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Nanowires with different nitrogen concentrations were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) using DEZn, N2O and NH3as zinc, oxygen and nitrogen doping sources respectively. Low temperature photoluminescence, Raman spectroscopy and Transmission Electron Microscopy are combined to study the incorporation of nitrogen in the wires. The observation of donor-acceptor pair band confirms that the incorporation nitrogen in ZnO nanowires is responsible for the creation of acceptor centers. The additional peaks observed in Raman are correlated to nano-sized inter-atomic distance fluctuations observed in TEM. These domains combined with a resonance effect are probably the explanation of the huge Raman cross section observed for the impurity related peaks.
Hydrogen incorporation is studied in two Microwave Plasma CVD nanocrystalline diamond films deposited with prolongated BIAS or not during the growth step. The hydrogen content and bonding forms are analysed by Secondary Ion Mass Spectrometry, Raman and Fourier Transformer Infrared Spectroscopy. Our results show a high hydrogen concentration up to 3.1021 cm-1, as expected in nanocrystalline diamond, and in good agreement with the sp2 phase rate measured by Raman spectroscopy . The FTIR spectra exhibit two sharp peaks at 2850 and 2920 cm-1 and show that a fraction of hydrogen is bonded to sp3 CH2 groups. Hydrogen desorption experiments are performed to analyse the local structure modification of the diamond films.
We report the multicentric French experience with transcatheter closure in children weighing 15 kilograms or less, with the aim of assessing the efficacy of the procedure in this age group.
We included all children weighing 15 kilograms or less, and seen between January, 1997, and June, 2004, who had successful transcatheter closure of an interatrial communication within the oval fossa.
Transcatheter closure was performed in 35 patients weighing 15 kilograms or less, of whom 14 were male and 21 female. The procedures were undertaken in 8 different centres, the patients having a median age of 3 years, with a range from zero to 6.2 years, and a mean weight of 13 kilograms, with a range from 3.6 to 15 kilograms. All the patients were symptomatic, with associated cardiac malformations present in 4 cases, and extracardiac anomalies in 4 patients, including Down’s syndrome in 3, and Adams Oliver syndrome in the other case. In 1 patient, emergency cardiac surgery was needed 24 h after the procedure to correct a previously undiagnosed divided right atrium. No other complication occurred. After a median follow-up of 2 years, with a range from 0.5 to 5.2 years, all the patients are asymptomatic, except for one long-standing patient with bronchodysplasia. In 1 other patient, a small residual bidirectional shunt was detected by echocardiography. No patient presented significant arrhythmia. In the patients followed-up for more than 12 months, we found a significant gain in weight gain.
Transcatheter closure of an interatrial communication within the oval fossa is efficient in children weighing 15 kilograms or less, and can be proposed as a first line of treatment in symptomatic patients. Children with retarded growth tend to have complete recovery within one year of closure.
The correlation between structural properties of ZnO sharp conical needles grown by Metallorganic Chemical Vapor Deposition (MOCVD) on sapphire substrate and their optical signature measured by low temperature cathodoluminescence (CL) is investigated. Transmission Electron Microscopy (TEM) shows the excellent structural properties of these needles from their base up to the end of the tip. In order to probe the emission of the needles along their length, UV CL mapping has been performed at low temperature on a single needle previously characterized by TEM. A clear blue shift of 25meV is observed for the excitonic emission close to the needle tip. This shift is too high to be fully attributed to quantum confinement. Although, it qualitatively agrees with previous observations which assigned it to a surface contribution becoming dominant upon size shrinking, the effect is less pronounced. The results are discussed in term of surface quality and other possible contributions associated to a decrease of the n-dopant concentration and to quantum confinement effect close to the tip.
We present a detailed analysis of inter- and intraband transitions in GaN/AlN self-organized quantum dots grown on sapphire, silicon (111) and 6H-SiC substrates. Quantum dot samples have been characterized by means of transmission electron microscopy, photoluminescence and photo-induced absorption spectroscopy. Interlevel transitions in the conduction band are observed in the 0.52–0.98 eV energy range, thus covering the telecommunication band. The s-pz absorption is peaked at 0.8 eV (0.52 eV) for samples with dot height of 1.5 nm (6 nm). Calculations show that in bigger dots the transition energy is governed by the value of the internal field.
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