The field electron microscope has been used previously to measure the work function of thermally smoothed single‐crystal tungsten planes. In this work the field ion microscope is used to create atomically perfect single‐crystal planes by field evaporation and then to observe and preserve these clean surfaces. The slope of the field emission Fowler‐Nordheim plot then gives the ratio of the three halves power of the work function to the field. Two techniques have been developed in order to obtain a second relationship between work function and field: (1) temperature dependence of field‐emission current density and (2) energy distribution of field‐emitted electrons. While investigating temperature dependence it was found that a reinterpretation of the Gel'berget al.data for the work function temperature dependence of molybdenum up to 1100°K revealed the following unexpected cubic temperature dependence: &phgr;T=&phgr;0+0.44×10−10T3ev.