Macroscopic CO diffusion on the (110) surface of Ni was found to be markedly impeded by surface contamination by only a few percent of a monolayer of S (table 13). The effect was even greater if the sample was annealed at high temperatures. The results were explained by proposing that S-covered steps led to a much higher energy barrier to CO diffusion.
X.D.Xiao, Y.Xie, C.Jakobsen, H.Galloway, M.Salmeron, Y.R.Shen: Physical Review Letters, 1995, 74[19], 3860-3
Table 13
Diffusivity of CO on (110)Ni, as a Function of S Contamination
Direction | S (%) | Temperature (C) | D (cm2/s) |
[1¯10] | 0 | -90 | 1.6 x 10-10 |
[1¯10] | 0 | -110 | 6.3 x 10-11 |
[1¯10] | 0 | -125 | 3.2 x 10-11 |
[1¯10] | 0 | -135 | 1.6 x 10-11 |
[1¯10] | 1 | -90 | 1.1 x 10-10 |
[1¯10] | 1 | -105 | 4.6 x 10-11 |
[1¯10] | 1 | -120 | 1.4 x 10-11 |
[1¯10] | 1 | -135 | 8.3 x 10-12 |
[1¯10] | 2 | -75 | 1.1 x 10-10 |
[1¯10] | 2 | -90 | 5.1 x 10-11 |
[1¯10] | 2 | -105 | 2.2 x 10-11 |
[1¯10] | 2 | -125 | 5.2 x 10-12 |
[1¯10] | 5 | -60 | 1.5 x 10-10 |
[1¯10] | 5 | -75 | 4.5 x 10-11 |
[1¯10] | 5 | -90 | 9.0 x 10-12 |
[1¯10] | 5 | -105 | 2.1 x 10-12 |
[1¯10] | 10 | -60 | 8.8 x 10-11 |
[1¯10] | 10 | -75 | 2.8 x 10-11 |
[1¯10] | 10 | -90 | 4.7 x 10-12 |
[1¯10] | 10 | -105 | 1.2 x 10-12 |
[1¯10] | 15 | -45 | 6.5 x 10-11 |
[1¯10] | 15 | -60 | 2.3 x 10-11 |
[1¯10] | 15 | -75 | 5.6 x 10-12 |
[1¯10] | 15 | -90 | 1.6 x 10-12 |
[1¯10] | 20 | -35 | 3.3 x 10-11 |
[1¯10] | 20 | -45 | 1.4 x 10-11 |
[1¯10] | 20 | -60 | 4.4 x 10-12 |
[1¯10] | 20 | -75 | 7.6 x 10-13 |
[001] | 0 | -65 | 3.2 x 10-11 |
[001] | 0 | -80 | 1.7 x 10-11 |
[001] | 0 | -95 | 5.1 x 10-12 |
[001] | 0 | -110 | 4.2 x 10-12 |
[001] | 2 | -35 | 9.4 x 10-11 |
[001] | 2 | -50 | 2.8 x 10-11 |
[001] | 2 | -65 | 1.2 x 10-11 |
[001] | 2 | -75 | 6.5 x 10-12 |
[001] | 2 | -90 | 2.2 x 10-12 |
[001] | 5 | -35 | 4.6 x 10-11 |
[001] | 5 | -40 | 2.3 x 10-11 |
[001] | 5 | -55 | 9.0 x 10-12 |
[001] | 5 | -60 | 6.3 x 10-12 |
[001] | 8 | -50 | 3.5 x 10-11 |
[001] | 8 | -60 | 1.5 x 10-11 |
[001] | 8 | -75 | 3.1 x 10-12 |
[001] | 8 | -80 | 1.8 x 10-12 |
[001] | 8 | -90 | 5.4 x 10-13 |
[001] | 10 | -35 | 3.5 x 10-11 |
[001] | 10 | -45 | 1.4 x 10-11 |
[001] | 10 | -55 | 5.7 x 10-12 |
[001] | 10 | -60 | 3.1 x 10-12 |
[001] | 10 | -70 | 1.4 x 10-12 |
[001] | 20 | -35 | 8.9 x 10-12 |
[001] | 20 | -55 | 3.0 x 10-12 |
[001] | 20 | -60 | 1.3 x 10-12 |