Ultrananocrystalline diamond (UNCD) films for field emission-based science and devices

Abstract

Ultrananocrystalline diamond (UNCD) films developed and patented at Argonne National Laboratory (ANL) exhibit a unique combination of outstanding mechanical, tribological, electrical, thermal, biological and electron field emission properties, which already resulted in industrial components and devices currently commercialized by Advanced Diamond Technologies, a company co-founded by ANL scientists in 2003. UNCD films are synthesized by a novel patented microwave plasma chemical vapor deposition technique using an Ar-rich/CH4 chemistry that produces films with 2–5 nm grains, thus the name UNCD to distinguish them from nanocrystalline diamond films with 30–100 nm grains produced by H-rich/CH4 plasma chemistry. In relation to the topic of this talk, UNCD films can be made electrically conducting via nitrogen incorporation into the grain boundaries (N-UNCD), which introduces states into the bandgap and allow hoping of electrons for conduction and final field emission through the grain boundaries, or by boron doping via substitutional replacement of C atoms in the diamond lattice. In this talk, a review will be presented of the synthesis of N-UNCD films, and studies to understand the mechanism for electron field emission from them, with studies showing that N-UNCD films exhibit low field emission thresholds (∼ 2–4 V/μm) with long lifetime emission (∼ 1000 hours), with the additional advantages of inherent field enhancement at the nanoscale grain boundaries and low threshold field, even in the presence of residual gases such as O2, in about 10 −4 Torr pressure. The electron field emission performance of N-UNCD fims enable their use as field emitter cathodes for planetary mass spectrometry, specifically, gas-phase ionization of target molecules, in which a low power means of generating an electron beam of the appropriate performance could benefit resource-constrained missions to remote planetary targets throughout the Solar System. On the technological side, the N-UNCD field emitters are promissing enough to be used for field emission displays and for massive parallel electron field emission lithography to fabricate ferroelectric nanostructures for the fabrication of the next generation high-density (Gb to Tb) non-volatile ferroelectric memories.