If you type "absorption" (or absorbtion :-) into the search field of the Rietveld archive http://www.mail-archive.com/[EMAIL PROTECTED]/ you will find an earlier discussion on this.
And also ~60 emails with the "absor(p/b)tion" keyword in the old Rietveld 1994-1998 archive : http://sdpd.univ-lemans.fr/forum/rietveld_l/ Most absorption formula and Fermi lengths were stable during the past ten years.
Armel
