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 °C → 140 °C → 30 °C) was conducted to isolate the pure spectra 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 (Tc↑) and cooling (Tc↓) decreased and increased, respectively, resulting in reduced temperature range between Tc↑ ↔ Tc↓ 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.
Bibliographical noteFunding Information:
This study was supported by “The National Research Program for the 0.1 Terabit Non-volatile Memory Development sponsored by Korea Ministry of Commerce, Industry and Energy” and Korea Science and Engineering Foundation (KOSEF) through the SRC/ERC Program of MOST/KOSEF (R11-2005-065). The authors (AAP and KJK) also wish to thank the Korea Research Foundation (KRF) for their partial financial support based on International Academic Exchange Program (KRF-2006-D00021).
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