Unreconstructed surfaces of metals

The unreconstructed low Miller index surfaces of fee, bcc and hep metals are illustrated schematically in fig. 1. The primary structural feature associated 

Structure of unreconstructed metal surfaces, ddu is the relaxation of the first inlerplanar spacing expressed as a percentage of the bulk inlerplanar spacing. A positive value implies an expansion of the first interplanar spacing, a negative value implies a contraction. M23, 8 23 and M34 are the corresponding relaxations of deeper layers. 

The majority of clean metal surfaces display a contraction of the spacing between the first and second atomic planes. However, there are several surfaces that exhibit the opposite behavior an expansion of the first interplanar spacing. Table 1 allows us to identify seven surfaces for which an expansion is implicated Be(1000), Al(lll), Al(100), Fe(110), Rh(100), Pd(100), Pt(lll). Of these seven surfaces, the error bars for the determinations of the first interlayer spacing of Rh(100), Fe(llO) and Pt(lll) do not allow us to conclusively ascribe an expansion to these surfaces. The authors of the Pd(100) determination note that the surface could be contaminated with hydrogen. This leaves only the group II and III metals Be and A displaying a reproducible expansion of the top layer spacing. 

The relaxation of deeper layers displays oscillatory behavior. Although many low Miller index surfaces exhibit strictly alternating relaxations (i.e. a 

---