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 nd Laser Science Conference meeting in California, Courtney Brewer of Colorado State University (brewerca@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@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)