Novel Local Free Energy Minimum on the Cu(001) Surface

Abstract

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...

Quantitative understanding of the growth of Cu/Cu(001) including the determination of the Ehrlich-Schwoebel barrier at straight steps and kinks

“…Further cleaning was checked with high-resolution low-energy electron diffraction ͑HR-LEED͒, which ultimately showed an average terrace length above 100 nm. 5,6,21,[31][32][33] The homoepitaxial growth experiments were monitored in situ with TEAS. 21,30 A thoroughly desulfurized thermal evaporation Cu source was used.…”

“…Even in the case of homoepitaxial growth adatom ͑or va-cancy͒ structures may result in strain effects with electronic consequences. [1][2][3][4] Although there is some experimental evidence for strain in homoepitaxial systems, 5,6 these effects are quite minor at not too low temperatures, still allowing monomer mobility. Therefore, we neglect these features and consider the fcc lattice model, i.e., the atoms at or near the surface occupy bulk-continued lattice sites, as a realistic framework for modeling the growth dynamics.…”

On the Origin, Growth and Application of Ripples

“…In figure 7 different ripple wavelengths can be observed, larger in the center and smaller at the edge. The larger wavelength of about 400 nm is due to an intensity effect [7] or a temperature effect as has been found in ion beam sputtering experiments [8]. The smaller wavelength at the edge is about 250 nm.…”

Superior Regularity in Erosion Patterns by Planar Subsurface Channeling

“…This is more surprising, as this damage is relevant whenever the scattered ions are used as a measuring tool for surface processes or structure (e.g., [5]). It is even crucial in applications of grazing ion beams like ion beam smoothening [6], thin film growth manipulation [7], nanopattern formation [8,9], or ion beam milling [10].One step towards an interpretation of morphologies resulting from grazing incidence ion bombardment is the distinction between terrace damage and step edge damage [11]. Here we show for the first time how a specific damage mechanism at step edges acting only under grazing incidence conditions couples into the formation of mesoscopic damage structures.…”

“…This is more surprising, as this damage is relevant whenever the scattered ions are used as a measuring tool for surface processes or structure (e.g., [5]). It is even crucial in applications of grazing ion beams like ion beam smoothening [6], thin film growth manipulation [7], nanopattern formation [8,9], or ion beam milling [10].…”