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

52 G. Antczak, G. Ehrlich / Surface Science Reports 62 (2007) 39–61
Fig. 35. Distribution of Re adatom displacements at 300 K on W(211), obtained from field ion observations [115]. Best fit to experiments obtained with an entirely
negligible contribution from long jumps.
Fig. 36. Displacement distribution for W adatom on W(211) at 307 K [117].
Best fit to field ion experiments derived with negligible contribution of β double
or longer jumps.
Fig. 37. Distribution of Pd atom displacements on W(211) at 133 K [118]. Best
fit with double/single jumps equal to 0.20, and triple/single of 0.13.
shown in Fig. 36 was found to be due entirely to single jumps
between nearest-neighbor sites, as expected at the time.
The same was found for the diffusion of palladium at 114
and 122 K. However, at 133 K, the distribution in Fig. 37 for
the first time gave a clear indication of significant contributions
from long jumps; the ratio of double to single jumps was 0.20,
Fig. 38. Distribution of Ni adatom displacements on W(211) plane at 179
K [117]. Best fit of observations with double/single jumps equal to 0.058.
and even triple jumps were detected, at a ratio of 0.13 for triple
to single transitions. In the diffusion of nickel atoms on W(211),
Senft [117] found a distribution shown in Fig. 38, best fit with
a ratio of doubles to singles of 0.058 at T = 179 K. What
was surprising about these findings is not just the detection
of long jumps, but long jumps at quite a low temperature, <
0.1T m , and at a rate very temperature sensitive. For palladium,
a diminution of the temperature by 11 K sufficed to eliminate
all long transitions.
With long jumps now firmly established in surface diffusion,
Linderoth et al. [119] decided to explore their rates in selfdiffusion
on the reconstructed Pt(110)-(1 × 2) plane, shown
in Fig. 39. Jumps were observed with the scanning tunneling
microscope, which yielded the distribution at 375 K in Fig. 40,
with a ratio of “double” to single jumps of 0.095. They also
made measurements over a temperature range of 60 K to come
up with the Arrhenius plot in Fig. 41, which gave a barrier
of 0.81 ± 0.01 eV for single jumps and a somewhat higher
value, 0.89 ± 0.06 eV, identified as coming from doubles.
This identification turned out to be premature, however. A year
passed and Montalenti and Ferrando [120] did simulations of
diffusion on Au(110)-(1×2), relying on RGL interactions [102,
103]. They discovered two prevalent jumps, illustrated in