Mapping of Fabry-Perot and whispering gallery modes in GaN microwires by nonlinear imaging.

Engineering nonlinear optical responses at the microscale is a key topic in photonics for achieving efficient frequency conversion and light manipulation. Gallium nitride (GaN) is a promising semiconductor material for integrated nonlinear photonic structures. In this work, we use epitaxially grown GaN microwires as nonlinear optical whispering gallery and Fabry-Perot resonators. We demonstrate an effective generation of second-harmonic and polarization-dependent signals of whispering gallery and Fabry-Perot modes (FPM) under near-infrared (NIR) excitation. We show how the rotation of the excitation polarization can be used to control and switch between Fabry-Perot and whispering gallery modes in tapered GaN microwire resonators. We demonstrate the enhancement of two-photon luminescence in the yellow-green spectral range due to efficient coupling between whispering gallery, FPM, and excitonic states in GaN. This luminescence enhancement allows us to conveniently visualize whispering gallery modes excited with a NIR source. Such microwire resonators can be used as compact microlasers or sensing elements in photonic sensors.

Enhanced Second-Harmonic Generation from Sequential Capillarity-Assisted Particle Assembly of Hybrid Nanodimers.

We show enhanced second-harmonic generation (SHG) from a hybrid metal-dielectric nanodimer consisting of an inorganic perovskite nanoparticle of barium titanate (BaTiO3) coupled to a metallic gold (Au) nanoparticle. BaTiO3-Au nanodimers of 100 nm/80 nm sizes are fabricated by sequential capillarity-assisted particle assembly. The BaTiO3 nanoparticle has a noncentrosymmetric crystalline structure and generates bulk SHG. We use the localized surface plasmon resonance of the gold nanoparticle to enhance the SHG from the BaTiO3 nanoparticle. We experimentally measure the nonlinear signal from assembled nanodimers and demonstrate an up to 15-fold enhancement compared to a single BaTiO3 nanoparticle. We further perform numerical simulations of the linear and SHG spectra of the BaTiO3-Au nanodimer and show that the gold nanoparticle acts as a nanoantenna at the SHG wavelength.

IVC agenesis: a rare cause of deep vein thrombosis.

We present the case of a healthy, young Caucasian female who presented to an outside hospital with phlegmasia cerulea dolens of both lower extremities. Computed tomography angiography revealed inferior vena cava (IVC) occlusion. She was initiated on heparin infusion and transferred to University of Virginia Medical Center. Our evaluation revealed aplasia of the IVC from the infrahepatic segment to the confluence of the common iliac veins and acute bilateral iliac vein thromboses. An extensive network of collateral veins was noted. These findings were consistent with IVC agenesis. She was not pregnant or using contraception. Primary thrombophilia workup was negative. She underwent bilateral iliac vein thrombolysis and was started on anticoagulation. While IVC agenesis is rare, it carries risk for development of thrombotic sequelae and bears consideration when evaluating young patients with unexplained deep vein thrombosis, especially if extensive and bilateral.

Retrograde pedal access technique for revascularization of infrainguinal arterial occlusive disease.

PURPOSE: To evaluate limb salvage after recanalization of lower extremity arteries using retrograde pedal access in patients with critical limb ischemia (CLI). MATERIALS AND METHODS: A retrospective review was performed of all patients in whom retrograde pedal arterial access was used for recanalization of infrainguinal occlusive disease between September 2002 and January 2013. Treatment was performed in 99 limbs in 92 patients (64 men and 28 women; median age, 71.6 y; range, 44-91 y) with CLI and no appropriate venous conduit for surgical bypass. Treated limbs were classified as Rutherford class 5 or 6 in 88% and class 4 in 12%. Retrograde and antegrade accesses were combined when occlusions could not be crossed from the antegrade direction. The treated occlusive segments were limited to the femoropopliteal arteries in 22% of procedures, runoff arteries in 32%, or both segments in 46%. Technical success was defined as successful crossing of the lesion and achievement of inline flow to the pedal vessel. Kaplan-Meier analysis was performed to determine limb salvage rate. RESULTS: Technical success was achieved in 88 of 99 (89%) treated limbs. Stents were placed for suboptimal angioplasty results in 41 of 88 (47%) successfully treated limbs. Major complications occurred in 8 of 99 (8%) procedures, 3 of which resulted in periprocedural mortality. Median follow-up was 8 months (mean, 17 mo; range, 1-98 mo). The limb salvage rate for technically successful cases was 74% at 6 months, 64% at 12 months, and 55% at 24 months. CONCLUSIONS: Retrograde pedal access is a viable revascularization technique for achieving limb salvage in patients with CLI.

Subintimal arterial flossing with antegrade-retrograde intervention (SAFARI) and rertograde access for critical limb ischemia.

Retrograde access techniques involve the addition of a retrograde access into the distal target vessel to aid in recanalization of chronic total occlusions. Many patients with critical limb ischemia are also poor surgical candidates because of comorbidities or lack of suitable landing zone for bypass procedures. This approach may be helpful in the setting of chronic occlusions that cannot be crossed via conventional antegrade true-lumen approaches. Subintimal arterial flossing with antegrade-retrograde intervention technique can be used when the occlusion was crossed in the subintimal plane and antegrade re-entry techniques failed. It may also be useful for flush superficial femoral artery occlusions or those lesions that extend into the trifurcation vessels. Proficiency in these techniques allows limb salvage in patients who lack surgical options and would otherwise undergo amputation.

Is fibromuscular dysplasia underdiagnosed? A comparison of the prevalence of FMD seen in CORAL trial participants versus a single institution population of renal donor candidates.

Renal artery fibromuscular dysplasia (FMD) may be underdiagnosed. We evaluated the prevalence of FMD in CORAL (Cardiovascular Outcomes in Renal Atherosclerotic Lesions) renal artery stent trial participants, in which FMD was an exclusion criterion for inclusion. We also evaluated the prevalence of FMD in a relatively healthy population of patients undergoing computed tomographic angiographic (CTA) screening for renal donor evaluation. All renal donor CTAs performed at our institution from January 2003 through November 2011 were retrospectively reviewed for the presence of FMD along with patient sex and age. These results were compared to angiographic core lab (ACL) findings for the CORAL trial. The CORAL ACL database contained 997 patients (mean age 69.3 years; 50% female). Fifty-eight (5.8%) CORAL trial patients (mean age 71.8 years; 75.9% female) demonstrated incidental FMD. The renal donor cohort included 220 patients (mean age 40.5 years; 64.5% female). Five (2.3%) demonstrated FMD (mean age 48.6 years; all female). The odds of FMD in the CORAL cohort were 2.65 times that seen in the renal donor cohort (95% CI: 1.12, 7.57). In C: onclusion, the 5.8% prevalence of renal artery FMD in the CORAL trial population, the presence of which was biased against, suggests underdiagnosis.

Solution processable high dielectric constant nanocomposites based on ZrO2 nanoparticles for flexible organic transistors.

A solution-based strategy for fabrication of high dielectric constant (κ) nanocomposites for flexible organic field effect transistors (OFETs) has been developed. The nanocomposite was composed of a high-κ polymer, cyanoethyl pullulan (CYELP), and a high-κ nanoparticle, zirconium dioxide (ZrO2). Organic field effect transistors (OFETs) based on neat CYELP exhibited anomalous behavior during device operation, such as large hysteresis and variable threshold voltages, which yielded inconsistent devices and poor electrical characteristics. To improve the stability of the OFET, we introduced ZrO2 nanoparticles that bind with residual functional groups on the high-κ polymer, which reduces the number of charge trapping sites. The nanoparticles, which serve as physical cross-links, reduce the hysteresis without decreasing the dielectric constant. The dielectric constant of the nanocomposites was tuned over the range of 15.6-21 by varying the ratio of the two components in the composite dielectrics, resulting in a high areal capacitance between 51 and 74 nF cm(-2) at 100 kHz and good insulating properties of a low leakage current of 1.8 × 10(-6) A cm(-2) at an applied voltage of -3.5 V (0.25 MV cm(-1)). Bottom-gate, top-contact (BGTC) low operating voltage p-channel OFETs using these solution processable high-κ nanocomposites were fabricated by a contact film transfer (CFT) technique with poly(3-hexylthiophene) (P3HT) as the charge transport layer. Field effect mobilities as high as 0.08 cm(2) V(-1) s(-1) and on/off current ratio of 1.2 × 10(3) for P3HT were measured for devices using the high-κ dielectric ZrO2 nanocomposite. These materials are promising for generating solution coatable dielectrics for low cost, large area, low operating voltage flexible transistors.

Facile colloidal lithography on rough and non-planar surfaces for asymmetric patterning.

Free-standing colloidal arrays can be easily transferred to supported fibers. These films conform and provide the template to have consistent submicrometer and nanometer features transferred to the periphery of rough, 7 µm diameter fibers. This technique is adjustable to a number of fiber surfaces and colloidal template sizes.

Hierarchically structured porous cadmium selenide polycrystals using polystyrene bilayer templates.

In this study, a novel approach is demonstrated to fabricate hierarchically structured cadmium selenide (CdSe) layers with size-tunable nano/microporous morphologies achieved using polystyrene (PS) bilayered templates (top layer: colloidal template) via potentiostatic electrochemical deposition. The PS bilayer template is made in two steps. First, various PS patterns (stripes, ellipsoids, and circles) are prepared as the bottom layers through imprint lithography. In a second step, a top template is deposited that consists of a self-assembled layer of colloidal 2D packed PS particles. Electrochemical growth of CdSe crystals in the voids and selective removal of the PS bilayered templates give rise to hierarchically patterned 2D hexagonal porous CdSe structures. This simple and facile technique provides various unconventional porous CdSe films, arising from the effect of the PS bottom templates.

Flexible low-voltage polymer thin-film transistors using supercritical CO2-deposited ZrO2 dielectrics.

The fabrication of low-voltage flexible organic thin film transistors using zirconia (ZrO(2)) dielectric layers prepared via supercritical fluid deposition was studied. Continuous, single-phase films of approximately 30 nm thick ZrO(2) were grown on polyimide (PI)/aluminum (Al) substrates at 250 °C via hydrolysis of tetrakis(2,2,6,6-tetramethyl-3,5-heptane-dionato) zirconium in supercritical carbon dioxide. This dielectric layer showed a high areal capacitance of 317 nF cm(-2) at 1 kHz and a low leakage current of 1.8 × 10(-6) A cm(-2) at an applied voltage of -3 V. By using poly(3-hexylthiophene) (P3HT) as a semiconductor, we have fabricated flexible thin film transistors operating at V(DS) = -0.5 V and V(G) in a range from 0.5 V to -4 V, with on/off ratios on the order of 1 × 10(3) and mobility values higher than 0.1 cm(2)/(V s).

Solvent-assisted soft nanoimprint lithography for structured bilayer heterojunction organic solar cells.

We introduce a novel method to easily fabricate nanopatterns at ambient conditions using solvent-assisted soft nanolithography. For this purpose, a P3HT/PCBM bilayer, one of well-known standard models of solar cell systems, was chosen to optimize bilayer solar cells using the new lithographic technique. The nanopatterns of P3HT made using this method have improved device efficiency compared to planar bilayer heterojunction of the solar cell. The new patterning process creates solar cell devices with a greater than 2-fold increase in power conversion efficiency (PCE) compared to an otherwise equivalent, flat device. This improvement in efficiency is due to the increased interfacial area created by the patterning process. This result demonstrates the feasibility of extensive applications toward nanolithography, relevant to device fabrication, such as electronic devices.