Vibronic coupling in the valence band photoemission of the ferroelectric copolymer: Poly(vinylidene fluoride) (70%) and trifluoroethylene (30%)

Two different vibrational contributions to the photoemission fine structure of the ferroelectric copolymer poly(vinlylidene fluoride) with trifluoroethylene (CH2-CF2:CHF-CF2, 70%:30%) are identified. The vibrational contributions at the higher photoemission binding energies are associated with two closely placed nu(a,s) (CH2) stretching modes while at the smaller photoemission binding energies, the fine structure is due to a delta (CH2) bending mode. The contribution of the delta (CH2) mode to the photoemission fine structure decreases with decreasing temperature. We associate this temperature dependence to the importance of symmetry in vibronic coupling to the photoemission process and increased dipole ordering with decreasing temperature in this organic ferroelectric system.