Semen Vasilev

Pyroelectric effect and polarization instability in self-assembled diphenylalanine microtubes

The natural ability of peptides and proteins to self-assemble into elongated fibrils is associated with several neurogenerative diseases. Diphenylalanine (FF) tubular structures that have the same structural motif as in Aβ-amyloid peptide (involved in Alzheimers disease) are shown to possess remarkable physical properties ranging from piezoelectricity to electrochemical activities. In this work, we also discover a significant pyroelectric activity and measure the temperature dependence of the pyroelectric coefficient in the temperature range of 20–100 °C. Pyroelectric activity decreases with temperature contrary to most ferroelectric materials and significant relaxation of pyrocurrent is observed on cooling after heating above 50 °C. This unusual behavior is assigned to the temperature-induced disorder of water molecules inside the nanochannels. Pyroelectric coefficient and current and voltage figures of merit are estimated and future applications of pyroelectric peptide nanostructures in biomedical appl...

Morphology and Piezoelectric Properties of Diphenylalanine Microcrystals Grown from Methanol-Water Solution

Morphology and piezoelectric properties of diphenylalanine microcrystals grown by drying the droplet of methanol and water mixture in various proportions have been studied. We have found that the increase of water concentration leads to the significant change of the microcrystal morphology from flat dendrite structures to elongated microcrystals: microtubes and microrods. The effect was attributed to increasing of the drying time. The morphology of the dendrite structures was revealed and empirical dependence of the dendrite thickness on diameter was found. Finally, the piezoelectric activity of the microtubes was demonstrated using the piezoresponse force microscopy.

Piezoelectric and ferroelectric properties of organic single crystals and films derived from chiral 2-methoxy and 2-amino acids

ABSTRACT Local piezoelectric and ferroelectric properties as well as morphology of single crystals and films of two novel chiral organic compounds derived from chiral 2-methoxy and 2-amino acids have been investigated. The crystals demonstrated piezoelectric response exceeding that of lithium niobate. The piezoelectric response was registered also in compound films. Piezoelectric properties and domain structure of single crystals and films have been studied by piezoresponse force microscopy.

Patterning and nanoscale characterization of ferroelectric amino acid beta-glycine

The formation of self-organized micro- and nano-islands of beta-glycine prepared by spin-coating is observed. It is shown that the islands are very stable and possess apparent piezoelectric and ferroelectric properties studied in detail by Piezoresponse Force Microscopy. The micro-Raman studies are conducted to confirm the crystallographic preferred orientation and formation of β-phase. The polarization reversal of individual ferroelectric islands is demonstrated by application of the relatively small bias voltage.

Glycine nanostructures and domains in beta-glycine: computational modeling and PFM observations

ABSTRACT In this work computational molecular modeling of β-glycine nanostructures is presented, using various approaches, mostly semi-empirical quantum approximation PM3 type in HyperChem software in restricted Hartree-Fock calculations. The main aims of present studies focus on the molecular modeling for the β-glycine domains and domain walls formation and interaction. Obtained results are presented in visual 3D-models of the glycine domains and domain walls, compared with experimentally observed by PFM domain walls structures. Modeling is arranged with calculated values of physical data (polarization, etc.). Analysis of these new computed and corroborated PFM experimental data for β-glycine domains are presented.

Probing ferroelectric behaviour in charge-transfer organic meta-nitroaniline

Potential ferroelectricity in charge-transfer organic materials is often masked by the intrinsic conductivity. Here, we report the compelling evidence of ferroelectricity in organic π-conjugated meta-nitroaniline (m-NA) crystals as shown by the local electromechanical measurements using the piezoresponse force microscopy (PFM) technique. m-NA is a charge-transfer molecular material with the exceptional optical non-linearity and perceptible conductivity along the crystallographic polar axis. While standard Sawyer-Tower measurements revealed an apparently lossy-dielectric hysteresis, The PFM switching spectroscopy indicated clear ferroelectric behaviour in this technologically important multifunctional material. Further study of the pyroelectric properties in m-NA crystals confirmed their high spontaneous polarization of 18 μC/cm2 at room temperature, comparable to the best known organic ferroelectrics.

Diphenylalanine-based microribbons for piezoelectric applications via inkjet printing

Peptide-based nanostructures are very promising for nanotechnological applications because of their excellent self-assembly properties, biological and chemical flexibility, and unique multifunctional performance. However, one of the limiting factors for the integration of peptide assemblies into functional devices is poor control of their alignment and other geometrical parameters required for device fabrication. In this work, we report a novel method for the controlled deposition of one of the representative self-assembled peptides-diphenylalanine (FF)-using a commercial inkjet printer. The initial FF solution, which has been shown to readily self-assemble into different structures such as nano- and microtubes and microrods, was modified to be used as an efficient ink for the printing of aligned FF-based structures. Furthermore, during the development of the suitable ink, we were able to produce a novel type of FF conformation with high piezoelectric response and excellent stability. By using this method, ribbonlike microcrystals based on FF could be formed and precisely patterned on different surfaces. Possible mechanisms of structure formation and piezoelectric effect in printed microribbons are discussed along with the possible applications.

Spin coating formation of self-assembled ferroelectric β-glycine films

ABSTRACT The formation of self-assembled ferroelectric glycine films of various morphologies by spin coating technique was investigated. The film morphology varied from dendritic feather-like structure to arrays of individual micro- and nanoislands and 15 nm-thick layers. It was confirmed by confocal Raman microscopy that most of the films belonged to ferroelectric beta phase. Piezoelectric properties and domain structure of the films were studied by piezoresponse force microscopy.

Piezoelectric properties and Young's moduli of diphenylalanine microtubes—oxide nanoparticles composites

ABSTRACT In this work, we investigated the influence of piezoelectric ZnO and nonpiezoelectric SiO2 and TiO2 nanoparticles on the structure and some physical properties of composite structures based on microtubes of diphenylalanine. We demonstrated that all types of used nanoparticles promoted formation of voids and cavities in diphenylalanine microtubes thus reducing the effective Youngs modulus and lateral piezoelectric coefficient of the composite. At the same time, embedding of piezoelectric ZnO nanoparticles provides noticeable vertical piezoresponse normally absent in single-component diphenylalanine microtubes. The obtained results demonstrate the ability to control the properties of self-assembling composite biomaterials by nanoparticles.