Two-dimensional ferroelectricity in monolayer PVDF Langmuir–Blodgett films studied by optical second-harmonic generation

• Published in: Surface science 2002-06, Vol.507, p.719-723
• Main Authors: Fokin, Yu.G., Misuryaev, T.V., Murzina, T.V., Palto, S.P., Petukhova, N.N., Yudin, S.G., Aktsipetrov, O.A.
• Format: Article
• Language: English
• Subjects: Non-linear optical methods; Second harmonic generation; Surface electronic phenomena (work function, surface potential, surface states, etc.); Surface thermodynamics (including phase transitions)
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/S0039-6028(02)01342-0

The two-dimensional (2D) ferroelectricity in monolayer Langmuir–Blodgett (LB) films of copolymer vinylidene fluoride with trifluoroethylene (PVDF/TrFE) is studied by optical second-harmonic generation (SHG). The SHG temperature dependences are studied in order to reveal the ferroelectric behaviour of the films. For the monolayer LB films of PVDF/TrFE, as well as for the multiplayer LB films, a wide hysteresis in the SHG intensity under heating and consequent cooling is observed. This hysteresis is attributed to the first-order ferroelectric–paraelectric phase transition in the extreme case of literally 2D ferroelectric films. It is demonstrated that the main contribution to the nonlinear response of the LB films of PVDF/TrFE originates from fluctuations of the nonlinear polarization in inhomogeneous film structure.