Speaker
Description
Synthetic granular ultra-nano-crystalline diamond with high n-type conductivity via nitrogen doping ((N)UNCD) has emerged as a high efficiency photo- or field-emission source in that it has high internal and external quantum efficiency in near UV/visible or low turn-on field, respectively. It is widely anticipated that graphitic grain boundaries (surrounding diamond grains) are behind the high efficiency of (N)UNCD. Grain boundary effect hypotheses rest upon the fact that (N)UNCD emission efficiency can be largely “tuned” through the diamond-to-graphite ratio typically quantified by optical and x-ray spectroscopy techniques.
In addition to high efficiency, we have experimentally observed that (N)UNCD demonstrates some unconventional behaviors that attend electron emission. These are 1) output current saturation [1,2] and 2) light emission [3] during field emission, and 3) intrinsic emittance/mean transverse electron energy independent of the excess photon energy during photoemission [4]. In this talk, we will summarize our recent experimental and theoretical work that further corroborate the critical role of defect grain boundary states on electron emission from (N)UNCD. Specifically, we will outline the role of
1) Density of grain boundary states induced inside diamond fundamental band gap and electron transport properties on the Fowler-Nordheim and saturation regimes of field emission;
2) Electron effective mass on light generation and spectrum during field emission;
3) Ground state photoemission from spatially confined grain boundaries on transverse photoelectron momentum (intrinsic emittance).
We will also outline how the models implying quantum effects associated with graphitic grain-boundary-promoted electron emission can simultaneously account for high efficiency and unconventional behavior of (N)UNCD in a non-contradictory way.
[1] ACS Appl. Mater. Interfaces 9, 33229 (2017)
[2] arXiv:1812.05726 (2018)
[3] arXiv:1811.04186 (2018)
[4] arXiv:1812.00323 (2018), Appl. Phys. Lett., accepted (2019)
