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We present a spatially resolved X-ray magnetic linear dichroism study of high quality micron-sized mixed nickel-cobalt oxide (NCO) crystals. NixCo1-xO was prepared in-situ by high-temperature oxygen-assisted molecular beam epitaxy on a Ru(0001) single crystal substrate. To check the effect of incorporating Ni into the cobalt oxide films, three different compositions were prepared. The element-specific XMLD measurements reveal strong antiferromagnetic contrast at room temperature and magnetic domains up to one micron in size, reflecting the high structural quality of the NCO islands. By means of vectorial magnetometry, the antiferromagnetic spin axis orientation of the domains was determined with nanometer spatial resolution, and found to depend on the stoichiometry of the prepared crystals.

Steps at metal surfaces are chemically active sites, and hence they have an enormous influence on catalytic reactions. However, their higher catalytic activity does not necessarily imply improving the efficiency in more complex reactions, such as Ullmann coupling. Here, by investigating the interplay of step and terrace sites in the polymerization of 4,4″-dibromo-para-terphenyl molecules on Au to form poly-p-phenylene (PPP), we demonstrate that the restriction in molecular diffusion imposed by steps makes polymerization difficult. Combining a battery of surface-sensitive techniques, we have monitored the entire Ullmann polymerization process across different crystal planes by using a crystal surface macroscopically curved around the (111) plane. With this approach, it is possible to smoothly tune the step type and density across the sample, while keeping all reaction parameters identical, to prove that despite the significant reduction of debromination temperature near atomic steps, there is a delay in the formation of long PPP chains at densely stepped planes. Thus, we disentangle the different reaction steps and determine how to speed up and optimize the entire process through a proper choice of the vicinal orientation of the substrate.

The challenge of synthesizing graphene nanoribbons (GNRs) with atomic precision is currently being pursued along a one-way road, based on the synthesis of adequate molecular precursors that react in predefined ways and form GNRs through self-assembly processes. Adding a new direction to this readily successful approach, the synthetic options for GNRs are expected to multiply, especially if both approaches can be combined. We show here how, still based on self-assembly to maintain the atomic precision not yet achievable with top-down methods, selectivity in the GNR synthesis can be guided, instead of by designed reactants, by an adequately nanotemplated substrate. This new strategy´s proof-of-concept compares experiments using 4,4´´-dibromo-para-terphenyl as molecular precursor on flat Au(111) and stepped Au(322) substrates. On Au(111), the reactant first polymerizes into poly-para-phenylene (PPP) at moderate temperatures below 200 ºC. Annealing to higher temperatures drives the lateral fusion of PPP chains through cyclo-dehydrogenation, ending up with graphene nanoribbons of varying width depending on the number of polymers involved. The resulting samples are thus interesting to study width-dependent properties and phenomena in GNRs. We have used such samples to characterize the width-dependent band gap of GNRs and, most importantly, the associated evolution of the energy level alignment of frontier bands. Doing so, a Fermi level pinning scenario of the valence band has been found for GNRs displaying band gaps below ~1.7 eV.[1] However, from the synthetic point of view, selectivity towards particular GNRs is completely missing. A completely different scenario is found on Au(322). The polymerization and cyclodehydrogenation reactions occur in a similar way. However, the periodic steps of Au(322) limits the number of fusing polymers to two, resulting in the selective synthesis of 6 atomwide armchair GNRs (6-aGNRs). In addition, all GNRs being uniaxially aligned along

Achieving the Ag(001)-supported synthesis of heptacene from two related reactants reveals the effect of the presence of Br atoms on the reaction process. The properties of reactants, intermediates and end-products are further characterized by scanning tunneling microscopy and spectroscopy.

When the shear stress on a compliant surface exceeds the yield strength of the material, a periodic wrinkle pattern is often observed. This phenomenon has been also recognized at the nanometer scale on polymers, metals, ionic crystals and semiconductors. In those cases, the mechanical stress can be efficiently provided by a sharp indenter elastically driven at constant velocity along the surface. Here we suggest that the formation of such surface ripples can be explained by the competition between the driving spring force and the plastic response of the substrate. In particular, we show how the ripples are expected to disappear when the indentation rate is below a critical value or, alternatively, when the sliding velocity or the lateral stiffness of the contact are too high. The model results are compared to atomic force microscopy experiments on a solvent-enriched polystyrene surface, where the rippling formation is enhanced at room temperature, compared to bulk melts. A similar approach could be employed to describe rippling phenomena on larger scales., SCOPUS: ar.j, info:eu-repo/semantics/published

Gold nanospheres have been manipulated by atomic force microscopy on a rippled glass surface produced by ion beam sputtering and coated with an ultrathin (10 nm thick) graphitic layer. This substrate is characterized by irregular wavy grooves running parallel to a preferential direction. Measurements in ambient conditions show that the motion of the nanoparticles is confined to single grooves ('channels'), along which the particles move till they are trapped by local bottlenecks. At this point, the particles cross the ripple pattern in a series of consecutive jumps and continue their longitudinal motion along a different channel. Moreover, due to the asymmetric shape of the ripple profiles, the jumps occur in the direction of minimum slope, resembling a ratchet mechanism. Our results are discussed, extending a collisional model, which was recently developed for the manipulation of nanospheres on flat surfaces, to the specific geometry of this problem.