|Aufstellung der Publikationen der Arbeitsgruppe 2014 und 2015|
Aufgeführt sind Arbeiten, die in den Jahren 2014 und 2015 publiziert
und zur Veröffentlichung eingereicht oder angenommen worden sind.
Sonderdrucke oder Preprints können von den Autoren oder im Sekretariat
des Lehrstuhls angefordert werden (Postanschrift: Humboldt-Universität
zu Berlin, Institut für Physik, Physik der Grenzflächen und
dünnen Schichten, Newtonstraße 15, 12489 Berlin, Tel.: (+49
30) 20 93 - 78 91, Fax: - 78 99).
Recently, quantum effects were observed for the scattering of fast atoms from surfaces under a grazing angle of incidence. We discuss basic features of Fast Atom Diffraction (FAD) which adds a further powerful method to the established tools in ion beam analysis. Attractive features of FAD in studies on the structure of surfaces comprise negligible radiation damage, no charging effects, and an extreme sensitivity to the topmost layer of surface atoms. Scanning the quantum wavelength associated with the motion of a massive particle by the variation of its kinetic energy allows one to apply interferometic concepts to surface analysis based on the scattering of fast atoms.
We have studied structures of the chiral amino acid alanine adsorbed on Cu(110) via low energy electron diffraction (LEED) as well as scattering of fast light atoms and molecules. The adsorption process was controlled in-situ by the intensity of specularly reflected 2keV He atoms. For projectile energies less than 1 keV we applied the method of fast atom diffraction (FAD) for studies on the structure of adsorbed alanine molecules on atomically flat Cu(110) surface with focus on a p(3 x 2) adsorbate phase. The results are consistent with LEED and explain distortions in LEED patterns via an elongated surface unit cell with incommensurate c(3.16 x 2) symmetry of parts of the adsorbate. From triangulation using fast atoms via the azimuthal rotation of the target surface, the positions of sticking out methyl groups are derived.
We have scattered He+ and Ar+ ions with energies of 10 and 20 keV from solid surfaces and investigated by means of a quadrupole mass spectrometer the emission of secondary ions. Compared to the established method of secondary ion mass spectroscopy (SIMS), the impact of ions proceeds under a grazing angle of incidence of about 2°. In experiments with a Cu(100) target covered with an ultrathin Fe3O4 film as well as ZnO and ZnMgO surfaces we have explored some basic features of this variant of SIMS concerning the potential application as surface analytical tool.
Fast H, He atoms, and H2 molecules with projectile energies ranging from 200 eV up to 3 keV were scattered under a grazing angle of incidence from a clean and flat "β-Ga2O3(100) surface. The bulk single crystal was grown by the Czochralski method and prepared via annealing under ultra-high vacuum conditions. For scattering along low-index directions, we observed defined diffraction patterns in the angular distributions for scattered projectiles. From the analysis of diffraction patterns, we derive the surface unit cell in good accord with the parameters b and c for the lattice of the bulk crystal and derive information on the termination of the surface.
A few years ago, quantum effects were observed for the scattering of fast atoms from surfaces under a grazing angle of incidence. We discuss basic features of Fast Atom Diffraction (FAD) which adds a further powerful method to the established tools in ion beam analysis and surface science. Attractive features of FAD in studies on the structure of surfaces comprise negligible radiation damage, cost effective operation of the complete setup, no charging effects in studies with insulators, and an extreme sensitivity to the topmost layer of surface atoms. The observation of diffraction patterns is based on the quantum coherence which is preserved during the scattering process with the target surface. We will discuss basic features of the coherence phenomena and its role for the observation of quantum effects in the angular distributions for grazingly scattered atoms. In a comparison of data obtained for H and He atoms we demonstrate that two different mechanisms for decoherence are important.
In a recent paper [A. J. Window et al., Phys. Rev. Lett. 107, 016105 (2011)], it was proposed that V2O3(0001) is terminated by the so-called O3 termination, a reconstruction with a terminating distorted hexagonal oxygen layer. We show that the surface is terminated by vanadyl (V=O) groups instead. This conclusion is based on quantitative low-energy electron diffraction combined with scanning tunneling microscopy, fast atom scattering, and density functional theory employing the Heyd-Scuseria-Ernzerhof functional. New insights into the subsurface sensitivity of ion beam triangulation show that results previously interpreted in favor of the O3 termination are reconcilable with vanadyl termination as well.