Mechanism of oxygen response in carbon-based sensors

The mechanism of oxygen response in several newly synthesized oxygen-sensit ive chars was studied with the use of EPR spectroscopy. The results suggest that the compounds contain two basic types of paramagnetic centers (PC). T he change in oxygen concentration leads to a mutual and reversible transfor mation of PCs in chars, which is reflected in EPR parameters. The adsorbed molecular oxygen progressively disturbs the wave functions of the PCs and s o breaks the Heisenberg exchange between them. At high oxygen concentration , the 2D dipole-dipole interaction between PCs at the surface comes into pl ay and determines the EPR lineshape. A suggested model quantitatively descr ibes the evolution of the basic EPR parameters of each PC as a function of oxygen concentration. (C) 2001 Academic Press.