Blue- and red-shifts of V2O5 phonons in NH3 environment by in situ Raman spectroscopy

A layer of similar to 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 degrees C. When the layer is placed at 25 degrees 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 degrees 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 degrees C/100 degrees C when NH3 interacts with V2O5 surface. Using the traditional and quantitative gas sensor tester system, we find that the V2O5 sensor at 25 degrees C responds faster than at 100 degrees C up to 20 ppm of NH3 beyond which it responds faster at 100 degrees C than at 25 degrees 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 similar to 51 nm globular particles with similar to 20 nm pore size and physisorption/chemisorption principles have been employed in the explanation of the data presented.