We measured diffusion constants of hydrogen adatoms on Cu(1 1 1) using a combination of enabling optical techniques. We observed a steep crossover from a strongly thermal activated hopping (T > 130 K) to a weakly thermal activated 'hopping' (T < 130 K). The diffusion at high temperatures is characterized by a large barrier Ediff (1) = 450 meV and a large pre-exponential factor D0 (1) = 162 cm2 / s, indicating that it is dominated by the kinetics of crossing step edges. The weakly activated diffusion at low temperatures is characterized by a much smaller 'barrier' of Ediff (2) = 22 meV and a pre-exponential factor D0 (2) = 6.8 × 10- 14 cm2 / s, characteristic of a quantum under-barrier tunneling.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Physics and Astronomy(all)