Influence of applied electric field on crystalline structure and thermo-optical effect of oriented PVDF thin films

The alpha phase oriented PVDF thin films were deposited using vacuum evaporation technology with a DC electric field applied on substrate holder during deposition process. X-ray Diffraction was used to examine the structural variations as a function of applied electric fields. DSC data allowed measurement of the melting temperatures and enthalpies of the PVDF granules and films deposited at various bias voltages, providing information on the changes in the crystallinity of the films. The thermo-optical (t.o) coefficient of alpha phase oriented PVDF thin films with different degree of crystallinity, which obtained by regulating the applied electric voltages varying from 0 to 5 KV, were determined by using spectroscopic ellipsometer (SE) equipped with a heating stage. At temperatures ranging from 20 to 100degC the refractive index of all the PVDF films was negatively correlated with the temperature between 600 and 1600 nm. The value of the t.o coefficient of PVDF films was calculated at all temperatures. During the deposition process, a decrease in the degree of crystallinity was observed with the increase of applied electric voltage. Furthermore, the absolute value of t.o. coefficient for film deposited at 5 kV was slightly higher and decreased with increase in the degree of its crystallinity.