MAP – FIS 2011/2012
Overview
Advanced materials science
Session
MAP-FIS conference
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Presentations
- Multiferroic materials
- Magnetocaloric
- Nanowires/nanotubes (magnetic, for photoelectrochemical
water splitting)
- Quantum dots
Preparation techniques:
- Templated growth
- Electodeposition
- Others
Applications
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
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)
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Top-down
-Top-down
- Litography
-e.g., focused ion-beam miling (FIB)
- e.g., electron-beam direct writing
FIB
EBDW
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Self-assembled porous templates
Porous templates:
- self-organized pores
- Block copolymers
- Anodic Aluminum oxide (Al2O3)
Porous Al2O3 template
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
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Electrophoretic Deposition
25V
p-Si(001)
Si/SiO2/TiO2/Pt
20mm
- 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)
- 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
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Nanocontacts
Pt nanowires
- Pt nanocontacts for nanocapacitors
- Electrochemically deposited
BaTiO3
Lower
electrode
0.2 m
Science
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Nanocapacitors
PZT nanocapacitors
Nano-capacitors for
integrated electronics
M. Alexe, et al, Advanced Materials
film-type
(with top nanocontacts)
island-type
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
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
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
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
λlaser=632.8 nm
Array of Fe nanowires
Nanotechnology
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Magnetocaloric Materials
- Magnetocaloric effect
- Changing magnetic fields induces changes in the materials temperature
- Magnetic refrigeration
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Magnetocaloric Materials
Magnetocaloric effect
- Application of a magnetic field H -> magnetic material is heated
- Reversible process (cooled upon H removal)
- Change in magnetic entropy
Entropy: S ( H , T )  SM(
H , T )  S E (T )  S L (T )

  
magnetic
Adiabatic
electronic
lattice
Isothermal
Effect is higher near Tc
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Magnetocaloric Materials
V.K. Pecharsky, Phys. Rev. Lett. (1997)
- Strong changes in entropy near Tc
- First order magnetic phase transition
 S mag   M 

  


H

T  T  H
- e.g., Gd5Si2Ge2
M (emu/g
Giant magnetocaloric effect
1 2  M 
Tad  
T
 dH
C H1  T  H
H
5Tesla
Gd5Si2Ge2
T
C(H ,T )
dT
T
0
S (H ,T )  
Gd5Si2Ge2 : PM->F(I) at T~300K (2nd order); F(I)->F(II) at T ~ 277 K (1st order); Magneto-structural (~282-289K)
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Magnetocaloric Materials
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
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Magnetocaloric Materials
Other effects for cooling
- Magnetic field dependant thermal conductivity
- Application of magnetic field increases K1 and decreases
K2 (changing heat transfer)
Giant electrocaloric effect
In ferroelectric materials
1 2  P 
Tad  
T
 dE
C E1  T  E
E
- Avoids refrigeration fluids completely
- e.g., LaCaMnO3 (K = 0.125 W/mK (0T), 0.085 W/mK (8T)
 S   P 
   
 E T  T  E
PZT
K1 ->
K2 ->
K1 < K2
K1 + K1 > K2 - K2
Science
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Multiferroic Materials
Multiferroic materiais combine, at least, two ferroic orders:
-Ferroelectricity
-Ferromagnetism
Some insulator oxides
-Ferroelasticity
Magnetoelectric materials exhibit a coupling
between their electric and magnetic degrees
of freedom
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
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
Pi  
1
1
F ( E , H )  F0  Pi S Ei  M iS H i   0 ij Ei E j   0 ij H i H j   ij Ei H j 
2
2
1
1
  ijk Ei H j H k   ijk H i E j Ek  
2
2
F
1
 Pi S   0 ij E j   ij H j  ijk H j H k   ijk H i E j  
 2
Ei
me
ij – induction of a polarization (magnetization) due to a
magnetic (electric) field. Linear ME effect
Magnetization
Mi  
F
1
 M iS  0 ij H j   ij Ei  ijk Ei H j   ijk E j Ek  



H i
2
me
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Multiferroic Materials
Potencial applications:
-magnetic field sensors, current measurement
probes, transducer, filters, oscillators, phase
Sensitive to low H freq. ac fields
shifters, memory devices
- Higher ME on laminated composites
Tunable microwave line
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Single-phase multiferroics
Multiferroic Materials
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
Charge-ordering
-2
2
- polarization in these materials is usually much smaller ( ~ 10 C/cm )
- e.g., TbMnO3, Ni3V2O6, or MnWO4
 me   m  e
tilt
Spiral magnetic
phase
- limitation of single-phase materials -> search new
materials, Or -> strain coupling ME -> composites
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Multiferroic composites
Piezoelectric Phase + Magnetostrictive Phase
Elastic interactions
Magnetoelectric (ME) response  E 
0-3 granular
2-2 multilayer
E
H
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.
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Multiferroic composites
Piezoelectric Phase + Magnetostrictive Phase
Elastic interactions
Magnetoelectric (ME) response  E 
E
H
Advantages
- High magnetization and electric polarization
- Higher ME response as compared with single phase
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Multiferroic nanostructures
Motivation:
- on nanostructures high electric fields can be applied with small voltages
- energy consumption
Magnetoresistance
Materials Science and Engineering R
Electroresistance
(bias E-field)
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
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.
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Multiferroic Nanostructures
 Self-assembled magnetoelectric nanostructures
- Imiscible materials
- Matrix: Piezoelectric. P, E.
- Colums: Magnetostrictive. M, H.
- Stress mediated coupling => P versus H.
M versus E
- Laser ablation
BaTiO3/CoFe2O4
Zheng et al., Science , (2004)
-Others: BaTiO3/NiFe2O4,
PZT/BaTiO3/CoFe2O4, etc
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
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
60
a)
(111)LSMO
3
Phil. Mag.
Intensity (10 cps)
50
40
(006)
LiNbO3
30
(0012)LiNbO3
20
(222)LSMO
10
0
20
30
40
50
60
70
80
90
2 (deg)
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Multiferroic Nanostructures
 Granular magnetoelectric thin films and composites
- Magnetostrictive grains in a piezo matrix
Grains
Matrix
-Matrix: Piezoelectric. P, E.
- Grains: Magnetostrictive. M, H.
- 0-3 composite
E 
E
~ 10  50 mV cm 1 Oe 1
H
BaTiO3/CoFe2O4
fCFO = 0.8
- e.g., BaTiO3/CoFe2O4, PZT/NiFe2O4
C.W. Nan, (1994)
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Multiferroic nanostructures
PZT-CoFe2O4 nanocomposites
Nanodots
ACS Nano
Nanograins inside a Matrix
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Conclusions
- New materials
- Combination of different physical properties and techniques
- Modeling physical behavior
- New designs for applications
Universidade do Minho, MAP-FIS Conf.
MAP – FIS 2011/2012
Session
15:45 Probing Electrostructural Coupling on Magnetoelectric CdCr 2S4
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
Universidade do Minho, MAP-FIS Conf.