Wednesday, August 06, 2008

Imaging Single Atoms on a Graphene Sheet

Single atoms spied on graphene sliver: Electron microscope spots hydrogen atoms resting on invisible carbon sheet.

Graphene is a single sheet of carbon atoms arranged in a hexagonal pattern. It can be used as a transparent "slide" so that a transmission electon microscope can image individual atoms, even hydrogen, the smallest.

A revolution occurred when it was discovered that the single atom sheets of graphene could be peeled off common graphite using adhesive tape!

Graphene at Wikipedia.

More Weird Quantum Behaviour

Paradoxical Reflection in Quantum Mechanics
This article concerns a phenomenon of elementary quantum mechanics that is quite counter-intuitive, very non-classical, and apparently not widely known: a quantum particle can get reflected at a potential step downwards. In contrast, classical particles get reflected only at upward steps. As a consequence, a quantum particle can be trapped for a long time (though not forever) in a region surrounded by downward potential steps, that is, on a plateau. Said succinctly, a quantum particle tends not to fall off a table. The conditions for this effect are that the wave length is much greater than the width of the potential step and the kinetic energy of the particle is much smaller than the depth of the potential step. We point out how the topic is accessible with elementary methods, but also with mathematical rigor and numerically.

An Exceptionally Simple Theory of Everything

This preprint by Garrett Lisi has been getting a lot of press in the popular media, in part because the author is a "surfer dude". Here's an article at the New Yorker: Surfing the Universe An academic dropout and the search for a Theory of Everything. Here's the discussion (some of it heated) at the backreaction physics blog and also at Woit's Not Even Wrong blog. Lisi himself comes off as an unassuming, pleasant, amiable fellow, much in contrast to many of the other commenters.
How can a "Theory of Everything" be "Exceptionally Simple"? Sorry, it's a pun, 'Exceptional' and 'Simple' are technical terms from mathematical Group Theory, the new theory relies on very advanced mathematics and theoretical physics.

Here's a pretty graphical illustration of the theory, but don't expect to watch it and actually understand anything.