Abstract
The most promising and utilized chemical sensing materials, WO3 and SnO2 were characterized by means advanced synchrotron based XPS, UPS, NAP-XPS techniques. The complementary electrical resistance and sensor testing experiments were also completed. A comparison and evaluation of some of the prominent and newly employed spectroscopic characterization techniques for chemical sensors were provided. The chemical nature and oxidation state of the WO3 and SnO2 thin films were explored at different depths from imminent surface to a maximum of 1.5 nm depth from the surface with non-destructive depth profiling. The adsorption and amount of chemisorbed oxygen species were precisely analyzed and quantified as a function of temperature between 25–400 °C under realistic operating conditions for chemical sensors employing 1–5 mbar pressures of oxygen (O2) and carbon monoxide (CO). The effect of realistic CO and O2 gas pressures on adsorbed water (H2O), OH− groups and chemisorbed oxygen species () and chemical stability of metal oxide surfaces were evaluated and quantified.
Highlights
The sheer size of the global gas sensor market valued at $2.05 billion last year and expected to increase up to $3.7 billion by 2025
NAP-X-ray photoelectron spectroscopy (XPS) was utilized with the experience and knowledge extracted from preceding steps in order to quantify and understand the target gas and semiconducting metal oxide (SMO) sensor surface during an interaction under realistic working conditions for chemical sensors
During the near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) measurements, heating was accomplished by electron beam heating from the back of the samples and the temperature measurement was completed with the thermocouple attached to a metal sample holder
Summary
The sheer size of the global gas sensor market valued at $2.05 billion last year and expected to increase up to $3.7 billion by 2025. Electron paramagnetic resonance (EPR) is capable of detecting the paramagnetic oxygen ions such as OH− , O− , O2− on metal oxides, this technique requires temperatures as low as −200 ◦ C, multiple treatment of the sample surface in addition to the fact that information collected is representative of bulk rather than a surface analysis. Provides an option for in-situ analysis under realistic operation conditions relevant to semiconducting metal oxide (SMO) based chemical gas sensors in combination with high surface sensitivity and quantitative analysis capability. NAP-XPS was utilized with the experience and knowledge extracted from preceding steps in order to quantify and understand the target gas and semiconducting metal oxide (SMO) sensor surface during an interaction under realistic working conditions for chemical sensors. It was reported that upon exposure to reducing gases of H2 S and SO2 , the p-type response was observed instead of the typical expected n-type response [3,20]
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