Microstructural Effect on the Enhancement of Field Electron Emission Properties of Nanocrystalline Diamond Films by Li-Ion Implantation and Annealing Processes

Abstract

The impact of lithium-ion implantation and postannealing processes on improving the electrical conductivity and field electron emission (FEE) characteristics of nitrogen-doped nanocrystalline diamond (nNCD) films was observed to be distinctly different from those of undoped NCD (uNCD) films. A high-dose Li-ion implantation induced the formation of electron trap centers inside the diamond grains and amorphous carbon (a-C) phases in grain boundaries for both types of NCD films. Postannealing at 1000 °C healed the defects, eliminated the electron trap centers, and converted the a-C into nanographitic phases. The abundant nanographitic phases in the grain boundaries of the nNCD films as compared to the uNCD films made an interconnected path for effectual electron transport and consequently enhanced the FEE characteristics of nNCD films.

Low Temperature Synthesis of Lithium-Doped Nanocrystalline Diamond Films with Enhanced Field Electron Emission Properties

“…Therefore, it is reasonable to assume that Li atoms are not doped inside the diamond grains but tend to aggregate or couple with other impurities in the NCD films. Restated, the diffused Li into the NCD films tend to reside at the grain boundaries, which can activate the formation of nanographitic phases, as like the case reported by Sankaran et al [ 32 ], and thereby, forming conduction nanochannels that provide grain boundary transport. While such an assumption for the role of Li incorporation into NCD films on enhancing the conductivity of the materials sounds quite reasonable, further microstructural investigation using transmission electron microscopy is required to directly elucidate the formation of nanographitic phases at the grain boundaries due to Li doping.…”

Microwave plasma modelling in clamshell chemical vapour deposition diamond reactors

“…Although PCD diamond growth with low non-diamond carbon impurities typically occurs at high MWPD, the lower pressure solutions are an imperative result for several purposes. The first is that some applications involve nano-crystalline diamond (NCD) and ultra-nanocrystalline diamond (UNCD) which is typically grown at lower power densities [50,51,52] as well as hybrid graphene-diamond films [53]. The second is to ensure that the plasma can actually be ignited at the right place in the chamber.…”

“…Amongst this diamond peak are several broad bands associated with various non-diamond carbon impurities. The weak band at approximately 1420 cm −1 and even weaker band at approximately 1120 cm −1 are both attributed to trans-polyacetylene (tPA), commonly found in CVD diamond Raman spectra although are only dominant at particularly low grain sizes such as nanocrystalline diamond (NCD) [63,52,64]. The broad band at approximately 1310 to 1340 cm −1 is attributed to the A 1g breathing mode of aromatic sp 2 carbon rings, while the peak at around 1580 to 1610 cm −1 is attributed to the E 2g bond stretching mode in sp 2 carbon [64].…”

Low-Defect Nanodiamonds and Graphene Nanoribbons Enhanced Electron Field Emission Properties in Ultrananocrystalline Diamond Films

“…3 Li ions were also introduced into NCD films by implantation to obtain better EFE properties. 4 UNCD films generally consist of NCD grains (∼5−10 nm) and grain boundaries (GBs) composed of sp 2 -phase carbon. This unique structure significantly enhanced EFE properties relative to those of conventional MCD films and NCD films.…”

“…For example, implantation of Ag ions into MCD films has achieved a turn-on voltage of 18 V/μm and an EFE current density of 89.6 μA/cm 2 at 30 V/μm . Li ions were also introduced into NCD films by implantation to obtain better EFE properties . UNCD films generally consist of NCD grains (∼5–10 nm) and grain boundaries (GBs) composed of sp 2 -phase carbon.…”