Angle-resolved UPS study of oriented thin film of tetratetracontane (n-C44H90) on Cu(100) and theoretical simulation by IAC approximation

The electronic structure and molecular orientation of tetratetracontane (n- C44H90; TTC) ultra-thin film on Cu(100) were studied by angle-resolved UPS (ARUPS). We observed 2x1 like LEED pattern at room temperature. This indica tes that the TTC molecule lies on the Cu(100) surface with its chain asis p arallel to the Cu[110] direction. The application of the dipole selection-r ule to normal emission spectrum revealed that the C-C-C plane of TTC is par allel to the surface (flat-on orientation). We also examined the dependence of the photoemission spectra on the take-off angle, and observed clear one -dimensional intramolecular energy-band dispersion. The simulated spectra f or flat-on orientation based on independent-atomic-center (IAC) approximati on combined with ab initio MO calculations are in good agreement with the o bserved spectra. These results verify the deduced molecular orientation and demonstrate the reliability of theoretical simulation with IAC approximati on.