Measurements of cooling by room-temperature thermionic emission across a nanometer gap

We have completed an investigation of cooling at room temperature by thermionic emission. The use of a small nm-sized gap lowered the vacuum barrier between the electrodes, enabling emission from surfaces with work functions of ∼1 eV at room temperature. We utilized a microfabricated cantilever with a cesiated metal coating on the tip, and an integrated thermometer to initiate and control an emission current of 1–10 nA, and to detect the resulting temperature changes. Using a lock-in technique, temperature changes of 0.1–1.0 mK were observed, corresponding to cooling power of 1–10 nW. The amplitude of this signal and its dependence on emission current and bias voltage are in good agreement with our model. Possible applications for cooling and energy conversion are discussed.