We show anomalously strong shear piezoelectric activity in self-assembled diphenylalanine peptide nanotubes (PNTs), indicating electric polarization directed along the tube axis. Comparison with well-known piezoelectric LiNbO(3) and lateral signal calibration yields sufficiently high effective piezoelectric coefficient values of at least 60 pm/V (shear response for tubes of approximately 200 nm in diameter). PNTs demonstrate linear deformation without irreversible degradation in a broad range of driving voltages. The results open up a wide avenue for developing new generations of "green" piezoelectric materials and piezonanodevices based on bioactive tubular nanostructures potentially compatible with human tissue.
The use of bionanostructures in real-world applications will require precise control over biomolecular self-assembly and the ability to scale up production of these materials. A significant challenge is to control the formation of large, homogeneous arrays of bionanostructures on macroscopic surfaces. Previously, bionanostructure formation has been based on the spontaneous growth of heterogenic populations in bulk solution. Here, we demonstrate the self-assembly of large arrays of aromatic peptide nanotubes using vapour deposition methods. This approach allows the length and density of the nanotubes to be fine-tuned by carefully controlling the supply of the building blocks from the gas phase. Furthermore, we show that the nanotube arrays can be used to develop high-surface-area electrodes for energy storage applications, highly hydrophobic self-cleaning surfaces and microfluidic chips.
We report on observation of photoluminescence (PL) in blue and UV regions of exciton origin in bioinspired material-peptide nanotubes (PNTs). Steplike optical absorption and PL measurements have allowed finding quantum confined (QC) phenomenon in PNTs. The estimations show that QC in these nanotubes occurs due to a crystalline structure of subnanometer scale dimension formed under the self-assembly process. Our new findings pave the way for the integration of PNT in a new generation of optical devices. A blue PL array of a PNT-patterned device is demonstrated.
Electron emission from ferroelectrics ͑FEE͒ is an unconventional electron emission effect. Methods of FEE excitation are quite different compared to classic electron emission from solids. Two kinds of FEE have been observed, ''weak'' and ''strong.'' ''Weak'' electron emission ͑current density 10 Ϫ12-10 Ϫ7 A/cm 2 ͒ occurs from polar surfaces of ferroelectric materials in the ferroelectric phase only. A source of the electric field for ''weak'' FEE excitation is an uncompensated charge, generated by a deviation of macroscopic spontaneous polarization from its equilibrium state under a pyroelectric effect, piezoelectric effect, or polarization switching. The FEE is a tunneling emission current which screens uncompensated polarization charges. It is shown that the FEE is an effective tool for direct domain imaging and studies of electronic properties of ferroelectrics. ''Strong'' FEE, which is 10-12 orders of magnitude higher than ''weak'' FEE, achieves 100 A/cm 2 and is plasma-assisted electron emission. Two modes of the surface flashover plasma formation followed by strong electron emission have been studied. The plasma of ferroelectric origin has been observed only in the ferroelectric phase and it is induced by polarization switching or a field-enforced phase transition, such as antiferroelectric-ferroelectric or relaxor-ferroelectric. The second mode of plasma is conventional surface flashover which may be initiated by a high voltage application in any phase from any dielectric, including ferroelectrics. In this review paper we consider numerous experimental results, as well as mechanisms of both types of electron emission from ferroelectrics. The main stress is placed on the material aspect in order to clarify the influence of ferroelectricity ͑ferroelectric phase transitions, polarization switching, etc.͒ on electron emission. Another aspect which is broadly discussed is the potential applications of these unconventional FEE emitters in various devices for development of high density FEE cathodes for microwave devices, as well as FEE converters of IR irradiation into visible light, x-ray imaging, FEE flat panel displays, etc.
A reconstructive phase transition has been found and studied in ultrashort di- and tripeptide nanostructures, self-assembled from biomolecules of different compositions and origin such as aromatic, aliphatic, linear, and cyclic (linear FF-diphenylalanine, linear LL-dileucine, FFF-triphenylalanine, and cyclic FF-diphenylalanine). The native linear aromatic FF, FFF and aliphatic LL peptide nanoensembles of various shapes (nanotubes and nanospheres) have asymmetric elementary structure and demonstrate nonlinear optical and piezoelectric effects. At elevated temperature, 140-180 °C, these native supramolecular structures (except for native Cyc-FF nanofibers) undergo an irreversible thermally induced transformation via reassembling into a completely new thermodynamically stable phase having nanowire morphology similar to those of amyloid fibrils. This reconstruction process is followed by deep and similar modification at all levels: macroscopic (morphology), molecular, peptide secondary, and electronic structures. However, original Cyc-FF nanofibers preserve their native physical properties. The self-fabricated supramolecular fibrillar ensembles exhibit the FTIR and CD signatures of new antiparallel β-sheet secondary folding with intermolecular hydrogen bonds and centrosymmetric structure. In this phase, the β-sheet nanofibers, irrespective of their native biomolecular origin, do not reveal nonlinear optical and piezoelectric effects, but do exhibit similar profound modification of optoelectronic properties followed by the appearance of visible (blue and green) photoluminescence (PL), which is not observed in the original peptides and their native nanostructures. The observed visible PL effect, ascribed to hydrogen bonds of thermally induced β-sheet secondary structures, has the same physical origin as that of the fluorescence found recently in amyloid fibrils and can be considered to be an optical signature of β-sheet structures in both biological and bioinspired materials. Such PL centers represent a new class of self-assembled dyes and can be used as intrinsic optical labels in biomedical microscopy as well as for a new generation of novel optoelectronic nanomaterials for emerging nanophotonic applications, such as biolasers, biocompatible markers, and integrated optics.
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