Understanding GaN/InGaN core-shell growth towards high quality factor whispering gallery modes from non-polar InGaN quantum wells on GaN rods.

GaN microrods are used as a basis for subsequent InGaN quantum well (QW) and quantum dot deposition by metal-organic vapor phase epitaxy. The coverage of the shell along the sidewall of rods is dependent on the rod growth time and a complete coverage is obtained for shorter rod growth times. Transmission electron microscopy measurements are performed to reveal the structural properties of the InGaN layer on the sidewall facet and on the top facet. The presence of layers in the microrod and on the microrod surface will be discussed with respect to GaN and InGaN growth. A detailed model will be presented explaining the formation of multiple SiN layers and the partial and full coverage of the shell around the core. Cathodoluminescence measurements are performed to analyze the InGaN emission properties along the microrod and to study the microresonator properties of such hexagonal core-shell structures. High quality factor whispering gallery modes with [Formula: see text] are reported for the first time in a GaN microrod/InGaN non-polar QW core-shell geometry. The GaN/InGaN core-shell microrods are expected to be promising building blocks for low-threshold laser diodes and ultra-sensitive optical sensors.

New risk and protective factors for severe hypoglycaemia in people with type 1 diabetes.

AIMS: To evaluate risk factors for severe hypoglycaemia (SH) in patients with type 1 diabetes (T1DM). METHODS AND RESULTS: Retrospective observational and comparative study. All SH occurring between 2007 and 2014 in a German population (Lippe-Detmold) were captured. Characteristics of patients with T1DM and SH were compared with a control group being equivalent concerning age, diabetes duration, HbA1c, comorbidity, and ß-blocker treatment. SH was defined as a symptomatic event requiring treatment with intravenous glucose or glucagon administration and being confirmed by a blood glucose measurement of <2.8 mmol/l. Predictive factors for SH were analysed by a multivariable regression model. As many as 405 cases of SH in T1DM occurred in 206 subjects; 50% of episodes were related to 31 patients who experienced ≥3 SH. Need for nursing care (OR 4.88), treatment with NPH (OR 3.68), and impaired hypoglycaemia awareness (OR 2.06) were the strongest risk factors for SH (all p < 0.05, all pFDR-adjusted < 0.10; false discovery rate (FDR)). Depression (OR 0.14), treatment with CSII (OR 0.39) and short-acting insulin analogues (OR 0.31) appeared to be protective (all p < 0.10; FDR-adjusted). The probability of SH onset was significantly higher in patients who had previously experienced recurrent SH episodes. ß-Blocker treatment did not appear to be a risk factor. CONCLUSION: The complex risk for SH in people with T1DM can be reduced by treatment with CSII and short-acting analogues. Future structures of diabetes care will be challenged by the need of treating increasingly geriatric subjects with T1DM having a high risk of SH.

Self-Catalyzed Growth of Vertically Aligned InN Nanorods by Metal-Organic Vapor Phase Epitaxy.

Vertically aligned hexagonal InN nanorods were grown mask-free by conventional metal-organic vapor phase epitaxy without any foreign catalyst. The In droplets on top of the nanorods indicate a self-catalytic vapor-liquid-solid growth mode. A systematic study on important growth parameters has been carried out for the optimization of nanorod morphology. The nanorod N-polarity, induced by high temperature nitridation of the sapphire substrate, is necessary to achieve vertical growth. Hydrogen, usually inapplicable during InN growth due to formation of metallic indium, and silane are needed to enhance the aspect ratio and to reduce parasitic deposition beside the nanorods on the sapphire surface. The results reveal many similarities between InN and GaN nanorod growth showing that the process despite the large difference in growth temperature is similar. Transmission electron microscopy, spatially resolved energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy have been performed to analyze the structural properties. Spatially resolved cathodoluminescence investigations are carried out to verify the optical activity of the InN nanorods. The InN nanorods are expected to be the material of choice for high-efficiency hot carrier solar cells.

Study of high quality spinel zinc gallate nanowires grown using CVD and ALD techniques.

High quality single crystalline zinc gallate (ZnGa2O4) nanowires (NWs) were grown using a combination of chemical vapor deposition and atomic layer deposition techniques. Morphological, structural and optical investigations revealed the formation of Ga2O3-ZnO core-shell NWs and their conversion into ZnGa2O4 NWs after annealing via a solid state reaction. This material conversion was systematically confirmed for single NWs by various measurement techniques including scanning and transmission electron microscopy, Raman spectroscopy and voltage-dependent cathodoluminescence. Moreover, a model system based on the obtained results has been provided explaining the formation mechanism of the ZnGa2O4 NWs.

High quality factor whispering gallery modes from self-assembled hexagonal GaN rods grown by metal-organic vapor phase epitaxy.

Self-assembled GaN rods were grown on sapphire by metal-organic vapor phase epitaxy using a simple two-step method that relies first on a nitridation step followed by GaN epitaxy. The mask-free rods formed without any additional catalyst. Most of the vertically aligned rods exhibit a regular hexagonal shape with sharp edges and smooth sidewall facets. Cathodo- and microphotoluminescence investigations were carried out on single GaN rods. Whispering gallery modes with quality factors greater than 4000 were measured demonstrating the high morphological and optical quality of the self-assembled GaN rods.

Electroluminescence from a single InGaN quantum dot in the green spectral region up to 150 K.

We present electrically driven luminescence from single InGaN quantum dots embedded into a light emitting diode structure grown by metal-organic vapor-phase epitaxy. Single sharp emission lines in the green spectral region can be identified. Temperature dependent measurements demonstrate thermal stability of the emission of a single quantum dot up to 150 K. These results are an important step towards applications like electrically driven single-photon emitters, which are a basis for applications incorporating plastic optical fibers as well as for modern concepts of free space quantum cryptography.