Juan Andrés

Department of Physical and Analytical Chemistry, Universitat Jaume I, Spain & CMDMC, Sao Carlos, Brazil

andres@qfa.uji.es

Connecting theory with experiment:

A survey to understand the behaviour of multifunctional

metal oxides

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 chemistry and materials science, the precise

architectural manipulation of nanocrystals with well 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 University discusses how the two sides of physical chemistry have necessarily developed together, and looks at how their synergy dictates the direction of 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.

ExperimentRealWord Theory

Model of the Word

ExperimentalData

Simulation

ClassificationAbstraction

SimplificationApproximation Generalization

PredictionsComparing is testing

ApplyingTheoretical Methods,

Computing Techniquesand Mathematical

Algorithms

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)

Electronic Structure

NMR (density of states DOS)XANES, EXAFS (“oxidation states”, density of states)XPS, AES (“oxidation states” and hybridation effects)

EELS (density of states)

Crystal Structure and local structure

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

SEM (micro, submicroscale)TEM (nanoscale)

XRD (nanometer scale crystalites)

Composition of the bulk

WDSEDSXPSEELS

Composition at the nano-microscale

SEM-EDS (microscale, elemental mapping)TEM-EDS (nanoscale, STEM elemental mapping)

TEM-ELLS (nanoscale, STEM)Energy-filtered TEM (EFTEM)

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.

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 to understand and rationalize optical properties, and

(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.

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.

(i) Surface Structure and Growth Processes

Illustration to show how mass transport coupled with pronounced reorganization of atomic coordination environments is required in solid-state 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).

M. J. Rosseinsky, Angew. Chem. Int. Ed. 2008, 47, 8778.

METASTABLE COMPOUNDS

18

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.

CRYSTALLIZATION

Crystal grwoth

Self-assembly

Crystal grwoth

Intermediate crystal

Nucleation

Intermediate crystal Rise-like

CrystalFlower-like Crystal

Crystal grwoth

H. Cölfen and M. Antonietti, Angewandte Chemie International Edition, 2005, 44, 5576-5591.

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 self-assembly of primary nanoparticles covered with organics.

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)

Thermodynamic stability

1. At zero temperature Esurf can be derived from a slab calculations as follows:

Reliable theoretical determination of Esurf from first principles is of particular importance

AENEE SnObulk

Nslab

Nsurf 2/·lim 2

. 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)

. 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

AEExENEE Snbulk

Sbbulk

SnObulk

OSnSbNslab

Nsurf

xx 2/lim 221

2. For SbxSn1-xO2 doped systems Esurf is calculated as follows:

AsurfEB

surfE3. The formation of macroscopic facets B of orientation (h2k2l2), and energy

(per unit area) , on a surface A of orientation (h1k1l1), and energy

depends of the sign of the formation energy:

If DE < O, the growth of facets B on A is stable,

If DE > O, their formation is unstable

q is the angle between the planes, cosq takes into account the change in surface area if facets were formed

Thermodynamic stability

THEORETICAL FOUNDATION (3)

222111 cos lkhElkhEE Bsurf

Asurf Wulff equation

AsurfE B

surfE

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

Thermodynamic stability

THEORETICAL FOUNDATION (4)

Wulff construction

Anatase (TiO2) (a) calculated, (b) Crystal sampleRutile (TiO2)

(010)

(101) _

[101]

Nanoribbon with rectangular cross section

Wide facet

Narrow facet

Growth direction

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

(a) HRTEM image perpendicular to

the (101) face of a SnO2 nanobelt

(010)

(101)

_

[101]

Wide facet

Narrow facet

Growth direction

(101)

(a) Proposed model for the SnO2 nanobelts _

[8] A. Beltrán, J. Andrés, E. Longo, E. R. Leite, Appl. Phys. Lett. 83, 635, 2003

Single-Crystalline SnO2 Nanorods

[9] E. T. Samulski et al. J. Am. Chem. Soc., 126 (19), 5972 -5973, 2004

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]

Wulff construction

Calculated surface energies and derived Wulff construction for pure SnO2 (rutile)

3.00 172.4

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.

HRTEM Image Simulation for (001) Faceting

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.

Predicted oriented attachment configurations for the modeled ATO nanocrystal for (a) (100), (b) (001), (c) (101), and (d) (110) facets.

Oriented attachment evaluation

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 to understand and rationalize optical properties

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

Valence band

Conduction band

Continuum

Trap statemanifold

Eg

ElectronicExcited States

ABO3 Structure

Clusters [BO6] and [AO12]

The ideal ABO3 perovskite structure

Perovskite Based Materials

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 short-range order or the periodicity inherent to crystalline materials.

Depictions of TiO6 octahedra in the (a) cubic (b) tetragonal (c) orthorombic and (d) rhombohedral structures. Ti displacements have been exaggerated for clarity.

Probing Local Dipoles and Ligand Structure in BaTiO3 NanoparticlesK. Page, T. Proffen, M. Niederberger, R. SeshadriChem. Mater. 2010, 22, 4386

We exemplify the potential of this concept

in the optical properties

(photoluminescence and

radioluminescence) of perovskite and

scheelite based materials.

[TiO6]

[SrO12]

s → 261 cm-1 en las 3D

Cubic to tetragonal

t* → 365 cm-1

s* → 336 cm-1 en cSr

Ti

O

TiO2 Anatase

Eg 169 101 R

Eg 206 237 R

Eu 286 201 IR

A2u 394 362 IR

B1g 408 379 R

Eu 445 391 IR

B1g 530 503 R

B2u 566 542 IR

A1g 639 627 R

Eg 656 577 R

Normal vibrational modes in cm-1

s s*

s s*

a 3.7991 3.9182

c 9.6929 9.7226

u 0.2057 0.2065

dTi-O 1.947(4) 2.004(4)

1.994(2) 2.008(2)

Structural data

ab

c

ab

c

b

c

a b

c

a ab

c

ab

c

(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

off-diagonal 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; OxfordUniversity 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

Growth of Ag nanofilaments

FESEM images

100 ºC

120 ºC

Electron beam radiation guides the growth process of Ag nanofilaments on a-Ag2WO4

-Ag2WO4

Ag5

Ag4

Ag6

Ag3

Ag1

Ag2

W1

W2

W3

Ag1Ag2

Ag3

Ag4Ag5

Ag6

W1W2W3

Cluster[AgO7] Distorted Triangular Prismatic

[AgO6 ] Distorted Octahedra

[AgO4 ] Distorted Tetrahedra

[AgO2 ] Twofold

[WO6 ] Distorted Octahedra

ac

b

Distance range (Å)

Ag1Ag2

Ag3

Ag4Ag5

Ag6

W1W2W3

Cluster

[AgO7] Distorted Triangular Prismatic

[AgO6 ] Distorted Octahedra

[AgO4 ] Distorted Tetrahedra

[AgO2 ] Twofold

[WO6 ] Distorted Octahedra

VASP(PBE+U)

2.33 - 3.042.34 - 3.042.28 - 2.582.23 - 2.442.23 - 2.442.141.83 - 2.111.80 - 2.231.80 - 2.23

N = 0 N = 10

NANODOMAINSPlane (100)

Ag5

Ag4

Ag6

Ag5

Ag4

W3

W2

179.77o

168.46o

170.47o

108.44o

107.43o

Ag6

Ag5

Ag4

W3

W2

Ag5

Ag4

179.02o

178.21o

175.38o

91.77o

90.26o

1.2 a.u.

0.0 a. u.

Charge Density

N = 0 N = 10

Ag5

Ag4Ag6

Ag4Ag5

Ag6

Cluster

[AgO4 ] Distorted Tetrahedra

[AgO2 ] Twofold

Ag5

Ag4

Plane (100)

Isodensity lines < 0.02 a. u. are coloured in whiteIsodensity lines > 0.02 a. u. are coloured in black

Ag6

W3

W2

W3

W2

2.4

2.6

2.8

0 1 2 3 4 5 6 7 8

[WO6] (W1)

-0.2

0

0.2

0.4

0.6

0.8

0 1 2 3 4 5 6 7 8 9 10

[AgO4] (Ag4/Ag5)

[AgO2] (Ag6)

Bader population analysis

Number of electrons

Atom

ic c

harg

e, q

()

q () = Z - N (()

N () = () dr

Silver is reduced!!!!!

Tungsten

Silver

0 1 2 3 4 5 6 7 8 9 101.8

1.9

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

[AgO2] x2

[AgO4] x2

[AgO4] x2

[WO6] x3

[WO6] x1

[WO6] x2

Number of electrons

dist

ance

Ag-

O/ W

-O (

Å)

~ ~

AIM analysis

BCP = Ag-O bond critical point

Laplacian 2b

Bond Density b

  BCP [AgO2]     BCP [AgO4]    

  Ag-O     Ag-O1   Ag-O2  

N e 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.

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 statesv) Photocatalytic, degradation, and antimicrobacterial proceses

Better coupling of design and process engineering

S t a t u s a n d m o v i n g f o r w a r d

SynthesisTesting

Characterization

Experiments, models

Theory

An integrated approach:

P r o m o t i n g D e v e l o p m en t

‘‘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 together theory, simulations, and experiments

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 LeiteDr. 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, andDr. 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.

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

Dedico, sinceramente, esta apresentação ao amigo e Professor Elson Longo.

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.

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.

Dedicatoria