No abstract

As the brightness of GaN-based light-emitting diodes (LEDs) has increased, they have recently attracted considerable interest for use in full-color display panels, traffic signals, and solid-state lighting, because of their many advantages, such as long lifetime, small size, and low energy consumption. [1,2] In spite of these advantages, the overall external quantum efficiency, which depends on the internal quantum efficiency (IQE) and the light extraction efficiency (LEE), is still low in conventional In x Ga 1-x N/GaN quantum well (QW) structures. The IQE is strongly influenced by nonradiative recombination processes, by dislocations and other defects, and by separation of the electron and hole wave functions by spontaneous polarization and strain-induced piezoelectric polarization. The LEE is limited by the total internal reflection of generated light and successive re-absorption due to the high refractive index difference between LED structures and air. Recently, it has been suggested that surface plasmons (SPs), excited on a rough metallic surface by the interaction between light and metal, can significantly enhance light emission by improving the IQE. [3][4][5][6][7][8][9][10][11][12][13][14] Although it has been shown that SPs can significantly enhance the quantum efficiency of InGaN emitters, the realization of a GaN-based LED structure with QW-SP coupling has not yet been reported. Here, we demonstrate for the first time an SP-enhanced InGaN/GaN multiple quantum well (MQW) blue LED with a Ag nanoparticle layer inserted between the n-GaN layer and the MQW layer. SPs have attracted great interest because optical properties can be greatly enhanced by coupling between SPs and the QW in LEDs. The coupling of spontaneous emission from the QW into the SP mode can be observed due to the increased absorption at the SP frequency.[10] Time-resolved photoluminescence (TR-PL) measurements showed that the recombination rate in the QW was 90 times faster than spontaneous emission from the QW, when the emission was resonantly coupled to a SP. [11] Recently, Okamoto et al. [12] reported a 14-fold PL enhancement and a 6.8-fold IQE enhancement of InGaN QWs by QW-Ag coupling. Despite the significant enhancement of the IQE of InGaN emitters by SPs, the realization of a GaN-based LED structure with QW-SP coupling is yet to be reported. In previous optical studies [10][11][12] a metal layer was deposited on the surface of the InGaN QW structure together with a GaN spacer layer of thickness 10$12 nm for efficient QW-SP coupling, in order to observe the PL enhancement of the QW, because electron-hole pairs located within the near-field of the QW surface can couple to the SP mode. To realize SP-enhanced LEDs, the metal layer should be deposited on a p-type GaN/MQW structure and the thickness of that p-type GaN layer is critical for QW-SP coupling. The penetration depth of the SP fringing field into the semiconductor is given by Z ¼ l=2p½ð"where " 0 GaN and " 0 metal make up the real part of the dielectric constant of the semicond...

MP shows potential as an effective novel type of resorbable biomaterial to reduce postoperative adhesion. The easy placement and handling of this material make the MP powder attractive as a tissue adhesion barrier.

An appropriate scaffold, which provides structural support for transplanted cells and acts as a vehicle for the delivery of biologically active molecules, is critical for tissue engineering. We developed a fully interconnected globular porous biphasic calcium phosphate ceramic scaffold by adopting a foaming method, and evaluated its efficiency as a bone substitute and a scaffold for bone tissue engineering by in vitro and in vivo biocompatible analysis and its osteogenic healing capacity in rat tibial bone defects. They have spherical pores averaging 400um in diameter and interconnecting interpores averaging 70um in diameter with average 85% porosity. They elicited no cytotoxicity and noxious effect on cellular proliferation and osteoblastic differentiation during the cell-scaffold construct formation. Also the bone defects grafted with fully interconnected globular porous biphasic calcium phosphate ceramic blocks revealed excellent bone healing within 3 weeks. These findings suggest that the fully interconnected porous biphasic calcium phosphate scaffold formed by the foaming method can be a promising bone substitute and a scaffold for bone tissue engineering.

<p>We report the feasibility of TaC production via self-propagating high temperature synthesis, and the influence of the initial green compact density on the final composite particle size. Experiments are carried out from a minimum pressure of 0.3 MPa, the pressure at which the initial green body becomes self-standing, up to 3 MPa, the point at which no further combustion occurs. The green density of the pellets varies from 29.99% to 42.97%, as compared with the theoretical density. The increase in green density decreases the powder size of TaC, and the smallest particle size is observed with 1.5 MPa, at 10.36 μm. Phase analysis results confirm the presence of the TaC phase only. In the range of 0.3-0.5 MPa, traces of unreacted Ta and C residues are detected. However, results also show the presence of only C residue in the matrix within the pressure range of 0.6-3.0 MPa.</p>