Sugato Ghosh

Palladium-silver-activated ZnO surface: highly selective methane sensor at reasonably low operating temperature.

Metal oxide semiconductors (MOS) are well known as reducing gas sensors. However, their selectivity and operating temperature have major limitations. Most of them show cross sensitivity and the operating temperatures are also relatively higher than the value reported here. To resolve these problems, here, we report the use of palladium-silver (70-30%) activated ZnO thin films as a highly selective methane sensor at low operating temperature (∼100 °C). Porous ZnO thin films were deposited on fluorine-doped tin oxide (FTO)-coated glass substrates by galvanic technique. X-ray diffraction showed polycrystalline nature of the films, whereas the morphological analyses (field emission scanning electron microscopy) showed flake like growth of the grains mainly on xy plane with high surface roughness (107 nm). Pd-Ag (70-30%) alloy was deposited on such ZnO films by e-beam evaporation technique with three different patterns, namely, random dots, ultrathin (∼1 nm) layer and thin (∼5 nm) layer as the activation layer. ZnO films with Pd-Ag dotted pattern were found show high selectivity towards methane (with respect to H2S and CO) and sensitivity (∼80%) at a comparatively low operating temperature of about 100°C. This type of sensor was found to have higher methane selectivity in comparison to other commercially available reducing gas sensor.

Linear regression based statistical approach for detecting proportion of component gases in manhole gas mixture

The present article proposes the issues in designing an intelligent recognizer for detecting proportion of component gases in manhole gas mixture. The major components found in manhole gas mixture are Hydrogen Sulfide (H2S), Ammonia (NH3), Methane (CH4), Carbon Dioxide (CO2), Nitrogen Oxide (NOx), and Carbon Monoxide (CO). The manhole gas is formed after the decomposition of waste products, domestic garbage etc. into the sewer pipelines which are built for exhausting these waste products out of our cities and towns. The manholes are built across these pipelines for cleaning purpose. Thus safety for the people working in this field is a matter of concern because all the above mentioned gases are harmful gases and they are potent to loss of human lives. Also detection of these gas components is of primary concern today as because a short exposure of these components with human physiology results endanger to their lives. So our focus is on developing an intelligent gas recognition system which can recognize multiple gases simultaneously. A gas sensor array is an array of sensors, consisting of two or more electrical type semiconductor gas sensors. Response of electrical type semiconductor gas sensors in presence of gases are either the change in resistance or change in voltage of the sensor. At an instant a gas sensor array contains as many sensors as many individual gases we are targeting to detect. Use of multiple gas sensors and presence of multiple gases together results cross-sensitivity. The cross-sensitivity is an overlapping effect of one gas on another sensor. We adopt linear regression based statistical approach to deal with issues of simultaneous detection of multiple gases notwithstanding cross-sensitivity issue.

A Novel Neuro Simulated Annealing Algorithm for Detecting Proportion of Component Gases in Manhole Gas Mixture

In present article we are exploring the design issues in development of an intelligent gas recognizer for detecting proportion of component gases in manhole gas mixture. Principally, the gas components found in manhole gas mixture are, Ammonia (NH3), Carbon Dioxide (CO2), Carbon Monoxide (CO), Hydrogen Sulfide (H2S), Methane (CH4), and Nitrogen Oxide (NOx). These gases are harmful for human health. We are focusing on the development of an intelligent sensory system which can detect the extent poisonous gases found in manhole gas mixture. A gas sensor array is used for this purpose. Sensor responses are cross-sensitive, because multiple gas sensors are simultaneously used to detect multiple gases. The cross-sensitivity is an overlapping effect of one gas on sensor of another, inducing thereby difficulty in sensing mechanism all together. We resort to artificial neural network (ANN) and simulated annealing (SA) algorithm for the development intelligent sensory system. The SA algorithm is used to search out optimized combination of synaptic weights for the ANN trained for sensing proportion of constituent gases.

Application of Real Valued Neuro Genetic Algorithm in Detection of Components Present in Manhole Gas Mixture

The article deals with the implementation of an Intelligent System for detection of components present in manhole gas mixture. The detection of manhole gas is important because the manhole gas mixture contain many poisonous gases namely Hydrogen Sulfide (H 2 S), Ammonia (NH 3), Methane (CH 4), Carbon Dioxide (CO 2), Nitrogen Oxide (NO x ), and Carbon Monoxide (CO). A short exposure to any of these components with human beings endangers their lives. A gas sensor array is used for recognition of multiple gases simultaneously. At an instance the manhole gas mixture may contain many hazardous gas components. So it is wise to use specific gas sensor for each gas component in the gas sensor array. Use of multiple gas sensors and presence of multiple gases together result a cross-sensitivity. We implement a real valued neuro genetic algorithm to unravel the multiple gas detection issue.

Electrochemical synthesis of p-CuO thin films and development of a p-CuO/n-ZnO heterojunction and its application as a selective gas sensor

p-CuO thin films have been synthesized on indium tin oxide (ITO)-coated glass substrates and on ZnO/ITO-coated glass substrates using a new, simple, cost-effective electrochemical technique (galvanic deposition) at room temperature. X-ray diffraction (XRD) studies of the films show a monoclinic phase of CuO, and UV-vis spectroscopy of the CuO/ITO film shows an indirect band-gap energy of about 1.85 eV. The surface morphology of CuO thin film consists of a c-axis-grown regular macroporous network structure with deep cavities surrounded by thin solid walls, which are suitable for gas trapping and sensing. Current–voltage characteristics of the formed p-CuO/n-ZnO film show good rectifying behavior. At 1 V reverse bias, the leakage current was as low as 2 × 10−9 A compared to a current of 1.2 × 10−7 A at the same forward bias, resulting in a forward-to-reverse current ratio of about 60. The ideality factor of the diode obtained was quite high, at about 9.5. The frequency dependence of the small signal AC response in both Rp–Cp and Rs–Cs mode of the fabricated heterojunction were measured at a reverse bias of 1.5 V. In the presence of 10 000 ppm gas exposure for gases, including CH4, H2S and CO, frequency-dependent changes in AC responses are different for different gases. The variation of the reactance of the fabricated device shows different behaviour with exposure to different types of gases. The minimum in reactance occurring at different frequencies for different gases indicates the selectivity of the device for gas sensing.

Sensor array for manhole gas analysis

A sensor array consisting of four individual gas sensors (methane, carbon dioxide, carbon monoxide, hydrogen sulfide, ammonia) has been developed for analysis of individual gases from a mixture of various explosive and toxic gases. Manhole gas of different areas has been collected and analyzed in lab by chemical process. The sensor array has been constructed by using different gas sensors like Methane, Carbon monoxide, Carbon dioxide, Hydrogen sulfide and Ammonia which are commonly available in manhole gas mixture. For cross sensitivity of the sensors an intelligent system is being developed to find out the actual concentration of gas from a gas mixture.

ZnO/γ-Fe2O3 Charge Transfer Interface toward Highly Selective H2S Sensing at a Low Operating Temperature of 30 °C

ZnO/γ-Fe2O3 heterostructure has been deposited in the form of thin films using a single step facile electrochemical technique. Considering the unique properties of both ZnO and γ-Fe2O3 toward the sensing of reducing gases, the concept of forming a heterostructure between them has been conceived. The structural characterization of the deposited material has been performed using X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy, which revealed a flowerlike morphology with the coexistence of both ZnO and γ-Fe2O3 leading to the formation of a heterostructure. The material showed excellent sensing properties toward the selective detection of H2S at room temperature (30 °C) among the three test gases, namely, CH4, H2S, and CO. The effect of relative humidity was also studied to have an idea about the performance of the device under a real situation. The results are promising and better than those of many commercially available sensors. The room temperature selective detection will help in facile fabrication of portable gadgets.

Enhanced hydrogen sensitivity and selectivity of ZnO-SnO 2 based sensor

We report on the fabrication of pure Zinc Oxide (ZnO) and composite ZnO-SnO2 material based H2 sensor using a simple chemical route. The surface morphology and crystal structure of the samples were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The gas sensing performance of the sensor to Hydrogen in dry air was studied using current-voltage measurements. Selectivity of the sensor against carbon mono-oxide is studied. The obtained result demonstrates a promising approach in the development of low cost selective hydrogen sensor.