The Synthesis of Needle-Like Monocrystalline Diamonds with a High Aspect Ratio up to 14.

Diamond exhibits nontrivial hardness and abrasion, ultra-high thermal conductivity, and light transmission over a wide wavelength range. All these properties are anisotropic. There is considerable literature on the synthesis of large-sized monocrystalline diamonds but the synthesis of highly oriented monocrystalline diamonds is limited. Here, [100] oriented monocrystalline needle-like diamonds are successfully synthesized with an aspect ratio of up to 14 by controlling the temperature gradient and carbon concentration gradient using FeCo alloy as the catalyst at ≈5.8 GPa and 1473 K. The distinctive morphology and microstructure of needle-like diamonds are characterized using Scanning Electron Microscopy, X-ray diffraction, and Focused Ion Beam-Transmission Electron Microscopy. A four-stage growth model is established to elucidate the growth mechanism along the [100], which sheds light on the synthesis of diamonds with predetermines crystal orientations. Increasing the aspect ratio of needle-like diamonds further may enable the development of diamond fibers and assist in the fabrication of laser diamonds with specific orientation requirements.