R. V. Gaynutdinov

Ferroelectric properties of Langmuir-Blodgett copolymer films at the nanoscale

Langmuir-Blodgett (LB) films are well known structures prepared as a result of successive transfer of monolayers (ML) from the gas-liquid interface onto solid substrates. One impressive possibility of LB method is the opportunity to vary the thickness of the film to an accuracy of one transfer, which could coincide with one ML. The ferroelectric properties of a copolymer of vinylidene fluoride and trifluorethylene P[VDF-TrFE] prepared by LB deposition are investigated in the region of a few monolayers.

Polarization switching at the nanoscale in ferroelectric copolymer thin films

The polarization switching kinetics were measured at the nanoscale in continuous thin films of a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene. The dependence of the switching rate on voltage for a 54-nm thick film exhibits extrinsic nucleation and domain-growth type kinetics with no true threshold coercive field, and is qualitatively different from the behavior of an 18-nm thick film, which exhibits intrinsic switching kinetics, and a true threshold field. The results are consistent with studies of thin film capacitors of much larger area and with a recent refinement of the theory of the critical size for intrinsic switching.

Polarization switching kinetics of ferroelectric nanomesas of vinylidene fluoride-trifluoroethylene copolymer

The polarization switching kinetics of ferroelectric polymer nanomesas was investigated using piezoresponse force microscopy. The nanomesas were made by self-organization from Langmuir–Blodgett films of a 70% vinylidene fluoride and 30% trifluoroethylene copolymer. The polarization switching time exhibits an exponential dependence on reciprocal voltage that is consistent with nucleation-type switching dynamics.

Polarization switching kinetics at the nanoscale in ferroelectric copolymer Langmuir–Blodgett films

The polarization switching kinetics of ferroelectric Langmuir–Blodgett films of vinylidene fluoride-trifluoroethylene copolymer were investigated by piezoresponse force microscopy with a resolution of 100nm. The switching time in response to a localized voltage pulse exhibits an exponential dependence on reciprocal voltage, which is consistent with nucleation-limited switching dynamics.

DISTINCT EFFECT OF XENOBIOTICS ON THE METAL-BINDING PROPERTIES OF PROTEIN MOLECULES

The X-ray standing-wave method was applied to study the elemental composition and molecular organization of ordered protein films of alkaline phosphatase exposed to different xenobiotics (drug compounds, lead). Binding of metal ions from triply distilled water to protein molecules has been experimentally observed. Definite differences in the arrangement of impurity metal ions in the films have been established. The considerable enhancement of protein-metal interactions is attributed to partial rearrangement of the protein native structure, induced by xenobiotics.

Scaling of the Coercive Field in Ferroelectrics at the Nanoscale

The scaling of the coercive field in ferroelectric films at the nanoscale is investigated experimentally. The scaling in the films of copolymer vinylidene fluoride and BaTiO3 with thickness equal by the order of value to the critical domain nucleus size 1–10 nm reveals deviation from the well-known Kay-Dunn law. At this thickness region coercive field does not depend on thickness and coincides with Landau-Ginzburg-Devonshire value.

The Homogenous Switching in the Ultrathin Ferroelectric Films

It is well known, that there are two possible switching mechanism in ferroelectric crystals and films (see f.e. A.Tagantsev et al, Domains in Ferroic Crystals and Thin Films, Springer, 2010). The first mechanism, which follows from mean field theory of Landau-Ginzburg, is homogeneous one and does not connect domains. This mechanism was never observed before 1998. The second mechanism, connected with nucleation and domains movement is common for the ferroelectrics and well known from the time of domain discovery (1956). In the present paper the existence of homogeneous mechanism of switching in ultrathin copolymer films is definitely confirmed. The results of the present paper permit to suppose, that homogeneous switching exists in other ultrathin ferroelectric films with thickness near to the critical one.

Growth and Switching of Ferroelectric Nanocrystals from Ultrathin Film of Copolymer of Vinylidene Fluoride and Trifluoroethylene

The ferroelectric nanocrystals of the copolymer of vinylidene fluoride and trifluoroethylene P(VDF-TrFE) were grown from ultrathin Langmuir-Blodgett (LB) films on Si substrate. The annealing of ultrathin LB films with thickness of 3 monolayers (5 nm) in air in paraelectric phase at temperature 125∘C was performed. The self-assembly leads to the growth of nanocrystals of ferroelectric copolymer 15–25 nm thick and 100–200 nm in diameter. The nanocrystals presumably belong to orthorhombic space group, where axis 2 is the direction of spontaneous polarization (and normal to substrate). By means of atomic force microscopy (AFM), the kinetics of ferroelectric nanocrystals growth and their switching were investigated. The obtained results confirm the conclusions that copolymer nanocrystals are candidates for high-density nonvolatile storage media devices.

Polarization switching kinetics of ferroelectric nanostructures of vinylidene fluoride-trifluoroethylene copolymer

The polarization switching kinetics of ferroelectric polymer Langmuir-Blodgett films and copolymer nanocrystals (nanomesas) was investigated using piezoresponse force microscopy. The nanocrystals were prepared by self-organization from Langmuir-Blodgett films of a 70% vinylidene fluoride and 30% trifluoroethylene copolymer. The polarization switching time exhibits an exponential dependence on reciprocal voltage and decreases with temperature being consistent with the nucleation switching dynamics.

Study of the growth and switching kinetics on ferroelectric nanocrystals of copolymer vinylidene fluoride and trifluoroethylene on an atomic force microscope

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 nanocrystal size parameters. The switching kinetics of individual ferroelectric nanocrystals with an average diameter 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.