On the Role of Oxygen Vacancies in the Determination of the Gas-Sensing Properties of Tin-Oxide Nanowires (original) (raw)
Related papers
Investigation of SnO2 nanowire based gas sensor
2010
Gas sensing characteristics of SnO 2 nanowires in two configurations namely isolated nanowires (Type I) and mat type nanowires thin films (Type II) have been investigated. Interestingly, Type I sensor exhibited anomalous behavior on exposure to Cl 2 in that the resistance reduced on exposure while response of type II sensors showed normal behavior with increase in resistance. Response to reducing gas, H 2 S was found to be normal for both type of sensors. Results have been understood in terms of different interactions of chlorine. Temperature dependence of response also showed that maximum response for Type II sensors occurs at 150°C towards both reducing (H 2 S) and oxidizing (Cl 2 ) gases while type I sensors have good response at room temperature. The results indicate different behavior of change in resistance of intragrain and intergrain regions. Isolated SnO 2 nanowires are found to be promising for detection of gases at room temperature.
The paper presents results of the research aimed at the engineering of nanostructures (NSs). SnO 2 nanowires (NWs) were grown via vapor-solid mechanism at a synthesis temperature of 900°С in a modified setup allowing the NS morphology be encoded in a programmable way along its length. The Ti/Au (20/500 nm) electrical contacts to individual NWs were deposited via consequent PVD vacuum deposition process to obtain gas sensitive chemiresistors. Electrical properties and gas-sensing performance of the obtained monocrystalline NSs with a modified shape were investigated using hydrogen and oxygen gases. It was established that structurally modified NWs, due to the presence of narrow segments, exhibit better gas-sensitive characteristics in comparison with straight NWs. Obtained results are discussed from the positions of single-crystal "neck" formation in NSs and their influence on transport properties of NWs.
Comparative study of gas sensor performance of SnO 2 nanowires and their hierarchical nanostructures
Sensors and Actuators B-chemical, 2010
In this study, SnO 2 nanowires (NWs) were synthesized by two different thermal evaporation processes and hierarchical SnO 2 nanostructures were prepared through a combination of the two processes without reseeding of Au catalyst. Field emission scanning electron microscopy studies showed that the shape of the core NWs become distorted and attached to large quantities of quasi-one-dimensional nanostructures, mostly NWs and nanobelts. The crystal structure of these as-prepared hierarchical SnO 2 nanostructures was identified to coincide to the normal rutile structure. Photoluminescence properties are similar among the samples with a strong peak emission band centered at 620 nm that is attributed to a defect-state-related emission. The gas sensing performance of SnO 2 NWs and their hierarchical nanostructures were simultaneously investigated by testing with liquefied petroleum gas and NH 3 gas at different concentrations and operating temperatures. Results reveal that hierarchical SnO 2 nanostructures have enhanced gas sensing performance in comparison with SnO 2 NWs materials. The gas sensing mechanism of SnO 2 hierarchical nanostructures was also discussed. Results indicate that hierarchically porous SnO 2 architectures are highly promising for gas sensor applications.
Gas sensing properties of individual SnO2 nanowires and SnO2 sol–gel nanocomposites
Beilstein Journal of Nanotechnology
This work is an investigation of the properties of semiconductor materials based on metal oxides, their catalytic properties, and their application as gas sensors, which were shown to exhibit high sensitivity, stability, and selectivity to target gases. The aim of this work is the comparison of gas sensing properties of tin dioxide in the form of individual nanowires and nanopowders obtained by sol–gel synthesis. This comparison is necessary because the traditional synthesis procedures of small particle, metal oxide materials seem to be approaching their limit. Because of this, there is increasing interest in the fabrication of functional materials based on nanowires, i.e., quasi-one-dimensional objects. In this work, nanocrystalline tin dioxide samples with different morphology were synthesized. The gas-transport method was used for the fabrication of well-faceted wire-like crystals with diameters ranging between 15–100 nm. The sol–gel method allowed us to obtain fragile gels from ...
Microstructure and H2 gas sensing properties of undoped and Pd-doped SnO2 nanowires
Sensors and Actuators B: Chemical, 2009
Tin oxide (SnO 2 ) nanowires with a tetragonal structure were synthesized by thermal evaporation of tin grains at 900 • C. The obtained nanowires were doped with palladium. The morphology, crystal structure, and H 2 gas sensing properties of undoped and Pd-doped SnO 2 nanowires were investigated. SnO 2 nanowires were approximately 30-200 nm in diameter and several tens of micrometers in length. Gas sensors based on undoped, 0.8 wt% Pd-doped, and 2 wt% Pd-doped SnO 2 nanowires were fabricated. These SnO 2 nanowire gas sensors showed a reversible response to H 2 gas at an operating temperature of RT-300 • C. The sensor response increased with increasing Pd concentration. The 2 wt% Pd-doped SnO 2 nanowire sensor showed a response as high as 253 for 1000 ppm H 2 gas at 100 • C. The results demonstrated that Pd doping improved the sensor response and lowered the operating temperature at which the sensor response was maximized.
Synthesis and Gas Sensing Properties of SnO2 Nanostructures by Thermal Evaporation
Advanced Materials …, 2013
Tin oxide nanostructures (NS) were grown on silicon substrates by thermal evaporation method with three different parameters. These parameters were temperatures (650 °C, 750 °C and 850 °C), nickel catalyst concentrations (0, 5 and 10 milimoles) and tin powder source to substrate distances (2 cm, 4 cm and 6 cm). The parameters were found to affect the size and morphology of the synthesized nanostructures. Formation of nanospheres (NSs), nano-needles (NNs) and nanowires (NWs) of tin oxide were observed by Scanning Electron Microscope (SEM) at different synthesis conditions. Synthesis temperature was found to have most pronounced effect on the size and morphology of the nanostructures. Catalyst concentration has affected the porosity and growth of the nanostructures. The distance between source and substrate affected the nanostructures predominately on distribution and particle size. Energy dispersion X-ray (EDX) analysis confirms the presence of tin and oxygen in all nanostructures at all synthesis conditions. X-ray diffraction (XRD) proves the formation of tin oxide phase in all samples. Significant formation of tin oxide nanowires was observed at 850 °C. Gas sensing properties of SnO 2 nanowires (NW) toward ethanol (C 2 H 5 OH) gas at 450°C with different volume concentration was measured. It was found SnO 2 NW had good sensing properties for C 2 H 5 OH at 100 ppm compared to measurements made at 25-50 ppm.
Nanowires of metal oxides for gas sensing applications
Surface and Interface Analysis, 2008
Nanowires of different metal oxides (SnO2, ZnO) have been grown by evaporation–condensation process. Their chemical composition has been investigated by using XPS. The standard XPS quantification through main photoelectron peaks, modified Auger parameter and valence band spectra were examined for the accurate determination of oxidation state of metals in the nanowires.Morphological investigation has been conducted by acquiring and analyzing the SEM images. For the simulation of working conditions of sensor, the samples were annealed in ultra high vacuum (UHV) up to 500 °C and XPS analysis repeated after this treatment. Finally, the nanowires of SnO2 have were used to produce a novel gas sensor based on Pt/oxide/SiC structure and operating as Schottky diode. Copyright © 2008 John Wiley & Sons, Ltd.
Novel fabrication of an SnO2 nanowire gas sensor with high sensitivity
2008
We fabricated a nanowire-based gas sensor using a simple method of growing SnO 2 nanowires bridging the gap between two pre-patterned Au catalysts, in which the electrical contacts to the nanowires are self-assembled during the synthesis of the nanowires. The gas sensing capability of this network-structured gas sensor was demonstrated using a diluted NO 2 . The sensitivity, as a function of temperature, was highest at 200 • C and was determined to be 18 and 180 when the NO 2 concentration was 0.5 and 5 ppm, respectively. Our sensor showed higher sensitivity compared to different types of sensors including SnO 2 powder-based thin films, SnO 2 coating on carbon nanotubes or single/multiple SnO 2 nanobelts. The enhanced sensitivity was attributed to the additional modulation of the sensor resistance due to the potential barrier at nanowire/nanowire junctions as well as the surface depletion region of each nanowire.
Influence of Metal Catalyst on SnO2 Nanowires Growth and Gas Sensing Performance
Proceedings
In the present work SnO2 nanowires were synthetized by using vapour-liquid-solid technique (VLS) on alumina substrates, using different metal nanoparticles as catalyst for the growth. In particular, the effect of Au, Sn and Pd nanoparticles was exploited. The growth was performed simultaneously on all substrates, keeping the same conditions for the three different catalysts used. Nanowires were investigated by FE-SEM, HR-TEM, and XRD measurements, confirming the morphology and the crystalline structure of the material. Moreover, conductometric sensing devices were fabricated depositing electrodes on top of these materials, and chemical sensing performances were evaluated toward some typical air pollutants.
Synthesis of SnO2 Nanowires on Quartz and Silicon Substrates for Gas Sensors
Journal of Inorganic and Organometallic Polymers and Materials
Tin oxide nanowires (SnO 2 NWs) were grown on quartz and silicon substrates via a modified chemical vapor deposition (CVD). Film of gold nanoparticle deposited on both types of substrates using the direct current DC-sputtering technique. The structure and morphology of the produced material were characterized by using atomic force microscopy, X-ray diffraction (XRD), scanning electron microscope (SEM) and ultraviolet-visible (UV-Vis) techniques. The XRD and SEM analysis confirmed the formation of tetragonal SnO 2 NWs with a wire length of 10-20 μm and a diameter of 40-100 nm. The UV-Vis spectrum shows a strong absorption peak in the UV and others in the visible regions. The bandgap was calculated for SnO 2 NWs grown on a quartz substrate within the value of 3.2 eV. It is slightly lower than the bandgap value of bulk. The successfully synthesized SnO 2 NWs via CVD with a large aspect ratio in the range of 250-200 was proved to be quite promising nanomaterials to use for sensor fabrication towards ethanol gas at room temperature. The high sensitivity of 2.7 at an ethanol gas concentration of 500 parts per million (ppm) was achieved. The proposed sensing mechanism of SnO 2 NWs towards ethanol gas was also discussed.