Structure determination for PF3 absorption on Ni(111)

The local adsorption structure of PF3 on Ni(111) has been investigated using a combination of P K-edge near-edge and surface extended X-ray absorption fine structure (NEXAFS and SEXAFS) and normal incidence standing X-ray wavefield absorption (NISXW) at both the P and F atoms in order to determine the adsorption site, the adsorbate-substrate bond-length, the molecular orientation and the internal structure of the adsorbed species. The molecule is found to be adsorbed atop a top layer Ni atom at a P-Ni nearest-neighbour distance of 2.07+or-0.03 AA, with its C3v symmetry axis perpendicular to the surface, and with an internal structure (both bond-lengths and bond angles) unchanged from that of the free molecule. The results also indicate that there is no change in the Ni(111) substrate structure induced by the adsorption, and the PF3 has a much larger vibrational amplitude parallel to the surface than perpendicular to the surface, presumably associated with a Ni-PF3 wagging mode.