Photoemission study of chemisorption of ${\mathrm{C}}_{60}$ on InP(100)

The growth mode and electronic structure of ${\mathrm{C}}_{60}$ molecules adsorbed on InP(100) were studied by x-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy as a function of coverage and annealing temperature. The C $1s,$ P $2p,$ In $4d$ core levels and the valence band photoemission spectra point to the presence of a localized covalent bond between the ${\mathrm{C}}_{60}$ molecules and the substrate. No filling of the lowest unoccupied molecular orbit derived bands was observed. The absence of any change in the surface components of the In $4d$ core level upon ${\mathrm{C}}_{60}$ adsorption indicates that the chemisorption bond exists between the fullerene molecules and P atoms rather than between ${\mathrm{C}}_{60}$ molecules and In atoms. This assertion is supported by the simultaneous desorption of both ${\mathrm{C}}_{60}$ and P upon annealing to 640 K and above.