermal evaporation with various growth durations of 1, 1.5 and 2 h. The morphology and structure of Sb-doped SnO₂ nanowires were characterized by a field emission scanning electron microscope (FESEM), an X-ray diffraction (XRD) spectrometer and a transmission electron microscope (TEM). Chemical composition and bonding were investigated by X-ray photoelectron spectroscopy (XPS), which shows that the Sb concentration of the nanowires increases with increasing growth durations. It is found that the electrical conductance of a single ATO nanowire- and nanowire films-based devices both increase with growth durations. Additionally, the photon-sensing measurement shows that the photon-sensing properties are improved with increasing growth durations, which provides a practicable method for the fabrication of ATO nanowire-based photodetectors.     

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.     

Hydrothermal synthesis of SnO2/SnS2 nanocomposite with high visible light-driven photocatalytic activity

SnO₂/SnS₂ nanocomposite with a heterojunction structure (that is, SnO₂ nanoparticles-decorated SnS₂ nanoplates) was synthesized via the hydrothermal reaction between SnO₂ nanoparticles and thioacetamide in 5 vol.% acetic acid aqueous solution at 150 °C for 3 h, and characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy and UV–vis diffuse reflectance spectra. The photocatalytic activity of the hydrothermally synthesized SnO₂/SnS₂ nanocomposite was tested by degrading methyl orange in distilled water under visible light (λ > 420 nm) irradiation. It was found that the hydrothermally synthesized SnO₂/SnS₂ nanocomposite exhibited superior photocatalytic activity to SnO₂ nanoparticles, SnS₂ nanoplates and physically mixed SnO₂/SnS₂ nanocomposite. The heterojunction structure of the hydrothermally synthesized SnO₂/SnS₂ nanocomposite, which can facilitate interfacial electron transfer and reduce the self-agglomeration of two components, was considered to play an important role in achieving its higher photocatalytic activity.     

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.     

Structural and optical properties of Al-doped SnO2 nanowires

We report a facile thermal evaporation method for the syntheses of Al-doped SnO₂ nanowires using Al-doped SnO₂ nanoparticles as precursors. High-density, single-crystalline Al-doped SnO₂ nanowires were directly grown on the 6H-SiC substrates without any catalyst. X-ray diffraction patterns show that the Al dopants are incorporated into the rutile SnO₂ nanowires. The X-ray photoelectron spectra confirm the SnO₂ nanowires doped with 5 at.% Al. The photoluminescence spectra of the Al-doped SnO₂ nanowires exhibit that the large blue shift of the emission band can be observed in the Al-doped SnO₂ nanowires compared with undoped nanowires. The distortion of the crystal lattices caused by incorporation of Al atoms at the interstitials should be responsible for the large blue shift of the emission band.     

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.     

Structure and photoluminescence properties of ZnS nanowires sheathed with SnO2 by atomic layer deposition

Influence of the thermal annealing atmosphere on the photoluminescence properties of ZnS-core/SnO₂-shell coaxial nanowires was investigated. ZnS nanowires were synthesized by a two-step process: the thermal evaporation of ZnS powders and the atomic layer deposition of SnO₂. Transmission electron microscopy and X-ray diffraction analyses reveal that two crystalline ZnS phases: one with a zinc blende structure and the other with an wurtzite structure coexist in the cores whereas the SnO₂ cores in the as-prepared coaxial nanowires are amorphous. The SnO₂ shells are found to be crystallized by thermal annealing. Photoluminescence (PL) measurements at room temperature show that the green emission of the ZnS/SnO₂ coaxial nanowires is enhanced in intensity by thermal annealing regardless of the annealing atmosphere. The PL emission is more significantly enhanced in intensity by annealing in a reducing atmosphere than in an oxidative atmosphere since Au_Zn ⁻ is more easily generated in the ZnS cores in the former atmosphere.     

Redox reaction-assisted growth of ZnO nanowires on SnO2 thin films

ZnO nanowires were grown onto SnO₂ film coated on Si substrate using a vapor transport method. Zn vapor was found to play important roles in reducing SnO₂ and in being oxidized as a ZnO layer. The growth mechanism of ZnO nanowires was revealed to be a two-step process of Zn-SnO₂ redox reaction and Sn catalyzed V-L-S (vapor-liquid-solid) growth; initially, Zn vapor atoms arriving at the SnO₂ surface reduce the SnO₂ to Sn and O atoms and diffuse into the SnO₂ layer to form a ZnO layer. The reduced Sn atoms diffuse out of the SnO₂ layer and are agglomerated to form Sn liquid droplets. Then, the Sn droplets on the surface of ZnO layer serve as a catalyst for the catalytic V-L-S growth of ZnO nanowires.     

Polymer-embedded stannic oxide nanoparticles as humidity sensors

Stannic oxide (SnO₂) nanoparticles have been suspended in polyvinyl alcohol (PVA) matrix in different PVA:SnO₂ molar ratios ranging from 1:1 to 1:5 using simple chemical route. This suspension was deposited on ceramic substrate and upon drying was carefully detached from the substrate. SnO₂-embedded self-standing, transparent and flexible thin films were hence synthesized. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques show the rutile tetragonal structure of SnO₂ with particle size ~ 5 nm. UV–Visible spectroscopy demonstrates the band gap of 3.9 eV, which does not alter when embedded in polymer. Fourier transform infrared spectroscopy (FTIR) reveals that the properties of SnO₂ do not modify due to incorporation in the PVA matrix. The structures work as excellent humidity sensors at room temperature. For a critical PVA:SnO₂ molar ratio of 1:3, the resistance changes to five times of magnitude in 92% humidity within fraction of second when compared with resistance at 11% humidity. The sample regains its original resistance almost instantaneously after being removed from humid chamber. Nanodimensions of SnO₂ particles and percolation mechanism related to transport through polymer matrix and water molecule as a carrier has been used to understand the mechanism.     

Preparation and properties of Ti/SnO2-Sb2O5 electrodes by electrodeposition

Sb and Sn coatings were deposited on Ti substrate by the method of cathode deposition, and the Ti/SnO₂-Sb₂O₅ electrodes were obtained by annealing at different temperatures for 3 h. Ti/SnO₂-Sb₂O₅ coating was characterized using technique such as X-ray diffraction (XRD), and scanning electron microscopy (SEM). Ti/SnO₂-Sb₂O₅ electrode calcined at 550 °C exhibits the best catalytic capacity. Ti/SnO₂-Sb₂O₅ electrode obtained by electrodeposition had longer service life and faster degradation capacity compared with that obtained by dip-coating. Accelerated service life tests were carried out in 0.5 mol L^− 1 H₂SO₄ solution with the current density of 100 mA cm^− 2. Service life of Ti/SnO₂-Sb₂O₅ electrode prepared in present study was 15 h, and it was only 0.14 h for Ti/SnO₂-Sb₂O₅ electrode obtained by dip-coating.     

Solid phase growth of tin oxide nanostructures

For the first time, single-crystalline SnO₂ nanostructures comprising of nanobelts, nanowires and nanosheets have been synthesised by solid phase crystal growth from tin oxide single crystals. The product was characterised by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, selected area electron diffraction, and Raman spectroscopy. The procedure consisted of two stages. In the first stage, a mixture of SnO₂ polyhedral single crystals attached with graphite particles were produced by heating a mixture of SnCl₂ and graphite. Then, the SnO₂ single crystals were grown into nanobelts, nanowires and nanosheets by further heating. The role of graphite in the process is also discussed to be the surface reduction of SnO₂ into oxides with lower oxygen content which provide a driving force for surface diffusion and subsequent crystal growth of tin oxide into the one and two dimensional nanostructures. The results provide insights for both fundamental research as well as technological production of SnO₂ nanostructures.     

Low temperature synthesis of SnO2 nanocrystals from tin, sulfur and ammonium chloride powders

Tetragonal phase SnO₂ nanocrystals were synthesized directly by heating the mixture of tin (Sn), sulfur (S) and ammonium chloride (NH₄Cl) powders in air at 400 °C for 2-5 h. The phase, size and purity of the resultant products were characterized by means of powder X-ray diffraction (XRD), filed emission scanning electronic microscope (FESEM), and energy dispersive X-ray (EDX) spectra. Besides, the effects of heating temperature, duration, and composition of the reactants on the phases of the resultant products were investigated. It was found that both of the S and NH₄Cl additives played important roles in the current low temperature (400 °C) synthesis of pure SnO₂.     

Synthesis,characterization and growth mechanism of ZnO nanowires on NiCl<Subscript>2</Subscript>-coated Si substrates

Well-crystallized ZnO nanowires have been successfully synthesized on NiCl₂-coated Si substrates via a carbon thermal reduction deposition process. The pre-deposited Ni nanoparticles by dipping the substrates into NiCl₂ solution can promote the formation of ZnO nuclei. The as-synthesized nanowires were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectrum. The results demonstrate that the as-fabricated nanowires with about 60 nm in diameter and several tens of micrometers in length are preferentially arranged along [0001] direction with (0002) as the dominate surface. Room temperature PL spectrum illustrates that the ZnO nanowires exist a UV emission peak and a green emission peak, and the peak centers locate at 387 and 510 nm. Finally, the growth mechanism of the nanowires is briefly discussed.     

Synthesis and field emission of patterned SnO2 nanoflowers

This article reports the synthesis and field emission of patterned SnO₂ nanoflowers obtained by a simple method. A patterned Au catalyst film was prepared on the silicon wafer by radio frequency (RF) magnetron sputtering and photolithographic patterning processes. The patterned SnO₂ nanoflowers arrays, with a unit diameter of ∼ 50 μm, were synthesized via vapor phase transport method. Field emission scanning electron microscopy (SEM) and X-ray diffraction (XRD) are used to identify the surface morphology and composition of the as-synthesized SnO₂ nanostructures. The mechanism of formation of SnO₂ nanostructures was also discussed. The measurement of field emission (FE) showed that the as-synthesized SnO₂ nanostructure arrays have a lower turn-on field of 2.6 V/μm at the current density of 0.1 μA/cm². This approach must have a wide variety of applications such as fabrications of micro-optical components and micropatterned oxide thin films used in FE-based flat panel displays and sensor arrays.     

One-pot synthesis of intestine-like SnO2/TiO2 hollow nanostructures

In the present study the intestine-like binary SnO₂/TiO₂ hollow nanostructures are one-pot synthesized in aqueous phase at room temperature via a colloid seeded deposition process in which the intestine-like hollow SnO₂ spheres and Ti(SO₄)₂ are used as colloid seeds and Ti-source, respectively. The novel core (SnO₂ hollow sphere)-shell (TiO₂) nanostructures possess a large surface area of 122 m²/g (calcined at 350 °C) and a high exposure of TiO₂ surface. The structural change of TiO₂ shell at different temperatures was investigated by means of X-ray diffraction and Raman spectroscopy. It was observed that the rutile TiO₂ could form even at room temperature due to the presence of SnO₂ core and the unique core-shell interaction.