Abstract
The potential application of nano- and ultrananocrystalline diamond thin films in nanotechnology demands a detailed knowledge of the optical properties and their relation to the structure. By varying the atomic bonding structure and morphological properties of nanodiamond layers we have explored a relation between the structure and the spectral dependence of the refractive index and extinction coefficient in nanodiamond. For this purpose nanodiamond layers were prepared from CH4, H2 and Ar gas mixture in a chemical vapor deposition process with different Ar-content of the feed gas and self-bias of the substrate material. Optical parameters were determined by using a three-layer model in the evaluation of the spectral ellipsometric data. Surface topography was monitored and the average grain size was obtained from scanning electron microscopy images. Bonding characteristics of diamond and non-diamond phases were analyzed by Raman spectroscopy.
Highlights
Nanocrystalline (NCD) and ultrananocrystalline (UNCD) diamond receive increasing scientific attention due to their promising properties and broad application potential
By varying the atomic bonding structure and morphological properties of nanodiamond layers we have explored a relation between the structure and the spectral dependence of the refractive index and extinction coefficient in nanodiamond
UNCD films with grain size of 5-15 nm [5] are grown from Ar-rich plasma, where diamond crystals re-nucleate continuously during film growth, which results in approximately 10% grain boundary fraction in the total volume
Summary
Nanocrystalline (NCD) and ultrananocrystalline (UNCD) diamond receive increasing scientific attention due to their promising properties and broad application potential. Microwave plasma assisted chemical vapor deposition (MW CVD) technique gives us the opportunity to change the morphology of diamond layers, as well as the grain size of diamond nanocrystals from μm to nm by fine tuning the deposition parameters. Main stages of MW CVD process has been established [4] as high density nucleation and plasma assisted film growth, these are completely different in case of NCD and UNCD layers. UNCD films with grain size of 5-15 nm [5] are grown from Ar-rich plasma, where diamond crystals re-nucleate continuously during film growth, which results in approximately 10% grain boundary fraction in the total volume. NCD films with grain size below 100 nm are grown in H-rich plasma, where the continuous etching of sp carbon by atomic hydrogen during growth results lower portion of non-diamond phases in the diamond matrix
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