Raman spectroscopic study of molecular orientation in AgTCNQ thin films

Preferential orientation of TCNQ− units in thin AgTCNQ films, which were prepared by thermal treatment of vapor-deposited materials on various substrates, is demonstrated by laser Raman spectroscopy. The polarization dependence of Raman intensities in four scattering arrangements have been obtained by varying the polarization direction of the incident light. The experimental results for Raman intensities as a function of substrate orientation are compared with those predicted for films with TCNQ− units with various postulated types of orientation relative to the substrate and to each other, and also compared with those obtained from AgTCNQ solution. The data show that AgTCNQ thin films are characterized by preferred orientation of the TCNQ− units relative to the substrate at an angle θ≂45°. The lack of other orientation in the sampled region is taken to indicate that there are many relatively small domains, within each of which θ≂45°, which are not oriented with respect to each other.