Phase transition, structural defects and stress development in superficial and buried regions of femtosecond laser modified diamond

Abstract Micro-Raman spectroscopy has been used to monitor structural defects and stress state developing in diamond due to formation of 3D graphitic electrodes 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 λ = 1030 nm. The same conditions were also used for the realization of two series of graphitic strips on the surface allowing buried pillars connections. Micro-Raman spectra of untreated regions exhibit the typical diamond peak at 1332 cm−1 which largely changes within the laser modified regions, where a G band in the range 1580–1600 cm−1 is also detected. Strength decrease, shifting and broadening of the diamond Raman peak are observed 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 structural disorder in the residual diamond tissue. In these regions, Raman spectra also exhibit 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 biaxial stress. From these results it is then tentatively suggested that conduction in the realized electrodes occurs through both conductive graphitic phases and disordered diamond paths, whereas detector performance is mainly related to charge transport within virgin diamond.