Electromechanical response of materials is a key property for various applications ranging from actuators to sophisticated nanoelectromechanical systems. Here electromechanical properties of the single-layer graphene transferred onto SiO2 calibration grating substrates is studied via piezoresponse force microscopy and confocal Raman spectroscopy. The correlation of mechanical strains in graphene layer with the substrate morphology is established via Raman mapping. Apparent vertical piezoresponse from the single-layer graphene supported by underlying SiO2 structure is observed by piezoresponse force microscopy. The calculated vertical piezocoefficient is about 1.4 nm V−1, that is, much higher than that of the conventional piezoelectric materials such as lead zirconate titanate and comparable to that of relaxor single crystals. The observed piezoresponse and achieved strain in graphene are associated with the chemical interaction of graphene's carbon atoms with the oxygen from underlying SiO2. The results provide a basis for future applications of graphene layers for sensing, actuating and energy harvesting.
The
difference in the crystal structure and growth kinetics of
microtubes formed from l- and d-enantiomers of diphenylalanine
dipeptide is investigated both experimentally and theoretically by
computer simulation. The microtubes of l- and d-enantiomers
grown simultaneously and under identical experimental conditions possess
different crystallographic space groups, have essential difference
in sizes, and demonstrate different growth kinetics. Computer simulation
by molecular mechanics methods revealed a fundamental difference in
the interaction between structural units of microtubes of different
chiralities. A model describing chirality-dependent growth of microtubes
is proposed.
Self-assembly of supramolecular biomaterials such as proteins or peptides has revealed great potential for their use in various applications ranging from scaffolds for cell culture to light-emitting diodes and piezoelectric transducers. Many of these applications require controlled growth of individual objects in the configuration allowing simple transfer to the desired device. In this work, we grew millimeter-long diphenylalanine (FF) self-assembled microtubes with high aspect ratio via evaporation-driven crystallization of nonsaturated FF solutions, making use of the Marangoni flow in the drying droplets. The growth mechanism was investigated by measuring the microtube length as a function of time. Jerky (steplike) growth behavior was observed and explained by a self-activated process in which additional activation energy is provided through condensation. The calculated growth rate due to the diffusion-controlled process is in agreement with the experimentally measured values. The grown microtubes were successfully transferred to metallized patterned substrates, and their specific conductivity and piezoelectric properties were evaluated as a function of the applied voltage and frequency. A number of piezoelectric resonances were observed and attributed to different vibrational modes excited by the piezoelectric effect inherent to the FF structure.
The structure and properties of diphenylalanine peptide nanotubes based on phenylalanine were investigated by various
molecular modeling methods. The main approaches were semi-empirical quantum-chemical methods (PM3 and AM1), and
molecular mechanical ones. Both the model structures and the structures extracted from their experimental
crystallographic databases obtained by X-ray methods were examined. A comparison of optimized model structures and
structures obtained by naturally-occurring self-assembly showed their important differences depending on D- and L-chirality.
In both the cases, the effect of chirality on the results of self-assembly of diphenylalanine peptide nanotubes was established:
peptide nanotubes based on the D-diphenylalanine (D-FF) has high condensation energy E0
in transverse direction and forms
thicker and shorter peptide nanotubes bundles, than that based on L-diphenylalanine (L-FF). A topological difference was
established: model peptide nanotubes were optimized into structures consisting of rings, while naturally self-assembled
peptide nanotubes consisted of helical coils. The latter were different for the original L-FF and D-FF. They formed helix
structures in which the chirality sign changes as the level of the macromolecule hierarchy raises. Total energy of the optimal
distances between two units are deeper for L-FF (–1.014 eV) then for D-FF (–0.607 eV) for ring models, while for helix coil are
approximately the same and have for L-FF (–6.18 eV) and for D-FF (–6.22 eV) by PM3 method; for molecular mechanical methods
energy changes are of the order of 2–3 eV for both the cases. A topological transition between a ring and a helix coil of
peptide nanotube structures is discussed: self-assembled natural helix structures are more stable and favourable, they have
lower energy in optimal configuration as compared with ring models by a value of the order of 1 eV for molecular mechanical
methods and 5 eV for PM3 method.
Glycine is the simplest amino acid and one of the basic and important elements in biology, as it serves as a building block for proteins. The interest in this material has recently arisen from its useful functional properties, such as its high value of nonlinear optical susceptibility and ferroelectricity. Three polymorphic forms with different physical properties are possible in glycine, the most useful β-polymorph being much less stable than the other two. In this work, we could grow stable microcrystals of β-glycine using a (111)Pt/SiO 2 /Si substrate as a template. The effects of the solution concentration and Pt-assisted nucleation on the crystal growth and phase evolution were evaluated using X-ray diffraction analysis and Raman spectroscopy. A second harmonic generation (SHG) method confirmed that the 2-fold symmetry is preserved in as-grown crystals, thus reflecting the expected P2 1 symmetry of the β-phase. Spontaneous polarization direction is found to be parallel to the monoclinic [010] axis and directed along the crystal length. These data are confirmed by computational molecular modeling. Optical measurements revealed also relatively high values of the nonlinear optical susceptibility (50% greater than in the z-cut quartz). The potential use of stable β-glycine crystals in nonlinear optical applications is discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.