Valence-band interorbital interaction at the Al–Sn interface observed by ultraviolet photoemission spectroscopy: implication for phase relations in metallic binary systems

Abstract

The valence-band interaction at the polycrystalline Al–Sn interface was investigated by ultraviolet photoemission spectroscopy. Al thin films were deposited on the Sn polycrystalline thick film by the vacuum evaporation technique. Only at small thicknesses of the Al film (less than 1.0 nm), two decreased and two increased regions of intensity were recognized in ultraviolet photoemission spectra. This phenomenon was explained by assuming that valence-band interorbital interaction between Al and Sn formed bonding and antibonding orbitals (bands) below the Fermi level. The interorbital interaction was first observed in s, p metal systems, although it has been reported in d-metal systems such as Au–Ru and Cu–Ru. The three systems, Al–Sn, Au–Ru and Cu–Ru, have a common nature in the thermodynamic phase relation; that is, they do not easily form a solid solution but form a mixture of two solid phases at room temperature. These experimental data suggest the hypothesis that the repulsive interaction between two elements in eutectic binary systems comes from such interorbital interaction.

Acknowledgements

We would like to acknowledge the continuing guidance and encouragement of Professor Atsushi Koma. We are grateful to Mr Tomohiko Chiaki for his assistance with UPS measurement. This research was supported by a Research Fellowship of the Japan Society for the Promotion of Science for Young Scientists (to S. I.), and a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (14GS0207), Japan.