PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 777  May 18, 2006  by Phillip F. Schewe, Ben Stein,
and Davide Castelvecchi        www.aip.org/pnu
                
EXTREME-ULTRAVIOLET MICROSCOPE PROVIDES RECORD RESOLUTION. At next
week's Conference on Lasers and Electro-Optics/Quantum Electronics
and Laser Science Conference meeting in California, Courtney Brewer
of Colorado State University (brewerca{at}holly.colostate.edu) and her
colleagues will present a tabletop optical imaging system that can
reveal details smaller than 38 nanometers (billionths of a meter) in
size, a world record for a compact light-based optical microscope.
The microscope can keenly inspect nanometer-scale devices designed
for electronics and other applications. It will also be capable of
catching subtle manufacturing defects in today's ultra-miniaturized
computer circuits, where defects just 50 nm in size that were once
too small to cause trouble could wreak havoc in the nanometer scales
of today's computer chips. Except for some high-tech details, the
microscope works very similarly to a conventional optical
microscope. Light shines through the sample of interest. The
transmitted light gets collected by an "objective zone plate," which
forms an image on a CCD detector, the same kind of device that
records images in a digital camera.
However, in the case of the sub-38-nm microscope, there are some
advanced technological twists. The microscope uses a laser that
produces light in the extreme-ultraviolet (EUV) spectrum, whose very
small wavelength makes it possible to see a sample's tiny details.
The EUV light is created by ablating (boiling away) the surface of a
silver or cadmium target material so that the vaporized material
forms a plasma (collection of charged particles) that radiates laser
light. To focus this light, the researchers avoid standard lenses
because they strongly absorb EUV radiation. Instead, the microscope
uses "diffractive zone plates," structures containing
nanometer-spaced concentric rings that focus the light in the
desired fashion.
Other state-of-the-art optical microscopes have achieved resolutions
as low as 15 nm, but they required the use of large synchrotrons.
This more compact and less expensive system has the potential to
become more widely available to researchers and industry. In
addition, since the extreme ultraviolet laser produces light pulses
with very short duration (4 picoseconds, or trillionths of a
second), the researchers believe it may be possible to create
picosecond-scale snapshots of important processes in other
applications. (Paper CME4, www.cleoconference.org)

FRICTION AT A DISTANCE, the friction between close objects that
aren't in contact, is poorly understood.  Seppe Kuehn and his
colleagues at Cornell have set out to change this.  First, what does
contact mean?  Kuehn (607-254-4685, sk288{at}cornell.edu) suggests that
when two objects are less than about 1 nanometer apart they are said
to be in contact.  One can think of contact friction as being a sort
of micro-velcro process---atomic "hills" in one surface scrape past
atomic "valleys" from the other surface.  To observe non-contact
friction, the friction between two surfaces separated by more than 1
nm, the Cornell researchers use a tiny single-crystal
microcantilever less than a millimeter long and only a few thousands
of atoms thick.
Brought vertically downwards toward a surface, and set in motion,
the cantilever will slow down in proportion to the friction it feels
from the surface beneath.  Surprisingly, the friction force between
the cantilever and sample depends on the chemistry of the sample.
By studying this dependence of non-contact friction on the chemistry
of the sample the Cornell scientists have made the first direct,
mechanical detection of non-contact friction arising from the weak
electric fields caused by motions of molecules in the samples.  The
samples included various polymer materials.  This work is motivated
by recent efforts towards single-molecule MRI which require the
detection of very small forces, and have been hindered by
non-contact friction. (Kuehn, Loring, Marohn, Physical Review
Letters, 21 April 2006) 

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