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Overview

Overview. Advanced materials science. Session. MAP-FIS conference. Presentations. Multiferroic materials Magnetocaloric Nanowires/nanotubes (magnetic, for photoelectrochemical water splitting) Quantum dots Preparation techniques: Templated growth Electodeposition Others

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Overview

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  1. Overview Advanced materials science Session MAP-FIS conference

  2. Presentations • Multiferroic materials • Magnetocaloric • Nanowires/nanotubes (magnetic, for photoelectrochemical water splitting) • Quantum dots • Preparation techniques: • Templated growth • Electodeposition • Others • Applications

  3. Nanowires/Nanofibres/Nanotubes • Wide range of application: • - Sensors, nanodevices, magnetic storage • - Tissue engineering • - Biodevices and systems, nanomedicine • Fundamental studies of cell biology • (role of cell nanostructures in guiding cell behavior) • Optics (e.g., metamaterials)

  4. Top-down • Top-down • Litography • e.g., focused ion-beam miling (FIB) • e.g., electron-beam direct writing FIB EBDW

  5. Self-assembled porous templates Porous Al2O3 template • Porous templates: • self-organized pores • Block copolymers • Anodic Aluminum oxide (Al2O3) • Porous alumina (anodic aluminum oxide) templates: • controllable pore diameter • narrow pore size distribution • self-ordered honeycomb lattice of nanopores after a two-step anodization process • Pore diameters of 11 nm and periods of 40 nm (or more) have been achieved • Electrodeposition • - DC or pulsed (smaller particles) • - Able to coat non-flat surfaces J. Vac. Sci. Technol. B Chem. Mater. Polycyclohexylethylene (PCHE) diblock co-polymer template

  6. Electrophoretic Deposition • Suspension of charged particles • Electric field applied to electrodes • Particles are deposited on the substates • Controled particle sizes. They can be very small (~30 nm or less) 25V 20mm p-Si(001) Si/SiO2/TiO2/Pt • Functional thin films • Can be applied with different materials and combinations of materials • Able to form films on a wide range of shapes and 3D complex and porous structures • It is able to be scaled-up to large volumes and sizes

  7. Nanocontacts Pt nanowires • Pt nanocontacts for nanocapacitors • Electrochemically deposited BaTiO3 Lower electrode 0.2 m Science

  8. Nanocapacitors PZT nanocapacitors Nano-capacitors for integrated electronics M. Alexe, et al, Advanced Materials film-type (with top nanocontacts) island-type

  9. Nanowires - Biomimetic • Biomimetic cilia • Sensing sound (acoustic) • Fluid flow Journal of Bionic Engineering Silicon-nitride suspending membranes with polymer cilia on top Electrodes on membrane and substrate form a variable capacitor for readout

  10. Nanowires - Magnetic • Magnetic nanowires • Patterned arrays • Information storage (high density) • Biological applications (e.g., magnetic carrier to manipulate functionalized particles in suspensions) • Magneto-optical • High-aspect ratio wires through anodic aluminum oxide templates (up to 50 m long) • Magnetic anisotropy studies Ni nanowires 200nm diam, 10m long Nanotechnology λlaser=632.8 nm Array of Fe nanowires

  11. MagnetocaloricMaterials • - Magnetocaloric effect • - Changing magnetic fields induces changes in the materials temperature • Magnetic refrigeration

  12. MagnetocaloricMaterials • Magnetocaloric effect • - Application of a magnetic field H -> magnetic material is heated • Reversible process (cooled upon H removal) • Change in magnetic entropy Entropy: Adiabatic Isothermal Effect is higher near Tc

  13. MagnetocaloricMaterials V.K. Pecharsky, Phys. Rev. Lett. (1997) • Giant magnetocaloric effect • Strong changes in entropy near Tc • First order magnetic phase transition • - e.g., Gd5Si2Ge2 M (emu/g 5Tesla Gd5Si2Ge2 Gd5Si2Ge2 : PM->F(I) at T~300K (2nd order); F(I)->F(II) at T ~ 277 K (1st order); Magneto-structural (~282-289K)

  14. MagnetocaloricMaterials • Applications - Magnetic refrigeration • e.g., cooling integrated circuits • avoids fans and complex dissipators • compact and fully solid-state • New materials to: • - widen the applicable temperatures • - use of lower magnetic fields

  15. MagnetocaloricMaterials • Other effects for cooling • Magnetic field dependant thermal conductivity • Application of magnetic field increases K1 and decreases K2 (changing heat transfer) • Avoids refrigeration fluids completely • - e.g., LaCaMnO3 (K = 0.125 W/mK (0T), 0.085 W/mK (8T) Giant electrocaloric effect In ferroelectric materials PZT K1 -> K2 -> K1 < K2 K1 + K1 > K2 - K2 Science

  16. MultiferroicMaterials Multiferroic materiais combine, at least, two ferroic orders: -Ferroelectricity -Ferromagnetism -Ferroelasticity Some insulator oxides Magnetoelectric materials exhibit a coupling between their electric and magnetic degrees of freedom

  17. Multiferroic Materials • The magnetoelectric response (ME), in multiferroic (MF) systems: • appearance of an electric polarization (P) upon applying a magnetic field (H) • and/or appearance of a magnetization (M) upon applying an electric field (E) • Single phase • Composites -> coupling through strain Free energy Polarization Magnetization ij – induction of a polarization (magnetization) due to a magnetic (electric) field. Linear ME effect

  18. Multiferroic Materials • Potencial applications: • magnetic field sensors, current measurement probes, transducer, filters, oscillators, phase shifters, memory devices • Higher ME on laminated composites Sensitive to low H freq. ac fields Tunable microwave line

  19. Multiferroic Materials Single-phase multiferroics Type I • ferroelectricity and magnetism have independent sources with some coupling between them • ferroelectricity typically appears at higher temperatures than magnetism • perovskyte type ferroelectrics, charge-ordering, tilting of unit cell blocks • spontaneous polarization P is often large (10 – 100 C/cm2) • e.g., BiFeO3 (TFE~1100K, TN= 643 K, P ~ 90 C/cm2); YMnO3 (TFE~914K, TN= 76 K, P ~ 6 C/cm2 ) Off-centering Lone pair Type II • magnetism causes ferroelectricity, implying a strong coupling • between them • polarization in these materials is usually much smaller ( ~ 10-2C/cm2) • e.g., TbMnO3, Ni3V2O6, or MnWO4 tilt Charge-ordering Spiral magnetic phase - limitation of single-phase materials -> search new materials, Or -> strain coupling ME -> composites

  20. Multiferroic composites Piezoelectric Phase + Magnetostrictive Phase Elastic interactions Magnetoelectric (ME) response 0-3 granular 2-2 multilayer 1-3 vertical • Laminated composites – high ME response • Thin films • When a magnetic field is applied to the composite, the magnetic phase changes its shape magnetostrictively. Strain is then passed along to the piezoelectric phase, resulting in an electric polarization. For the converse effect a similar coupling is obtained.

  21. Multiferroic composites Piezoelectric Phase + Magnetostrictive Phase Elastic interactions Magnetoelectric (ME) response • Advantages • High magnetization and electric polarization • Higher ME response as compared with single phase

  22. Multiferroic nanostructures • Motivation: • on nanostructures high electric fields can be applied with small voltages • energy consumption Magnetoresistance Electroresistance (bias E-field) Materials Science and Engineering R

  23. Pulsed laser ablation (PLD) • -Feixe laser, pulsado, incide no alvo. • -Radiação laser é absorvida pela superfície sólida do alvo e a energia electromagnética é convertida em energia térmica, causando assim a evaporação explosiva, ou seja a “pluma”. • No interior da pluma, o livre percurso médio é pequeno e, como tal, logo depois da irradiação do laser no alvo a pluma rapidamente se expande sob a forma de um jacto que é perpendicular ao alvo. • - As partículas são recolhidas num substrato de modo a formar um filme. Depende da distância alvo-substrato, e da posição da pluma em relação ao substrato.

  24. Multiferroic Nanostructures  Self-assembled magnetoelectric nanostructures • Imiscible materials • Matrix: Piezoelectric. P, E. • Colums: Magnetostrictive. M, H. • Stress mediated coupling => PversusH. • M versus E • Laser ablation BaTiO3/CoFe2O4 Zheng et al., Science , (2004) • Others: BaTiO3/NiFe2O4, PZT/BaTiO3/CoFe2O4, etc

  25. Multiferroic Nanostructures • Magnetic thin film on a piezoelectric substrate • R(1-x)A(x)MnO3 Manganite films • Strain: changes Mn-O bond-lenghts and Mn-O-Mn angles • Mismatch with substrate affects: structural (unit cell distortion), electrical (metallic phase) and magnetic properties (anisotropy, Tc changes) • CMR tuning and CO-melting • e.g., LaCaMnO3/PMN-PT, LaSrMnO3/LiNbO3 Phil. Mag.

  26. Multiferroic Nanostructures  Granular magnetoelectric thin films and composites • Magnetostrictive grains in a piezo matrix • Matrix: Piezoelectric. P, E. • Grains: Magnetostrictive. M, H. • 0-3 composite BaTiO3/CoFe2O4 fCFO = 0.8 • e.g., BaTiO3/CoFe2O4, PZT/NiFe2O4 C.W. Nan, (1994)

  27. Multiferroic nanostructures PZT-CoFe2O4 nanocomposites ACS Nano Nanodots Nanograins inside a Matrix

  28. Conclusions • New materials • Combination of different physical properties and techniques • Modeling physical behavior • New designs for applications

  29. Session 15:45 Probing Electrostructural Coupling on Magnetoelectric CdCr2S4 Speaker: Gonçalo Oliveira 16:00 Effect of la substitution on Tb5Si2Ge2 compound: structural and magnetic properties Speaker: João Horta Belo 16:15 - 17:00 Coffee Break + Poster Session 17:00 Ordered arrays of electrodeposited nanowires and nanotubes: comparing magnetic properties Speaker: Mariana Proença 17:15 Hematite nanowires for solar water splitting: development and structure optimization Speaker: João Azevedo 17:30 Critical behaviour of a three-dimensional hardcore cylinders composite system Speaker: Jaime Silva 17:45 Dynamic electronic interactions at nanoscopic scale Speaker: Marcelo Barbosa 18:00 Exchange coupled donor dimers in nanocrystal quantum dots Speaker: António José Almeida

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