Chemically modified semiconductor surfaces: 1,4-phenylenediamine on Si(100)

The formation of inorganic/organic hybrid systems in ultra-high-vacuum (UHV) is studied for the adsorption of 1,4-phenylenediamine (PDA) and aniline on Si(100)(2 × 1) single crystal surfaces. X-ray photoemission spectra (XPS) of PDA and aniline adsorbed on silicon are interpreted in terms of an adsorbate configuration involving two covalent bonds between one amino group per molecule and the dangling bonds of the clean silicon surface. Vibrational high resolution electron energy loss spectroscopy (HREELS) allows us to identify the remaining amino groups in the PDA-adsorbate. Ultraviolet photoemission spectroscopy (UPS) and electron energy loss (EELS) data in the valence band range indicate that the aromatic ring stays intact after the chemisorption of PDA. Changes in work function and energetic shifts of the electronic transitions characterize the charge transfer between adsorbate and substrate. The experimental results are finally discussed in the framework of semi-empirical cluster calculations using MNDO-PM3.