The work function of the W(100) surface has been successfully reduced to 2.6 eV by heating with a thin layer of lutetium oxide, as measured by use of the Fowler-Nordheim plot. Lu2O3 fine powder is attached on shank of a sharp W(100) needle and heated at 10(-7) Pa. Field emission pattern has a fourfold symmetry with a bright center spot. The lowered work function of Lu2O3/W(100) surface was also measured by using photoemission electron microscope. The measured value of work function is 2.56 eV. This resultant value of optical work function is in fairly good agreement with that from the Fowler-Nordheim plot. (C) 2009 American Vacuun Society. [DOI: 10.1116/1.3058726]