Jump processes in surface diffusion - Bilkent University - Faculty of ...

44 G. Antczak, G. Ehrlich / Surface Science Reports 62 (2007) 39–61
Fig. 11. Arrhenius plot for in- and cross-channel diffusion of Ni on Ni(110)
plane [15]. Left: Substrate after thermal treatment. Right: Nickel substrate had
been hydrogen fired and field evaporated before experiments.
Fig. 9. Adatom trajectories in diffusion on fcc(110) plane at 0.4T m [11].
Transitions across the [1¯10] channels are apparent.
Fig. 12. Self-diffusion of Pt on Pt(110) surface [18]. In-channel diffusion:
E D = 0.72 ± 0.07 eV, D o = 6 × 10 −4 cm 2 /s. Cross-channel diffusion:
E D = 0.69 ± 0.07 eV, D o = 3 × 10 −4 cm 2 /s.
Fig. 10. Early Arrhenius plot for the cross-channel diffusion of iridium atoms
on Ir(110) [14].
Kellogg did not rely on an atom probe, he was able to
discriminate between Ni and Pt atoms through differences in the
voltages necessary for field evaporation—the platinum atoms
were removed at significantly higher voltages; they also had
a much larger image spot. When a Pt atom was deposited
on the cold surface, the image looked as in Fig. 15(a). After
heating to 112 K, the image in Fig. 15(b) yielded a much
smaller spot size, indicative of Ni. Upon removing the adatom,
in Fig. 15(c), and field evaporating the topmost layer, as is
shown in Fig. 15(d), a platinum atom was retrieved from
the surface layer. Clearly exchange had occurred between a
Fig. 13. Self-diffusion of Ir on Ir(110) plane [19]. Both in-channel and crosschannel
motion is observed.
platinum adatom and a nickel atom from the substrate, and the
atom entering the lattice was platinum not nickel. Assuming
a prefactor of 1 × 10 −3 cm 2 /s, a barrier of 0.28 eV was
determined for the displacement of platinum. The distribution
of displacements was also observed in these experiments and it
was found that in 62.5% the replacement atom appeared in the
〈112〉 direction, never along 〈001〉; the remaining experiments