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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).