Microstructure and its effect on field electron emission of grain-size-controlled nanocrystalline diamond films

Abstract

Nanocrystalline diamond films were grown by microwave plasma assisted chemical vapor deposition using N2 and CH4 as precursors . The microstructure of the films such as the diamond grain size, graphite content, and N incorporation, was controlled by introducing a small amount of hydrogen gas (0-10 sccm) in the growth. Effects of the growth parameters on the film microstructure were investigated using transmission electron microscopy, x-ray diffraction, Raman spectroscopy, and secondary ion mass spectroscopy. A surface stabilizing model is suggested to explain the formation mechanism of the uniformly grain size-controlled nanocrystalline diamond. A systematic investigation on the film microstructure and their field electron emission (FEE) property is presented for varoius films of different diamond grain sizes and graphite contents. It was found that the FEE property highly depended on the diamond/graphite mixed phase structure. Novel field emission properties (1 V/mum emission threshold an 10mA/cm² emission current) are obtained by optimizing the growth parameters. A transport-tunneling mechanism is applied to explain the experimental observations. Our results showed that nanocrystalline diamond film can be a very promising cold cathode material for field emission applications

Correlation between diamond grain size and hydrogen incorporation in nanocrystalline diamond thin films

“…The C 2 species are known to nucleate easily in hydrogen-poor environment, resulting in ultra-small diamond clusters [1]. The CH species present in the plasma are presumed to adhere instantaneously to the nanosized diamond clusters, forming hydrocarbon layer, which prevents direct contact of the incoming C 2 species with the diamond surface [3]. Therefore, the incoming C 2 species can only re-nucleate again to form another nanosized diamond clusters, rather than attach to the existing diamond surface to enlarge the size of the diamond grains.…”

“…The unique structure of UNCD, consisting of nanometre-sized (2À5 nm) sp 3 -bonded grains and a relatively large volume (10%) of grain boundaries consisting of mixed bonding states of sp 2 , sp 3 and intermediates, makes the structure more interesting. Thus, there is a possibility for incorporated hydrogen to make bonds with non-diamond phases.…”

“…How the processing parameter, i.e. the hydrogen concentration altered the microstructure of the diamond films has been widely investigated [3,4], but the results are controversial. Hydrogen is the key component of the gas mixture usually used for diamond nucleation and growth by CVD methods.…”

“…The non-diamond contents and the crystal size of diamond grains in the films play a crucial role in applications such as electron field emitters. Unlike the synthesis of MCD films that used H 2 -rich plasma, the growth of UNCD films usually used hydrogen-poor plasma [3]. How the processing parameter, i.e.…”

Precursors for CVD Growth of Nanocrystalline Diamond

“…Wu et al [14,15] grew NCD films using N 2 /CH 4 /H 2 in MPCVD system. NCD films with grain size of 8 nm embedded in a-C matrix was obtained without any hydrogen.…”