Electron field emission for ultrananocrystalline diamond films

Abstract

Microstructure and its effect on field electron emission of grain-size-controlled nanocrystalline diamond films Ultrananocrystalline diamond ͑UNCD͒ films 0.1-2.4 m thick were conformally deposited on sharp single Si microtip emitters, using microwave CH 4 -Ar plasma-enhanced chemical vapor deposition in combination with a dielectrophoretic seeding process. Field-emission studies exhibited stable, extremely high ͑60-100 A/tip͒ emission current, with little variation in threshold fields as a function of film thickness or Si tip radius. The electron emission properties of high aspect ratio Si microtips, coated with diamond using the hot filament chemical vapor deposition ͑HFCVD͒ process were found to be very different from those of the UNCD-coated tips. For the HFCVD process, there is a strong dependence of the emission threshold on both the diamond coating thickness and Si tip radius. Quantum photoyield measurements of the UNCD films revealed that these films have an enhanced density of states within the bulk diamond band gap that is correlated with a reduction in the threshold field for electron emission. In addition, scanning tunneling microscopy studies indicate that the emission sites from UNCD films are related to minima or inflection points in the surface topography, and not to surface asperities. These data, in conjunction with tight binding pseudopotential calculations, indicate that grain boundaries play a critical role in the electron emission properties of UNCD films, such that these boundaries: ͑a͒ provide a conducting path from the substrate to the diamond-vacuum interface, ͑b͒ produce a geometric enhancement in the local electric field via internal structures, rather than surface topography, and ͑c͒ produce an enhancement in the local density of states within the bulk diamond band gap.

Boron-doped ultrananocrystalline diamond synthesized with an H-rich/Ar-lean gas system

“…5a, exhibits the characteristic features of diamond [42], namely the edge jump at ~289.0 eV, the exciton peak at ~289.3 eV, and the second band gap at ~302.5 eV. All these features are due to the C 1s → σ* transition for sp 3 -hybridized carbon-carbon bonds in the crystalline diamond configuration. Besides the characteristic peaks of diamond, a small absorption band at 285.0 eV was detected.…”

“…[1][2][3] While maintaining most of the exceptional physical/chemical properties of conventional diamond materials, UNCD has an extremely low grain size (3-5 nm) and roughness (sub-10 nm) independent of thickness, which drives its popularity as an engineering and functional martial, especially in the fields of tribology, biology, and micro/nano-technology. [4][5] In conventional polycrystalline diamond coatings, for either nanocrystalline diamond (NCD) or microcrystalline diamond (MCD), the gas composition usually consists of CH 4 or other carbon source with majority of hydrogen gas in a chemical vapor deposition (CVD) reactor.…”

Are Diamonds a MEMS' Best Friend?

“…Such breakdown behavior is strongly affected by the geometry (corners) and surfaces (roughness, work function) of the gap structures; hence small process variations and defects could lead to catastrophic failure of higher frequency devices. Although it has been shown that UNCD exhibits good electric field-induced electron emission, this only occurs at high vacuum levels of about 10 −6 to 10 −8 Torr [42]. Conversely, the dc characterization of UNCD-based resonators is done at atmospheric pressure where the mean free path of any electron emitted from the UNCD surface is negligible and therefore electrons would not be emitted or accelerated from that surface.…”

Selectively Deposited Silver Coatings on Gold‐Capped Silicon Nanowires for Surface‐Enhanced Raman Spectroscopy

“…Other applications make use of the large aspect ratio of NWs and their sharp tips, which enable semiconductor NWs to be used as field emitters. [8][9][10] In contrast to the aforementioned applications, in this paper we will show how to employ the metal catalyst atop VLS NWs for sensing, making use of the surface-enhanced Raman scattering (SERS) effect. [11][12][13] SERS is an experimental technique that is nowadays used to detect extremely small quantities of molecules by determining their characteristic Raman signal, that is, their characteristic vibrational modes.…”