Raman Spectra of Graphene and Carbon Nanotubes

Mildred Dresselhaus discusses Raman spectroscopy of graphene and carbon nanotubes.



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The 20th Anniversary of the Nanotubes

Carbon nanotubes was first described in 1991, so 2011 is the 20th Anniversary of this amazing structure.

This lecture, I presume, was given in conjunction with this occasion. It presents a new nanotube not made of carbon, but rather, of boron nitride nanotube. If you have an hour to spend, it might be an interesting lecture to sit through, especially in the beginning that should give you a brief history and the physics of nanotubes.



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Meet WANDA

WANDA at Berkeley Lab is ".. one of the world's first nanomaterials synthesis robots... "



Too bad WANDA doesn't look as attractive as EVE from "Wall-E".

Er... I need to get out more often....

Zz.

Carbon Nanotubes as Cooper-Pair Beam Splitters

An amazing experimental feat. This experiment is along the lines of previous experiments that tries to split a Cooper pair into its entangled individuals.

Now, a new experiment by L. G. Herrmann in France, working with colleagues in France, Spain, and Germany, published in Physical Review Letters [1] demonstrates that electrons entangled in a superconducting Cooper pair can be spatially separated into different arms of a carbon nanotube, a material thought favorable for the efficient injection and transport of split, entangled pairs. This work may help pave the way for tests of nonlocal effects in solid-state systems, as well as applications such as quantum teleportation and ultrasecure communication.

If they can be separated at large enough distances to remove the locality loophole, then this would be the source of the first no-loophole EPR-type experiment.

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Feynman and the Futurists

For once, I really don't know what to make of this. So I'm going to just throw it out there and let you people decide for yourself.

This article is citing a little-known after dinner lecture that was given by Richard Feynman before he won the Nobel Prize and because well-known. It somehow connects it to our current "craze" in nanotechnology, albeit the side that is a little bit more dubious than the current mainstream research line.

The most prominent scientists involved in this mainstream version of nanotechnology have admitted that Feynman's "Plenty of Room" talk had no influence on their work. Christopher Toumey, a University of South Carolina cultural anthropologist, interviewed several of nanotech's biggest names, including Nobel laureates; they uniformly told him that Feynman's lecture had no bearing on their research, and several said they had never even read it.

But there is another kind of nanotechnology, one associated with much more hype. First described in the 1980s by K. Eric Drexler, this vision involves building things "from the bottom up" through molecular manufacturing. It was Mr. Drexler who first brought the term "nanotechnology" to a wide audience, most prominently with his 1986 book "Engines of Creation." And it is Mr. Drexler's interpretation that has captured the public imagination, as witness the novels, movies and video games that name-drop nanotechnology with the same casual hopefulness that the comic books of the 1960s mentioned the mysteries of radiation.

I'm almost tempted to argue that this could be an example of not a "bastardization of science", but rather a "bastardization of a speech". There's also something close to a "hero worship" going on here, especially by those outside of this field of study. I think that for most physicist (and I'm probably talking mainly about myself), we definitely respect the WORK of many of the great physicists that have blazed a trail for us to follow. But we don't worship them, or give them god complex, because many of us have actually interacted with them and see them as not just ordinary people, but people with their own faults and point of view that we may not share. In other words, their "words" are not gospel!

I've "discussed" with many crackpots in which they try to argue physics using a series of quotes from this physicist and that physicist, without barely understanding the physics itself. This made it seem as if these "words" are the final words of god and therefore, must be correct, which is of course, utterly silly. And I can't help but think that this is what is going on based on what I've read in this article.

Hoping to dissociate their nanotechnology work from dystopian scenarios and fringe futurists, some prominent mainstream researchers have taken to belittling Mr. Drexler and his theories. And that is where Feynman re-enters the story: Mr. Drexler regularly invokes the 1959 lecture, which broadly corresponds with his own thinking. As he told Mr. Regis, the science writer: "It's kind of useful to have a Richard Feynman to point to as someone who stated some of the core conclusions. You can say to skeptics, 'Hey, argue with him!'" It is thanks to Mr. Drexler that we remember Feynman's lecture as crucial to nanotechnology, since Mr. Drexler has long used Feynman's reputation as a shield for his own.

Ignoring the possibility that Feynman could be wrong, it is difficult to argue when someone not only deflects a criticism by redirecting it to someone else, but that someone else is also dead! We can also argue that maybe there are other ways to interpret what Feynman said - when was the last time there is one single, non-ambiguous interpretation of a statement, much less, a whole speech?

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Nanocrystals Shown to Generate More Than One Electron Per Absorbed Photon

This is rather interesting, especially when I missed all the controversy regarding the earlier, similar claim.

Scientists out of Los Alamos have reconfirmed their findings that in certain nanocrystal, one absorbed photon can produce more than one free electron in the conduction band.

When a conventional solar cell absorbs a photon of light, it frees an electron to generate an electrical current. Energy in excess of the amount needed to promote an electron into a conducting state is lost as heat to atomic vibrations (phonons) in the material lattice. Through carrier multiplication, excess energy can be transferred to another electron instead of the material lattice, freeing it to generate electrical current—thereby yielding a more efficient solar cell.

Klimov and colleagues have shown that nanocrystals of certain semiconductor materials can generate more than one electron after absorbing a photon. This is partly due to strengthened interactions between electrons squeezed together within the confines of the nanoscale particles.

If this finding is true, then one immediate direct implication is that one could produce a more efficient solar cells.

I'll try to hunt for the exact reference (I hate press releases like this since they do not include the exact citation) and post it here when I find it.

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Casimir–Lifshitz Effect Causes Levitation

I suppose the big news making its round in the media this week is the work published in this week's Nature of the demonstration of the repulsive Casimir-Lifshitz effect[1] {the link is open for free only for a limited time}.

Casimir's original theoretical design and Capasso's group's experiment are different. Capasso's team replaced the vacuum with a liquid, bromobenzene, and, instead of metal plates, used a gold-coated polystyrene sphere attached to a cantilever, and a silica plate.

The key to the experiment is the dielectric permittivity of each of these materials. This property represents a material's ability to carry an electric field. To get a repulsive force out of the system, the dielectric permittivity of one plate must be higher than that of the surrounding liquid, and the dielectric permittivity of the second plate must be lower than that of the surrounding liquid. "We're talking about a repulsion that is controlled by the ordering of the dielectric properties of the materials, not the shape," says Capasso.

In the set-up used by Capasso's group, gold has the highest dielectric permittivity, followed by bromobenzene, followed by silica. The Casimir-Lifshitz force works so that the liquid is attracted into the gap between the two, forcing them apart.

Capasso used the cantilever attached to the gold-coated sphere to measure the size of the repulsive force. A change in a beam of light reflected off the top of the cantilever signalled movement in the system, and revealed that as the gold sphere was brought close to the silica plate it got pushed back. The results are published in Nature.

I suppose the reason why the media picked it up is the "sexiness" in the story involving "levitation".

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[1] J.N. Munday et al., Nature v.457, p.170 (2009).

The Hottest Field in Physics Is Ultracold?

That is certainly what this Wired article seems to imply. People working in this field certainly think it is a very "hot" area of study. People working in nanoscience might have a strong argument with them, though. Certainly, in terms of funding, nanoscience and nanotechnology seems to be getting a lot of funding.

Zz.

The Longest Carbon Nanotubes You've Ever Seen

Researchers from University of Cincinnati have created the worlds longest carbon nanotube. It is so long, it isn't "nano" anymore! :)

It's pretty neat. They use a CVD technique at a company's facility that specializes in such a thing.

So what do you use something this big for?

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