Responsivity optimization of methane gas sensor through the modification of hexagonal nanorod and reduction of defect states (original) (raw)
Hydrogen Gas Sensor Based on ZnO Nanoroads Grown on Si by Thermal Evaporation
Journal of Materials Science and Engineering A, 2016
High-quality ZnO (Zinc oxide) nanorods grown on Si substrate have been synthesized for hydrogen gas sensor application through a low-cost catalyst-free process by thermal evaporation at 800 º C. The morphological, structural and optical properties of the ZnO nanorods have been examined. In this study, Pd/ZnO/Pd MSM (Metal-semiconductor-metal) gas sensor has been fabricated based on the ZnO nanorods. The absence of a seed layer and the coalescence of ZnO nanorods were the key factors responsible for the high sensitivity of the gas sensor at room temperature. The sensitivity of ZnO nanorods is measured at different concentrations from 25 ppm to 150 ppm of H 2 gas at room temperature. The highest response of the ZnO/Si sensor was 110% in the presence of 500 ppm of H 2. This high sensitivity can be attributed to the high surface-area-to-volume ratio of the nanorods between the Pd contacts of the MSM configuration.
Highly efficient Zinc Oxide nanostructure based gas sensor for domestic application
Journal of the Pakistan Institute of Chemical Engineers
In this work, Zinc Oxide (ZnO) nanorods with high surface to volume ratio were fabricated through the hydrothermal synthesis process on a glass slide and highly conductive alumina ceramic based gold interdigitated electrode (IDE). The ZnO nanorods structure on substrates were characterized through X-ray diffraction (XRD) and UV absorption spectroscopy followed by growth verification by Scherrer’s equation. The sensitivity characterization of fabricated sensor was determined for 2000 ppm and 4000 ppm natural gas in the air through high resistance electrometer at room temperature. The 2000 ppm concentration of gas shows 11.3% sensitivity, response time of 66 seconds and recovery time of 92 seconds to the sensor. The 4000 ppm concentration of gas shows 64% sensitivity, the response time of 106 seconds and a recovery time of 174 seconds to the sensor. The higher sensitivities with slow response and recovery times exhibit the behavior of redox reactions of sensor surface to the higher ...
Sensors and Actuators B: Chemical, 2013
Novel cacti-like structure and nanoneedles of zinc oxide (ZnO) were grown onto glass substrate using chemical route at comparatively low temperature (90 • C), and employed for the application of gas sensor. The grown nanostructures were characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FE-SEM) and Transmission Electron Microscope (TEM) and photoluminescence (PL) spectroscopy. FE-SEM and TEM images showed that vertically aligned ZnO nanoneedles were formed on substrate and secondary branches emanated from primary aligned nanoneedles. PL spectra showed distinctively different peaks for nanoneedles and cacti-like structure where the peak intensities for cacti structures are as high as the one compared for aligned nanoneedles. Also, the intense visible peak detected for cacti structure confirmed the presence of defects due to oxygen vacancy in the grown nanostructures. Further, gas sensing behaviors were studied for these two different nanostructures against nitrogen dioxide (NO 2 ) gas, and their selectivities toward reducing gases such as hydrogen disulfide, ethanol and liquefied petroleum gas were compared. It was found that cacti-like structure exhibited high gas response at 200 • C and is selective for NO 2 gas as compared with that for nanoneedles. The improved gas response is due to high surface area of cacti structure and presence of oxygen vacancies. Moreover, the contact between two adjacent cacti branches creates barrier potential at junction, which controls its resistance of sensors resulting in high gas sensing. Therefore, novel cacti-like nanostructure demonstrated to be the best candidate as NO 2 gas sensor at low cost and temperature. (C.S. Lee).
The superior performance of the electrochemically grown ZnO thin films as methane sensor
Sensors and Actuators B: Chemical, 2008
Pd-Ag/ZnO/Zn and Rh/ZnO/Zn MIM (metal-insulator-metal) gas sensors were fabricated using nanoporous ZnO thin films, obtained by an electrochemical deposition method in the absence and presence of UV light. A high-purity Zn anode, a Pt cathode, a calomel reference electrode and a 0.3-M oxalic acid electrolyte were used for deposition. Pd-Ag (26%) and Rh were used separately as the catalytic metal electrodes to fabricate the two different types of MIM configurations. A gas response of the order of 3.85 ± 2, a response time of 5 ± 0.5 s and a recovery time of 16 ± 0.5 s were obtained with the Pd-Ag contact, while the Rh contact showed a response of the order of 4.82 ± 2, a response time of 24 ± 0.5 s and a recovery time of 72 ± 0.5 s, at the optimum temperature of 220 • C, which is the lowest temperature so far reported for metal oxide sensors to sense 1% methane in a N 2 carrier gas. The undoped zinc oxide thin films grown by UV-assisted electrochemical anodization of high-purity Zn demonstrated a better performance for methane sensing. The experiments were repeated in synthetic air and a somewhat reduced performance was observed. The selectivity in the presence of hydrogen and the stability of the sensors were studied.
Development of gas sensors using ZnO nanostructures
Journal of Chemical Sciences, 2010
Different ZnO nanostructures such as nanowires, nanobelts and tetrapods have been grown and used for preparation of thick film (with random grain boundaries) as well as isolated nanowire/nanobelt gas sensors. Sensitivity of different type of sensors has been studied to H2S and NO gases. The results show that the response of ZnO sensors to H2S arises from grain boundary only whereas both grain boundaries and intragrain resistances contribute towards response to NO. In addition, oxygen vacancies in the lattice were also seen to help in improvement of sensor response. Room temperature operating H2S and NO sensors based on ZnO nanowires have been demonstrated. Further, sensors based on isolated nanobelts were found to be highly selective in their response to NO.
Novel hydrogen gas sensor based on single ZnO nanorod
Microelectronic Engineering, 2008
For extensive use in an industrialized process of individual ZnO nano/microrods as building nanoblock in novel hydrogen sensors, a simple, inexpensive, and bio-safe synthesis process and nanofabrication route is required. Here, we report a cost-effective and fast synthesis route for ZnO one-dimensional nanorod using an aqueous-based approach in a reactor. Our synthesis technique permits nano/microrods to be easily transferred to other substrates and to be distributed on the surface. This flexibility of substrate choice opens the possibility of using focused ion beam (FIB/SEM) system for handling and fabricating nanosensors. The main advantage of this procedure is a quick verification/testing of concept and is compatible with micro/nanoelectronic devices. The described nanofabrication steps permitted us to obtain a 90% success rate for building single nanorod sensor. A sensitivity of $4% was obtained for a single ZnO nanorod hydrogen sensor at 200 ppm H 2 in the air at room temperature. The nanosensor has a high selectivity for H 2 , since its sensitivity for O 2 , CH 4 , CO, ethanol or LPG are less than 0.25%.
Gas Sensor Properties of ZnO Nanorods Grown by Chemical Bath Deposition
Advanced Materials Research, 2014
The present work shows a study about the growing of ZnO nanorods by chemical bath deposition (CBD) and its application as gas sensor. It was prepared ZnO nanorods and Au decorated ZnO nanorods and the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and gas sensing response measurements. The results obtained by XRD show the growth of ZnO phase. It was possible to observe the formation of uniform dense well-aligned ZnO nanorods. The results obtained also revealed that Ag nanoparticles have decorated the surface of ZnO nanorods successfully. Au nanoparticles with diameter of a few nanometers were distributed over the ZnO surface nanorods. The gas sensing response measurements showed a behavior of n type semiconductor. Furthermore, the Au-functionalized ZnO nanorods gas sensors showed a considerably enhanced response at 250 and 300 °C.
Fabrication of Zinc Oxidenanorods Based Gas Sensor
Zinc oxide (ZnO) nanorods are considered as most suitable materials for the fabrication of gas sensors due to their high sensing properties. In this research a simple gas sensor has been fabricated based upon the principle of change in resistivity due to oxygen vacancies which make its surface chemically and electrically active. When charge accepting molecules adsorb at the vacanciessignificant variation appears in conductivity. A comb like structure was made on a substrate through photolithography. Gold was sputtered on the substrate for making contacts as well as catalyst for ZnO nanorods. Chromium was used as adhesive layer prior to gold sputtering. For ZnO nanorods growth hydrothermal method was adopted. The as prepared Zn Onanostructures, distribution and morphologies were characterized by scanning electron microscope (SEM) and x-ray diffraction. The SEM reveals the wurtzite hexagonal crystalline nanostructure grown along the [0001] direction. The ZnO nanosensor was tested for different concentrations of ethanol gas and different operating temperatures. The resistance between the two contacts has beenevaluated as a function oftemperature and gas concentration. The best sensor response was recorded at operating temperature of 300°C.
Journal of Electronic Materials
Three different ZnO nanostructures, dense nanorods, dense nanowires, and sparse nanowires, were synthesized between Pt electrodes by on-chip hydrothermal growth at 90°C and below. The three nanostructures were characterized by scanning electron microscopy and x-ray diffraction to identify their morphologies and crystal structures. The three ZnO nanostructures were confirmed to have the same crystal type, but their dimensions and densities differed. The NO 2 gas-sensing performance of the three ZnO nanostructures was investigated at different operation temperatures. ZnO nanorods had the lowest response to NO 2 along with the longest response/recovery time, whereas sparse ZnO nanowires had the highest response to NO 2 and the shortest response/recovery time. Sparse ZnO nanowires also performed best at 300°C and still work well and fast at 200°C. The current-voltage curves of the three ZnO nanostructures were obtained at various temperatures, and the results clearly showed that sparse ZnO nanowires did not have the linear characteristics of the others. Analysis of this phenomenon in connection with the highly sensitive behavior of sparse ZnO nanowires is also presented.
Nanomaterials
In this work, a simple, facile growth approach for a vertically aligned ZnO thin film is fabricated and its application towards methane gas sensors is demonstrated. ZnO thin film was prepared by a combination of hydrothermal and sputtering methods. First, a ZnO seed layer was prepared on the substrate through a sputtering technique, then a ZnO nanorod was fabricated using a hydrothermal method. The surface morphology of the ZnO film was observed by scanning electron microscopy (SEM). A ZnO nanorod coated on the dense seed layer is clearly visible in the SEM image. The average size of the hexagonal-shaped ZnO rod was around 50 nm in diameter, with a thickness of about 1 mm. X-ray absorption near-edge structures (XANES) were recorded to characterize the structural properties of the prepared film. The obtained normalized Zn K-edge XANES of the film showed the characteristic features of ZnO, which agreed well with the standard ZnO sample. The measurement of Zn K-edge XANES was performed...