A few LEGO AFM talking points
for use by
Nano Day Student Guides
2013
What is an AFM
The atomic force microscope (AFM) was first demonstrated in
1986 to image the surface of a material with high spatial
resolution. The AFM is the most popular family member from a
broad class of instruments called Scanning Probe Microscopes
(SPMs). SPMs generally use the atomic force between atoms on a
sharp tip and atoms on the surface of a material to image the
surface features of that material.
Note the acronyms AFM (Atomic Force Microscope) and SPM
(Scanning Probe Microscope) tend to be used interchangeably.
The AFM was developed to solve a wide-spread need – the need
to reliably image nanometer scale surface features on materials
with high resolution. In the 1980s, existing optical and electron
microscopes could not meet this need.
Overview
During NanoDays, the LEGO Scanning Probe Microscope (SPM)
will start scanning once in the morning (~9 AM) and once in the
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afternoon (~1 PM). When visitors arrive at the Birck Center, the
LEGO SPM will be acquiring an image of a LEGO landscape.
Depending on when a group arrives, the LEGO SPM image will be
at different stages of completion.
As a NanoDay guide, it is important that you clearly tell visitors
what to note as the LEGO SPM goes about its job of imaging the
LEGO landscape. Emphasize that the LEGO SPM is a model of a
real instrument; but is different in many ways. You must help
them understand the similarities and differences.
What is an AFM used for and why is it necessary?
Research-quality Scanning Probe Microscopes are used
everywhere in the world to image objects with nanometer
dimensions. Such features are way too small to be seen with
conventional optical microscopes. The capabilities provided by
Scanning Probe Microscopes were one of the prime reasons why
Nanotechnology grew so rapidly in the late 1980s.
It is amazing that modern science and technology have
developed in the past 30 years to make functional “things” with
nanometer scale dimensions – transistors, sensors, medical
devices. Progress ALWAYS requires you to view what you’ve
made. Research-quality Scanning Probe Microscopes serve this
purpose.
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Many of the images displayed around the Birck lobby were
acquired at Purdue with real SPMs. A few of the images were
even taken by the LEGO SPM!
Suggested Topics for Discussion
A. The scale of “nano;” (give a perspective)
A nanometer is really small!
Nano comes the Greek word νανοσ that means dwarf.
A useful way to convey the small size of a nanometer is provided
by the “meter-stick” poster that hangs on the side of the LEGO
SPM exhibit. It tells how long it would take to walk a distance of 1
meter if you took nanometer-size steps.
How is it possible to make things with nanometer dimensions
(1 nanometer=0.000000001 m) when you really cannot see what
you are making? Nanotechnology requires that you know the
shapes and locations of things you have no way of actually
“seeing.” The LEGO Scanning Probe Microscope (SPM) is a
working model designed to help you understand how scientists
have solved this very fundamental problem of imaging at the
nanoscale.
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B. The Purdue LEGO SPM
 Built in 2003-2004 by a group of undergraduates at Purdue
for use in science museums and middle schools throughout
Indiana.
 Was featured in 2005 exhibit at the Children’s Museum of
Oak Ridge (Tennessee)
 Has been in the Birck Center at Purdue since ~2008.
 Majority of funds for the design and construction came from
a NASA grant.
There are ~6 research-grade Scanning Probe Microscopes used in
nanoscale research in the Birck Center here at Purdue.
C. It’s a Different type of “microscope”!
Explain that the SPM is a different “kind” of microscope than
those that might be familiar to kids:
 It does not use “light.” (Ask students if they might know
why. The wavelength of visible light is way too big to
“reflect” from nanometer-size objects)
 Use the LEGO SPM to define S (scanning), P (probe) and M
(microscope).
 An SPM only tells us about the surface, not what is inside.
 When using an SPM, we can’t actually “see” anything; the
data obtained is a representation (a map) generated by the
computer. It looks a lot like a 3-dimensional graph.
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Students tend to have confused meanings about the vocabulary.
Ask them to think about what these words mean:
Scan
Probe
Atom
Lever
Cantilever
Periodic
Force
Clarify what these words mean using the LEGO SPM as a demo
tool so students can follow the discussion.
D. Features of the SPM
The “model” LEGO SPM faithfully captures all the essential
features of a research-grade SPM.
1. A sharp tip is moved across an unknown sample that has
features that you want to measure.
2. The tip is attached to a cantilever and the deflections of the
cantilever are monitored by a focused laser beam.
3. The distance between the sample and a sharp tip is
decreased in a systematic way until the tip “feels” the
sample.
4. From this information, an accurate 3-dimensional image of
the unknown sample can be obtained.
E. How the LEGO model SPM works
The LEGO SPM acquires an image at a rate of ~10 data points
per minute. Image acquisition is slowed down so you can see
how the SPM actually works.
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 The instrument measures 48 “data points” in each direction.
Explain that a data point in a measurement of height at one
specific point.
 What we see is a representation of all those data points.
 An entire image of the LEGO landscape requires ~ 3 hours
and has ~2300 data points.
The LEGO SPM is designed to image LEGO landscapes with
overall dimensions of 15 inches x 15 inches. As you can see, the
surface under study today has features made from stacked LEGO
bricks. The features appear in a periodic (repeating) pattern, in
much the same way as atoms are arranged on the surface of a
crystalline solid.
The computer software interprets the probe position at the point
of contact to create a color map of the surface of our sample on
the monitor (look at the image in the red box below).
 Different colors represent different heights.
 The image is updated every few seconds.
Imagine you put a blanket over the entire LEGO SPM, so you are
unable to directly observe the LEGO landscape by eye. If you look
at the computer image of the LEGO landscape, what conclusions
might you make about the actual LEGO landscape?
ANSWER: After careful study of the entire LEGO SPM image, you
might surmise the LEGO landscape is comprised of localized
features arranged in a 6 x 6 periodic pattern.
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Ask students “What changes do you think you could make to the
LEGO SPM to improve the image?”
POSSIBLE ANSWERS: use a sharper tip, make it go faster, take
smaller steps so the image will have more data points.
F. Additional Information
Real SPMs acquire an image once every few minutes. Real SPMs
map areas with dimensions that are about 1 million times smaller
than the LEGO landscape that you see.
R. Reifenberger
Birck Center
Purdue University
April 17, 2013
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