Magnetism of 3d-4d metal systems: Fe and Co thin films on Rh(111) A. Lehnert1, S. Rusponi1, G. Moulas1, M. Etzkorn1, P. Bencok3, P. Gambardella2, and H. Brune.1 1 2

Institute of Condensed Matter Physics, EPFL, CH-1015 Lausanne, Switzerland.

Catalan Institute of Nanotechnology, ICREA, and Universitat Autonoma de Barcelona,E-08193 Bellaterra (Barcelona), Spain. 3

European Synchrotron Radiation Facility (ESRF), Grenoble, France.

We report on the magnetic properties of Fe and Co thin films on Rh(111). We find a ferromagnetic order for 1 ML Fe with an easy magnetization axis perpendicular to the surface and a spin moment close to 2.8 muB. For 1 ML Co the easy axis lies in-plane and the atoms have a magnetic moment of 2.0 muB in good agreement with theory. Increasing the Co film thickness, we observe a spin reorientation transition with the easy axis turning from in-plane to out-of-plane for a 2 ML thick film and turning back in-plane for a thickness ≥ 3 ML. In the case of the Fe films, the easy axis stays out-of-plane for the first 3 MLs and turns in-plane for films being thicker than 4 ML thick. Lehnert et al., Phys. Rev. B 82, 094409 (2010).

1

Response of nanometal and nanoalloy surface to exposure to gases at normal pressure. Zbigniew Kaszkur, Piotr Rzeszotarski Institute of Physical Chemistry PAS, Kasprzaka 44/52, 01-224 Warszawa, Poland.

Structure of nanoparticles of metals and alloys supported on chemically inert supports was monitored in situ using carefully designed technique based on x-ray powder diffraction. The XRPD was tuned to precisely monitor metal phase diffraction peaks position, intensity and width (shape) during sample normal pressure exposure to gases (He, H2, O2, NO, CO). No phase transition is observed but subtle changes in peak position, intensity and width are interpreted in terms of crystallite surface structure modification via atomistic simulations. For pure metal nanoclusters the interaction with inert (He) or strongly bonding gases (H2, O2, NO, CO) causes, depending on temperature, deep or shallow roughening of the surface (affecting at room temperature even 2-3 surface shells). For the gases reacting at the surface the surface disorder is caused by the reaction dynamics. As a result of these processes the diffraction peak shift is however markedly different for various gases being indicative of a stress imposed on crystall lattice by the reacting surface. In the case of nanoalloy crystallites the picture has to be supplemented by the surface segregation phenomena that, depending on temperature, in different way adjust concentration profile within the nanocrystal to a changing state of the surface. The examples given concern Pd, Pt and PdAg nanocrystals.

2

Core-Shell Metal Nanoparticles: Case Study of Pt@Cu and Cu@Pt for NO Reduction Nicola Luckas, Francesc Viñes, Andreas Görling Lehrstuhl für Theoretische Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany [email protected] Core-shell nanoparticles have risen in the last years as promising nanostructured materials for a variety of technologically purposes, such as drug-delivery, photochemistry, photocatalysis, sensoring, and heterogeneous catalysis.1,2 In the latter field, core-shell nanoparticles have emerged as promising candidates for a variety of reactions, such as CO oxidation, NO reduction, olefin separation, etc... since they present enhanced activities, reactivities and resistance to poisoning compared to the parent isolated metals they are formed from, in other words, present synergistic properties. Despite such properties, little is known about which factors are the responsible for such enhanced/hindered activity. Is it due to a perturbation of the electronic structure of the shell metal? Is mainly affected by the effect of the subsurface core? Does it come from a change in the structure of the core and/or shell phases? Is on the contrary the core playing the main role by inducing the shell to adopt a special crystal structure? For a better design of tailor-made core-shell catalysts, a detailed and microscopic knowledge of the main factors responsible of the enhanced/hindered properties of coreshell nanoparticles is mandatory, in order to exploit/avoid them for practical purposes. Such knowledge can only be obtained with the help of theoretical methods carried out on adequate nanoparticle models. In the present study3 such knowledge is gained for a case study, namely core-shell nanoparticles of the Pt/Cu binary system, which has been found to be a novel catalyst for NO reduction.4 The study is devoted to the study by Density Functional (DF) methods of the electronic and geometric structure of Pt and Cu nanoparticles of different sizes (up to ≈ 310 atoms) and shapes (cuboctahedral, icosahedral and spheric) and core-shell nanoparticles made of them (see Figure 1). The changes in the electronic and geometric structures of the cores and shells are used to interpret the changes in the adsorption of NO on their facets, in order to quantify the importance of such effects in the enhancement/hindering of the core-shell nanoparticle activity. Figure 1: Cu@Pt nanoparticle nanoparticlesnanoparticle.

1

R. Ferrando, J. Jellinek, R. L. Johnston, Chem. Rev. 2008, 108, 846. W. Schärtl, Nanoscale 2010, 2, 829. 3 N. Luckas, F. Viñes, A. Görling, in preparation 4 S. Zhou, B. Varughese, B. Eichhorn, G. Jackson, K. McIlwrath, Angew. Chem. Int. Ed. 2005, 44, 4539. 2

3

First-principles study of methanol steam reforming on Pd-Zn alloy Zhao-Xu Chen, Yucheng Huang, Xiang He Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210093, P.R. China. Methanol steam reforming (MSR) is an important means to produce hydrogen used in-situ for clean vehicles. Pd/ZnO is investigated to replace the conventional Cu/ZnO catalyst that loses activity at higher temperatures. One active component of Pd/ZnO is believed to be 1:1 PdZn alloy. Recently the Pd(111) surface on which 0.03 – 0.06 monolayer (ML) Zn is deposited was thought to be active for MSR reaction. Our Monte Carlo simulations reveal that at very low coverage of zinc small surface clusters with 3 to 5 atoms exist preferentially on the Pd (111) surface. Density functional periodic calculations demonstrate that formaldehyde dehydrogenation is difficult on the supported surface Zn clusters whereas this process is facile on the clusters composed of Pd or Pd and Zn. In addition, formation of dioxymethylene (H2COO) is also very feasible on the small surface clusters of Zn. There results imply that the surface Zn clusters are likely the active phase for MSR reaction if the Pd(111) surfaces with low coverage of Zn are really active for MSR reaction. We also performed calculations of MSR reactions on the (111) surface of 1:1 PdZn alloy in the presence of hydroxyl group. It is shown that the preferred process is: CH3OH  CH3O  CH2O  (H2COOH)  H2COO  HCOO  CO2. The rate-determining step is the dehydrogenation of methoxy. The presence of hydroxyl favors both C-H and O-H bond breaking thermodynamically, but exhibits different kinetic behavior towards the two types of bond scission reactions.

References: *1+ E. Jeroro, J. M. Vohs, J. Am. Chem. Soc., 2008, 130, 10199–10207. *2+ X. He, Y. C. Huang, Z. X. Chen, Phys. Chem. Chem. Phys., 2011, 13, 107–109.



This work is supported by Natural Science Foundation of China No. 20973090 and Provincial Science Fund for Excellent Young Scholars of High Schools No. 2010SQRL024.

4

Wet-chemistry synthesis of small (Cu, Sn, Bi)-oxide and metallic particles V. Gandovaa, N. Milchevaa, H. Ipserb, J. Vrestalc, G. Vassileva a b

University of Plovdiv, Faculty of Chemistry, 4000 Plovdiv, Bulgaria

University of Vienna, Department of Inorganic Chemistry / Materials Chemistry, A-1090 Wien, Austria c

Masaryk University, Natural Sciences Faculty, Brno, Czech Republic

Corresponding author: G.P. Vassilev, University of Plovdiv, Faculty of Chemistry, 24 Tsar Asen str., 4000 Plovdiv, Bulgaria. E-mail: [email protected], [email protected]

Preliminary studies on the design of lead-free solders precursors by wet chemistry methods are presented. The main objective is to assess the impact of the way of hydroxide precipitates preparation on the metal elements content of the precipitates. Namely, ternary hydroxide mixtures of the system Cu(II), Bi(III), Sn(II) were prepared, firstly, by single-element precipitation and, secondly, by coprecipitation. Thereafter, all mixtures were reduced by using hydrogen gas. Both, the initial mixtures and the reduced samples were studied by X-rays diffraction, optical and scanning electron microscopes. The chemical compositions of the precipitates were determined experimentally and their dependence on the pH was verified. It was found that alloying occurred during the reduction procedure, but in some cases the reduction was not complete (i.e. oxide phases rest in the samples). This might be a huge obstacle to use such an approach for the preparation of lead-free solders. Moreover, the materials obtained after reductions were predominantly bulk alloys, thus, the preparation of small-sized metal particles would be a challenge. Another key feature to be addressed in future studies is the correlation between the chemical compositions of the parent solution and these of the corresponding precipitates.

Keywords: Cu–Bi–Sn, ternary systems, lead-free solders precursors, hydroxide mixtures, precipitation, co-precipitation, reduction.

5

Heterogeneous bi-magnetic core-Fe3O4 |shell-γ-Mn2O3 nanoparticles A. López-Ortega1, M. Estrader1, G. Salazar-Alvarez1,2, S. Estradé3, J. Sort4, F. Peiró3, S. Suriñach5, M.D. Baró5, J. Nogués6 1

Centre d'Investigació en Nanociència i Nanotecnologia, Campus UAB, Bellaterra, Spain. 2

Materials Chemistry Group, Dept. of Physical, Inorganic and Structural Chemistry, Arrhenius Laboratory, Stockholm Univ., Stockholm, Sweden.

3

MIND-IN2UB, Departament d'Electrònica, Universitat de Barcelona, Barcelona, Spain. 4

ICREA and Dept. de Física, Univ. Autònoma de Barcelona, Bellaterra, Spain.

5

Departament de Física, Universitat Autònoma de Barcelona, Bellaterra, Spain.

6

ICREA and Centre d'Investigació en Nanociència i Nanotecnologia, Campus UAB, Bellaterra, Spain. [email protected]

The experimental and theoretical interest on bi-magnetic core-shell nanoparticles, where both the core and the shell are magnetic is steadily increasing *1-3+. However, in many of these systems the core and the shell are composed of the same transition metal ion. Nevertheless, in the search for multifunctional materials a new type of core-shell systems composed of different transition metal materials, with new degrees of freedom to control the magnetic properties, are emerging *4+. In this work we present the study of heterocore-Fe3O4(ferrimagnetic, FiM) |shell-γ-Mn2O3 (FiM) nanoparticles. The nanoparticles were synthesized by following a multi-step procedure, where preformed iron oxide nanoparticles were used as seeds for the subsequent growth of manganese (II) oxide and its passivation to form -Mn2O3*5+. Briefly, the Fe3O4 seeds were prepared by thermolysis of the iron (III) oleate *6+ and the manganese oxide layers were laid on them modifying an earlier reported procedure used for the synthesis of MnO|γ-Mn2O3 nanoparticles *7+. The system was studied by X-ray diffraction, transmission electron microscopy, electron energy loss spectroscopy (EELS) and magnetic measurements (SQUID). Magnetic measurements reveal that core-shell nanoparticles exhibit an extra transition at the known TC of Mn2O3 (TC ~ 40 K). The results show that the coercivity increases significantly while MS decreases compared with that of the Fe3O4 seeds. Both effects are consistent with the incorporation of -Mn2O3 which has a much larger anisotropy and smaller MS than Fe3O4. Interestingly, the hysteresis loop the core-shell nanoparticles shows a two stage behavior, implying that the core and the shell switch independently. This is probably due to a spring-magnet effect *8+ given the diameter-thickness of the constituents. Also, the core-shell nanoparticles show larger exchange bias than the seeds, which is expected since the seeds should only have surface effects while the core-shell should have FiM-FiM coupling *3+.

References: *1+ O. Iglesias, et al. J. Nanosci. Nanotechnol. 8 (2008) 2761; W. Liu, et al. J. Nanosci. Nanotechnol. 8 (2008) 2781. *2+ V. Skumryev, et al. Nature. 423 (2003) 850. *3+ J. Nogués, et al. Phys. Rep. 422 (2005) 65. *4+ O. Masala et al. J. Am. Chem. Soc. 127 (2005) 9354 *5+ G. Salazar-Alvarez, et al. to be submitted (2010). *6+ J. Park, et al. Nat. Mater. 3 (2004) 891. *7+ G. Salazar-Alvarez, et al. J. Am. Chem. Soc. 129 (2007) 9102. *8+ E.E. Fullerton, et al. J. Magn. Magn. Mater. 200 (1999) 392.

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Magnetic properties of inverted Antiferromagnetic-core|Ferrimagnetic-shell, FeO|Fe3O4, nanoparticles M. Estrader1, A. López-Ortega1, G. Salazar-Alvarez1,2, S. Estradé3, J. Sort4, J.D. Ardison5, W.A.A. Macedo5, F. Peiró3, S. Suriñach6, M.D. Baró6, J. Nogués7 1

Centre d'Investigació en Nanociència i Nanotecnologia, Campus UAB, Bellaterra, Spain.

2

Dept. of Materials and Environmental Chemistry, Stockholm Univ., Stockholm, Sweden. 3

MIND-IN2UB, Dept. d'Electrònica, Univ. de Barcelona, Barcelona, Spain.

4

ICREA and Dept. de Física, Univ. Autònoma de Barcelona, Bellaterra, Spain. 5

Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, Brazil. 6

Dept. de Física, Univ. Autònoma de Barcelona, Bellaterra, Spain.

7

ICREA and Centre d'Investigació en Nanociència i Nanotecnologia, Campus UAB, Bellaterra, Spain. [email protected]

Passivated ferromagnetic (FM) nanoparticles coated with the corresponding antiferromagnetic (AFM) oxide shell have been extensively investigated *1+. However, studies of core-shell nanoparticles with AFM cores are rather scarce *2+. Here we present the study of inverted AFM-core|FiM-shell (FeO|Fe3O4) in contrast to the archetypical FM-core|AFM-shell systems. Monodispersed AFM-FeO nanoparticles of different core sizes (5-15 nm) are synthesized by thermolysis of metal organic salts. They are subsequently passivated in different conditions to obtain FiM-Fe3O4 shells of different thicknesses, from 1-2 nm to completed oxidation, (Figure 1). The samples were characterized by means of X-ray diffraction, Small Angle X-ray Scattering (SAXS), Transmission Electron Microscopy (TEM), Electron Energy Loss (EELS), Mössbauer spectroscopy and magnetic measurements. The coupling between the AFM-core and FiM-shell leads to a strong dependence of the magnetic properties on the passivation layer, where the coercivity, HC and the exchange bias (loop shift), HE, decrease for increasing shell thickness.

(a)

*

*

(b)

Intensity (a.u.)

* FeO *

* * Fe3O4 30

40

50

60

70

80

90

100

Scattering angle (2

Figure 1 : (a) HRTEM image of FeO|Fe3O4 core-shell nanoparticle. (b) XRD pattern of FeO|Fe3O4 coreshell particle. References: *1+ J. Nogués, et al. Phys. Rep. 422 (2005) 65. *2+ G. Salazar-Álvarez, et al. J. Am. Chem. Soc. 129 (2007) 9102. 7

Structural and spectroscopic study of bimetallic nanoparticles Pierre Lecante, Marie-José Casanove, and Jean-Gabriel Mattei

CEMES / CNRS Groupe Matériaux Cristallins sous Contrainte 29, Rue Jeanne Marvig – 31055 Toulouse - France.

The analysis of very small bimetallic nanosystems is by principle challenging: because of the small size of the particles and of the influence of stabilizing ligands, unusual structures may be induced, with features difficult to evidence using conventional techniques such as XRD or TEM. Chemical order inside bimetallic particles adds another dimension to the investigation: different levels of association, or segregation, can be induced and are indeed essentials to the properties of interest, either magnetic, catalytic…

We found that the combination of in-lab techniques such as WAXS, HRTEM, EFTEM, eventually XPS, with XAS on large instruments is a way to obtain the comprehensive description needed for the correlation between synthesis conditions and properties of the material. Such approach will be supported by the study of different bimetallic systems, especially FeRh and FeBi elaborated by solution chemistry.

8

Surface modifications of PtCo/TiO2 catalysts upon reduction-oxidation cycles studied by ambient pressure photoelectron and absorption spectroscopies. V. Papaefthimiou a*, T. Dintzera, M. Lebedevaa, D. Teschnerb, R. Blumeb, M. Häveckerb, A. Knop-Gerickeb, R. Schlöglb , F. Garina, E. Savinovaa, S. Zafeiratosa a

b

LMSPC, UMR 7515 du CNRS, 25 Rue Becquerel, 67087 Strasbourg, France. Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin (Dahlem), Germany. *[email protected]

Carbon supported platinum is the most widely used electrocatalyst for fuel cell applications. In an effort to minimize the cost of such catalysts, Pt-based bimetallic alloys have been used, with PtCo catalysts being potential candidates, since they show improved electrochemical characteristics. In addition, replacement of the commonly used carbon support by electron conducting oxides like non-stoichiometric TiOx can be in favour of the 1,2 performance and the long term stability of the electrocatalyst * +. In the present work ambient pressure photoelectron and absorption spectroscopies (APPES and XAS) were applied in situ to monitor the surface composition and the chemical state of PtCo/TiO 2, thermally treated (420670K) in 0.2 mbar H2 and O2 and subsequently in CH3OH+O2 or CH3OH+H2O (in various proportions). The position of the Pt 4f peak is not sensitive to the gas phase. The photoemission spectra of Ti also indicate that the TiO 2 substrate is not influenced by the gas phase and remains fully oxidized in both oxygen and hydrogen atmospheres. However, a considerable increase in the T2g peak of the Ti L-edge absorption spectra is observed after treatment with CH3OH+O2, which then remains invariable despite the treatment. This increase can be related to the formation 3 of Co:TiO2 * +.Concerning Cobalt, it’s PES and XAS peaks are extremely sensitive to the variations of the gas phase environment; in pure O2 the Co3O4 spinel phase is formed, while in H2 the reduction of Co3O4 to CoO is observed. However, no full reduction to Co was observed under the experimental conditions used in this study. Quantitative calculations based on the PES results indicate that the redox potential of the gas above the sample not only influences the oxidation state of Co, but also the composition over the first few atomic layers of PtCo/TiO 2. Finally, non destructive depth profiling by varying the photon energy was used, to determine the spatial distribution between Pt, Co and Ti in the first few atomic layers. From these results one can suppose the formation of an initial CoO film on the TiO2 substrate followed by a mixed Co:TiO2 state. Pt on the other hand is diluted/diffused inside the Co:TiO2 matrix. Therefore, direct indications of Pt encapsulation under TiO2 and cobalt oxide layers are given. On the whole, our results unambiguously showed that significant surface reorganization takes place due to the interaction of the PtCo/TiO2 catalyst with the gas phase and help to understand the complex system behaviour under operating catalytic and electrocatalytic conditions. Acknowledgements Contribution from V. Pierron-Bohnes and M. Acosta is gratefully acknowledged. Financial support from FP7-FCH-JU2008-1-CP: ROBANODE, DEMMEA and IRAFC projects is gratefully acknowledged. Financial support from ANR and BESSY II EUSA programmes is highly appreciated. References *1+ Handbook of fuel cells: Fundamentals, Technology and Applications. Vol. 2 Electrocatalysis. Vielstich, W.; Lamm, A.; Gasteiger, H.A.. (Eds.), John Wiley and Sons, Chichester, 2003. *2+ S.H. Kang, Y-E. Sung, W.H. Smyrl, J. Electrochem. Soc. 155 (2008) B1128. *3+ J.W. Quilty, A. Shibata, J.-Y. Son, K. Takubo, T. Mizokawa, H. Toyosaki, T. Fukumura, M. Kawasaki, Phys. Rev. Lett. 96, (2006) 027202.

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Evaluation Of The Trade-Off Between Structure, Particle Size And Thermodynamic Data Of The Ag-Cu Nanoalloys Processed By Mechanical Alloying Route Speranta Tanasescu,1 Oana Gingu2 1

Institute of Physical Chemistry „Ilie Murgulescu” of the Romanian Academy, Department of Chemical Thermodynamics, Bucharest, Romania. 2

University of Craiova, Faculty of Engineering and Management of Technologycal Systems, Drobeta Turnu Severin, Romania.

The research is part of a collaborative project between the University of Craiova - Faculty of Engineering and Management of Technological Systems, and the Department of Chemical Thermodynamics from the Institute of Physical Chemistry of the Romanian Academy. In this project a special interest is devoted to the investigation of the correlation between the structure, particle size (method of synthesis) and the thermodynamic data of the Ag-Cu nanoalloys with potential applications as lead-free solders or as novel optical sensors based on the SPR (surface plasmon resonance) technique. Mechanical Alloying (MA) is a solid state processing route to obtain new materials as powder particles like. Structural changes, as well as grains morphology modification could be evidenced. At the University of Craiova, the MA route will be used to process Ag-Cu nanoalloys with different compositions, starting from elemental micronic powders. The new Ag-Cu nanosized/nanostructured powder particles will be characterized from morphological point of view (shape, size, particle size distribution, and internal structure) depending on the processing parameters (milling time, milling balls, powders ratio, milling atmosphere). The powder mixtures nearby the eutectic concentration (Ag = 60…70 % wt., Cu balance), as well as some copper rich compositions will be investigated. The experimental determination of thermodynamic properties of nanoalloys (energies, enthalpies of formation), the study of structural transformations, and the determination of heat capacity Cp will be performed by using the resources available in the Department of Chemical Thermodynamics - IPC, Romanian Academy: SetSys DSC-TG/DTA Setaram Equipment (ambient-1750oC); Set-Sys Evolution Dillatometer/TMA Setaram (ambient - 1650 oC); Drop Calorimeter MHTC-96 Setaram (ambient - 1600 o C). Formulation of equilibrium diagrams based on the experimental results will be compare with the calculated phase diagram of the Ag-Cu system by using THERMOCALC software for Ag-Cu solder. The performance for metal enhanced luminescence of some Cu-rich compositions will be analysed in terms of three parameters: sensitivity, signal-to-noise ratio (SNR) and operating range for the sensing layer refractive index values by using an SPR equipment.

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PdZn nanoalloys for methanol steam reforming: PM-IRAS, XPS and DFT studies Christian Weilach1*, Harald Holzapfel1, Karin Föttinger1, Sergey M. Kozlov2, Konstantin M. Neyman2 and Günther Rupprechter1 1

Vienna University of Technology, Getreidemarkt 9/BC, 1060 Vienna, Austria 2 Universitat de Barcelona c/ Martí i Franquès, 1, 08028 Barcelona, Spain * [email protected]

PdZn alloys have recently raised great interest as catalysts for hydrogen production via methanol steam reforming (MSR) since they show good conversion and high selectivity towards CO2 and hydrogen. We have utilized well-defined model 1:1 PdZn/Pd(111) surface alloys to study alloy formation, thermal stability and catalytic properties applying XPS, TPD, and PM-IRAS (Polarization-Modulation IR Reflection Absorption Spectroscopy). To gain further insights, additional DFT calculations have been carried out. 1:1 PdZn surface alloys were prepared by physical vapor deposition of Zn in UHV onto a Pd(111) single crystal substrate at 90 K or 300 K and subsequent annealing. A well-ordered LEED pattern was obtained, suggesting a coexistence of 3 rotational domains of a (2x1) structure. In this structure, the surface consists of alternating rows of Pd and Zn atoms. XPS detected alloy related features at a binding energy of 335.6 eV (Pd 3d5/2) and 1021.0 eV (Zn 2p3/2), indicating electron density transfer from Zn to Pd atoms upon alloy formation in good agreement with DFT calculations. As demonstrated by PM-IRAS, CO adsorbed exclusively on-top of single Pd atoms in the alloy layer, giving rise to a characteristic IR band at 2070 cm-1. Even at mbar CO pressure no bands of multiple-bound CO species could be identified. The CO saturation coverage was found to be 0.5 ML by TPD. By following the spectral evolution during annealing upon Zn deposition at 300 K, a window for alloy formation at annealing temperatures between ~473 K and 623 K was deduced from XPS, TPD and PMIRAS. The characteristic IR band at ≈2070 cm-1 and corresponding CO-TPD desorption peaks are first observed after annealing (in 1x10-6 mbar CO) to 473 K and show a maximum at 573 K. However, a great difference was observed when the annealing procedure was performed at a higher CO pressure of 5 mbar. The onset of alloy formation was then shifted by about 75 K towards higher annealing temperatures. Up to now, the reason for this effect is not completely understood, but it might well be related to gas phase induced surface reconstruction like recently predicted by DFT. It was found, that at high CO coverage (i.e. high CO pressure) a PdZn “zigzag” structure is by 0.16 eV per surface atom more stable compared to the “row” structure. The occurrence of IR bands attributed to multiple-bound CO and additional desorption features in TPD upon annealing to temperatures higher than 623 K were taken as an indication for the onset of alloy degradation via Zn depletion into the Pd bulk. In this case, no difference was observed between low and high pressure annealing.

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Theoretical studies of CO adsorption on PdZn surface alloys and induced structural modifications of the substrate Sergey M. Kozlov,1 Christian Weilach,2 Harald Holzapfel,2 Karin Föttinger,2 Günther Rupprechter2 and Konstantin M. Neyman1,3 1

Departament de Química Física & Institut de Química Teòrica i Computacional, Universitat de Barcelona c/ Martí i Franquès, 1, Barcelona 08028, Spain. 2 3

Vienna University of Technology, Getreidemarkt 9/BC, 1060 Vienna, Austria.

Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona 08010, Spain.

One of the most promising ways of hydrogen production is methanol steam reforming (MSR). Several catalysts, including Pd/ZnO, Pd/Ga2O3 and Pd/In2O3 ones were proposed as a replacement for presently used Cu/ZnO catalysts. The active phase of a model catalyst produced by Zn deposition on Pd(111) was found to be 1:1 PdZn surface alloy with a p(2×1) surface periodicity and Pd and Zn atoms aligned in rows. Selectivity of PdZn-based catalysts strongly depends on the preparation conditions. Recent PM-IRAS experiments by Rupprechter et al. suggested that surface composition of PdZn-based catalysts may change in the presence of CO or in the reaction atmosphere of MSR. We performed a density-functional study of CO adsorption on monolayer and multilayer PdZn surface alloys on Pd(111) revealing that adsorption of CO greatly facilitates restructuring of the PdZn surface. Both previously reported vertical reconstruction (corrugation) and lateral reconstruction are considered. Lateral reconstruction manifests itself in transformation of rows of surface Pd and Zn atoms to zigzags (Figure 1). Our calculations show that the zigzag structure of monolayer PdZn surface alloy on Pd(111) is more stable than the so far commonly accepted row structure. Stability of the reconstructed zigzag surface alloy is greatly enhanced by CO adsorption at high coverage. Adsorption of CO also induces structural changes in PdZn surface alloys, inverting “Zn-out/Pd-in” corrugation of the multilayer alloy to “Pd-out/Zn-in” one characteristic for monolayer PdZn/Pd(111) system.

Figure 1: PdZn monolayer on Pd(111) arranged in rows (A) and zigzags (B)

We have found that the preferable site for CO adsorption and consequently vibrational frequency of CO molecules depend on the structure of PdZn surface alloy. On PdZn surface alloys with the row structure CO molecules favorably adsorb on bridge sites between two Pd atoms. At contrast, CO prefers to adsorb on top of Pd atoms on PdZn surface alloy with row structure. Thus, due to pronounced difference in IR frequencies of CO adsorbed on top and bridge sites, these two structures of PdZn with adsorbed CO molecules may be clearly distinguished by IR spectroscopy.

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Metal nanoparticles with luminescent properties Hynd Remita1, Priyanka Ray,1 Selvakannan Periasamy,1 Isabelle Lampre,1 Marie Erard,1 Vincent Huc, 2 Cyril Martini 2 1

Laboratoire de Chimie Physique, Université de Paris-Sud, 91400 Orsay , France. Laboratoire de Chimie Inorganique, ICMMO, Université de Paris-Sud, 91400 Orsay, France.

2

Metal nanoparticles are an interesting field of study due to their optical properties which have a wide range of applications. For instance nanoparticles of gold and silver exhibit strong absorption in the visible–near infrared (NIR) spectral region due to the surface plasmon resonance (SPR) which is caused by the interaction of coherent motion of the conduction band electrons with an electromagnetic field. The frequency and width of the SPR depends on the size and shape of the metal nanoparticles. It has also been observed that small clusters of gold or silver possess luminescent properties. Radiolytic reduction is a powerful tool used for the synthesis of nanoparticles and clusters of controlled size. In this context we have synthesized nanoparticles and clusters of platinum and silver stabilized by ligands and / or calixarene1. Chini clusters *Pt3(CO)6+n2- were synthesized by radiolytic reduction of platinum complexes H2PtCl6 in alkaline methanol under CO atmosphere. These clusters exhibit two intense absorption bands in the visible–near infrared domain The position of the bands depends on the cluster nuclearity n, and shift to higher wavelength with n.2 The luminescence study of *Pt3(CO)6+42revealed that these clusters present two emission bands for single visible excitation.

Fig.1. TEM image of Silver nanoparticles stabilized by by calixarene

Fig.2. TEM image of platinum nanoparticles stabilized by calixarene

The synthesis of silver and platinum nanoparticles was performed in ethanol in the presence of calixarene. The TEM images revealed that nanoparticles of Silver are mono with an average size between 1.5-2nm.(Fig.1), while those of Platinum are linearly arranged (Fig.2) with an average size of 3.2 nm. These nanoparticles are believed to possess unique optical properties which are currently under study for biological application. References 1 V. Huc and K.Pelzer; J. Coll. Inter. Sc. 318, 2008, 1-4. 2 P. R. Selvakannan, I. Lampre, M. Erard, and H. Remita; J. Phys. Chem. C 2008, 112, 18722.

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Characterization of Bimetallic Rh-Au Nanostructures R. L. Chantry1, W. Siriwatcharapiboon2, S. L. Horswell2, A. J. Logsdail2 R. L. Johnston2, and Z. Y. Li1 1

Nanoscale Physics Research Laboratory, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, U.K. 2

School of Chemistry, University of Birmingham, Birmingham B15 2TT, U.K.

Shaped metallic nanocrystals are potential candidates as building blocks for novel catalysts, and in optical and magnetic applications. When they act as the nucleation centre for the overgrowth of a second metal, new opportunities arise for the manipulation of their properties via atomic composition and atomic structures, in addition to size and shape. In this paper, we present atomic resolution structural characterization of rhodium (Rh) grown on shaped gold (Au) nanorods and correlate the atomic structure with their optical properties. Au nanorods of cylindrical shape, with mean length and diameter of 35 nm and 13 nm respectively, were synthesized through colloid-chemical seed-mediated growth. Rh was deposited on the Au nanorods through nucleation growth for a range of Au:Rh atomic-composition ratios: 10:1, 7:3, 1:1 and 1:2. A range of characterization techniques, including high-resolution aberration-corrected scanning transmission electron microscopy (STEM) equipped with a high-angle annular dark field detector (HAADF), has been employed for structural characterization. It is shown that Rh nanoclusters (of ~1-5 nm) have formed on the surface of Au rods, with a preference for the nanorod ends, and with no clear interface apparent between the Au-core and Rh-overgrowth. These results are compared with a similar AuPd-nanorod system, where Pd forms a complete shell over Au nanorods through layer-by-layer growth, with a clear interface apparent between the two metals. The marked difference in structure between these two similar systems has been attributed to the difference in lattice mismatch, surface energies and cohesive energies. The optical properties of Rh/Au nanorods in solution have been investigated using UV-vis absorption spectroscopy. A red-shift of the longitudinal surface plasmon frequency is observed with increasing atomic-composition of Rh:Au. This is in contrast with the Pd/Au system where Au absorption peaks are quenched completely upon Pd overgrowth. The discrete dipole approximation (DDA) method has been applied to investigate the correlation between the plasmon shifts and the structural modification observed.

Corresponding Author: [email protected]

14

Study of magnetic phases in mechanically alloyed Fe50Zn50 powder A. Grabias1, M. Pękała2*, D. Oleszak3, M. Kowalczyk3 1

Institute of Electronic Materials Technology, Wólczyoska 133, 01-919 Warsaw, Poland.

2

Warsaw University, Chemistry Department, Al. Żwirki i Wigury 101, 02-089 Warsaw, Poland.

3

Warsaw University of Technology, Faculty of Materials Science and Engineering, Wołoska 141, 02-507 Warsaw, Poland. *

[email protected]

Due to the proper mechanical properties and high atmospheric corrosion resistance the Fe-Zn systems are widely used as protective coatings for steel surfaces. Large differences in melting temperatures and diffusivities of Fe and Zn hamper the traditional melting technology. Recently it was confirmed that the ball milling technique operating at relatively low temperatures allows one to overcome these limitations and produce the Fe80Zn20 alloy. This initial result along with similar studies encourages to test, which other Fe-Zn systems could be synthesized by ball milling. The elemental powders of Fe and Zn with a purity of at least 99.8% and particles size less than 50 μm were used for mechanical alloying processes. Fe50Zn50 mixture (at. %) was subjected to high-energy ball milling. Fritsch Pulverisette P5 planetary ball mill, equipped with hardened steel vial and balls (10 mm in diameter), was employed for milling with a rotational speed of 250 rpm. The mass of the milled powders was 10 g and ball-to-powder weight ratio was 10:1. The milling experiments and all powder handling were performed under protective atmosphere of argon. Small amounts of powders were withdrawn after selected milling times for structural examinations. The structure of the powders at different stages of milling and after completion of the process, as well as after annealing, was investigated by X-ray diffraction (XRD) method in a Rigaku MiniFlex II diffractometer using CuKα radiation (λ = 0.15418 nm). The Mössbauer measurements of all powder samples were performed in transmission geometry at room temperature. A constant-acceleration spectrometer with a 25 mCi 57Co-in-Rh source was used. The spectra were fitted assuming Lorentzian profile of lines using NORMOS program. The relative fractions of the spectral components related to the identified phases were calculated as a ratio of the area of the relevant subspectrum to the total spectral area, assuming similar Debye-Waller factors for each phase. Isomer shifts are referred to -Fe standard. Temperature variation of magnetization was measured by means of Faraday balance up to 1000 K in magnetic field of 1.5 T. Magnetic hysteresis loops were recorded with vibrating sample magnetometer in magnetic fields amplitude of 0.16 T. Temperature was regulated with 0.1 K accuracy. Magnetic field was stabilized when measuring hysteresis loop point by point. Nanocrystalline bcc Fe(Zn) solid solution was formed after 20 h high-energy ball milling of elemental powders with the starting composition of Fe50Zn50. Heating of the final powder up to 900 K led to the formation of the structure with a fairly equilibrium phase composition, consisting of magnetic Fe-rich bcc Fe(Zn) regions and non-magnetic Zn-rich -Fe4Zn9 compound. Mössbauer measurements revealed two distinctive magnetic Fe environments in both the as-milled and heated samples. The strong exchange interactions are confirmed by Curie temperatures close to 900 K. A decrease of magnetic coercivity observed at longer milling time was attributed to the reduction or averaging of local magnetic anisotropies.

15

Sputter deposited FeCoZr nanoalloy particles embedded in Al2O3 matrix M. Milosavljevid1, Suzana Petrovid1, D. Peruško1, J. Fedotova2, J. Kasiuk2, A. Maximenko2 1

VINČA Institute of Nuclear Sciences, Belgrade University, POBox 522, 11001 Belgrade, Serbia. 2

NC PHEP Belarusian State University, 53 M. Bogdanovich str., 220040 Minsk, Belarus.

Granular structures with metallic nanoparticles incorporated in a dielectric matrix allow variation of their magnetic, transport and magnetotransport properties by changing composition, size, shape and state of the nanocomposites. Most metals are insoluble in the insulating Al2O3 matrix, so they have a tendency to segregate and form nanogranules. Nanoparticles of a soft ferromagnetic FeCoZr alloy embedded in Al2O3 have very promising unique combination of properties (high-saturation magnetization, low coercivity, high electrical resistance) for magnetic recording media and magnetic sensors. In this work we present structural and magnetic properties of (FeCoZr)X(Al2O3)100-X nanogranular thin films, deposited by ion sputtering on Al and ceramic substrates to a thickness of ~ 2 m. The films were deposited in a single vacuum run, using a target composed of the corresponding metallic and dielectric constituents (Al2O3 strips pasted on Fe45Co45Zr10 alloy plates). The target was arranged to provide the nominal metal to dielectric atomic ratio close to the percolation threshold, (FeCoZr)36(Al2O3)64 and (FeCoZr)59(Al2O3)41. Inert argon gas was used for sputtering, and in some cases oxygen was added to the vacuum system in order to modify the film properties. The resulting films, grown both in inert or reactive ambient, consist of isolated metallic nanoalloy particles embedded in insulating alumina matrix. The films grown in inert ambient contain metallic particles of up to ~10 nm diameter or more, many of them irregularly shaped and consisting of a few single crystalline grains. Adding the reactive oxygen gas to the system resulted in smaller metallic grains, rather uniform in size and mainly spherical in shape, with a mean diameter of ~5 nm. Moreover, in the latter case the metallic nanoparticles have a coreshell structure, the core being a crystalline nanoalloy and the shell amorphous oxide. In all cases the identified metallic crystalline phase was bcc, inherited from the pure FeCoZr alloy. The corresponding magnetic properties of the films are in good agreement with the results of structural analysis, clearly distinguishing between the different structures, as will be presented in this work.

16

Synthesis of Ti-based nanoalloys in multilayered structures by ion and laser beam irradiation Suzana Petrovid, M. Milosavljevid, D. Peruško VINČA Institute of Nuclear Sciences, Belgrade University, POBox 522, 11001 Belgrade, Serbia Multilayered nanometric thin films are attractive due to their properties, such as enormous hardness or unusual phase composition, which cannot be obtained in uniform bulk materials. Titanium-aluminium and titanium-nickel alloys possess very good physicochemical characteristics such as thermochemical stability for high temperature wear and corrosion protection in mechanical applications. Multilayers of Al/Ti and Ni/Ti were sputter deposited on (100) Si substrates in a single vacuum run, by switching from one target to the other. Total thickness of the deposited structures was ~250 nm, each consisting of 1020 individual layers. Ion irradiations were performed with 180 keV Ar+ ions at normal incidence. Implanted fluences ranged from 1x1016 to 6x1016 ions/cm2. The beam current was maintained at ~1 A/cm2, to avoid beam heating. Laser processing was done by a defocused Nd:YAG laser beam, wavelength 1064 nm, pulse duration 150 ps and pulse energy ~20 mJ. Structural and compositional characterizations were done by X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Implantation of Ar+ ions in the (Al/Ti)/Si system to the fluences of 2-4x1016 ions cm-2 induced nanoalloying at Al/Ti interfaces, formation of AlTi3 and -AlTi nanoparticles. Subsequent vacuum annealing of sample implanted to 6x1016 ions cm-2 at 500 oC, for 30 min, leaded to a complete transformation of all deposited layers into AlTi3 and -AlTi intermetallic phases. The same argon implantation into the (Ni/Ti)/Si system resulted in solid state amorphization, starting at the original interfaces and most pronounced around the projected ion range. However, subsequent annealing of sample implanted to 4x1016 ions cm-2 at 400 oC, for 30 min, yielded a crystallization of the amorphous phase, while in the unmodified layers it yielded interdiffusion and amorphisation. During irradiation of (Al/Ti)/Si and (Ni/Ti)/Si systems with picosecond laser pulses, the main part of the absorbed energy was rapidly transformed into heat, thus intensive modification of composition and morphology occurred. Beside surface oxidation, the results show an increase in surface roughness due to appearance of periodical nano-structures at the Al/Ti multilayer and partial ablation and microcracking of the Ni/Ti multilayer thin films. Changes of composition by laser irradiation included intensive mixing of components and formation of Ti-based intermetallics in both systems.

17

Synthesis of Supported Gas-phase Gold-based Nanoclusters: a Catalytic Study B. Moens,a W. Janssens,a G. De Cremer,a C. Romero,b Didier Grandjean,b J. Hofkens,c P. Lievens,b B. F. Selsa a

Center for Surface Chemistry & Catalysis, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, B-3001 Leuven, Belgium. b

c

Solid State Physics and Magnetism Section, Katholieke Universiteit Leuven, Celestijnenlaan 200d, B-3001 Leuven, Belgium.

Molecular and Nanomaterials, Katholieke Universiteit Leuven, Celestijnenlaan 200f, B-3001 Leuven, Belgium.

Until the eighties there was little interest in gold nanoparticles (NPs) for catalytic purposes. This changed after Haruta discovered that Au NPs on a solid oxide support could oxidize CO with O2, even at low temperatures *1+. He noticed that the size of the Au particles was critical for the catalytic activity. These findings stimulated the interest in NPs, initiating an exponential increase of the research within this field. Au-based NPs, mostly prepared by wet chemical methods (impregnation, deposition precipitation…), proved to be highly efficient in an extensive number of catalytic reactions *2, 3+. However, reliable synthesis of very small nanoparticles (2 nm and below) is still not possible with the latter wet techniques. Hereby, we present gas-phase cluster deposition as an alternative way to prepare very small homogeneous gold-based mono and bimetallic NPs. Catalytic activity of pure gold deposited clusters is tested in the CO oxidation reaction at low temperature; careful analysis of the test reaction with a mass spectrometer allows us to measure up to ppm scale. Further optimization of the synthesis and catalytic reaction will result in the production of homogeneous series of supported mass-selected Au-based mono and bimetallic clusters and the development of a model to describe the impact of the size, structure and composition of the nanoparticles on their catalytic performance.

*1+ Haruta, M., Kobayashi, T., Sano, H., Yamada, N. (1987), Chemistry Letters, 405-408. *2+ Yu, Y., Huang, J., Ishida, T., Haruta, M. (2009), Modern Heterogenous Oxidation Catalysis: Design, Reactions and Characterisation. Mizunu, N. (eds.), Whiley-VCH Verlag GbmH&Co. KGaA, Weinheim, 77124. *3+ Haruta, M. (2002) Cattech, 6: 102-115.

18

Structural and magnetic properties of CoPt nanoparticles epitaxied on a NaCl substrate I. Florea,1 O. Ersen,1 C. Ulhaq,1 C. Goyhenex,1 V. Pierron-Bohnes,1 N. Braidy,2 D. Alloyeau,2 C. Ricolleau,2 Y. Le Bouar3 1

Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS-UdS, 23, rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France. 2

Laboratoire Matériaux et Phénomènes Quantiques (MPQ) UMR 7162 CNRS - Université Paris 7 Denis Diderot, Bâtiment Condorcet Case courrier 7021, 75205 Paris Cedex 13, France. 3

Laboratoire d'Etude des Microstructures (LEM) UMR 104 ONERA-CNRS, BP 72 29 avenue de la Division Leclerc, 92322 Chatillon Cedex, France.

CoPt nanoparticles (NPs) were prepared using pulsed laser deposition at 400°C on a freshly cleaved NaCl substrate. The particles were then transferred on an amorphous C membrane and annealed under vacuum. TEM was performed on a Jeol 2100FCs microscope. HAADFSTEM (High Angle Annular Dark Field-Scanning electron microscopy) images were compared with the image contrast calculations in Auto STEM Programme (M. Robertson) and yields some information on the order state and the shape. Electron tomography was performed to have an insight on the 3D-morphology of the particles. The magnetic properties of NPs were studied using SQUID. The nanoparticles have an octahedron-type morphology as prepared. They are found to be ordered following a 1h-700°C annealing with a change of morphology. A lognormal blocking temperature distribution was deduced from the SQUID measurements; the average temperature increases from around 20K to around 35K as expected from a partial ordering.

(a) Electron tomography of the as prepared disordered NPs: sections at constant x, z and y. (b) HAADF-STEM on NPs annealed 1h at 700°C (top: contrast profile): L10 phase with x and z concentration modulations.

19

Are small L10 ordered particles mono-domain? TEM investigation of CoPt and FePt nanoparticles Florent Tournus,1 N. Blanc,1 V. Dupuis,1 K. Sato,2 T. Konno,2 T. Epicier3 1

Laboratoire de Physique de la Matière Condensée, CNRS & Université Lyon 1, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne, France.

2

Materials Processing and Characterization Division, Institute for Materials Research, Tohoku University,2-1-1 Katahira, Sendai 983-0836, Japan. 3 Université de Lyon, INSA-Lyon, MATEIS, UMR CNRS 5510, Bât. B. Pascal, F-69621 Villeurbanne Cedex, France. CoPt and FePt alloys display exciting features at nanosizes: despite a large number of experimental and theoretical studies, there remain open questions regarding the structure of small nanoparticles: threshold size for L10 ordering, surface segregation, exotic (non fcc or fct) structures… While it is well known that several planar defects and in particular c-domain boundaries or antiphase boundaries are met in macroscopic materials or thin films, their relevance for particles of a few nanometers has not been examined. Therefore, an implicit belief is that small CoPt or FePt nanoparticles, if they can reach a chemically ordered state, would be mono-variant (single c-domain). By TEM investigations on annealed CoPt and FePt nanoparticles, we have detected the coexistence of different structures, including L10 ordered decahedra which had been theoretically predicted. Our results also demonstrate that, surprisingly, particles as small as 2 nm in diameter can present several L10 variants.

Figure 1. TEM observations of chemically ordered CoPt and FePt nanoparticles (HRTEM and STEMHAADF images). Except for the leftmost particle on the bottom line, all particles display several L10 domains. 20

Nanostructure effects on the performance and deactivation of multifunctional bi-metallic catalysts Krassimira Kumbilieva Institute of Catalysis, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria. As is recognized, most of the bimetallic catalysts are bi- or multifunctional. Addition of catalytically inactive metals (e.g. Sn, In, Zn, Pb, Mo promoters) to the active phase of Pt, Pd, Ni, Fe catalysts may substantially change the reaction kinetics and selectivity. The influence of promoters on the performance of structure-sensitive reactions is put to discussion. In association with the dispersion of the active phase as nano-structured islands on the support, the suggested approach distinguishes different types of active sites responsible for different routes of processes occurring on bimetallic catalysts. The diversities in the structure and coordination characteristics of the site types give rise to diversities of their adsorption and catalytic properties, different vulnerability to coke action. In most multifunctional catalytic systems two or three types of active sites realize contribution to the catalytic performance. For avoiding discrepancy with the Hinshelwood-Langmuir kinetics, the suggested approach considers the surface of poly-functional catalysts as containing 2 or 3 co-existing ideal adsorbed layers, each of which is characterized by private individual parameters. The function of overall catalyst activity is defined as a vector sum of the “individual activity” functions related to the performance exerted by the particular types of active sites. Active sites located inside the active phase islands and sites located on interfaces with carrier or promoters of bimetallic catalysts may facilitate different routes of the reaction network. The developed model suggests regularities associating the selectivity with the size of the active phase nano-structures. The analysis performed points out that, when the process is accompanied by coke formation, increase of the selectivity towards the reactions occurring on interfacial active sites should be expected. The analysis accounts as a distinct type of sites the catalytic clusters – ensembles involving a definite number of adjacent surface atoms in proper configuration. In the course of coke building, the probability for the formation of catalytic clusters may decrease in different modes, stipulating various effects on the selectivity in regard of the structure-insensitive and structure-sensitive reactions. Models of catalyst deactivation are developed describing the contribution of different site types to the evolution of activity. The kinetic regularities following from the postulated model are in agreement with the regularities established from experimental data.

21

Size-selected Pt nanoparticles for use in electrochemical reactions D.N. McCarthy, C. Strebel, A. Nierhoff, F.P. Alonso, T. Johansson, A. Den Dunnen, I. Stephens, J.H. Nielsen, I. Chorkendorff CINF, Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark We present results from both UHV and electrochemical experiments of Pt nanoparticles and Pt crystals, as well as preliminary results from Platinum-Yttrium nanoparticles. Our studies are motivated by the need for lower Pt loadings at the cathode of polymer electrolyte membrane fuel cells, for improvements to their long-term performance, and for improvements to their activity for the oxygen reduction reaction. The presented experiments consider effects such as nanoparticle size, coverage, and composition, on the electrochemical activity. In our UHV experiments, we have investigated the absorption of CO via temperature programmed desorption, on both Pt nanoparticles grown via the gas aggregation technique, and on Pt(111) single crystals. CO is a useful probe molecule, as the desorption profile of CO has distinctive features that can be related with particular adsorption sites e.g. terrace sites, or under coordinated sites such as the terrace steps of single crystals, or facet edges of nanoparticles. Our experiments have identified two main CO desorption features from nanoparticles dosed at 10-7 mbar; a central peak at 400K, and a secondary peak at 500K. These two features are also observed when CO desorbs from sputtered Pt(111) crystals, whereas only the low temperature peak is observed for annealed Pt(111) crystal. Interestingly, for samples dosed at pressures of 2-10 mbar and 600K, a comparison of the CO desorption profiles of nanoparticles to that from sputtered single crystals finds an apparent roughening of the nanoparticles, compared with an annealing-out of the sputtered single crystal. The observed roughening of Pt particles at elevated CO pressures and temperature is consistent with reported roughening of stepped Pt surfaces under high CO pressure (Tao et al, Science 327 (2010) 850). We also present experimental results for Pt, and Pt-Y nanoparticles, deposited under vacuum onto Glassy Carbon (GC) electrodes, which are then characterized ex-situ in a rotating disc electrochemical setup. To date we have studied the effects of particle size, and coverage, on the electrochemical signatures of the oxygen reduction reaction, and CO stripping peak position of Pt nanoparticles. Results show that the electrochemical performance of 9nm diameter Pt nanoparticles is comparable to that of polycrystalline Pt electrodes, whereas for smaller nanoparticles sizes there is a progressive decrease in activity, in tandem with a shift of the CO stripping peak position to higher potentials, consistent with the tighter binding of reactive species to the particle surface. The activity of the Pt nanoparticles will be compared with preliminary results from Pt-Y nanoparticles.

22

Structures of Au and AuPd clusters on stepped MgO(001) K. Damianos, R. Ferrando Department of Physics, Genoa University and IMEM/CNR, Via Dodecaneso 33 – I-16146 Genoa Italy.

The structures of Au and AuPd clusters adsorbed at a step on MgO(001) are studied by densityfunctional calculations in the size range below 20 atoms. Calculations are performed by means of the PBE exchange-correlation functional and by taking into account the relaxation of the step atoms. Different structural motifs such as two-dimensional vertical and horizontal leaflets, open cages and compact structures are considered. It turns out that the presence of the step significantly alters the most stable structures compared to those found on the flat surface.

23

Ionomer optimization through analysis of the hydrogen oxidation and oxygen reduction reactions on PtRu/C-Nafion and Pt/C-Nafion electrocatalysts for fuel cells Amado Velázquez-Palenzuela, Francesc Centellas, Jose Antonio Garrido, Conchita Arias, Rosa María Rodríguez, Enric Brillas, Pere Lluís Cabot* Laboratori d’Electroquímica dels Materials i del Medi Ambient, Departament de Química Física, Universitat de Barcelona, Martí i Franqués, 1-11, 08028 Barcelona, Spain. *E-mail address: [email protected] Polymer electrolyte fuel cells (PEFCs) are severely limited by two problems: (i) the CO-poisoning of Pt atoms, when hydrogen from reforming process is used as fuel, and (ii) the relatively slow kinetics of the oxygen reduction reaction (ORR), even on Pt catalysts. Besides, the influence of the ionomer fraction in the membrane electrode assembly (MEA) needs to be examined in order to determine the optimum electrocatalyst-ionomer ratio. The ionomer influence in the kinetics of the hydrogen oxidation reaction (HOR) and of the oxygen reduction reaction on high performance (HP) 20 wt. % carbon (Vulcan XC-72)-supported PtRu (alloy 1:1) and HP 20 wt. % carbon Vulcan (XC-72) electrocatalysts, respectively, were studied by means of the technique of rotating disc electrode (RDE) coupled to cyclic voltammetry in hydrogen/oxygen-saturated 0.5 mol dm-3 H2SO4 electrolyte, using the thin-layer RDE technique and Nafion as ionomer. The catalyst/ionomer inks were prepared in one step by arranging catalyst suspensions in water/ionomer solutions. A drop of the ink was pippeted onto the glassy carbon (GC) of the rotating electrode and afterwards, it was dried overnight at room temperature. Electrodes with different Nafion fractions from 0 to 80% were prepared. In the case of the PtRu/C catalyst, CO tolerance was also taken into account. CO stripping experiments showed that the electrochemical active surface area of the Pt-Ru nanoparticles was a function of the ionomer fraction in the catalyst ink, being maximum with 35%. This behavior is explained by a poorer proton conductivity at low ionomer percentages and the isolation of carbon-metal particles by the polymer when highest Nafion fractions are used. On the other hand, the hydrodynamics experiments reveal that the Nafion creates an additional diffusion resistance when the HOR and the ORR are under mass-transport control. This effect can be suppressed using Nafion fractions below ≈15% for the HOR on PtRu/C and ≈30% for the ORR on Pt/C. In the absence of mass transfer control by Nafion, kinetic parameters, such as Tafel slopes and exchange current densities can also be calculated. Acknowledgements. The authors thank the financial support given by the Spanish MEC (Ministerio de Educación y Ciencia) through the project NAN2004-09333-C05-03. The FPU fellowship from Spanish MEC received by A. Velázquez is also acknowledged.

24

Electrochemical approach for the synthesis of multifunctional intermetallic nanoparticles G. Pigozzi1, D. Mukherji2, P. Schmutz1 1

Departament of Corrosion and Materials Integrity, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland. 2

Institute of Materials, Technical University, Braunschweig, Germany.

The synthesis of nanoalloys with controlled size and composition is of fundamental and technological interest. Recent advancement in nanotechnology provides the capability to design physical properties not only by changing the material but also by changing the particle size into nano-scale. Multifunctional nano-systems are gaining importance and surface modifications of nano-particles have emerged as an important class of functional nanomaterials. Core-shell nanoparticles have attracted recent attention as they are finding interesting applications in the field of biomedicine. In the core-shell nanoparticles, the core and the shell are of different material/structure, having different properties. In particular, systems with a magnetic core surrounded by an inert shell material, are modern solutions that are being developed for applications in e.g., tumour destruction via hyperthermia, drug and gene delivery and MRI contrast enhancement. In order to boost the signal, and improve the ability of MRI to detect the smallest tumours, researchers also try to produce stronger magnetic signal from the iron oxide nanoparticles. This clearly shows the need for alternate nano-particle compositions with stronger magnetic properties. Recently, we have developed an electrochemical selective phase dissolution (ESPD) method to produce nanoparticles of different intermetallic phases, some of them cannot be pproduced with standard nano-crystal synthesis routes. By this method, a core-shell structure can be formed in-situ in a single step. A wide range of nanoparticles can be produced from multi-component alloys containing precipitates, by an electro-chemical extraction technique. Many intermetallic compounds, some of which show strong magnetic properties, were produced (e.g. Ni3Si, Ni3Al, Ni3Fe, Co3Al). An example of one of these particles is shown in the Figure 1. The coreshell structure could be produced under widely varying conditions of the electro-chemical extraction processing and from different alloy compositions. Possible applications of our intermetallic nanoparticles include, medical treatments (like magnetic drug delivery, hyperthermia and MRI contrast agents), reinforcement of joining materials (brazing and soldering), improvement of corrosion resistance of metal coatings, and magnetic fluids. The same ESPD method is very versatile and allows for other nanostructured materials to be produced, like nanoporous membranes, hollow silica capsules and nanopatterned surfaces. Results will be presented on the characterization of the nanoparticles produced by ESPD and the long-term technology development strategy will be drawn with respect to the possible applications.

5 0 nm

Figure 2 TEM image of 20nm core-shell Ni3Si-silica nanoparticles produced by ESPD.

25

Synthesis and Characterization of Cu-Ni Nanoparticles Jiri Pinkas, Jan Vrestal, Jiri Sopousek, Pavel Broz, David Skoda, Ales Styskalik Department of Chemistry, Masaryk University, Brno, Czech Republic. E-mail: [email protected] The main goal of our project Phase diagrams of nanoalloys, their calculations and verifications is calculation of phase equilibria in nanoalloys including experimental verification of calculations *1+ by examining synthesized nanoparticles of particular size and composition. The systems of interest include Cu-Ni, Ag-Cu, and other prospective lead-free solder nanoalloys. The first step in this direction is the chemical synthesis of nanoparticles *2+ and their characterization by DLS, DTA/DSC/TGA, UV-vis, IR, SEM, TEM, and XRD methods. The Cu-Ni alloy nanoparticles were prepared for the purpose of verification of the phase diagram affected by Cu-Ni nanoeffects by the solvothermal reaction from nickel acetylacetonate Ni(acac)2 and copper acetylacetonate Cu(acac)2 in a particular stoichiometric ratio under an inert atmosphere of nitrogen with the use of the vacuum line. As a heating bath Sn-Pb solder was used. The molecular precursors were dissolved in oleylamine and this solution was injected into a hot solvent composed of 1-octadecen and oleylamine at 230 ° C. In this reaction mixture the precursor metal cations were reduced at a high temperature and formed the Cu-Ni nanoalloy. The product was precipitated with methanol and washed with hexane several times and separated by centrifugation. The nanoalloy products were characterized by the DLS, SEM, TEM, and XRD analysis. The TEM/HRTEM analysis revealed the particle size 1015 nm.

Acknowledgement: Financial support by the Ministry of Education, Youth and Sports of the Czech Republic under grant COST CZ LD 11046 Phase diagrams of nanoalloys, their calculations and verifications and by the Grant Agency of the Czech Republic GACR 106/09/0700 are gratefully acknowledged. References: *1+ J. Park, J. Lee: Calphad, 32 (2008) 135. *2+ Y. Zhang, W. Huang, S. E. Habas, J. N. Kuhn, M. E. Grass, Y. Yamada, P. Yang, and G. A. Somorjai: J. Phys. Chem. C 112 (2008) 12092.

26

Structural And Electronic Studies Of Supported Pt And Au Epitaxial Clusters On Tungsten Oxide Surface K. Mašek1, P. Blumentrit1, J. Beran1, T. Skála2, I. Píš1, J. Polášek1, V. Matolín1 1

Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma Sciences, V Holešovičkách 2, CZ-180 00 Prague 8, Czech Republic. 2 Sincrotrone Trieste, Strada Statale 14, km 163.5, 34149 Basovizza-Trieste, Italy. Corresponding author: [email protected]

Tungsten oxide is a base material in a variety of applications such as electrochromic devices, catalysts and chemical sensors. The studies of their fundamental physical and chemical properties are often performed on well-defined epitaxial (model) systems. The physical and chemical properties of the tungsten oxide can be strongly influenced by doping the surface by any active metal. We investigated the structure and electronic properties of epitaxial Pt and/or Au clusters prepared “in-situ” on tungsten oxide surface by deposition under vacuum. The epitaxial tungsten oxide thin films were prepared by oxidation of W(110) single-crystal surface using a RF oxygen plasma source followed by thermal annealing. The crystallographic structure and epitaxial orientation were determined by reflexion highenergy electron diffraction (RHEED). The chemical state of the system, the interaction between the deposit and substrate and formation of Pt-Au alloy were investigated by photoelectron spectroscopy excited by synchrotron radiation (SRPES) and by X-ray source (XPS). The tungsten oxide thin film exhibited a pseudocubic structure giving rise from a monoclinic structure of tungsten trioxide having (111) plane parallel to the W(110) substrate surface. This system was used as a substrate for deposition of oriented Pt and/or Au three-dimensional clusters. The (111) epitaxial and polycrystalline phases of the clusters were observed by RHEED. It was found that Pt deposition at 300°C leads to the formation of clusters and strong metal substrate interaction (SMSI). SMSI effect was indicated mainly by increasing intensity of the W4+ oxidation state in the W 4f photoelectron spectrum. The results evoked a hypothesis of the encapsulation of Pt clusters by tungsten oxide. On the other hand Au deposition did not influence chemical state of the substrate. Formation of Pt-Au clusters is a complex process which is determined by the thermodynamic characteristics of both metals as well as by the kinetics of the growth. The results have shown that the Pt and Au deposition leads to formation of bimetallic Pt-Au clusters having core-shell structure. The structural details of the clusters and their electronic properties depend on the order of deposited materials. It was found that if the Pt is deposited at first the Pt clusters serve as nucleation sites for the growth of Pt-Au clusters. Due to immiscibility of Pt and Au in this concentration range the core of the cluster is formed by Pt while Au atoms segregate on the surface and form the shell. Due to the lower mobility of Pt atoms than Au ones, in the case of pre-deposited Au layer the Pt-Au alloy clusters grow preferentially and the pure Pt clusters nucleate on the free tungsten oxide surface. Thus the clusters are composed of Pt-Au alloy core and shell enriched by Au due to the segregation of Au into the near surface region. These findings can explain physical and chemical properties of Pt/WOx, Au/WOx and Pt-Au/WOx catalysts and gas sensors.

27

Oxidative Steam Reforming Of Propanol On Bimetallic Ni-X (X = Pt, Ru, Ir) Catalysts L. Yermán 1, P. Ramírez de la Piscina 1, N. Homs 1,2 1

Departamento de Química Inorgánica e Institut de Nanociència i Nanotecnologia, C/ Martí i Franquès 1-11, Universitat de Barcelona, 08028 Barcelona, Spain.

2

Catalonia Institute for Energy Research (IREC) C/Jardins de les Dones de Negre 1, 08930 Barcelona, Spain. [email protected]

Hydrogen uptake (a.u.)

Biomass-derived resources can be considered as alternative feedstock for hydrogen and syngas production. In this context, propanol which can be produced via fermentation of sugary biomass *1+, can be considered because of its high energy density and low hygroscopic characteristics. Hydrogen production from propanol can be carried out by catalytic steam reforming process. However, an energetically favored process is the oxidative steam reforming (OSR) for which little research about effective catalysts has been done *2+. In this work, bimetallic Ni-X (7% Ni, ~0.2% X; X = Pt, Ru, Ir) catalysts with K as promoter (0.8% K), were prepared, characterized and tested in OSR of propanol under quasi neutral thermal conditions. Binary oxide system ZrO2-Y2O3 (YSZ) (10% w/w Y2O3) was used as support. Catalysts were characterized by B.E.T. surface-area, XRD, H2-chemisorption, Raman spectroscopy and temperature programmed reduction (TPR). Catalytic behaviour of fresh 581 620 (calcined) catalysts was analized at the temperature range of 723-773 K under a GSHV= 5000 h-1. Reactant feedstock was 559 597 Ni-Ru 612 adjusted to have O/C= 4 and S/C= 9.6 atomic ratios, and molar ratio O2/propanol= 0.7(thermo-neutral condition): 495 Ni-Pt 541

616

C3H8O + 0.7O2 + 3.6H2O  7.6H2 + 3CO2

636

Ni-Ir

The calcined (873 K) support, has specific B.E.T. area of 79 m2.g-1 Ni and XRD analysis indicated the solely presence of tetragonal 400 500 600 700 800 900 ZrO2 with crystallite size of 11 nm. XRD analysis of calcined Temperature (K) catalysts showed also the presence of NiO orthorombic phase with ca. 11 nm of crystallite size. Raman spectroscopy Figure 1. H2 uptake as function of confirmed the presence of stabilized tetragonal ZrO2 phase. temperature in TPR experiments for the Figure 1 shows TPR results of calcined catalysts. Hydrogen different catalysts. consumption maxima within the range of 495-636 K were observed, which are ascribed to the NiO reduction to metallic Ni. For bimetallic systems, hydrogen uptake profiles were displced to lower temperature than those encountered for the monometallic Ni catalyst. Thus indicating an intimate effect favouring the NiO reduction due to the presence of the noble metal. All catalysts were active in OSRP reaction, reaching almost total propanol conversion within the range of temperatures studied. Ni-Ir system gave over 90% of theoretically expected H2-selectivity. Catalyst were also characterized after reaction. References [1] C. R. Shen, J. C. Liao, Metabolic Eng. 2008, 10, 312. *2+ P. Ramírez de la Piscina, N. Homs, Chem. Soc. Rev. 2008, 37, 2459.

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Investigation of melting temperature of PdnCon (n=2-50) Nanoalloys Ali Kemal Garip* and Haydar Arslan* *

Zonguldak Karaelmas University, Department of Physics, 67100 Zonguldak, Turkey.

The energetic, structures, segregation and melting dynamics of PdnCon (n=2-50) nanoalloys have been studied using a genetic algorithm global optimization technique with the Gupta empirical potential. The melting dynamics of nanoalloys was studied by canonical molecular dynamics simulation. Single melting runs exhibit a sharp transition from cluster ground structures to the melt, while averaged results indicate that melting occurs in a size dependent temperature range. The melting temperatures of the Pd-Co nanoalloys increase monotonically with size up to 56 atoms. Then, they reach a plateau presenting almost a constant value about 700 K. We also investigated the radial distributions of atoms during the melting transition.

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Influence of Alloying Additions on Atomic Order of FeCo Nanoparticles: A Monte Carlo Study Muratahan Aykol, Amdulla O. Mekhrabov and M. Vedat Akdeniz Novel Alloys Design and Development Laboratory (NOVALAB), Department of Metallurgical and Materials Engineering, Middle East Technical University, 06531-Ankara, Turkey.

Atomic level ordering in magnetic nanoparticles affects the final magnetic properties significantly. Due to their excellent magnetic properties in bulk form, such nanoparticles of FeCo alloys have attracted great attention recently but there have been no studies on the extent of atomic level order induced in the final products. In this respect, with site-exchange Monte Carlo simulations, we investigated the effects various alloying element additions on B2-FeCo nanoparticles up to size of 5 nm, which are promising for utilization in applications such as drug delivery. It was found that alloying elements additions may have more drastic effects on induced order at room temperature or higher temperatures than varying the size of the nanoparticles.

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Amorphous Co-Mo Catalyst for Hydrogen Evolution Piotr R. Zabinski*, W. Gagatek, R. Kowalik AGH University of Science and Technology, Faculty of Non-Ferrous Metals, Al. Mickiewicza 30, 30-059 Krakow, Poland *[email protected]

Tailoring of active cobalt alloy cathodes for hydrogen evolution in hot concentrated sodium hydroxide solution was attempted by electrodeposition. Enhancement of cathodic activity of cobalt for electrolytic hydrogen evolution has been carried out by the formation of cobalt alloys containing molybdenum. The present work aims to prepare the Co-Mo alloys with high cathodic activity for hydrogen evolution by electrodepositing. Also we try to clarify the effect of the molybdenum addition in enhancing the high activity for hydrogen evolution and changes of electrodeposits morphology. The hydrogen evolution activity of the electrodes was examined in 8M NaOH solutions at 90oC by the galvanostatic polarization curves measurement. The structure of the deposited alloys was identified by XRD. According to X-ray diffraction patterns electrodeposited of Co-Mo alloys with high molybdenum content are nanocrystalline/amorphous. When the molybdenum contents in the deposit are low, the linear dependence between logarithms of current density and potential is observed (Tafel dependence). It suggests that the ratedetermining step was proton discharge on the cathode surface. The hydrogen evolution is mainly the same as for pure cobalt. If the alloys contain high molybdenum content and the surface is mostly amorphous alloy and the activity for hydrogen evolution is much higher. For those alloys we do not observed Tafel dependence. It means that proton discharging is so fast that rate-determining step seems to be desorption of hydrogen from the surface of the electrode after recombination of two discharged protons.

The authors express their acknowledgment for financial support under grant No. 3 T08B 016 29.

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CALPHAD type modeling of phase diagrams of nanomaterials, experimental preparation of nanoalloys Ales Kroupa1, R. Mishra2, A. Zemanova1, H. Ipser2 1

Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, 616 62 Brno, Czech Republic.

2

Institut für Anorganische Chemie/Materialchemie, Universität Wien, Währingerstr. 42, A-1090 Wien, Austria.

CALPHAD approach is a very useful technique for calculation of phase diagrams of bulk materials based on thermodynamic database containing data such as chemical potentials of pure substances and excess Gibbs energy of mixtures as a function of composition, temperature and pressure. In order to extend the use of CALPHAD approach to small metallic particles on sub-micron and nano scale, due to the surface effect, the chemical potentials and the excess Gibbs energy should be expressed with an additional parameter: the particle size. The preliminary calculations for Ag-X systems will be presented here and existing experimental data from literature will be used to verify the calculations. Together with the development of theoretical methods for the calculations of phase diagrams of nanomaterials, experimental synthesis of nanoalloys, allowing the verification of theoretical modeling. The synthesis of Sn-Sb-Ni alloys was carried out, preparing 10 different compositions. The morphology of powders and their properties were measured, using DSC, XRD, SEM, TEM and EDX.

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Oxidation induced void formation in aluminium-lithium thin films at room temperature David A. Tanner*,#, S. Belochapkine*, F. Laffir* and S. Nakahara*,& *

Materials & Surface Science Institute, #Department of Manufacturing and Operations Engineering, & Department of Physics, University of Limerick, Limerick, Ireland.

Oxidation phenomena involving thin films is of interest to the semiconductor industry, as integratedcircuit devices utilize a thin oxide layer as a high dielectric at the gate in order to achieve better dielectric materials. Development of an oxidation-induced void formation mechanism in thin films containing surface oxide layers will help develop better dielectric oxide materials. In a preliminary study, sputtered aluminium thin films have been analysed using Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). It has been observed that the presence of lithium in aluminium sputtered thin films leads to the formation of nanometre sized voids. The results indicate these voids form at room temperature as a result of the Kirkendall effect.

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Confinement effects in Au-Pd nanoalloy clusters and wires encapsulated in carbon nanotubes. M. Hou1, B. Zhu1, I. Atanasov1, Y. Wang1,2,3 1 2

3

Université Libre de Bruxelles CP 234, Bd du Triomphe, B-1050 Bruxelles, Belgium

Applied Ion Beam Physics Laboratory, Fudan University, Key Laboratory of the Ministry of Education, China

Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, Shanghai 200433, China

Equilibrium configurations of icosahedral Au-Pd nanoalloy clusters (AuPd55 and AuPd147) and of a 130 atoms AuPd nanowire segment are studied at 100K over the whole composition range from pure Pd to pure Au by Metropolis Monte Carlo importance sampling. The effect of size on phase stability, ordering and segregation states are compared between situations where these systems are free standing or encapsulated in carbon nanotubes (CNT). Two armchair CNTs,(12, 12) and (15, 15), provide suitable encapsulation spaces. An embedded atom model is used for intermetallic interactions, the Brenner potential for C-C interactions and Lenard Jones potentials for the metal-carbon interactions. Stable phases are identified in the icosahedral clusters corresponding to well-defined structural ordering. The nanowire segment displays no significant phase stability, although ordered Au-Pd arrangements could be identified. As an effect of the presence of interface between the CNT and the clusters, their thermodynamic stability is reduced and a cylindrical symmetric chemical ordering is induced for some stoichiometries. The CNTs are found to favour Pd surface segregation while Au segregation is found at the surface of the free standing systems. Temperature and size effects are briefly discussed.

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