Tuning Lasing Emission toward Long Wavelengths in GaAs-(In,Al)GaAs Core-Multishell Nanowires.

Semiconductor nanowire (NW) lasers are attractive as integrated on-chip coherent light sources with strong potential for applications in optical communication and sensing. Realizing lasers from individual bulk-type NWs with emission tunable from the near-infrared to the telecommunications spectral region is, however, challenging and requires low-dimensional active gain regions with an adjustable band gap and quantum confinement. Here, we demonstrate lasing from GaAs-(InGaAs/AlGaAs) core-shell NWs with multiple InGaAs quantum wells (QW) and lasing wavelengths tunable from ∼0.8 to ∼1.1 µm. Our investigation emphasizes particularly the critical interplay between QW design, growth kinetics, and the control of InGaAs composition in the active region needed for effective tuning of the lasing wavelength. A low shell growth temperature and GaAs interlayers at the QW/barrier interfaces enable In molar fractions up to ∼25% without plastic strain relaxation or alloy intermixing in the QWs. Correlated scanning transmission electron microscopy, atom probe tomography, and confocal PL spectroscopy analyses illustrate the high sensitivity of the optically pumped lasing characteristics on microscopic properties, providing useful guidelines for other III-V-based NW laser systems.

Primary cutaneous aspergillosis in six leukemic children.

We report a cluster of primary cutaneous aspergillosis in six children with hematologic malignancy. When first seen, they had hemorrhagic bullae caused by Aspergillus flavus, Aspergillus fumigatus, and Aspergillus niger at the sites of insertion of intravenous cannulas or where arm boards had been taped to the extremities. Rapid diagnosis of cutaneous aspergillosis was made by direct examination of the blister roof with potassium hydroxide before it progressed to a necrotic ulcer. Intravenous amphotericin was instituted promptly in five of six patients, and none died of disseminated aspergillosis. Epidemiologic investigation tracked the source of aspergillus to a storeroom with a false ceiling that had recently been repaired for a water leak.