Abstract
Phenylphosphonic acid (PPA) adsorbed on Cu(111) has been studied by synchrotron radiation-based techniques in combination with density functional theory calculations. The dehydrogenated phenylphosphonic acid molecule (PP) strongly bound in a tridentate geometry through oxygen atoms to Cu(111) is shown to be the dominant surface species in the temperature range 150-300 °C.
The stable PP adlayer substantially protects the Cu(111) surface from oxidation during exposure to ambient conditions. Thermal treatment of the PPA adlayer at 375 °C initiates molecular decomposition through several channels: P-O bond scission forming C6H5PO2; C-P bond scission forming phenyl and PO3; and C-H bond scission forming C6H4PO3.
All three reaction steps have activation barriers of 1.7-1.8 eV. Small products such as O, H, and phenyl can immediately react further and desorb, while the remaining phosphonate species undergo condensation.
After annealing at a higher temperature, the phosphonate group is further reduced from oxygen-rich to phosphorus-rich species, which form the majority of remaining adsorbates after 500 °C treatment.