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Among all transition metals, Palladium (Pd) has the highest density of states at the Fermi energy yet does not fulfill the Stoner criterion for ferromagnetism. However, its close vicinity to magnetism renders it a nearly ferromagnetic metal, which hosts paramagnons, strongly damped spin fluctuations. In this letter we compare the total and the differential conductance of mono-atomic Pd and Cobalt (Co) contacts between Pd electrodes. Transport measurements reveal a conductance for Co of 1 $G_0$ , while for Pd we obtain 2 $G_0$. The differential conductance of mono-atomic Pd contacts shows a drop with increasing bias, which gives rise to a peculiar {$\Lambda$}-shaped spectrum. Supported by theoretical calculations we correlate this finding with the life time of hot quasi-particles in Pd which is strongly influenced by paramagnon scattering. In contrast to this, Co adatoms locally induce magnetic order and transport through single cobalt atoms remains unaffected by paramagnon scattering, consistent with theory., Comment: 5 pages, 4 figures

Interfacial properties of organic adsorbates featuring aromatic π‐orbitals on metal surfaces play an important role for organic electronics and spintronics. Pyrene is a flat aromatic molecule with a size between ultimately small benzene and extended graphene segments. The deposition of pyrene molecules onto clean and reactive surfaces with a sub‐monolayer coverage under ultra‐high vacuum (UHV) conditions is challenging, since pyrene is a solid with a high vapor pressure. Here, a sublimation procedure under UHV and image pyrene adlayers on in situ prepared Au(111) and Fe/W(110) substrates by means of low‐temperature scanning tunneling microscopy is presented. For Au(111), the molecule–surface interaction is weak as indicated by the specific herringbone reconstruction of the Au(111) surface that is visible through the self‐assembled pyrene adlayer. Pyrene desorption due to weak intermolecular interaction self‐limits the growth to one monolayer (ML). On the more reactive 2–4 ML thick Fe films on W(110), the molecular order of the pyrene adlayer sensitively depends on the Fe thickness‐dependent dislocation pattern at the substrate surface. Irregular arrangements occur for 1 ML Fe and near substrate dislocations for 2–4 ML Fe. Self‐assembled ordered arrays form predominantly for 2 ML Fe, where the dislocation pattern leaves sufficiently large unperturbed areas between the dislocation lines.

Nonlocal addressing—the “remote control”—of molecular switches promises more efficient processing for information technology, where fast speed of switching is essential. The surface state of the (111) facets of noble metals, a confined two-dimensional electron gas, provides a medium that enables transport of signals over large distances and hence can be used to address an entire ensemble of molecules simultaneously with a single stimulus. In this study we employ this characteristic to trigger a conformational switch in anthradithiophene (ADT) molecules by injection of hot carriers from a scanning tunneling microscope (STM) tip into the surface state of Cu(111). The carriers propagate laterally and trigger the switch in molecules at distances as far as 100 nm from the tip location. The switching process is shown to be long-ranged, fully reversible, and isomer selective, discriminating between cis and trans diastereomers, enabling maximum control. Postprint

Single molecular switches are basic device elements in organic electronics. The pentacene analogue anthradithiophene (ADT) shows a fully reversible binary switching between different adsorption conformations on a metallic surface accompanied by a charge transfer. These transitions are activated locally in single molecules in a low-temperature scanning tunneling microscope . The switching induces changes between bistable orbital structures and energy level alignment at the interface. The most stable geometry, the “off” state, which all molecules adopt upon evaporation, corresponds to a short adsorption distance at which the electronic interactions of the acene rings bend the central part of the molecule toward the surface accompanied by a significant charge transfer from the metallic surface to the ADT molecules. This leads to a shift of the lowest unoccupied molecular orbital down to the Fermi level (EF). In the “on” state the molecule has a flat geometry at a larger distance from the surface; consequently the interaction is weaker, resulting in a negligible charge transfer with an orbital structure resembling the highest occupied molecular orbital when imaged close to EF. The potential barrier between these two states can be overcome reversibly by injecting charge carriers locally into individual molecules. Voltage-controlled current traces show a hysteresis characteristic of a bipolar switching behavior. The interpretation is supported by first-principles calculations., We acknowledge funding by the EmmyNoether-Program of the Deutsche Forschungsgemeinschaft, the SFB 767, and the Baden-Württemberg Stiftung. R.P. and A.A. thank the Basque Departamento de Universidades e Investigacion (grant no. IT-756-13) and the Spanish Ministerio de Economia y Competitividad (grant no. FIS2013-48286-C2-8752-P) for financial support.

We report here on the molecular self-assembly of 7, 7', 8, 8' tetracyanoquinodimethane (TCNQ) (schematic representation of the molecule on figure 1(b)) on a single-crystal Cu(111) surface, followed by deposition of Fe and Mn, and on the formation of an ordered metal–organic coordination network of Fe (or Mn)–TCNQ units, which contains magnetic ions separated by 0.9 nm.

D. Stradi et al., Monolayer graphene grown on Ru(0001) surfaces forms a superstructure with periodic modulations in its geometry and electronic structure. The large dimension and inhomogeneous features of this superstructure make its description and subsequent analysis a challenge for theoretical modeling based on density functional theory. In this work, we compare two different approaches to describe the same physical properties of this surface, focusing on the geometry and the electronic states confined at the surface. In the more complex approach, the actual moiré structure is taken into account by means of large unit cells, whereas in the simplest one, the graphene moiré is completely neglected by representing the system as a stretched graphene layer that adapts pseudomorphically to Ru(0001). As shown in previous work, the more complex model provides an accurate description of the existing experimental observations. More interestingly, we show that the simplified stretched models, which are computationally inexpensive, reproduce qualitatively the main features of the surface electronic structure. They also provide a simple and comprehensive picture of the observed electronic structure, thus making them particularly useful for the analysis of these and maybe other complex interfaces. © 2013 American Physical Society., Work supported by the MICINN Projects No. FIS2010-15127, No. FIS2010-18847, No. CTQ2010-17006, No. FIS-2010-19609-C09-00, No. ACI2008-0777, No. 2010C-07-25200, and No. CSD2007-00010, the CAM program NANOBIOMAGNET S2009/MAT1726 and the Gobierno Vasco-UPV/EHU Project No. IT-366-07. S.B. acknowledges financial support from MEC under FPU Grant No. AP-2007-00157. D.S. acknowledges financial support from the FPI-UAM grant program.

The interpretation of scanning tunneling spectroscopy (STS) and scanning tunneling microscopy measurements of epitaxial graphene on lattice-mismatched substrates is a challenging problem, because of the spatial modulation in the electronic structure imposed by the formation of a moiré pattern. Here we describe the electronic structure of graphene adsorbed on Ru(0001) by means of density functional theory calculations that include van der Waals interactions and are performed on a large 11×11 unit cell to account for the observed moiré patterns. Our results show the existence of localized electronic states in the high and low areas of the moiré at energies close to and well above the Fermi level, respectively. Localization is due to the spatial modulation of the graphene-Ru(0001) interaction and is at the origin of the various peaks observed in STS spectra. © 2012 American Physical Society., Work supported by the MICINN Projects No. FIS2010-15127, No. FIS2010-18847, No. CTQ2010- 17006, No. FIS-2010-19609-C09-00, No. ACI2008-0777, No. 2010C-07-25200, and No. CSD2007-00010, the CAM program NANOBIOMAGNET S2009/MAT1726, and the Gobierno Vasco-UPV/EHU Project No. IT-366-07. S.B. acknowledges financial support from MEC under FPU Grant No. AP-2007-00157.

4 páginas, 3 figuras.-- PACS numbers: 73.22.Pr, 68.37.Ef, 68.55.-a, 71.15.Mb.-- et al., Elaborate density functional theory (DFT) calculations that include the effect of van der Waals (vdW) interactions have been carried out for graphene epitaxially grown on Ru(0001). The calculations predict a reduction of structural corrugation in the observed moiré pattern of about 25% (∼0.4 Å) with respect to DFT calculations without vdW corrections. The simulated STM topographies are close to the experimental ones in a wide range of bias voltage around the Fermi level., Work supported by the MICINN projects FIS2010-15127, FIS2010-18847, CTQ2010-17006, FIS2010-19609-C02-00, ACI2008-0777, 2010C-07- 25200, and CSD2007-00010, the CAM program NANOBIOMAGNET S2009/MAT1726, and the Gobierno Vasco—UPV/EHU project IT-366-07.

4 páginas, 4 figuras.-- PACS numbers: 73.20.-r, 68.37.Ef, 68.55.-a, 73.22.Pr.-- et al., We explore the spatial variations of the unoccupied electronic states of graphene epitaxially grown on Ru(0001) and observed three unexpected features: the first graphene image state is split in energy; unlike all other image states, the split state does not follow the local work function modulation, and a new interfacial state at þ3 eV appears on some areas of the surface. First-principles calculations explain the observations and permit us to conclude that the system behaves as a self-organized periodic array of quantum dots., Financial support by the Spanish MICINN through project CONSOLIDER-INGENIO 2010 on Molecular Nanoscience and Grants No. FIS2007-61114 and No. FIS2007-6671, Comunidad de Madrid through the program NANOBIOMAGNET S-2009/MAT1726, the Basque Government (Grant No. IT-366-07 and inanoGUNE projects) is gratefully acknowledged., S-2009/MAT-1726/Nanobiomagnet

International audience; We report a detailed magnetic study of a new type of self-organized nanowires disclosed briefly previously [B. Borca et al., Appl. Phys. Lett. 90, 142507 (2007)]. The templates, prepared on sapphire wafers in a kinetically-limited regime, consist of uniaxially-grooved W(110) surfaces, with a lateral period here tuned to 15nm. Fe deposition leads to the formation of (110) 7 nm-wide wires located at the bottom of the grooves. The effect of capping layers (Mo, Pd, Au, Al) and underlayers (Mo, W) on the magnetic anisotropy of the wires was studied. Significant discrepancies with figures known for thin flat films are evidenced and discussed in terms of step anisotropy and strain-dependent surface anisotropy. Demagnetizing coeffcients of cylinders with a triangular isosceles cross-section have also been calculated, to estimate the contribution of dipolar anisotropy. Finally, the dependence of magnetic anisotropy with the interface element was used to tune the blocking temperature of the wires, here from 50K to 200 K.

The Comment by B. Wang et al. [1] states that according to their ab initio calculation, the periodically rippled graphene monolayer epitaxially grown on Ru(0001), whose spatially resolved electronic structure we unravelled recently [2], presents a large (0.15–0.17 nm) geometrical corrugation. They further state that this contradicts our structural model of a flat, van der Waals-bonded graphene layer [2]. We never mention in our Letter [2] that the actual graphene monolayer on Ru(0001) was geometrically flat, nor that the Ru-C interaction was van derWaals-like. Quite on the contrary, a geometrical corrugation is expected to occur, as it happens with incommensurate overlayers on almost all surfaces [3], but we highlighted the additional electronic contribution to the corrugation. In order to show that any periodic potential applied to the graphene layer will result in periodic charge inhomogeneities, as revealed by local tunnelling spectroscopy, we described in [2] a very simple model calculation, in which a flat, isolated graphene monolayer under the influence of an adjustable 2D periodic potential showed the appearance of electron and hole pockets, as detected in the Scanning Tunneling Spectroscopy experiment. We never claimed that this flat isolated graphene monolayer reflected the actual geometry of the graphene or Ru(0001) case. The fact that our simple tight binding calculation shows both the appearance of superlattice effects and the spatial separation of occupied and empty states in agreement with experiment indicates that the effect is robust and of quite general nature [4]. In effect, the periodic potential could be applied to the graphene monolayer by different physical means: a periodic variation of the interaction potential with the substrate caused by modulation of the perpendicular C-Ru distances, an external voltage applied with nanofabricated gates, or the ordered adsorption of donor or acceptor molecules. We, thus, maintain that in addition to a certain degree of geometric modulation of the perpendicular C-Ru distances unavoidable by geometrical constraints, there is a spatially modulated charge redistribution, detectable by STS. This is not only directly seen in the spatially resolved STS maps, but it is also reflected in the voltage dependence of the apparent corrugation of the ripples, briefly mentioned in Ref. [2] and shown in more detail in Fig. 1. The corrugation of the ripples in graphene on Ru(0001) changes from 0.11 nm at-0:8 V to 0.05 nm at þ0:8 V. The corrugation is larger when sampling the occupied electronic states because of the charge accumulation in the upper part of the ripples. It becomes smaller when sampling the empty density of states, since the empty states accumulated at the lower part of the ripples, as shown also in Fig. 3 of Ref. [2]. Notice that the geometrical corrugation calculated by Wang et al. [1] (0.15–0.17 nm) is substantially larger than the largest experimental value (0.11 nm). This, together with the fact that the calculated spatially resolved DOS, which correctly predicts the asymmetry between occupied and empty states, does, however, predict the existence of peaks in the DOS not in agreement with our STS data [2], indicates that the calculation reported in [1] is not quantitatively consistent with some of our observations and calls for a precise experimental determination of the extent of the geometrical buckling in the system. Fil: Lopez Vazquez de Parga, A.. Universidad Autónoma de Madrid; España Fil: Calleja, F.. Universidad Autónoma de Madrid; España Fil: Borca, B.. Universidad Autónoma de Madrid; España Fil: Passeggi, Mario Cesar Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Hinarejos, J.. Universidad Autónoma de Madrid; España Fil: Guinea, F.. Instituto de Ciencia de Materials; España Fil: Miranda, R.. Universidad Autónoma de Madrid; España

We have revisited the epitaxial growth modes of Fe on W(110) and Mo(110), and propose an overview or our contribution to the field. We show that the Stranski-Krastanov growth mode, recognized for a long time in these systems, is in fact characterized by a bimodal distribution of islands for growth temperature in the range 250-700°C. We observe firstly compact islands whose shape is determined by Wulff-Kaischev's theorem, secondly thin and flat islands that display a preferred height, ie independant from nominal thickness and deposition procedure (1.4nm for Mo, and 5.5nm for W on the average). We used this effect to fabricate self-organized arrays of nanometers-thick stripes by step decoration. Self-assembled nano-ties are also obtained for nucleation of the flat islands on Mo at fairly high temperature, ie 800°C. Finally, using interfacial layers and solid solutions we separate two effects on the preferred height, first that of the interfacial energy, second that of the continuously-varying lattice parameter of the growth surface., Comment: 49 pages. Invited topical review for J. Phys.: Condens. Matter

We have self-organized versatile magnetic nanowires, ie with variable period and adjustable magnetic anisotropy energy (MAE). First, using the kinetic roughening of W(110) uniaxial templates of trenches were grown on commercial Sapphire wafers. Unlike most templates used for self-organization, those have a variable period, 4-12nm are demonstrated here. Fe deposition then results in the formation of wires in the trenches. The magnitude of MAE could be engineered up or down by changing the capping- or underlayer, in turn affecting the mean superparamagnetic temperature, raised to 175K so far., 3 pages

We studied the growth of an epitaxial graphene monolayer on Ru(0001). The graphene monolayer covers uniformly the Ru substrate over lateral distances larger than several microns reproducing the structural defects of the Ru substrate. The graphene is rippled with a periodicity dictated by the difference in lattice parameter between C and Ru. The theoretical model predict inhomogeneities in the electronic structure. This is confirmed by measurements in real space by means of scanning tunnelling spectroscopy. We observe electron pockets at the higher parts of the ripples., Comment: 5 pages

We report the fabrication of self-organized arrays of Fe nanostripes with a period of 3.5 nm, by sequential deposition of Fe and Ag on Mo(110). The wires display a strong in-plane uniaxial anisotropy along their length, and are superparamagnetic above Tb=185+/-15K. The large value of nucleation volumes, inferred from the analysis of the thermal dependence of coercivity below TB, suggests the existence of interactions between the wires., 3 pages journal-style Proceedings of MMM05

Among the prerequisites for the progress of single‐molecule‐based electronic devices are a better understanding of the electronic properties at the individual molecular level and the development of methods to tune the charge transport through molecular junctions. Scanning tunneling microscopy (STM) is an ideal tool not only for the characterization, but also for the manipulation of single atoms and molecules on surfaces. The conductance through a single molecule can be measured by contacting the molecule with atomic precision and forming a molecular bridge between the metallic STM tip electrode and the metallic surface electrode. The parameters affecting the conductance are mainly related to their electronic structure and to the coupling to the metallic electrodes. Here, the experimental and theoretical analyses are focused on single tetracenothiophene molecules and demonstrate that an in situ‐induced direct desulfurization reaction of the thiophene moiety strongly improves the molecular anchoring by forming covalent bonds between molecular carbon and copper surface atoms. This bond formation leads to an increase of the conductance by about 50 % compared to the initial state., The authors acknowledge the Emmy‐Noether‐Program of the Deutsche Forschungsgemeinschaft, the SFB 767, Core Program PN19‐03 (contract number 21 N/08.02.2019) founded by the Romanian Ministry of Research and Innovation, Basque Departamento de Universidades e Investigación (grant no. IT‐756‐13), the Spanish Ministerio de Economía y Competitividad (grant no. FIS2013‐48286‐C2‐8752‐P and FIS2016‐75862‐P) and the Operational Programme Research, Development and Education financed by European Structural and Investment Funds and the Czech Ministry of Education, Youth and Sports (Project No. SOLID21 CZ.02.1.01/0.0/0.0/16_019/0000760). P.M. and P.J. acknowledge access to computing and storage facilities owned by parties and projects contributing to the Czech National Grid Infrastructure MetaCentrum provided under the programme “Projects of Large Research, Development, and Innovations Infrastructures” (CESNET LM2015042). P.J. acknowledges support from Praemium Academie of the Academy of Science of the Czech Republic and MEYS LM2015087.