Entropy-controlled fully reversible nanostructure formation of Ge on miscut vicinal Si(001) surfaces
Sprache des Titels:
Entropy effects substantially modify the growth of self-assembled Ge nanostructures on vicinal Si(001)surfaces, on which one-dimensional nanowire-like structures are formed. As shown by variable temperaturescanning tunneling microscopy, these nanostructures are not only tunable in size and shape, but can be fullyreversibly erased and reformed without changes in sizes and composition. This unprecedented behavior is causedby the strong free surface energy renormalization due to the large step entropy of vicinal surfaces that stronglyincreases with increasing temperature. This favors a planar two-dimensional surface at higher temperatures inthermodynamic equilibrium, whereas the nanostructured surface is the preferred low-temperature configuration.Taking the step entropy into account, the critical transition temperature between these surface states derivedby free-energy minimization is shown to scale nearly linearly with the Ge coverage?in excellent agreementwith the experiments. Most importantly, the nanowire sizes are found to be deterministically controlled by theGe thickness and vicinal angle, independently of the growth or annealing conditions. Thus, highly reproduciblestructures with tunable nanogeometries and -dimensions are obtained, which opens promising avenues for deviceapplications.