Abstract
Diamond films are advanced engineering materials for various industrial applications requiring a coating material with extremely high thermal conductivity and low electrical conductivity. An approach for the synthesis of diamond films via high-speed jet deposition of thermally activated gas has been applied. In this method, spatially separated high-speed flows of methane and hydrogen were thermally activated, and methyl and hydrogen radicals were deposited on heated molybdenum substrates. The morphology and structure of three diamond films were studied, which were synthesized at a heating power of 900, 1700, or 1800 W, methane flow rate of 10 or 30 sccm, hydrogen flow rate of 1500 or 3500 sccm, and duration of the synthesis from 1.5 to 3 h.The morphology and electronic state of the carbon on the surface and in the bulk of the obtained films were analyzed by scanning electron microscopy, Raman scattering, X-ray photoelectron, and near-edge X-ray absorption fine structure spectroscopies. The diamond micro-crystals with a thick oxidized amorphous sp2-carbon coating were grown at a heating power of 900 W and a hydrogen flow rate of 1500 sccm. The quality of the crystals was improved, and the growth rate of the diamond film was increased seven times when the heating power was 1700–1800 W and the methane and hydrogen flow rates were 30 and 3500 sccm, respectively. Defective octahedral diamond crystals of 30 μm in size with a thin sp2-carbon surface layer were synthesized on a Mo substrate heated at 1273 K for 1.5 h. When the synthesis duration was doubled, and the substrate temperature was decreased to 1073 K, the denser film with rhombic-dodecahedron diamond crystals was grown. In this case, the thinnest hydrogenated sp2-carbon coating was detected on the surface of the diamond crystals.
Highlights
The development of new technical strategies for the rapid synthesis of high-quality diamond films remains an attractive and challenging task
Diamond growth rate was calculated as the ratio between the diameter of the largest particle and the synthesis duration
Since oxygen was not introduced in the synthesis process, we propose that disordered graphitic-like surface carbon contained introduced in the synthesis process, we propose that disordered graphitic-like surface carbon many dangling-bond defects that formed chemical bonds with oxygen atoms when the sample came contained many dangling-bond defects that formed chemical bonds with oxygen atoms when the in contact with laboratory air
Summary
The development of new technical strategies for the rapid synthesis of high-quality diamond films remains an attractive and challenging task. A combination of properties, namely good electrical insulation, high hardness, excellent thermal conductivity, low dielectric constant, and transparency in Materials 2020, 13, 219; doi:10.3390/ma13010219 www.mdpi.com/journal/materials. Thin diamond films can be used as a coating for cutting tools [5], fiber-optic low coherence sensors [6], biosensors [7], ultraviolet photodetectors [4], etc. The conductive diamond films can be applied as an electrode for electrochemistry, electrosynthesis, and electrocatalysis [8]. Polycrystalline diamond films synthesized usingthe energy-assisted chemical vapor deposition (CVD). The CVD technique is based on the dissociation of carbon-containing precursor molecules on the surface of a solid substrate and the subsequent reaction between the decomposition products with the formation of a diamond film
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