Spectroscopic Understanding of SnO and WO Metal Oxide Surfaces with Advanced Synchrotron Based; XPS-UPS and Near Ambient Pressure (NAP) XPS Surface Sensitive Techniques for Gas Sensor Applications under Operational Conditions.

The most promising and utilized chemical sensing materials, WO and SnO 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 WO and SnO 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 (O) and carbon monoxide (CO). The effect of realistic CO and O gas pressures on adsorbed water (HO), OH groups and chemisorbed oxygen species ( O 2 ( a d s ) - ,   O ( a d s ) ,   - O 2 ( a d s ) 2 - ) and chemical stability of metal oxide surfaces were evaluated and quantified.