Locally Resolved Electron Emission Area and Unified View of Field Emission from Ultrananocrystalline Diamond Films

Abstract

In this paper, we study the effect of the actual, locally resolved, field emission area on electron emission characteristics of uniform planar conductive nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) field emitters. High resolution imaging experiments were carried out in a field emission microscope with a specialty imaging anode screen such that electron emission micrographs were taken concurrently with measurements of I-V characteristics. An automated image processing algorithm was applied to process the extensive imaging data sets and calculate the emission area per image. It was routinely found that field emission from as-grown planar (N)UNCD films was always confined to a counted number of discrete emitting centers across the surface, which varied in size and electron emissivity. It was established that the actual field emission area critically depends on the applied electric field and that the field emission area and overall electron emissivity improve with the sp-fraction present in the film, irrespective of the original substrate roughness or morphology. Most importantly, when as-measured I-E characteristics were normalized by the electric field-dependent emission area, the resulting j-E curves demonstrated a strong kink and departed from the Fowler-Nordheim law, finally saturating at a value on the order of 100 mA/cm. This value was nearly identical for all studied films regardless of substrate. It was concluded that the saturation value is specific to the intrinsic fundamental properties of (N)UNCD.

Field emission microscopy of carbon nanotube fibers: Evaluating and interpreting spatial emission

“…The presented results are an experimental evidence that support the earlier PIC findings. This result is also supported by our earlier studies of nanodiamond emitters in which δS grows nonlinearly with the electric field [16]. Together, this result adds to concerns raised in recent literature [18,19] about the validity of FN equation application for extracting the emission area.…”

“…The calculated dependence δS(E) for sample B is shown in Fig.6 as the decaying blue solid line. However, the results obtained using a custom image processing algorithm developed by our group before [16] show opposite trend: δS is predicted to increase as the applied field increases (red solid line in Fig.6). Field emission micrographs taken concurrently with I − E curves and processed in batches point out that local emitting maxima multiply with the field.…”

High power conditioning and benchmarking of planar nitrogen-incorporated ultrananocrystalline diamond field emission electron source

“…In addition, the (N)UNCD emitting surface was visualized in the rf gun environment with high resolution which showed a large number of localized emitters (density over 100/cm 2 ) distributed across the surface. This result is consistent with results obtained in dc setups [18,27,28]. This paper is organized as follows: Sec.…”

“…Under the experimental conditions (E c,max of 36 MV/m, B f of 750 Gauss, B i of 250 Gauss, and the aperture diameter of 1 mm), R ρ , R ϕ , and mag are simulated to be ∼300 µm, ∼10 µm, and 3.7, respectively. It should be noted that the resolution is not adequate to resolve the fine structure of (N)UNCD emitters whose sizes were determined to be on the order of µm and below in previous dc studies [18,27,28]. The achievable resolution in the experiment could be worse than in the simulation due to the camera resolution, the low signal-to-noise ratio images, the rf amplitude jitter, the variation of E c within the rf pulse, etc.…”

Theoretical evaluation of electronic density-of-states and transport effects on field emission from n-type ultrananocrystalline diamond films

“…It means that the emission area, which contributes to the current density, varies with the electric field as well. The methodology 30 developed for determining the FE area from large-area electron emitters makes it possible to study the current-density saturation effect present in n-type (N)UNCD films and to confirm or reject various hypotheses, which were proposed in the past, on the nature of this effect.…”