On the growth mechanisms of nanocrystalline diamond films

Abstract

Nanocrystalline diamond/amorphous carbon (NCD/a‐C) composite films have been deposited by microwave chemical vapour deposition from methane‐rich CH4/N2 mixtures and characterized carefully by a variety of methods with respect to morphology and structure, composition, crystallinity, and bonding environment. The films consist of diamond nanocrystals of 3–5 nm diameter, which are embedded in an amorphous carbon matrix of 1–1.5 nm width. The matrix is a mixture of sp2 (20–30%) and sp3 bonded carbon and contains about 20% of hydrogen, mostly bonded to sp3 carbon atoms. New experiments are reported carried out to study the nucleation and the growth on a microscopic and macroscopic scale. No differences to standard deposition of polycrystalline diamond (PCD) with respect to the nucleation step were observed, i.e. in order to achieve a high nucleation density an appropriate substrate pretreatment is required. In contrast, there are strong differences in the growth mechanisms of NCD and PCD, respectively. Most importantly, there is a high rate of secondary nucleation observed in NCD deposition. On a macroscopic scale, this leads to a spherulitic growth of NCD films. The microscopic mechanisms leading to this high rate of secondary nucleation are discussed in terms of the deposition parameters leading to NCD growth, namely gas phase constituents and composition, pressure, substrate temperature, and bias voltage. Defect formation under the special conditions of NCD deposition is identified as a major reason. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Modelling the Influence of the Nucleation Density on Ultra Nano Crystalline Diamond Growth Morphology: Preliminary Results

“…The diamond spheres were randomly distributed over the surface following the secondary nucleation rate and the probability to nucleate on the bare substrate. The simple geometrical model leads, in these first results, to a good comparison with published experimental data in the literature; [2] low primary nucleation layers result in the growth of separated diamond islands. Surfaces with a stabilized surface roughness after 2000 nucleation layers are obtained only with the highest primary nucleation density.…”

“…[1][2][3] One remarkable characteristic feature of this material is a grain size independent of the film thickness, obtained by the high secondary nucleation rate during deposition. [1] The small grain size allows the deposition of very smooth diamond films with rms values down to 10 nm.…”

“…[14,15] Experimentally, it was found that the morphology of the UNCD/NCD films depends strongly on the diamond nucleation density on the substrate material; low nucleation densities result in a surface consisting of an arrangement of separated diamond spheres, whereas each sphere consists of UNCD. [2,6] High primary nucleation densities around 10 10 cm À2 (on silicon usually obtained after a seeding procedure, e.g., a slurry of diamond powder in an ultrasonic bath or by applying a bias voltage during the first growth steps) allow the deposition of smooth films. [16] To obtain very thin coalescent UNCD films it is useful to know the primary nucleation density required to achieve a fully closed diamond film.…”

Surface modification of nanocrystalline diamond/amorphous carbon composite films

“…Owing to their mechanical, electrical and electrochemical properties, and biocompatibility, polycrystalline diamond films (PCD), and especially nanocrystalline diamond films (NCD) due to their reduced surface roughness [1,2] are most promising candidates for applications in fields such as electrochemistry, MEMS, biotechnology, biosensors, etc. [3,4].…”

Enhancement in Tribological and Mechanical Properties of Cemented Tungsten Carbide Substrates using CVD-diamond Coatings

“…Hence, increase in methane concentration gives secondary diamond nucleation and therefore, a cauliflower type of grain shape is mainly observed at the NCD surface. In case of MCD coating the columnar structure of grains and faceted form of surface morphology was generally observed at methane concentration of 1 % [23]. Figure 5 (a, b) and Fig.…”