Spatial Self-Organization of Laser-Induced Graphite Nanonetwork in Diamond

The interior of spontaneously growing graphitized microstructures formed in diamond bulk by picosecond laser pulses has been studied. Longitudinal and cross sections of microstructures, prepared using mechanical polishing and focused ion beam, have been studied by Raman spectroscopy and scanning electron-ion microscopy. The laser irradiation of diamond bulk is found to induce formation of a graphite nanonetwork in the processed region and its subsequent spontaneous growth towards the laser beam by a distance of similar to 60 mu m. The graphite nanonetwork consists of many similar to 130-nm-thick graphite sheets clustered into segments. It is shown that the thickness of graphite sheets decreases with a decrease in the laser fluence at the modification front, whereas the segment length (similar to 2.6 mu m) is independent of the laser fluence at the modification front. A three-dimensional structural model of microsegment has been constructed based on the analysis of several longitudinal and cross sections of microstructures. The mechanism of graphite nanosheet clustering into microsegments is discussed.