Films For Gas Sensing Applications Research Articles

Fabrication of Gadolinium Oxide-doped Fe2O3-LaFeO3-La2O3 Thick Films by Screen Printing Technique and Their Electrical Properties for Ethanol Gas Sensors

Recently, there have been many researchers who discussed screen printing techniques (SPT) as a good approach to fabricate the thick films for gas sensor applications. In this work, the SPTs were conducted to fabricate the thick films based on gadolinium oxide-doped Fe2O3-LaFeO3-La2O3 that were applied as ethanol gas sensors. The crystal and morphological structures were investigated using x-ray diffraction and scanning electron microscopy, respectively. It shows that there are three phases of the crystal structure of gadolinium oxide-doped Fe2O3-LaFeO3-La2O3 i.e., rhombohedral, orthorhombic, and hexagonal. The morphological structure shows an average particle size of about 0.61 μm. Furthermore, the electrical properties measurements were explored to ensure the performance of thick films in detecting the ethanol gases. Th measurements were conducted in the range of temperature of about 310 ∘C to 325 ∘C and in the various ethanol gas containing, it is 0 ppm, 100 ppm, 200 ppm, and 300 ppm. This result showed that the highest response of thick films in the existence of ethanol gases (300 ppm) is 427 with an optimum temperature of 319 ∘C. It is also confirmed that SPT has an excellent approach in thick film fabrication to produce gas sensor devices with good performance.
 Keywords: fabrication, gadolinium oxide, doped, thick films, screen printing, electrical properties, ethanol, sensors

Investigation of Adsorption Kinetics on the Surface of a Copper-Containing Silicon–Carbon Gas Sensor: Gas Identification

The low selectivity of materials to gases of a similar nature may limit their use as sensors. Knowledge of the adsorption kinetic characteristics of each gas on the surface of the material may enable the ability to identify them. In this work, copper-containing silicon–carbon films were formed using electrochemical deposition on the Al2O3 substrate with interdigitated Cr/Cu/Cr electrodes. These films showed good adsorption characteristics with several different gases. The adsorption kinetics of nitrogen dioxide, sulfur dioxide, and carbon monoxide on the film surface were investigated by the change in the resistivity of the material. Pseudo-first-order and pseudo-second-order kinetics, Elovich, Ritchie, and Webber intraparticle diffusion models were applied. It was found that the largest approximation factor and the lowest Root-Mean-Square Error and Mean Bias Error for all three gases were for the Elovich model. The advantages of silicon–carbon copper-containing films for gas sensor applications were shown. An algorithm for gas recognition was proposed based on the dependence of the change in the resistivity of the material under stepwise gas exposure. It was found that parameters such as the values of the extrema of the first and second derivatives of the R vs. t dependence during adsorption and the slope of R vs. t dependence in the Elovich coordinates are responsible for gas identification among several one-nature gases.

Physical properties of thermal annealing induced In2O3 thin films for sensing layer applications

Detection and monitoring of flammable, toxic and explosive gases are crucial, where active research on nanostructured metal oxide materials and thin films is enthusiastically performed to explore new paths for improving the characteristic parameters of sensors. The higher stability and appropriate electrical properties along with wide band gap of In2O3 material make it suitable for active layer to gas sensors where properties of In2O3 films could be engineered by post treatments. The present work demonstrates an influence of thermal annealing on structural, optical, topographical, morphological, elemental and electrical properties of In2O3 films for gas sensor applications. The In2O3 films of thickness 500 nm are grown onto soda lime glass and conducting ITO substrates employing physical vapor deposition based thermal evaporation technique followed by thermal annealing at 200 °C, 300 °C and 400 °C for one hour in air atmosphere. The XRD analysis indicated phase transformation from metastable rhombohedral to stable cubic phase where crystallite size corresponding to associated preferred (110) and (222) peaks is tuned in range of 32–51 nm with annealing. Optical analysis unveiled higher transmittance in ultraviolet and visible regions whereas absorbance of films is fluctuated with thermal annealing. All the In2O3 films indicated the Ohmic nature where the resistivity is detected to be enhanced with annealing. EDS patterns confirmed deposition of the films. The SEM analysis showed nanospheres like grain morphology and such well connected nanospheric features offer large surface area and stimulate adsorption of gas effectively. Hence structural, optical, electrical and morphological properties of gas sensitive In2O3 layers are greatly stimulated by thermal annealing.

Physical properties of mixed TiO2-CdO thin films for gas sensor applications

TiO2-CdO thin films were grown by Nd: YAG pulsed laser deposition (PLD) at different laser energies of (500-900) mJ. According to the findings of the XRD analysis, each film possessed a cubic polycrystalline crystal structure with a predominant peak along the (111) plane. The average crystallite size was corrected using Warren-Scherrer's corrections, and their values were found to lie between (12.23 and 83.40) nm. The AFM images indicate that the average particle size reduced as the laser energy increased, while surface roughness and root mean square values were raised as the laser energy increased. Optical properties showed that the bandgap decreases from 2.09- 1.8 eV with increasing laser energy. The increment in laser energy results in a rise in particle size and the average roughness. The maximum Sensitivity of TiO2-CdO films towards H2 gas was 72.3%, and the response time was within 24– 67.9 sec.

Electron beam evaporated nanostructure WO3 films for gas sensor application

In the recent years, metal oxide semiconductors such as SnO2, CuO, Fe2O3, TiO2, WO3 and ZnO were investigated for the detection of ethanol gas in the environment. Among these, WO3 is one of the best n-type semiconductor material for ethanol gas detection. In this paper, nanostructured WO3 thin films were prepared by electron beam evaporation on glass substrate and investigated their ethanol gas sensing properties. Surface morphology, structural and elemental analysis of the WO3 thin films were analysed by scanning electron microscopy (SEM), atomic microscopy (AFM), X-ray diffraction and X-ray photoelectron spectroscopy. The as deposited films exhibited nanostructure and highly influenced by the substrate temperature. From the X-ray photoelectron spectroscopy analysis, we found that substrate temperature increases the binding energy shift in lower energy regions and shows that WO3 films contain oxygen vacancies. The gas sensor sensitivities were measured for different gases with different concentrations at various operating temperatures. The obtained results show that the nanostructure WO3 films are suitable sensing material for ethanol gas. The nanostructure WO3 films deposited at substrate temperature of 100 °C shows best sensitivity with quick response and recovery time, which is attributed to the formation of nanorods and possess a very high surface to volume ratio.

Enhance The Gas-Sensing Performances Of Graphene Oxide (GO) Thin Films For Detecting Nitrogen Dioxide Gas

In this work, graphene oxide (GO) synthesized via a modified Hummer method was utilized to manufacture thin films for gas sensor applications. The films were prepared on glass substrates using the spin coating technique, the concentration of GO was varied in the precursor liquid. The crystall ographic properties of the prepared GO films were analyzed using XRD and the results showed a polycrystalline structure with a crystallite size of 15.51 nm. Using the weighing method, the average film thickness was determined to be about 200 nm. UV-Vis absorption spectrometry combined with the Tauc method confirmed the indirect nature (allowed and forbidden) of electronic transitions in the samples and it also showed a decrease in the optical energy gap with an increasing amount of GO in the samples. Values for Eg ranged from 2.4 eV to 2.15 eV for allowed transitions and from 3.05 eV to 2.6 eV for forbidden transitions. Gas sensing measurements were performed using NO2 as target gas at different operating temperatures (50, 100, 200 and 300 oC), as well as four target gas concentration (100 ppm, 400 ppm, 700 ppm, and 1000 ppm) have been tested and shows the good response in the range of 10%. It can be seen that the sensitivity increases with increasing operating temperature and gas concentration. At 300 oC operating temperature response and recovery time decrease to their lowest value or 2.6 and 5 seconds, respectively.

Influence of Heat Treatment on the Characteristic of SnO2 Thin Films for Gas Sensor Application

Nano-crystalline SnO2 films were deposited on glass substrates using dip coating by sol–gel technique for gas sensor applications. These films have been annealed in air at 300, 350 400, and 450 °C for 60 min, and at 400 °C for 15, 30 min. The films have been analyzed through x-ray diffraction and optical absorption spectroscopy. The deposited films have shown tetragonal rutile structures. The average crystallite size increased as annealing temperature increased. The crystallite sizes of the annealed films were 8 nm at 300 °C, 10 nm at 350 °C, 14 nm at 400 °C, and 22 nm at 450 °C for 60 min. Whereas the crystallite sizes showed 16 and 15 nm at annealing temperature of 400 °C for 15 and 30 min, respectively. The energetic values of optical band gaps of the films showed increment with the elevation in annealing temperatures. The optical band gap energies were 2.86, 2.86, 3.14 and 3.35 eV at annealing temperatures of 300, 350, 400, and 450 °C, for 60 min, respectively, and 3.43 and 3.35 eV at annealing temperature of 400 °C for 15 and 30 min, respectively. Electrical D.C. conductivity were measured at temperatures ranging from 30 °C to 170 °C, and these measurements showed an exponential increment as the temperature and time increased. The films were studied in the matter of sensing capabilities for CO gas through evaluation at various times and temperatures. The optimum sensitivity was found at annealing temperature 400 °C. The outcomes revealed a high sensitivity of the deposited films for carbon monoxide at operation temperature of 200 °C.

Sensitivity of Nanostructured Mn-Doped Cobalt Oxide Films for Gas Sensor Application

Sensitivity of Nanostructured Mn-Doped Cobalt Oxide Films for Gas Sensor Application

Characterization and NO2 gas sensing performance of CdO:In2O3 polycrystalline thin films prepared by spray pyrolysis technique

Polycrystalline CdO:In2O3 thin films for gas sensor applications were prepared on glass and silicon substrates by using one-step spray pyrolysis technique from the aqueous solution of CdCl2 and InCl3 at a substrate temperature of 300 °C. The structure, surface morphology, and the optoelectronic properties of prepared films were characterized respectively by means of X-ray diffraction (XRD), atomic force microscope and UV–visible spectroscopy. Based on the XRD results, the polycrystalline nature of CdO films has been confirmed, and In2O3 films were found to exhibit a preferred orientation along (222) diffracted plane. The grain size varies between 9.0 and 28.4 nm. The results of Hall effect measurement of CdO:In2O3 thin films confirms that all films were an n-type semiconductor. The electrical properties of prepared thin films and their sensitivity to nitrogen dioxide (NO2) gas are also studied. The influence of the operating temperature and In2O3 concentration on the NO2 response were investigated. It is found that all films are sensitive to NO2 gas, and the ideal operating temperature for the film contented 20 vol% of In2O3 was found to be 200 °C at a gas concentration of 25 ppm. The sensing mechanism of the CdO:In2O3 thin film is discussed and attributed to electron transfer between the sensing element and NO2 molecules.

Free Standing Graphene Oxide Films for Gas Sensing Applications

Free standing films of graphene oxide (GO) were synthesized using an improvisation of Tour’s method [ACS Nano, 4, 4806-4814 (2010)]. Reaction time and temperature were significantly modified to reduce the presence of graphitic residues in the as synthesized GO. These films were characterized for phase purity and we report their performance for ammonia sensors.

Development of Silver Doped Titanium Oxide Thin films for Gas Sensor Applications

Gas sensors find numerous applications in fields of automotives, medical, industries and others. A number of studies focused on synthesis of silver doped titanium dioxide films with various doping concentrations of silver. The objective of the research work is to optimize gas sensing properties of Ag-TiO2 thin films using orthogonal array experimentation with different dopants, concentration, annealing temperatures and gas concentrations exposure time. Synthesis of Ag-TiO2 thin films on quartz substrates was carried out by sol-gel spin coating. TiO2 films were characterized optical, chemical and mechanical and sensing properties. Surface roughness of TiO2 Thin films are RSM 11 to 45 nm and decrease of transmittance from 74% to 45% and energy bad gap from 3.44 to 3.29 eV for variation of annealing temperature from 400 to 600 °C. Surface roughness in RSM of 15 to 67 nm and decrease in transmittance from 85 to 63 % and band gap from 3.40 to 3.28 eV from 3 to 7 layers of coating was found. Ag-TiO2 thin films showed highest sensor response of 1.247 for 300 °C annealing temperature, 0.025 atomic ratio, 5 ppm CO gas exposure. Analysis of variance showed CO gas exposure influenced sensor response by 72.95%, and annealing temperature influenced sensor response by 18.39 %. Response surface methodology showed desirability of 70.7% with maximum response value to be 1.2346.

Effect of Oxygen Sputter Pressure on the Structural, Morphological and Optical Properties of ZnO Thin Films for Gas Sensing Application

ZnO thin films were prepared on glass substrates at low (5 × 10−4 mbar) and high (3 × 10−3 mbar) sputter pressure using dc reactive magnetron sputtering. The structural, morphological, compositional and optical properties of the thin films were investigated. XRD patterns of both films confirmed the polycrystalline nature of the films with hexagonal Wurtzite structure. SEM study indicates that the surface of the film formed at high sputter pressure was more uniform, compact and porous in nature. From the EDAX analysis, no other characteristic peaks of other impurities were observed and the formation of single phase of ZnO was confirmed. From the study of photoluminescence, three peaks were observed, one strong near band-edge emission at 390 nm followed by weak and broad visible emissions around 420–480 nm. Room temperature ammonia sensing characteristics of ZnO nanothin films formed at higher sputter pressure were studied for different ammonia vapour concentration levels. The response of the Ammonia sensor at room temperature (30 °C) operation was observed to be of high sensitivity with quick response and recovery times.

V2O5 thin films for gas sensor applications

V2O5 thin films were deposited onto fused silica, alumina and conductometric sensor supports by means of rf reactive sputtering from a metallic vanadium target. Film thickness was varied between 200 and 600nm. Argon-oxygen gas mixtures of different compositions controlled by the flow rate were used for sputtering. Temperature of the film substrate was kept constant at 560K. Structural properties and phase composition of as-sputtered thin films were studied by X-ray diffraction at glancing incidence, GIXD, and Raman scattering while Scanning Electronic Microscopy (SEM) was used to investigate film morphology. Electrical properties were determined by means of impedance spectroscopy (0.1–1MHz) over the temperatures range extending from RT to 620K. Thin films of V2O5 exhibited good response towards hydrogen (5–300ppm), methane and propane (50–3000ppm).

Preparation and Study the Characteristics of Tungsten Trioxide Thin Films for Gas Sensing Application

In this study, Tungsten Trioxide thin films were successfully synthesized at different substrate temperatures by pulse laser deposition. Structural, morphological and electrical properties of WO3 thin films, were investigated by X-ray diffraction (XRD), Atomic Force Microscope AFM), Scanning Electron Microscope (SEM), Hall Effect and sensing measurements. The results was indicated that WO3 thin films prepared at 450ᵒC was optimum condition where sensitivity toward H2S gas has been measured, sensitivity was higher than other films preparation at (250ᵒC,350ᵒC) temperature.

Enhancing gas sensing properties of graphene by using a nanoporous substrate

Substrate engineering is shown to be a viable approach for improving the use of graphene thin films for gas sensor applications. The performance of two-terminal devices fabricated on smooth SiO2 and nanoporous anodized aluminum oxide (AAO) substrates are compared. Raman studies indicated that both types of samples exhibit similarly low point-defect densities, but the mobility values of the SiO2-supported films were found to be three times larger than those on porous AAO substrates. However, the AAO-supported graphene devices exhibit a 3-fold enhanced sensitivity to both NO2 and NH3 gases when compared to the devices supported on SiO2. We attribute this sensitivity enhancement to the inhomogeneous electrostatic potential landscape that results from the porous nature of the AAO substrate, as well as extended defects made of wrinkles or folds originated from AAO. This substrate design strategy could be extended to other semiconductor-based sensor devices.

Nanostructured SnO2 thick films for gas sensor application: analysis of structural and electronic properties

This research is focused on structural and electrical characterisation of tin oxide (SnO2) applied as a thick film and investigation of its properties as gas sensitive material. Micron sized SnO2 powder was milled in an agate mill for six hours to fabricate SnO2 nanopowder, which was afterwards sieved by 325 mesh sieve and characterized by XRD and SEM. This powder was used as functional part in the production of thick film tin oxide paste containing a resin vehicle with 4 wt. % nanosize glass frits acting as permanent binder. The glass frits where additionally milled for twelve hours in the agate mills to nanosized powder and sieved by a 325 mesh sieve as well. The achieved thick film paste was screen printed on alumina and fired at 850oC peak temperature for 10 minutes in air. After the sintering process, thick film samples where characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The reflectivity was measured on the same samples by UV-VIS spectrophotometer: the band gap was determined from the slope of reflectance. After that a matrix of different interdigitated electrode structure of PdAg paste was printed and sintered using the mentioned sintering conditions. The tin oxide thick film was printed over the interdigitated electrodes as a top layer and sintered again under the same conditions. The total electrical resistance was measured as a function of the electrode spacing and temperature. A negative temperature coefficient (NTC) was identified and measured in the range from room temperature (27°C) to 180°C in a climate chamber. Finally the samples were placed into a gas reactor with NOx and CO gas and the resistance was measured in the same temperature range (27°C-200°C).

Hydrothermally Synthesized NanoTiO2 Thick Films for Gas Sensing Application

TiO2 nanoparticals were prepared by hydrothermal synthesis technique. The thick films of TiO2 were prepared by screen printing technique; gas sensing performance of this film was tested for various gases. The film showed highest response and selectivity to H2S gas. The gas response selectivity of film were measured and presented. The films were characterized by x-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area diffraction and optical absorption spectroscopy technique. The quick response and fast recovery are the main features of these films. The effect of temperature on the optical, structural, morphological and gas sensing properties of the films were studied and discussed.

Controlled synthesis of few layer graphene films for gas sensor applications

ABSTRACTA novel approach for synthesis of few layer graphene films on SiC has been developed which uses halogen based inductively coupled-reactive ion etching (ICP-RIE) and rapid thermal annealing (RTA) in atmospheric pressure argon. These films have been characterized using x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Surface characterization by XPS reveals the presence of defects similar to those observed for graphene oxide (GO) but at a much lower levels that those observed for GO. As in the case for GO, the defect density could be further reduced by chemical methods which improved carbon to defect ratio based on XPS analyses. Raman spectroscopy showed the presence of D, G and 2D peaks at 1330 cm-1, 1599 cm-1 and 2671 cm-1, respectively, which is comparable with similar graphene films formed by thermal annealing of SiC. The full widths at half max (FWHM) for these peaks was, however, comparable to those observed for GO. Electrical characterization of these graphene films using collinear four point probe measurements showed the electrical resistivity of these films is consistent with the observed values for few layer exfoliated graphene. Gas sensor structures were fabricated using lithography free methods, and initial gas response studies were performed for H2.

Influence of film thickness on the properties of sprayed ZnO thin films for gas sensor applications

Transparent conducting ZnO films were prepared at substrate temperature 400°C with different film thicknesses by nebulizer spray pyrolysis method on glass substrates. XRD studies reveal that the films are polycrystalline in nature having hexagonal crystal structure with preferred grain orientations along (002) and (101) directions. The crystallite size increases along (002) plane with the thickness increase and attains a maximum 109nm for 913nm film thickness. Analysis of structural parameters indicates that the films having thickness 913nm are found to have minimum dislocation density and strain values. The HRSEM measurements show that the surface morphology of the films also changes with film thickness. EDAX estimates the average atomic percentage ratio of Zn and O in the ZnO films. Optical studies reveal the band gap energy decrease from 3.27 to 3.14eV with increase of film thickness. Room temperature PL spectra show the near-band-edge emission and deep-level emission due to the presence of defects in the ZnO thin films. Impedance spectroscopy analysis indicates that grain boundary resistance decreases with the increasing ammonia concentration up to 500ppm and the maximum sensitivity is found to be 1.7 for 500ppm of ammonia.

Characterization of reactive sputtered TiO2 thin films for gas sensor applications

The technology for preparing and characterisation of titanium dioxide (TiO2) thin films with properties appropriate for usage as gas sensors are discussed. For preparing the samples the methods of reactive radio frequency (RF) and direct current (DC) magnetron sputtering were used. The composition and microstructure of the films were studied by XPS, EPMA, XRD and Raman spectroscopy and the surface of the films was observed by high resolution SEM. Thorough profile analyses on the structure changes were performed by XPS. Interactions with the substrate and changes between the different modifications of the crystal structure also were investigated. For measuring the thickness and to identify the refractive indices of the films laser ellipsometry was used. The research was focused on the sensing behaviour of the sputtered TiO2 thin films. Films of various thickness were deposited on quartz resonators and the quartz crystal microbalance (QCM) method was used. This enables highly sensitive gas sensor capable of detecting changes in the molecular range to be constructed. Prototype QCM sensors with TiO2 sensitive films made in our laboratory, showed good sensitivity to ammonia at room temperature, and are currently being tested for sensitivity to other gasses.