The document summarizes Mohd Rehan Ansari's PhD research on synthesizing copper oxide (CuO) thin film sensors using spray pyrolysis for detecting NO2 gas. Key points: - CuO thin films were deposited on substrates using spray pyrolysis of copper chloride solutions at different concentrations and heated to produce solid particles. - XRD and SEM analysis showed the 0.15M solution produced well-crystallized CuO thin films with a rough net-like morphology providing more active sites. - Sensing tests found the 0.15M CuO thin film had the best response to NO2 gas at 200°C, with a sensitivity of 56% and ability to detect down to 5

1. Department of Electronic Science
South Campus, University of Delhi
Supervisor
Dr. P. Koteswara Rao
Presented By:
Mohd Rehan Ansari
PhD Scholar

2. Presentation Title
“Synthesis of CuO thin film sensor by Spray Pyrolysis method for NO2 gas
detection”

3. OUTLINES
INTRODUCTION
WHY METAL-OXIDE
METHODOLOGY
SYNTHESIS TECHNIQUES
STRUCTURAL STUDIES
CONCLUSION
APPLICATIONS

4. INTRODUCTION
 Toxic gases such as CO, CO2 and NO2 , these gases are contributing a large air pollution, effect on lungs
and respiratory system.
 Therefore gas sensing measurement for such toxic gases is very important.
 So far various materials like polymers, metal oxide, mixed metal oxide have been studied for the
detection of various oxidizing and reducing gases like CO, CO2, SO2, H2S etc.
 N-type semiconducting metal oxide like ZnO, TiO2, WO3, In2O3 have been explored to large extent as a
gas sensing material.
 CuO is one of the p-type semiconducting metal oxide with energy band gap of 1.3 eV to 2.1 eV and
melting point is 1326°C.
 In present investigation, we report study of NO2 gas sensing properties of CuO thin films deposited by
Spray Pyrolysis method for different solution concentration.

5. WHY METAL-OXIDE
Most effective as a gas
sensor
Low cost
High Stability
High Sensitivity
Suitable Morphology
Provide high surface area
to react with gas

6. METHODOLOGY
First precursor solution copper Chloride (CuCl2) is dissolved in Distilled
water.
Stirrer and ultrasonication for 3 hours for the homogeneity of the solution.
This homogeneous solution used for deposition of thin film.
Spray rate 1-20 ml/min.
The precursor must be dissolved in liquid, but must not react with it.
The final product must not dissolved in liquid, and must not react with the
liquid.

7. SPRAY PYROLYSIS
AN AEROSOL PROCESS THAT ATOMIZES A SOLUTION AND HEATS THE DROPLETS TO PRODUCE SOLID
PARTICLES
Simple and low cost
thin film deposition
process
Solution sprayed to
the heated substrate
Applicable to large area
High vacuum environment
not required
SYNTHESIS TECHNIQUE

8. Experimental-Setup

9.  The droplet resides on the surface as the solvent evaporates, leaving behind a solid that may further
react in the dry state.
 The solvent evaporates before the droplet reaches the surface and the dry solid impinges on the
surface where decomposition occur.
Droplets --> evaporation --> solute condensation --> decomposition & reaction --> sintering

10. STRUCTURAL STUDIES
X-Ray Diffraction
SEM
UV-Visible Spectra
Computer interfaced static gas sensing system

11. XRD
 Lower Concentration of 0.05 and 0.1
shows small hump at 20 degree to 30
degree indication the amorphous
nature of the material.
 For solution 0.15M small peaks at
35.44 degree and 38.66 degree
shows crystallinity of the sample.
 For solution 0.2M peaks at 35.44
degree and 38.66 degree shows the
exact crystallinity of CuO thin film.
 XRD pattern shows that
crystallinity of CuO thin film
increases with increase in the
solution concentration.

12. MORPHOLOGICAL STUDIES (SEM)
 It is seen from the SEM images
that net like rough morphology is
evolving from lower
concentration to higher
concentration.
 It is seen that highest roughness
is in the 0.15M solution.
 For 0.2M solution the surface
becomes smooth.

13. ABSORBTION SPECTRA
Figure shows the optical absorption
spectra with strong absorption peak
at approx. 415nm and 470nm
wavelengths.
Absorption peaks increases as
concentration of solution 0.015M to
O.15M but when concentration is
0.2M the peaks again down.

14. GAS SENSING MEASUREMENT
 When CuO thin films are subjected
to NO2 gas, the resistance of CuO is
decreases.
 The change in resistance of CuO
with respect to time is shown.
 The prepares samples are exposed
to 100 ppm of NO2 gas at 200℃.
 The Cu film with concentration
0.15M shows better response
towards 100 ppm of NO2 at 200℃
is observed.

15.  Further study of C-
0.15M sample
 This sample exposed in
different oxidising and
reducing gases.
 CuO thin film exhibit
excellent sensitivity of
NO2 gas and less
sensitive towards other
gases.

16.  Now C-0.15 sample of CuO thin film
exposed to 100 ppm of NO2 at
different operating temperatures.
 It is clear from graph that sensitivity
increases with increase in
temperature becomes maximum at
200℃ and again decreases at 250℃.
 Maximum sensitivity S=56% @
200℃
 Therefore this temperature is
treated as optimized temperature
for thin film of C-0.15 sample.

17.  The C-0.15 sample is exposed
to various concentration of
NO2 gas.
 It is clear from the graph
sensitivity increases with
increasing gas concentration.
Different Concentration of NO2 Gas

18. This graph shows the response
and recovery time of the C-
0.15M sample of CuO thin film.
The response time is observed to
be 20.57 sec and recovery time is
observed to be 3.93 min for 100
ppm of NO2.
The lowest detection level
reached by CuO thin films is 5
ppm which is worth considering
for the practical applications.
Response and Recovery Time

19. CONCLUSION
 The rough surface played major role in providing more active sites for gas
adsorption.
 Gas sensing measurement of CuO thin films has shows the optimum sensing at
200℃ with sensitivity of 56% is obtained for 0.15M solution.
 CuO thin film are selective towards NO2 gas, so effectively used for
detecting NO2 gas.
 CuO sensing material can detect 5 ppm of NO2 gas which is noteworthy.
 So we conclude that along with the n-type metal oxide semiconductors, p-
type metal oxide semiconductors are also efficient towards gas sensing
applications.

20. Applications
Automotive industry Environmental
Pollution Detector
Breath Analyser Medical field