Abstract Microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films were synthesized on Si substrates by a microwave plasma chemical vapor deposition in methane-hydrogen gas mixtures with a wide range of methane concentrations of 0.5–40%. The samples were investigated with scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. We observed an unusual transition of the produced material structure from MCD to NCD and again to MCD with the increase in CH4 content in the gas. The deposition rate, grain size, and the roughness of the films exhibited extrema in the middle of the methane concentration range ([CH4] = 20%). Further increase of CH4 percentage leads to improvement of the diamond film quality, as confirmed by Raman spectra and SEM images while keeping a high deposition rate. These results may be used for the growth of the wide range of PCD films to be used as multipurpose protective layers, hard coatings for the cutting tools, and the diamond base for composite MCD/NCD structures.

中文翻译：

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在不同的 CH4-H2 混合物中通过微波等离子体 CVD 在 Si 上沉积金刚石薄膜：在非常高的甲烷浓度下反转纳米晶到微晶结构的转变

摘要 微晶金刚石 (MCD) 和纳米晶金刚石 (NCD) 薄膜是通过微波等离子体化学气相沉积在甲烷浓度为 0.5-40% 的甲烷-氢气混合物中在 Si 衬底上合成的。用扫描电子显微镜、原子力显微镜和拉曼光谱研究样品。我们观察到随着气体中 CH4 含量的增加，产生的材料结构从 MCD 到 NCD 再到 MCD 的异常转变。沉积速率、晶粒尺寸和薄膜的粗糙度在甲烷浓度范围（[CH4] = 20%）的中间表现出极值。正如拉曼光谱和 SEM 图像所证实的，在保持高沉积速率的同时，CH4 百分比的进一步增加会导致金刚石膜质量的提高。