Blue- and red-shifts of V₂O₅phonons in NH₃environment byin situRaman spectroscopy

Abstract

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.

Application of Raman Spectroscopy to Working Gas Sensors: From in situ to operando Studies

“…Despite the potential of Raman spectroscopy for studying gas sensors at work, only a few In situ Raman studies on metal oxide gas sensors have been published [21,22,23,24,25,26,27,28,29,30,31,32], which in part were done with simultaneous recording of the resistance [22,23,24]. For nanocrystalline SnO 2 [22] and CuO/SnO 2 [23] at 100 °C, upon exposure to 300 ppm H 2 S, the reversible formation of sulfide species (SnS x , Cu 2 S) was reported, which was correlated with the simultaneously measured decrease in resistance ( operando -pellet approach).…”

“…Despite the potential of Raman spectroscopy for studying gas sensors, only a small number of studies have been published, compared with other characterization techniques (e.g., IR spectroscopy). Previous work published in the context of metal-oxide gas sensors ranges from the (ex situ) use of Raman characterization [13,14,15,16,17,18,19,20] to In situ Raman studies [21,22,23,24,25,26,27,28,29,30,31,32] and operando Raman studies [5,6,33,34,35,36], part of which were done in combination with operando UV-Vis spectroscopy [6,35]. In these studies typical gas sensor materials, such as SnO 2 , WO 3 , and In 2 O 3 were investigated towards a variety of target gases, e.g., H 2 S, CH 4 , H 2 , CO, NH 3 , NO 2 , ethanol (EtOH), and acetaldehyde (acetald.).…”

Micro Nano Manufacturing Methods for Chemical, Gas and Bio Sensors, Water Purification and Energy Technologies

“…X-ray diffraction spectroscopy which is commonly used technique for characterization of crystalline materials provides information about elemental analyses such as structures, phases and preferred crystal orientations. Physical measurements like average particle size of material, homogeneous and inhomogeneous strain and crystal defect could also be estimated from the data collected using XRD technique [8][9][10][11]. The HRTEM approach has been severally employed in sensors material research to unveil material's crystallographic structures at an atomic scale [8][9].…”

“…The HRTEM approach has been severally employed in sensors material research to unveil material's crystallographic structures at an atomic scale [8][9]. The scanning electron microscope (SEM), scanning tunneling microscope (STM) and atomic force microscope (AFM) are important for all surface structure studies such as morphology, particles distribution, nanoscale topography and surface roughness [9][10][11][12][13]. These are also essential properties needed to be analyzed for chemical, gas and bio sensors devices fabrication.…”

“…Other properties necessary to be investigated for these types of application include quantitative analysis of the material's elemental composition and chemical state. This study is often achieved using X-ray photoelectron spectroscopy (XPS) [9][10][11]. The adsorption ability and properties of the sensors materials are usually evaluated using the popular Brunauer-Emmett-Teller (BET) technique which relies on the physical adsorption (physisorption) of gas molecules on the surface of solid-state materials.…”