The induction of a graphite-like phase on diamond films by a Fe-coating/post-annealing process to improve their electron field emission properties

Abstract

The electron field emission (EFE) process for diamond films was tremendously enhanced by Fe-coating and post-annealing processes. Microstructural analysis indicates that the mechanism for the improvement in the EFE process is the formation of nanographites with good crystallinity that surround the Fe (or Fe3C) nanoclusters. Presumably the nanographites were formed via the reaction of Fe clusters with diamond films, viz. by the dissolution of carbons into Fe (or Fe3C) clusters and the reprecipitation of carbon species to the surface of the clusters, a process similar to the growth of carbon nanotubes via Fe clusters as catalyst. Not only is a sufficiently high post-annealing temperature (900°C) required but also a highly active reducing atmosphere (NH3) is needed to give a proper microstructure for enhancing the EFE process. The best EFE properties are obtained by post-annealing the Fe-coated diamond films at 900°C in an NH3 environment for 5 min. The EFE behavior of the films can be turned on at E0 = 1.9 V/μm, attaining a large EFE current density of 315 μA/cm2 at an applied field of 8.8 V/μm (extrapolation using the Fowler–Nordheim model leads to Je = 40.7 mA/cm2 at a 20 V/μm applied field).

The induction of nanographitic phase on Fe coated diamond films for the enhancement in electron field emission properties

“…The Raman spectra of (UNCD) 0 and (Fe/UNCD) 900 films are shown in Figure 4. Contrary to the phenomenon that the Raman spectra of MCD films were predominated with sharp D-band at 1332 cm À1 , the characteristic C 2g Raman resonance of diamond crystals, [14][15][16] the Raman spectra of (UNCD) 0 films contain broad peak positions at 1143, 1333, 1364, 1481, and 1549 cm À1 , which are marked as 1 , D*, D, 3 , and G, respectively (curve I, Fig. 4).…”

“…The Fe coated UNCD films were annealed in H 2 atmosphere, with a flow rate of 100 sccm for 5 min with heating and cooling rate of around 15 C/min. In the previous studies for MCD films, 14,16 it is known that the Fe-to-diamond interaction mainly occurred at 900 C. Therefore, in the present study, we did the Fe coating and annealing processes for the UNCD films at the same high temperatures of 900 C to study the effect of Fe-coating/post-annealing processes on the evolution of microstructure of diamond films on the reaction mechanism and its subsequent effect on EFE properties. The as-deposited and Fe-coated/post-annealed UNCD films at 900 C are designated as (UNCD) 0 and (Fe/ UNCD) 900 , respectively.…”

“…1(b)). These small nanoparticles could be the Fe or Fe 3 C nanoparticles formed by the reaction of Fe with diamond when annealed at high temperature [14][15][16] as discussed later. The occurrence of the new phase like Fe 3 C is also evident from the GIXRD pattern of the (Fe/UNCD) 900 film, shown in Fig.…”

“…Among the various approaches, a thin layer of metallic coating (Au, Cr, Ni, Fe) improves the EFE properties of microcrystalline diamond films significantly. [12][13][14][15][16] Previous study shows improved EFE properties of MCD films by Fe coating and subsequent annealing processes. 14,16 It is expected that the same Fe-to-diamond interaction may also occur for the UNCD films.…”

“…[12][13][14][15][16] Previous study shows improved EFE properties of MCD films by Fe coating and subsequent annealing processes. 14,16 It is expected that the same Fe-to-diamond interaction may also occur for the UNCD films. However, it is not clear whether the difference in granular structure between the MCD and UNCD films will impose different Fe-to-diamond interactions and resulted in different effects on the EFE properties of UNCD films.…”