The influence of the relative humidity
on the domain growth during
local switching by a conductive tip of a scanning probe microscope
has been studied in Rb:KTP single crystals. The abnormal formation
of the elongated hexagonal domains during the local switching in an
axial-symmetric field has been attributed to the anisotropy of the
domain wall velocity. The increase and subsequent decrease in a hexagonal
domain aspect ratio as a function of the pulse duration for high humidity
have been attributed to the influence of the high-resistivity water
layer. We assume that the domain elongation by the fast walls is limited
by the water layer representing the series resistance, which depends
on the wall position, while the domain widening by the slow walls
is limited by their mobility. The computer simulation of the spatial
distribution of the electric field has demonstrated that the appearance
of a water meniscus decreases the field close to the tip and increases
it far from the tip. This result has allowed explaining the published
alternative effects of humidity on the domain size: (1) decrease in
size for small domains and (2) increase in size for large ones. The
obtained results highlight the necessity of humidity control for domain
engineering.
Self-assembled peptide nanostructures are being intensively investigated due to their potential applications such as biosensors, piezotransducers, and microactuators. It was predicted that their formation and hence piezoelectric property strongly depend on the water content and acidity of the stock solution. In this paper, simple diphenylalanine (FF) tubular structures were fabricated from the solutions with added hydrochloric acid in order to understand the influence of chloride ions on the self-assembly process and resulting piezoelectricity. Low-frequency Raman scattering, atomic, and piezoresponse force microscopies were used to characterize both the morphology and piezoelectric properties of the grown samples. The mechanism of chloride anions' effect on the formation of self-assembled peptide nanostructures is discussed based on the acquired Raman data and quantum-chemical modeling. It is shown that the addition of chloride anions causes a significant reduction of the dipole moments of FF tubes accompanied with the concomitant decrease of tube dimensions and apparent shear piezoelectric coefficients.
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