Using the electron spin resonance to detect the functional centers in materials for sensor devices

The paper reports and comments the results of several electron spin resonance investigations, performed on semiconductor oxides for gas sensing. The main aspects, related to the comparison between spectroscopic and electric data, are concerning on (i) the role of the oxide defects in interacting with the gas atmosphere; (ii) the origin of the sensing enhancement, which follows the doping of the oxide by transition metal ions; and (iii) the effects of different particle morphology and of the controlled particle shape on the sensing functionality. The electron spin resonance results have been associated, when possible, to those deriving from X-ray photoelectron spectroscopy, in order to investigate the electronic configuration of the transition metal centers. Special emphasis has been deserved to the oxide synthesis procedures, in several cases well related to the electrical response. The data have been drawn from several studies, performed in different time periods, and have been compared to suggest a possible common interpretation of the sensing mechanism, based on either electronic or morphological properties.