The National Center for HREM

Funktionella Material nanotillämpningar 6
Piezoelektriska nanoverktyg
Magnetism - hur visualisera?
Syntes av nanopartiklar
Rat-on-a-chip
The National Center for HREM, , Lund University, Reine Wallenberg

The piezoelectric effect
F
Single
Crystal
+ + + + +
- - - - - -
Charging
on opposite
sides
Applying a force will create
charges - a polarity
F
Contraction/expansion
proportional to voltage
-
+
The National Center for HREM, , Lund University, Reine Wallenberg

Piezoelectric effect occurs only for non-centrosymmetric crystal
structures
Common: Quarts, BaTiO 4
, Pb(Zr,Ti)O 3 (PZT)
Only certain directions are piezoelectric – poling (never heat it!)
No net charge
displacement
-No Piezo
Piezo!
The National Center for HREM, , Lund University, Reine Wallenberg

STM, Scanning Tunneling
Microscope
Tunneling current extremely
sensitive to distance
1 Å 0.9 Å
It
10 x I
t
All three motion directions
performed by piezos;
Tip
approach Z, Scanning x and y
What does a scanner look like?
Sample surface
The National Center for HREM, , Lund University, Reine Wallenberg

Magnetism
• Un-paired electrons
• Each atom acts as a
magnetic dipole
• In ferromagnetic
materials the dipoles
align within a domain
• Ferrimagnet Fe 3 O 4, Spinell
(load stone)

Magnetic domains
• Magnetisation of
magnetic materials
• Change size by
domain wall motion

Magnetic domains
Closed flux
structure
• Alignment cost energy – hysteresis.
Especially large single domains
• Soft vs. Hard magnets
• Surface patterns visualise bulk domains –
but also surface specific domains

Methods for Characterisation of
domain patterns
Based on interactions
with the magnetic
fields above the
sample surface.
• Electrons (TEM, SEM)
• Neutrons
• (X-rays)
• Polarised light
• Bitter patterns
• Scanning probe

Scanning Probe Techniques
(SPM)
• STM, AFM, EFM, MFM
Magnetic Force Microscopy

Magnetic Force Microscopy
(MFM)
• Scanning a magnetic tip
over the sample surface

Floppy disc (80(
80×80
µm )
• Two images of the same spot
• Left: topographic image (AFM)
• Right: magnetic image (MFM)

Bitter patterns
• Magnetic powder or
colloidal nanoparticles
• Arranging to the
magnetic stray fields
on the surface

A practical example
• Soft magnetic iron
powder
• Electro-magnetic
applications
• Different magnetic
characteristics due to
treatment
• Bitter vs. MFM
• Different domain
patterns for the
samples?

Bitter patterns
Low Mag
High Mag

Bitter vs. MFM

Bitter vs. MFM

1 7
(40×40
µm )
(40×40
µm )

1 7
(40×40
µm )
Bilder av Karl Thydén

Funktionella Material nanotillämpningar 6
Vi antar att en guldspets till ett
STM förs ner i en vätska som
håller 35 o C. Hur hög spänning
måste vi lägga över piezon
(BaTiO 4 ) för att kompensera för
detta?
α(Au) = 1.4 10 -5 K -1
Length of tip : 4 microns
ξ(BaTiO 4
) = 100 10 -12 mV -1
Scanner length 2 cm
Uniaxiell töjning
The National Center for HREM, , Lund University, Reine Wallenberg

Funktionella Material nanotillämpningar 6
Biologiska
tillämpningar
The National Center for HREM, , Lund University, Reine Wallenberg

Vad är detta?
En råtta!!!?
Lab-on-a-chip med
odlade celler -
ersätter djur- och
människoförsök?
Problem: kiselchip
mellan PMMA-skivor
--> blåsbildning i kanaler
Lösning:
bättre materialval;
gaspermeabel silikongel
The National Center for HREM, , Lund University, Reine Wallenberg

Nästa
version:
Ventilstyrning
med Brailleskrivmaskin!
The National Center for HREM, , Lund University, Reine Wallenberg

Funktionella Material nanotillämpningar 6
Cellodling på
spikmattor?
Nervceller från en
snigel, odlad på
en matta av
nanotrådar.
Underlättar
näringstillförsel,
kan guida
växande
nervtrådar
(axoner)
Bild: Waldemar Hällström
The National Center for HREM, , Lund University, Reine Wallenberg

Funktionella Material nanotillämpningar 6
Nanowires kan
”lyssna av”
nervimpulser i
framtiden?
The National Center for HREM, , Lund University, Reine Wallenberg