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Details of Grant 

EPSRC Reference: GR/J55274/01
Principal Investigator: Hamilton, Professor B
Other Investigators:
Bangert, Professor U
Researcher Co-Investigators:
Project Partners:
Department: Physics
Organisation: UMIST
Scheme: Standard Research (Pre-FEC)
Starts: 01 October 1993 Ends: 30 September 1995 Value (£): 108,594
EPSRC Research Topic Classifications:
Optoelect. Devices & Circuits
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Summary on Grant Application Form
To directly image the chemical structure of and optical emission from a range of porous silicon. To develop STEM, x-ray fluorescence and STM techniques for the characterisation of porous silicon. To predict optimal structures for devices. Progress:The work has proceeded at a fast pace: as a crude indicator the work has resulted in the publication of seven papers to date and our results have been presented at five international meetings (including two invited talks). We anticipate that at least five more papers will result from this work.The key aspect of this work is to try to find experimental ways to link the chemical nature and optical properties of porous silicon. This chemical identification of the luminescence centres involved is absolutely key to any mature exploitation of the material for display devices. The work so far has mainly involved (a) chemical analysis using scanning transmission electron microscopy (STEM) in the electron energy loss spectroscopy mode and (b) tunable (synchrotron) X ray excitation of luminescence.The STEM work has shown that Oxygen plays an important role in the matrix of the film. Even passivated material, i.e. rich in surface Si-H bonds, has a high O content with a good deal of SiO2 'debris' the in pore regions. In addition very rapid stoichiometry changes, averaged over dimensions of a round 10+ are apparent. Rapid, oxidation which produces stable light emitting material smooths out the chemical variation, and can be controlled to give similar emission properties. These data suggest that H is truly not an active constituent in the luminescence 'centre'. The synchrotrons work has helped us link the luminescence to the chemistry of the matrix. The much studied slow band can only be excited by x-ray absorption at Si-Si bonded material, regardless of the details of oxidation/ passivation. We have for the first time spectrally resolved the absorption processes for the slow (red emission) and the fast (blue) emission which is seen in oxidised material. This was done for material which had been processed to yield both emission bands. It is clear that the blue emission is due entirely to porous SiO2 glass; probably originating at defects in the glass. The two bands then, result from different materials in a highly heterogeneous matrix, and exploitation of each band will require a different device philosophy.
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