Useful analysis method of angle-resolved ultraviolet photoemission spectra

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We measured Angle-resolved ultraviolet photoemission spectra (ARUPS) for the thin films of bis (1,2,5-thiadiazolo)-rho-quinobis (1,3-dithiole) (BTQBT) and naphthacene on HOPG graphite and MoS_2 substrate. Through the quantitative comparison between the observed and calculated take-off angle dependencies of the photoelectron intensities, we succeeded in determining the polar and azimuthal orientations of such large organic molecules. In these calculations, we applied the independent-atomic-center (IAC) approximation which includes the self-scattering of the photoelectrons by the emitting atoms. Further, the measured take-off angle dependence of the full valence-band spectra is compared with the calculated one by considering both the self- and single-scattering. The effect of the phenomenologically induced mean free path of the photoelectrons is also included in the calculation.Our developing calculation program (IAC31) enables us to determine the quantitative molecular orientation in the thin films of the large organic molecules.