an applet-based variable size-scale adventure for
materials astronomers and/or nano-detectives
Below find a web-interactive "copper
TEM grid" (in this case a grid 3 mm in diameter with a 200 line
per inch mesh) like that shown in the image on the right
next to an ordinary staple. Suspended across the grid you'll
find pieces of a 10 nm thick "holey carbon film", like those
often used to support a wide variety of particulates. Such grids
and carbon films are often used also to mount soft (e.g. tissue or cell)
sections sliced by an ultramicrotome. Using your mouse, you can rotate, spin,
as well as zoom around on or even inside the
structure, thanks to an intersecting-axis goniometer
with no rotation limits.
The wide tilts, the large focal depth, and the
geometric contrast mechanisms of the web-microscope used
here allow one to also obtain topographic information of
the sort that atomic force and scanning electron microscopes
can generate. We have plans to allow you to explore
this and other specimens on the micron, nanometer, and even
atomic scales in the days ahead, as well as
to taylor stories for the use of such models
in classrooms from kindergarten through grad school.
One objective is to provide visitors with a visceral
feel for scale changes that the nano-explorer
experiences, in the process of "getting small".
How astute are your
observational skills? What information would you bring
back from a "fantastic voyage" into the nanoworld? Don't mind the robot in
the background. If you look carefully, you may
be able to find grid bars and some
holey carbon support film, plus a clino-enstatitite
lath collected in the earth's stratosphere which contains
solar flare tracks from space exposure while in orbit around
the sun. Other astrophysical puzzles
will be added in days ahead. Of course,
unfamiliar contrast mechanisms are needed to observe objects
smaller than the wavelength of light, so be prepared for a few
Note: The mouse allows you to
re-orient and or spin the specimen, while the Shift key plus
vertical mouse motion allows zooming in on the model for a closer look.
The Home key returns you to the original
point of view, and the buttons above let you estimate goniometer
angles and field-width. The rotation-center may be moved
along scope cartesian (xyz) axes by tapping the xXyYzZ
keys (hint: rotate between taps). If this version bogs down on zooming (e.g. with an older PC),
try a 400x400
for less surface topography, and
if you wish to rotate "the camera" rather than the specimen plus see objects
2 million lightyears away in the background to boot!
Puzzler #1: If the diameter of the grid is 3[mm], what is
it's thickness? Also what is the exact mesh of the grid (i.e.
the number of lines per inch)? The manufacturer claimed that it
was 200 mesh, but it might be fun to see how close that claim was
to the truth. Also, how wide are the grid bars, and what fraction
of the grid area is open, i.e. transparent to electrons.
Puzzler #2: Now take a close look at some of the holey carbon
film. Can you determine the film thickness experimentally? How large
are the holes in this film? What is an average diameter?
What is the shape of the holes. Do they vary in size and
shape? What is the standard deviation in size? What fraction
of the holey film area is comprised of the holes themselves?
What is the distribution of hole sizes, i.e. are the sizes
normally distributed, does the distribution have multiple peaks,
Puzzler #3: Next, see if you can locate the
enstatite lath. What are the lath's dimensions? What is it's
shape? Is it faceted, or irregular in shape? If it has
faces, what are the angles between them? What is the
lath's volume and surface area?
Puzzler #4: Check out the solar flare tracks
in the enstatite lath. Are the tracks randomly distributed,
or is there evidence of a preferential orientation which
might occur if the lath was buried near the surface of
an object much larger than the range of solar flare
tracks therein? How many tracks do you find in
this grain? How many tracks per unit area was this
grain exposed to? If you know that the lath was
removed from a 10 micron interplanetary dust particle
too small to shield it from track-forming solar flare
particles, how much time spent at 1 AU (earth's orbit)
around the sun would have been necessary to create
the observed track density? What is
the uncertainty in this exposure time due to counting
Puzzler #5: Take a
close look at the exit and entry holes for the track
in that part of the crystal which hangs over the
edge of a hole in the carbon film. How has the
previously flat surface been disturbed? Can you
distinguish the entrance and exit holes? Do the
rearranged atoms show signs of order, or disorder?
What are the crater diameters, depths, and rim heights?
How might one go about determining the ion mass, energy
and direction from these surface features?
Puzzler #6: (NOT YET IMPLEMENTED) Decipher
the hidden message (an extraterrestrial palimpsest
ala Carl Sagan's Contact) buried in the unit-cell
ordering of an interstellar silicon carbide grain.
Puzzler #7: (NOT YET IMPLEMENTED) Examine
the structure of unlayered graphene in the core of
a graphite onion formed in the atmosphere
of a red giant star, for clues to precipitation
processes in the cool atmosphere of such giant
Storylines for Classroom Use: Suggestions invited.
This is one of several web-based "active mnemonics", designed:
(i) to offer complementary perspectives and resources for achieving
present day teaching goals among students with a wide range of learning
styles; (ii) to do this in the context of emergent topics in modern
day science (e.g. nanoscale exploration, information physics,
allpaths/action/aging and metric-based anyspeed dynamics), many of which
have only begun to work their way into textbooks and curriculum goals; and
(iii) to be reliably available for use by individual teachers in class
and by students out of class. Nanoworld exploration is especially
interesting in this regard since it can offer an open-ended challenge
to one's skills at empirical observation and reporting, allowing
students to "participate in scientific investigations based on
real-life questions that
progressively approximate good science". This is, for example, a
primary goal of the K-12 Show-Me Standards on scientific inquiry,
the basis for Missouri Assessment Program tests.
Most classroom challenges instead focus on factual knowledge and
skills at theoretical prediction, perhaps since robust empirical
challenges have been more difficult to set up.
The generic storyline for probing student skills and biases
for empirical observation might go something like this:
"Someone has just prepared a specimen for a
closer look in your web microscope. You see it spinning
in front of the robot's image when you move your mouse
over the picture containing it. By dragging your mouse
with a button down, you can rotate or even spin the
specimen. By dragging the mouse vertically with the shift
key pressed you can move in toward the rotation center for
a closer look. Check out the specimen, and report back on
what you are able to find out." This of course will not be
specific enough for most students, or in fact most teachers.
By that same token, with added specifics it might prove
useful for students at various levels in topic areas ranging
from materials microscopy to gestalt psychology. Revisiting
the same model, with a new assignment in a different class, would
also reinforce students' corollary awareness of the challenges faced
in doing detective work at the nanoscale.
Thermal physics and uncertainty: Fleas on fleas on fleas...
(e.g. in a general studies course on the physical principles
"In this exercise at empirical discovery, you will be assessed on your
ability to describe what you found and did not find, as well as on the
quality of the data you managed to come back with. Basically, so far
in this course we've talked of baseballs and tables and other macroscopic
objects as just that: Individual objects. In fact, they are composed of
tiny building blocks. A key parameter in thermal physics (e.g. the
way temperature works) turns out to be uncertainty about the
microscopic state of those building blocks. Since detective work on
these nanoscales is increasingly important in fields ranging from
engineering to medicine, this exercise gives you a feel for detective
work on the state of atoms making up a small 3mm disk." Assignment:
"Zoom in and around on the tiny disk that you'll find in this
web microscope. Feel free to assume the disk diameter is 3mm,
and to use the superposed grid to help estimate sizes of smaller
things. The field-width estimator can also be used, although this
might add additional uncertainty to your measurement. Then do the
best you can to determine the spacing between gray atoms in the
specimen's disk, a few of which are visible if you zoom in enough
to see them. In the panel below then report: (i) your measured value,
(ii) an estimate of your uncertainty in your measured value, and
(iii) a description of the method you used to come up with it."
Measuring Size Scales and Densities: Powers of 10... (e.g. as supplement
to the opening "measurement" chapter of a standard introductory physics
textbook): "Zoom down for a closer
look at this 3mm diameter web specimen, to see if you can determine
the distance between atoms in it, and/or the number of atoms it
contains per cubic centimeter." You might be inclined to let
them determine spacings on the superposed grids on their own.
Alternatively, you might tell them to assume that the level 2
grid squares are about a micron across, and the level 5 squares
about a nanometer across. Advantages to this exercise: It
is an experimental challenge (something students often don't
get outside of a lab), it offers a visceral feel for the
large number of intervening worlds between that of humans and
that of atoms, and it facilitates self-discovery about the nature
of these concepts in a cutting-edge but practical setting
frequented by today's nanoscale explorer.
Frequently Asked Questions: Suggestions invited.
How do I measure distances? You can assume that the diameter of
the disc is 3mm, and extrapolate all other dimensions from that. The
superposed grid lines may be of qualitative, and in some cases quantitative, help.
Serious detectives might also try to propagate uncertainties through the
extrapolation as well. On the other hand, your teacher may tell you to
start with different assumptions, e.g. the distance between atoms in a
certain object. The "Estimate Field Width" button may also come in
handy, although you might want to avoid taking the manufacturer's estimate
blindly at face value. Quantitative comparisons are probably best done between
objects whose distance from your vantage point is the same, and thus to set
up may require some rotation and zooming on your part.
How do I measure angles? In some cases the superposed
grid lines, or other aspects of the geometry of objects, can be
used to determine angles. Another trick for angles at the rotation
point might be to note that you can spin an object at a constant rate
of speed. If the spin takes you through the two directions of interest,
the angle between them is simply 360 degrees multiplied by the
time_between_directions divided by
the rotation_period. Given that the beta applet also allows you to
move the rotation center, in principle any two angles can be measured
with arbitrary precision (e.g. using slower rotations) by this means.
Lastly, the viewing direction is also roughly specified by values accessible
from the Tilt and Rotation angle buttons. For those who enjoy
spherical trigonometry, the angle between two
different viewing angles (e.g. T1,R1 and T2,R2) is
How do I record observations for later analysis, and reports?
Although movies of what you see may be difficult to record, still photos
of what you see on the screen should be possible to print out using
File/Print (some browsers will let you select and print only the
applet window), or capture as digital images using
any of a number of screen capture utilities (e.g. Paint Shop Pro
under Windows) or even with a camera. When saving an image, it's
good practice to save relevant data (like field width at the rotation
center) along with it. For example, you might append "w6p67n" to
the filename of the image if the field width is 6.67 nanometers.
When recording images on film, microscopists generally record useful
information (along with the number of each negative) in a logbook.
This is also recommended here, since not all information corollary
to an image can be recorded in its filename. Note: Unlike
magnification, field width and scale bar labels are not changed
when the image is portrayed on larger or smaller screens. They also allow
one to easily determine magnification e.g. by dividing field width into
the width of the viewed image.
(for which technology is essentially in hand) include:
Push buttons to estimate the field width (now available),
goniometer angles, and working distance.
A couple of adenovirus particles and perhaps some other
stray molecules, hidden elsewhere on the specimen.
Ability to translate the rotation center in 3D, if
desired with a dynamically-regenerated grid overlay and specimen to
facilitate navigation plus offer non-trivial atom-scale detail
throughout the specimen. This may seem like a modest task until
one realizes that this specimen contains something akin to 10^20 atoms,
i.e. around 10^12 gigabytes of information encoded in atom
Ability to pass observation parameters back into a calculation engine that
can provide the explorer with HREM images, diffraction patterns,
X-ray or roughness spectra, etc. of
the field of view.
This page is
is due particularly to
for his robust
help adapting it to this application. A background image from
the Takanishi Lab
webpage on robot expressions has been put up
temporarily because we don't have a "first specimen" background
showing curious students looking at an object in the lab. Yet.
Although there are many
contributors, the person responsible for errors is P. Fraundorf. This
site is hosted by the Department of Physics and Astronomy (and Center for
Molecular Electronics) at UM-StL, and is part of the Physics Instructional
Resource Association webring (see below). The number of visits here since
last reset on 23 Aug 2003 is [broken counter].
site page requests to UM-StL around 2000/day, hence more than 500,000/year.
Requests for a "stat-counter linked subset of pages" since 4/7/2005: