Effect of Ni substitution on the antiferromagnetic domains of cobalt oxide.

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.

On-surface synthesis of heptacene on Ag(001) from brominated and non-brominated tetrahydroheptacene precursors.

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.

Switching from Reactant to Substrate Engineering in the Selective Synthesis of Graphene Nanoribbons.

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 through self-assembly processes. The synthetic options for GNR generation would multiply by adding a new direction to this readily successful approach, especially if both of them can be combined. We show here how GNR synthesis can be guided by an adequately nanotemplated substrate instead of by the traditionally designed reactants. The structural atomic precision, unachievable to date through top-down methods, is preserved by the self-assembly process. This new strategy's proof-of-concept compares experiments using 4,4''-dibromo-para-terphenyl as a molecular precursor on flat Au(111) and stepped Au(322) substrates. As opposed to the former, the periodic steps of the latter drive the selective synthesis of 6 atom-wide armchair GNRs, whose electronic properties have been further characterized in detail by scanning tunneling spectroscopy, angle resolved photoemission, and density functional theory calculations.

Channeling motion of gold nanospheres on a rippled glassed surface.

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.

Molecular resolution friction microscopy of Cu phthalocyanine thin films on dolomite (104) in water.

The reliability of ultrathin organic layers as active components for molecular electronic devices depends ultimately on an accurate characterization of the layer morphology and ability to withstand mechanical stresses on the nanoscale. To this end, since the molecular layers need to be electrically decoupled using thick insulating substrates, the use of AFM becomes mandatory. Here, we show how friction force microscopy (FFM) in water allows us to identify the orientation of copper(ii)phthalocyanine (CuPc) molecules previously self-assembled on a dolomite (104) mineral surface in ultra-high vacuum. The molecular features observed in the friction images show that the CuPc molecules are stacked in parallel rows with no preferential orientation with respect to the dolomite lattice, while the stacking features resemble well the single CuPc crystal structure. This proves that the substrate induction is low and makes friction force microscopy in water a suitable alternative to more demanding dynamic AFM techniques in ultra-high vacuum.

Spinning and translational motion of Sb nanoislands manipulated on MoS2.

Antimony nanoislands grown on a MoS2 surface in ultra-high vacuum have been manipulated by atomic force microscopy (AFM) in ambient conditions. The island profiles have been digitized and provided as an input to a collisional algorithm based on classical mechanics. Assuming that the islands are rigid and static friction is high enough to prevent further motion after the passage of the probing tip, the direction of motion and the angle of rotation of the islands have been reproduced numerically. For a given spacing between the scan lines, the angle of deflection with respect to the fast scan direction and the angular speed of the islands are expected to vary with the friction between islands and substrate. From a comparison between model and experiment a shear strength in the order of 0.2 MPa is estimated.