X-ray absorption and diffraction investigations of iodine-intercalated conducting Langmuir-Blodgett film

Abstract

X-Ray absorption and diffraction have been used to study a Langmuir-Blodgett film of an iodine-intercalated charge transfer (CT) salt based on EDT-TTF(SC 18) 2. The polarized X-ray absorption near-edge structure (XANES) of I 3 − exhibits a strong angular dependence of the 2s–5p(σ ∗) resonance intensity. To obtain precise information about the I 3 − orientation, the observed polarization dependence is compared with the theoretical calculation. It is shown that the I 3 − molecular axes are distributed randomly in a plane parallel to the substrate. From the viewpoint of the I 3 − distribution, the effect of annealing is also investigated with polarized XANES spectroscopy and X-ray diffraction. It is confirmed that an annealing process is necessary to achieve a well-stabilized and highly conducting film of the present CT salt. In addition, a possible molecular assembly of this annealed purple phase is proposed via a simulation of the X-ray diffraction profile based on the XANES results.