Laser-irradiation-induced structural changes on graphite

Abstract

Pyrolytic graphite has been irradiated with high-energy density laser pulses ͑248 nm wavelength, 20 ns duration, and up to 250 J/cm 2 energy density͒. Craters with depth up to 5 m have been obtained by irradiating with a single pulse and the bottom of the craters has been analyzed with many techniques to investigate the possible morphological and structural modifications induced in the irradiated material where temperature and pressure fields, appropriate to the graphite-diamond phase transition, may be achieved. Melting of the surface layers of the irradiated graphite was realized, as established with scanning electron microscopy, while the estimated and measured pressure attained a maximum value on the order of 2.5 GPa. The temperature profile depends on the depth below the irradiated surface and the observed structural modifications are associated with different depths. Just below an ordered sp 2 hybridized nanocrystalline graphite surface layer, a disordered graphitic layer was formed, within which diamond particles with spheroidal geometry are embedded.

Target-plane deposition of diamond-like carbon in pulsed laser ablation of graphite

“…The postannealing process also converted the DLC at the narrow ring back to the graphite. This work disputed the graphite-to-diamond transformation based on the volume contraction via rapid cooling after laser-induced melting, as was also briefly mentioned in other reports [16][17][18]. These reports did not mention about any target-plane deposition of DLC.…”

Transformation of graphite into nanodiamond following extreme electronic excitations

“…41 Notice that even when bombarding particles are absent, such as when irradiating with intense uv laser pulses highly oriented pyrolytic graphite, a TEM analysis of the irradiated target showed the presence of sherelike nanocrystalline diamond particles formed when a shock wave was generated towards the bulk of the target upon violent evaporation of a cloud of particles ͑atoms and small clusters͒ from the molten surface layer. 42 As reported in Ref. 43, during shock-compression experiments, "only small particles of diamond can be produced because of the very short time at high temperature and pressure and the necessity for the individual particles to be small in order to satisfy the fast thermal quench requirement."…”

The effect of laser wavelength on the ablation rate of carbon

“…In this paper, the ablation of graphite is studied as a function of laser fluence for various wavelength of a Nd:YAG laser. The ablation of graphite is used to obtain a wide variety of carbon allotropes, such as diamond-like carbon films [9,10], diamond crystallites [11] fullerene carbon molecules [12], carbon nanotubes [13,14], carbon nanowalls [15] and graphene [16,17] as well as for the removal of co-deposited layers from plasma limiters in tokamaks [18]. However, there are only a sparse measurements of such factors as the ablation or explosive boiling threshold for nanosecond laser pulse [3,4,[19][20][21].…”