Determination of gas sensing properties of thermally evaporated WO3 nanostructures (original) (raw)
Related papers
Low temperature response of nanostructured tungsten oxide thin films toward hydrogen and ethanol
Sensors and Actuators B: Chemical, 2012
Semiconducting metal oxide based gas sensors usually operate in the temperature range 200-500 • C. In this paper, we present a new WO 3 thin film based gas sensor for H 2 and C 2 H 5 OH, operating at 150 • C. Nanostructured WO 3 thin films were synthesized by thermal evaporation method. The properties of the as-deposited films were modified by annealing in air at 300 • C and 400 • C. Various analytical techniques such as AFM, TEM, XPS, XRD and Raman spectroscopy have been employed to characterize their properties. A clear indication from TEM and XRD analysis is that the as-deposited WO 3 films are highly amorphous and no improvement is observed in the crystallinity of the films after annealing at 300 • C. Annealing at 400 • C significantly improved the crystalline properties of the films with the formation of about 5 nm grains. The films annealed at 300 • C show no response to C 2 H 5 OH (ethanol) and a little response to H 2 , with maximum response obtained at 280 • C. The films annealed at 400 • C show a very good response to H 2 and a moderate response to C 2 H 5 OH (ethanol) at 150 • C. XPS analysis revealed that annealing of the WO 3 thin films at 400 • C produces a significant change in stoichiometry, increasing the number of oxygen vacancies in the film, which is highly beneficial for gas sensing. Our results demonstrate that gas sensors with significant performance at low operating temperatures can be obtained by annealing the WO 3 films at 400 • C and optimizing the crystallinity and nanostructure of the as-deposited films.
Nanostructured WO 3 deposited by modified thermal evaporation for gas-sensing applications
Thin Solid Films, 2005
In this work, we present a simple method, based on a modified thermal evaporation technique, to obtain films of nanostructured WO 3 with high surface roughness. This method consists on sublimation from a metallic tungsten wire followed by oxidation in low vacuum conditions and reactive atmosphere ( p O2 = 0.22 mbar), with substrates heated at high temperature (600 -C). Electron microscopy (SEM, TEM) and atomic force microscopy (AFM) analysis revealed that the deposited films are composed of agglomerates with nanometric size and present high surface roughness and large effective area suitable for gas-sensing applications. Sensing measurements highlighted promising performances, particularly at the working temperature of 100 -C: high responses towards sub-ppm concentrations of NO 2 have been observed compared to the lower ones observed for NH 3 and CO. NO 2 tests performed with sensors based on sputtered thin films highlighted that sensors obtained by this thermal evaporation like method exhibit improved performances. D
Ethanol sensing performance of gas sensors made of Fe doped and Fe implanted nanostructured WO 3 thin films prepared by a thermal evaporation technique was investigated. Three different types of nanostructured thin films, namely, pure WO 3 thin films, iron-doped WO 3 thin films by co-evaporation and Fe-implanted WO 3 thin films have been synthesized. All the thin films have a film thickness of 300 nm. The physical, chemical and electronic properties of these films have been optimized by annealing heat treatment at 300ºC and 400ºC for 2 hours in air. Various analytical techniques were employed to characterize these films. Atomic Force Microscopy and Transmission Electron Microscopy revealed a very small grain size of the order 5-10 nm in as-deposited WO 3 films, and annealing at 300ºC or 400ºC did not result in any significant change in grain size. This study has demonstrated enhanced sensing properties of WO 3 thin film sensors towards ethanol at lower operating temperature, which was achieved by optimizing the physical, chemical and electronic properties of the WO 3 film through Fe doping and annealing. Introduction Of the different gas sensors, semiconductor based chemiresistor sensors are most investigated and widely used for detection of combustible and toxic gases owing to their low cost and relative simplicity. The Chemiresistive gas sensor works on the principle of a change in electrical resistance due to an interaction between the semiconductor and the gas. Various semiconducting oxides, catalytic oxides and mixed oxides [1-10] have been investigated for gas sensing properties and many more oxides are now currently being explored. The gas sensing properties of these oxides are determined by their intrinsic properties, however, can be modified by addition of impurities and modifying the microstructure including particle size, orientation and distribution, surface morphology and porosity [11]. The operating temperature strongly influences the sensitivity of the sensor [12] since the reactions occurring at the surface of the sensor (chemisorption/redox reaction) are functions of temperature. Use of additives such as Pd, Pt, In, Cu, Nb, Mn, Si to improve the sensor response has been extensively reported in the literature [13-15]. Tungsten trioxide (WO 3) is a well-known n-type semiconductor with a band gap of 2.6 eV that has been used not only in catalytic/photocatalytic [16], electrochromic applications [17] but also in solid state gas sensors. It has been successfully used to detect NH 3 , H 2 S, NO 2 , O 3 , H 2 and VOC. However, it is less sensitive to carbon monoxide and hydrocarbons [18]. Iron addition lower than 10 at% to WO 3 films prepared by reactive RF sputtering produced an enhancement in sensor response when exposed to NO 2 [19]. Iron addition was found to be advantageous in sensing ozone, CO and ethanol. NO 2 and humidity sensing characteristics of WO 3 thin films prepared by vacuum thermal deposition and subsequent annealing in the temperature range of 300-600 o C were investigated by Xie et al [20]. It was found that NO 2 sensing was strongly dependant on annealing and working temperature. In the present work, WO 3 thin films were deposited by thermal evaporation technique to produce nanostructured films with higher porosity that are suitable for gas sensing applications. Small amount of iron was added to WO 3 films by co-evaporation as well as implantation. The affect of physical, chemical and electronic properties on ethanol sensing performance of these films has been investigated.
Semiconductor gas sensors based on nanostructured tungsten oxide
Thin Solid Films, 2001
Semiconductor gas sensors based on nanocrystallline WO films were produced by two different methods. Advanced reactive 3 Ž . gas evaporation was used in both cases either for a direct deposition of films deposited films or to produce ultra fine WO 3 powder which was used for screen printing of thick films. The deposited films sintered at 480ЊC and the screen-printed films sintered at 500ЊC displayed a mixture of monoclinic and tetragonal phases and had a mean grain size of approximately 10 and 45 nm, respectively. We studied the influence of the sintering temperature T of the films on their gas sensitivity. Unique and s excellent sensing properties were found upon exposure to low concentrations of H S in air at room temperature for both 2 deposited and screen-printed films sintered at T s 480ЊC and at T s 500ЊC, respectively. ᮊ 2001 Elsevier Science B.V. All rights s s reserved.
Gas sensing properties of nanocrystalline tungsten oxide synthesized by acid precipitation method
Sensors and Actuators B-chemical, 2010
a b s t r a c t WO 3 ·2H 2 O samples were prepared by acidic precipitation of sodium tungstate solution. Nanocrystalline WO 3 powders were obtained after 350 and 600 • C calcinations. XRD patterns of these samples showed a diffraction profile similar to that of monoclinic WO 3 . Calcinations at 600 • C yield WO 3 powders with particle sizes ranging from 60 to170 nm whereas that for 350 • C calcinations are in the range of 30-150 nm. The gas sensing properties of these powders in the form of thick film were investigated with and without platinum doping. Gas response of thick films sintered at two different temperatures was measured at four different operating temperatures. We confirm that the sensor elements made from 600 • C calcined powders doped with platinum sintered at 800 • C are highly responsive and selective to ammonia vapour at 350 • C operating temperature as compared to sensor elements made from commercial powders.
THERMAL EVAPORATED WO 3 NANOPARTICLES FILM UNDER DIFFERENT EVAPORATION PRESSURES FOR NO 2 SENSING
In this study, the fabrication of tungsten oxide (WO 3) nanoparticles in effective size using thermal evaporation method under different conditions was reported. The fabricated WO 3 were examined and characterized by X-ray diffraction, and field-emission scanning electron microscope. Our examination showed that WO 3 nanoparticles with a monoclinic structure were assembled with large quantity. Both of the crystallite and particle size are increase with increasing the evaporation pressure and substrate temperature. In addition, we check the ability of the fabricated WO 3 for nitrogen dioxide (NO 2) sensing at different operating temperatures. The gas sensing properties showed highest sensitivity of 204 to 1 ppm NO 2 at an operating temperature of 140˚C, which was observed for a sensor made of particles as small as 123 nm. The electrical resistance of WO 3 showed a unique thermal behavior of the fabricated sensor.
Development of Tungsten Oxide Based Gas Sensor for Ethanol Vapor Detection
In this work, tungsten oxide (WO3) powder with average grain size of 50 nm was prepared using modified Nishide-Mizukami sol-gel method. The powder was characterized using X-Ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with transmission electron microscopy (TEM). The ethanol vapor sensing properties were investigated at different operating temperatures and gas concentrations. The WO3 pellet ethanol sensor exhibited excellent sensitivity to ethanol vapor with maximum sensitivity value of 29 at low temperature which is 200 °C. It was shown that the WO3 pellet can be reliably used to monitor high concentration of vapor above 1,500 ppm. This study demonstrated the possibility of utilizing WO3 pellet as a sensor element for the detection of ethanol vapor.
Structural and optical characterization of WO3 thin films for gas sensor applications
Journal of Applied Physics, 2005
The structural and optical properties of WO 3 nanorods prepared by oblique angle depositions were studied and compared with WO 3 thin films. The x-ray diffraction analysis revealed that both the thin films and nanorods annealed at temperatures of 400 and 500°C had an orthorhombic structure, while only the thin films showed a monoclinic phase when annealed at 300°C. The band gap energies of the thin films and nanorods all decreased with increasing annealing temperature. The polarized optical absorbance spectra of the as-deposited nanorod samples initially showed anisotropy, but after annealing at temperatures above 400°C, they became isotropic. This is believed to result from the changes in morphology, crystal structure, and orientation of the nanorod arrays after annealing.
Journal of Petroleum Research and Studies, 2022
In this research, the structural and sensitivity properties of the toxic gases of films tungsten oxide (WO3) nanoparticles prepared by the pulsed laser deposition method were manufactured and studied using a Nd:YAG laser. To show the effect of different temperatures (400, 600 and 800 oC) on films deposited on quartz substrate for all samples. The results of X-Ray diffraction (XRD) showed that all the thin films have polycrystalline structure and have a peak direction (010) for all samples, and that increasing the temperature led to an increase in the particle size. The decrease in the values of the full width and half maximum (FWHM) of the films (WO3) for (010) modes from 0.19 to 0.14 with increasing temperature. The nature of the topography of tungsten oxide (WO3) nanoparticles was studied using atomic force microscopy (AFM), which proved that the films grown in this way have good crystallization and have a homogeneous surface. The root mean square (RMS) values of the tungsten...
Sensors and Actuators B …, 2003
Structural and NO 2 and H 2 S gas-sensing properties of nanocrystalline WO 3 powders are analysed in this work. Sensor response of thickfilm gas sensors was studied in dry and humid air. Interesting differences were found on the sensor response between sensors based on 400 and 700 8C-annealed WO 3 , what motivated a structural study of these materials. Crystalline structure and defects were characterised by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). Experimental results showed that both triclinic and monoclinic structures are present in the analysed materials, although their amount depends on the annealing treatment. Crystalline shear planes, which are defects associated to oxygen deficient tungsten trioxide, were found in 400 8C-annealed WO 3 and their influence on XRD spectra was analysed by XRD simulations. Moreover, XRD and Raman spectra were also acquired at normal metal oxide-based gas sensor working temperatures in order to relate both crystalline structure and sensor response. #