The growth of ultrathin tetragonal CuO films by pulsed laser deposition was reported several years ago. In this work, we demonstrate that the same phase can be synthesized using oxygen-plasma–assisted molecular beam epitaxy. We show that it remains stable up to a thickness of 6 nm, significantly exceeding the thickness range previously achieved by PLD.Using x-ray diffraction, we resolve its crystal structure and confirm that it consists of a tetragonally distorted rock-salt phase in coherent epitaxy on SrTiO3(001), as initially hypothesized. We precisely determine the tetragonal distortion, obtaining a c/a ratio of 1.342(2) for a 3 nm thick film. Using resonant x-ray diffraction, we also demostrate that Co can partially replace Cu without altering the crystal structure. The structural stability of this novel CuO phase upon doping is a key asset for potential future applications in both magnetism and superconductivity.

Graphene nanostructures can be engineered with atomic precision to display customized electronic states with application in spintronics or quantum technologies. In order to take advantage of their full potential, their charge and spin state must be precisely controlled. Graphene systems exchange charge to reach thermodynamic equilibrium with their environment, requiring external gating potentials to tune their ground state. Alternative strategies like intrinsic doping or substrate modifications provided small variations of their equilibrium charge and poor control over their spin. Here, we show systematic manipulation of the electron occupation in graphene nanoribbons (GNRs) laying on MgO layers grown on Ag(001). Owing to the extraordinary decoupling properties of MgO, and the electropositive character of the substrate, GNRs are found to host an integer number of electron charges that depend on their length and shape. This results in the alternation between a non-magnetic closed-shell state and an open-shell paramagnetic system for even and odd electron occupations respectively. For the odd case, we found the spectral fingerprint of a narrow Coulomb correlation gap, which is the smoking gun of its spin 1/2 paramagnetic state. Comparisons of scanning tunnelling microscopy (STM) data with mean-field Hubbard (MFH) simulations confirm the practical discretization of the GNR electronic states and point to charge excess of up to 19 electrons in a single ribbon. We anticipate that GNRs supported by MgO ultra-thin insulating films can open the door to customized devices for quantum sensing and quantum processing applications..

We have grown CuO in epitaxy on SrTiO3(001) following a two steps method. Cu is first deposited in situ in an ultra-high vacuum chamber, then CuO tenorite phase is obtained by oxidation thanks to ex situ annealing in molecular oxygen. This is simpler to implement than processes employed previously at this purpose, which required monoatomic oxygen during deposition. CuO islands grown in this way are oriented with the b axis perpendicular to the surface. This is also the direction of ferroelectric polarization in the bulk multiferroic phase, making them attractive for applications. An epitaxy induced distortion of the monoclinic β angle, which is a key parameter in determining the magnetic properties, is also observed.

Evolution of c-lat strain (blue), cell volume (black) and island size (red) with T. c-lat evolves from compressive to tensile strain with T (black arrow down or red arrow up). (a,b)-lattice parameters are under compression (parallel arrows). The cell volume is compressed in the experimental range of T.

The epitaxial growth of anatase (001) films deposited by pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) on SrTiO3 (001) (STO) single crystals has been studied using X-ray diffraction and surface sensitivity UHV techniques. The evolution of the strain represented by the microstrain and the change of the in-plane and out-of-plane lattice parameters with film growth temperature, the effect of the annealing temperature and the influence of the oxygen content of the film have been investigated. The out-of-plane lattice strain shows a compressive (-0.2 %) or expansive (+0.3 %) behavior, in the range 600-900 degrees C, for temperatures below or above 700 degrees C, respectively. The in-plane lattice parameters, as well as the cell volume of the film, remain under compression over the entire temperature range explored. PLD films grow into square islands that align with the surface lattice directions of the STO substrate. The maximum size of these islands is reached at growth temperatures close to 875-925 degrees C. Film annealing at temperatures of 800 degrees C or higher melts the islands into flat terraces. Larger terraces are reached at high annealing temperatures of 925 degrees C for extended periods of 12 h. This procedure allows flat surface terrace sizes of up to 650 nm to be achieved. The crystalline quality achieved in anatase films prepared by PLD or MBE growth methods is similar. The two-step anatase growth process used during the synthesis of the films with both methods: film growth and post-annealing treatment in oxygen or air at ambient pressure, using temperature and time as key pa-rameters, allows to control the surface terrace size and stoichiometry of the films, as well as the anatase/rutile intermixing rates at sufficiently high temperatures. This growth process could allow the substitution of their equivalent single crystals. The range of applicability of these films would include their use as structural and electronic model systems, or in harsh experimental conditions due to their low production cost.

Orientation, structure and morphology in the early growth stages of CuO films on strontium titanate were studied by synchrotron radiation X-ray diffraction. Nanostructured CuO films were obtained by ex situ heat treatment at 970 K in oxygen flow at ambient pressure after an initial deposition of Cu on SrTiO3(001) at 10(-4) Pa oxygen pressure using the molecular beam epitaxy technique. These films at low coverages grow forming islands a few tens of nanometers wide, with the [010] direction perpendicular to the substrate surface. Two types of epitaxies are observed, CuO[001]//SrTiO3[100] and CuO[100]//SrTiO3[100], the former being the preferred one. The combination of these epitaxies with the P4mm surface symmetry of the substrate generates 16 different orientations of nanostructures. The lattice constant values obtained from X-ray diffraction are very close to those of bulk tenorite, with the exception of the monoclinic angle beta, which is reduced from 99.54 degrees to 96.76(8)degrees by the epitaxy constraints. This angle is a key parameter in determining the magnetic properties of CuO.

The synthesis of novel organic prototypes combining different functionalities is key to achieve operational elements for applications in organic electronics. Here we set the stage towards individually addressable magneto-optical transducers by the on-surface synthesis of optically active manganese-phthalocyanine derivatives (MnPc) obtained directly on a metallic substrate. We created these 2D nanostructures under ultra-high vacuum conditions with atomic precision starting from a simple phthalonitrile precursor with reversible photo-induced reactivity in solution. These precursors maintain their integrity after powder sublimation and coordinate with the Mn ions into tetrameric complexes and then transform into MnPcs on Ag(111) after a cyclotetramerization reaction. Using scanning tunnelling microscopy and spectroscopy together with DFT calculations, we identify the isomeric configuration of two bi-stable structures and show that it is possible to switch them reversibly by mechanical manipulation. Moreover, the robust magnetic moment brought by the central Mn ion provides a feasible pathway towards magneto-optical transducer fabrication. This work should trigger further research confirming such magneto-optical effects in MnPcs both on surfaces and in liquid environments.

MgO ultrathin films are of great technological importance as electron tunneling barrier in electronics and spintronics, and as template for metallic clusters in catalysis and for molecular networks for 2D electronics. The wide band-gap of MgO allows for a very effective decoupling from the substrate. The films morphology and the detailed structure of the interface are crucial for applications, controlling the electronic transfer. Using surface x-ray diffraction, we studied the growth-mode and the structure of MgO/Ag(001) ultrathin films elaborated by reactive molecular beam epitaxy as function of the substrate temperature. We observed that deposition of about 1 monolayer results in an MgO(001) film in coherent epitaxy, with the oxygen atoms on top of silver as predicted by DFT calculations, and an interlayer distance at the interface of about 270 pm. Under well-defined conditions, a sharp MgO bilayer is formed covering a fraction of the substrate surface.

Two-dimensional molecular assemblies on surfaces have opened a way to design and control chirality, featuring promising electronic and chemical properties that depend on the local handedness of the layer. Yet, the mechanisms leading to spontaneous chiral resolution are not fully understood at every reaction stage. Here, starting from achiral 10-bromoanthracene-9-boronic acid as a molecular precursor, we demonstrate enantiomeric induction in products during the stage of covalent bonding, stemming from the competing point symmetries of the Ag(001)-supporting surface and the reaction products. Upon dehalogenation and dehydration of precursors, hexagonal boroxine rings linked by organometallic anthracene dimers are formed, which undergo a strong interaction with a fourfold symmetric substrate. The prochiral structural character of the resulting oligomer and its impact over the spatial distribution of the electronic molecular states are revealed by high-resolution scanning tunneling microscopy and spectroscopy.

A detailed study of poly-para-phenylene (PPP) obtained by light-assisted on-surface-synthesis (OSS) on Ag(100) was carried out by scanning tunneling microscopy and spectroscopy together with density functional theory calculations. The use of light in combination with heat allows to lower by 50 K annealing temperature the each stage of the Ullmann coupling. Debromination of the 4,4 '' dibromo-p-terphenyl precursors was thus realized at 300 K, the formation of the first oligomers from the organometallic intermediate by silver bridging atom release at 423 K and PPP by complete elimination of the silver at 473 K. This approach to lower the reaction temperature permits to enhance the Ag(100) surface reactivity to become comparable to that of Cu(111). The underlying mechanism of light effect was proposed to occur via surface mediated excitation, with the creation of photoexcited electrons known as hot electrons correlated with surface plasmon excitation. This original pathway combining both light and heat provides an additional parameter to control OSS by separating the precursor activation stage from the diffusion.

Cobalt ferrite ultrathin films with the inverse spinel structure are among the best candidates for spin filtering at room temperature. High-quality epitaxial CoFe2O4 films about 4 nm thick have been fabricated on Ag(001) following a three-step method: an ultrathin metallic CoFe2 alloy was first grown in coherent epitaxy on the substrate and then treated twice with O2, first at room temperature and then during annealing. The epitaxial orientation and the surface, interface and film structure were resolved using a combination of low-energy electron diffraction, scanning tunnelling microscopy, Auger electron spectroscopy and in situ grazing-incidence X-ray diffraction. A slight tetragonal distortion was observed, which should drive the easy magnetization axis in-plane due to the large magneto-elastic coupling of such a material. The so-called inversion parameter, i.e. the Co fraction occupying octahedral sites in the ferrite spinel structure, is a key element for its spin-dependent electronic gap. It was obtained through in situ resonant X-ray diffraction measurements collected at both the Co and Fe K edges. The data analysis was performed using FDMNES, an ab initio program already extensively used to simulate X-ray absorption spectroscopy, and shows that the Co ions are predominantly located on octahedral sites with an inversion parameter of 0.88 (5). Ex situ X-ray photoelectron spectroscopy gives an estimation in accordance with the values obtained through diffraction analysis.

Cobalt ferrite ultrathin films with inverse spinel structure are among the best candidates for spin-filtering at room temperature. We have fabricated high-quality epitaxial ultrathin CoFe2O4 layers on Ag(001) following a three-step method: an ultrathin metallic CoFe2 alloy was first grown in coherent epitaxy on the substrate, and then treated twice with O2, first at RT and then during annealing. The epitaxial orientation, the surface, interface and film structure were resolved combining LEED, STM, Auger and in situ GIXRD. A slight tetragonal distortion was observed, that should drive the easy magnetization axis in plane due to the large magneto-elastic coupling of such a material. The so-called inversion parameter, i.e. the Co fraction occupying octahedral sites in the ferrite spinel structure, is a key element for its spin-dependent electronic gap. It was obtained through in-situ x-ray resonant diffraction measurements collected at both the Co and Fe K edges. The data analysis was performed using the FDMNES code and showed that Co ions are predominantly located at octahedral sites with an inversion parameter of 0.88 +- 0.05. Ex-situ XPS gave an estimation in accordance with the values obtained through diffraction analysis.

The adsorption of the iron tetraphenylporphyrin (FeTPP) molecule in its deckchair conformation was investigated on Au(111), Ag(111) and Cu(111) surfaces by performing spin-polarized density functional theory (DFT) calculations taking into account both van der Waals (vdW) interaction and on-site Coulomb repulsion. The deckchair conformation of the molecule favours intermolecular π–π-type interactions in a less densely packed monolayer than the saddle conformation. The activation barrier between the two stable magnetic states (high spin, S = 2 and intermediate spin, S = 1) of the molecule in vacuum disappears upon adsorption on the metal surfaces. The high-spin state of physisorbed FeTPP is stable on all adsorption sites. This result reveals that an external permanent element such as a STM tip or an additional molecule is needed to use FeTPP or similar molecules as model system for molecular spin switches.

Epitaxial iron oxide layers with different orientations were grown on Ag(001) surface by choosing the appropriate preparation conditions. A film with a hexagonal surface mesh interpreted as (111)-oriented magnetite was formed by reactive deposition of iron in molecular oxygen at room temperature (RT), followed by annealing in UHV. Instead, highly ordered epitaxial layers with P4m symmetry were obtained by a three-step process, optimized through in situ experiments. Following this method, an ultrathin Fe layer was first grown in coherent epitaxy on the substrate and then dosed twice with O2, first at RT and next during annealing. A structural analysis combining low-energy electron diffraction, scanning tunneling microscopy, and accurate surface x-ray diffraction measurements confirmed that these films consist of (001)-oriented magnetite, although with a slight tetragonal distortion induced by the substrate constraints. Both its surface and interface are atomically sharp, an essential requirement for its integration into spintronic based devices.

The adsorption of single hexamethoxyltriphenylene molecules on KBr(001) at low temperature (T < 10 K) was studied by low-temperature (T = 5 K) noncontact atomic force microscopy in ultrahigh vacuum. Images of the frequency shift, Measured at constant height, show intramolecular features that are interpreted on the basis of molecular force-field calculations. The main conclusion is that the experimental contrast originates from the electrostatic interaction between a negatively terminated ionic tip and the atomic charges of the molecule. The main trends of the experimental observations of lateral manipulations could also be reproduced by the same method, giving some insight into the manipulation mechanisms. In particular, it is shown that the strong interaction of the oxygen atoms of the molecule with positive ions of the tip plays a major role by facilitating the partial lifting of the molecule from the substrate during the intermediate stages of these manipulation processes.

The facies associations of the overflow deposits associated with turbidite channels were studied in the outcrops of the Maastrichtian Pab Sandstone, in SW Pakistan. In this area, a basin-floor fan was preserved from the platform to the deep basin setting. In the mid-fan setting, a channel complex crops out in three dimensions, and consists of a dozen channels and their overflow deposits, including levees, crevasse lobes and spill-over lobes. The overbank deposits can be directly in contact with the channel-fill, but, in many cases, matrix-supported debris-flow deposits made lenses close to the channel base. Heterolithic drapes of thin-bedded turbidite deposits were also preserved along the channel margins. A three-dimensional (3D) static model describing the heterogeneity distribution within the turbiditic channel complex was compiled using both stochastic and deterministic approaches in a site where two channels were laterally connected by overbank deposits. Petro-acoustic properties derived from a subsurface database were then assigned to the facies to perform seismic simulations. The synthetic seismic simulations showed that the channel base can easily be misinterpreted compared to the geological model. Dynamic modelling, such as well test and streamline simulations, was also performed using the model to assess the transition between the channel and overbank deposits from a dynamic point of view. As a result of the streamline simulations, the overbank deposits connecting the channel homogenized the pressure regime in the reservoir. However, the sweeping efficiency of water injection can be affected by the heterogeneity distribution along the channel margins. A significant volume of oil could also be by-passed because of the occurrence of early water breakthrough through the spill-over lobes, or because the flow slowed down when it reached the heterogeneity along the channel margin.

The design of molecular systems as functional elements for use in next-generation electronic sensors and devices often relies on the addition of functional groups acting as spacers to modify adsorbate substrate interactions. Although advantageous in many regards, these spacer groups have the secondary effect of amplifying internal conformational effects of the parent molecule. Here we investigate one such molecule-2,5,8,11,14,17-hexa-tert-butyl-decacyclene (HBDC, C60H66)-deposited on Cu(100) at monolayer and submonolayer coverages using an ultra-high vacuum (UHV) scanning tunneling microscope (STM). By combining submolecular resolution imaging with computational methods, we describe a variety of properties related to the effects of adding tert-butyl spacers to a decacyclene core, including the molecular conformation, structure, and chiral separation of the molecular adlayer, strong intermolecular interactions, and a metastable pinned conformation of the molecule brought on by deformation under high-bias conditions that enable an examination of its diffusive 2D molecular gas at room temperature. Collectively, these observations provide direct insight into the effect of adding spacers to a flexible molecular core such as decacyclene as relates to both intermolecular and adsorbate substrate interfaces.

In a combined scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM) study, we characterize the reversible switching between two stable states of an organometallic complex, namely, bis-dibenzoylmethanato-copper [Cu(dbm)${}_{2}$] adsorbed on an insulating thin film. The switching is due to the transfer of an electron between the STM tip and the molecule, accompanied by a conformational change, i.e., a transition from a square-planar to a tetrahedral geometry. Evidence is given by STM topography and spectroscopy and nc-AFM electrostatic force measurements. Similar experiments conducted on bis-dibenzoylmethanato-nickel [Ni(dbm)${}_{2}$] show that this complex does not switch under comparable experimental conditions. We discuss these findings within the framework of crystal-field theory, stating that the occupation of the $d$ orbitals determines the favored coordination geometry of a complex. Accordingly, only the copper complex can undergo a conformational change that facilitates stable storing of the additional electron.

This article demonstrates that permeability upscaling, which can require complex techniques, is not necessary to significantly decrease the CPU time in reactive transport modeling. CPU time depends more on the geochemistry than the flow calculation. Flow rate upscaling is proposed as an alternate method to permeability upscaling, which is more suited to time-consuming flow resolution. To apply this method, a finite volume approach is most convenient.Considering the equality of flow as the equivalence criterion, when the coarse grid overlays the fine grid, flow rate upscaling leads, by construction, to the exact results, whereas the accuracy of permeability upscaling methods often depends on specific conditions. Some focus is put on the limitations of a common permeability upscaling technique, the simplified renormalization. In stationary flow, the gain in CPU time is the same for both flow rate upscaling and permeability upscaling. In transient flow, flow rate upscaling is slightly less time-efficient but the ratio between both CPU times decreases when the geochemistry is more complex.Working with an accurate flow rate field in the upscaled case reveals that porosity upscaling is a surprisingly tricky issue. Solution mixing is induced and residence times can be significantly affected. These changes have potentially important consequences on reactive transport modeling. They are not specific to the flow rate upscaling method; they are a general issue. Some simplified cases, assuming a homogeneous mineralogy, are examined. At this stage, a simple heuristic method is proposed, which yields reliable results under particular conditions (high heterogeneity). Porosity upscaling remains an open research field. (C) 2011 Elsevier Ltd. All rights reserved.