Thermionic Cooling Devices

摘要

The work functions of Au and Nb films with and without O2 implantation and with Cs film coatings were measured Work functions with values in the range of 1.2-1.3 eV on Nb and Au surfaces coated with Cs were measured. A series of micromachined silicon device structures which featured silicon nitride membranes and fixed pyramidal tips suitable for measuring thermionic currents were fabricated. Numerical predictions for tunneling, field emission and thermionic emission as a function of electrode work function, bias voltages, and electrode gaps made using Simmons model showed that thermionic cooling should be achievable with reasonable parameters. However an error of a factor of 1/2 was found in Simmon's calculation of the image-charge correction to the barrier height which reduces the requirement for the work function from about 1.3eV to about 0.9-1.0eV. No evidence for thermionic currents was observed using Au and Pt electrodes with or without Cs overlayers as expected for the experimental conditions with the modeling based upon the corrected formula.