Field emission in air and space-charge-limited currents from iridium-iridium oxide tips with gaps below 100 nm

Field emission diodes made with Ir/IrO2 tips separated by gaps below 100 nm and operating in air gave currents of up to 1 mu A just above 10 V and largely survived potentials up to 200 V. The current-voltage characteristics included signatures of Fowler-Nordheim emission and both coherent and incoherent space-charge limited emission, where both behaviors implied molecular-scale effective emission areas. The significant, nanoampere currents that flowed at biases below the expected bulk work functions corroborate the 0.1 eV work functions from Fowler-Nordheim analysis, and are attributed to molecular scale oxide structures and adsorbates shifting the surface Fermi level. Electron transit time analysis indicates that on average only one electron crossed the gap at a time, implying that the space-charge effects are due to self-interactions. (C) 2011 American Institute of Physics. [doi:10.1063/1.3573514]