Precipitation and delamination of crystalline graphite bubbles from molten iron, nickel and cobalt by splat cooling

Nearly ideal graphite crystals have been precipitated from molten transition metals for several decades. Curved crystals of graphite have recently been synthesized by precipitation of dissolved carbon from millimeter-scale drops of molten iron, nickel and cobalt, under high vacuum. The surface of a small molten metal drop provides a convenient template for curved graphite crystal growth. When graphite-encapsulated molten metal is splat-cooled in situ, free-standing crystalline graphite membranes spontaneously form. Some of these graphite membranes are spherical bubbles with diameter exceeding 100 μm and thickness on the order of 10 nm. We propose that the curved membranes are inverted replicas of pits in the parent metal. Splat-cooled samples are characterized by SEM, AFM and Raman spectroscopy. Gradually cooled samples are characterized by XRD.