Enhanced Cooper-Pair Injection into a Semiconductor Structure by Resonant Tunneling.

We demonstrate enhanced Andreev reflection in a Nb/InGaAs/InP-based superconductor-semiconductor hybrid device resulting in increased Cooper-pair injection efficiency, achieved by Cooper-pair tunneling into a semiconductor quantum well resonant state. We show this enhancement by investigating the differential conductance spectra of two kinds of samples: one exhibiting resonant states and one which does not. We observe resonant features alongside strong enhancement of Cooper pair injection in the resonant sample, and lack of Cooper pair injection in the nonresonant sample. The theoretical modeling for measured spectra by a numerical approach agrees well with the experimental data. Our findings open a wide range of directions in condensed matter physics and in quantum technologies such as superconducting light-emitting diodes and structures supporting exotic excitations.

Proximal Femoral Fractures in Geriatric Patients: Identifying the Major Risk Factors for Postoperative Infection in a Single-Center Study.

BACKGROUND: Proximal femoral fractures (PFF) are among the most common injuries in the elderly population treated by orthopedic surgeons. Postoperative complications, especially infections, are of great importance due to their effect on patient mortality and morbidity and healthcare costs. OBJECTIVES: To assess the main causes for postoperative infection among PFF patients. METHODS: We conducted a retrospective analysis of PFF patients in our medical center between 2015 and 2017. Patients were divided into two groups based on whether there was postoperative infection during immediate hospitalization and 30 days after surgery. Factors such as time from admission to surgery, duration of surgery, and length of stay were analyzed. Groups were analyzed and compared using a t-test, chi-squared and Fisher's exact tests. RESULTS: Of 1276 patients, 859 (67%) underwent closed reduction internal fixation, 67 (5%) underwent total hip arthroplasty, and 350 (28%) underwent hemiarthroplasty. Of the total, 38 patients (3%) were diagnosed with postoperative infection. The demographics and co-morbidities were similar between the two study groups. The incident of infection was the highest among patients undergoing hemiarthroplasty (6%, P < 0.0001). Length of hospitalization (15 vs. 8 days, P = 0.0001) and operative time (117 vs. 77 minutes, P = 0.0001) were found to be the most significant risk factors for postoperative infection. CONCLUSIONS: Predisposition to postoperative infections in PPF patients was associated with prolonged length of surgery and longer hospitalization. We recommend optimizing fast discharge, selecting the appropriate type of surgery, and improving surgical planning to reduce intraoperative delays and length of surgery.

Andreev Reflection in a Superconducting Light-Emitting Diode.

We experimentally demonstrate Cooper-pair injection into a superconducting light-emitting diode by observing Andreev reflection at the superconductor-semiconductor interface, overcoming the contradicting requirements of an electrically transparent interface and radiative recombination efficiency. The device exhibits electroluminescence enhancement at the quasi-Fermi energy at temperatures below Tc. The theoretically predicted conductance and electroluminescence spectra based on Cooper-pair injection into the semiconductor correspond well to our experimental results. Our findings pave the way for practical superconductor-semiconductor quantum light sources.

Controlled axial and radial growth of InP nanowires by metal-organic molecular beam epitaxy using the selective-area vapor-liquid-solid approach.

Controlling the transition from axial to radial growth is essential for advanced III-V nanowire (NW) technology. Growth temperature and precursor flux affect this transition in a complicated manner. Here, we report on experiments designed to map the axial to radial growth transition of InP NWs prepared by the selective-area vapor-liquid-solid method during metal-organic molecular beam epitaxy. An optimized growth procedure for axial to radial switching was obtained, maintaining the pure wurtzite crystal phase of the NWs.

Pure wurtzite GaP nanowires grown on zincblende GaP substrates by selective area vapor liquid solid epitaxy.

We report on the growth of single phase wurtzite (WZ) GaP nanowires (NWs) on GaP (111) B substrates by metal organic molecular beam epitaxy following the selective area vapor-liquid-solid (SA-VLS) approach. During the SA-VLS process, precursors are supplied directly to the NW sidewalls, and the short diffusion length of gallium (or its precursors) does not significantly limit axial growth. Transmission electron microscopy (TEM) images reveal that no stacking faults are present along a 600 nm long NW. The lattice constants of the pure WZ GaP obtained from the TEM images agree with values determined previously by x-ray diffraction from non-pure NW ensembles.

InP Nanoflag Growth from a Nanowire Template by in Situ Catalyst Manipulation.

Quasi-two-dimensional semiconductor materials are desirable for electronic, photonic, and energy conversion applications as well as fundamental science. We report on the synthesis of indium phosphide flag-like nanostructures by epitaxial growth on a nanowire template at 95% yield. The technique is based on in situ catalyst unpinning from the top of the nanowire and its induced migration along the nanowire sidewall. Investigation of the mechanism responsible for catalyst movement shows that its final position is determined by the structural defect density along the nanowire. The crystal structure of the "flagpole" nanowire is epitaxially transferred to the nanoflag. Pure wurtzite InP nanomembranes with just a single stacking fault originating from the defect in the flagpole that pinned the catalyst were obtained. Optical characterization shows efficient highly polarized photoluminescence at room temperature from a single nanoflag with up to 90% degree of linear polarization. Electric field intensity enhancement of the incident light was calculated to be 57, concentrated at the nanoflag tip. The presented growth method is general and thus can be employed for achieving similar nanostructures in other III-V semiconductor material systems with potential applications in active nanophotonics.

Native-oxide-based selective area growth of InP nanowires via metal-organic molecular beam epitaxy mediated by surface diffusion.

The growth of InP nanowires on an InP(111) B substrate is reported. The substrate native oxide was not removed from the surface prior to growth. Nanowires were grown at 400 °C from gold catalysts in a selective area manner, without bulk growth. Unlike SiO(2)-based metal-organic molecular beam epitaxy selective area growth, the growth reported here is mediated by surface diffusion with a characteristic diffusion length of 4 µm, about an order of magnitude larger than values for diffusion on bare substrates. A pre-growth heating treatment at 450 °C was found to increase the yield of nanowire nucleation from the gold catalysts.

Light emission rate enhancement from InP MQW by plasmon nano-antenna arrays.

Arrays of gold single-strip and double-strip nano-antennas, with resonance in the wavelength range of 1200-1600 nm, were fabricated on the top of InGaAs/InP multi quantum well structure. Photo-luminescence from the quantum-wells was measured and shown to be enhanced by a factor of up to 9, with maximum enhancement wavelength corresponding to the nano-antennas resonance. Emission enhancement is attributed to the coupling of emitting charge-carriers to the plasmonic nano-antennas, causing an estimated increase in the radiative recombination rate by a factor of ~25, thus making it dominant over non-radiative recombination. This effect will enable fast modulation of InP-based nano-emitters spontaneously emitting at telecom-wavelength.

Strain-Mediated Bending of InP Nanowires through the Growth of an Asymmetric InAs Shell.

Controlling nanomaterial shape beyond its basic dimensionality is a concurrent challenge tackled by several growth and processing avenues. One of these is strain engineering of nanowires, implemented through the growth of asymmetrical heterostructures. Here, we report metal-organic molecular beam epitaxy of bent InP/InAs core/shell nanowires brought by precursor flow directionality in the growth chamber. We observe the increase of bending with decreased core diameter. We further analyze the composition of a single nanowire and show through supporting finite element simulations that strain accommodation following the lattice mismatch between InP and InAs dominates nanowire bending. The simulations show the interplay between material composition, shell thickness, and tapering in determining the bending. The simulation results are in good agreement with the experimental bending curvature, reproducing the radius of 4.3 µm (±10%), for the 2.3 µm long nanowire. The InP core of the bent heterostructure was found to be compressed at about 2%. This report provides evidence of shape control and strain engineering in nanostructures, specifically through the exchange of group-V materials in III-V nanowire growth.

Catalyst shape engineering for anisotropic cross-sectioned nanowire growth.

The ability to engineer material properties at the nanoscale is a crucial prerequisite for nanotechnology. Hereunder, we suggest and demonstrate a novel approach to realize non-hemispherically shaped nanowire catalysts, subsequently used to grow InP nanowires with a cross section anisotropy ratio of up to 1:1.8. Gold was deposited inside high aspect ratio nanotrenches in a 5 nm thick SiNx selective area mask; inside the growth chamber, upon heating to 455 °C, the thin gold stripes agglomerated, resulting in an ellipsoidal dome (hemiellipsoid). The initial shape of the catalyst was preserved during growth to realize asymmetrically cross-sectioned nanowires. Moreover, the crystalline nature of the nanowire side facets was found to depend on the nano-trench orientation atop the substrate, resulting in hexagonal or octagonal cross-sections when the nano-trenches are aligned or misaligned with the [1̄10] orientation atop a [111]B substrate. These results establish the role of catalyst shape as a unique tool to engineer nanowire growth, potentially allowing further control over its physical properties.

Sterility of glaucoma medications among chronic users in the community.

PURPOSE: To evaluate the sterility of topical glaucoma medications among chronic glaucoma medication users in the community. SETTING: Glaucoma service, Sanz Medical Center, Laniado Hospital, Netanya. Research mode: Cross-sectional laboratory and clinical study. PATIENTS AND METHODS: Chronic glaucoma patients were asked to submit their topical glaucoma preparations to the microbiology laboratory at Laniado hospital. Samples taken from the interior of the bottle and the tip were cultured using MacConkey agar, blood agar, and chocolate agar plates. RESULTS: Sixty-two bottles of topical glaucoma medications used by 27 patients were tested. Bacterial growth was detected in eight (12.9%) preparations, three of which revealed Pseudomonas aeruginosa, three Staphylococcus epidermidis, one Streptococcus viridans, and one Klebsiella. During the study, acute conjunctivitis was found in one patient, possibly due to the use of infected drops. In another case, two identical medications, which had been used simultaneously for more than 6 weeks by the same patient, were found to be infected. CONCLUSIONS: Glaucoma topical preparations are generally found safe in terms of sterility, though bacterial growth may be found in a small percentage. In most cases, the cause of the loss of sterility could not be determined. However, in two preparations, contamination was related to the noncompliance of the patient who continued using the same preparation longer than instructed. It is imperative to increase the awareness of glaucoma patients to the fact that improper use can lead to eye-drop contamination.