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.     

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.     

Ultraviolet photodetectors made from SnO2 nanowires

SnO₂ nanowires can be synthesized on alumina substrates and formed into an ultraviolet (UV) photodetector. The photoelectric current of the SnO₂ nanowires exhibited a rapid photo-response as a UV lamp was switched on and off. The ratio of UV-exposed current to dark current has been investigated. The SnO₂ nanowires were synthesized by a vapor-liquid-solid process at a temperature of 900 °C. It was found that the nanowires were around 70-100 nm in diameter and several hundred microns in length. High-resolution transmission electron microscopy (HRTEM) image indicated that the nanowires grew along the [200] axis as a single crystallinity. Cathodoluminescence (CL), thin-film X-ray diffractometry, and X-ray photoelectron spectroscopy (XPS) were used to characterize the as-synthesized nanowires.     

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.     

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.     

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.     

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.     

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.     

Optical,morphological, electrical properties of ZnO-TiO2-SnO2/CeO2 semiconducting ternary nanocomposite

Low dielectric constant and low dielectric loss with moderate wide bandgap, novel semiconducting metal oxide composites are useful materials for applying optoelectronic, microwave dielectric ceramics. A less dielectric constant is required for wireless communication to reduce the cross pairing between conductors and also for fast signal transmission. In the present study, the structural, optical, and dielectric properties of ternary ZnO - TiO₂ added with SnO₂/CeO₂ semiconducting nanocomposite materials were investigated and synthesized by the solid-state gelation method. The samples were sintered at a temperature of 450 ⁰C. The X-ray diffraction patterns of composites revealed the existence of TiO₂ anatase phase, SnO_2, and CeO₂. The average crystallite size at d₁₀₁ was measured using the Scherer method, ranging from 6.18 nm to 9.13 nm. The overall crystallite size was calculated using the Size-strain plot method, and it is in the range of 14.8 nm to 17.16 nm. The surface morphology of all samples appears uniform in size and spherical shape. The average particle size of grains was 35 nm. The absorbance properties studied by UV–Visible spectroscopy and bandwidth were 2.6 eV calculated using Tauc’s plot method, and it reveals the formation of new energy levels. The dielectric properties of pellet dimensions of 1 mm thickness and 10 mm diameter, measured from the LCR meter, are indicated at 1 kHz frequency. The most significant dielectric constant (ε_r) and lowest loss tangent (Tan δ) are 53.89 and 0.25 for pure ZnO - TiO₂, and the lowest dielectric constant (ε_r) and less loss tangent (Tan δ) are 9.69 and 0.38 for 1 wt% CeO₂ doped to ZnO - TiO₂. The conductivity of the composite is in the range of 10^-7 S/cm. With additive concentration to ZnO - TiO₂, both SnO₂ and CeO₂ are equally potential and modifies the parameters due to the similar bandgaps and more oxygen availability.     

Effects of Ni co-doping concentrations on dielectric and magnetic properties of (Co,Ni) co-doped SnO<Subscript>2</Subscript> nanoparticles

In this work, the dielectric and magnetic properties of (Co, Ni) co-doped SnO₂ nanoparticles were studied using ac impedance spectroscopy and magnetic properties measurement system or quantum design superconducting quantum interference device. Results showed that dielectric constant (ε _r ), dielectric loss (ε″), and ac electrical conductivity (σ _AC ) are strongly frequency dependent. A decrease in frequency was accompanied with an increase in ε _r and ε″ values, whereas, a decrease in the dielectric constant was observed with the increase of Ni co-doping concentration. It was found that the dielectric constant and dielectric loss values decrease, whilst AC electrical conductivity increases with increase in co-doping concentration. Magnetization measurements revealed that the Ni co-doped SnO₂ samples exhibits room temperature ferromagnetism. The results illustrate that (Co, Ni) co-doped SnO₂ nanoparticles have an excellent dielectric, magnetic properties, and high electrical conductivity than those of co-doped samples reported previously, indicating that these (Co, Ni) co-doped SnO₂ materials can be suitable for the purpose of high frequency device and spintronic applications.     

Controlled growth,characterization and thermodynamic behavior of bismuth–tin nanostructures sheathed in carbon nanotubes

We report the controlled synthesis of bismuth–tin (Bi–Sn) nanostructures sheathed in graphitic shells that resemble carbon nanotubes (CNTs). Our approach is based on a simple catalytic chemical vapor deposition over a mixture of Bi₂O₃ and SnO₂ supplied as starting materials. Shape control of the nanostructures strongly relies on the weight ratio of Bi₂O₃ and SnO₂. Sheathed nanoparticles and nanorods are formed at SnO₂ to Bi₂O₃ weight ratios of less than 4:1. They are composed of two separate crystals: rhombohedral Bi and tetragonal Sn₁₉Bi crystals. On the other hand, the sheathed nanowires are formed at SnO₂ to Bi₂O₃ weight ratios above 4:1. The nanowires have only tetragonal Sn₁₉Bi structure with a diameter of approximately 100 nm. Elementary analyses support the core/shell heterostructure of the resulting products. A favorable temperature for the Sn-rich Sn₁₉Bi nanowires is in the range of 700–800 °C, more specifically around 750 °C. Thermodynamic analysis reveals that the CNTs play a significant role in the protection of the Bi–Sn nanostructures during phase transition by temperature change. This simple and reproducible method may be extended to the fabrication of similar binary or ternary nanostructures.     

Effect of Sb doping on the opto-electronic properties of SnO2 nanowires

Antimony (Sb) doping of SnO₂ nanowires (NWs) was investigated for its optical and electrical effects. The low-temperature photoluminescence spectra of SnO₂ NWs varied significantly with increasing Sb content, where the temperature-dependence of the visible emission at ca. 400 nm was distinctive with Sb-doping, indicating different defect states, such as neutral and positively charged oxygen vacancies. Field effect transistors (FETs) with low-level Sb-doped SnO₂ NW channels exhibited higher mobility, charge concentration, and faster response and recovery to UV light than intrinsic SnO₂ NW FETs.     

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.     

Ab initio study of electronic structures of InAs and GaSb nanowires along various crystallographic orientations

InAs and GaSb nanowires oriented along different crystallographic axes—the [0 0 1], [1 0 1] and [1 1 1] directions of zinc-blende structure—have been studied utilizing a first-principles derived nonlocal screened atomic pseudopotential theory, to investigate the band structure, polarization ratio and effective masses of these semiconductor nanowires and their dependences on the wire lateral size and axis orientation. The band energy dispersion over entire Brillouin zone and orbital energy are determined and found to exhibit different characteristics for three types of wires. There is an explicit dispersion hump in the conduction bands of [0 0 1] nanowires with two larger diameters and [1 0 1] nanowires with the smallest diameter considered. Moreover, the [1 1 1] nanowires are shown to exhibit very different orbital energy for the maximum valence state at the zone-boundary point, compared with [0 0 1] and [1 0 1] nanowires. These differences present significant and detailed insight for experimental determination of the band structure in InAs and GaSb nanowires. Furthermore, we study the polarization ratio of these nanowires for different orientations. Our calculation results indicate that, for the same lateral size, the [1 1 1] nanowires give extraordinarily higher polarization ratio compared to nanowires along the other two directions, and at the same time have larger band-edge photoluminescence transition intensity. Consequently, the [1 1 1] nanowires are predicted to be better suitable for optoelectronic applications. We also significantly find that polarization ratio and transition intensity displays different varying trend of dependence on lateral size of nanowires. Specially, the calculated polarization ratio is shown to increase with the decreasing size, which is opposite to the behavior displayed by the optical transition intensity. The predicted polarization ratios of [1 0 1] and [1 1 1] nanowires for 10.6 Å diameter approach the limit of 100%. In addition, the electron and hole masses for InAs and GaSb nanowires with different crystallographic axes have been calculated. For the [1 0 1] and [1 1 1] oriented nanowires, the hole masses are predicted to be around 0.1–0.2 m₀, which are notably smaller than the values (∼0.5 m₀) along the same direction for their bulk counterparts. Thus, we demonstrates an inspired possibility of obtaining a high hole mobility in nanowires that is not available in bulk. The small hole mobility is interpreted as to be associated with the strong electronic band mixing in nanowires.     

The effect of Pt nanoparticles loading on H2 sensing properties of flame-spray-made SnO2 sensing films

SnO₂ nanoparticles loaded with 0.2–2 wt% Pt have successfully been synthesized in a single step by flame spray pyrolysis (FSP) and investigated for gas sensing towards hydrogen (H₂). According to characterization results by X-ray diffraction, nitrogen adsorption, scanning/high resolution-transmission electron microscopy and analyses based on Hume-Rothery rules using atomic radii, crystal structure, electronegativities, and valency/oxidation states of Pt and Sn, it is conclusive that Pt is not solute in SnO₂ crystal but forms nanoparticles loaded on SnO₂ surface. H₂ gas sensing was studied at 200–10,000 ppm and 150–350 °C in dry air. It was found that H₂ response was enhanced by more than one order of magnitude with a small Pt loading concentration of 0.2 wt% but further increase of Pt loading amount resulted in deteriorated H₂-sensing performance. The optimal SnO₂ sensing film (0.2 wt% Pt-loaded SnO₂, 20 μm in thickness) showed an optimum H₂ response of ∼150.2 at 10,000 ppm and very short response time in a few seconds at a low optimal operating temperature of 200 °C. In addition, the response tended to increase linearly and the response times decreased drastically with increasing H₂ concentration. Moreover, the selectivity against carbon monoxide (CO) and acetylene (C₂H₂) gases was also found to be considerably improved with the small amount of Pt loading. The H₂ response dependence on Pt concentration can be explained based on the spillover mechanism, which is highly effective only when Pt catalyst is well-dispersed at the low Pt loading concentration of 0.2 wt%.     

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.     

Dielectric inspection of BaZr0.2Ti0.8O3 ceramics under bias electric field: A survey of polar nano-regions

The structure and dielectric properties of BaZr_0.2Ti_0.8O₃ ceramics prepared by citrate method were investigated. Structural analysis of the ceramics indicated a cubic perovskite structure and a fine-grained (about 250 nm) microstructure. The ceramics displayed a frequency dispersion of the dielectric loss and a slim polarization versus electric field (P–E) hysteresis loop. These results were related to the existence of polar nano-regions (PNRs) embedded in the non-polar matrix of the ceramics. The nonlinear dielectric properties under bias electric field were found to be dependent on holding time of applied bias field. The phenomenon was qualitatively explained with polarization reorientation of PNRs under the bias field. Fitting the dielectric constants under the bias field to a multipolarization mechanism model resolved the contribution of PNRs from the overall dielectric response. From the fitting, the polarization and size of PNRs in the ceramics were determined to be around 0.4 μC/cm² and 9 nm, respectively.     

Photocatalytic degradation of pendimethalin over Cu2O/SnO2/graphene and SnO2/graphene nanocomposite photocatalysts under visible light irradiation

The Cu₂O/SnO₂/graphene (CSG) and SnO₂/graphene (SG) nanocomposite photocatalysts were prepared by simple sol-gel growth method, and characterized by Fourier transform infrared spectra (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) measurements, respectively. The photocatalytic efficiency of catalysts were evaluated by degradation of pendimethalin under visible light irradiation (λ > 420 nm), which conformed that CSG and SG exhibited better photocatalytic activity than SnO₂ or graphene alone. An effort has been made to correlate the photoelectro-chemical behavior of these samples to the rate of photocatalytic degradation of pendimethalin.     

Temperature dependent growth and optical properties of SnO<Subscript>2</Subscript> nanowires and nanobelts

SnO₂ nanowires and nanobelts have been grown by the thermal evaporation of Sn powders. The growth of nanowires and nanobelts has been investigated at different temperatures (750–1000°C). The field emission scanning electron microscopic and transmission electron microscopic studies revealed the growth of nanowires and nano-belts at different growth temperatures. The growth mechanisms of the formation of the nanostructures have also been discussed. X-ray diffraction patterns showed that the nanowires and nanobelts are highly crystalline with tetragonal rutile phase. UV-visible absorption spectrum showed the bulk bandgap value (∼ 3–6 eV) of SnO₂. Photoluminescence spectra demonstrated a Stokes-shifted emission in the wavelength range 558–588 nm. The Raman and Fourier transform infrared spectra revealed the formation of stoichiometric SnO₂ at different growth temperatures.