Ripple patterns forming on Pt͑111͒ due to 5 keV Ar + grazing-incidence ion bombardment were investigated by scanning tunneling microscopy in a broad temperature range from 100 to 720 K and for ion fluences up to 3 ϫ 10 20 ions/ m 2 . A detailed morphological analysis together with molecular dynamics simulations of single ion impacts allow us to develop atomic scale models for the formation of these patterns. The large difference in step edge versus terrace damage is shown to be crucial for ripple formation under grazing incidence. The importance of distinct diffusion processes-step adatom generation at kinks and adatom lattice gas formation-for temperature dependent transitions in the surface morphology is highlighted. Surprisingly, ion bombardment effects like thermal spike induced adatom production and planar subsurface channeling are important for pattern ordering.

Ripple patterns formed on Pt(111) through grazing incidence ion beam erosion coarsen rapidly. At and below 450 K coarsening of the patterns is athermal and kinetic, unrelated to diffusion and surface free energy. Similar to the situation for sand dunes, coarsening takes place through annihilation reactions of mobile defects in the pattern. The defect velocity derived on the basis of a simple model agrees quantitatively with the velocity of monatomic steps illuminated by the ion beam.

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High-resolution LEED (low-energy electron diffraction) data of Cu(001) reveal an uniaxial in-plane lattice reconstruction by 1%. One-dimensional nanogrooves induced by ion bombardment involve the creation of steps that enable this reconstruction. This is the first verification of van der Merwe's prediction of step facilitated reconstruction. We confirm the predicted dependence on step orientation: h100i steps allow stress-relief and h110i steps do not, consistent with the known elastic anisotropy. Similar behavior is predicted for other nonreconstructed (001) (001)-surfaces of transition and noble metals do reconstruct. Their termination is a (111)-like overlayer that periodically matches the (001)-bulk structure. The decision whether the (001)-surface does reconstruct or not is quite subtle. The adsorption of small amounts of atoms or molecules can lead to deconstruction [5,6]. In an ab initio density-functional-theory study, Fiorentini et al. [7,8] investigated the tendency for (001)-transition metal surfaces to reconstruct. They find that surfaces of the metals at the end of the 5d transition series such as Ir, Pt, and Au reconstruct, whereas their 4d counterparts Rh, Pd, and Ag do not. Reconstruction requires bond rearrangements, leading to significant energy losses due to the disruption or stretching of bonds between the mismatched layer and that underneath. The reconstruction results from a delicate balance between surface-substrate mismatch and strain related energy gain [7,8]. Their high strain energy favors reconstruction for the 5d (001)-surfaces, while it is too small for their 4d and 3d counterparts. The surfaces of the 3d and 4d metals remain unreconstructed in agreement with experimental observations. The claim by Müller et al. [9] of an in-plane reconstruction of clean Cu(001) created a sensation. They found a contraction of about 1% from their LEED (low-energy electron diffraction) I-V-analysis. Their finding provided a nice framework for the contraction of 1% found for the pseudomorphic growth of Fe/Cu(001) [10 -12]. The Cu(001) in-plane reconstruction was challenged both experimentally [13,14] and theoretically [15]. Müller et al. [16] conceded and attributed their findings to either a ''lower lateral crystallinity'' of their surface or ''systematic errors affecting the accuracy of their analysis.'' In a later LEED-I-V-study, Walter et al.[17] indeed obtained smaller in-plane relaxation by introducing an energy dependent inner potential.We find experimental evidence for a new local minimum in the free energy of Cu(001). Indeed, Cu(001) has a strong tendency for an in-plane lattice contraction of 1%. It only prevails on surfaces with a finite amount of steps, when oriented along the h100i-azimuth. Note that h100i is the soft direction with respect to deformation [18]. This geometry permits to relieve tensile stress. This result is of general importance to the 3d and 4d (001)-metal surfaces with implications for the creation of nanostructures on or in these surfaces and the structure of hetero...

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