Artikel,
Adsorption of oxygen on Pt(111)
Surf. Sci., 123 (1): 1 - 17 (1982)
DOI: DOI: 10.1016/0039-6028(82)90124-8
Zusammenfassung
Oxygen adsorbed on Pt(111) has been studied by means of temperature
programmed thermal desorption spectroscopy (TPDS). high resolution
electron energy loss spectroscopy (EELS) and LEED. At about 100 K
oxygen is found to be adsorbed in a molecular form with the axis
of the molecule parallel to the surface as a peroxo-like species,
that is, the OO bond order is about 1. At saturation coverage (thetamol=
0.44) a diffraction pattern is observed. The sticking probability
S at 100 K as a function of coverage passes through a maximum at
theta = 0.11 with S = 0.68. The shape of the coverage dependence
is characteristic for adsorption in islands. Two coexisting types
of adsorbed oxygen molecules with different OO stretching vibrations
are distinguished. At higher coverages units with v-OO = 875 cm-1
are dominant. With decreasing oxygen coverages the concentration
of a type with v-OO = 700 cm-1 is increased. The dissociation energy
of the OO bond in the speices with v-OO = 875 cm-1 is estimated from
the frequency shift of the first overtone to be ~ 0.5 eV. When the
sample is annealed oxygen partially desorbs at ~ 160K, partially
dissociates and orders into a p(2�2) overlayer. Below saturation
coverage of molecular oxygen, dissociation takes place already at92
K. Atomically adsorbed oxygen occupies threefold hollow sites, with
a fundamental stretching frequency of 480 cm-1. In the non-fundamental
spectrum of atomic oxygen the overtone of the E-type vibration is
observed, which is #dipole##forbidden# as a fundamental in EELS.
