Tuesday, September 08, 2009

This week in cond-mat

Three quick blurbs from the arxiv this week.  I'm going to a workshop in Germany next week and have a bunch to do in the meantime, so blogging will likely be light.

arxiv:0909.0628 - Bocquet and Charlaix, Nanofluidics, from bulk to interfaces
This paper is an outstanding overview of fluids confined to the nanoscale.  I will definitely be referring to this the next time I teach my graduate course that touches on this topic.  Two of the central questions that comes up when thinking about fluids at the nanoscale are, when do large-scale assumptions about hydrodynamics (e.g., that fluid right at the walls of a container is at rest relative to the walls, even when the fluid away from the walls is flowing - the so-called "no slip" boundary condition) break down, and when does the continuum picture of the fluid (i.e., that fluid may be modeled as a homogeneous medium with some density, rather than a collection of strongly coupled particles) fall apart?  This article looks at these issues in detail, with many useful references.

arxiv:0909.0951 - Saikin et al., On the chemical bonding effects in the Raman response: Benzenethiol adsorbed on silver clusters
This one is of interest to me because of its relevance to some of the research done in my group.  Raman scattering is inelastic light scattering, where light can lose (or gain) energy to a molecule by exciting (or de-exciting) molecular vibrations.  It's been known for more than 30 years that the Raman scattering process can be greatly (many orders of magnitude) enhanced on nanostructured metal surfaces.  This happens for two reasons.  First, nanostructured metals support local plasmon modes, so that the metal acts like a little optical antenna, helping the molecule to "receive" (and "transmit") light.  This is called electromagnetic enhancement.  Second, there can be additional enhancing effects due to resonances involving charge transfer between the molecule and the nearby metal.  This latter effect is called chemical enhancement, and this paper takes a detailed look at how this can arise, considering specific configurations of molecules on Ag clusters.  It is very challenging to do calculations like this and get realistic results!

arxiv:0909.1205 - Martineau et al, High crystalline quality single crystal CVD diamond
I picked this one because (a) the fact that it is possible to grow high quality single crystal diamond by chemical vapor deposition is just plain cool, as well as of great technological potential; and (b) the x-ray topographs in this paper showing crystallographic defects in the crystals are very pretty.

3 comments:

Uncle Al said...

Benzenethiol is cute, but the ring carbon connection to the sulfur is a rotor and the S-H bond is problematic. Wouldn't rigidized fluorenethione be nicer? It would be a prettier color and not stink In-between we have benzophenonethione. Both are easily available from the respective ketones via H2S and HCl continuously added to toluene solvent, progressively azeotroping out water to drive the equilibrium. Perhaps phosphorus pentasulfide in refluxing toluene would do both.

Doug Natelson said...

Al, the point is to use a very simple conjugated molecule w/ thiol linkers to bind it to the Ag. The S-H bond is meant to be problematic, since the hydrogen is supposed to come off and the S is then supposed to bind to the Ag.

Tobias said...

The program for your meeting looks pretty interesting.
If you find some time away from the meeting or are looking for a place to have a nice dinner discussion, check out the "Schlachte" - it's a street right by the river that hosts several good restaurants and bars. I can especially recommend the Japanese place (can't come up with the name right now) and the Pancake ship. It's located very central and Bremen's inner city somehow survived ww2 pretty nicely, so it's well worth a visit apart from science.