Decrystallization of diamond by Nd:YAG and excimer lasers and subsequent lattice relaxation

This paper reports a new phenomenon-decrystallization of a solid by 1-5 eV photons, in a few seconds. A polycrystalline, 20 μm thick layer of CVD diamond on a WC substrate was exposed to two simultaneous pulsed laser beams 308 nm excimer, and 1.06 μm Nd:YAG in air ambient. The rough surface was ablated and smoothed, but the upper exposed half of the diamond layer was shown by Raman spectroscopy and X-ray diffraction to have been transformed to a non-crystalline phase. The 1332 cm− 1 Raman peak disappeared, demonstrating that lattice periodicity had been destroyed. Interestingly, the atomic disorder was gradually relaxed during five years at room temperature, and the Raman signature reappeared. The effect of decreasing intensity of diamond Raman peak has been demonstrated in single-crystal diamond. The distorted diamond lattice relaxed upon annealing in hydrogen plasma. The combination of pressure waves and the heating and cooling cycles is responsible for the creation and subsequent freezing of the atomic disorder, all in the solid state. The metastable states are introduced when atoms in the perfect lattice become displaced from the equilibrium positions. This is the process we term decrystallization-to distinguish it from glass formation, which requires the intermediary liquid state.