HREM OBSERVATIONS OF THE CONVERSION OF BETA-SN INTO PTSN4, IN THE PT-SN THIN-FILM SYSTEM

The conversion of beta-Sn into PtSn4 during in situ heating of thin fi lms of Pt and Sn has been observed by high-resolution electron microsc opy (HREM). In situ heating of the metal films in the transmission ele ctron microscope (TEM) allows the establishment of orientation relatio nships between the unreacted Sn film and the intermetallic phases form ed during the reactions. Initial observations reveal the formation of PtSn4 in the [110] orientation where the (002) fringes of PtSn4 are or iented parallel to the (011) fringes of beta-Sn. This observation sugg ests that the (002) planes of PtSn4 are formed by the doubling of the (011) planes of beta-Sn during the transformation, rather than the (02 0) planes of beta-Sn as previously reported.