Biomedical subjects

S Blügel

Publications and source records attributed to S Blügel.

At least 19 recordsLinked to original sources

PubMed2002

Element specific surface reconstructions of islands during surfactant-mediated growth on Si (111).

The early stages of surfactant- (As, Sb) mediated homoepitaxial growth on Si (111) are examined by scanning tunneling microscopy and extensive ab initio calculations of Si(n) clusters (n</=12). The results reveal the different microscopic behavior of the two surfactants: On As-covered Si (111), one exclusively finds two-dimensional islands with double-layer height which show the (1 x 1) terrace structure. On Sb-covered Si (111), the islands show two different reconstructions: at the rim of the islands a (1 x 1) structure appears, while in the center the (square root 3 x square root 3) terrace structure is observed.

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PubMed2002

Magnetization-direction-dependent local electronic structure probed by scanning tunneling spectroscopy.

Scanning tunneling spectroscopy (STS) of thin Fe films on W(110) shows that the electronic structure of domains and domain walls is different. This experimental result is explained on the basis of first-principles calculations. A detailed analysis reveals that the spin-orbit induced mixing between minority d(xy+xz) and minority d(z(2)) spin states depends on the magnetization direction and changes the local density of states in the vacuum detectable by STS. As a consequence nanometer-scale magnetic structure information is obtained even by using nonmagnetic probe tips.

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PubMed2002

Novel sb induced reconstruction of the (113) surface of ge.

Sb induces on Ge(113) a c(2 x 2) reconstruction in which Sb breaks one Ge-Ge bond and occupies an interstitial site, in contrast to Sb adsorption on other Si or Ge surfaces. Sb saturates the three dangling bonds per unit cell of the (113) surface inducing a large strain which is released by occupation of the interstitial site. Two neighboring Sb at interstitial sites form a dimer. The structure has been determined by x-ray diffraction, applying direct methods, and ab initio density-functional-theory calculations. The adsorption geometry and the high binding energy lead one to expect that Sb cannot be used as a surfactant for the growth of Si/Ge layers on the (113) surface.

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PubMed2002

Surfactant mediated heteroepitaxy versus homoepitaxy: kinetics for group-IV adatoms on As-passivated Si(111) and Ge(111).

Using ab initio calculations we have determined the paths and activation energies for diffusion of group-IV atoms (Si, Ge, and Sn) on top of the As layer on As-passivated Si(111), and for exchange with an As atom. The kinetics of Si, Ge, and Sn adatoms is substantially different: Si adatoms are readily incorporated under the As layer. Ge adatoms diffuse far on top of the As layer and can reach existing steps. We show for the first time that the ratio between diffusion and exchange barriers depends strongly on the strain of the growing Ge film. Sn atoms remain on top of the As layer.

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PubMed2001

Resolving complex atomic-scale spin structures by spin-polarized scanning tunneling microscopy.

The spin-polarized scanning tunneling microscope (SP-STM) operated in the constant current mode is proposed as a powerful tool to investigate complex atomic-scale magnetic structures of otherwise chemically equivalent atoms. The potential of this approach is demonstrated by successfully resolving the magnetic structure of Cr/Ag(111), which is predicted on the basis of ab initio vector spin-density calculations to be a coplanar noncollinear periodic 120 degrees Néel structure. Different operating modes of the SP-STM are discussed on the basis of the model of Tersoff and Hamann.

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PubMed2001

Three-dimensional spin structure on a two-dimensional lattice: Mn/Cu(111).

Based on first-principles vector spin-density total-energy calculations of the magnetic and electronic structure of Cr and Mn transition-metal monolayers on the triangular lattice of a (111) oriented Cu surface, we propose for Mn a three-dimensional noncollinear spin structure on a two-dimensional triangular lattice as magnetic ground state. This new spin structure is a multiple spin-density wave of three row-wise antiferromagnetic spin states and comes about due to magnetic interactions beyond the nearest neighbors and due to higher order spin interactions (i.e., four spin). The magnetic ground state of Cr is a coplanar noncollinear periodic 120 degrees Néel structure.

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PubMed1996