J. de la Figuera

Dislocation emission around nanoindentations on a (001) fcc metal surface studied by scanning tunneling microscopy and atomistic simulations.

We present a combined study by scanning tunneling microscopy and atomistic simulations of the emission of dissociated dislocation loops by nanoindentation on a (001) fcc surface. The latter consist of two stacking-fault ribbons bounded by Shockley partials and a stair-rod dislocation. These dissociated loops, which intersect the surface, are shown to originate from loops of interstitial character emitted along the <110> directions and are usually located at hundreds of angstroms away from the indentation point. Simulations reproduce the nucleation and glide of these dislocation loops.

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.

Real-Space Imaging of the First Stages of FeSi2 Epitaxially Grown on Si(111): Nucleation and Atomic Structure

The first stages of the growth of iron disilicide on Si(111) have been studied with Scanning Tunnelling Microscopy. Nucleation and growth of two-dimensional, epitaxial islands of disilicide are obtained by means of a Solid Phase Epitaxy method. Atomically resolved images show that the islands present a hexagonal closed-packed symmetry and correspond to the first stage of a new metastable cubic phase of FeSi2 which grows matching its (111) plane to the Si(111) surface. The surface of the islands shows a 2 × 2 reconstruction explained on the basis of the reduction in number of Si dangling bonds. The results allow us to visualize in the real space that metastable phases can be stabilized by heteroepitaxial growth on suitable substrates.

Surface characterization of epitaxial, semiconducting, FeSi2 grown on Si(100)

We have identified the composition and range of thermal stability of FeSi and FeSi2 films grown on Si(100) by solid phase epitaxy and reactive deposition epitaxy. Evidence for the semiconducting character of FeSi2 is obtained from photoemission measurements giving a low density of states at the Fermi level. Si enrichment at the outer surface of the silicides at temperatures much lower than previously thought has been found by depth profiling. Scanning tunneling microscopy reveals a rather inhomogeneous growth with a tendency towards epitaxial growth favored by the presence of surface steps on the Si substrate.

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).

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.

Geometric and electronic structure of epitaxial iron silicides

The geometric and electronic structure of several iron silicide phases epitaxially grown on Si(111)7×7 have been characterized by means of surface sensitive techniques including scanning tunneling microscopy (STM), x‐ray photoelectron spectroscopy, ion scattering spectroscopy (ISS), and ultraviolet photoelectron spectroscopy. The silicides were grown by solid‐phase and reactive‐deposition epitaxy, and their stability range was determined in situ as a function of iron coverage and annealing temperature. In particular, we have studied the phases appearing in the low‐coverage low‐temperature region. Additionally, the crystallites of the most important FeSi2 phases (γ‐FeSi2 and β‐FeSi2) have been characterized at atomic level with STM, while the surface termination was analyzed with ISS.

Structure and magnetism in ultrathin iron oxides characterized by low energy electron microscopy

We have grown epitaxial films a few atomic layers thick of iron oxides on ruthenium. We characterize the growth by low energy electron microscopy. Using selected-area diffraction and intensity-versus-voltage spectroscopy, we detect two distinct phases which are assigned as wüstite and magnetite. Spin-polarized low energy electron microscopy reveals magnetic domain patterns in the magnetite phase at room temperature.

A new metastable epitaxial silicide: FeSi2/Si(111)

Abstract A metastable phase of FeSi 2 that is not present in the bulk phase diagram can be grown epitaxially on Si(111). Scanning tunneling microscope images reveal the surface reconstruction of this phase and allows one to model its crystallographic structure. It crystallizes with a cubic structure, probably a fluorite structure like CoSi 2 and NiSi 2 , lattice-matched to Si. The (111) surface has a 2×2 reconstruction according to LEED. The origin of this reconstruction is reported here for the first time. It is due to a superstructure of Si adatoms with local bonding similar to that of the adatoms in the Si(111)7×7 reconstruction.

Structural characterisation and homoepitaxial growth on Cu(111)

Abstract A comprehensive study of the homoepitaxial MBE growth of Cu on Cu(111) is presented. This system displays a wealth of features and a large accumulation of morphological and structural defects. It is demonstrated that all of them can be ascribed to two basic characteristics of fcc-(111) faces: the presence of two threefold adsorption sites at the surface, which allows the formation of stacking faults, and the existence of high Ehrlich–Schwoebel barriers at steps, hindering interlayer diffusion. This behaviour, therefore, must be common during growth on compact metallic faces, and could have important implications for the preparation of low-dimensional heterostructures.