The tungsten (100) surface modified by praseodymium oxide is observed by x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED). Pr metal is deposited on single-crystalline W(100). Then, when the Pr on the sample is oxidized, it changes into Pr2O3. The sample is flash heated in an ultrahigh-vacuum chamber between 1100 and 2000 K at 100 K intervals and is observed by XPS and LEED simultaneously. No peak shift or periodic pattern is observed. Next, under the same conditions, the work function of the sample is measured by photoelectron emission microscopy yielding a value of 3.1 eV. The results suggest that although the W(100) modified by Pr oxide has no Pr-O composite and no particular atomic arrangement like ZrO/W(100), the work function is reduced. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3070656]