ADSORPTION OF OXYGEN ON AU(111) BY EXPOSURE TO OZONE

Atomic oxygen coverages of up to 1.2 ML may be cleanly adsorbed on the Au(lll) surface by exposure to O-3 at 300 K. We have studied the adso rbed oxygen layer by AES, XPS, HREELS, LEED, work function measurement s and TPD. A plot of the O(519 eV)/Au(239 eV) AES ratio versus coverag e is nearly linear, but a small change in slope occurs at theta(0)=0.9 ML. LEED observations show no ordered superlattice for the oxygen ove rlayer for any coverage studied. One-dimensional ordering of the adlay er occurs at low coverages, and disordering of the substrate occurs at higher coverages. Adsorption of 1.0 ML of oxygen on Au(lll) increases the work function by +0.80 eV, indicating electron transfer from the Bu substrate into an oxygen adlayer. The O(ls) peak in XPS has a bindi ng energy of 530.1 eV, showing only a small (0.3 eV) shift to a higher binding energy with increasing oxygen coverage. No shift was detected for the Au 4f(7/2) peak due to adsorption. All oxygen is removed by t hermal desorption of O-2 to leave a clean Au(lll) surface after heatin g to 600 K. TPD spectra initially show an O, desorption peak at 520 K at low theta(0) and the peak shifts to higher temperatures for increas ing oxygen coverages up to theta(0)=0.22 ML. Above this coverage, the peak shifts very slightly to higher temperatures, resulting in a peak at 550 K at theta(0)=1.2 ML. Analysis of the TPD data indicates that t he desorption of O-2 from Au(111) can be described by first-order kine tics with an activation energy For O-2 desorption of 30 kcal mol(-1) n ear saturation coverage. We estimate a value for the Au-O bond dissoci ation energy D(Au-O) to be similar to 56 kcal mol(-1). (C) 1998 Elsevi er Science B.V. All rights reserved.