BUCKY BEAMS

Once nanochip manufacturers have made their multi-layered structures it is necessary also for them to verify precisely that the layers are composed in the proper way. One way of doing this is to shoot beams of ions which, like meteorites striking the Moon, eject material from below, providing information about subsurface layering. The ejected material is characterized using mass spectrometry. It seems that to do this large molecules or clusters of atoms are better than single-atom ions since the clusters excavate more cleanly and provide more unambiguous signs of deep structure in the sample being imaged. The lab of Nick Winograd (nxw@psu.edu) of Penn State has pioneered the use of beams of carbon-60 molecules (buckyballs). (See this site for pictures illustrating the difference between single atom probes and C60 beams: http://nxw.chem.psu.edu/nxw/pdf%5C327.pdf ). Recently Winograd and his students have greatly improved the sensitivity of detection of the ejected material by using an infrared laser for photoionization prior to analysis by the mass spectrometer. The infrared laser is effective since electrons can be removed from molecules with high efficiency via tunneling and without significant photofragmentation. (Results presented this week at the AVS meeting in Boston, http://www.avssymposium.org/overview.asp, Paper AS-TuM10)