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www.helsinki.fi/yliopisto
Acoustic atomic force
microscopy
Dr. Ari Salmi
12.2.2014 1
www.helsinki.fi/yliopisto
Revisit to resonances
(lecture #3)
12.2.2014
Matemaattis-luonnontieteellinen tiedekunta /
Henkilön nimi / Esityksen nimi 2
• 2008: 0.29 zg resolution
• Chaste et al., Nature Nanotechnology 2012
• Based on a resonating carbon nanotube (f = 2 GHz)
12.2.2014 3
Even more precise nanoparticle
weighing
• Xe atoms added resonance frequency changes
• 1.7 yg (yoctogram) resolution!
• Mass of proton
12.2.2014 4
Even more precise nanoparticle
weighing
12.2.2014 5
Resonances in fullerenes?
• Very little research on resonances in fullerenes
• However... Giannopolous, Physica E 2014
• Fullerenes as mass sensors?
‒ Computational study
5 Å
12.2.2014 6
Resonances in fullerenes?
• Problem with fullerenes – very high frequencies
5 Å
12.2.2014 7
Resonances in fullerenes?
• Problem with fullerenes – very high frequencies
5 Å
12.2.2014 8
Resonances in fullerenes?
• Could perhaps be used as mass sensors
• Ma = 1.9943*10-23 g ~ 20 yg (yoctograms)
• Sensitive up to 0.1 ma = 2 yg!
5 Å
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Revisit to actuation
12.2.2014
Matemaattis-luonnontieteellinen tiedekunta /
Henkilön nimi / Esityksen nimi 9
12.2.2014 10
How fast is Brillouin cooling?
• Equation for the effective temperature has no time
dependency
5 Å
Stokes scatteringAnti-stokes scattering
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Elasticity
12.2.2014
Matemaattis-luonnontieteellinen tiedekunta /
Henkilön nimi / Esityksen nimi 11
12.2.2014 12
Physics: Static elasticity
• Static modulus of elasticity in an isotropic case:
Stress/strain
• The system also ’thins’ when extended
• Poisson ratio
• Shear modulus = ’elastic modulus in shearing’
5 Å
12.2.2014 13
Physics: Elasticity
• Determined by the elastic tensor
• In general form, stress is related to strain by the
stiffness tensor
• Due to symmetricity of the tensors, 36 elements in
the stiffness tensor
• Voigt notation
5 Å
1
2
3
12.2.2014 14
Physics: Elasticity
• Symmetries reduce the components
• Orthothropic: 9 components
5 Å
https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcRHFEL5-uTNB27T-3sjpDNDP0BZi4nX8WY9lf9G_6pAYHN2338p
12.2.2014 15
Physics: Elasticity
• Symmetries reduce the components
• Cubic: 3 components
5 Å
http://www.ndt.net/article/brown/cubic.gif
12.2.2014 16
Physics: Elasticity
• Symmetries reduce the components
• Isotropic materials: 2 components
5 Å
12.2.2014 17
Physics: Dynamic elasticity
• Elasticity under vibratory conditions
• Arises from viscoelasticity
• = phase lag between stress and strain
• Storage modulus
• Elastic portion, stored energy
• Loss modulus
• Viscotic portion, energy lost in heat
5 Å
http://www.continuummechanics.org/cm/images/stress-strain-sines.png
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Atomic force microscopy
12.2.2014
Matemaattis-luonnontieteellinen tiedekunta /
Henkilön nimi / Esityksen nimi 18
• A technique to scan the nanoscopic properties of a
surface
• Based on a contacting tip that is attached to a cantilever
that bends according to the surface features
12.2.2014 19
What is atomic force
microscopy?
• Contact and non-contact modes
• ’Contact’ mode
‒ Repulsive forces due to exchange interactions
• ’Non-contact’ mode
‒ Attractive forces due to van der Waals interactions
12.2.2014 20
What is atomic force
microscopy?
http://hone.mech.columbia.edu/wiki/lib/exe/detail.php?id=wiki%3Aatomic_force_microscope&me
dia=wiki:lennard-jones.jpg
• The tip is repulsed cantilever bends surface
features
12.2.2014 21
Contact mode AFM
• Example image
‒ Carbon nanotube bucky paper
12.2.2014 22
Contact mode AFM
http://www.nrel.gov/pv/measurements/atomic_force.html
• September 2013: First LEGO AFM
• University College of London
• Based on Arduinos, piezo stages and LEGO bricks
‒ Some structures 3D-printed
‒ Total cost ~500$
12.2.2014 23
AFM itself is quite old news...
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Dynamic AFM
12.2.2014
Matemaattis-luonnontieteellinen tiedekunta /
Henkilön nimi / Esityksen nimi 24
• The tip is driven with a oscillation frequency
• The properties of the oscillation change as a function of
surface features
12.2.2014 25
Non-contact mode AFM
(dynamic AFM)
• Gross et al., Science 2009
• Based on a quartz tuning fork design of Giessibl,
APL 2000
12.2.2014 26
NC-AFM of molecules
• A repulsive force acts on the upper prong
• causes surface charges which are collected by the
metal electrodes
‒ No optics required
• Measures the change in the resonant frequency from
the displacement
• Base resonance frequency 23165 Hz
12.2.2014 27
NC-AFM of molecules
• Idea: Modify the gold AFM tip by picking up a CO
molecule that attaches to the tip
• Significantly enhances the force (frequency) resolution
12.2.2014 28
NC-AFM of molecules
• Results: Imaging of pentacene molecular structure!
12.2.2014 29
NC-AFM of molecules
• De Oteyza et al., Science 2013
• Similar functionalization of tip with an CO molecule
• Imaging of chemical reactions!
12.2.2014 30
NC-AFM of chemical reactions
• Ashino et al., PRL 2009 and Ashino et al., Nature
Nanotechnology 2008
• Measurement of the damping of the AFM vibration
• CNT ’peapod’ structures
12.2.2014 31
Damping force spectroscopy
• Damping of AFM vibrations (f = 159 kHz, A = 21 Å)
• At point A (approaching cantilever), abrupt change to
point B
• When retracting, similar abrupt change from C to D
‒ Compensation forces of the cantilever and substrate
12.2.2014 32
Damping force spectroscopy
• The vibrations lose energy when they are close to
the ’peas’
• Not exactly on top, though
12.2.2014 33
Damping force spectroscopy
• SWCNT’s, diameter 16.2 ± 0.5 Å
• Filled with metallofullerines (Dy@C82), d = 8 Å
• Empty tube shows very little damping (characterized
by energy loss in meV) (1 and 5)
• Tube with metallofullerines features damping
12.2.2014 34
Damping force spectroscopy
• When the tube diameter is decreased to 15 ± 0.5 Å
(3 and 7) or 13 ± 0.5 Å (4 and 8), the damping
increases
• 4 appears thicker due to surface undulation
12.2.2014 35
Damping force spectroscopy
12.2.2014 36
Dynamic AFM and charge
distributions
• Mohn et al., Nature Nanotechnology 2012
• LCPD (local contact potential difference)
• Try to minimize the frequency shift
12.2.2014 37
Dynamic AFM and charge
distributions
• A LCPD image of naphthalocyanine
5 Å
12.2.2014 38
Multiharmonic atomic force
microscopy
• Raman et al., Nature Nanotechnology 2011
• Drive the cantilever with one frequency, listen to the
harmonics
5 Å
12.2.2014 39
Multiharmonic atomic force
microscopy
• Measurement on in vivo rat fibroblast cells
• Determine both storage and loss moduli
5 Å
12.2.2014 40
AFM nanomechanical
multifrequency force spectroscopy
• Herruzo et al., Nature Communications 20.1.2014
• Tip vibrates and is in contact with the sample
• Multimode use higher order cantilever resonances
• Keep the first mode amplitude and frequency shift
constant (change the excitation)
• Keep the second mode amplitude constant
‒ quantitative determination of elasticity and viscosity!
5 Å
12.2.2014 41
AFM nanomechanical
multifrequency force spectroscopy
• The results obtained for known materials match
well with theoretical predictions
• Should yield a straight line
5 Å
12.2.2014 42
AFM nanomechanical
multifrequency force spectroscopy
• Results: Calibration
• LDPE (nominal E = 0.1 GPa) embedded in PS (nominal
E = 2 GPa)
5 Å
750 nm
12.2.2014 43
AFM nanomechanical
multifrequency force spectroscopy
• Results: Block co-polymer (PS embedded in PMMA)
• Results compare very well with prediction
‒ Nominal MOEs agree
‒ Scale bar 100 nm
12.2.2014 44
Scanning Near-field ultrasonic
holography (SNFUH)
• Shekhawat et al., Science 2005
• A technique that allows sub-surface
characterization
• Based on two ultrasonic transducers and
dynamic AFM
• The two transducers form an acoustic standing
wave
• The perturbation of the standing wave is measured
12.2.2014 45
Scanning Near-field ultrasonic
holography (SNFUH)
• Results: Validation
• Model nanoparticle system (Polymer-gold
nanoparticle-polymer-silicon)
• Nanoparticles clearly visible
12.2.2014 46
Scanning Near-field ultrasonic
holography (SNFUH)
• Results: 2nd test system
• Polymer-SiN-Polymer structures
• Detected voids at the SiN-polymer interfaces
12.2.2014 47
Scanning Near-field ultrasonic
holography (SNFUH)
• Results: Detection of malaria infection in red blood
cells
12.2.2014 48
Scanning Near-field ultrasonic
holography (SNFUH)
• Tetard et al., Nature Nanotechnology 2008
• Detection of single walled carbon nanohorns
(SWCNHs) inside cells
12.2.2014 49
Scanning Near-field ultrasonic
holography (SNFUH)
• Carbon nanoparticles still clearly visible in mice
lungs after a week
• Not detected with normal AFM
12.2.2014 50
Scanning Near-field ultrasonic
holography (SNFUH)
• Also in red blood cells
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Take-home
12.2.2014
Matemaattis-luonnontieteellinen tiedekunta /
Henkilön nimi / Esityksen nimi 51
12.2.2014 52
Take-home: Acoustic atomic
force microscopy
• A method of determining (in nanoscale)
• Sub-surface features
• Elasticity
• Viscosity
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