1. Book:
-Nanotechnology For Dummies Page 54 – 62
- Springer Handbook of Nanotechnology Page 331 - 369
Atomic scale characterization
techniques
AFM & STM
ETE444 / ETE544
Nanotechnology
Lecture 2
22 June 2009 at NSU Bosundhora Campus

2. Introduction
• Seeing is believing.
• We want to see what is happening in mol

3. Microscope today

4. SPM histrory
• 1981: The Scanning Tunneling Microscope
(STM) developed byDr.Gerd Binnig and his
colleagues at the IBM Zurich Research
Laboratory, Rueschlikon, Switzerland.
• 1985: Binnig et al. developed an Atomic Force
Microscope (AFM) to measure ultra-small forces
(less than 1µN) present between the AFM tip
surface and the sample surface
• 1986: Binnig and Rohrer received a Nobel Prize
in Physics

5. Rohrer in a Conference at Japan

6. Atomic force microscope (AFM)
• phonograph record
• crystal-tipped stylus (―needle‖)
• spinning vinyl platter
• when the motion vibrated the needle, the
machine translated that vibration into
sound.

7. • tiny tip made of a ceramic or semiconductor material as
it travels over the surface of a material. When that tip,
positioned at the end of a cantilever (a solid beam), is
attracted to or pushed away from the sample’s surface, it
deflects the cantilever beam — and a laser measures
the deflection.

8. Features of AFM
• It can get images of samples in air and
underneath liquids.
• The fineness of the tip used in an AFM is an
issue — the sharper the tip, the better the
resolution.
• While STMs require that the surface to be
measured be electrically conductive, AFMs are
capable of investigating surfaces of both
conductors and insulators on an atomic scale.

9. Contact mode
• Known as static mode or repulsive mode.
• A sharp tip at the end of a cantilever is
brought in contact with a sample surface.
• During initial contact, the atoms at the end
of the tip experience a very weak repulsive
force due to electronic orbital overlap with
the atoms in the sample surface.

10. Dynamic mode AFM
• noncontact imaging mode: the tip is brought in close
proximity (within a few nm) to, and not in contact with the
sample.
• The cantilever is deliberately vibrated either in
– amplitude modulation (AM) mode or
– frequency modulation (FM) mode.
• Very weak van der Waals attractive forces are present at
the tip–sample interface.
• Although in this technique, the normal pressure exerted
at the interface is zero (desirable to avoid any surface
deformation), it is slow, and is difficult to use, and is
rarely used outside research environments.

11. More
• In the contact (static) mode, the interaction force
between tip and sample is measured by
measuring the cantilever deflection.
• In the noncontact (or dynamic) mode, the force
gradient is obtained by vibrating the cantilever
and measuring the shift of resonant frequency of
the cantilever.
• In the contact mode, topographic images with a
vertical resolution of less than 0.1nm (as low as
0.01 nm) and a lateral resolution of about 0.2 nm
have been obtained

12. Measuring scale
• With a 0.01 nm displacement sensitivity,
10 nN to 1 pN forces are measurable.
These forces are comparable to the forces
associated with chemical bonding, e.g.,
0.1μN for an ionic bond and 10 pN for a
hydrogen bond.

14. AFM tips

15. Commercial AFM
• Digital Instruments Inc., a subsidiary of Veeco
Instruments, Inc., Santa Barbara, California
• Topometrix Corp., a subsidiary of Veeco Instruments,
Inc., Santa Clara, California;
• Molecular Imaging Corp., Phoenix, Arizona
• Quesant Instrument Corp., Agoura Hills, California
• Nanoscience Instruments Inc., Phoenix, Arizona
• Seiko Instruments, Japan
• Olympus, Japan.
• Omicron Vakuumphysik GMBH, Taunusstein, Germany.

16. Tools for observation in nanoscale
• Scanning Probe Microscopy
– scanning tunneling microscopy
– atomic force microscopy
– AFM instrumentation and analyses:
• Noncontact mode
• Contact mode
• Dynamic Force Microscopy
• Molecular Recognition Force Microscopy

17. AFM tips

18. AFM tips
A schematic overview of the fabrication of Si and Si3N4 tip fabrication
p.373 Springer Handbook of Nanotechnology

19. AFM tip :: electron beam deposition
A pyramidal tip before (left,2-µm-scale bar) and after (right,1-µm-scale bar) electron
beam deposition
p.376 Springer Handbook of Nanotechnology

20. Carbon nanotubes for AFM tips
• Because the nanotube is a cylinder, rather than
a pyramid, it can move more smoothly over
surfaces. Thus the AFM tip can traverse hill-and-
valley shapes without getting snagged or
stopped by a too-narrow valley (which can be a
problem for pyramid-shaped tips).
• Because a nanotube AFM tip is a cylinder, it’s
more likely to be able to reach the bottom of the
valley.
• Because the nanotube is stronger and more
flexible, it won’t break when too much force is
exerted on it (as some other tips will)

21. • Carbon nanotube tips having small
diameter and high aspect ratio are used
for high resolution imaging of surfaces and
of deep trenches, in the tapping mode or
noncontact mode. Single-walled carbon
nanotubes (SWNT) are microscopic
graphitic cylinders that are 0.7 to 3 nm in
diameter and up to many microns in
length.

23. diameters ranging from3 to 50 nm
Carbon Nanotube Tips
Pore-growth CVD SEM image of such a tip with a TEMof a nanotube
nanotube tip small nanotube protruding protruding from the
fabrication. fromthe pores pores
(scale bar is 1µm). (scale bar is 20 nm)
p.379 Springer Handbook of Nanotechnology

24. Surface-growth nanotube tip fabrication
(a)Schematic represents
the surface growth
process in which
nanotubes growing on
the pyramidal tip are
guided to the tip apex.
(b)SEM(200-nm-scale
bar)
(c) TEM (20-nm-scale
bar) images of a
surface growth tip
p.380 Springer Handbook of Nanotechnology

25. Application of AFM
• AFM imaging
• Molecular Recognition AFM
• Single-molecule recognition event
• Nanofabrication/Nanomachining

26. AFM image
DNA on mica by
MAC mode AFM The constant frequency-shift
(scale 500 nm) topography of aDNAhelix on a
mica surface.
Source: MSc thesis of Mashiur
Rahman, Toyohashi University of p.404 Springer Handbook of Nanotechnology
Technology

27. Molecular Recognition AFM
p.475 Springer Handbook of Nanotechnology

28. Single-molecule recognition event
Raw data from a force-distance cycle with 100 nm z-amplitude at 1Hz sweep
frequency measured in PBS. Binding of the antibody on the tip to the antigen on
the surface during approach (trace points 1 to 5) physically connectstip to probe.
This causes a distinct force signal of distinct shape (points 6 to 7) during tip
retraction, reflecting extension of the distensible crosslinker-antibody-antigen
connection. The force increases until unbinding occurs at an unbinding force of
268 pN (points 7 to 2).

29. Nanofabrication/Nanomachining

30. References
• G. Binnig, H. Rohrer, C. gerber, E. Wiebel,
Phys. Rev. Lett. 49, 57 (1982)
• R. Wiesendanger, Scanning Probe
Microscopy and Spectroscopy, Methods
and applications, Cambridge University
Press, 1994