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  • The Electronic Aladdin Newsletter

    No.3, March 1996

    This series provides a monthly update on new developments at the Synchotron Radiation Center.

    1) New MCD Endstation Available for Users

    An x-ray magnetic circular dichroism (MCD) measurement chamber is now available for SRC users. The chamber was constructed specifically for dichroism measurements on ex-situ prepared samples. This includes sputter deposited and MBE-grown magnetic multi-layers and sandwich structures. A large sample capacity is included in order to minimize down-time between measurements. When coupled to the 10M TGM, the 2P MCD spectra for the entire 3d transition metal series can be obtained with the new chamber. The MCD chamber was designed and built by a collaboration between Prof. Gerry Harp, University of Ohio at Athens, and Bill O'Brien, SRC. For information on using the MCD chamber contact Bill O'Brien .

    2) PGM Undulator Beamline

    The Accelerator Development groups are implementing a Global Orbit Feedback and Control System. This system uses feedback from 48 beam position monitors throughout the ring to stabilize the beam when undulators are tuned.

    Improvements in monitor stability are being made to ensure the accuracy of the system. First tests demonstrated stabilization of the beam to one micron, without undulators in operation. This value is promising since the target size for vertical beam fluctuation with the undulators in operation is 10 microns.

    In addition, magnetic lattice corrections are underway to limit beam size variations at normal source points to less than a few percent. These corrections are in the form of dynamic quadrupole compensation and skew quadrupole cancellation.

    Steady progress is being made in the construction of the PGM beamline which utilizes radiation from the new permanent magnet undulator. The entrance mirror, entrance slit, and both sets of beam position monitors are installed and currently are in the process of being conditioned using the beam. All of the mirror boxes for the beamline have been completed and most are already bolted into position on the vault floor. The grating chamber tank is nearing completion. Internal components for the grating chamber have all been cleaned and assembly of these parts is underway. The cable trays and main instrument racks have also been installed.

    3) SRC Researchers Unlock Some Of The Mysteries Of Silicon Luminescence

    In recent work at the SRC, Z. H. Lu et.al. have shed light on the origins of luminescence in silicon by fabricating well-defined silicon nanostructures (for details see their article in Nature 378, 258 (1995) and the review in Physics Today, February 1996, p. 9). They used a superlattice with alternating layers of silicon and silicon dioxide as the medium for their experiments, where the electrons are confined to the silicon layers by the oxide barriers. By varying the thickness of the silicon layers they found that the band structure of the silicon changed. The conduction band moved up and the valence band moved down as the films were made thinner. This was due to the narrower confinement of the electrons. As a consequence, the light emitted from the conduction band minimum to the valence band maximum changes in wavelength. Due to this change, the color of the emitted light can be varied by the thickness of the layers.

    The new results build on earlier work at SRC by T.K. Sham et. al., where it was shown that the luminescence of electrochemically etched, porous silicon is due to a confinement of electrons to nanometer size pieces of silicon.

    The discovery of silicon luminescence is an area of interest for information and communication technologies. Light emission from silicon is essential to the integration of photonics and silicon-based micro-electronics.

    4) The Electronic Aladdin Newsletter Reaches The Web

    All issues of this newsletter are posted on the SRC homepage under the SRC Newsletters link.