The adsorption and incorporation of oxygen on Cu(100) and its reaction with carbon monoxide; comparison with Cu(111) and Cu(110)

Abstract

Ellipsometry, LEED, Auger electron spectroscopy and monitoring of work function changes have been used to study the interactions of 02 and N20 with a clean annealed Cu(100) surface and of the reaction of CO with sorbed oxygen. Gas pressures were in the range IO-'--lo4 Torr and crystal temperatures varied between 25-4OO'C. The initial interaction of oxygen with Cu(100) occurs in three stages. Oxygen chemisorbs with an initial sticking coefficient of -10T2 at room temperature and an apparent activation energy of 1.3-3.5 kcal/mol, depending on the substrate temperature. The first stage is the formation of a (42 X J2)R4S0 LEED pattern up to a coverage of 0.5, which is converted with an apparent activation energy of 3.2 kcal/mol to a (,/2 X 242}R45' structure at a coverage of 0.75 in the second stage. The work function increases inthe ftrst stage in an amount of -300 meV, but decreases in the second stage to the value of the clean surface. In a third stage after an induction period further oxygen uptake could be registered only with ellipsometry. The apparent activation energy is 4.5 kcal/mol. The initial decomposition probability of N20 at room temperature is 5 X 10m5, its apparent activation energy 3.2 kcal/mol. The LEED patterns observed were the same as with 02. The sorbed oxygen can be removed at all coverages with CO. The reaction appears to follow LangmuirHinshelwood kinetics with an activation energy for the reaction Goad + oad + CO2 of lP-20 kcal/mol. A comparison is made with the data obtained for Cu(ll1) and Cu(ll0).

Interaction of hydrogen with oxygen on Cu(111)

“…We can thus conclude that the hydrogen-oxygen reaction on Cu surfaces is determined by the initial formation of adsorbed OH groups (with activation energies in the range 80-92 kJ/mol) and that the reaction is not particularly plane-specific. Similar conclusions have been drawn with respect to the CO oxidation on the low index copper faces [4]. The activation energy for the Langmuir-Hinshelwood reaction of adsorbed CO and 0 is 75-84 kJ/mol, independent of the crystallographic orientation.…”

Spectroscopic ellipsometric investigation of clean and oxygen covered copper single crystal surfaces

“…With the combination ellipsometry-AES-LEED, Habraken et al have observed linear relations between the change in the ellipsometric parameter A at h = 632.8 nm and the oxygen coverage 6 in the chemisorption stage on Cu( 111) [ 11, Cu( 100) [2] and Cu(ll0) [3,4] (0 5 0.5 oxygen atoms per surface metal atom). After this stage a further uptake takes place, accompanied by reconstruction of the surface.…”

An AES and LEED study of carbon and oxygen sorption on copper surfaces

“…The observed constant coverage in the range of 45-3 X l0~L may be ascribed to a nucleation process prior to the formation of the c(6 X 2) structure as has been observed for Cu (100) [15]. As the equilibrium oxygen pressure for bulk oxide formation at room temperature is less than 10'~Torr [16], the observed constant coverage can not be due to an equilibrium process.…”