X-ray beam monitor made by thin-film CVD single-crystal diamond.

A novel beam position monitor, operated at zero bias voltage, based on high-quality chemical-vapor-deposition single-crystal Schottky diamond for use under intense synchrotron X-ray beams was fabricated and tested. The total thickness of the diamond thin-film beam monitor is about 60 µm. The diamond beam monitor was inserted in the B16 beamline of the Diamond Light Source synchrotron in Harwell (UK). The device was characterized under monochromatic high-flux X-ray beams from 6 to 20 keV and a micro-focused 10 keV beam with a spot size of approximately 2 µm × 3 µm square. Time response, linearity and position sensitivity were investigated. Device response uniformity was measured by a raster scan of the diamond surface with the micro-focused beam. Transmissivity and spectral responsivity versus beam energy were also measured, showing excellent performance of the new thin-film single-crystal diamond beam monitor.

Structural dynamics of GaN microcrystals in Evolutionary Selection Selective Area Growth probed by X-ray microdiffraction.

A method to grow high quality, single crystalline semiconductor material irrespective of the substrate would allow a cost-effective improvement to functionality and performance of optoelectronic devices. Recently, a novel type of substrate-insensitive growth process called Evolutionary Selection Selective Area Growth (ES-SAG) has been proposed. Here we report the use of X-ray microdiffraction to study the structural properties of GaN microcrystals grown by ES-SAG. Utilizing high resolution in both direct and reciprocal spaces, we have unraveled structural dynamics of GaN microcrystals in growth structures of different dimensions. It has been found that the geometric proportions of the growth constrictions play an important role: 2.6 µm and 4.5 µm wide growth tunnels favor the evolutionary selection mechanism, contrary to the case of 8.6 µm growth tunnels. It was also found that GaN microcrystal ensembles are dominated by slight tensile strain irrespective of growth tunnel shape.

Induced magnetic moment of Eu(3+) ions in GaN.

Magnetic semiconductors with coupled magnetic and electronic properties are of high technological and fundamental importance. Rare-earth elements can be used to introduce magnetic moments associated with the uncompensated spin of 4f-electrons into the semiconductor hosts. The luminescence produced by rare-earth doped semiconductors also attracts considerable interest due to the possibility of electrical excitation of characteristic sharp emission lines from intra 4f-shell transitions. Recently, electroluminescence of Eu-doped GaN in current-injection mode was demonstrated in p-n junction diode structures grown by organometallic vapour phase epitaxy. Unlike most other trivalent rare-earth ions, Eu(3+) ions possess no magnetic moment in the ground state. Here we report the detection of an induced magnetic moment of Eu(3+) ions in GaN which is associated with the (7)F(2) final state of (5)D(0)→(7)F(2) optical transitions emitting at 622 nm. The prospect of controlling magnetic moments electrically or optically will lead to the development of novel magneto-optic devices.