Effect of thickness on the crystallinity and Curie transition behavior in P(VDF/TrFE) (72/28) copolymer thin films using FTIR-transmission spectroscopy

The effect of thickness on the ferroelectric behavior in spin-cast poly(vinylidene fluoride/trifluoroethylene) (P(VDF/TrFE)) (72/28 mol%) random copolymer films with varying degree of crystallinity was analyzed qualitatively and quantitatively using Fourier transform infrared-transmission spectroscopy (FTIR-TS) data. From the qualitative analysis of raw IR data, the critical thickness of crystallization was observed near 130 nm, below which the films exhibited significant changes in crystalline peak (1292 cm(-1)) absorption. Using factor analysis (FA) of their raw IR data, we have isolated the pure crystalline and amorphous phase spectra, and also quantitatively calculated their degree of crystallinity as a function of thickness. FA of the mixture spectra obtained at varying temperatures during a heating-cooling cycle (30 degrees C -> 140 degrees C -> 30 degrees C) was conducted to isolate the purespectra of the low-temperature (ferroelectric) and high-temperature (paraelectric) crystalline phases and to determine the content of each phase quantitatively as functions of thickness and temperature. Curie transition temperature during heating (T-c(1)) and cooling (T-c(1)) decreased and increased, respectively, resulting in reduced temperature range between T-c(1) <-> T-c(1) with decreasing film thickness used in our study and the quantitative data obtained from FA were quite comparable with the qualitative data obtained from raw IR analysis. (C) 2008 Elsevier B.V. All rights reserved.