COPPER PHTHALOCYANINE ON SI(111)-7X7 AND SI(001)-2X1 SURFACES - AN X-RAY PHOTOEMISSION SPECTROSCOPY AND SYNCHROTRON X-RAY-ABSORPTION SPECTROSCOPY STUDY

The chemical bonding and molecular orientation of copper phthalocyanin e (CuN8C32H16), deposited on clean single crystal silicon substrates o f (111) and (001) orientation, were studied using X-ray photoemission spectroscopy (XPS) of the Cu 2p, C 1s, and N Is core-levels and synchr otron radiation X-ray absorption spectroscopy (XAS) at the Cu L(2,3), edges. In the monolayer range, the strong interaction of the molecule with the Si(111) surface is mostly evidenced by changes in the Cu 2p X PS spectra that indicate a partial reduction (up to 30%) of the Cu(II) atoms to Cu 3d(10). The linear dichroism of the XAS spectra shows tha t those molecules, whose copper is still Cu(II), lie down on the surfa ce. On the other hand, the bonding of the molecule on Si(001) is weake r, as Cu 2p XPS spectra do not exhibit Cu(II) reduction, while XAS spe ctroscopy indicates a random orientation of the molecules with respect to the surface. N 1s XPS spectra exhibit, on both surfaces, very inte nse satellites which present, on Si(111), a sharp dependence on the el ectron take-off angle. With the growth of thicker films, the XPS line shapes of the molecular solid are recovered, and the average tilt angl e of the molecules (around 70 degrees) does not depend on the chosen S i surface. We conclude that the structure of the first deposited layer strongly depends on the specific substrate, but does not affect the s uccessive growth of thick layers.