(blurb started here
May 2003)Visualizations:
simulated
experimental
ico-twin butterfly
reciprocal nanocone
Papers on tableaus and picometer differences for Microscopy and Microanalysis 2006 in Chicago IL.
Digital darkfield decompositions: Manfred Rühle Interfaces Symposium, August 2004 Microscopy and Microanalysis, Savannah GA. [slides]
More detailed eprint.
Researchers
in the UM-StL Scanned Tip and Electron Image Lab have
expanded on digital versions of optical darkfield strategies
(similar to looking for dust on a mirror face-on
while shining a strong light from the side), with simple but
not widely known
mathematical connections to the wavelet analysis used for
compressing images. These are being applied to lattice images
of technologically-interesting materials from across the
region, taken with the Missouri's only atomic (two Ångstroms
point-to-point) resolution electron microscope.This digital darkfield detective work helps researchers at industries and universities across the region to find and identify hidden structures in images (e.g. twinning in metal nanocrystals, or reaction rims on catalysts), as well as to map atom position deviations as small as a hundreth of an atom across. These deviation maps in turn allow "strain-mapping" as illustrated here, below an image of white tunnels between atom columns in a cross-section of wafer silicon on silicon-germanium under development by industry for the next generation of smaller and faster computer chips.
Starsmoke nano-cones photographed at UM-StL (Ap J Lett 578 L153-156, 2002) as continuation of the long-standing role of St. Louis researchers in the laboratory study of dust from around our star and other stars
Paper on presolar atom-sheet bending for Microscopy and Microanalysis 2006.
Slides on materials astronomy
Astrobiology provides realtime feedback on the
evolution of stars and planets like our own. One source of this
information on the changing world around us is the collection of
tiny astrophysical objects (space dust) which has made its way
to earth for study in sophisticated ground-based labs. For example,
thanks to ion probe studies done in the past couple of decades at
Washington University's McDonnell Center for Space Sciences,
we now have first hand evidence that the carbon atoms inside
you were manufactured in red giant stars spread out across
the Milky Way throughout the first five billion years of our galaxy's
lifetime.
Now researchers only 15 minutes away at the
University of Missouri-StL
have obtained pictures of carbon atom sheets whose arrival in our solar
system was concurrent with the carbon atoms in you, but which remain
bonded to sibling atoms that made the trip across the galaxy with them
from the star in which they were born. In other words, we now have
pictures of molecules like those in which your carbon atoms made their
interstellar voyage to earth.
These observations, made with a high resolution
electron microscope at UM-StL and reported in the
astrophysics community's journal for rapid publication,
indicate that much of the carbon on earth traveled here in the form
of high-purity unlayered graphene. This is the stuff of which buckyballs
and single-walled carbon nanotubes are made, and a material not
reported to occur naturally in high purity elsewhere. Although man
has only in recent years begun figuring how to create single-walled
carbon nano-structures of abundance, it appears now that red giants
used such a process to bring solidify freshly-made carbon atoms
before sending them off with the help of starlight
to form new stars, planets, and eventually life. Moreover, the wide
cone angles which connect the atom-thick sheets together in
the low density carbon of these specimens suggest that the
process by which they were formed is different from any known on earth.
Circumstantial evidence suggests dendritic solidification of droplets
of liquid carbon from erupting jets originating deep in the star.
UM-StL researchers have reported, and are continuing to study,
tiny defects that form spontaneously at room
temperature on silicon surfaces prepared by a variety of methods
but which have so far been possible to ignore by the electronic
device industry because of their
small size and weak strain fields. Experiments with researchers
at MEMC Electronic Materials in O'Fallon Missouri on the
trapping of impurities in gigascale
integrated circuit silicon (computer chips) during device
manufacture created the need for this study, because the
size of trapping defects in the silicon interior has
now moved down into the 10 nm (50 atoms on a side) range.
Looking for such small objects required that researchers at UM-StL
take a closer look at "pesky nanodots" that had been showing
up in electron microscope images of thin silicon specimens for
years.A breakthrough came when Iris Mack, an exchange student from Stuttgart, discovered that "running down the hall after thinning a specimen" to put it into the electron microscope not only suppressed defect formation, but allowed microscopists to thereafter observe the spontaneous formation of these defects in real time. The results were reported in ESSL, the rapid publication journal of The Electrochemical Society. Researchers here suspect that these defects in effect harden the surface of air-exposed silicon much like the formation of a film on cooling but unstirred soup, and hence may prove to be worthy allies or adversaries as computer chip line-widths move into the nanometer range. Current work is focussing on the possible role of transition metals in their formation.
Fingerprinting nanocrystals from lattice images at two tilts (Ultramicroscopy v94 n3-4 245-262, 2003)
More on visibility maps and making sense of lattice fringes now available in: J. Appl. Phys. 98 (2005) 114308 and the vJournal of Nanoscale Sci & Tech 12 (2005).
Some interactive fringe visibility and Kikuchi maps.
Additional papers for aberration-corrected microscopy meetings, and other stuff on digital interferometry, are linked here.
Notes on covariance profiling.
This paper considers how nano-humans might determine the 3D structure of crystals, if they were able to re-orient the crystal in their hand while trying to peer down along tunnels between the columns of atoms which run in various directions. If you could see these tunnels, you could formulate rules for folks to use in recognizing a face-centered cubic crystal, a body-centered cubic crystal, etc. Precisely this type of manipulation (imagine a hand which can only tilt the crystal through a limited angle, over one or two fixed axes) is becoming possible with modern day million-dollar atomic resolution transmission electron microscopes.
| To illustrate, click below to rotate the silicon nanosphere at left over the 35.3 degrees separating the four-fold symmetric <001> zone from the two-fold <112> zone in two steps: 20 degrees over a vertical (e.g. stage-tilt) axis, followed by 30 degrees over a horizontal (e.g. goniometer) axis. The second button reverses the sequence. Lattice planes visible edge-on, before and after, allow unambiguous identification of the crystal's diamond-fcc lattice. You can also freely turn the model with the mouse. Which orientation do you like best? A more detailed version of the model is here. |
(blurb started here
May 2003)Tales of a cool device, bogeyman code, plus multiscale time and values.
Notes on layered niche-networks for the May 2006 Understanding Complexity meeting at UIUC. Notes and paper from a talk at the 2005 meeting.
"Net surprisals ala Tribus: correlations from reversible thermalization" (poster/MS for ICCS 2004 in Quincy MA, May 2004).
"Heat capacity in bits" in Amer J Phys 71, 11 (2003) 1142-1151 in the long-standing tradition of Missouri researchers (including E. T. Jaynes) applying gambling theory to physical systems.
AAPT summer 2003 talk notes.
How about courses with few prereqs on everyday inventions, or informatics?
In a paper for AJP, the most prestigous but also least understandable physics education journal, researchers at UM-StL examined how these developments impact our understanding of simpler things e.g. why temperature is a useful concept, or how the heat capacity of water changes as it cools from gas to liquid to solid form. In the process, one discovers that temperature is a measure of the energy needed to decrease the mutual information about a system of molecules by one bit, and heat capacity measures the number of bits of information lost per two-fold increase in temperature. Although these insights are unlikely to affect the way weather is reported on the morning news anytime soon, they are already providing insight for students into the physical laws that underlie complex systems ranging from lasers, through computers, to human communities. One set of connections in this regard is illustrated below...
(blurb started here Aug 2004).
St. Louis Science Cyberville splash screen for our Oct 2005 nanoday, links for a 2006 book chapter on nanoed, an intro-chem nanochallenge, and a web journal for peer reviewing empirical observation reports.
Some interactive...
A web/lab course in nanoscale science practicals
Savannah 2004 poster
Recent NSF proposal summary
Some variable size scale adventure links.
AAPT crackerbarrel on deep simplifications
Nano-exploration can serve up a rich
source of modern-day inquiry-based empirical observation challenges
to science students at all levels, if their classes have some form of
access to the world-wide web. We are therefore working to develop
resources accessible to teachers at the grass-roots level, to bring
figures in existing textbooks to life with content-modernizing
opportunities for
student exploration, reporting, and peer review which make use of
real-world data and problem-solving techniques whenever possible.
Metric-based
approaches to anyspeed motion
empower students and explode myths (blurb started here
Jun 2003)
"Live remote" spacetime explorer and artificial gravity laboratories for data acquisition by students in web-connected classrooms.
Note on introducing mechanics metric-smart from day one.
An anyspeed acceleration applet.
Storylines for use of these tools in existing courses.
Many of our notes for teachers are archived in citable form. The collection single-frame views of spacetime is an exception.
Roadmap to content modernization on this site.
Which of the following is fact and not fiction?
"When traveling from point A to B, objects travel
over all possible paths at once provided they are not being watched."
"Wristwatch time passes more quickly
for a couch potato, since from a map-frame's perspective
we travel at lightspeed through time only when we're
not traveling through space."
"Absent external forces, traveling objects tend to
follow paths from A to B that result in the maximum amount of aging
during the course of the trip." "Practical
consequences of these arcane
facts (to your everyday life) already exist and will increase in
days ahead."
If any of these assertions sound ridiculous to you, then you have some
pleasant surprises to look forward to since nature is indeed stranger than
most of us can imagine. Moreover, insight into this strangeness
is becoming easier thanks to recent followup work on "deep
simplifications" first offered by Richard Feynman
and Hermann Minkowski in the first half of the last century. In particular...Allpaths/Action/Aging approaches to introducing the quantum-mechanical causes of motion (even in curved spacetime) under development for introductory classes, e.g. by E. F. Taylor at MIT, are complemented by map-based (single-frame metric-based) "anyspeed" descriptions of motion being refined at UM-StL. One element of these approaches is to "maximize insight while minimizing misconceptions" from the beginning. The work at UM-StL, using Minkowski's spacetime version of Pythagoras' theorem to define anyspeed variables and rules (referenced to a coordinate-grid and clocks co-moving with a selected "map-frame"), shows students with few to no prerequisites how:
- to predict readings on clocks traveling at any speed with respect to the map frame, in comparison to the reading on nearby map-frame clocks;
- to track constant acceleration at any speed, as well as how the finite speed of light (strangely enough) expands possibilities for travelers wishing to travel hundreds or thousands of map-distance lightyears in ten years of time on their own wristwatches; and
- force and Newton's laws remain useful but frame dependent, not only at any speed but also locally on accelerated and curved-spacetime maps with help from "affine-connection forces" (like gravity) that act on every ounce of an object's being.