Blueshift

Abstract: We study surface plasmon excitation in pairs of identical Au nanoparticles by optical transmission spectroscopy. The samples produced by electron beam lithography consist of 2D particle arrangements with varying interparticle distance. With decreasing interparticle distance the surface plasmon resonance shifts to longer wavelengths for a polarization direction parallel to the long particle pair axis whereas a blueshift is found for the orthogonal polarization. These experimental findings can be explained by a dipolar interaction mechanism.

Abstract: The optical properties of wurtzite-structured InN grown on sapphire substrates by molecular-beam epitaxy have been characterized by optical absorption, photoluminescence, and photomodulated reflectance techniques. These three characterization techniques show an energy gap for InN between 0.7 and 0.8 eV, much lower than the commonly accepted value of 1.9 eV. The photoluminescence peak energy is found to be sensitive to the free-electron concentration of the sample. The peak energy exhibits very weak hydrostatic pressure dependence, and a small, anomalous blueshift with increasing temperature.

Abstract: Emission mechanisms of InGaN single quantum well blue and green light emitting diodes and multiquantum well structures were investigated by means of modulation spectroscopy. Their static electroluminescence (EL) peak was assigned to the recombination of excitons localized at certain potential minima in the quantum well. The blueshift of the EL peak caused by the increase of the driving current was explained by combined effects of the quantum‐confinement Stark effect and band filling of the localized states by excitons.

Abstract: Titanium dioxide (TiO2 ) nanocrystals are prepared by a hydrolysis process of tetrabutyl titanate. Nanocrystal samples with various sizes of 6.8-27.9 nm are obtained after annealing from 100 to 650 °C. The crystal structures and the average particle sizes are examined using x-ray diffraction. Raman scattering was employed to investigate the evolution of the anatase phase in the nanocrystals during annealing. Phonon confinement and non-stoichiometry effects are responsible for the blueshift and broadening of the lowest-frequency Eg Raman mode. The influence of interfacial vibrations on the Raman linewidth is also discussed.

Abstract: Phase separation and thermal crystallization of SiO/SiO2 superlattices results in ordered arranged silicon nanocrystals. The preparation method which is fully compatible with Si technologies enables independent control of particle size as well as of particle density and spatial position by using a constant stoichiometry of the layers. Transmission electron microscopy investigations confirm the size control in samples with an upper limit of the nanocrystal sizes of 3.8, 2.5, and 2.0 nm without decreasing the silicon nanocrystal density for smaller sizes. The nanocrystals show a strong luminescence intensity in the visible and near-infrared region. A size-dependent blueshift of the luminescence and a luminescence intensity comparable to porous Si are observed. Nearly size independent luminescence intensity without bleaching effects gives an indirect proof of the accomplishment of the independent control of crystal size and number.