Many peptide nanostructures, self-assembled from chemically synthesized biomolecules, have drawn much attention in the fi eld of nanotechnology due to their physical, chemical, and biological properties, which make them promising candidates for applications in bionanomedicine, [ 1 ] bionanotechnology, [ 2,3 ] electronics, [ 4,5 ] optics, [ 6 ] energy storage, [ 7,8 ] etc. Some of these properties, such as ferro-and piezoelectricity observed in diphenylalanine nanotubes (FF-PNT) [ 9 ] are directly related to the nanocrystalline structural asymmetry of the elementary building blocks comprising these supramolecular materials. [ 6,10 ] One basic physical effect that depends on both the crystalline symmetry and the electronic properties of dielectric materials is second harmonic generation (SHG). SHG is observed only in crystals with no center of symmetry [ 11 ] and is related to ferroelectric phenomena together with linear electrooptical and piezoelectric effects. Ferroelectric effects have been observed in many biological materials such as plants, animals, and human tissues (amino acids, pineal gland of brain, skin, tendon, etc.). [ 12 ] Today, the SHG effect is also exploited in optical microscopy, especially in medical and biological research. [ 13 ] It allows the detection of two-photon emission from biomaterials and biopolymers [ 14 ] lacking a center of symmetry. The effect has been used with quantitative metrics for diagnosing a wide range of diseases. [ 15 ] Recently, second-order responses have also been found in bioinspired aromatic FF-PNT with hexagonal space group P6 1 using nonlinear optical microscopy. [ 16 ] Both the elementary crystalline symmetry and the electronic structure of bioinspired peptide nanostructures can be significantly changed by deep reconstruction process, such as phase transformation at a nanoscale level, which results in the disappearance of an SHG response. [ 17 ] Another method to modulate these fundamental properties is to use different solvents, [18][19][20][21] which strongly infl uence the self-assembly process and defi ne peptide nanostructures' morphologies. Modifi cation of the physical properties in peptide nanomaterials is a new way to fabricate basic nanoscale units for future bottom-up nanotechnologies. [ 6 ] Bioinspired peptide nanostructures, much like other organic nanostructures, [ 22,23 ] have ultra-small sizes and are easily produced by a rapid self-assembly fabrication process. All these properties make them favorable for implementation in diverse applications, and especially in biophotonics devices.In this work, we have studied the SHG effect in bioorganic peptide nanostructures of different morphologies and symmetries, such as nanotubes, nanofi bers, nanobelts, and nanospheres. These nanostructures were self-assembled in different solvents from peptide precursors with a variable number of A nonlinear optical effect of a second harmonic generation (SHG) was fi rst observed in quartz and then found in many inorganic materials that have an asymmetric crystalline s...

Second harmonic generation (SHG) of a high intensity was found in MoS2 flakes of different thicknesses exfoliated on a silicon substrate. Reduction of the SHG intensity was observed only for a small portion of flakes, for both very thin and quite thick ones. This was attributed to the presence of polytypism, i.e., of 3R non-centrosymmetric and 2H centrosymmetric polytypes, in a source bulk crystal grown by the chemical vapor transport technique. The presence of two polytypes in the sample was confirmed by the spectral structure of the photoluminescence of bound excitons observed in flakes at low temperature. Absolute values of nonlinear susceptibility of MoS2 flakes of different thicknesses were estimated.

In this review, our recent results on the electron-beam domain writing (EBDW) on the nonpolar surfaces of LiNbO3 crystals of different compositions are presented. Under EB irradiation of the nonpolar surfaces, domains nucleated in irradiation points grow frontally along the polar [Formula: see text]-direction in a thin (of microns in thickness) surface layer; the driving force is the tangential component of space-charge fields induced by EB in irradiation points. This geometry of the experiment provides a possibility of three-dimensional (3D) characterization of domain patterns using the combination of atomic force microscopy (AFM) and second harmonic generation (SHG) confocal microscopy methods. The obtained results permitted us to relate the main characteristics of domain formation (the domain sizes and velocity [Formula: see text] of the frontal motion) to the irradiation conditions (the accelerating voltage [Formula: see text] of scanning electron microscopy (SEM), EB current [Formula: see text], the inserted charge [Formula: see text]). The domain depth [Formula: see text] is controlled by [Formula: see text] via the electron penetration depth; the domain length [Formula: see text] increases linearly with [Formula: see text] owing to the domain frontal growth by the viscous friction law. The electron emission coefficient [Formula: see text] affects the domain formation due to the fundamental dependence of [Formula: see text] on [Formula: see text]. In the framework of current approach to EB charging of insulators, the effect of an enhanced conductance on EBDW characteristics is analyzed. The difference between EBDW characteristics observed in varied LiNbO3 compositions is discussed in the framework of the intrinsic defect structure of LiNbO3. The obtained results extend the possibility of EBDW application to a wider range of crystals.

Diphenylalanine peptide nano- and microtubes formed by self-assembly demonstrate strongly enhanced and tunable single-photon and two-photon luminescence in the visible range, which appears after heat- or laser treatment of these self-organized peptide microtubes. This process significantly extends the functionality of these microstructures and can trigger a new interest in the optical properties of structures based on short peptides.

We report on characterization of the electron-beam fabricated planar domain gratings on the nonpolar (Y-) surface of LiNbO3 crystals performed with the use of AFM and confocal second harmonic generation (SHG) microscopy. The dependence of domain formation on the irradiation conditions was investigated. The relation of domain thicknesses to the electron penetration depth is experimentally proved. In particular, the possibility of controlling the thickness of planar domains by varying acceleration electron-beam voltages is demonstrated. The observed specificity of SHG is analyzed in the framework of the Kleinman-Boyd theory [G. D. Boyd and D. A. Kleinman, J. Appl. Phys. 39, 3597 (1968)] and Uesu approach [Kaneshiro et al., J. Appl. Phys. 104, 054112 (2008); Kaneshiro et al., J. Opt. Soc. Am. B 27, 888 (2010)] extended in our case to reflection geometry. The calculations performed predict the dependence of SHG conversion efficiency η on the domain thickness, which is in a qualitative agreement with the experiment. It is shown that planar domains on top of the nonpolar surface always enhance the value of η as compared with the bare surface.