Electron emission concentrates selectively on the (100) surface at the top of a needle-shaped tungsten tip when a slight amount of Y2O3 powder is put on the side surface of the tip and heat-treated afterward [T. Kawakubo , J. Vac. Sci. Technol. B 22, 1258 (2004)]. The work function determined by the Fowler-Nordheim plot shows an extremely low value of 2.0 eV. The value is much lower than the 4.6 eV of the bare tungsten (100) surface and lower than the 2.7 eV of the ZrO/W(100) thermal field-emission cathode, which is used for electron sources for scanning-electron microscopes and for some mask-patterning equipment for the semiconductor industry. The apparently low value of the work function motivated us to investigate the surface using x-ray photoelectron spectroscopy and low-energy electron diffraction. The experimental results do not agree with the results of the ZrO/W(100) surface. (c) 2008 American Vacuum Society.