ELECTRONIC-STRUCTURE AND FIM IMAGING MECHANISM OF FE-AL INTERMETALLICCOMPOUNDS

The electronic structure and some one-electron properties of binary in termetallic compounds Fe3Al (tbe F11Al4 model cluster) and FeAl (the F e7Al8 and Fe4Al4 model clusters) are investigated by the SCF-X-alpha-S W method. The results show that the binding tendency between an Fe ato m and the Fe3Al cluster is a little weaker than that between an ill at om and the Fe3Al cluster, which is in contrast to the case in FeAl. An d charge is transferred from Al atoms to Fe atoms in both systems. Thu s it is concluded that Al atoms contribute to the FIM image oi Fe3Al w hatever the imaging mechanism, selective evaporation or selective ioni zation is, which is in good agreement with our FIM experimental result s. For FeAl, no definite experimental evidence regarding FIM imaging a tom species is available so far. Bur our calculated result that Al ato ms will be evaporated preferentially leads to the prediction that Fe a toms will be imaged in FIM micrographs.