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 films of Pt and Sn has been observed by high-resolution electron microscopy (HREM). In situ heating of the metal films in the transmission electron microscope (TEM) allows the establishment of orientation relationships between the unreacted Sn film and the intermetallic phases formed during the reactions. Initial observations reveal the formation of PtSn4 in the [110] orientation where the (002) fringes of PtSn4 are oriented parallel to the (011) fringes of beta-Sn. This observation suggests that the (002) planes of PtSn4 are formed by the doubling of the (011) planes of beta-Sn during the transformation, rather than the (020) planes of beta-Sn as previously reported.