An experimental and theoretical investigation of the thiophene/aluminum interface

The adsorption of thiophene and 2, 2'-bithiophene on Al(111) has been studi ed using thermal desorption spectroscopy (TDS), angle-resolved UV photoemis sion (ARUPS), and work function measurements. Ab initio density functional theory calculations have been performed for thiophene on Al(111). Both thio phene and bithiophene bond only very weakly to Al(111), as indicated by TDS and calculations of the thiophene absorption energy, which is found to be only 0.54 eV. There is no indication of pi -bonding in either the ARUPS dat a or the calculations. The calculated S-Al distance, 3.7 A, is much greater than either measured or calculated S-metal distances for covalent bonding. The bonding is shown to be almost entirely electrostatic, with a small con tribution from the sulfur lone pair. This is in direct contrast to calculat ions for Al-thiophene complexes which show covalent bonds between the Al at oms and the thiophene alpha carbons. The calculations show the molecule to be essentially flat, with a tilt angle of only 2 degrees of the molecular p lane relative to the surface. There is some indication of self-assembly of bithiophene on Al(111). (C) 2001 American Institute of Physics.