Controlled Growth of Large-Area Graphite Single Crystals at Atmospheric Pressure and High Temperature from a Metal Flux

In this study, the growth of high-quality graphite single crystals from a molten metal flux at atmospheric pressure was optimized. The crystals were precipitated from a saturated iron–carbon solution by slowly cooling (4 °C/h) from a maximum temperature to reduce the carbon solubility. The graphite flakes were >25 square millimeters in area and >10 microns thick, with individual crystal grains as large as 1.2 mm2. The crystals were (0002) oriented, as determined by X-ray diffraction. The high structural quality of the graphite crystals was verified by Raman spectroscopy. For graphite with the natural distribution of carbon isotopes, the G-peak at 1580 cm−1 was narrow (~12 cm−1) and the defect peak (D-peak) was absent. To demonstrate the process versatility, graphite crystals enriched in the 13C isotope were grown at 5 degrees of enrichment. The Raman G-peak linearly shifted from 1580 cm−1 to 1520 cm−1 for graphite crystals enriched from 1 to 99% 13C. The etch pit densities from defect-sensitive etching ranged from 0 to 1.6 × 108 per cm2. The process was refined by examining the grain size and quality as functions of the carbon concentration in the starting sources, the carrier gas composition, and maximum temperature. The simplicity of this process suggests it can be scaled to produce very large graphite crystals that would be suitable for a wide range of technologies.