Palash Kumar Basu

Schottky Junction Methane Sensors Using Electrochemically Grown Nanocrystalline-Nanoporous ZnO Thin Films

Nanocrystalline-nanoporous ZnO thin films were prepared by an electrochemical anodization method, and the films were tested as methane sensors. It was found that Pd-Ag catalytic contacts showed better sensing performance compared to other noble metal contacts like Pt and Rh. The methane sensing temperature could be reduced to as low as 100°C by sensitizing nanocrystalline ZnO thin films with Pd, deposited by chemical method. The sensing mechanism has been discussed briefly.

A Suspended Low Power Gas Sensor With In-Plane Heater

An ultralow power suspended gas sensor with in-plane heater and nano gap sensor electrodes is presented. The heater and sensing electrodes, separated by 1-

Methane Detection by MIM Sensor Devices Based on Nano ZnO Thin Films Obtained by Sol-Gel and by Anodization: A Comparative Study

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MEMS based nano crystalline zinc oxide methane gas sensors

air gap, are processed using single lithography step with standard micro-fabrication techniques. Controlled electromigration is used to create a nanogap in the middle of the sensing electrode. The sol–gel grown ZnO is dispensed using a picoliter dispenser to bridge the nanogap electrode, created by electromigration, to get required metal oxide film as a sensing element. The gap between the electrode and heater is optimized by electrothermal simulation to obtain desired temperature profile on ZnO. The resulting device exhibits excellent sensing performance for hydrogen (~86% at 20 ppm) at 0.5 mW. A detailed characterization was carried out to analyze the performance of the device. This unique, in-plane structure is superior compared with the conventional out of plane structure in terms of the power efficiency and ease of processing. [2016-0162]

Structural stability of coplanar 1T-2H superlattice MoS2 under high energy electron beam

Amongst various gas sensor structures developed so far probably the least investigated one is the Metal- (Active) Insulator-Metal or (MIM) structure. It has been reported that the vertical electron transport mechanism of this structure offers high response with fast response and recovery for gases like H2 and methane compared to the conventional planar configuration. In this paper we report on the comparative performances of two kinds of MIM sensors based on nanocrystalline-nanoporous ZnO as the active sensing layer derived by sol-gel and by the UV assisted electrochemical anodization method respectively. The sensor structures based on Pd-Ag (26%)/ZnO/Zn were investigated in presence of five methane concentrations (0.01, 0.05, 0.1, 0.5 and 1.0%) and in the temperature range 150°C to 300°C. The electrochemically developed ZnO showed superior performance in terms of operating temperature, response magnitude, response time and recovery time. Moreover, it showed response to much lower concentrations (like 0.01% and 0.05 %) of methane that could not be detected by the sol-gel derived sensor. The possible reason for the superiority of the electrochemically grown ZnO compared to the sol-gel derived one was shown to be the significantly lower grain size and appreciably high porosity. But, in spite of its promising performance the electrochemically developed MIM sensor has no selection of the substrate and so it is not compatible to the standard IC technology. It leads to its restricted use to develop only the stand-alone sensor devices. On the other hand, sol-gel derived MIM device is based on the Si substrate. So, it is IC compatible and is suitable for the integrated sensor platform.

Sensitivity characteristics of Ag doped BaTiO 3 -CuO mixed oxide as carbon-dioxide sensor

Detection and estimation of methane gas for continuous environmental monitoring is of growing importance for prevention of explosions inside coalmines and asphyxiations in cramped localities and green house warning. For continuous monitoring in field locations, low power and sometimes low temperature operation of methane sensors are essential. This could be achieved by employing MEMS structure for low power operations and nanocrystalline Zinc oxide for low temperature activation. The present communication reports the design, fabrication, characterization and laboratory testing of MEMS based nano ZnO methane sensors. Power consumption range 100-150 mW and temperature range of 150-200degC have been achieved with moderately high (Gt50%) sensitivity and response time (les15 sec). Further improvement is expected through optimization.

Surface Modified Nanoporous Materials for Hydrogen Sensing

Coplanar heterojunctions composed of van der Waals layered materials with different structural polymorphs have drawn immense interest recently due to low contact resistance and high carrier injection rate owing to low Schottky barrier height. Present research has largely focused on efficient exfoliation of these layered materials and their restacking to achieve better performances. We present here a microwave assisted easy, fast and efficient route to induce high concentration of metallic 1T phase in the original 2H matrix of exfoliated MoS2 layers and thus facilitating the formation of a 1T-2H coplanar superlattice phase. High resolution transmission electron microscopy (HRTEM) investigations reveal formation of highly crystalline 1T-2H hybridized structure with sharp interface and disclose the evidence of surface ripplocations within the same exfoliated layer of MoS2. In this work, the structural stability of 1T-2H superlattice phase during HRTEM measurements under an electron beam of energy 300 keV is reported. This structural stability could be either associated to the change in electronic configuration due to induction of the restacked hybridized phase with 1T- and 2H-regions or to the formation of the surface ripplocations. Surface ripplocations can act as an additional source of scattering centers to the electron beam and also it is possible that a pulse train of propagating ripplocations can sweep out the defects via interaction from specific areas of MoS2 sheets.

Fast response methane sensor using nanocrystalline zinc oxide thin films derived by sol–gel method

Ag doped BaTiO3-CuO mixed oxide thin films are evaluated for their carbon-dioxide sensing characteristics. The metal oxide films of different thicknesses are deposited on oxidized p type Si <;100> substrate by RF Sputtering. Sensing characteristics for different CO2 concentration, (300 ppm - 1000 ppm) are obtained for different operating temperatures, (100° C - 400° C). Optimum temperature for maximum sensitivity is found to be 250° C. The effect of annealing on sensing properties is also evaluated. The unannealed films give better sensitivity than that of annealed films. Response time and recovery time are also calculated.

The superior performance of the electrochemically grown ZnO thin films as methane sensor

Nanoporous silicon and nanoporous ZnO were prepared by the electrochemical anodization of crystalline Si and Zn substrate. To passivate the defect states (arise due to the nano structure of the PS and ZnO thin film and introduce a barrier for the current conduction) and to improve the gas sensitivity the porous silicon and nano crystalline ZnO surfaces were modified by PdCl2 solution. The Pd modified sensors having Pd-Ag (26%)/PS/Si/Al (MIS) and Pd-Ag (26%)/ZnO/Zn (MIM) device structures were investigated in different hydrogen concentrations (0.01, 0.05, 0.1, 0.5 and 1.0%) regarding optimum biasing voltage and temperature. Both the sensor showed superior performance in terms of operating temperature, response magnitude, response time and recovery time.