Statistics – Applications
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aipc..458..679l&link_type=abstract
Space technology and applications international forum -1999. AIP Conference Proceedings, Volume 458, pp. 679-684 (1999).
Statistics
Applications
Diffusion Of Impurities, Chemical Composition Analysis, Chemical Depth And Dopant Profiling
Scientific paper
Diffusion is one of the major concerns for materials operating at high temperatures. Graphite is being considered as the prime candidate material for a receiver-absorber-converter used in Integrated Solar Upper Stage (ISUS). One of the anticipated problems is the loss of graphite at high temperatures. Rhenium has been proposed as a diffusion barrier for graphite to prevent excessive loss of the material. The diffusion of rhenium in graphite is not well understood. A technique to study the diffusion of rhenium in graphite was developed based on the Rutherford Backscattering Spectroscopy (RBS) technique. The graphite samples used in this experiment were Poco graphite purchased from Unocal. The sample coated with rhenium was given a diffusion anneal at a temperature of 1373 K in a vacuum electron beam furnace. The diffusion profiles were determined by examining the energy distribution of backscattered helium ions. It is therefore necessary to convert the RBS spectra into concentration profiles. RUMP (Rutherford Universal Manipulation Program) is a commercially available computer program which is limited to thin films with thicknesses of approximately 300 nm. When the thickness of the thin film is greater than 300 nm. RUMP simulated spectra differ significantly from the experimental data and it is not suitable for our diffusion study which requires thicker rhenium films. This limitation is possibly due to the incorrect approximation for the energy loss calculation. A new algorithm for interpreting RBS spectra was developed by comparing the calculated spectra with the experimental data. A better fit for RBS data was successfully obtained. The diffusion coefficients were obtained using the Matano method.
Li Jinglong
Zee Ralph H.
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