Nanocrystalline SnO2 and Au:SnO2 thin films prepared by direct current magnetron reactive sputtering

Nanocrystalline pure and gold doped SnO₂(Au:SnO₂) films were prepared on unheated glass substrates by dc magnetron reactive sputtering and, subsequently, the as deposited films were annealed in air. The films structure, surface morphology, photoluminescence, electrical and optical properties were investigated. After annealing the as deposited SnO₂ films, crystallinity increased and the surface roughness decreased. The intensity of PL peaks increases sharply with the annealing temperature. The optical transmittance of the films was around 89% after annealing the as deposited SnO₂ films at 450 °C. The as deposited Au:SnO₂ films show better crystallinity than the as deposited SnO₂ films, the average grain size was around 4.4 nm. The emission peaks of Au:SnO₂ films are slightly blue shifted as compare to undoped SnO₂ films. The Au:SnO₂ films show the lowest electrical resistivity of 0.001 Ωcm with optical transmittance of 76%, after annealing at 450 °C.     

Preparation of porous SnO2 helical nanotubes and SnO2 sheets

We report a surfactant-free chemical solution route for synthesizing one-dimensional porous SnO₂ helical nanotubes templated by helical carbon nanotubes and two-dimensional SnO₂ sheets templated by graphite sheets. Transmission electron microscopy, X-ray diffraction, cyclic voltammetry, and galvanostatic discharge–charge analysis are used to characterize the SnO₂ samples. The unique nanostructure and morphology make them promising anode materials for lithium-ion batteries. Both the SnO₂ with the tubular structure and the sheet structure shows small initial irreversible capacity loss of 3.2% and 2.2%, respectively. The SnO₂ helical nanotubes show a specific discharge capacity of above 800 mAh g⁻¹ after 10 charge and discharge cycles, exceeding the theoretical capacity of 781 mAh g⁻¹ for SnO₂. The nanotubes remain a specific discharge capacity of 439 mAh g⁻¹ after 30 cycles, which is better than that of SnO₂ sheets (323 mAh g⁻¹).     

SnO2和SnO2-Ag薄膜的电学特性

用磁控溅射法在集成了铂加热电极的Si基膜片型微结构单元上制备了SnO     

The effect of Au and Pt nanoclusters on the structural and hydrogen sensing properties of SnO2 thin films

Au and Pt nanoparticle modified SnO₂ thin films were prepared by the sol-gel method on glass substrates targeting sensing applications. Structural and morphological properties of these films were studied using X-ray Diffraction and Scanning Electron Microscopy. It was proved that the films crystallized in tetragonal rutile SnO₂ crystalline structure. Scanning Electron Microscopy observations showed that the metallic clusters' dimensions and geometry depend on the kind of the metal (Au or Pt) while SnO₂ films surface remains almost the same: nanostructured granular very smooth. Optical properties of the films were studied using UV-visible spectroscopy. The modified SnO₂ films were tested as hydrogen sensors. The response of SnO₂, SnO₂-Au and SnO₂-Pt thin films against hydrogen was investigated at different operating temperatures and for different gas concentrations. The addition of metal nanoparticles was found to decrease the detection limit and the operating temperature (from 180 °C to 85 °C), while increasing the sensing response signal.     

Silver layer instability in a SnO2/Ag/SnO2 trilayer on silicon

Trilayers of SnO₂/Ag/SnO₂ deposited on oxidized Si (100) substrates at room temperature become unstable after annealing at 100 °C and 200 °C, exhibiting five phenomena - formation of internal Ag hillocks, cracking of the top SnO₂ layer above internal Ag hillocks, penetration of Ag/Ag grain boundaries by SnO₂ leading to grain pinch-off, formation of Ag whiskers and islands on the free surface of the SnO₂ through the cracked top layer, and void formation in the Ag layer. The possible driving forces and evolution path for the observed instabilities resulting from thermal expansion mismatch stresses and the reduction in interfacial energy are discussed.     

Lithographic patterning of benzoylacetone modified SnO2 and SnO2:Sb thin films

The synthesis of directly UV-photopatternable pure and antimony-doped organo-tin materials is presented. UV-photopatternability has been achieved by using the synthesized benzoylacetone modified tin and antimony 2-isopropoxyethoxides. Photopatterned pure and antimony-doped organo-tin films are crystallized by thermal annealing in order to obtain conductive SnO₂ and Sb:SnO₂ thin films. The molar ratio between benzoylacetone and metal alkoxides has to be 2 in order to obtain crack-free, good-quality structures. The effects of UV-irradiation, increasing antimony doping level and benzoylacetone concentration on the electrical properties of the single-layered films are analyzed. The highest obtained conductivity was 20 S/cm. Benzoylacetone concentration and UV-irradiation has only a negligible effect on the film electrical conductivities.     

Characterizations of SnO2 and SnO2:Sb thin films prepared by PECVD

Structural characterizations of tin oxide (SnO₂) thin films, deposited by plasma-enhanced chemical vapor deposition (PECVD), were investigated with scanning electron microscope (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that the films are porous, the crystalline structure transforms from crystalline to amorphous phase as deposition temperature changes from 500°C to 200°C, and the chemical component is non-stoichiometric (Sn:O is 1.0716 prepared at 450°C with a value of O₂ flow 3.5 l/min). Sheet resistance of the thin films decreases with increasing of deposition temperature. Whereas, sheet resistance increases with increasing of oxygen flow. Tin oxide doped with antimony (SnO₂:Sb) thin films prepared by same method have a better selectivity to alcohol than to carbon monoxide; the maximum sensitivity is about 220%. The gas-sensing mechanism of SnO₂ thin films is commentated.     

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%.     

Characterization of interface states at Au/SnO2/n-Si (MOS) structures

The purpose of this paper is to characterize the interface states in Au/SnO₂/n-Si (MOS) structures. The characteristic parameters of the interface states are derived from capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements as a function of frequency. The C-V and G/ω-V measurements have been carried out in the frequency range of 1 kHz to 1 MHz at room temperature. At each frequency, the measured capacitance and conductance decrease with increasing frequency due to a continuous distribution of the interface states. The frequency dispersion in capacitance and conductance can be interpreted in terms of the interface state density (N_ss) and series resistance (R_s). Especially at low frequencies, the interface states can follow the ac signal and yield an excess capacitance. Due to a continuous density distribution of interface states, the C and G/ω values decrease in depletion region with increasing frequencies. At high frequencies, the effect of series resistance on the capacitance is found appreciable due to the interface state capacitance decreasing with increasing frequency. Experimental results show that the locations of interface states between SnO₂/Si and series resistance have a significant effect on electrical characteristics of MOS structures.     

Effects of CdCl2 treatment and annealing on CdS/SnO2/glass heterostructures for solar cells

Effects of CdCl₂ post-growth treatments and annealing under different conditions on the surface and interface properties of CdS/SnO₂/glass heterostructure were studied. CdS thin films were grown on SnO₂-coated glass substrates for CdS/CdTe heterojunction solar cells by the solution growth technique. It was found that CdCl₂ post-growth treatments and annealing enhanced the CdS-related XRD peaks, narrowed the CdS characteristic Raman bands, removed or depressed the disorder related Raman features, and improved the CdS film crystalline quality significantly, which are advantageous to the application in solar cells as a window layer material.     

Active Stainless Steel/SnO2-CeO2 Anodes for Pollutants Oxidation Prepared by Thermal Decomposition

Stainless steel plates were successfully coated with SnO₂-CeO₂ films (SS/SnO₂-CeO₂) by brush coating with a solution of stannous chloride and cerium trichloride followed by thermal decomposition. It is proven that the properties of SnO₂ films can be evidently improved by Ce doping, and 600°C is the optimum temperature to prepare SS/SnO₂-CeO₂ anodes. The physicochemical and electrochemical properties as well as the electrocatalytic activity of the electrodes were investigated. It is found that the novel electrodes have compact microstructure, high overpotential for oxygen evolution (1.60 V vs SCE), excellent electrochemical stability, relatively low cost and excellent catalytic activity for oxidizing pollutants. An industrial dye wastewater, which is hard to be purified by using conventional chemical flocculation methods, was oxidated by employing the SS/SnO₂-CeO₂ anodes, and 83.00% of color and 48.62% of chemical oxygen demand (COD) removal was achieved under the cell voltage of 5 V within only 2 min, and the electricity consumption is only 1.83 kWh for oxidizing 1 m³ of dye wastewater.     

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.     

Preparation of antimony-doped SnO2 nanocrystallites

The antimony-doped SnO₂ nanocrystallite was synthesised by the co-precipitation reaction and subsequent calcination from the antimony(III) chloride and tin(IV) chloride. The crystal size, pore size distribution and properties of the nanocrystalline powders were examined by differential thermal analysis, thermogravimetric analysis, X-ray diffraction and desorption isotherm(Barrett-Joyner-Halenda method). Calcination of the precipitate powder at 650°C led to the formation of Sb-SnO₂ nanocrystallite of ∼6 nm in crystal size. Most of the pores in the nanocrystallite are about 5-10 nm in diameter. Effect of doped antimony on the crystal size of the nanocrystallite is discussed.     

Energetic electronic processes and negative resistance in amorphous TaTa2O5Au and AlAl2O3Au diodes

Voltage-controlled negative resistance (VCNR) can be established in metal-insulator-metal structures by applying a potential to the diode, which is usually in vacuum. Light emission due to electroluminescence (E.L.), and electron emission into vacuum, accompany the formation of conductivity; these energetic electronic phenomena are closely related to the “forming” of VCNR and to the resultant current-voltage characteristics. For Al₂O₃ diodes with impure oxides, VCNR forms at constant voltage, independent of oxide thickness; for clean oxides, forming depends on field and on the metal counterelectrode. The intensity and energy distribution of light emitted from TaTa₂O₅Au diodes have been measured, and are compared to E.L. from AlAl₂O₃Au diodes. The voltage threshold for the appearance of E.L. in TaTa₂O₅Au diodes is 1.2 V, for AlAl₂O₃Au it is 1.4 V. The respective voltages for maximum current, V_m, are 1.9 V and 2.8 V. In Al₂O₃, the E.L. spectrum covers the visible range with peaks at 1.8 eV, 2.3 eV, and 4.0 eV. For Ta₂O₅, the E.L. intensity is constant over most of the visible, but has a maximum between 1.6 eV and 1.8 eV which is also the energy of E.L. of TaTa₂O₅Au diodes before the establishment of VCNR. For both Al₂O₃ and Ta₂O₅ diodes, electron emission into vacuum is anomalous since emission is detectable at diode voltages of ∼2 V. Electron emission in the two insulators, though qualitatively similar, shows differences that depend on differences in trapping levels and band gaps of the insulators.     

纳米SnO2/TiO2复合粉体制备及其红外特性研究

以溶胶-凝胶方法制备纳米SnO2/TiO2复合粉体,并用XRD、TEM等方法对其进行了表征,给出了相关的工艺参数.研究了纳米SnO2及SnO2/TiO2复合材料的红外吸收特性.结果表明,本文制备的纳米SnO2/TiO2复合材料在4000～1500cm-1和1000～400cm-1范围内有较好的红外吸收.     

Preparation and super-hydrophilic properties of TiO2/SnO2 composite thin films

SnO₂-TiO₂ composite thin films were fabricated on soda-lime glass with sol-gel technology. By measuring the contact angle of the film surface and the degradation of methyl orange, we studied the influence of SnO₂ doping concentration, heat-treatment temperature and film thickness on the super-hydrophilicity and photocatalytic activity of the composite films. The results indicate that the doping of SnO₂ into TiO₂ can improve their hydrophilicity and photocatalytic activity, and the composite film with 1-5 mol% SnO₂ and heat-treated at 450°C is of super-hydrophilicity. The optimal SnO₂ concentration for the photocatalytic activity is 10 mol% and larger film thickness is helpful to reduce the contact angle of the composite films.     

Ion irradiation induced amorphization of SnO2 nanoparticles embedded in SiO2

SnO₂ nanoparticles (NPs) of average diameter of ∼10.5 nm, synthesized in SiO₂ using Sn⁻ ions implantation combined with thermal annealing, were irradiated with 1.5 MeV Au²⁺ ions at room temperature. The NP structure was studied as a function of ion fluence by transmission electron microscopy and micro-Raman spectroscopy. Prior to ion irradiation, SnO₂ NPs have been found to exhibit the rutile crystal structure. Upon irradiation, amorphization in the nanocrystals has been seen to increase with increase in ion fluence. In particular, at a fluence of 1 × 10¹⁴ ions cm⁻² we argue for the presence of an amorphous SnO₂ phase. Beyond this fluence, the NPs have been found to dissolve in the matrix. The observed results are explained in the frame work of ion irradiation induced defects production in the NPs as well as in the NP/matrix interface.     

TiO2 coated SnO2 nanosheet films for dye-sensitized solar cells

TiO₂-coated SnO₂ nanosheet (TiO₂-SnO₂ NS) films about 300 nm in thickness were fabricated on fluorine-doped tin oxide glass by a two-step process with facile solution-grown approach and subsequent hydrolysis of TiCl₄ aqueous solution. The as-prepared TiO₂-SnO₂ NSs were characterized by scanning electron microscopy and X-ray diffraction. The performances of the dye-sensitized solar cells (DSCs) with TiO₂-SnO₂ NSs were analyzed by current-voltage measurements and electrochemical impedance spectroscopy. Experimental results show that the introduction of TiO₂-SnO₂ NSs can provide an efficient electron transition channel along the SnO₂ nanosheets, increase the short current density, and finally improve the conversion efficiency for the DSCs from 4.52 to 5.71%.     

In-situ preparation of TiO2/SnO2 nanocrystalline sol for photocatalysis

A novel preparation method to synthesize TiO₂/SnO₂ nanocrystalline sol under mild conditions was presented. Ti(OC₄H₉)₄ used as a precursor was hydrolyzed in the rutile SnO₂ nanocrystalline sol, and in-situ formed TiO₂/SnO₂ nanocrystalline sol. The crystal structure, morphology and photocatalysis performance of samples were investigated. The results show that the additional rutile SnO₂ nano grains serve as heterogeneous crystal nucleus and exhibite the inducing effect on TiO₂ grains growth, thus leading to the changes in crystalline phase and particle morphology. In addition, the photoluminescence (PL) spectra analysis indicates that TiO₂/SnO₂ composite structure induces a better charge separation, and thus the photocatalytic activity of TiO₂/SnO₂ sol is increased significantly compared with TiO₂ sol.     

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.