Volume 97, Issue 5, 01 March 2005
Index of content:
97(2005); http://dx.doi.org/10.1063/1.1851593View Description Hide Description
Pulsed electrically detected magnetic resonancemeasurements are presented showing that centers at the crystalline silicon (111) to silicon dioxide interface can cause recombination of strongly coupled spin pairs in singlet and triplet configurations. The implication of these findings is that two different electron capture cross sections can exist at a single defect. This shows that the previously observed two capture cross sections at the interface do not necessarily imply the existence of additional non--like centers such as oxygen-backbonded silicon dangling bonds.
97(2005); http://dx.doi.org/10.1063/1.1853493View Description Hide Description
We report on a simple and low-cost route to produce SiCnanotubes without the need for the more usual oxide based reactions using a high temperature substitution reaction between multiwall carbon nanotubes as a frame and Si powder. Local scale studies using transmission and scanning electron microscopy are also presented. The SiCnanotubes are carbon filled and open ended. Both their mean diameter and diameter distribution are smaller than previously reported for SiCnanotubes. Bulk scale studies using Raman and infrared as a probe showed the sample to be comprised of multiple polytypes and that finite size effects are present.
Micro-Raman-scattering study of stress distribution in GaN films grown on patterned Si(111) by metal-organic chemical-vapor deposition97(2005); http://dx.doi.org/10.1063/1.1856211View Description Hide Description
GaNfilms were grown by metal-organic chemical-vapor deposition on Si(111) substrates patterned with arrays of squares and rectangular stripes with a height and various lateral dimensions. Spatial distributions of tensile stress in the GaN pattern units were mapped out using micro-Raman spectroscopy. At the center of a square GaNfilm, the tensile stress is the largest and relaxes symmetrically towards the square edges where stress-release free facets are available. The largest crack-free square size for a -thick GaNfilm is in the order of , which is much larger than a theoretically predicted value .
Enhanced emission by frequency-doubling of the one-micron Nd:yttrium vanadate laser in gadolinium calcium oxoborate97(2005); http://dx.doi.org/10.1063/1.1851594View Description Hide Description
It is shown that owing to the improvement of the laser emission parameters at the fundamental frequency and to the reduction of the heat generated by nonradiative processes, the direct pumping into the emitting level of enhances considerably the power emitted at the second harmonic in an intracavity frequency-doubling device. In the case of a laser with an -cut crystal frequency-doubled with a (GdCOB) crystal cut for Type I frequency doubling in the plane , an enhancement of the emitted power at by about 100% was obtained for incident Ti:sapphire laser pump at compared with the traditional pumping at . It is inferred that besides the improvement of the efficiency, this modality of pumping would enable the scaling of these devices to higher power.
97(2005); http://dx.doi.org/10.1063/1.1861142View Description Hide Description
The correlations among stoichiometry variation, preparation route, and microstructure as well as superconductingproperties were investigated in bulk samples. We demonstrate that the different initial weight ratios of Mg and B between and are only slightly shifted towards Mg depletion during the mechanical alloying preparation at room temperature followed by a short annealing step. The samples with Mg surplus show the highest critical temperature, highest critical current density at 7.5 K in self-field, and a homogeneous microstructure. In contrast, the Mg-depleted samples exhibit a rather porous and multiphase microstructure with a broad grain size distribution. A direct correlation of stoichiometry variation and superconductingproperties was not found, but rather a strong influence of the Mg content on lattice strain and grain connectivity.