Study of the growth and switching kinetics on ferroelectric nanocrystals of copolymer vinylidene fluoride and trifluoroe
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ACE AND THIN FILMS
Study of the Growth and Switching Kinetics on Ferroelectric Nanocrystals of Copolymer Vinylidene Fluoride and Trifluoroethylene on an Atomic Force Microscope R. V. Gaynutdinova, O. A. Lysovaa, A. L. Tolstikhinaa, V. M. Fridkina, S. G. Yudina, and S. Ducharmeb a
Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskii pr. 59, Moscow, 119333 Russia email: [email protected] b Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, USA Received July 5, 2012
Abstract—The growth of nanocrystals obtained from Langmuir–Blodgett films of ferroelectric copolymer consisting of 70% vinylidene fluoride and 30% trifluoroethylene has been investigated by atomic force microscopy (AFM). The radius and concentration of nanocrystals are found to depend on the annealing time of the film. A model for nanocrystal growth is proposed which yields adequate time dependences for nanoc rystal size parameters. The switching kinetics of individual ferroelectric nanocrystals with an average diame ter of 100–200 nm and a height of 15–20 nm has been investigated in the piezoelectric response mode. It is shown that the switching of nanocrystals has an activation character. DOI: 10.1134/S1063774513020090
INTRODUCTION In view of the development of nanotechnologies, interest in the fabrication and study of ferroelectric nanostructures constantly increases. The implemen tation of energyindependent memory with ultrahigh density imposes stringent requirements on such ferro electric parameters as switching time and coercive voltage. Switching time depends generally on the applied field magnitude, and, in the case of bulk crys tals, switching times on the order of few microseconds can be attained only at very high field strengths. To implement fast switching at fairly low field strengths, one needs ferroelectric nanocrystals. Many studies were devoted to ultrathin films of the ferroelectric copolymer composed of 70% vinylidene fluoride and 30% trifluoroethylene (P[VDF–TrFE]) [1–3]. These films are considered a promising mate rial for ferroelectric digital memory cells [4]. Crystals of this copolymer from 100 nm to 4 μm in size were obtained for the first time in Langmuir–Blodgett (LB) films in [1]. According to the transmission electron microscopy data, they are rounded isolated copolymer islands, the sizes of which depend on the annealing time and temperature. In this paper we report the results of studying the growth and switching kinetics of ferroelectric nanoc rystals based on (P[VDF–TrFE]) copolymer by atomic force microscopy (AFM). The analysis was performed using an electric modification of AFM, piezoelectric force microscopy (PFM), which makes it possible to record ferroelectric domains, investigate
their dynamics, and measure local electrical charac teristics [5, 6]. EXPERIMENTAL Polyvinylidene fluoride belongs to the class of crys tallizing polymers [7]. Its structural unit (–(CH2–CF2)–) has a dipole moment μ = 7 × 10–30 C m (2 deby
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