Photochemistry on ultrathin metal films

A morphology study on the epitaxial growth of graphene and its buffer layer

“…The first is called "step-nucleation" (Figure 8(a-b)) and describes the case where small domains form along the lower side of step edges. Based on the theory of heteroepitaxy, nucleation at step edges implies near equilibrium growth conditions with a diffusion length λ dif larger than the terrace width (w terrace ≈ 1 µm) such that the species have sufficient time to migrate on the terrace until a stable edge position is found [24,32]. The comparison of the morphology described in Figure 8(a) and that of the AFM measurements in Figure 8(b) shows increasing the annealing time by 15 min leads to the formation of continuous buffer layer stripes (light phase contrast) along the lower side of the edges from where they continue to grow onto the terrace.…”

“…The second type of 2D-layer growth shown in Figure 8(c-d) is called "terrace-nucleation" and describes the case where buffer layer domains form on the terraces and not along the step edges. Based on theory, nucleation on the terrace is obtained under supersaturated conditions once the effective diffusion length λ dif becomes smaller than the terrace width [24,32]. On the SiC surface, the reduction of λ dif leading to a transition from step-nucleation to terrace-nucleation of buffer layer nuclei is achieved by increasing the amount of the deposited carbon.…”