A layer of ~30 nm V2O5/100 nm-SiO2 on Si was employed in the in situ Raman spectroscopy
in the presence of NH3 effluent from a thermal decomposition of ammonium acetate salt with
the salt heated at 100 °C. When the layer is placed at 25 °C, we observe a reversible red-shift of
194 cm−1 V2O5 phonon by 2 cm−1 upon NH3 gas injection to saturation, as well as a reversible
blue-shift of the 996 cm−1 by 4 cm−1 upon NH3 injection. However when the sensing layer is
placed at 100 °C, the 194 cm−1 remains un-shifted while the 996 cm−1 phonon is red-shifted.
There is a decrease/increase in intensity of the 145 cm−1 phonon at 25 °C/100 °C when NH3
interacts with V2O5 surface. Using the traditional and quantitative gas sensor tester system, we
find that the V2O5 sensor at 25 °C responds faster than at 100 °C up to 20 ppm of NH3 beyond
which it responds faster at 100 °C than at 25 °C. Overall rankings of the NH3 gas sensing
features between the two techniques showed that the in situ Raman spectroscopy is faster in
response compared with the traditional chemi-resistive tester. Hooke’s law, phonon confinement
in ~51 nm globular particles with ~20 nm pore size and physisorption/chemisorption principles
have been employed in the explanation of the data presented.