Strong thermo-induced single and two-photon green luminescence in self-organized peptide microtubes.

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.

Bioinspired peptide nanotubes: deposition technology, basic physics and nanotechnology applications.

Synthetic peptide monomers can self-assemble into PNM such as nanotubes, nanospheres, hydrogels, etc. which represent a novel class of nanomaterials. Molecular recognition processes lead to the formation of supramolecular PNM ensembles containing crystalline building blocks. Such low-dimensional highly ordered regions create a new physical situation and provide unique physical properties based on electron-hole QC phenomena. In the case of asymmetrical crystalline structure, basic physical phenomena such as linear electro-optic, piezoelectric, and nonlinear optical effects, described by tensors of the odd rank, should be explored. Some of the PNM crystalline structures permit the existence of spontaneous electrical polarization and observation of ferroelectricity. The PNM crystalline arrangement creates highly porous nanotubes when various residues are packed into structural network with specific wettability and electrochemical properties. We report in this review on a wide research of PNM intrinsic physical properties, their electronic and optical properties related to QC effect, unique SHG, piezoelectricity and ferroelectric spontaneous polarization observed in PNT due to their asymmetric structure. We also describe PNM wettability phenomenon based on their nanoporous structure and its influence on electrochemical properties in PNM. The new bottom-up large scale technology of PNT physical vapor deposition and patterning combined with found physical effects at nanoscale, developed by us, opens the avenue for emerging nanotechnology applications of PNM in novel fields of nanophotonics, nanopiezotronics and energy storage devices.

Patterned arrays of ordered peptide nanostructures.

Methods for the deposition of ordered nanostructures on various substrates are a key factor in nanotechnological devices. There is a special interest in the development of methods for the organization of organic nanostructures that are not compatible with some of the conventional fabrication methods. The unique chemical and physical properties of the peptide nanotubes make them excellent component in various devices and the useful application were already demonstrated in the case of biosensors. Here we demonstrate the ability to deposited aromatic dipeptide nanotubes using electron beam treatment of surfaces to control their wettability. The use of a low energy electron irradiation results in the formation of pre-defined surfaces with controlled level of wettability. This treatment allows the precise patterning of the organic tubular assemblies at high resolution. The differential wettability of the surface resulted in organization of the peptide assemblies according to the properties of the different areas of the surface. In the current work, we describe the use of wettability patterned surfaces for the control patterning of horizontal peptide nanotubes and nanospheres. Furthermore, lift-off lithography is used to make patterned arrays of peptide nano-forests, vertically aligned peptide nanotubes. In summary, the novel patterning techniques together with the unique properties of the peptide nanostructures represent an important step in the integration of these assemblies into functional nanosystems and devices.

Wettability Modification of Nanomaterials by Low-Energy Electron Flux.

Controllable modification of surface free energy and related properties (wettability, hygroscopicity, agglomeration, etc.) of powders allows both understanding of fine physical mechanism acting on nanoparticle surfaces and improvement of their key characteristics in a number of nanotechnology applications. In this work, we report on the method we developed for electron-induced surface energy and modification of basic, related properties of powders of quite different physical origins such as diamond and ZnO. The applied technique has afforded gradual tuning of the surface free energy, resulting in a wide range of wettability modulation. In ZnO nanomaterial, the wettability has been strongly modified, while for the diamond particles identical electron treatment leads to a weak variation of the same property. Detailed investigation into electron-modified wettability properties has been performed by the use of capillary rise method using a few probing liquids. Basic thermodynamic approaches have been applied to calculations of components of solid-liquid interaction energy. We show that defect-free, low-energy electron treatment technique strongly varies elementary interface interactions and may be used for the development of new technology in the field of nanomaterials.

Noncollinear second-harmonic generation in sub-micrometer-poled RbTiOPO(4).

We have generated noncollinear quasi-phase-matched second harmonic wave in an RbTiOPO(4) crystal that was poled using the high-voltage atomic force microscope (HV-AFM). To the best of our knowledge, this is the first systematic nonlinear frequency conversion study of samples produced by the HV-AFM method. The short poling period of 1.18 microm enabled us to observe second harmonic generation at very large angles with respect to the fundamental wave. The setup was used to optically explore the homogeneity of the poled area. The measurements are in a reasonable agreement with an analytic calculations.

Mid-infrared difference-frequency generation in periodically poled KTiOAsO(4) and application to gas sensing.

Tunable mid-infrared radiation (3.45-3.75 microm) with a power level of 0.14 microW is generated by quasi-phase-matched difference-frequency mixing of a Nd:YAG laser and a tunable-diode laser (near 1.5 microm) in multigrating periodically poled KTiOAsO(4) . The wavelength and temperature bandwidths are approximately 65 nm cm and approximately 62 degrees C, respectively. The temperature-tuning slope of the phase-matched idler wavelength, -0.94 nm/ degrees C, is almost twice that of periodically poled KTiOPO(4) . We use the measurements to derive a mid-infrared-corrected Sellmeier equation for the Z axis of KTiOAsO(4). The generated mid-infrared radiation is applied to sensitive high-resolution spectroscopy of the nu(3) band of methane.

Efficient quasi-phase-matched frequency doubling with phase compensation by a wedged crystal in a standing-wave external cavity.

In standing-wave enhancement cavities for frequency doubling, second-harmonic fields are generated in both directions of propagation. To add the fields coherently, one should compensate for the phase shifts introduced by dispersive elements in the cavity. We experimentally demonstrate phase compensation in a compact standing-wave frequency-doubling cavity by use of a wedged periodically poled KTP crystal. The highest conversion efficiency and second-harmonic power obtained by pumping with a 1064-nm cw Nd:YAG laser were 69.4% and 268 mW, respectively.

Efficient resonant frequency doubling of a cw Nd:YAG laser in bulk periodically poled KTiOPO(4).

A cw Nd:YAG laser was quasi-phase-matched frequency doubled by a bulk periodically poled flux-grown KTiOPO(4) crystal in an external resonant cavity. The conversion efficiency and the second-harmonic power with a pump of 225 mW were 55% and 123.5 mW, respectively. The loss of the 1-cm-long crystal, which operated near room temperature, was 1.3% and was dominated by scatter from the cleaved facets of the crystal. No damage, photorefractive or other, was observed at intensites of 370Wmm(-2) , but beam size had to be optimized to eliminate thermal-induced instabilities in the doubling cavity.

Continuous-wave optical parametric oscillator based on periodically poled KTiOPO(4).

We report what is to our knowledge the first demonstration of a continuous-wave optical parametric oscillator (OPO) based on periodically poled KTiOPO(4) . The 10-mm-long flux-grown crystal had a quasi-phase-matched period of 9mum . The pump source was a miniature frequency-doubled Nd:YAG laser, and the threshold power of this doubly resonant device was 51 mW. The OPO was operated near room temperature. The signal and the idler wavelengths could be tuned in the range 1037-1093 nm by variation of the crystal temperature (32-38 degrees C) and the cavity length. Unlike in other nonlinear crystals, green-induced infrared absorption was not observed up to the highest pumping intensity of approximately 4.5kW/cm(2) .

Highly efficient doubling of a high-repetition-rate diode-pumped laser with bulk periodically poled KTP.

An internal doubling efficiency of 64% at 2 MW/cm(2)was obtained in a single-pass configuration with an uncoated, 1-cm-long, bulk periodically poled KTP crystal placed outside the resonator of a pulsed, diode-pumped Nd:YAG laser. An average of 4.8W of green light was obtained from a 7.5-W pump beam inside the crystal. Doubling efficiency exceeded 50% at levels of 0.75 MW/cm(2). The measured thermal tolerance of the doubling process (FWHM) was 3.3( degrees )C cm, and the measured temperature tuning coefficient was 0.053 nm/( degrees )C .