Growth, structural and optical properties of GaAs/AlGaAs Core/shell nanowires with and without quantum well shells

We have investigated the growth, structural properties and photoluminescence of novel GaAs/AlGaAs radial heterostructure nanowires, fabricated by metalorganic chemical vapour deposition. The effect of growth temperature on nanowire morphology is discussed. Strong photoluminescence is observed from GaAs nanowires with AlGaAs shells. Core/multishell nanowires, of GaAs cores clad in several alternating layers of thick AlGaAs barrier shells and thin GaAs quantum well shells, exhibit a blue-shifted photoluminescence peak believed to arise from quantum confinement effects. A novel two-temperature growth procedure for obtaining GaAs cores is introduced, and other nanowire heterostructures are addressed. © 2006 IEEE.

Temperature dependence of photoluminescence from single core-shell GaAs-AlGaAs nanowires

Temperature-dependent polarized microphotoluminescence measurements of single GaAsAlGaAs core-shell nanowires are used to probe their electronic states. The low-temperature emission from these wires is strongly enhanced compared with that observed in bare GaAs nanowires and is strongly polarized, reflecting the dielectric mismatch between the nanowire and the surrounding air. The temperature-dependent band gap of the nanowires is seen to be somewhat different from that observed in bulk GaAs, and the PL rapidly quenches above 120 K, with an activation energy of 17 meV reflecting the presence of nonradiative defects. © 2006 American Institute of Physics.

Award Winner in the Young Investigator Category, 2014 Society for Biomaterials Annual Meeting and Exposition, Denver, Colorado, April 16-19, 2014: Periodically perforated core-shell collagen biomaterials balance cell infiltration, bioactivity, and mechanical properties.

Orthopedic tissue engineering requires biomaterials with robust mechanics as well as adequate porosity and permeability to support cell motility, proliferation, and new extracellular matrix (ECM) synthesis. While collagen-glycosaminoglycan (CG) scaffolds have been developed for a range of tissue engineering applications, they exhibit poor mechanical properties. Building on previous work in our lab that described composite CG biomaterials containing a porous scaffold core and nonporous CG membrane shell inspired by mechanically efficient core-shell composites in nature, this study explores an approach to improve cellular infiltration and metabolic health within these core-shell composites. We use indentation analyses to demonstrate that CG membranes, while less permeable than porous CG scaffolds, show similar permeability to dense materials such as small intestine submucosa (SIS). We also describe a simple method to fabricate CG membranes with organized arrays of microscale perforations. We demonstrate that perforated membranes support improved tenocyte migration into CG scaffolds, and that migration is enhanced by platelet-derived growth factor BB-mediated chemotaxis. CG core-shell composites fabricated with perforated membranes display scaffold-membrane integration with significantly improved tensile properties compared to scaffolds without membrane shells. Finally, we show that perforated membrane-scaffold composites support sustained tenocyte metabolic activity as well as improved cell infiltration and reduced expression of hypoxia-inducible factor 1α compared to composites with nonperforated membranes. These results will guide the design of improved biomaterials for tendon repair that are mechanically competent while also supporting infiltration of exogenous cells and other extrinsic mediators of wound healing.

Influence of ZnS and MgO Shell on the Photoluminescence Properties of ZnO Core/Shell Nanowire

Chinese Academy of Sciences；National Science Fund for Distinguished Young Scholar 60925016；National High Technology Research and Development program of China 2009AA034101；Postdoctoral Foundation 0971050000

Zn2SiO4/ZnO Core/Shell Coaxial Heterostructure Nanobelts Formed by an Epitaxial Growth

Si-doped ZnO can be synthesized on the surface of the early grown Zn2SiO4 nanostructures and form core/ shell coaxial heterostructure nanobelts with an epitaxial orientation relationship. A parallel interface with a periodicity array of edge dislocations and an inclined interface without dislocations can be formed. The visible green emission is predominant in PL spectra due to carrier localization by high density of deep traps from complexes of impurities and defects. Due to band tail localization induced by composition and defect fluctuation, and high density of free-carriers donated by doping, especially the further dissociation of excitons into free-carriers at high excitation intensity, the near-band-edge emission is dominated by the transition of free-electrons to free-holes, and furthermore, exhibits a significant excitation power-dependent red-shift characteristic. Due to the structure relaxation and the thermalization effects, carrier delocalization takes place in deep traps with increasing excitation density. As a result, the green emission passes through a maximum at 0.25I(0) excitation intensity, and the ratio of the violet to green emission increases monotonously as the excitation laser power density increases. The violet and green emission of ZnO nanostructures can be well tuned by a moderate doping and a variation in the excitation density.

Characterization of CdSe and CdSe/CdS core/shell nanoclusters synthesized in aqueous solution

CdSe nanoclusters overcoated with CdS shell were prepared with macapoacetic acid as stabilizer. The optical properties of CdSe nanoclusters and the influence of CdS shell on the electronic structures of CdSe cores were studied by optical absorption, photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. Based on PL and PLE results and the theoretical calculation on fine structure of bandedge exciton, a model of formation of excimer within the small clusters was proposed to explain the large Stokes shift of luminescence from absorption edge observed in PL results. (C) 2000 Elsevier Science B.V. All rights reserved.

Synthesis and luminescence of CdS/ZnS core/shell nanocrystals

CdS/ZnS core/shell nanocrystals were prepared from an aqueous/alcohol medium. A red shift of the absorption spectrum and an increase of the room temperature photoluminescence intensity accompanied shell growth.

The fabrication of TiO2-supported zeolite with core/shell heterostructure for ethanol dehydration to ethylene

The TiO2-supported zeolite with core/shell heterostructure was fabricated by coating aluminosilicate zeolite (ASZ) on the TiO2 inoculating seed via in situ hydrothermal synthesis. The catalysts were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), nitrogen physisorption (BET), and Fourier transform infrared spectroscopy (FT-IR). The surface acidity of the catalysts was measured by pyridine-TPD method. The catalytic performance of the catalysts for ethanol dehydration to ethylene was also investigated. The results show that the TiO2-supported zeolite composite catalyst with core/shell heterostructure exhibits prominent conversion efficiency for ethanol dehydration to ethylene.

Characterization of CdSe and CdSe/CdS core/shell nanoclusters synthesized in aqueous solution

CdSe nanoclusters overcoated with CdS shell were prepared with macapoacetic acid as stabilizer. The optical properties of CdSe nanoclusters and the influence of CdS shell on the electronic structures of CdSe cores were studied by optical absorption, photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. Based on PL and PLE results and the theoretical calculation on fine structure of bandedge exciton, a model of formation of excimer within the small clusters was proposed to explain the large Stokes shift of luminescence from absorption edge observed in PL results. (C) 2000 Elsevier Science B.V. All rights reserved.

Synthesis and luminescence of CdS/ZnS core/shell nanocrystals

CdS/ZnS core/shell nanocrystals were prepared from an aqueous/alcohol medium. A red shift of the absorption spectrum and an increase of the room temperature photoluminescence intensity accompanied shell growth.

Fabrication and luminescent properties of the core-shell structured YNbO4 : Eu3+/Tb3+@SiO2 spherical particles

The core-shell structured YNbO4:Eu3+/Tb3+@SiO2 particles were realized by coating the YNbO4:Etr(3+)/Tb3+ phosphors onto the surface of spherical silica via a sol-gel process. The obtained materials were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform IR spectroscopy (FT-IR), photoluminescence (PL) spectra, and cathodoluminescence (CL) spectra.

Synthesis of magnetite core-shell nanoparticles by surface-initiated ring-opening polymerization of L-lactide

Fe3O4-polylactide (PLA) core-shell nanoparticles were perpared by surface functionalization of Fe3O4 nanoparticles and subsequent surface-initiated ring-opening polymerization of L-lactide. PLA was directly connected onto the magnetic nanoparticles surface through a chemical linkage. Fourier transform infrared (FT-IR) spectra directly provided evidence of the PLA on the surface of the magnetic nanoparticles. Transmission electron microscopy images (TEM) showed that the magnetic nanoparticles were coated by PLA with a 3-nm-thick shell.

Multilayered core-shell structure of the dispersed phase in high-impact polypropylene

The multiphase morphology of high impact polypropylene (hiPP), which is a reactor blend of polypropylene (PP) with ethylene-propylene copolymer, was investigated by transmission electron microscopy, selected area electron diffraction, atomic force microscopy, and field-emission scanning electron microscopy techniques in conjunction with an analysis of the hiPP composition and chain structure based on solvent fractionation, C-13-NMR, and differential scanning calorimetry measurements.