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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 2×1 like LEED pattern at room temperature. This indicates that the TTC molecule lies on the Cu(100) surface with its chain axis parallel to the Cu[110] direction. The application of the dipole selection-rule to normal emission spectrum revealed that the C-C-C plane of TTC is parallel 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 for flat-on orientation based on independent-atomic-center (IAC) approximation combined with ab initio MO calculations are in good agreement with the observed spectra. These results verify the deduced molecular orientation and demonstrate the reliability of theoretical simulation with IAC approximati on.