update.339 (fwd)

[Jim Choate <ravage@ssz.com>]

Forwarded message:

> From physnews@aip.org Thu Oct  2 16:07:42 1997
> Date: Thu, 2 Oct 97 12:42:29 EDT
> From: physnews@aip.org (AIP listserver)
> Message-Id: <9710021642.AA00390@aip.org>
> To: physnews-mailing@aip.org
> Subject: update.339
> 
> 
> PHYSICS NEWS UPDATE                         
> The American Institute of Physics Bulletin of Physics News
> Number 339  October 1, 1997   by Phillip F. Schewe and Ben
> Stein
> 
> A NEW THEORY OF NMR FOR EXTENDED OBJECTS. 
> Nuclear magnetic resonance (NMR) isn't just an imaging
> technique, but a valuable spectroscopic tool for deducing the
> chemical environment and structural layout of atoms in different
> environments. This is because the NMR spectrum of an atom (or
> to be more precise, the spectrum of the atom's nuclear magnetic
> states) is different depending on the local geometry, just as an
> atom's allowed electron energies will be different if the atom is
> suddenly lodged in a crystal with many other atoms.  Previous
> NMR theories have been able to explain accurately what the
> NMR spectrum ought to be only for atoms or atom clusters in
> isolation. Now, physicists at UC Berkeley (Steven Louie,
> louie@jungle.berkeley.edu, 510-642-1709) have devised a
> method which for the first time makes possible rigorous
> calculations of the NMR spectra of extended systems such as
> crystals, surfaces, polymers, or even amorphous materials; given
> the coordinates of the atoms, the Berkeley researchers were able
> to predict the spectrum. They tried out their theory on an
> industrially important material---synthetic diamond films used,
> for example, as coatings for tools and engine parts.  The
> prediction of the NMR spectrum for carbon atoms in the diamond
> films was in close agreement with the observed spectrum. 
> (Francesco Mauri et al., Physical Review Letters, 22 Sept.
> 1997.)

Hell of a way to reverse-engineer just about anything. How long you figure
it will be before they start coming out wit industrial units just for
materials analysis?  I wonder how good it would be at determing the layout
of a die through the carrier...

> PARTICLE IDENTIFICATION WITH PROBE MICROSCOPY. 
> Scanning tunneling microscopes (STM) provide pretty pictures of
> atoms and can even be used to pluck single atoms from the
> sample surface.  But often the identity of that atom (especially if
> it is an impurity) remains unknown.  Physicists at Arizona State
> (John Spence, Uwe Weierstall, weierstall@asu.edu) have
> addressed this problem.  First, they use a small voltage to remove
> a surface atom or molecule with an STM probe; then a larger
> voltage launches the object from the probe toward a distant
> detector.  A measurement of the time of flight (TOF) supplies a
> mass-to-charge ratio for the mystery particle, which in most cases
> will supply the identity of the unknown species. The best
> resolution achieved by other methods of chemical identification
> on surfaces is about 2 nm.  This new STM + TOF identification,
> with essentially atomic-level resolution, should be handy in a
> number of research areas, such as catalysis and the study of the
> role of foreign atoms at kinks and steps in crystal growth.  This
> work will be reported in a session (NS-TuA, Oct. 21) at the
> upcoming meeting of the American Vacuum Society (Oct. 20-24
> in San Jose). The program for this meeting can be viewed on the
> Internet at this address:
> www.vacuum.org/symposium/program.html.  (General press
> contact at the meeting: 408-271-6000.)

Pretty nifty materials analysis tool. Maybe they should shoot the atom toward
the NMR...

> FISSION HELPS SUPERCONDUCTIVITY.  One of the
> problems of using high temperature superconductors as wires in
> magnets is that the bundles of magnetic field lines that normally
> stay put in the presence of low currents start to move around
> (dissipating energy thereby) when larger currents are sent through
> the wire sample. Scientists working at Los Alamos have now
> used a proton beam to induce nuclear fission in mercury atoms in
> a mercury/copper oxide superconductor.  The defects caused by
> the fissioning atoms splay out in all directions in the
> superconductor crystal and help to snag the wayward field lines.
> This permits the sample to carry much more current.  (Nature, 18
> Sept.) 




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