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 /png)
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.)
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