On the Temperature-Dependent Surface Structure of Metals

Recent experimental results based on X-ray photoelectron diffraction from a Pb(110) crystal are discussed in terms of surface roughening and surface melting. In comparison to other reports on Pb(110) surface roughening it is recognized that the correct determination of the roughening transition on (110) surfaces of fcc metals may be intrinsically difficult because of anisotropy. A novel technique for investigating the temperature-dependent surface free energy is described. The method involves the quasi-steady-state shape of periodic surface profiles on Au(111) and Au(100) single crystals. First results are reported for two crystallographic zones (111)⟨112⟩ and (100)⟨110⟩ of Au. These results illustrate the strong anisotropy of Δγ/γ of ~23% and ~ 4% at T = 0 K for the (111)⟨112⟩ and (100)⟨110⟩ zones, respectively. The data suggest that the low-index surfaces of Au(111) and (100) are not likely to roughen at T ≤ T_{M}.