Optical Performance of Top-Down Fabricated AlGaN Nanorod Arrays with Multi-Quantum Wells Embedded.

Deep ultraviolet AlGaN-based nanorod (NR) arrays were fabricated by nanoimprint lithography and top-down dry etching techniques from a fully structural LED wafer. Highly ordered periodic structural properties and morphology were confirmed by scanning electron microscopy and transmission electron microscopy. Compared with planar samples, cathodoluminescence measurement revealed that NR samples showed 1.92-fold light extraction efficiency (LEE) enhancement and a 12.2-fold internal quantum efficiency (IQE) enhancement for the emission from multi-quantum wells at approximately 277 nm. The LEE enhancement can be attributed to the well-fabricated nanostructured interface between the air and the epilayers. Moreover, the reduced quantum-confined stark effect accounted for the great enhancement in IQE.

Fabrication of AlGaN nanorods with different Al compositions for emission enhancement in UV range.

Highly ordered AlxGa1-xN nanorods with varied aluminum alloy compositions (0.18 ≤ x ≤ 0.8) are fabricated with nanoimprint lithography and top-down dry etching techniques. And the structural properties and morphology are obtained by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Compared with as-grown AlGaN samples, nanorod samples reveal outstanding optical performance on account of strain releasing and light extraction enhancement. Through Raman scattering and cathodeluminescence measurements, it has been observed clear red-shifts of E2h modes and near band edge emission (NBE) peaks of AlGaN nanorods compared to the planar ones, indicating the residual strain releasing after nano-fabrication. The integrated intensities of NBE peaks of AlGaN nanorods manifest light emission enhancement up to 2.7 at deep-UV range. Finite-difference time-domain (FDTD) simulations have been adopted to investigate the light extraction and far-field distribution of such structures, it turned out that ordered nanorod array can enhance the TM polarized emission extraction 2-7 folds compared to the planar structure. The optical regulation in nanorod arrays should take the responsibility for the observed optical enhancements, which is proved by the far-field distribution of light, thus it can improve the performance of ultraviolet LEDs.

Significant improvements in InGaN/GaN nano-photoelectrodes for hydrogen generation by structure and polarization optimization.

The photoelectrodes based on III-nitride semiconductors with high energy conversion efficiency especially for those self-driven ones are greatly desirable for hydrogen generation. In this study, highly ordered InGaN/GaN multiple-quantum-well nanorod-based photoelectrodes have been fabricated by a soft UV-curing nano-imprint lithography and a top-down etching technique, which improve the incident photon conversion efficiency (IPCE) from 16% (planar structure) to 42% (@ wavelength = 400 nm). More significantly, the turn-on voltage is reduced low to -0.6 V, which indicates the possibility of achieving self-driven. Furthermore, SiO2/Si3N4 dielectric distributed Bragg reflectors are employed to further improve the IPCE up to 60%. And the photocurrent (@ 1.1 V) is enhanced from 0.37 mA/cm(2) (original planar structure) to 1.5 mA/cm(2). These improvements may accelerate the possible applications for hydrogen generation with high energy-efficiency.

Great enhancement in the excitonic recombination and light extraction of highly ordered InGaN/GaN elliptic nanorod arrays on a wafer scale.

A series of highly ordered c-plane InGaN/GaN elliptic nanorod (NR) arrays were fabricated by our developed soft UV-curing nanoimprint lithography on a wafer. The photoluminescence (PL) integral intensities of NR samples show a remarkable enhancement by a factor of up to two orders of magnitude compared with their corresponding as-grown samples at room temperature. The radiative recombination in NR samples is found to be greatly enhanced due to not only the suppressed non-radiative recombination but also the strain relaxation and optical waveguide effects. It is demonstrated that elliptic NR arrays improve the light extraction greatly and have polarized emission, both of which possibly result from the broken structure symmetry. Green NR light-emitting diodes have been finally realized, with good current-voltage performance and uniform luminescence.

Antiangiogenic treatment prevents adventitial constrictive remodeling in graft arteriosclerosis.

BACKGROUND: Lumen loss in graft arteriosclerosis is the consequence of the development of a thick neointima and constrictive arterial remodeling. The latter is due to adventitial chronic inflammation and excessive perivascular collagen deposition. We reasoned that blockade of the portal of entry of inflammatory effectors may constitute a strategy to prevent constrictive arterial remodeling. METHODS AND RESULTS: We found that an anti-angiogenic therapy (ABT-510 nonapeptide), devoid of direct immunomodulatory properties, dramatically reduced adventitial angiogenesis by 66% (P<0.0001) in the rat aortic interposition model of graft arteriosclerosis. The associated decreased entry of inflammatory cells (44%; P<0.00001) resulted in drastic reduction of collagen deposition (57%; P<0.0001) thereby preventing subsequent adventitial constrictive remodeling and reduction of lumen surface area (5.26+/-0.74 vs. 8.58+/-2.48 microm2; Control vs. ABT-510-treated rats; P<0.0001). ABT-510 had no effect on the development of the neointima. CONCLUSION: This work supports the idea that targeting angiogenesis may act synergistically with conventional immunosuppressive therapy in preventing graft arteriosclerosis, a crucial feature of chronic graft rejection.

Aortic aneurysms in a rat model: in vivo MR imaging of endovascular cell therapy.

PURPOSE: To prospectively evaluate in rats whether magnetic cell labeling can be used to noninvasively assess the technical success of endovascular cell therapy for abdominal aortic aneurysms (AAAs). MATERIALS AND METHODS: The study was approved by an institutional animal care and use committee. Vascular smooth muscle cells (VSMCs) labeled with iron oxide nanoparticles were seeded endovascularly in already formed AAAs. T2*-weighted gradient-echo and T2-weighted spin-echo magnetic resonance (MR) imaging was performed in vivo at 1.5 T before and 30 minutes after the injection of iron-loaded VSMCs (14 rats), nonlabeled VSMCs (three rats), or iron-free particles (three rats). Ten rats were euthanized shortly after the injection (day 0). Of the 10 remaining rats, which were seeded with iron-loaded cells, three were imaged on day 7 after cell delivery; three, on day 14; and four, on day 28; then they were euthanized. Ex vivo high-field-strength MR imaging of two AAAs was performed 28 days after cell delivery. Histologic examination of cross sections of all AAAs was performed. Statistical evaluations were performed with a nonparametric Wilcoxon correlation test. RESULTS: Magnetic cell labeling did not alter the capability of VSMCs to stabilize the diameter of the aneurysms. T2*-weighted gradient-echo images showed areas of hypointense signal within the aortic wall immediately and up to 1 month after cell therapy. The mean signal intensity decreased significantly after cell delivery (from 2362 +/- 244 [standard deviation] before to 434 +/- 275 after delivery, P < .001). Areas of hypointense signal and iron-loaded VSMCs were colocalized in the area of aortic wall reconstruction at both high-field-strength MR imaging and histologic analysis. CONCLUSION: MR imaging with magnetic cell labeling can be used to document endovascular cell delivery in already formed AAAs in rats.