Vertically Aligned Boron-Doped Diamond Hollow Nanoneedle Arrays for Enhanced Field Emission

Abstract

Lower turn-on field (E TO) and threshold field (E THR), as well as a higher current density, are desired characteristics of materials and structures for field emission (FE) applications. In this work, the properties of a boron-doped diamond (BDD) hollow nanoneedle array (HNNA) structure were remarkably enhanced through surface state modulation. By designedly controlling the surface roughness and boron concentration of the BDD film, a uniform and dense HNNA with a high aspect ratio (∼21.3) was constructed by applying O2 + Cl2 inductively coupled plasma reactive ion etching (ICP-RIE) for an optimal duration (90 min). Although the maximum HNNA density (∼5.5 × 106 mm–2) is produced at a shorter duration, the overall FE performance is even worse than that of the BDD film without an HNNA, arising from the field shielding effect and incomplete elimination of defective needles. The finally formed Actiniaria tentacle-like HNNA structure is associated with the masking role of oxidized Si and amorphous carbon on the top edge of the needle embryos, resulting from the electric field edge effect and Si supply accompanying the substrate. Meanwhile, the sp2 carbon generated by ICP-RIE on the surface of the as-etched HNNA promotes the FE, showing a minimum E TO of 0.11 V/μm. After moderate hydrogen plasma treatment, owing to the negative electron affinity (NEA) of C–H on p-type BDD with downward band bending of the conduction band minimum and local electric field enhancement induced by the hollow nanostructure, the hydrogen-terminated BDD–HNNA shows excellent FE stability and a linear Fowler–Nordheim relation with a lower E TO of 0.38 V/μm and E THR of 2.21 V/μm and a desirable current density of 6532 μA/cm2 at 3.75 V/μm. The comprehensive FE properties of the surface-modulated high-quality BDD–HNNA exceed those of the vast majority of other conventional or popular nanostructural counterparts.

Improvement of field emission performances by DMSO and PEDOT:PSS treated freestanding CNT clusters

“…Hence, although the turn-on electric field is not significantly improved and is still much higher than those of many reported ultralow turn-on field emitters, these two treatment methods greatly extend the lifetime of CNT emitters, which is longer than the lifetime of those field emitters with lower turn-on electric fields. [16][17][18][19][20][21][22]24,44,45 Therefore, this simple and costsaving treatment gives CNT emitters an advantage over other types of CNT emitters as well as other carbon material-based emitters.…”

“…Hence, because of the low lifetime of CNT field emitters, researchers gradually turned to finding other carbon materials with better field emission properties, such as diamond or nano walls. [16][17][18][19][20] These carbon-based field emitters have been found to have lower turn-on voltages and more stable emission currents and longer lifetime, especially after certain chemical treatments. However, these types of emitters usually have a relatively more complex and costly fab-rication process.…”