The natural ability of peptides and proteins to self-assemble into elongated fibrils is associated with several neurogenerative diseases. Diphenylalanine (FF) tubular structures that have the same structural motif as in Ab-amyloid peptide (involved in Alzheimer's disease) are shown to possess remarkable physical properties ranging from piezoelectricity to electrochemical activities. In this work, we also discover a significant pyroelectric activity and measure the temperature dependence of the pyroelectric coefficient in the temperature range of 20 100 C. Pyroelectric activity decreases with temperature contrary to most ferroelectric materials and significant relaxation of pyrocurrent is observed on cooling after heating above 50 C. This unusual behavior is assigned to the temperature-induced disorder of water molecules inside the nanochannels. Pyroelectric coefficient and current and voltage figures of merit are estimated and future applications of pyroelectric peptide nanostructures in biomedical applications are outlined. Published by AIP Publishing.

Nanostructured silicon has generated a lot of interest in the past decades as a key material for silicon-based photonics. The low absorption coefficient makes silicon nanocrystals attractive as an active medium in waveguide structures, and their third-order nonlinear optical properties are crucial for the development of next generation nonlinear photonic devices. Here we report the first observation of stimulated Raman scattering in silicon nanocrystals embedded in a silica matrix under non-resonant excitation at infrared wavelengths (~1.5 μm). Raman gain is directly measured as a function of the silicon content. A giant Raman gain from the silicon nanocrystals is obtained that is up to four orders of magnitude greater than in crystalline silicon. These results demonstrate the first Raman amplifier based on silicon nanocrystals in a silica matrix, thus opening new perspectives for the realization of more efficient Raman lasers with ultra-small sizes, which would increase the synergy between electronic and photonic devices.

ore WO 3 nanofibers (140-300 nm in diameter, several hundred mm long) are made by a novel, water-based electrospinning process using ammonium metatungstate (AMT) and polyvinylpyrrolidone (PVP) as precursors. TiO 2 shells (1.5-20 nm) are grown by atomic layer deposition (ALD) using TiCl 4 and water at 2508C. The WO 3 /TiO 2 composite fibers are analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM)-energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Raman spectroscopy (RS), UV-Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). The optimal photocatalytic conversion under visible light is reached by the WO 3 /1.5 nm TiO 2 nanofibers, which have higher activity compared to bare WO 3 and Degussa TiO 2 . Thicker TiO 2 layers fill the pores of the nanowires and reduce the specific surface area, weakening the photocatalytic activity.

We study the properties of Si-rich silicon oxide SiOx (x < 2) films grown on silica substrates by molecular beam deposition, in a wide range of Si content and annealing temperatures. The measured refractive index and absorption coefficient are successfully described using the effective medium approximation and the chemical compositions measured by x-ray photoelectron spectroscopy (XPS). The Si–SiO2 phase separation and the degree of Si crystallization increase with the annealing temperature; however, even after annealing at 1200 °C, the samples contain a large proportion of suboxides and partially disordered Si. The Si Raman signal and the absorption coefficient are nearly proportional to the amount of elemental Si provided by XPS. On the other hand, the Si Raman signal is much weaker than it is expected from the amount of elemental Si, which can be explained by the presence of ultra-small Si nanocrystals (diameters < 2 nm) and/or by the difference in the properties of bulk and nanoscale Si. The 1.5-eV photoluminescence (PL) intensity is the highest for annealing at 1100–1150 °C and x = 1.8–1.9. In contrast, the PL quantum yield steadily increases when the intensity of the Si Raman signal decreases. This observation suggests that the Si nanocrystals observed in the Raman spectra are not direct light-emitting centers. The temperatures induced by laser light in these films are surprisingly high, especially at the highest Si content (x ∼ 1.3). The laser-induced temperature (up to ∼350 °C) substantially down-shifts the Raman band of Si nanocrystals (in our experiments from ∼518 to ∼512 cm−1) and increases the absorption coefficient (by a factor of ∼1.4).

The diameter of single-walled carbon nanotubes (SWNTs) is an important characteristic to determine their electronic properties and direct further applications in electronics and photonics. A demand currently exists for an accurate and rapid method of evaluating the mean diameter and diameter distribution of bulk SWNTs. Here, we provide an effective means for quantifying the diameter distribution of SWNTs using optical absorption spectroscopy without a strict prior assumption on the form of the diameter distribution. Verification of this assignment protocol is based upon statistical analysis of hundreds of high-resolution transmission electron microscopy (HRTEM) images as well as comparison with Raman measurements on the same SWNT samples. A good agreement among different techniques indicates that this approach enables accurate and rapid assessment of diameter distribution and can be extended to bulk SWNT samples with various diameter distributions.