The work function of ``unactivated'' tantalum carbide is 4.22±0.06 eV. The decrease of work function produced by the so‐called ``activation'' process is attributed to a loss of carbon. The deposition of low‐energy cesium ions (2–5 eV) reduced the work function to a minimum value of 1.40±0.02 eV. Cesium ions with energies of 7–28 eV sputter previously adsorbed cesium in the form of neutral atoms. The energy required to produce this sputtering decreases with increasing cesium coverage.