Influence of the First Preparation Steps on the Properties of GaN Layers Grown on 6H-SIC by Mbe

AbstractThe Gan heteroepitaxy on 6H-SiC is affected by the bad morphology of the substrate surface. We performed a hydrogen etching at 1550°C on the 6H-SiC(0001) substrates to obtain atomically flat terraces. An improvement of the structural properties of GaN grown by MBE on such substrates after deposition of a LT-AIN buffer layer is observed. A value of less than 220 arcsec of the FWHM of the XRD rocking curve, showing a reduced screw dislocations density, is comparable with the best results reported until now for thick GaN samples. Photoluminescence showed a structured near band edge emission spectrum with evidence of the A, B and C free exciton recombinations

Recovery after unilateral knee replacement due to severe osteoarthritis and progression in the contralateral knee: a randomised clinical trial comparing daily 2000 IU versus 800 IU vitamin D.

To test whether daily high-dose vitamin D improves recovery after unilateral total knee replacement. Data come from a 24-month randomised, double-blind clinical trial. Adults aged 60 and older undergoing unilateral joint replacement due to severe knee osteoarthritis were 6-8 weeks after surgery randomly assigned to receive daily high-dose (2000 IU) or standard-dose (800 IU) vitamin D <sub>3</sub> . The primary endpoints were symptoms (Western Ontario and McMaster Universities Arthritis Index pain and function scores) assessed at baseline, 6, 12, 18 and 24 months in both knees, and the rate of falls over 24 months. The secondary outcomes were sit-to-stand performance, gait speed, physical activity and radiographic progression in the contralateral knee. We recruited 273 participants, 137 were randomised to receive 2000 IU and 136 were randomised to receive 800 IU vitamin D per day. 2000 IU vitamin D increased 25-hydroxyvitamin D levels to 45.6 ng/mL and 800 IU vitamin D to 37.1 ng/mL at month 24 (p<0.0001). While symptoms improved significantly in the operated knee and remained stable in the contralateral knee over time, none of the primary or secondary endpoints differed by treatment group over time. The rate of falls over 24 months was 1.05 with 2000 IU and 1.07 with 800 IU (p=0.84). 30.5% of participants in the 2000 IU and 31.3% of participants in the 800 IU group had radiographic progression in the contralateral knee over 24 months (p=0.88). Our findings suggest that a 24-month treatment with daily 2000 IU vitamin D did not show greater benefits or harm than a daily standard dose of 800 IU among older adults undergoing unilateral total knee replacement

Röntgenographische Untersuchungen über die Mischkristallbildung im System SrO-EuO mit der Debye-Scherrer-Pulvertechnik

Im binären System SrO-EuO wurde die Mischkristallbildung röntgenographisch untersucht. Die Mischkristallpräparate wurden aus feingepulverten und verdichteten Mischungen der reinen Ausgangsphasen durch mehrstündiges Tempern bei Temperaturen um 1150 °C in Mikroautoklaven unter Ausschluß von Luft und Feuchtigkeithergestellt. Die Gitterparameter der gebildeten Mischphasen wurden durch Ausmessen der Rückstrahlbereiche von Debye-ScherrerPulver- Aufnahmen ermittelt. Die Untersuchungen ergaben, daß die Bildung von Mischkristallen über den gesamten Zusammensetzungsbereich erfolgt. Die experimentell gefundenen Gitterparameter der Mischphase sind etwas kleiner als sie dem Grenzgesetz für ideale feste Lösungen (Vegard' sche Regel) entsprechen würden. Die Ergebnisse dieser Arbeiten sollten Hinweise für die Möglichkeit einer Stabilisierung von Ytterbium-(II)-Oxid in Calciumoxid als Wirtsgitter geben

Epitaxial orientation of MBE grown Ru2Si3 films on Si(111) and Si(001)

Epitaxial, textured Ru2Si3 films were grown by the template technique, a special molecular beam epitaxy method, on Si(111) and Si(001). Epitaxial relationships of the films with respect to the substrate were determined by X-ray diffraction. Two competing orientations were found on Si(111), while on Si(001) two different orientations of comparable strength are present. The observed orientations will be discussed and possible lattice matchings will be proposed. (C) 2000 Elsevier Science S.A. All rights reserved

Structural, electrical and optical characterization of semiconducting Ru2Si3

Recent band structure calculations indicate, that ruthenium silicide (Ru2Si3) is semiconducting with a direct band gap. Electrical measurements lead to a band gap around 0.8 eV which is technologically important for fiber communications. This makes Ru2Si3 a promising candidate for silicon-based optical devices, namely LEDs. We present results on the epitaxial growth of ruthenium silicide films on Si(100) and Si(111) fabricated by the template method, a special molecular beam epitaxy technique. We structurally characterized the films by Rutherford backscattering and ion channeling, X-ray diffraction and transmission electron microscopy. To determine the electrical resistivity at high temperatures films were grown on insulating substrates to prevent parallel conduction through the substrate. Finally we show first results of the optical absorption performed by photothermal deflection spectroscopy indicating pronounced absorption above 1.5 eV. (C) 2000 Elsevier Science B.V. All rights reserved