We report the formation of single-crystal diamond nanoneedles

microneedles and thin films on sapphire (0001). By using nanosecond excimer laser pulses

we convert amorphous carbon into a new state of Q-carbon by rapid melting and quenching. The Q-carbon consists of amorphous mostly sp

3

bonded carbon and rest 10–15% sp

2

from which diamonds are nucleated. These nanodiamond nuclei in Q-carbon provide a seed for growth of diamond. These nanoneedles and microneedles are found to be single crystals often oriented along ⟨110⟩ directions. The (111) single-crystal diamond film are formed

when sapphire (0001) provides a seed for diamond growth from super undercooled liquid.