Sn-doped ZnO Research Articles

Ultrasound-assisted synthesis, characterization and optical property of 0–3 wt% Sn-doped ZnO

Sn-doped ZnO samples were successfully synthesized by an ultrasonic solution method, and characterized by X-ray diffraction and electron microscopy. All samples were specified as hexagonal wurtzite ZnO with flower-like structure for pure ZnO and 1wt% Sn-doped ZnO, and with agglomerates of nanoparticles for 2 and 3wt% Sn-doped ZnO. Room temperature UV–visible spectra exhibited 373nm band edge absorption for wurtzite hexagonal pure ZnO, and were red-shift broad absorption bands from ultraviolet for pure ZnO to visible region for 1, 2 and 3wt% Sn-doped ZnO. The improvement of visible absorption in the Sn-doped ZnO samples was suggested to be the result of lattice defects caused by Sn dopant.

Barrier-controlled electron transport in Sn-doped ZnO polycrystalline thin films

We present a study of the temperature-dependent electrical conductivity in Sn-doped ZnO polycrystalline thin films with different Sn contents (0, 1, 3, 5, and 7at.%). The electrical conductivities show unusual temperature dependence in a temperature range of 110–400K, where electronic spatial potential fluctuations at the grain boundaries are observed. By applying a model supposing potential fluctuations at the grain boundaries we find that the potential barrier height decreases from 0.269eV down to 0.112eV and the homogeneity coefficient, which describes the homogeneity of films, decreases from 4.41 to 2.91 with increases in Sn content from 1at.% up to 7at.%. From these results, we see that the electron transport is essentially controlled by potential fluctuations at the grain boundaries for Sn-doped ZnO polycrystalline thin films. Our findings could be important for the design of high efficiency solar cell based on ZnO thin films.

Synthesis and Characterization of Ultrathin Tin‐Doped Zinc Oxide Nanowires

Ultrathin tin-doped zinc oxide (Sn-doped ZnO) nanowires with uniform diameters of 2.3 ± 0.2 nm were synthesized by means of a facile colloidal method employing an aminolysis approach. This finding suggests that the introduction of group IV dopants may serve as an effective strategy to control the shape of doped ZnO nanocrystals. This doping procedure may be extended to the synthesis of other doped oxide nanocrystals.

Effect of dopants on the structural, optical and electrical properties of sol–gel derived ZnO semiconductor thin films

Undoped, Ga-, In-, Zr-, and Sn-doped ZnO transparent semiconductor thin films were deposited on alkali-free glasses by sol–gel method. 2-methoxyethanol (2-ME) and diethanolamine (DEA) were chosen as a solvent and a stabilizer, respectively. The doping concentration was maintained at 2 at.% in the impurity doping precursor solutions. The effects of different dopants on the structural, optical, and electrical properties of ZnO thin films were investigated. XRD results show that all annealed ZnO-based thin films had a hexagonal (wurtzite) structure. ZnO thin films doped with impurity elements obviously improved the surface flatness and enhanced the optical transmittance. All impurity doped ZnO thin films showed high transparency in the visible range (>91%). The Ga- and In- doped ZnO thin films exhibited higher Hall mobility and lower resistivity than did the undoped ZnO thin film.

Fabrication of tin-doped zinc oxide by parallel flow co-precipitation with enhanced photocatalytic performance

Sn-doped ZnO photocatalysts with different molar ratios of Sn/Zn (1%, 2% and 3%) were prepared by a parallel flow precipitation. The photocatalysts fabricated were characterized by BET surface area, X-ray diffraction, scanning electron microscope, UV/Vis diffuse reflectance spectroscopy and surface photovoltage spectroscopy, respectively. The results showed that doping ZnO with Sn increased BET surface area of ZnO. The XRD patterns of Sn-doped ZnO photocatalysts calcined at 573K showed only the characteristic peaks of wurtzite-type. Doping ZnO with Sn changed the morphology of ZnO, the morphology changed from irregular lump and particle to irregular honeycomb. The photoinduced charge separation rate of 1% Sn doped-ZnO was higher than that of ZnO, while 2% and 3% Sn doped-ZnO had lower photovoltage than that of ZnO. The photocatalytic activity of Sn-doped ZnO photocatalysts for decolorization of methyl orange solution was evaluated, of all photocatalysts prepared, Sn-doped ZnO with 1% Sn exhibited the best photocatalytic activity and the underlying reason was discussed.

Sn-doped Zinc Oxide thin films for LPG sensors

Sn doped zinc oxide (ZnO:Sn) thin films have been prepared by chemical spray pyrolysis technique using Zn(CH3COO)2 as a precursor solution and SnCl4 as a doping solution respectively. The dopant concentration (Sn/Zn at%) is varied from 0 to 1.5 at%. The structural, morphological, optical and electrical properties of the films are explored and then tested for LPG sensing. The resistivity of the Sn-doped films decreases with the Sn doping up to 0.5 at%, while at a higher doping concentration the disorder produced in the lattice causes an increase in resistivity of the films. Exposure of LPG decreases the resistance of undoped and doped films. The response of the film is measured for both ZnO and ZnO:Sn films at different operating temperature (275-400 0 C) and concentration (vol %) of LPG in air. It is observed that Sn-doped ZnO films are more sensitive to LPG than undoped ZnO film. In this work, maximum response (~88 %) is observed for 0.5 at% ZnO:Sn film for 1 vol% of LPG in air at 300 0 C. Further all the films have shown faster response and recovery times at higher operating temperatures.

New Polytypoid SnO2(ZnO:Sn)m Nanowire: Characterization and Calculation of Its Electronic Structure

A new SnO2(ZnO:Sn)m polytypoid nanowire has been synthesized through a two-step chemical vapor deposition (CVD) method. Cs-corrected scanning transmission electron microscopy (STEM) studies indicate the crystal structure consists of an alternating stack of a Sn–O octahedral layer and a (Sn/Zn)–O wurtzite slab. First-principles density-functional theory (DFT) calculations suggest Sn atoms in the Sn-doped ZnO slabs have both 4- and 6-fold coordination, forming an inversion boundary of polarity. The SnO2(ZnO:Sn)m nanowires may exhibit unique anisotropic electronic properties: poor conductivity along the wire axis, but metallic conductivity along the diametrical directions according to the calculations.

Influence of Sn doping on ZnO sensing properties for ethanol and acetone

Nanostructured pure ZnO (PZO) and Sn doped ZnO (SZO) were deposited on glass templates by chemical deposition method. Before the deposition, electrically conductive silver paste was pasted at the two ends of the glass templates as electrodes. The gas sensing properties of the nanostructured PZO and SZO were systematically investigated by our home-made system, and the results show that Sn doping decreases the response to tested gases. However, it remarkably shortens the response time and recovery time of the sensor. Both PZO and SZO show higher response to acetone than to ethanol, while the response time and recovery time of PZO and SZO to ethanol are shorter than those to acetone, which indicates that the selectivity of ZnO nanostructures to ethanol and acetone are different.

Electronic structure and optical properties of Sn-doped ZnO

A deeper understanding on the atomic and electronic structure of ZnO material is crucial for explaining, predicting, and optimizing its properties, and to suggest materials for better performance. In this work, we present our first-principle studies of the energy bands associated with Sn impurity in ZnO using supercell models. We find that, due to Sn doping, the conduction band moves to the low-energy region, and the band gap becomes smaller than that of pure ZnO. In terms of the calculated band structures, we are also able to explain qualitatively the measured optical properties of Sn-doped ZnO powders.

Fabrication of Sn-Doped ZnO Varistor by Solid State Processing

In this work, systematic substitution of ZnO with SnO2 in ZnO-based varistor composition was investigated through analysis of densification, phase formation, microstructure and non-linear properties. The general formula was Zn0.96-xSnxBi0.02Co0.02Oβ with x = 0, 0.01, 0.02 and 0.04. The high rate of densification starting at 800°C is believed to be related to Bi2O3 via liquid-phase sintering. The complex nature of this multi-phasic varistor system was demonstrated through occurrence of different phases at different sintering temperatures. The low-temperature pyrochlore (Bi2Sn2O7) started to dissociate at approximately 1100°C with the spinel (Zn2SnO4) forming afterwards. The grain size variation with composition might be induced by the changes in the availability of Bi2O3 which has been reported to help facilitate abnormal grain growth. All samples sintered at 1200°C, with data extrapolation, possessed breakdown voltages of higher than 1400 V/cm.

Synthesis of Sn-doped ZnO nanorods and their photocatalytic properties

Sn-doped ZnO nanorods were fabricated by a hydrothermal route, and characterized by X-ray diffraction, field emission scanning electron microscope, UV–vis spectroscopy, Raman spectra, solid-state nuclear magnetic resonance (NMR) spectra, and room temperature photoluminescence spectroscopy. Solid-state NMR result confirms that Sn 4+ was successfully incorporated into the crystal lattice of ZnO. Room temperature photoluminescence showed that all the as-synthesized products exhibited a weak UV emission (380 nm) and a strong visible emission (540 nm), but the intensities of the latter emission increased with increase in Sn concentration. The improvement of visible emission at 540 nm in the Sn-doped ZnO samples was suggested to be a result of the lattice defects increased by doping of Sn in zinc oxide. In addition, the photocatalytic studies indicated that Sn-doped ZnO nanorods are a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes.

Ab initio studies of the Sn-doped ZnO transparent conductive oxide

Based on density functional theory within the generalized gradient approximation, Sn-doped wurtzite ZnO transparent conducting oxide (TCO) was investigated, where structures relaxations, formation energies, and electronic structure of Sn doped in ZnO are studied. It was found that the lattice parameters of the Sn-doped ZnO increased with increasing Sn concentration. The substitutional Sn (SnZn) atom has low formation energy and introduces impurity levels below the conduction band minimum. Also, substitutional Sn atoms contribute significantly delocalized s orbitals in the conduction band states, which are expected to increase the conductivity of the material. Additionally, with increase of Sn concentration, the band gap is narrowed. We further identify that the lower concentration of heavily doped of Sn, the conductivity of ZnO is stronger. The calculated results are helpful to gain a systematic understanding of structure, electrical properties of Sn-doped ZnO transparent conducting oxide.

Effects of Co and/or Sn doping on crystal structures and optical properties of ZnO thin films

The Co and/or Sn doped ZnO thin films are deposited on the glass substrates by the sol-gel method. The effects of Co and/or Sn doping on surface morphologies and mircrostructures of ZnO films are investigated by metallurgical microscope and X-ray diffraction (XRD). The XRD results indicate that all the ZnO samples show preferential orientation along the (002) direction, and that the Sn-doped ZnO thin film exhibits the best c-axis orientation and largest grain size. XPS results reveal that Co and Sn elements exist as Co2+ and Sn4+, indicating that Co and Sn ions have entered into the ZnO crystal lattices successfully. Strong blue double emission and weak green emission are observed in the PL spectra of all the samples. In addition, the ultraviolet peaks appear in the undoped and the Co-doped ZnO thin films. Our results reveal that the Co and/or Sn doping can tune the band gap, meanwhile, such a doping can also affect oxygen dislocation, zinc oxygen and zinc interstial defect concentrations. Finally, the possible luminescence mechanisms of Co and/or Sn doped ZnO films are discussed.

CdO activated Sn-doped ZnO for highly sensitive, selective and stable formaldehyde sensor

Sn-, Ni-, Fe- and Al-doped ZnO and pure ZnO are prepared by coprecipitation method, and characterized by scanning electron microscope (SEM), energy diffraction spectra (EDS) and X-ray diffraction (XRD). Their formaldehyde gas sensing properties are evaluated and the results show that 2.2mol% Sn dopant can increase the response of ZnO by more than 2 folds, while other dopants increase little response or even decrease response. Further, CdO is used to activate ZnO based formaldehyde sensing material. It is demonstrated that 10mol% CdO activated 2.2mol% Sn-doped ZnO has the highest formaldehyde gas response, with a linear sensitivity of ∼10/ppm at lowered work temperature of 200°C than 400°C of pure ZnO, and high selectivity over toluene, CO and NH3, as well as good stability tested in 1 month.

Enhanced sunlight photocatalytic performance of Sn-doped ZnO for Methylene Blue degradation

In the present study, nano-structured ZnO and Sn-doped ZnO photocatalysts with high sunlight photocatalytic activity were successfully synthesized through the decomposition of zinc acetate and glucose by microwave heating. The prepared ZnO and Sn-doped ZnO photocatalyst were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectrum (PL), UV–vis absorption spectrum (UV–vis), N 2 adsorption and UV–vis diffuse reflectance spectra (DRS). The results showed that the doping greatly changed the microstructure, morphology and optical properties of ZnO, which may contribute to the enhancement of photocatalytic activity. The sunlight photocatalytic activity of the prepared pure ZnO and Sn-doped ZnO photocatalyst was investigated by the degradation of Methylene Blue (MB) solution under sunlight irradiation. Compared with pure ZnO, 13% higher decolorization rate and 29–52% higher mineralization efficiency were obtained by the Sn-doped ZnO. The results indicated that Sn-doped ZnO had a higher photocatalytic activity and Sn dopant greatly increased the photocatalytic activity of ZnO.

Enhancement of green emission from Sn-doped ZnO nanowires

Oxygen vacancies play a crucial role in the emission characteristics of oxide nanomaterials. In this study, we found that the green emission intensity of ZnO nanowires can be enhanced through a Sn-doping concentration which increases the number of oxygen vacancies. Undoped ZnO nanowires showed blue emission at 380nm, but as the concentration of Sn was increased, the green emission peak at around 500nm, which is attributed to oxygen vacancies, showed drastic enhancement. On the basis of XPS compositional analysis, it was confirmed that the green luminescence intensity was closely related to the number of oxygen vacancies in Sn-doped ZnO nanowires. These results pave the way to a greater understanding of tunable light emission from nanowires, which could be a key technology for next-generation display devices, including flexible and transparent displays.

Comparison of the Structural and Morphological Properties of Sn Doped ZnO Films Deposited by Spray Pyrolysis and Chemical Bath Deposition

Comparison of the Structural and Morphological Properties of Sn Doped ZnO Films Deposited by Spray Pyrolysis and Chemical Bath Deposition

Improvement of the performance of dye-sensitized solar cells using Sn-doped ZnO nanoparticles

Sn-doped and undoped ZnO nanoparticles were synthesized by hydrothermal method and their performance as the photoanode of dye-sensitized solar cells (DSSCs) was investigated. Energy dispersive X-ray spectroscopy and X-ray diffraction showed that the Sn had been doped into the ZnO lattice. A red shift of photoluminescence spectra which was induced by Sn doping was observed. The photocurrent density–voltage curves of DSSCs indicated that the efficiency was increased by as high as 140% on bare-FTO substrate and 105% on ZnO compact layer/FTO substrate via Sn doping. Also the effect of the ZnO compact layer was discussed by both of Sn-doped or undoped DSSCs.

Observation of Photoconductivity in Sn-Doped ZnO Nanowires and Their Photoenhanced Field Emission Behavior

Sn-doped ZnO nanowire films have been successfully synthesized by electrodeposition on zinc foil followed by annealing in air at 400 °C for 4 h. The XRD patterns of the annealed specimens exhibit a set of well-defined diffraction peaks indexed to the wurtzite phase of ZnO. The surface morphology of the as-synthesized films showed a network of densely packed flakes/sheets on the substrate. However, upon annealing, the formation of ZnO nanowires, processing length in the range of several micrometers and diameter less than 150 nm, on the entire substrate is observed. The relative atomic percentage of Sn, estimated from the energy dispersive spectra, was found to be 0.5 and 2.0 in the ZnO films deposited for 10 and 40 min durations, respectively. From the field emission studies, the values of the turn-on field and threshold field, required to draw emission current density of 10 and 100 μA/cm2, are observed to be 0.68 and 1.1 V/μm for 0.5% Sn-doped ZnO and 1.72 and 2.25 V/μm for 2.0% Sn-doped ZnO, respectively. The field emission current stability investigated for a duration of 6 h at the preset value of 100 μA is found to be excellent. A prominent photoenhancement in the field emission current upon visible light illumination of the Sn-doped ZnO nanowires films has been observed. This enhancement has been attributed to the photoconductivity of the Sn-doped ZnO.

A template-free alcoholthermal route to Ti(Sn)-doped ZnO nanorods

Ti(Sn)-doped single-crystalline ZnO nanorods with an average diameter of 20 nm and length up to nearly 1 μm were synthesized by a facile ultrasonic irradiation-assisted alcoholthermal method without involving any templates. Photoluminescence spectra of the Ti-doped ZnO nanorods were measured at room temperature and three emitting bands, being a violet emission at 400–415 nm, a blue band at 450–470 nm and a green band at around 550 nm, were detected. The emission intensities of the Ti-doped ZnO nanorods enhance gradually with increasing the doping concentrations. As to the Sn-doped ZnO nanorods, the green emission shifts to 540 nm and the emission intensities increase first but decrease later with increasing the doping concentrations.