Structuring nanodiamond cone arrays for improved field emission

Abstract

A structuring method capable of producing uniform, large-area cone arrays of diamond films was developed. The technique employs bias-assisted reactive ion etching and is applicable to any structure of diamond films ranging from microcrystalline to nanocrystalline. Variation of the etching conditions enables control of the cone density, geometry, and height. Surface nanostructuring of cone arrays significantly improves the field emission properties of diamond films of all kinds. The turn on field is reduced to 6 and 10 V/μm for nanodiamond and microdiamond films, respectively, (compared to >25 V/μm for as deposited surfaces). Lower cone density yields better field electron emission (lower turn-on electrical field) due to the screening in high-density cone arrays. The field emission properties are determined by both the enhancement factor of the cone array and the emitting properties of the material. The field electron emission properties of nanodiamond arrays are better than cone arrays of single crystalline diamond with a similar cone density and cone geometry.

Field electron emission from individual diamond cone formed by plasma etching

“…In our experiments, the electrical field at the cone tip is 25 V / m at the voltage of 10 V between diamond cone and anode probe, which is determined using the equation 14 The emission current from the individual cone is about 1 ϫ 10 −2 A at 25 V/ m. The field enhancement factor ␤ for conical structure is expressed by 2.1͑h / r + 0.8͒ 0.73 , 15 and it is calculated as 325 for the present individual diamond cone when assuming the cone height of 5.1 m and cone apex radius R tip of 5 nm. At the same electrical field ͑25 V / m͒, Zhang et al reported an emission current density of about 10 2 mA/ cm 2 from single-crystal diamond cone arrays, 6 from which the emission current of a single diamond cone can be estimated as 5 ϫ 10 −4 A assuming a cone density of 2 ϫ 10 8 cm −2 . The present study indicates that the emission properties of individual diamond cone are greatly improved due to the exclusion of field shield effect.…”

“…Zhang et al reported the FEE properties of diamond cone arrays formed by bias-assisted reactive etching process. 5,6 However, the FEE properties of individual diamond cone, which can present the intrinsic FEE properties of diamond cone due to the exclusion of field shield effect, have not been studied so far. Recently, a maskless technique using ion sputtering has been developed for the formation of sharp silicon cone arrays on porous silicon.…”

Nanodiamonds for field emission: state of the art

“…As reported in ref. 95, the turn-on fields were 26.9, 6.2, 18.2, and 10.1 V μm −1 for the pristine flat nanocrystalline diamond film, a low-density nanocone array, a highdensity nanocone array, and an array of single-crystal diamond nanocones, respectively. The significant reduction of the turnon field by lowering the nanocone density from 10 8 cm −2 to 10 6 cm −2 is likely due to the elimination of the screening effect acting between adjacent emitters.…”

“…14 shows the SEM image (Fig. 14a) of an array of diamond nanocones produced by plasma etching of nanosized grains 95 and the TEM image (Fig. 14b) detailing dimensions and single-crystalline nature of a single nanotip.…”

“…The removal of the material starts from the grain boundaries, and the process proceeds by sharpening the isolated nanograins to obtain the final conical features as a consequence of an etching rate that is faster across the height of the gradually protruding diamond structures. [95][96][97] A programmed treatment consisting of nitrogen plasma immersion ion implantation has been carried out on crystalline diamond nanotips (∼1 µm in height, ∼200 nm bottom diameter) produced by MW-enhanced CVD. 78 After the nitrogen treatment a turn-on field of 3 V μm −1 and a current density up to 4 mA cm −2 at the applied field of 9 V μm −1 were measured.…”