Measurement of the barrier height of the reflective W {110} plane boundaries in surface diffusion of single atoms

Origins of scale invariance in growth processes

“…One motivation for considering different values of q comes from the observation [199] that the Hamiltonian (5 .10) mimics, for q > 1, the effect of step edge barriers (also referred to as Schwoebel barriers [200,201]) which are known to exist on certain metal surfaces . Field-ion microscopy studies [202,203,204] show that atoms diffusing on a terrace can be reflected when attempting to jump down from the terrace edge . This is interpreted in terms of an increased energy barrier for inter-layer diffusion, due to the reduced bonding experienced by the atom at an edge position (the energy landscape is illustrated in Figure 28).…”

“…The step edge barrier arguments of Schwoebel and Villain focus on one particular set of bonding environments, however it is clear that many other configurations potentially play a role in determining the overall current . This implies, in particular ; that nonequilibrium surface currents can appear also on surfaces where the simplest kind of step edge barriers [202,203] is absent or undetectably weak. An analogy may be useful in clarifying the spirit of this argument .…”

Direct observation of atomic exchange during surface self-diffusion

“…W has a narrow temperature range over which descent over the edge is reasonably probable and the boundary is stable. If the temperature is ∼470 K the average number of heating periods required for the descent of an adatom over the step edge is 21.5 as reported by Wang and Tsong [48]. They reported an average number of 7.3…”

“…The long series of jumps of a single adatom showed that the laser could controllably heat the substrate to temperatures required for diffusion studies. The boundary of the W(110) plane becomes mobile at 400 K [48]. The observation of some slight boundary change in combination with the number of heating periods compared to the data in [48] gives a rough indication that the temperature of the tip was between 370 and 400 K. This is above the temperatures needed to initiate diffusion on Ir surfaces, ∼260 K, thus proving the laser capable of tip heating for all substrates.…”