RESUMO
We report on in situ electromigration and potentiometry measurements on single-crystalline Ag nanowires under ultra-high vacuum (UHV) conditions, using a four-probe scanning tunnelling microscope (STM). The Ag nanowires are grown in place by self-organization on a 4° vicinal Si(001) surface. Two of the four available STM tips are used to contact the nanowire. The positioning of the tips is controlled by a scanning electron microscope (SEM). Potentiometry measurements on an Ag nanowire were carried out using a third tip to determine the resistance per length. During electromigration measurements current densities of up to 1 × 10(8) A cm(-2) could be achieved. We use artificially created notches in the wire to initiate electromigration and to control the location of the electromigration process. At the position of the notch, electromigration sets in and is observed quasi-continuously by the SEM.
RESUMO
By means of our novel self-learning kinetic Monte Carlo model (Latz et al 2012 J. Phys.: Condens. Matter 24 485005) we study the electromigration-induced drift of monolayer voids and islands on unpassivated surfaces of single crystalline Ag(111) and Ag(001) films at the atomic scale. Regarding the drift velocity, we find a non-monotonic size dependence for small voids. The drift direction is aligned with the electromigration force only along high symmetry directions, while halfway between, the angle enclosed by them is maximal. The magnitude of these directional deviations strongly depends on the system parameter, which are investigated in detail. The simulation results are in accordance with void motion observed in experiments performed on Ag(111).
RESUMO
Test structures for electromigration with defined grain boundary configurations can be fabricated using focused ion beam (FIB). We present a novel approach of combining epitaxial growth of Ag islands with FIB milling. Depending on the growth parameters, bi-crystalline Ag islands can be grown on Si(111) surfaces and can be structured into wires by FIB. To avoid doping effects of the used Ga FIB, silicon on insulator (SOI) substrates are used. By cutting through the device layer of the SOI substrate with deep trenches, the Ag wire can be electrically separated from the rest of the substrate. In this way, Ag wires with one isolated grain boundary of arbitrary direction can be assembled. Using scanning electron microscopy we demonstrate the feasibility of our approach.
RESUMO
The periodic shell structure and surface reconstruction of metallic FePt nanoparticles with icosahedral structure has been quantitatively studied by high-resolution transmission electron microscopy with focal series reconstruction with sub-angstrom resolution. The icosahedral FePt nanoparticles fabricated by the gas phase condensation technique in vacuum have been found to be surprisingly oxidation resistant and stable under electron beam irradiation. We find the lattice spacing of (111) planes in the surface region to be size dependent and to expand by as much as 9% with respect to the bulk value of Fe52Pt48. Controlled removal of the (111) surface layers in situ results in a similar outward relaxation of the new surface layer. This unusually large layerwise outward relaxation is discussed in terms of preferential Pt segregation to the surface forming a Pt enriched shell around a Fe-rich Fe/Pt core.
RESUMO
Single (Co/Pt)_{7} multilayer nanowires prepared by electron beam lithography with perpendicular magnetic anisotropy are locally modified by means of Ga-ion implantation generating 180 degrees domain walls which are pinned at the edges of underlying thin Pt wires. Since we can exclude contributions from the anisotropic and the Lorentz magnetoresistance this allows us to determine the resistance of a single domain wall at room temperature. We find a positive relative resistance increase of DeltaR/R=1.8% inside the domain wall which agrees well with the model of Levy and Zhang [Phys. Rev. Lett. 79, 5110 (1997)10.1103/PhysRevLett.79.5110].