Surface structure of ultrathin Fe films on Cu(001) revisited

Young-type interference for scattering of fast helium atoms from an oxygen covered Mo(112) surface

In studies on two structures of oxygen adsorbates on Mo(112), we demonstrate the potential of fast atom diffraction to derive the surface unit cell size and its symmetry. Helium atoms with energies of 1-2 keV are scattered from an adsorbate covered Mo(112) surface along low indexed surface directions under grazing angles of incidence. From the observed diffraction patterns, the lateral periodicity of the surface structures is derived. In addition to the periodic lattice, information on the structure within the unit cell can be obtained from double slit type of interference.

The effect of lattice structure on dipole-exchange spin waves in ultrathin ferromagnetic films

Calculations are reported relating to the dipole-exchange spin waves in ultrathin ferromagnetic films with different lattice structures such as simple cubic, body-centred cubic and face-centred cubic, using a microscopic, or Hamiltonian-based, theory. Both the short-range exchange and the long-range dipolar interactions are included in the Hamiltonian, together with an external magnetic field applied either parallel or perpendicular to the film surfaces. The use of phenomenological dipole-exchange boundary conditions, as in macroscopic theories, is avoided. Comparisons between our results and macroscopic theories generally give good agreement in a small wavevector limit. At larger wavevectors for the microscopic theory, it is found that the frequencies and the localization properties of the discrete spin waves show a sensitive dependence on the lattice structure.

Out-of-plane nesting driven spin spiral in ultrathin Fe/Cu(001) films

Epitaxial ultrathin Fe films on fcc Cu(001) exhibit a spin spiral (SS), in contrast to the ferromagnetism of bulk bcc Fe. We study the in-plane (IP) and out-of-plane (OP) Fermi surfaces (FSs) of the SS in 8 monolayer Fe/Cu(001) films using energy-dependent soft-x-ray momentum-resolved photoemission spectroscopy. We show that the SS originates in nested regions confined to OP FSs, which are drastically modified compared to IP FSs. From precise reciprocal-space maps in successive zones, we obtain the associated real space compressive strain of 1.5+/-0.5% along c axis. An autocorrelation analysis quantifies the incommensurate ordering vector q=(2pi/a)(0,0, approximately 0.86), favoring a SS and consistent with magneto-optic Kerr effect experiments. The results reveal the importance of IP and OP FS mapping for ultrathin films.

Evidence for 2D-network structure of monolayer silica film on Mo(112)

The structure of a monolayer silica film on a Mo(112) surface is investigated by grazing scattering of 25 keV H0 atoms. By detection of the number of projectile induced emitted electrons as function of azimuthal angle of rotation of the target surface, the geometrical structure of atoms forming the topmost layer of the silica film is determined via ion beam triangulation. From our data we find evidence for the arrangement of surface atoms in terms of a two-dimensional Si-O-Si network model.

Ion beam triangulation based on electron detection for studies on the structure of 1 ML Mn on Cu(001)

Recent developments in studies on the structure of surfaces based on ion beam triangulation are discussed. We will outline recent experimental progress in the application of this method, which is closely related to the detection of the number of emitted electrons per incident ion during scattering under surface channeling conditions. Key features are the pronounced change of electron emission for the projectile beam aligned along a low index crystallographic direction in the surface plane ('axial surface channeling') and the interpretation of data in terms of classical trajectory computer simulations. As a representative example we will discuss here studies on the structure of the low temperature c(8 × 2) Mn/Cu(001) phase.

Ferromagnetic Fe on Cu(001) throughout the fcc-like phase: arguing from the viewpoint of the electronic structure

The scientific enthusiasm for ultrathin Fe films on Cu(001) has now lasted for more than 20 years. Is there ferromagnetic iron with a face-centred cubic (fcc) structure? Does ferromagnetism in Fe hinge on the body-centred cubic (bcc) structure? In this contribution, we try to establish that the electron system gives evidence of ferromagnetic behaviour with fcc-like electronic bands. We examine a crystal-induced surface state, which is characteristic of fcc surface order. Furthermore, we compare electronic signatures of fcc and bcc: the d-band exchange splitting, image-potential-state energies and the work function. We conclude that, from the viewpoint of the electronic structure, Fe on Cu(001) is found to be ferromagnetic throughout the fcc-like phase. This result raises a new question: how much deviation from the relaxed fcc order is acceptable without losing the electronic signature of fcc?