Phase Transition, Structural Defects and Stress Development in Superficial and Buried Regions of Femtosecond Laser Modified Diamond

Micro-Raman spectroscopy has been used to monitor structural defects and stress state developing in 3D graphitic electrodes realized by laser irradiation for the achievement of optimized carrier collection in ionizing radiation and particle diamond detectors. Buried graphitic pillars were fabricated in a single-crystal CVD-diamond sample by means of a 400 fs pulsed laser operating at ?=1030 nm. The same conditions were also used for the realization of two series of graphitic strips on the surface allowing buried pillars connections. MicroRaman spectra of untreated regions exhibits the typical diamond peak at 1332 cm-1 which changes in intensity, width and position within the graphitic surface strips, where a G band in the range 1580-1600 cm-1 is also detected suggesting a mixed composition of the laser modified material. Strength decrease, shifting and broadening of the diamond Raman peak is detected by crossing graphitic electrodes and along buried pillars, pointing out that phase transition from diamond to graphitic carbon is accompanied both by stress development and by structural disorder in the residual diamond tissue. In these regions, Raman spectra also exhibits a broad photoluminescence background signal, whose intensity appears related to graphitization process. In particular, a splitting of the diamond Raman peak is detected around pillars on the top surfaces suggesting the occurrence of a laser-induced anisotropic stress. From these results it is then tentatively suggested that charge transport in laser modified regions occurs through both graphitic carbon and disordered diamond paths, thereby affecting the 3D carrier collection.