The optical absorption spectrum in nanocrystalline silicon $(n\ensuremath{-}\mathrm{Si})$ was determined from both light transmittance and reflectance measurements. We observed that $n\ensuremath{-}\mathrm{Si}$ has a phonon structure in the optical absorption spectrum. This structure originates from momentum-conserving TO phonon absorption and emission, and provides direct evidence that $n\ensuremath{-}\mathrm{Si}$ is an indirect-band-gap semiconductor with quantum size effects. By using small-angle x-ray scattering to measure the nanocrystal size distribution, we found that the band-gap widening varies as ${(1/L)}^{1.6}$ with decreasing nanocrystal diameter L.
The hydrogen (H) isotope deuterium (D) has attracted special interest for the manufacture of silicon (Si) semiconductors, Si microchips, and optical fibers, as well as for the synthesis of isotopically labeled compounds. However, the efficient production of D or H deuteride in a controlled manner is challenging, and rational H isotope enrichment protocols are still lacking. Here, we demonstrate a highly efficient exchange reaction from H to D on the surface of nanocrystalline Si (n-Si). Fourfold enrichment of D termination was successfully achieved by dipping n-Si into a dilute D solution. By determining the surface-localized vibrational modes for H- and D-terminated n-Si using inelastic neutron scattering spectroscopy, we found that the physical mechanism responsible for this enrichment originates from the difference in the zero-point oscillation energies and entropies of the surface-localized vibrations. Theoretically, the extent of enrichment could be greatly enhanced (\ensuremath{\sim}15 times) using a gas-phase reaction. This enrichment protocol, which avoids the use of precious metal catalysts, opens the way for sustainable H-to-heavy H exchange reactions.
We investigated interference effect between two whispering gallery modes in a system of ultrahigh-Q silica microspheres in which the resonance frequencies of spheres were precisely controlled through thermal tuning. A symmetric transmission peak of coupled—resonator—induced transparency reshaped into a sharp asymmetric spectrum similar to Fano effect in atomic system as the resonance frequency of the second sphere was detuned. The resonance modes showed frequency shifts as a function of the coupling strength between the two spheres, indicating that two whispering gallery modes were configurationally mixed. The observations were compared with calculations and discussed using double-spiral structures in the phase space in the transmitted field.
A stable field emission (FE) under a high residual pressure (10−5Torr) was obtained by the thermal field operation of a nanoneedle cathode with a two dimensional graphene sheet structure. A high brightness electron emission of the order of 1012Asr−1m−2, as well as stable emission, was achieved. The performance of the stabilized cathode was demonstrated by the construction of a compact FE scanning electron microscope (SEM) system, and clear FE-SEM images were obtained at a residual pressure above 10−5Torr. The emission current fluctuation as a function of cathode temperature was discussed based on the Poisson distribution.
Here we describe that graft polyions (elastin-like peptide (ELP)-grafted polyacrylic acid and polyallylamine) are successfully prepared and the ELP graft chains display thermo-responsive conformational change from hydrous coil to dehydrated β-turn structure similar to that of the polymer-free ELP. The layer thickness in the layer-by-layer films from these graft polyions is significantly affected by the deposition temperature because of the existence of ELP, and the resultant layer-by-layer films show layer-number dependent structural color changes that are completely thermo-reversible.
The phase-matching characteristic of a quasi-phase-matched second-harmonic generation in a periodic-lens sequence waveguide on z -face KTiOPO 4 (potassium titanyl phosphate) crystal was obtained by measuring, as a function of input optical wavelength, the intensity of frequency-doubled radiation. The fabricated waveguide is a kind of segmented domain-inverted waveguide of which grating pitch is 4 µ m. The phase-matching was observed in the fundamental wavelength region of 850-860 nm. The half-width of the peak around 854 nm is about 0.3 nm. The broadening of phase-matching in wavelength was explained using geometrical optics.
Abstract Ethenylbenzene-terminated poly(2-acetoxyethyl methacrylate) macromonomer, 2-methyl-2-propenoate-terminated poly (2-acetoxyethyl methacrylate) macromonomer, and 2-methyl-2-propenoate-terminated poly (methyl methacrylate) macromonomer were synthesized. The number-average molecular weight of the macromonomers could be controlled by adjusting the feed composition. Comb-type polymers and graft copolymers were prepared by homopolymerization and copolymerization of macromonomer with comonomer. Unreacted macromonomer in the resulting polymers could be determined by calculating the areas of the macromonomer peaks on gel permeation chromatograms (GPC).
