Microfabricated field emission devices using carbon nanofibers as cathode elements

Abstract

The digital electrostatic electron beam array lithography concept under development at the Oak Ridge National Laboratory proposes performing direct write electron beam lithography with a massively parallel array of electron emitters operating simultaneously within a digitally programmable microfabricated field emitter array (FEA). Recently we have concentrated our research efforts on the field emission (FE) properties of deterministically grown vertically aligned carbon nanofibers (VACNFs). We have measured the FE properties of isolated VACNFs using a moveable current probe and found that they have low FE turn-on fields and can achieve stable emission for extended periods of time in moderate vacuum. In order to use the VACNF in microfabricated FEA devices we have subjected them to a variety of processing phenomenon including reactive ion etching and plasma enhanced chemical vapor deposition, and found them to be quite robust. Using these processes we have fabricated operational gated cathode structures with single VACNFs cathodes. The issues involved in this fabrication process and the performance of these devices are discussed.

Investigating the plasma chemistry for the synthesis of carbon nanotubes/nanofibres in an inductively coupled plasma enhanced CVD system: the effect of different gas mixtures

“…Some radical and ionic species (e.g. C 3 H x , C 3 H y + ,…) as well as the negative ions are not incorporated in the model, although they might be present in a CH 4 plasma, but they have much lower densities. Note that the electron impact reactions are treated with energy dependent cross sections, whereas the ion and neutral reactions are described by rate coefficients.…”

“…Two-dimensional carbon nanowalls were deposited in CCP-PECVD with C 2 F 6 (CH 4 /CF 4 )/H 2 mixtures by Hiramatsu et al [16]. Indeed, the authors found that the carbon nanowalls grown using CH 4 /H 2 were waved and thin instead of vertically aligned.…”

“…Since then CNTs gained a lot of attention due to their unique physical, chemical and electronic properties, as well as their wide potential applications including nanoelectronics [2], hydrogen storage [3], and field emission devices [4]. Carbon nanobutes are divided into two categories due to their different structures [5]: singlewalled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).…”

“…They suggested that the diffusion of carbon on the catalyst surface is the rate-determining step at low temperature. Okita et al [15] investigated the effects of hydrogen on CNT formation in a capacitive CH 4 /H 2 plasma in the pressure range of 1~10 Torr, a total flow rate of 30 sccm, 4 W input power and a growth time of 10~90 minutes. They concluded that the gas ratio of CH 4 /H 2 = 27/3 at a growth time of 10 minutes was efficient for CNT growth, and the amount of carbon atoms in the CNT agreed well with results from 1D fluid simulations (see below).…”

“…Among these growth techniques, PECVD has become a very promising technology for the direct synthesis of vertically aligned CNTs/CNFs used for field emission devices [32][33][34][35]. A variety of plasma sources, such as microwave discharges(MW) [9,10], hot-filament(HF) [11], dc-glow discharges(DC) [12-14, 26, 27], RF capacitively coupled plasmas(CCP) [15,16] and RF inductively coupled plasmas(ICP) [17-24, 30, 31], have been used to generate a plasma of typical feedstock mixtures such as CH 4 or C 2 H 2 mixed with either H 2 or NH 3 . The recent progress in PECVD for CNT/CNF synthesis has been summarized in table 1 and 2.…”