Method whittles sharp metal tips

Ultrasharp metal tips can be prepared via a novel electric-field-assisted etching technique developed by researchers at Canada's National Institute for Nanotechnology, in Edmonton, Alberta (J. Chem. Phys. 2006, 124, 204716). Such tips may be useful in scanning probe microscopy, in multiprobe electrical measurements, and as bright sources of coherent electron beams. To prepare the tips, Mohamed Rezeq, Jason Pitters, and Robert A. Wolkow set up a conventional field ionization microscopy experiment, in which an electrochemically treated tungsten needle is subjected to high electric fields to image the atoms near the apex. Then, by exposing the specimen to nitrogen, the team triggers surface reactions that form tiny tungsten protrusions around the periphery of the apex. By tuning the applied electric field, the team confines the regions of maximum field strength to the protrusions and causes those atoms, but not the ones at the tip of the apex, to be stripped away. A video of the atom-by-atom evaporation process is available on C&EN Online, www.cen-online.org/video/NanotipMovie.avi.