Sprayed ZnO thin films for ethanol sensors

Chemically synthesized PbS Nano particulate thin films for a rapid NO2 gas sensor

“…The oxygen molecules adsorb on the surface and capture the electrons from the conduction band of the semiconductor which leads to its ionosorption in molecular (O − 2 ) and atomic (O − , O 2− ) forms [29]. The adsorption kinematics are explained as follows [30]: …”

ZnO: PVP Quantum Dot Ethanol Sensor

“…To study sensing [7][8][9][10][11][12][13][14][15][16][17][18], at first, ZnO quantum dot sample is heated in a chamber in air in the absence of test vapour when atmospheric oxygen is adsorbed chemically [18] …”

“…When the vapour is released by opening the enclosure of the sensing chamber, the reverse process takes place and ZnO quantum dot resistance regains its original value. Adsorption and desorption causing changes in sample resistance (that is gas sensing property) are absolutely surface phenomena [7,8,18]. Due to large surface area (S/V ratio) [5,13] of quantum dot, adsorption and desorption occur very fast resulting in sharp and fast changes in the resistance and thereby producing fast response with small changes in pre-heating temperature or concentration of vapour (ethanol).…”

“…At 300˚C the response is maximum. This is attributed to the availability of sufficient adsorbed ionic species of oxygen on ZnO surface which reacts most effectively and rapidly with ethanol molecules at this particular temperature [18] and produces large numbers of charge carriers (e -) resulting in rapid change (decrease) in sample resistance and hence higher is the response.At temperature higher than 300˚C, the mount of adsorbed (chemisorbed) oxygen is decreased with increasing temperature, but change in surface coverage in chemisorbed oxygen becomes smaller due to increased chemisorption rate of oxygen gas, leading to smaller response. A decrease in intrinsic sensor resistance in air (a larger electron concentration in air) with increasing operating temperature is another reason for lower response at temperatures higher than 300˚C.…”

“…ZnO quantum dots embedded in PVP) has been examined by exploring the variation of sample resistance with time in presence of ethanol vapour [7]. Vapour sensing property of semiconductor is purely a surface phenomenon [7][8][9][10][11][12][13][14][15][16][17][18][19]. That is why low dimensional specimen possessing large surface area are suitable for this purpose.…”