J. E. Prieto

Rashba effect at magnetic metal surfaces

Exchange-split two-dimensional electronic states at the magnetic Gd(0001) surface change their energy dispersion upon magnetization reversal owing to the Rashba effect. The Rashba parameter is found to be substantially enhanced and to change sign when an epitaxial metal-oxide surface layer is formed. The experimental observations are quantitatively described by ab initio calculations giving a detailed account of the near-surface charge-density gradients that are responsible for the Rashba effect.

Fabrication of magnetic quantum wires by step‐flow growth of cobalt on copper surfaces

One‐dimensional‐like Co structures 50‐A‐wide and 3000‐A‐long have been grown by decoration of the monoatomic steps of a Cu(111) surface and visualized with scanning tunneling microscopy. In order to achieve step‐flow growth, terrace width, evaporation rate, and substrate temperature have been carefully adjusted. The choice of the (111) terrace orientation and 〈110〉 compact steps ensures a homogeneous width of the Co wires and a lateral confinement of minority‐spin electrons.

Surface etching and enhanced diffusion during the early stages of the growth of Co on Cu(111)

Abstract The deposition of Co on Cu(111) at room temperature gives rise to the appearance of monoatomically-high, laterally extended holes, as well as room temperature motion of surface features, which is observed in real time by a scanning tunneling microscope. The holes are produced by a spontaneous surface etching process related to the formation of a surface alloy which, in turn, produces an enhancement of the surface diffusion. As a result of these phenomena there is a noticeable and unexpected mass transport at the surface during growth. We illustrate how these processes have an impact on the growth mode of Co on Cu(111).

Influence of surfactants on atomic diffusion

Abstract We have used Monte Carlo simulations with realistic interatomic potentials, combined with experimental results obtained by He diffraction (thermal energy atom scattering) and STM to investigate the effect of a surfactant agent such as Pb on the mechanisms of atomic diffusion involved in epitaxial metal growth. We find that the main role of the surfactant is to hinder fast diffusion by hopping over the surface, which is the dominant mechanism on a compact face such as Cu(111), and to promote exchange. As a side effect, this facilitates interlayer diffusion and hence layer-by-layer growth, because islands are smaller and have rougher borders; adatoms reaching an edge have more opportunities to cross them by exchange with a step atom.

Creation and motion of vacancy islands on solid surfaces: A direct view

Abstract By means of the Scanning Tunneling Microscope (STM), we have purposely created monolayer-deep vacancy islands on a Cu (1 1 1) surface covered with submonolayer amounts of Co and observed their motion in real time at room temperature. A quantitative evaluation of their random walk allows us to obtain their diffusion coefficient.

A structural analysis of the Co(0001) surface and the early stages of the epitaxial growth of Cu on it

The epitaxial growth of copper on Co(0001) was investigated by combined quantitative LEED and STM, including the clean surfaces Cu(111) and Co(0001). The mode of growth is a modified Stranski‐Krastanov type, i.e. pseudomorphic and approximately layer-like up to four monolayers of copper; later on, three dimensional islands develop. The stacking of the copper adlayers is exclusively fcc from the very beginning, whereby the ABAB stacking on a given terrace of the substrate is continued as ABABca. Since there are also terraces with an ABA stacking, fcc-twins (e.g. ABAcb) develop in the Cu films. Whilst in the submonolayer coverage regime of copper the cobalt substrate remains hcp stacked, films with more than about two copper layers are found to have induced a stacking fault in the substrate corresponding to a registry shift of the uppermost cobalt layer. As indicated by the analysis of a film slightly above one monolayer coverage, the registry shift seems to be triggered when the terraces of the substrate are fully covered by copper whereby the rearrangement of atoms probably starts at the step edges.

Rashba effect at the surfaces of rare-earth metals and their monoxides

We present a systematic study of the Rashba-type spin–orbit interaction at the (0001) surfaces of rare-earth metals and their surface monoxides, specifically of Tb metal and the O/Tb, O/Lu and O/Y surfaces. By means of photoemission experiments and ab initio band-structure calculations, we uncover the influence of this interaction on the surface electronic structure. In turn, the dramatic impact of the charge-density distribution of the surface/interface states on the strength of the Rashba-type spin splitting is demonstrated. We discuss the Rashba effect at magnetic and non-magnetic rare-earth surfaces, and compare with cases where it is negligible. The difference between the Rashba effect and magnetic linear dichroism in photoemission is pointed out to help avoid possible confusion in connection with the simultaneous appearance of these two effects at a magnetic surface.

Crystallography and morphology of the early stages of the growth of CoCu(111) by LEED and STM

We report on a quantitative investigation of the structure and morphology of ultrathin films of Co deposited on Cu(111) by an in situ combination of real space (STM) and diffraction (LEED) techniques. The film grows initially as bilayer islands with strict fcc stacking. Part of them are covered by Cu. The lateral distribution of Co- and Cu-terminated domains as well as of uncovered patches is both quantitatively determined by intensity analysis and visualized by STM images. Their simultaneous presence correlates nicely to known magnetic properties of ultrathin films, in particular with the observed magnetic anisotropy.

Surfactant-induced surface restructuring: (4×4)-Pb/Cu(111)

The atomic structure of a monolayer of Pb on Cu(111) was investigated by an in situ combination of low-energy electron diffraction, scanning tunnelling microscopy and Auger electron spectroscopy. The pronounced (4 × 4) superstructure observed is found to be due to a (in surface projection) hexagonally close-packed but vertically buckled Pb layer which induces a substantial complex restructuring of the first three Cu layers. In this interface to the copper bulk no intermixing of Pb and Cu atoms is observed. Surprisingly, the overall buckling amplitude of the first Cu layer is even larger than that of the lead layer and the positional height of Pb atoms residing on top of Cu atoms is lower than for all other atoms. The structural results agree qualitatively with recent effective-medium-theory calculations. The reconstruction induced by the lead adatoms shows that the substrate reacts in a structurally flexible way to their presence. It is proposed that this might be related to the surface-active (‘surfactant’) role that Pb plays in homogeneous and heterogeneous epitaxial growth on Cu(111).

The structure of Co films on Cu(111) up to 15 ML

Abstract New structural results of the epitaxial growth of Co Cu (111) in the coverage regime 1.5–15 ML are presented as investigated by quantitative LEED and STM. In the low coverage regime there is pure fcc stacking with copper diffused on top of 30% of the domains. The growth is ideally pseudomorphic. At intermediate coverages hcp stacked domains develop on the cost of fcc domains whereby the latter seem to be stabilized by their top copper layer. At high coverages the film is predominantly hcp exhibiting the ideal lattice parameter of Co(0001).