Supported nanomaterials are mainly studied for the modifications of electronic structure induced by their low dimension: Rashba effect, topological insulators, interface-induced gaps in graphene, bias/exchange effect, magnetic anisotropies... But the simultaneous control of composition, size, morphologies and chemical configurations raise many questions of thermodynamical order.<br />In this talk, we shall illustrate the equilibrium thermodynamics of pure or alloyed thin films, and supported nanowires and nanoparticles, built from transition metals, on a metallic surface. None of these objects forms a phase in the thermodynamical sense, - now widely named complexions- as their thermodynamic properties strongly rely on their environment (i.e. the underlying substrate and their companion particles for 1D and 2D systems). They can either be obtained in the monolayer or submonolayer regime, at equilibrium by gas deposition due to a strong segregation of one component (Ag/Cu, Ag/Ni...) or observed in situ via electrochemical co-deposition (Ni-Pd/Au(111)). Atomic-scale computations (Monte Carlo simulations, Quenched Molecular Dynamics) can be carried out to predict or comprehend their size, shape and composition, as a complement to Scanning Tunneling Microscopy studies. We shall in particular focus on the equilibrium size and composition distribution of a collection of finite supported particles. Statistics on a particle distribution will be linked to the much more studied characteristics of an isolated cluster, may it be free or isolated while experimentally investigated. The role of strain will be underlined via a comparison with experiments on heteroepitaxial systems (Ag/Cu, Ni-Pd/Au), and highly strained nanoislands (Ag/Ni(100)).<br />Keywords: Nanoislands; Thin Films; Atomic-Scale Simulations;

Complex Metallic Alloys (CMAs), intermetallic compounds made of at least two elements, have a crystalline structure that differs from usual alloys by the number of atoms in their unit cell and the occurrence of highly symmetric clusters as alternative structural units. Recently, quantum chemical calculations performed on several types of Al-TM (TM=Cu, Co, Fe) CMAs have highlighted the existence of specific covalent interactions within the bulk. In the case of the Al13TM4 systems, this has led to a better understanding of their physical properties and to a description of their structure as 3-D cage compounds. While well identified in the bulk materials, a question arises on how these chemical bonding networks will affect the atomic structure of CMA surfaces.
Here, we will present recent structural investigations of complex Al-TM surfaces using both experimental and ab initio computational methods. It will be demonstrated that the surface terminations can be associated to planes present in the bulk crystal structure. For several phases, these planes remain incomplete when exposed at the surface. We will show how this reduced atomic density can be related to the presence of chemical bonding network in the materials.
Finally, among the systems studied, some of them have been recently considered as promising candidate for the heterogeneous hydrogenation catalysis. We will discuss how their atypical surface structure could explain the catalytic properties reported in line with the site-isolation concept. We will also present the latest results on the growth of molecular thin films on these complex metallic alloy surfaces.

Permanent magnets are vital components in the rapidly-developing renewable energy sector, where the motors for electric vehicles and the generators in wind turbines require strong magnets with the ability to operate at temperatures well over 100°C. To achieve high coercivity, remanence and consequently high energy product at elevated temperatures, the addition of heavy rare earth (HRE) to the basic Nd-Fe-B composition is needed. To minimize the amount of critical elements such as dysprosium or terbium, the grain boundary diffusion process is applied on sintered magnets. Instead of using dipping in slurry of HRE or expensive sputtering, a new chemical process was invented – electrophoretic deposition (EPD). EPD-modified GBDP showed much better coercivities after an optimum heat treatment; it was shown that the coercivity can be also tailored; it depends on the DyF3 powder thickness on the magnet before heat treatment. From our results, it is apparent that the EPD process has two advantages: extra materials costs associated with the heavy-rare-earth component of the magnets can be minimised and a reduction of the environmental impact because we are not wasting any heavy rare earth during the procedure. By this new method, we could minimize the amount of HRE used to 0.2 at %. The improvement of coercivity was 30 % with minimal loss in remanence. To study the mechanism for such an improvement in coercivity without significantly decreasing the remanence, a detailed microstructure investigation was performed.
The technology was transferred to the industrial partner on a pilot production level and the final products will be used in the demonstrating motors for electric car and a wind turbine.
Acknowledgment: FP7-NMP-2012-SMALL-6 Contract No.: 309729

The outstanding physical properties of novel carbon-based materials (nanotubes, graphene) strongly depend on their structure: chirality for single wall carbon nanotubes (SWNT), number of layers and stacking for graphene. However, materials produced are far from being ideal and a detailed atomic scale understanding of the nucleation and growth of SWNT and graphene, as provided by computer simulation, is still highly desirable.
In this presentation, I will first introduce the field and discuss some key issues relevant to the controlled Chemical Vapor Deposition synthesis of SWNTs and Graphene on a metal catalyst. I will show how various computer simulation techniques, from DFT based calculations to Monte Carlo or Molecular Dynamics simulations based on more empirical models, lead to a better understanding of the processes involved.
I will then focus on our approach, based on a tight binding model for nickel and carbon implemented in Grand Canonical Monte Carlo simulations, to numerically investigate different aspects of the CCVD synthesis. We first study the chemical and physical states of the metal catalyst as a function of size, temperature and carbon chemical potential conditions corresponding to nucleation and growth of SWNTs and graphene. We then show how the growth modes of carbon nanotubes that have been identified experimentally critically depend on metal/carbon interfacial properties that are directly controlled by carbon solubility. This leads to an understanding of different growth regimes, and ultimately should provide routes to the chirality selective synthesis of SWNT that is the remaining challenge, pioneered by a number experimental groups.

The talk will focus at friction and wetting on Al-based quasicrystals and complex metallic alloys (CMAs), which comprise a significant number of crystalline compounds of changing lattice complexity, according to composition. Such compounds are thermodynamically stable and may be prepared into various sample shapes that allow measurement of surface physical properties. Surface energy (I³S) is one of the few fundamental properties of condensed matter: it defines the equilibrium shape of a crystal, it determines the interfacial behavior of any piece of liquid or solid against another body, etc. The talk will summarize a number of attempts to estimate the surface energy of a large variety of CMAs, including the stable, icosahedral AlCuFe and AlPdMn quasicrystals. Pin-on-disk experiments, after appropriate calibration, lead to reliable data that fall in the range 0.5 < I³S < 0.8 J/m2 for these quasicrystals. This average value of I³S is about one half that of pure aluminum (I³S = 1.15-1.2 J/m2), and less than a quarter that of iron (I³S = 2.2-2.4 J/m2). It is consistent with the low wetting behavior and reduced adhesion force against hard steel observed in high vacuum for these quasicrystals. The correlation to specific features of the electronic density of states will be emphasized, in line with the varying complexity of the studied CMA compounds. Potential applications in low-wetting and high vacuum technologies will be addressed with a view to finding sustainable, alternative coating solutions to fluorinated surface layers.

Environmental-friendly lead-free oxides in the K-Nb-O (KN), K-Ta-Nb-O (KTN) and K-Na-Nb-O (KNN) systems have attracted great interest for various applications in microelectronics, electro-optics and photocatalysis. In this work, KN, KTN and KNN thin films were grown on different substrates and electrodes by pulsed laser deposition which allows the control of both composition and structural properties, which strongly impacts the morphology and the physical behavior. The influence of deposition parameters, such as temperature, target composition or target-substrate distance was studied with adopting a phase diagram approach. Thin films of pure phases (KNbO3, K4Nb6O17, K6Nb10O30, KNb3O8, K3Nb7O19) were analysed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, precession electron diffraction, energy dispersive X-ray spectrometry and piezoresponse force microscopy.
In this study, we evidenced i) the first synthesis of thin films of K6Nb10O30, KNb3O8, K3Nb7O19 phases; ii) the epitaxial growth of all these phases on SrTiO3 (100) and (110); iii) the nanostructuration of some compounds under the form of nanorods, nanowires or nanosheets; iv) the synthesis of a new form of the well-known KNbO3 perovskite phase.

Metallic silicides are used as contact materials on source/drain and gate in MOS structure since the 1970's. From the 65 nm technology node, NiSi is the preferred material for contact in microelectronic due to low resistivity, low thermal budget and low Si consumption. Ni(Pt)Si with 10 at.% Pt is currently employed in recent technologies since Pt allows to stabilise NiSi at high temperature. The presence of Pt and the very low thickness (< 10 nm) needed for the contact in the devices bring new concerns for actual devices. Indeed, for such film thicknesses, phenomena like nucleation, lateral growth, interfacial reaction, stress, texture and transient phase formation can play an important role. The presence of alloy elements (Pt, Pd) as well as stress and defects induced by the confinement in devices have some effects on the silicide formation mechanism and on the alloying element redistribution. In this work, in situ techniques (XRD, sheet resistance, DSC) were combined with atom probe tomography (APT) and transmission electron microscopy (TEM) to study the formation mechanisms as well as the redistribution of dopants and alloy elements (Pt, Pd) during the silicide formation. In particular, APT has been used for the local analysis of MOSFET in 3D and at the atomic scale [3]. The advances in the understanding of the mechanisms of formation and redistribution will be discussed.

A large number of today's technological processes rely on catalytic reactions to synthesize chemical and pharmaceutical compounds, refine fuels or treat exhaust gases. Developing optimized and efficient catalysts is therefore a key faculty for the reduction of primary materials and energy resources as well as for the reduction of harmful emission to the environment. In recent years, intermetallic compounds, characterized by interatomic bonds of partially ionic and covalent character, have emerged as interesting materials class to look for new catalyst to be used in heterogeneous catalysis. The extensive number of possible binary intermetallic compounds, with electronic and structural properties that can strongly differ from their constituting elements, open a vast field to find catalyst optimized in the properties triangle of activity, selectivity and stability.
In our presentation, we will review the recent developments in the field of intermetallic compounds in heterogeneous catalysis and also review the particularities of the surface terminations of these materials, which arise from multiple, inequivalent atomic planes present for a given crystallographic direction and the partially covalent bond character. We will then turn our attention to the PdGa compound, which has been found to combine high selectivity and activity in acetylene semi-hydrogenation [1]. We will discuss the atomic structure of the low Miller index planes of PdGa and present experimental and theoretical results from the adsorption of small molecules (CO, C2H2 and C2H4) on the (111) and (-1-1-1) PdGa surface, which differ significantly in the local structure of the top most Pd atoms and therefore are model surfaces to study active site isolation and ensemble effects on catalyst selectivity [2]. In the last part, we will explore the possibilities of chiral selective adsorption on these surfaces made possible by the intrinsic chiral nature of the P213 space group PdGa belongs to [3].
[1] M. Armbruster, M. Kovnir, M. Behrens, D. Teschner, Y Grin, and R. Schlogl, JACS 132, 14745 (2010)
[2] J. Prinz, C. A. Pignedoli, Q. S. Stockl, M. Armbruster, H. Brune, O. Groning, R. Widmer, D. Passerone
JACS 136, 11792 (2014).
[3] J. Prinz, O. Groning, H. Brune, and R. Widmer, Angew.Chem. 127,3974 (2015)

Our group specializes in CVD coating processes. Both our applied and fundamental projects aim at establishing the process-structure-properties relationship. For instance, in collaboration with SME's and end users of the space research field, we successfully coat polymer composite surfaces to tailor their electrical conductivity and light absorption properties. In the meantime, we also develop polymer surface models with the combination of surface science experiments and DFT calculations, in order to improve our understanding of polymer surface reactivity.
The applied and fundamental aspects of our activity will be presented with a first focus on the development of low reflectivity coatings (<2%), and a second focus about the development of an experimental and theoretical model of a poly-epoxy surface – a material relevant to a variety of applications.

Currently, titanium and its alloys constitute the most favoured implant metallic materials in the field of trauma and orthopaedic surgery. However, despite the high rates of success of Ti-based implant materials, there still are serious problems of safety and long-term durability in the human body, resulting in repeat of surgical operations. For an implant material in contact with bone, both bulk and surface properties of the material have to be considered in order to improve cell–substrate interactions by the surface nano-featuring and to maintain long-term stability of the implant materials. Therefore, much research effort is dedicated to the development of new metastable Ti-based alloys with improved mechanical performance and biological compatibility expressed in low rigidity, high strength, composition of non-toxic elements and optimum surface conditions for osseointegration.
Ti-based alloys offer a wide range of adaptable structures for use in different medical applications, especially in orthopedics. In the focus of our studies are the Ti-Nb-based alloys with various metastable structures (beta-type, martensitic, nanostructured, glassy), which are processed by controlled casting and severe plastic deformation as bulk material or by powder metallurgy as porous compacts.
In the present paper, we will show that by tailoring specific nanostructures (for example with bimodal grain-size distribution or ultrafine/nano-scaled grains with non-equilibrium grain boundaries) unique combinations of properties can be produced, such as extraordinarily high strength and good ductility combined with high corrosion and wear resistance.
The possibility of applying different surface modification techniques for tailoring Ti-Nb implant surfaces at the nano-scale will be presented. The effective applicability of an oxidative H2SO4 treatment for nano-roughening the alloy surface without altering the corrosion resistance will be highlighted. This surface state sensitively determines the cell biological response, e.g. nano-roughening accelerates the adhesion and spreading of human mesenchymal stromal cells and increases the osteogenic differentiation. Another approach is the anodization in F’-containing electrolytes for growth of oxide nanotubes (Ti,Nb)O2. Tube diameter and length are controllable by the applied potential and polarization time and determine critically the cell response.

Acknowledgement: Funding from the DFG in the framework of SFB/TR79 and from the EC in the 7. FP MC-ITN VitriMetTech is acknowledged.

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