Control of the growth of ordered C-60 films by chemical modification of Pt(111) surfaces

The chemisorption of C-60 on Pt(111) results in strong bonding of the adsor bed molecules to the surface and immobile adsorbates, that lead to the grow th of disordered C-60 films. We show that the Pt(111) surface can be chemic ally modified in a controlled manner, in order to grow ordered C-60 films. Modification of the Pt(111) surface was accomplished by pre-adsorbing oxyge n adatoms, hydrogen adatoms, a graphite adlayer and an ordered C-60 adlayer . Growth of C-60 films on these modified surfaces was studied by Auger elec tron spectroscopy (AES), low energy electron diffraction (LEED), high resol ution electron energy loss spectroscopy (HREELS) and UV photoelectron spect roscopy (UPS). Chemical modification of the surface inhibited charge transf er to the C60 molecule in all cases, leading to weaker bonding and greater adsorbate mobility on the surface that contributed to the growth of ordered C-60 films. The ordering of the film can be expressed quantitatively as th e intensity ratio of the dipole active T-1u(1) mode to the non-dipole activ e H-g(4) mode as determined by vibrational spectroscopy using HREELS. C-60 films grown on the graphite adlayer on Pt(111) were highly ordered because of the weak physisorption interactions between the adsorbate and surface. T he degree of ordering upon modification of the Pt(111) surface in this stud y compares well to that of previous studies using different methods. (C) 19 99 Elsevier Science S.A. All rights reserved.