The kinetics of the interactions of O2 and N20 with a Cu(110) surface and of the reaction of CO with adsorbed oxygen studied by means of ellipsometry, AES and LEED

Abstract

Ellipsometry, LEED and Auger electron spectroscopy have been used to study the interactions of Oa and NzO with a clean annealed Cu(ll0) surface and the reaction of CO with adsorbed oxygen in the monolayer range. Gas pressures were in the range 1O-8-1O-4 Torr and crystal temperatures varied between 23-4OO'C. The changes in the ellipsometric angles A and $I per oxygen atom upon adsorption and removal of oxygen depend on the coverage 0, the temperature and on the azimuth of the plane of incidence of the light beam. The kinetics of the chemisorption of oxygen is independent of the crystal temperature, initial sticking probabiiity ~0.2. The LEED data and the adsorption kinetics indicate an attractive interaction in the adsorbed layer in the [OOl] direction. The initial decomposition probabi~~y of NaO at room temperature is 0.15 and decreases with increasing temperature; the maximum coverage is 0.5 monolayer. The LEED patterns observed were the same as those with 0s. The reaction probability of CO with adsorbed oxygen increases with decreasing oxygen coverage (order of mag nitude -1O-5, apparent activation energy -6 kcaI/mol). This increase has been attributed to the operation of the Langmuir-Hinshelwood mechanism.

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

“…2). No dependence on the crystal temperature T (T< 4OO*C) was observed, contrary to the results on Cu(l10) [27]. The plane of incidence made an angle of about 45' with the [Ol l] direction.…”

“…After the CO exposures, a small amount of oxygen was still present on the surface, as could be detected with AES. As in the case of this reaction on Cu(l10) [27], the increase in the rate of change of 6A with decreasing oxygen coverage is explained by .the occurrence of the Langmuir-Hinshelwood mechanism; thus for the reaction to take place the CO molecule must be adsorbed on a free copper site. In our experimental conditions only a very small amount of CO is adsorbed on Cu(100) [24, 34,35], this amount being proportional to the CO pressure.…”

“…[26] and [27]. The work function measurements were performed with a self-compensating Kelvin probe, which was purchased from the Kernforschungsanlage Jtilich GmbH.…”

“…Eact = 6.4 kcallmol at &A = 0.5"). A strong decrease of s with 0 and an increasing activation energy have also been observed for N20 on Cu(ll0) [27]. Both for Cu(ll1) and for Cut1 10) a precursor-state model has been proposed to explain the kinetics of the NzO decomposition [26,27].…”

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

“…Then w = 0 also and the precursor-state parameter K, defined in refs. [27,31], must be equal to one to give eq. (2).…”