СЕКЦИЯ 6. «ЗОЛЬ-ГЕЛЬ МАТЕРИАЛЫ ДЛЯ ПРИМЕНЕНИЙ В ОБЛАСТИ
ОХРАНЫ ПРИРОДЫ, СЕЛЬСКОГО ХОЗЯЙСТВА И БИОМЕДИЦИНЫ»
98
SELECTIVE ACETONE SENSOR BASED ON SPRAYED CU-DOPED INDIUM OX-
IDE THIN FILMS
Pramod N.G.
1
, Pandey S.N.
2
1. Faculty of Basic Science, Sharda University, Andijan, 170100, Uzbekistan
2. Department of Physics, Motilal Nehru National Institute of Technology, Allahabad-211004,
India.
Cu-doped (1, 1.5 and 2 at.%) In
2
O
3
films were grown on cleaned glass substrates by spray py-
rolysis. The influence of Cu doping on the structural, optical, electrical and acetone sensing of In
2
O
3
films has been carried out. The films were characterized by XRD for structural analyses and UV-Vis
spectroscopy for optical data retrieval. It is observed
that Cu doping into In
2
O
3
reduces the value of the
average crystallite size and the optical transmittance in the visible region. The electrical resistivity is
also found to vary with Cu doping throughout the temperature range 25-300°C. Further, the films have
been tested for acetone vapor to check their suitability to detect the presence of the same in air. The
1.5 at.% Cu:In
2
O
3
film exhibits the highest sensitivity for acetone at a concentration of 60
ppm at a
temperature of 275°C. Also, the response is found to be selective in nature for the detection of acetone
vapor.
We have tested four samples (undoped, 1at% , 1.5at% & 2at% Cu-doped Indium oxide films) re-
sponse characteristics as a function of the operating temperatures (200-300°C) at four different acetone
vapor concentrations viz. 20, 40, 60 and 80 ppm in air. From the response characteristics, it is clear that
the 1.5 at.% Cu-doped In
2
O
3
thin film has the highest response for acetone vapor in comparison with oth-
er films under study. A response of 92% is recorded for this sample at a concentration of 60 ppm at an
operating temperature of 275°C. This sample has the smallest crystallite size, which leads to an increase
in the surface area of the film exposed to the atmosphere, resulting in more adsorption of oxygen species
on the film surface and thus creating a number of sensing sites. The dopant ion creates some vacant sites
into the host In
3+
lattice which causes more oxygen from the atmosphere to attach and interact with the
conduction electrons, thus converting into active sites. Surface roughness as well as the presence of voids
in the film also contributes to the enhancement in the sensor response since they result in larger contact
area with the gaseous species. The rapid increase in response is attributed to the availability of sufficient
adsorbed oxygen species on the film surface as well as the enhanced chemical activation of acetone mol-
ecules.
For any gas sensor, the study of selectivity is an important factor to determine its use in vari-
ous technological and industrial applications. In this regard, the undoped and the Cu-doped thin films
have been tested for different Volatile Organic Compound (VOC) gases to check their selective na-
ture. We present the response characteristics of the 1.5 at.%
Cu-doped In
2
O
3
thin film sample. The
concentration of the test gas was fixed at 60 ppm, and the sensors were operated at a temperature of
275°C. Among all the test gases, it can be inferred that the response to acetone is relatively quite high
and selective in nature for the 1.5 at.% Cu:In
2
O
3
thin film.It is evident that the response time is least
for acetone. The response time is found to be about 2.5 minutes in case of methanol, 3 minutes for eth-
anol vapor and 3.5 minutes for propan-2-ol. It is observed that the response time increases with the
increase
in the molecular
weight of the test gas, with methanol vapor having the least molecular
weight and propan-2-ol, possessing the highest. A higher response time for formaldehyde may be be-
cause of the influence of the chemical reactivity of the formaldehyde vapor with the adsorbed oxygen
species on the oxide film surface.
A comparison of acetone sensors fabricated on various metal oxides has been presented. It is
very much evident that 1.5 at.% Cu-doped indium oxide thin film grown by spray pyrolysis is a prom-
ising material for the selective detection of acetone as it exhibits a higher sensor response
towards ace-
tone vapor at a low concentration of 60 ppm when operated at a temperature of 275°C.
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