Arijit Chowdhuri

Response speed of SnO2-based H2S gas sensors with CuO nanoparticles

CuO nanoparticles on sputtered SnO2 thin-film surface exhibit a fast response speed (14 s) and recovery time (61 s) for trace level (20 ppm) H2S gas detection. The sensitivity of the sensor (S∼2.06×103) is noted to be high at a low operating temperature of 130 °C. CuO nanoparticles on SnO2 allow effective removal of excess adsorbed oxygen from the uncovered SnO2 surface due to spillover of hydrogen dissociated from the H2S–CuO interaction.

H2S gas sensing mechanism of SnO2 films with ultrathin CuO dotted islands

H2S gas interaction mechanisms of sputtered SnO2 and SnO2–CuO bilayer sensors with a varying distribution of the Cu catalyst on SnO2 are studied using Pt interdigital electrodes within the sensing film. Sensitivity to H2S gas is investigated in the range 20–1200 ppm. Changes induced on the surface, the SnO2–CuO interface, and the internal bulk region of the sensing SnO2 film upon exposure to H2S have been analyzed to explain the increasing sensitivity of three different sensors SnO2, SnO2–CuO, and SnO2 with CuO islands. SnO2 film covered with 0.6 mm diameter ultrathin (∼10 nm) CuO dots is found to exhibit a high sensitivity of 7.3×103 at a low operating temperature of 150 °C. A response speed of 14 s for 20 ppm of H2S, and a fast recovery time of 118 s in flowing air have been measured. The presence of ultrathin CuO dotted islands allow effective removal of adsorbed oxygen from the uncovered SnO2 surface due to spillover of hydrogen dissociated from the H2S–CuO interaction, and the spillover mechanism is ...

Fast response H2S gas sensing characteristics with ultra-thin CuO islands on sputtered SnO2

Response characteristics of undoped SnO2 are compared with two different types of Cu–SnO2 thin film bilayer structures: (a) SnO2 surface covered by an ultra-thin (� 10 nm) Cu layer, and (b) SnO2 surface covered with thin Cu dots, and the bilayers were annealed in air/O2 to form CuO. Response speed for sensing H2S gas concentration in the range 20–1200 ppm was measured using platinum (Pt) inter-digital electrodes underneath the SnO2 film. SnO2 film with CuO dotted islands is found to exhibit a high sensitivity of 7:4 � 10 3 at 150 8C, and a fast response time of 15 s to 20 ppm of H2S, and the recovery time is approximately 118 s. The high sensitivity and the fast response are shown to be primarily due to a dominant role played by the spill-over mechanism. # 2003 Elsevier Science B.V. All rights reserved.

Enhanced catalytic activity of ultrathin CuO islands on SnO/sub 2/ films for fast response H/sub 2/S gas sensors

H/sub 2/S gas-sensing properties of a novel SnO/sub 2/-CuO structure consisting of ultrathin (/spl sim/10 nm) CuO dotted islands (600 /spl mu/m diameter) on 120-nm thick, sputtered SnO/sub 2/ film are compared with a pure SnO/sub 2/ and a SnO/sub 2/-CuO bilayer sensor. The SnO/sub 2/-CuO-dotted sensor exhibited a high sensitivity of 7.3/spl times/10/sup 3/ at a low operating temperature of 150/spl deg/C. A fast response time of 14 s for 20 ppm of H/sub 2/S gas and a recovery time of 118 s under flowing air have been measured. The electronic interaction due to modulation of the space charge regions between the distributed p-type CuO islands on the n-type SnO/sub 2/ thin-film surface and the presence of adsorbed oxygen on the SnO/sub 2/ support have been analyzed. Dissociated hydrogen available from the CuO-H/sub 2/S interaction spills over and its chemical interaction with the adsorbed oxygen on the SnO/sub 2/ surface is found to play a dominant role in the observed fast response characteristics.

Enhanced LPG response characteristics of SnO 2 thin film based sensors loaded with Pt clusters

In the present study, rf sputtered SnO2 thin films (90 nm thick) loaded with clusters of ultra-thin (8 nm) metal catalysts (Pt, Ag, Ni, Pb, Al, Pd) are investigated for LPG detection. It is noted that SnO2 film loaded with Pt catalyst clusters exhibits enhanced response (~ 750) to 200 ppm of LPG at a relatively low operating temperature (210degC) with a fast response time of 100s. Variation of thickness of Pt clusters in the nanoscale range (2 to 20 nm) is seen to significantly influence the sensor response characteristics. Enhanced performance is observed for SnO2 thin films loaded with 10 nm thick platinum clusters that exhibited a high response (~ 5 times 103) at an operating temperature of 220degC. Preliminary results indicate the potential application of prepared sensor structure of Pt clusters (10 nm)/SnO2 (90 nm)/IDE/glass substrate for efficient detection of LPG at relatively low temperature.

Influence of CuO catalyst in the nanoscale range on SnO2 surface for H2S gas sensing applications

The dispersal of CuO catalyst on the surface of the semiconducting SnO2 film is found to be of vital importance for improving the sensitivity and the response speed of a SnO2 gas sensor for H2S gas detection. Ultra-thin CuO islands (8 nm thin and 0.6 mm diameter) prepared by evaporating Cu through a mesh and subsequent oxidation yield a fast response speed and recovery. Ultimately nanoparticles of Cu (average size = 15 nm) prepared by a chemical technique using a reverse micelle method involving the reduction of Cu(NO3)2 by NaBH4 exhibited significant improvement in the gas sensing characteristics of SnO2 films. A fast response speed of ∼14 s and a recovery time of ∼60 s for trace level ∼20 ppm H2S gas detection have been recorded. The sensor operating temperature (130° C) is low and the sensitivity (S = 2.06 × 103) is high. It is found that the spreading over of CuO catalyst in the nanoscale range on the surface of SnO2 allows effective removal of excess adsorbed oxygen from the uncovered SnO2 surface due to spill over of hydrogen dissociated from the H2S-CuO interaction.

Enhanced catalytic activity of ultra-thin CuO islands on SnO/sub 2/ films for fast response H/sub 2/S gas sensors

Trace level detection of H/sub 2/S is of immense interest in diverse fields ranging from gas and oil exploration to dentistry. In the present work 0.12 /spl mu/m thick sputtered SnO/sub 2/ films, and a novel SnO/sub 2/-CuO bilayer structure consisting of ultra thin (/spl sim/10 nm) CuO dotted islands (0.6 mm diameter) are investigated for H/sub 2/S gas sensing. With the SnO/sub 2/-CuO-dotted sensor, a high sensitivity of 7.3/spl times/10/sup 3/ at a low operating temperature of 150/spl deg/C is obtained with a fast response time of 14 seconds for 20 ppm of H/sub 2/S gas and a recovery time of 118 seconds under flowing air have been measured. The electronic and chemical interactions of the CuO catalyst layer on SnO/sub 2/ in the presence of H/sub 2/S have been analyzed in the light of space charge regions formed due to distributed p-type CuO islands on the n-type SnO/sub 2/ thin film surface. Dissociated hydrogen available from the CuO-H/sub 2/S interaction spills over and is found to be primarily responsible for the observed fast response characteristics.

Enhanced oxygen adsorption activity by CuO catalyst clusters on SnO 2 thin film based sensors

Resistance characteristics of thin film sensors based on uncoated SnO₂, SnO₂ with CuO overlayer and SnO₂ with CuO dotted clusters are compared in three different backgrounds of air, oxygen and vacuum. Measurements for the three sensor configurations are carried out as a function of temperature. The novel dispersal method of CuO catalyst in the form of dotted clusters is seen to enhance the oxygen adsorption activity on surface of SnO₂ thin film sensors. Conversion of molecular oxygen (O₂ ^-) to atomic oxygen (O^-) is shown to reduce the concentration of charge carriers in the conduction band of SnO₂ film. Co-existence of a greater amount of adsorbed oxygen on the SnO₂ film surface in conjunction with modulation of the space-charge region at the CuO-SnO₂ interface are attributed to influence the resistance of the sensor structures under reducing gas.

Fabrication of SnO 2 thin film based electronic nose for industrial environment

Nowadays e-nose is attracting the attention of many researchers due to its wide spread applications. The most important application falls in the category where human beings cannot afford to risk smelling toxic gases. Other important applications are continuous monitoring of pollutant and explosive gases, in oil and natural gas exploration, possible predictions of volcanic eruptions, medical applications, etc [1]. The fast paced technology has helped develop sophisticated devices that have led to miniaturization of electronic nose with advanced capabilities. This work reports on the performance of an array of four different sensor structures, using tin oxide as the base material, developed in order to detect (200 ppm) of LPG, methane, ammonia and H2S. The array, developed is composed of SnO2 thin films loaded with nanoclusters of four different catalysts namely Platinum, Palladium, Silver and Copper oxide by sputtering or evaporation technique. A good classification, success rate and prediction have been achieved for different target gases.

Enhanced photo-response of thermally treated Zinc oxide ultra-violet photon detector with furnace method and pulsed laser irradiation

Ultra-Voilet (UV) photodetector is fabricated by rf magnetron sputtered ZnO thin films of different thickness (50 to 400 nm). ZnO film with thickness 100nm is found to exhibit enhanced UV photo response in comparison to that observed in the thicker films and is thermally treated by two different techniques, one by furnace method and another by pulsed laser irradiation. In the furnace method, the as-grown 100nm ZnO thin film is post annealed in a range of temperature from 100°C to 400°C for 1hr. The Ion/Ioff ratio of furnace annealed ZnO film of thickness 100 nm at 300°C is found to be (7 × 103) with fast response time of 50 ms in comparison to other annelead films. In the second method, as-grown 100nm ZnO film is irradiated by pulsed Nd:YAG laser corresponding to both fundamental wavelength (1064 nm) and forth harmonics (266 nm) to modify its defects profiles. Laser (λ=266 nm) irradiated detector exhibits enhanced response (3.7 × 104) with fast response speed (30ms), showing its promising application for detection of low intensity UV photons.