Natural Science Forum / Physics / General Physics / July 2008

INSIDE SCIENCE RESEARCH---PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Research News
Number 867  July 28, 2008      www.aip.org/pnu
by Phillip F. Schewe, James Dawson, and Martha Heil
   
TO OUR READERS: PHYSICS NEWS UPDATE has been prepared by the Media
and Government Relations division of the American Institute of
Physics.  Since its founding almost 18 years ago, PNU has aimed to
provide science journalists with breaking news from physics journals
and meetings.  PNU has now joined forces with another AIP news
service, Inside Science News Service (ISNS).  ISNS reports on
breaking news and the science behind current affairs and is
distributed to newspapers, to reporters who do not normally cover
science, and to science journalists.  PNU will now transition into
"Inside Science Research --Physics News Update," the research
section of this broader AIP news service. We hope that the readers
of PNU will appreciate this effort to keep physics in the news by
preparing reports suitable for a wider audience, a step taken in
order to address the increasing scarcity of science reporters and
science sections at newspapers. Some of the news items presented
here will be longer than before and will provide a more general
background.  We invite reader comments on this evolutionary
development at the following address: insidescience@aip.org

WORLD’S STRONGEST MATERIAL: Graphene, a two-dimensional sheet made
of pure carbon, is 200 times stronger than steel. A new experiment
at Columbia University in New York City has for the first time
directly measured the strength of two-dimensional carbon and found
it to be unprecedentedly strong.  Carbon sheets only a single atom
thick might be used in making super-lightweight composite materials.
The study of carbon exemplifies this symbiotic relation between
science and engineering.  Scientists and engineers have worked
together for centuries to fill our material world with amazing
devices, from airplanes to microscopes, from atom bombs to
blenders.  Generally scientists probe the inner workings of nature,
increasingly at a microscopic level, while engineers snatch up the
new basic knowledge and convert it into the sophisticated innovative
products that characterize our nanotech society.

Carbon is, of course, one of the most important elements for both
living and non-living things.  In its myriad chemical combinations
it provides the inner scaffolding for our body and for all the
proteins and chemical processes that make life possible.  Carbon in
pure form is rarer but still noticeable.  Bulk three-dimensional
carbon can appear in the form of graphite, which consists of loosely
bound sheets of carbon atoms (making graphite a good pencil-writing
substance and a good lubricant), and diamond, the more elaborately
bonded web of carbon with unequaled hardness.

In the last few decades scientists have discovered carbon with other
dimensionalities.  For example, buckyballs are molecules in the
shape of a soccer ball and contain 60 carbon atoms.  This
nearly-perfectly-round molecule, whose official name,
buckminsterfullerene, is practically a zero-dimensional form of
carbon; that is, it resembles a point .  The discovery of carbon-60
molecules won three chemists a Nobel prize but it hasn’t yet led to
any practical applications.

Then one-dimensional carbon tubes were discovered.  These tubes,
only nanometers wide (billionths of a meter) but microns (millionths
of a meter) long, have very interesting electrical, optical, heat,
and mechanical properties.  Engineers and scientists working
together are trying to turn carbon nanotubes into useful elements in
micro-circuitry, either because of the tubes’ tunable electrical
properties (they can be conductor, like a metal, or a semiconductor
depending on the way they’re grown) or because they might be able to
carry away waste heat from hotspots in microchips.

Still more recently, only a few years ago, single-atom-thick sheets
of carbon were discovered.  Again, scientists and engineers are
working together to explore new materials and exploit new properties
of this marvelous material, referred to as graphene.  Carbon
nanotubes are really just rolled up version of graphene.
In the new experiment at Columbia, mechanical engineer James Hone
and his colleagues Changgu Lee, Xiaoding Wei, and Jeffrey W. Kysar,
stretched an ultrapure, ultrathin sliver of graphene across a hole
drilled in a plane of silicon.  Then they lowered a diamond-tipped
needle.  The needle is part of a sensor called an atomic force
microscope, or AFM, which, while scanned above a microscopic sample,
will adjust its position to maintain a constant tension.  The
probe’s tiny motions can be converted into a map of the sample
itself.  Or the motion of the probe can be used to measure the force
operating between the probe and sample.

In this case the probe tip pushes down into the graphene sheet and
measures the reaction force.  (See the accompanying drawing to see
what this looks like at the atomic level:
http://www.aip.org/png/2008/304.htm)  The probe measures the
strength of the material, the force needed to break the material.
(The accompanying figure shows a graph of the strengths of many
materials along with their densities, or their mass per volume.)
Organic materials (those containing carbon) like wood and polymers
often have a small density and a small strength.  Metals have a
higher strength, but composite materials, like epoxy, will have just
as much strength but weigh a lot less.  That’s why they’re used in
auto bodies and bullet-proof vests.  On this same chart, graphene is
way off by itself, with a middle-level density but a record high
strength.  The new results were reported last week in Science
magazine.

Dr. Hone says that his new measurements will serve to reinforce the
theories formulated by physicists in their own work.  The result of
this ongoing synergy between scientists and engineers might be even
stronger materials yet to come.
                               
WORLD ON FIRE.  Every summer, hundreds of wildfires burn millions of
acres across the United States.  The Santa Ana wind drives fire
across Southern California, and forest fires fill the skies over the
Western U.S. with smoke.  NASA has turned its high-tech eyes toward
the fires in a new website called "Fire and Smoke," unveiled just
last week at
http://www.nasa.gov/mission_pages/fires/main/index.html.  The site,
with its stunning images of the world on fire, is an interactive
combination of images from NASA satellites, aircraft and other
research tools.  The images are so good, and the fires so
widespread, that the Earth begins to look like something out of a
high-quality end-of-the-world science fiction movie.  You can watch
the smoke plumes drift for hundreds of miles from the California
fires, or switch to a NASA image of the carbon monoxide being
generated by those fires.  There are images of fires in Greece,
biomass burning in South America, and atmospheric particles from
fires in Alaska.  There is even a link to a NASA Goddard site that
shows all of the past year's fires on a rotating globe.

LIGHTS OUT FOR THE BIRDS.  Birds, like moths, are attracted to light
at night and if they become disoriented, will fly in circles around
the lights in a tall building, often hitting the building or
dropping exhausted to the ground. The phenomenon is not understood
by scientists, but a researcher at the Bell Museum in Minneapolis,
along with the Minnesota Department of Natural Resources, is
spearheading a program to turn off the lights to protect migrating
birds.  Participants in the programs, including the owners, tenants,
and management companies from 32 buildings Minneapolis, St. Paul,
Bloomington, and Rochester, will dim their building lights during
the spring and fall bird migration seasons.  Similar programs are in
place in Toronto, New York, and Chicago.

Adding the Minnesota cities is important, said Bell Museum
ornithologist Bob Zink, because they are located along the
Mississippi River flyway, a major thoroughfare for migrating birds.
In addition to lowering the light in the night migration routes,
researchers are also trying to determine why birds fly into some
buildings at a much higher rate than others.  In Minneapolis, 67
percent of the bird kills were caused by just two of the city's
skyscrapers.

***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources.  It is provided free of charge
as a way of broadly disseminating information about physics and
physicists. For that reason, you are free to post it, if you like,
where others can read it, providing only that you credit AIP.
Physics News Update appears approximately once a week.