Optical properties of narrow high quality GaAs/AlGaAs quantum wells grown by MOVPE

We report optical characterization of high quality quantum well (QW) structures grown by metal-organic vapour-phase epitaxy (MOVPE). Thin QW layers of GaAs of thicknesses between 20 Å and 80 Å inserted between Al_0.36Ga_0.64 As confining layers as well as nominally 20 Å QW's in Al_xGa_1−xAs with varying x have been studied. Exciton confinement energies exceeding 250 meV and a FWHM of 6 meV for the thinnest QW have been observed. The photoluminescence (PL) data allows the observation of monolayer fluctuations in the QW widths and indicates an interface abruptness of about one atomic layer. Photoluminescence excitation spectroscopy allows electronic excited states to be seen.     

High-spin states above 3.5 MeV in 91Nb

High-spin states in ⁹¹Nb populated by the ⁸⁹Y(α, 2nγ) reaction were studied at 24.0 MeV and 35.7 MeV incident α-particle energy. Gamma-gamma coincidence and γ-ray angular distribution measurements were made. Several high-spin states in ⁹¹Nb were observed at 35.7 MeV bombarding energy which were not observable at 24.0 MeV. The shell model structure of these states is discussed.     

Photovoltaic Performance Enhancement in Dye-Sensitized Solar Cells with Periodic Surface Relief Structures

One-dimensional and two-dimensional periodic TiO₂ relief structures were incorporated in dye-sensitized solar cells. The periodic TiO₂ structures were fabricated using surface relief gratings photoinscribed on azobenzene functionalized polymer films as templates and TiO₂ sol-gel solution. Enhancement of power conversion of the solar cells made with the relief TiO₂ structures was achieved. This enhancement suggests that the relief TiO₂ structures can offer efficient light-trapping with the increased effective optical-path length in the solar cells.     

Synthesis of a self organizable curcumin derivative and investigation of its interaction with metals in 100% aqueous media

We report the synthesis of a self organizable and water dispersible bis PEGylated (bis polyethyleneglycolated) curcumin (1) using an efficient synthetic method. Compound 1 forms nanoparticles on the order of 90 nm in water. Even though it forms nanoparticles, compound 1 interacts strongly with metal ions, Al⁺³, Cu⁺², and Hg⁺². Fluorescence and absorption spectroscopic techniques were employed to investigate the metal interactions of these nanoparticles. Al⁺³ and Cu⁺² ions interact with compound 1 leading to enhancement and dramatic quenching in the fluorescence of the latter in 100% water, respectively. Addition of Hg⁺² ions to compound 1 in water produces a ratiometric change in the absorption spectra of the nanoparticles. Although PEGylated curcumin derivatives were reported in the past, there have been no reports on their self organization into nanoparticles and extensive studies on their metal interaction properties in 100% water using its fluorescence and absorption properties.