Sarin-simulant detection by phthalocyanine/palladium structures: From modeling to real sensor response

Abstract

The full recognition of a sensing mechanism is a key issue in the gas sensors investigation. Therefore within presented work we proposed the new approach for the comprehensive sensing mechanism description: theoretical analysis and experimental investigation of the sensing structure. The object of our study was metal-free phthalocyanine/palladium structure utilized in sarin-simulant dimethyl methylphosphonate (DMMP) detection at room temperature. In the theoretical evaluation semi-empirical simulations have been performed revealing bonding energies between sensing materials and DMMP molecule. Different variants of metallic overlayer were considered in the modeling including bare palladium and palladium oxide (PdO). The results of the simulations indicated physisorption as a main sensing mechanism, especially enhanced in presence of PdO phase. Theoretical estimation of electron affinity and band bending changes during gas adsorption was conducted indicating strong impact of surface dipole effect. The experimental investigations was based on X-ray photoelectron spectroscopy (XPS) chemical characterization of DMMP exposed surface supported by atomic force microscopy imaging. The XPS results coincided with theoretical statements demonstrating no traces of chemical interaction with analyzed gas. Simultaneously, the presence of PdO was corroborated. Finally, the real sensor response was analyzed confirming outcome of the theoretical simulations and results of the experimental investigations.