| 학회 | 한국고분자학회 |
| 학술대회 | 2005년 봄 (04/14 ~ 04/15, 전경련회관) |
| 권호 | 30권 1호, p.347 |
| 발표분야 | 고분자 구조 및 물성 |
| 제목 | Spectroscopic analysis of ferroelectricity and electric field effects in thin P(VDF/TrFE) (72/28) films |
| 초록 | The copolymers of vinylidene fluoride (PVDF) and trifluoroethylene (TrFE) have recently attracted a great deal of attention in their applications to nonvolatile memory devices1. In early research, the ferroelectricity of these polymers was studied using thick polymer films(~9µm or thicker). Hence, in the first step towards understanding ferroelectric characteristics of thin VDF/TrFE copolymer film, an attempt has been made to study the nanostructure of thin films(~100 nm thick) using IR spectroscopy and electric field effects. The ~100 nm thick films of P(VDF/TrFE)(72/28) copolymer were prepared by spin casting its methylethylketone solution with a spinner over the KBr windows and subsequently annealed at different temperatures for three hours in vacuum. Transmission and reflectance I.R. spectra were collected using Bruker-IFS 66V spectrometer. For heating-cooling studies, the sample was mounted in a heating cell in the temperature range between 30~150oC at the rate of 0.4oC/min. The chain conformation, crystal structure and electric properties of VDF/TrFE copolymer are altered significantly at the Curie transition temperature (Tc) where a ferroelectric-paraelectric phase transition occurs and is highly dependent on the content of VDF in the copolymer and also on the thermal and solution history and poling (time and temperature)2,3. Tc for VDF/TrFE copolymers range from 65 to 130oC depending on the mol % of VDF (52-90 mol%). Annealing above Tc produces a significant increase in the degree of crystallinity, and by factor analysis using I.R. spectra2, we have isolated the pure amorphous and crystalline phases as shown in Fig. 1(a). The crystalline phase spectrum shows sharp absorption bands while the amorphous-phase spectrum shows broad bands as in the case of ~9µm thick film2. Also, we have found explicit evidence of significant increase in the crystalline phase upon annealing above Curie transition temperature range as shown in Fig. 1(b). From heating-cooling cycle using factor analysis, we extracted the pure spectra of ferroelectric and paraelectric phases and calculated the relative concentration of these phases as a function of temperature. The variation in ferroelectric phase with temperature and its hysteresis is shown in Fig. 1(c). The phase transition is observed to be reversible, although thermal hysteresis exists. To study the ferroelectric behavior of ~100nm thick PVDF/TrFE film near its Tc, we measured the capacitance during a thermal heating-cooling cycle at 10 kHz with an amplitude voltage of 1 V. We also carried out studies on the effect of electric field on the dipole changes and the results are reported here. References (1) T.J. Reece, S. Ducharme, A.V. Sorokin and M. Poulsen, Appl. Phys. Letters, 82, 142 (2003). (2) K.J. Kim, N.M. Reynolds and S.L. Hsu, Macromolecules, 22, 4395 (1989). (3) K.J. Kim, N.M. Reynolds, and S.L. Hsu, J.Polym.Sci.:Polym.. Phys., 31, 1555 (1993). This study was supported by "The National Research Program for the 0.1 Terabit Non-Volatile Memory Development Sponsored by Korea Ministry of Science & Technology" |
| 저자 | A. Anand Prabu1, 이종순1, 이한섭2, 김갑진1 |
| 소속 | 1경희대, 2인하대 |
| 키워드 | Spectroscopic analysis; ferroelectricity; Curie transition; crystallinity; electric field; P(VDF-TrFE) (72/28); thin film |
