The migration of CO on the (111) and (115) planes was studied as a function of coverage by using the field emission method at temperatures of between 130 and 219K (table 16). In the case of (111), the activation energy was 6.8kcal; regardless of the degree of coverage. The pre-exponential factor was of the order of 0.001cm2/s. When near to a coverage (CO/Ni) of 0.4, there was a peak in the diffusivity at all temperatures. The mean square fluctuations increased only slightly with increasing temperature, but exhibited marked oscillations at coverages ranging from 0.3 to 0.5; for all temperatures. When the diffusivity was divided by a so-called thermodynamic factor, the result was not constant (as a function of coverage). This suggested that there was compensation between the thermodynamic factor and the remaining terms in the diffusivity. In the case of (115), which consisted of (100)-oriented terraces of various widths, the activation energy was equal to 6.4kcal and the pre-exponential factor was equal to 0.001cm2/s; for coverages of up to 0.6 (9.6 x 1014CO/cm2). At higher coverages, the activation energy and the pre-exponential factor decreased rapidly to reach 4.5kcal and 2 x 10-6cm2/s, respectively, when close to saturation. The thermodynamic factor decreased markedly with increasing coverage, but was only slightly temperature-dependent. There was a strong compensation, of changes in the thermodynamic factor, by other factors in the diffusivity.
T.S.Lin, H.J.Lu, R.Gomer: Surface Science, 1990, 234[3], 251-61
Table 16
Surface Diffusivity of CO on Ni
Face | CO/Ni | Temperature (C) | D (cm2/s) |
(111) | 0.41 | -78 | 1.2 x 10-10 |
(111) | 0.41 | -93 | 2.9 x 10-11 |
(111) | 0.41 | -98 | 1.3 x 10-11 |
(111) | 0.41 | -108 | 4.9 x 10-12 |
(111) | 0.41 | -113 | 2.9 x 10-12 |
(111) | 0.46 | -78 | 1.1 x 10-10 |
(111) | 0.46 | -88 | 4.4 x 10-11 |
(111) | 0.46 | -93 | 2.1 x 10-11 |
(111) | 0.46 | -98 | 8.1 x 10-12 |
(111) | 0.46 | -108 | 3.3 x 10-12 |
(111) | 0.46 | -113 | 1.4 x 10-12 |
(111) | 0.46 | -123 | 5.8 x 10-13 |
(111) | 0.38 | -78 | 7.2 x 10-11 |
(111) | 0.38 | -88 | 2.5 x 10-11 |
(111) | 0.38 | -93 | 1.2 x 10-11 |
(111) | 0.38 | -98 | 5.6 x 10-12 |
(111) | 0.38 | -108 | 2.8 x 10-12 |
(111) | 0.38 | -113 | 9.7 x 10-13 |
(111) | 0.52 | -63 | 1.2 x 10-10 |
(111) | 0.52 | -73 | 7.5 x 10-11 |
(111) | 0.52 | -78 | 4.1 x 10-11 |
(111) | 0.52 | -78 | 3.3 x 10-11 |
(111) | 0.52 | -88 | 1.6 x 10-11 |
(111) | 0.52 | -88 | 1.4 x 10-11 |
(111) | 0.52 | -93 | 6.3 x 10-12 |
(111) | 0.52 | -98 | 3.0 x 10-12 |
(111) | 0.52 | -98 | 3.2 x 10-12 |
(111) | 0.52 | -108 | 1.3 x 10-12 |
(111) | 0.52 | -108 | 9.6 x 10-13 |
(111) | 0.52 | -113 | 5.6 x 10-13 |
(111) | 0.52 | -113 | 4.8 x 10-13 |
(111) | 0.25 | -68 | 4.1 x 10-11 |
(111) | 0.25 | -78 | 1.6 x 10-11 |
(111) | 0.25 | -88 | 7.4 x 10-12 |
(111) | 0.25 | -93 | 2.9 x 10-12 |
(111) | 0.25 | -98 | 1.5 x 10-12 |
(111) | 0.25 | -108 | 4.6 x 10-13 |
(111) | 0.25 | -113 | 2.6 x 10-13 |
(111) | 0.04 | -68 | 6.1 x 10-12 |
(111) | 0.04 | -78 | 2.9 x 10-12 |
(111) | 0.04 | -88 | 1.4 x 10-12 |
(111) | 0.04 | -93 | 5.6 x 10-13 |
(115) | 0.46 | -63 | 9.3 x 10-10 |
(115) | 0.46 | -68 | 5.8 x 10-10 |
(115) | 0.46 | -78 | 2.9 x 10-10 |
(115) | 0.46 | -88 | 1.7 x 10-10 |
(115) | 0.46 | -93 | 8.5 x 10-11 |
(115) | 0.46 | -98 | 5.3 x 10-11 |
(115) | 0.46 | -108 | 1.8 x 10-11 |
(115) | 0.46 | -113 | 9.4 x 10-12 |
(115) | 0.46 | -123 | 5.0 x 10-12 |
(115) | 0.46 | -128 | 1.4 x 10-12 |
(115) | 0.59 | -68 | 6.3 x 10-10 |
(115) | 0.59 | -78 | 3.6 x 10-10 |
(115) | 0.59 | -88 | 2.0 x 10-10 |
(115) | 0.59 | -93 | 1.1 x 10-10 |
(115) | 0.59 | -98 | 5.8 x 10-11 |
(115) | 0.59 | -108 | 2.1 x 10-11 |
(115) | 0.59 | -113 | 1.0 x 10-11 |
(115) | 0.59 | -128 | 1.8 x 10-12 |
(115) | 0.40 | -58 | 9.2 x 10-10 |
(115) | 0.40 | -63 | 6.4 x 10-10 |
(115) | 0.40 | -68 | 3.9 x 10-10 |
(115) | 0.40 | -78 | 2.1 x 10-10 |
(115) | 0.40 | -88 | 9.1 x 10-11 |
(115) | 0.40 | -93 | 4.2 x 10-11 |
(115) | 0.40 | -98 | 1.9 x 10-11 |
(115) | 0.40 | -108 | 7.9 x 10-12 |
(115) | 0.40 | -113 | 3.5 x 10-12 |
(115) | 0.23 | -58 | 4.0 x 10-10 |
(115) | 0.23 | -63 | 2.9 x 10-10 |
(115) | 0.23 | -68 | 1.7 x 10-10 |
(115) | 0.23 | -78 | 9.3 x 10-11 |
(115) | 0.23 | -88 | 4.7 x 10-11 |
(115) | 0.23 | -93 | 2.4 x 10-11 |
(115) | 0.23 | -98 | 1.2 x 10-11 |
(115) | 0.23 | -108 | 3.7 x 10-12 |
(115) | 0.23 | -113 | 1.7 x 10-12 |
(115) | 0.52 | -78 | 7.7 x 10-10 |
(115) | 0.52 | -88 | 4.4 x 10-10 |
(115) | 0.52 | -93 | 2.8 x 10-10 |
(115) | 0.52 | -98 | 1.6 x 10-10 |
(115) | 0.52 | -108 | 5.1 x 10-11 |
(115) | 0.52 | -123 | 1.1 x 10-11 |
(115) | 0.52 | -128 | 4.0 x 10-12 |
(115) | 0.52 | -138 | 1.3 x 10-12 |
(115) | 0.61 | -73 | 4.7 x 10-10 |
(115) | 0.61 | -78 | 3.3 x 10-10 |
(115) | 0.61 | -88 | 2.3 x 10-10 |
(115) | 0.61 | -93 | 1.4 x 10-10 |
(115) | 0.61 | -98 | 7.5 x 10-11 |
(115) | 0.61 | -108 | 3.8 x 10-11 |
(115) | 0.61 | -113 | 2.7 x 10-11 |
(115) | 0.61 | -123 | 1.4 x 10-11 |
(115) | 0.61 | -128 | 7.5 x 10-12 |
(115) | 0.61 | -138 | 2.5 x 10-12 |
(115) | 0.61 | -148 | 1.2 x 10-12 |
(115) | 0.64 | -93 | 8.3 x 10-11 |
(115) | 0.64 | -98 | 5.9 x 10-11 |
(115) | 0.64 | -108 | 2.9 x 10-11 |
(115) | 0.64 | -113 | 1.6 x 10-11 |
(115) | 0.64 | -123 | 8.7 x 10-12 |
(115) | 0.64 | -128 | 5.5 x 10-12 |
(115) | 0.64 | -138 | 2.0 x 10-12 |
(115) | 0.69 | -78 | 5.3 x 10-11 |
(115) | 0.69 | -88 | 3.2 x 10-11 |
(115) | 0.69 | -93 | 1.9 x 10-11 |
(115) | 0.69 | -98 | 1.3 x 10-11 |
(115) | 0.69 | -108 | 6.0 x 10-12 |
(115) | 0.69 | -113 | 5.7 x 10-12 |
(115) | 0.69 | -123 | 2.3 x 10-12 |
(115) | 0.69 | -128 | 9.9 x 10-13 |
(115) | 0.69 | -138 | 4.5 x 10-13 |