Scientists create world's thinnest balloon, just 1 atom thick
September 19, 2008 By Lauren Gold
Scientists have developed the world's thinnest balloon that is impermeable to even the smallest gas molecules. Above is a multi-layer graphene membrane that could be used in various applications, including filters and sensors. Image: Jonathan Alden
(PhysOrg.com) -- Using a lump of graphite, a piece of Scotch tape and a silicon wafer, Cornell researchers have created a balloonlike membrane that is just one atom thick -- but strong enough to contain gases under several atmospheres of pressure without popping.
And unlike your average party balloon -- or even a thick, sturdy glass container -- the membrane is ultra-strong, leak-proof and impermeable to even nimble helium atoms.
The research, by former Cornell graduate student Scott Bunch (now an assistant professor at the University of Colorado), Cornell professor of physics Paul McEuen and Cornell colleagues, could lead to a variety of new technologies -- from novel ways to image biological materials in solution to techniques for studying the movement of atoms or ions through microscopic holes.
The work was conducted at the National Science Foundation-supported Cornell Center for Materials Research and published in a recent issue of the journal Nano Letters.
Graphene, a form of carbon atoms in a plane one atom thick, is the strongest material in the world, with tight covalent bonds in two dimensions that hold it together even as the thinnest possible membrane. It's also a semimetal, meaning it conducts electricity but changes conductivity with changes in its electrostatic environment.
Scientists discovered several years ago that isolating graphene sheets is as simple as sticking Scotch tape to pure graphite, then peeling it back and re-sticking it to a silicone dioxide wafer. Peeled back from the wafer, the tape leaves a residue of graphite anywhere from one to a dozen layers thick -- and from there researchers can easily identify areas of single-layer-thick graphene.
To test the material's elasticity, the Cornell team deposited graphene on a wafer etched with holes, trapping gas inside graphene-sealed microchambers. They then created a pressure differential between the gas inside and outside the microchamber. With a tapping atomic force microscope, which measures the amount of deflecting force a tiny cantilever experiences as it scans nanometers over the membrane's surface, the researchers watched the graphene as it bulged in or out in response to pressure changes up to several atmospheres without breaking.
They also turned the membrane into a tiny drum, measuring its oscillation frequency at different pressures. They found that helium, the second-smallest element (and the smallest testable gas, since hydrogen atoms pair up as a gas), stays trapped behind a wall of graphene -- again, even under several atmospheres of pressure.
"When you work the numbers, you would expect that nothing would go through, so it's not a scientific surprise," said McEuen. "But it does tell you that the membrane is perfect" -- since even an atom-sized hole would allow the helium to escape easily.
Such a membrane could have all kinds of uses, he added. It could form a barrier in an aquarium-like setup, for example, allowing scientists to image biological materials in solution through a nearly invisible wall without subjecting the microscope to the wet environment. Or, researchers could poke atomic-sized holes in the membrane and use the system to study how single atoms or ions pass through the opening.
"This could serve as sort of an artificial analog of an ion channel in biology," McEuen said -- or as a way to measure the properties of an atom by observing its effect on the membrane.
"You're tying a macroscopic system to the properties of a single atom," he said, "and that gives opportunities for all kinds of single atom sensors."
The paper's co-authors are Cornell physics graduate students Arend van der Zande and Jonathan Alden; postdoctoral researcher Scott Verbridge; and professors Jeevak Parpia and Harold Craighead.
Provided by Cornell University
Feb 18, 2007 |
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and this articvle is a valuable resource to scientists
jscroft's comment is not made
irrelevent by the fact of tritium's
half-life! There is a big diff
between 'recharging every few
months' and the 12 years'
half-life!
Ultra thin for maximum experience.
Cybrbeast: good point. It really would make a difference, though... I believe the recharge rate on current warheads is a matter of weeks. A graphene envelope would extend this considerably, although to nothing like 12 years, since the decay products of tritium actually POISON the thermonuclear reaction.
It's interesting to note that the tritium recharge issue is one of two essential reasons why "missing" Soviet suitcase nukes are not really to be feared (at least, not for their explosive qualities).
Tritium is devilishly difficult and expensive to manufacture, far beyond the capabilities of any terrorist group or even a fairly advanced sovereign nation like Iran. Also, because of the storage issues I cited above, any group hoping to maintain a thermonuclear arsenal must manufacture or purchase a continuous supply. And fortunately, while a few suitcase nukes DID go missing after the fall of the USSR, literally every MICROGRAM of tritium on the planet is accounted for, several times a year.
I'd like to see Al Qaida try to mail order some of the stuff! :)
Incidentally, the other reason not to fear those suitcase nukes is that an implosion-style thermonuclear device is, among other things, a super-high-precision machine. The elements of its plutonium shell are machined to tolerances well below a micrometer... and such precision machinery doesn't ride well behind a camel's hump.
So, in the unlikely event that a terrorist actually manages to detonate one of the things with evil intent, by far the most likely outcome is a small, VERY dirty, conventional explosion.