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Connecting theory with experiment: A survey to understand the behaviour of multifunctional metal oxides.
 

Connecting theory with experiment: A survey to understand the behaviour of multifunctional metal oxides.

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Palestra plenária do XII Encontro da SBPMat (Campos do Jordão, setembro/outubro de 2013). Palestrante: Juan Andrés - Universitat Jaume I ( Espanha).

Palestra plenária do XII Encontro da SBPMat (Campos do Jordão, setembro/outubro de 2013). Palestrante: Juan Andrés - Universitat Jaume I ( Espanha).

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    Connecting theory with experiment: A survey to understand the behaviour of multifunctional metal oxides. Connecting theory with experiment: A survey to understand the behaviour of multifunctional metal oxides. Presentation Transcript

    • Connecting theory with experiment: A survey to understand the behaviour of multifunctional metal oxides Juan Andrés Department of Physical and Analytical Chemistry, Universitat Jaume I, Spain & CMDMC, Sao Carlos, Brazil andres@qfa.uji.es
    • Despite the significant attention and numerous works devoted to nano-sized materials, the physics and chemistry driving their properties are sometimes not adequately explored. Hence, understanding and controlling the properties of nanoscale materials continue to be significant challenges to the scientific community. This is where theory and simulation come in to play.
    • The future of nanotechnology rests upon approaches to making new, useful nanomaterials and testing them in complex systems.
    • The rapid increase is based on three pillars: a) In modern architectural chemistry manipulation and of materials science, nanocrystals with the well precise defined morphologies and accurately tunable sizes remains a research focus and a challenging issue because it is well-known that the properties of the materials are closely interrelated with geometrical factors such as shape, dimensionality, and size. New preparation and growth methods allow one to obtain nanomaterials in a controlled way.
    • b) By observing the microscopic structures of nanocrystals, insight into growth mechanism may provide means to control nucleation, one of the most secretive processes in nanoscience and nanotechnology. Advanced spectroscopies and microscopies guarantee a characterization of nanomaterials at the atomic scale.
    • c) Electronic structure theory has shown great value, not only in the interpretation of experiments, but also in the prediction of new properties and in the design of new devices.
    • Mark A. Johnson at Yale two sides of physical developed together, and dictates the direction of University discusses how the chemistry have necessarily looks at how their synergy contemporary research. Equations such as Schrödinger‟s famous contribution to quantum mechanics underpin much of physical chemistry. Nature Chemistry, 1, 8 (2009)
    • No single experiment reveals every detail and no calculation is perfect, but the combination provides the most profound and detailed insights to understand and rationalize chemical/physical properties and how we can control their finest details.
    • Theory Theoretical simulations of systems that represent nanomaterials constitute one of the main tools in the research for new nanomaterials. Theory plays a role in the three stages of the development ladder: characterisation, understanding and prediction. Due to the complexity of the computational methods, there is a strong need to integrate different models and cover the relevant scales. This requirement constitutes an important drawback as scientists need training in several aspects of the problem including chemical, physical and engineering views of the modelling while keeping the experimental and industrial interests and needs in perspective.
    • Experiment Real Word Classification Abstraction Simplification Approximation Generalization Experimental Data Theory Applying Theoretical Methods, Computing Techniques and Mathematical Algorithms Comparing is testing Model of the Word Simulation Predictions
    • Most suited techniques for the characterization of the electronic structure, crystal and local structures, morphology, and composition of materials both at the macroscale and at the nano/microscale. The most important contribution of DFT calculations to the interpretation of the different techniques is also shown. Electronic Structure Crystal Structure and local structure NMR (density of states DOS) XANES, EXAFS (“oxidation states”, density of states) XPS, AES (“oxidation states” and hybridation effects) EELS (density of states) NMR (local probe) EXAFS (local probe) EELS (DOS signature) XRD, neutron diffraction High-resolution TEM DFT contributions NMR (chemical shifts, simulated NMR spectra, density of states) XANES, EXAFS (density of state) XPS(density of state, electron density maps) EELS (density of state, simulated ELNES) NMR (chemical shifts, simulated NMR spectra) DFT (structure optimization, electron density maps) EELS (DOS signature) Morphology at the nano-microscale Composition of the bulk Composition at the nano-microscale SEM (micro, submicroscale) TEM (nanoscale) XRD (nanometer scale crystalites) WDS EDS XPS EELS SEM-EDS (microscale, elemental mapping) TEM-EDS (nanoscale, STEM elemental mapping) TEM-ELLS (nanoscale, STEM) Energy-filtered TEM (EFTEM) XPS (X-ray Photoelectron Spectroscopy, AES (Auger Electron Spectroscopy, XANES/ EXAFS (X-ray Absorption Spectroscopy), EELS (Electron Energy Loss Spectroscopy), NMR (Nuclear Magnetic Resonance), EDS (energy-dispersive X-ray spectroscopy) WDS (wavelength-dispersive X-ray spectroscopy) STEM (scanning transmission electron microscope), DFT (Density Functional Theory)
    • Here, we outline different published papers as well our work who have propelled the field of Nanoscience and Nanotechnology, and then I glimpse into their childhood years to see if there lays the key. We restrict ourselves to methods that are firmly based on quantum mechanics and it presents a subjective account of the research conducted as collaboration between CMDMC/INCTMN at Federal University of Sao Carlos (Brazil) and our Laboratory at UJI (Spain).
    • This talk examined three main areas: (i) Surface structure as the key to manipulating the physical and chemical properties as well as growth mechanisms of nanomaterials. (ii) Characterization of electronic excited states understand and rationalize optical properties, and to (iii) Calculation of three dimensional electron density distribution in materials, as an observable property, determining in whole or in part their physical/chemical properties.
    • (i) Surface Structure and Growth Processes Investigation on nanocrystals growth is a rich field of research that impacts on fundamental as well as applied science because the importance of controlling nanostructural sizes and morphologies which affects directly on the functional applications. By observing the microscopic structures of nanocrystals, insight into growth mechanism may provide means to control nucleation, one of the most secretive processes in nanoscience and nanotechnology.
    • (i) Surface Structure and Growth Processes As size of materials drops to nanometer size range, interface/volume ratio increases, and , a greater proportion of the atoms exist at the surface, increasing the ratio of undercoordinated atoms ratio of unsatisfied surface bonds relative to the bulk. There is significant fraction of atoms associated with the imperfection of the coordination numbers at the surface, which induces their properties differently from their bulk counterpart because of size effects. As Wolfgang Pauli once famously said: ‘‘God made the bulk; surfaces were invented by the devil’’.
    • (i) Surface Structure and Growth Processes Challenges Accurate surface energy data are essential for calculating and predicting the thermodynamic stability of nanosized structures. From the perspective of thermodynamics, the growth of nanostructures and the eventual morphology are driven by the minimization of total free energies, which normally include surface energy, elastic energy, electrostatic energy and so on. Among them, anisotropic surface energy and high growth speed along particular directions are often believed to underpin the growth process.
    • METASTABLE COMPOUNDS Illustration to show how mass transport coupled with pronounced reorganization of atomic coordination environments is required in solidstate reactions forming new crystalline extended structures from solid precursor phases. In this case, the two phases BaO and TiO2 react to form the ternary oxide BaTiO3, which forms at the interface between two reacting oxide particles; the particles are represented as cuboids (BaO purple, TiO2 lilac, BaTiO3 green). 18 M. J. Rosseinsky, Angew. Chem. Int. Ed. 2008, 47, 8778.
    • CRYSTALLIZATION How do crystals nucleate? According to classical nucleation theory, calcium carbonate nucleation proceeds by addition of ions to a single cluster (top). Gebauer et al. now suggest a different mechanism, in which nucleation of ACC occurs by aggregation of stable, amorphous, precritical clusters (bottom). The nucleated ACC phase subsequently crystallizes to generate the final stable crystal product. F. C. Meldrum, R. P. Sear, Science 2008, 322, 1802.
    • Self-assembly Nucleation Crystal grwoth Intermediate crystal Rise-like Crystal Crystal grwoth Intermediate crystal Flower-like Crystal Crystal grwoth
    • Mesocrystals Schematic representation of classical and non-classical crystallization. (a) Classical crystallization pathway, (b) oriented attachment of primary nanoparticles forming an iso-oriented crystal upon fusing, (c) mesocrystal formation via selfassembly of primary nanoparticles covered with organics. H. Cölfen and M. Antonietti, Angewandte Chemie International Edition, 2005, 44, 5576-5591.
    • A. Menzel et al., J. Phys. Chem. Letters, 3, 2815 (2012)
    • JACS, DOI 10-1021/ja202184wl
    • CuO
    • 26
    • Defining Rules for the Shape Evolution of Nanomaterials The morphology, shape and exposed facets of materials have been shown to have a significant influence on their functional properties. The understanding of the growth mechanism of nanoparticles is very important for technological application, indeed growth control might result in shape control, which is necessary to obtain reproducible results. The morphology, shape and exposed facets of materials have been shown to have a significant influence on their functional properties. Therefore the controlled synthesis of nanomaterial morphology and structure (nanomorphology) is of vital importance. Nanomorphology
    • Thermodynamic stability of the different surfaces is associated to the surface energy of the crystallographic orientations Surface energy, Esurf It is experimentally not trivial to determine Esurf !!!
    • THEORETICAL FOUNDATION (1) Reliable theoretical determination of Esurf from first principles is of particular importance Thermodynamic stability 1. At zero temperature Esurf can be derived from a slab calculations as follow Esurf N lim Eslab N SnO N·Ebulk 2 / 2 A . Ebulk is the bulk cohesive energy per SnO2 unit formula . Eslab is the total energy of a slab composed of N SnO2 units . A is the area of surface unit cell . the ½ factor comes from the fact that each slab has two surfaces
    • THEORETICAL FOUNDATION (2) 2. For SbxSn1-xO2 doped systems Esurf is calculated as follows: Esurf N lim EslabSbx Sn1 xO2 N SnO N Ebulk 2 Sb x Ebulk Sn Ebulk / 2A . Ebulk is the bulk cohesive energy per SnO2, Sb or Sn unit formula . Eslab is the total energy of the slab . N is the number of SbxSn1-xO2 units . N·x is the number of Sn atoms substituted by Sb
    • THEORETICAL FOUNDATION (3) Thermodynamic stability 3. The formation of macroscopic facets B of orientation (h2k2l2), and energy (per unit area) B B A Esurf , on a surface A of orientation (h1k1l1), and energy Esurf EA surf depends of the sign of the formation energy: E A Esurf h1k1l1 cos B Esurf h2k2l2 is the angle between the planes, cos surface area if facets were formed Wulff equation takes into account the change in If E < O, the growth of facets B on A is stable, If E > O, their formation is unstable
    • THEORETICAL FOUNDATION (4) Thermodynamic stability 4. According to the Wulff equation, the crystalline morphology can be predicted from the surface energy of different faces. Thus, the crystalline form can be derived from a construction in which the distance between a facet and an arbitrary point is proportional to the surface energy of the respective crystallographic plane Wulff construction Rutile (TiO2) Anatase (TiO2) (a) calculated, (b) Crystal sample
    • Nanoribbon with rectangular cross section Narrow facet (010) Wide facet _ (101) Growth direction [101]
    • The high-resolution transmission electron microscopy, HRTEM, allows the investigation of the nanomaterials‟ microstructures. The calculation of surface energies, Wulff construction and HRTEM images, allowed us to modelize the preferential growth directions ofSnO2 nanobelts (010) Narrow facet (101) Growth direction _ (101) [101] Wide facet (a) HRTEM image perpendicular to _ the (101) face of a SnO2 nanobelt [8] A. (a) Proposed model for the SnO2 nanobelts Beltrán, J. Andrés, E. Longo, E. R. Leite, Appl. Phys. Lett. 83, 635, 2003
    • In our calculations the order of increasing energy is:, (110) < (100) < (101) < (001). Since the (110) and (001) surfaces have the lowest and the highest surface energies, respectively, and the [001] direction is the favored growth direction and should result in particles with a high aspect ratio. The experimental findings[9] for SnO2 nanorods agree very well with our calculations, i.e., the single-crystalline nanorods show a mean aspect ratio of ~ 4:1 with the [001] direction along the major axis. [001] [110] Single-Crystalline SnO2 Nanorods [9] E. T. Samulski et al. J. Am. Chem. Soc., 126 (19), 5972 -5973, 2004
    • Wulff construction 3.00 172.4 Calculated surface energies and derived Wulff construction for pure SnO2 (rutile)
    • HRTEM Image Simulation for (001) Faceting Atomic arrangement of ATO nanocrystals with different (001) faceting and their respective simulated HRTEM images along the [111] zone axis. These results show that the contrast at the edges of the HRTEM simulated images is strongly dependent on the (001) facets dimension.
    • Proposed and actual ATO nanocrystals observed along the [111] zone axis. a) proposed ATO nanocrystal habit superimposed on its Wulff construction. b) Multislice simulated HRTEM image obtained from the proposed nanocrystal habit. c) Comparison of the nanocrystal multislice simulated HRTEM nanocrystal image and d) the experimental HRTEM image.
    • Oriented attachment evaluation Predicted oriented attachment configurations for the modeled ATO nanocrystal for (a) (100), (b) (001), (c) (101), and (d) (110) facets.
    • Figure 3. FEG-SEM micrographs of PbMoO4 micro-octahedrons processed by hydrothermal method at 100oC/10 min (a, b) PMO/ACC and (c,d) PMO/PVP.
    • Figure 4. Schematic representation of the synthesis and growth mechanism for PbMoO4 crystals by FEG-SEM (a) without surfactant, (b) with acetylacetone (ACC) and (c) polyvinylpyrrolidone (PVP).
    •  Schematic process of CTO Microwave-Assisted Hydrothermal sinthesis.
    • Fig. 5 FE-SEM images and schematic model to illustrate the synthesis and assembly of STO as cubes.
    • Characterization of electronic excited states understand and rationalize optical properties to
    • Nanoparticles in Retrospect Helmut Goesmann and Claus Feldmann Angew. Chem. Int. Ed. 2010, 49, 1362 – 1395
    • C. Feldmann, Nanoscale, DOI: 10.1039.clnr90008k
    • J. Phys. Chem. C 2012, 116, 11849-11851
    • Continuum Conduction band Eg Valence band Trap state manifold Electronic Excited States
    • ABO3 Structure Clusters [BO6] and [AO12]
    • Perovskite Based Materials The ideal ABO3 perovskite structure
    • While the concept of a crystalline solid as a perfect, periodic structure is at the core of our understanding of a wide range of material properties, disorder is in reality ubiquitous, and is capable of influencing various properties drastically. Our understanding of the atomic structure of materials relies on our ability to describe structural characteristics such as the shortrange order or the periodicity inherent to crystalline materials.
    • Probing Local Dipoles and Ligand Structure in BaTiO3 Nanoparticles K. Page, T. Proffen, M. Niederberger, R. Seshadri Chem. Mater. 2010, 22, 4386 Depictions of TiO6 octahedra in the (a) cubic (b) tetragonal (c) orthorombic and (d) rhombohedral structures. Ti displacements have been exaggerated for clarity.
    • We exemplify the potential of this concept in the optical properties (photoluminescence and radioluminescence) of perovskite and scheelite based materials.
    • [SrO12] [TiO6]
    • Cubic to tetragonal s → 261 cm-1 en las 3D t* → 365 cm-1 Sr Ti O s* → 336 cm-1 en c
    • TiO2 Anatase Normal vibrational modes in cm-1 s Eg 169 101 R Eg 206 237 R Eu 286 201 IR A2u 394 362 IR B1g c s* 408 379 R Eu 445 391 IR c b b a a b Structural data s s* a 3.7991 3.9182 B1g 530 503 R c 9.6929 9.7226 B2u 566 542 IR u 0.2057 0.2065 A1g 639 627 R 1.947(4) 2.004(4) Eg 656 577 R 1.994(2) 2.008(2) dTi-O
    • (iii) Calculation of three dimensional electron density distribution in materials, as an observable property, determining in whole or in part their physical/chemical properties. The electron density distribution in a system determines its stability, geometry, physical/chemical properties and reactivity, in short its chemistry.
    • Theory Charge density [ (x,y,z)] defines the structure and chemical and physical properties of the compound
    • We need a little history “Chemistry is a consequence of the short-range nature of the one-electron density matrix that determines all the mechanical properties of an atom in a molecule with the additional important proviso that all of the necessary physical information is obtained in its expansion up to second-order with regard to both the diagonal and offdiagonal terms” . R. F. W. Bader, Atoms in molecules: a quantum theory, Oxford University Press, Oxford UK 1990. R. F. W. Bader, Int. J. Quantum Chem. 1995, 56 409–419.
    • The electron density, ρ(r), is a fundamental Dirac observable that defines completely the ground state of an electronic system. Hohenberg, P.; Kohn, W. Phys. Rev. 1964, 136, B864–B871. In this regard, an experimental or theoretically determined charge density yields a wealth of information about the electronic structure of atoms, molecules, and solids. Koritsanszky, T. S.;Coppens, P. Chem. Rev. 2001, 101, 1583–1628. Coppens, P. “The interaction between theory and experiment in charge density analysis” Phys. Scr. 87, 2013, 048104
    • Experiment and Theory (r) Retrieving all information from quantum mechanical wave function
    • Bader’s Quantum Theory of Atoms in Molecules (QTAIM), in which he put the main emphasis on the charge distribution ρ(r), represents one of the pioneering efforts of this new school of thought.
    • In particular, the topological analysis of ρ(r) has enabled the development of a theory of molecular structure, which has proven useful in the study of a diverse range of chemical phenomena. Bader, R. F. W. Atoms in molecules: A Quantum Theory; Oxford University Press: Oxford, UK, 1990.
    • QTAIM goes far beyond a simple topological study of a scalar field. It rather provides a full consistent quantum mechanical framework for the definition of the atoms or group of atoms in a molecule or crystal and for the treatment of the mechanics of their interaction. C. Gatti in “Challenging chemical concepts through charge density of molecules and crystals” Phys. Scr. 2013, 87, 048102
    • A bridge for fertile research Topological analysis of ρ(r) provides a mathematical bridge between quantum mechanics and chemistry/physics. Thanks to this machinery, it is possible to correlate topological properties of ρ(r) with elements of molecular structure (atoms and bonds), making quantum chemistry concepts compatible with traditional chemical/physical ideas.
    • Nature Scientific Reports, 3, 1676-1680 (2013).
    • Here we focus primarily on two main aspects: structural and electronic properties in order to answer three central questions: What happens with the electron excess as it approaches the surface and bulk of –Ag2WO4? How are the electrons distributed in this material and how can it is related with the structural and electronic evolution? Can QTAIM properties tell us anything about the strength of the bonds after electron irradiation on –Ag2WO4? Specifically, we have studied the geometric and electronic structure of – Ag2WO4, and then we have derived a mechanism produced in the scenario of electron irradiation of AgOx (x= 2, 4, 6, and 7) and WO6 clusters, as constituent polyhedra of –Ag2WO4, relevant to formation and growth of Ag filaments.
    • An electron beam of high energy electrons generated within transmission electron microscopy (TEM) is employed to obtain high-resolution imaging, as well as to observe and confirm elemental and crystal structure on single nanoparticles. However, it is well known that electron beam causes considerable changes in the physical and chemical properties, and lead to the formation of unexpected and very exciting structures in nanoscale materials.
    • e- irradiation 100 ºC Growth of Ag nanofilaments 120 ºC FESEM images Electron beam radiation guides the growth process of Ag nanofilaments on -Ag2WO4
    • -Ag2WO4 Ag 3 Ag4 Ag1 Ag2 W1 W3 [AgO6 ] Distorted Octahedra Ag4 Ag5 W2 Ag1 [AgO7] Distorted Triangular Prismatic Ag3 Ag2 Ag6 Ag5 Cluster [AgO4 ] Distorted Tetrahedra Ag6 [AgO2 ] Twofold W1 W2 W3 [WO6 ] Distorted Octahedra b c a
    • Distance range (Å) VASP (PBE+U) 2.33 - 3.04 2.34 - 3.04 2.28 - 2.58 2.23 - 2.44 2.23 - 2.44 2.14 1.83 - 2.11 1.80 - 2.23 1.80 - 2.23 Ag1 Ag2 Ag3 Ag4 Ag5 Ag6 W1 W2 W3 Cluster [AgO7] Distorted Triangular Prismatic [AgO6 ] Distorted Octahedra [AgO4 ] Distorted Tetrahedra [AgO2 ] Twofold [WO6 ] Distorted Octahedra
    • Plane (100) NANODOMAINS N=0 N = 10 W3 W3 108.44o 91.77o Ag4 Ag4 168.46o 170.47o Ag6 Ag4 178.21o 179.77o Ag5 175.38o Ag6 179.02o Ag5 Ag5 107.43o 90.26o W2 W2 Ag4 Ag5
    • Plane (100) Charge Density N=0 N = 10 W3 W3 1.2 a.u. Cluster Ag4 Ag5 [AgO4 ] Distorted Tetrahedra Ag4 Ag4 Ag6 Ag6 Ag5 Ag5 0.0 a. u. W2 W2 Isodensity lines < 0.02 a. u. are coloured in white Isodensity lines > 0.02 a. u. are coloured in black Ag6 [AgO2 ] Twofold
    • Bader population analysis q ( ) = Z - N (( ) [WO6] (W1) 2.8 Atomic charge, q ( ) 2.6 N( )= ( ) dr Tungsten 0.8 2.4 0 1 2 0.6 3 4 5 6 7 8 Silver 0.4 0.2 [AgO4] (Ag4/Ag5) 0 Silver is reduced!!!!! [AgO2] (Ag6) -0.2 0 1 2 3 4 5 6 Number of electrons 7 8 9 10
    • ~~ 2.9 2.8 distance Ag-O/ W-O (Å) 2.7 2.6 [AgO2] x2 2.5 [AgO4] x2 [AgO4] x2 2.4 [WO6] x3 2.3 [WO6] x1 [WO6] x2 2.2 2.1 2 1.9 1.8 0 1 2 3 4 5 6 Number of electrons 7 8 9 10
    • AIM analysis Laplacian BCP = Ag-O bond critical point 2 Bond Density BCP [AgO2] Ag-O1 b BCP [AgO4] Ag-O b Ag-O2 Ne Density Laplacian Density Laplacian Density Laplacian 0 0.49 6.80 0.26 3.29 0.42 4.91 1 0.42 4.56 0.23 2.93 0.39 4.35 2 0.34 3.88 0.21 2.67 0.35 3.86 3 0.26 3.10 0.20 2.56 0.28 3.10 4 0.20 2.26 0.19 2.35 0.22 2.56 5 0.17 1.84 0.16 1.96 0.19 2.17 6 0.17 1.76 0.15 1.83 0.19 2.08 7 0.16 1.71 0.13 1.65 0.19 2.12 8 0.14 1.55 0.12 1.39 0.17 1.80 9 0.14 1.47 0.10 1.23 0.17 1.76 10 0.13 1.40 0.10 1.14 0.16 1.51
    • The Ag formation on –Ag2WO4 is a result of the order/disorder effects generated in the crystal when electron irradiation provokes a structural and electronic rearrangement within it. Both experimental and theoretical results point out that this patterning was due to structural and electronic changes of the AgO2 and AgO4 clusters and in minor extent one WO6 cluster, as constituent building blocks of –Ag2WO4.
    • S t a t u s a n d m o v i n g f o r w a r d More basic understanding–theory-simulation-experiment Key role of quantum mechanics; Recent advances of quantum chemistry show the applicability of quantum chemical theory in Nanotechnology. Integration of the conceptual framework for understanding: i) Structure, physical/chemical properties and chemical reactivity ii) Heterogeneous, homogeneous and enzyme catalysis iii) Size and shape dependent properties at nanoscale iv) Fundamental and excited electronic states v) Photocatalytic, degradation, and antimicrobacterial proceses Better coupling of design and process engineering
    • P r o m o t i n g D e v e l o p m en t An integrated approach: Experiments, models Synthesis Testing Characterization Theory
    • „„The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them‟‟ William Henry Bragg “We can't solve problems by using the same kind of thinking we used when we created them.” Albert Einstein
    • In this presentation, some of the critical challenges for the field of Nanotechnology and Nanoscience are discussed. Three main guides are fundamental in our research: (a) Instigating creativity, innovation, and questioning scientific assumptions (b) Instigating interdisciplinary research (c) Bringing experiments together theory, simulations, and
    • A broad team is necessary to probe this type of physics and chemisty. It takes a high level of expertise in materials, measurement, characterization, theory, simulation, and calculation that is not often found at one institution. It is the depth of talent at CMDCM and ability to easily work with researchers in other areas that made these achievements possible. The resulting cross-fertilisation between disciplines has already yielded an awesome cornucopia of multitasking devices, and no doubt the best is yet to come.
    • Acknowledgments Prof. Jose A. Varela, Prof. Elson Longo, Prof. Edson Leite Dr. Mario Moreira, Dr. Valeria Longo, Dr. Diogo Volanti, Dr. Laecio Cavalcante, Dr. Marcelo Orlandi, Dr. W. Awansi, Dr. Y. Santana, Felipe Laporta, Amanda Gouveia, Matheus Ferrer (CMDCM, Sao Carlos and Araraquara, Brazil) Prof. Armando Beltrán, Dr. Lourdes Gracia, Dr. Silvia Ferrer, and Dr. Patricio Gónzalez-Navarrete, (Universitat Jaume I. Castelló. Spain) Dr. Valmor R. Mastelaro and Dr. Luis F. da Silva (Sao Carlos) Dr. Mauricio Bomio (Natal) Dr. Fabricio Sensato (Sao Paulo) Dr. Daniel Stroppa and Dr. Antonio Ramirez (Campinas) Dr. Julio Sambrano (Bauru) 90
    • Acknowledgments Brazilian agencies Fapesp and CNPq by the financial support. 91
    • Acknowledgments Spanish research funds provided by Ministerio de Economia y Competitividad of the Spanish Government, Generalitat Valenciana (Prometeo Project), and Programa de Cooperación Científica con Iberoamerica 92
    • Newton‟s remark that we are “dwarfs in the shoulders of giants” is as valid as ever, and Prof. Elson Longo was certainly one of those giants.
    • Dedicatoria Dedico, sinceramente, esta apresentação amigo e Professor Elson Longo. ao Tive o grande prazer de conhecê-lo em 1988 e deste então nossa amizade tem-se intensificado ao longo dos anos. Poucas pessoas irradiam entusiasmo e confiança como ele. Uma pessoa com primorosa experiência de vida – pessoal e profissional. Trata-se de um homem com uma lucidez e generosidade inusuais, extraordinariamente amável, aguerrido e rigoroso cientificamente. Uma bela pessoa e um grande pesquisador, que tem uma visão privilegiada das relações interpessoais, dos processos de ensino-aprendizagem e da inovação tecno-científica.
    • Dedicatoria De suas experiências, aprendi que os países não son suas bandeiras, hinos ou línguas, mas sim lugares e pessoas que povoam nossas recordações e nos enebria de nostalgia, que nos confere a fraternal sensação que teremos sempre um lugar aconchegante ao qual sempre podemos retornar.