Niyanta Datta

ZnO Nanowires As H2S Sensor

Hydrothermal growth of ZnO nanowires were performed using ZnO nanoparticles as a seed layer. The growth was found to depend strongly on the reaction duration. These nanowires detected H2S with faster response and recovery time of 13 and 78 s, respectively towards 20 ppm at 350° C. The lowest detection limit was improved to 0.6 ppm upon annealing in O2 flow of 50 sccm. The response time was further improved to just 6 s towards 20 ppm of H2S at 350° C. The enhanced response characteristics have been attributed to the high surface area to volume ratio of nanowires. Photoluminescence (PL) studies showed increase in the green emission related to defect states in ZnO. This is also expected to contribute for the improved sensing characteristics.

Opposite response of CO for WO3 and Au: WO3 sensors

Pure and Au incorporated WO3 thin films have been investigated for their sensing properties towards CO. Pure WO3 sensor film exhibited an increase in resistance while Au: WO3 films showed opposite behavior i.e. a decrease in resistance. We propose mechanism(s) for this anomalous sensing behavior of CO.

Ammonia sensor based on WO3 thin films

WO3 thin films deposited using a simple method of vacuum evaporation has been investigated for their NH3 sensing properties. Effect of process parameters namely operating temperature, film thickness and amount of Au in the WO3 host matrix have been investigated and correlated with the observed sensitivity values to obtain the optimum sensor with improved sensing characteristics towards NH3. Pure WO3 films with thickness of 600 nm and the Au incorporated WO3 containing 0.034 wt.% Au were observed to exhibit a superior sensing property towards NH3.

Improved H2S and Cl2 Sensing Characteristics of Pure and Au Incorporated WO3 Thin Films

Gas sensing properties of pure and Au incorporated WO3 thin films towards H2S and Cl2 have been investigated. The sensor films were able to detect H2S and Cl2 selectively at an operating temperature of 150 and 200 °C, respectively. Effect of gas concentration and Au loading have been investigated and correlated with the observed sensitivity values. Pure WO3 films exhibited better sensing characteristics towards H2S (S = 17, 10 ppm, 150 °C) while sensor film containing Au thickness of 21.6 nm exhibited a maximum sensitivity towards Cl2 (S = 89, 10 ppm, 200 °C)..

Kelvin probe studies of H2S exposed CuO:ZnO nanowires random networks

The Kelvin Probe (KP) studies have been carried out on CuO:ZnO nanowires random networks before and after H2S exposure. The results show that on exposure to H2S, the work function of the CuO:ZnO NWs increases by 200 meV. Using conductance and KP data, both the components of work function i.e. band bending and electron affinity has been obtained. It was observed that the affinity values changed substantially with H2S gas exposure.

Evaluation of compatibility of SnO 2 : CuO thin film based H 2 S sensor on LTCC substrates

Integrated SnO2: CuO thin-film based H2S gas sensor has been realized using low temperature co-fired ceramics (LTCC) tapes with heater and thermister buried inside the LTCC multilayer structure. The SnO2: CuO thin films are deposited on top of the structure. At operating temperature of 180°C, these films revealed sensing properties very similar to the reference films deposited on Alumina substrates. Further, effect of operating temperature on sensitivity was studied and sensor films on LTCC substrate were found to detect H2S with maximum sensitivity at a lower operating temperature of 100°C. The developed sensors have been tested for a period of more than one year and found to show a stable response.

ZnO nanowires coated with CuO films as highly sensitive H2S sensors

The gas sensing characteristics of ZnO nanowires (NWs) coated with different thickness of CuO film have been investigated. ZnO NWs were grown on Si/SiO2 by hydrothermal method and CuO films were deposited by thermal evaporation. It has been found that ZnO NWs exhibit characteristic n-type behavior upto a CuO thickness of 50 nm; whereas at higher thickness the samples show p-type behavior (typical of CuO). At a CuO thickness of 10 nm the sensitivity towards H2S was 500% more as compared to pure ZnO NWs films. In addition, the operating temperature was reduced to 200°C.

H2S DETECTION BY CuO NANOWIRES AT ROOM TEMPERATURE

Room temperature gas sensing properties of CuO nanowires synthesized by thermal oxidation of copper foils was studied in different configurations: (i) isolated nanowires aligned between two electrodes, (ii) as grown CuO foil consisting of nanowires and (iii) CuO nanowire films. Sensors were studied for response to different gases. Different sensors showed qualitatively different response on exposure to H2S. Isolated nanowires showed high sensitivity, (~200% for 10 ppm of gas) and fast response (30 s) and recovery times (60 s). In these samples, the resistance mainly decreased on exposure to H2S (though a small initial increase was observed). In CuO foils, resistance increased for low concentrations (5–10 ppm) but decreased at high concentrations. In the case of CuO nanowire films, resistance only increased on exposure of H2S (upto 400 ppm). Since CuO is a p-type semiconductor, on exposure to H2S an increase in resistance is expected due to oxygen adsorption related process. Decrease in resistance in some of the sensors was understood in terms of reaction of CuO with H2S resulting in the formation of CuS.

Growth And Gas Sensing Properties Of Dielectrophoretically Isolated CuO‐W18O49 Heterostructures

Hierarchical heterostructures consisting of W18O49 nanowires grown on CuO nanowires have been prepared and studied for their gas sensing properties. SEM images show that W18O49 initially grow as an shell over core CuO nanowire with protusion like branches whose thickness depends on oxygen partial pressure. These CuO:W18O49 structures were dielectrophoretically isolated and studied for their gas sensing properties. The results show potential of use of tailored hierarchical heterostructures for the fabrication of gas sensors.

Commercial H 2 s sensor based on SnO 2 :CuO thin films

In the present work, a commercial device for the detection of H2S using SnO2; CuO thin film as a sensing material has been demonstrated. A complete device consist of SnO2: CuO sensor thin film deposited on alumina substrate, teflon head in stainless steel housing containing the temperature control circuit with Pt-50 based heater and Pt-100 as reader, and a stand-alone monitor consisting of Data Acquisition & Control Board (DACB) and touch screen based human-machine interface (HMI) module. The monitor measures the change in resistance of sensor element on exposure to gas and displays the result in concentration (ppm). The monitor is also provided with a programmable alarm set point, touch switch to change between Normal/ Calibration Mode and provision to enter the historical logs like last sensor installation date, last sensor calibration date, last fault detail etc,.