For Nanotech Class

4. Atomic Force Microscopy
Fundamentals
Sebastián Caicedo Dávila
EIEE
Universidad del Valle
Cali-Colombia

5. Background: The STM
The scanning tunneling microscope was developed in 1981 by Gerd Binnig
and Heinrich Rohrer (IBM labs in Zürich), based on the quantum tunnel
effect
3

6. Background: The STM
4

7. Background: The STM
For this achievement, Binnig and Rohrer received the Nobel Prize in
physics in 1986.
The STM work in two modes:
5

8. Background: The STM
In order to work properly, it is necessary to use other physical effects such
as the piezoelectric effect.
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9. Background: The STM
The STM can achieve resolutions of 0.1nm lateral and 0.01nm in depth.
With such resolutions, individual atoms can be imaged and
MANIPULATED
STM image of Si (111)
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10. PUBLISHED ONLINE: 22 MARCH 2009 | DOI: 10.1038/NNANO.2009.48
ling readout of hydrogen-bonding-based Background: The STM
ition
STM has a variety of applications, which include characterization
, Jin He2, Ashley Kibel1,2, Myeong Lee1, Otto Sankey1, Peiming Zhang2 of
dsay1,2,3 * electrical and chemical properties of nanostructures, lithography, etc.
has a ubiquitous role in electron transport1,2
ecognition, with DNA base pairing being the
ple3. Scanning tunnelling microscope images4
s of the decay of tunnel current as a molecu-
led apart by the scanning tunnelling micro-
ensitive to hydrogen-bonded interactions. I
at these tunnel-decay signals can be used to
ength of hydrogen bonding in DNA base
hat are held together by three hydrogen
pair (for example, guanine–cytosine inter-
r than junctions held together by two hydro-
base pair (for example, adenine–thymine V
lar, but less pronounced effects are observed
f the tunnelling probe, implying that attrac-
pend on hydrogen bonds also have a role in
rise of current. These effects provide new
aking sensors that transduce a molecular rec-
o an electronic signal.
ng through an analyte molecule can yield chemi-
Given that hydrogen bonds enhance electron tun-
vacuum tunnelling9, we have proposed a new
-assembled, hydrogen-bonded tunnel junctions
ovide good contacts10 and chemical selectivity5,11.
feasibility of this approach, we functionalized a
Measure of the strength1 |of hydrogenmeasurements. A sharp gold probe, base-pairs using STM
nelling microscope (STM) probe with a DNA
ht into contact with a monolayer of nucleosides
Figure Illustration of the STM
bonding in DNA
e under 1,2,4-trichlorobenzene (Fig. 1; see (Shuai Chang et al. 2009)
functionalized with a thiolated base, is caused to approach a gold (111)
y tunnel current set-point (ISP) was established
surface functionalized with a monolayer of thiolated nucleosides until the
, the servo broken, and the current recorded as desired set-point current (ISP) is obtained, and then retracted while the
d away from the surface. Current decay curves tunnel current is recorded. The current–distance curves can be used to 8
drogen-bond molecular junctions are shown in characterize the strength of the hydrogen-bonded interactions. I is the

11. AFM Basics
AFM imaging information is gathered by “feeling” the sample surface with
a mechanical probe (cantilever with a sharp -ideally one atom- tip). When
probe and sample come to proximity, different kinds of forces come into
action, and deflect the cantilever:
Cantilevers and probes
are commonly fabricated
of silicon or silicon
nitride, due to their
elastic properties.
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12. .spnng force co
AFM Basics tpt
damping force
thp-sample
forc e
sample wh
Depending on the distance between the probe and sample surface, the AFM in
can work in three modes: Figure 2. The cantilever-tip model (driving force omitted).
★ Non-contact mode
Forr
glsivIe)tTce
★ Intermittent or tapping mode rep
★ Contact mode de
Th
sw
distance T
tip-to-sanple separation)
re
ev
sy
)n-contad
A.
a JtJah foice
si
fr
re
Figure 3. Typical tip-sample interaction force vs. distance curve. ch
10 th