AFM lecture 1
• TLA – three letter acronym
• SPM – Scanning Probe Microscopy
• AFM – Atomic Force Microscopy
• SFM – Scanning Force Microscopy aka AFM
• STM – Scanning Tunneling Microscopy
SPM
STM static
AFM dynamic
SNOM
AFM lecture 1
• Outline the basics required for a practical working knowledge of AFM.
• Introduce the two most widely applied techniques
‘Tapping Mode’ and ‘Contact Mode’ in air.
Reference text for this course
‘Scanning Probe Microscopy – The Lab on a Tip’
Meyer, Hug and Bennewitz,
2004, X, 210 p. 117 illus.,
ISBN: 978-3-540-43180-0
Springer Verlag
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AFM lecture 1
•1972 Russel Young’s topografiner
•1981 First STM results in the lab by Binnig, Rohrer and Gerber
•1982 First publication - PRL
•1984 Near field Optical Microscope
•1985 Invention of AFM at Stanford by Binnig, Gerber and
Quate
•1986 Nobel Prize to Ruska, Binnig and Rohrer
•1987 Dynamic AFM by Wickramasinghe
•1987 First commercial instruments – spin-off from Quate
Group in Stanford (Park Scientific) and Hansma Group in UCSB (Digital Instruments)
•1989 IBM in atoms, by Don Eigler
•1990 First microfabrication of AFM tips by Albrecht et al.
AFM lecture 1
• localised / near field / fast decaying signal
• vibration isolation
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AFM lecture 1
AFM lecture 1
• fast decaying signal – tunneling current
I D e -cd d is the separation between tip and surface c is a constant
Tunneling through a controllable vacuum gap
Binnig, Rohrer, Gerber and Weibel
APL 40(2),178, 1982 http://dx.doi.org/10.1063/1.92999
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AFM lecture 1
Si (111) 7 by 7
15 nm by 15 nm
Aarhus STM – SPECS www.specs.de
y x
AFM lecture 1
Atomic Force Microscope
Binnig, Quate and Gerber
PRL 56, 930-933, (1986) http://dx.doi.org/10.1103/PhysRevLett.56.930
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AFM lecture 1
SURFACE FORCE APPARATUS
SFA can measure forces of ~ 10 -8 N and has been used for example to look at structured water at surfaces over lengthscales ~ 0.1 nm.
It has no x-y scanning capacity.
AFM lecture 1
STYLUS PROFILOMETER
Profilometers can measure surface profiles with a z resolution down to < 1 nm, and spatial resolution down to < 100 nm, but exert a high loading force ~ 10 -4 N and are designed for large area scanning (usually line profiles).
taken from Pacific Nanotech AFM book
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AFM lecture 1
Forces in nN attractive at long range repulsive at short range
Forces
Van der Waals
‘contact’ capillary electrostatic magnetic
‘chemical’
Giessibl Rev. Mod. Phys. 1993
AFM lecture 1
G z
F
Hooke’s law
F = k G z
Spring constant should be k ~ 1 nN nm -1 l t
Spring constant of a cantilever can be controlled by changing its length ( l ), width ( w ) and thickness ( t ).
w
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AFM lecture 1
• For spatial mapping a sharp probe is required.
• Conical tips are integrated into the cantilever fabrication.
microfabricated Si tip, scale bar 20 P m tip apex, scale bar 25 nm
AFM lecture 1
A B
(A+B) - (C+D) = 0
A B
(A+B) - (C+D) > 0
C D no deflection C D deflected up
Amplification of movement ~ 1000
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AFM lecture 1
Afmmodel.exe
• Tip approaches surface
• Cantilever bends on contact
• ‘Setpoint’ deflection adjusted for contact
• Constant deflection implies constant force
• Tip scanned across sample
• Feedback loop maintains constant deflection by altering z
• z recorded to form image
AFM lecture 1 z displacement
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AFM lecture 1
AFM lecture 1
A B
C D
(A+C) - (B+D) = 0 no deflection
A B
C D
(A+B) - (C+D) > 0 lateral deflection
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AFM lecture 1
• Binnig’s Nobel Prize Lecture
• Candid cameras for the real world http://dx.doi.org/10.1126/science.276.5321.1982
• The man who almost saw atoms http://dx.doi.org/10.1126/science.276.5321.1984
• In touch with atoms
Binnig and Rohrer
Rev. Mod. Phys. 71, S324-S330 (1999) http://dx.doi.org/10.1103/RevModPhys.71.S324
• Atomic Force Microscope
Binnig, Quate and Gerber
PRL 56, 930-933, (1986) http://dx.doi.org/10.1103/PhysRevLett.56.930
• SPM: Probing the future - Mervyn Miles http://dx.doi.org/10.1126/science.277.5333.1845
• Cal Quate’s research pages http://www.stanford.edu/group/quate_group/index.html
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