update.294 (fwd)

[Jim Choate <ravage@ssz.com>]

Forwarded message:
>From physnews@aip.org Wed Nov  6 15:22:21 1996
Date: Wed, 6 Nov 96 10:14:13 EST
From: physnews@aip.org (AIP listserver)
Message-Id: <9611061514.AA06755@aip.org>
To: physnews-mailing@aip.org
Subject: update.294


PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 294  November 6, 1996    by Phillip F. Schewe and Ben
Stein

NANOSCALE ABACUS.  Scientists at IBM Zurich have used a
scanning tunneling microscope (STM) probe to reposition C-60
molecules on a copper substrate, making in effect the first room-
temperature device capable of storing and manipulating numbers
at the single molecule level.  The buckyballs (which are big,
sturdy molecules) act as the counters of a tiny abacus in which
low (indeed mono-atomic) terraces in the copper surface
constrain the buckyballs to move accurately in a straight line.
(The abacus is perhaps the first human calculating device, and the
Greek word means "sand on a board.")  IBM researcher James
Gimzewski (gim@zurich.ibm.com) admits that his device is
slow: "The tool we use (the STM probe) is the equivalent of
operating a normal abacus with the Eiffel Tower."  But things
should improve in coming years; with this new advance,
hundreds of buckyball ranks could fit neatly inside the same
linewidth that characterizes features on a Pentium processor chip. 
As for speed, engineers expect to fabricate arrays of hundreds
and even thousands of STM probes for simultaneously imaging
(and repositioning) many atoms and molecules.  (M.T. Cuberes
et al., to appear in the 11 November issue of Applied Physics
Letters; an associated figure can be obtained on the Web at
http://www.aip.org/physnews/graphics)

THE SHORTEST X-RAY PULSES yet produced have been
made at LBL by shooting 100-femtosecond bursts of infrared
laser light at right angles into a beam of electrons.  Some of the
photons are converted into x rays by scattering (through 90
degrees) into the same direction as the electrons.  The resultant
x-ray bursts are themselves short---about 300 fsec---and potent,
with an energy of 30 keV (or, equivalently, a wavelength of 0.4
angstroms).  By narrowing the electron beam further (currently it
is a mere 90 microns wide), even sharper x-ray pulses (50 fsec)
are in the offing.  Theses pulses are ideal probes---their small
wavelength permits studies of atomic structure with high
resolution.  Meanwhile their short duration make them an
excellent strobe light for glimpsing ultrafast phenomena. For
example, the LBL researchers are using the x-ray pulses to study
the melting of silicon.  (R.W. Schoenlein et al., Science, 11
October 1996.)

PHOTONIC CRYSTALS NOW OPERATE IN THE NEAR
INFRARED.  These structures are to optics what semiconductors
are to electronics: they allow the passage of light at some
wavelengths but exclude light in certain other energy ranges (also
called photon bandgaps).  Since the first photonic crystals
(operating at microwave wavelengths) were developed several
years ago, researchers have attempted to move toward the visible,
where potential technological applications beckon.  Scientists at
the University of Glasgow and the University of Durham have
now constructed a tiny wafer riddled with 100-micron holes
which exhibits the lowest-wavelength photonic bandgap yet: 800-
900 nm.  (Thomas F. Krauss et al., Nature, 24 October 1996.)

CORRECTION: Harold Kroto (not Croto) is the correct spelling
for the chemistry Nobelist (Update 291).