Electrical and Raman-imaging characterization of laser-made electrodes for 3D diamond detectors

• Fabrication of superficial and buried graphitic structures in diamond by means of ns- and fs-pulsed laser radiation
• Quantitative 2-dimensional maps of the phase composition and of the stress conditions were obtained by micro-Raman imaging.
• A correlation between electrical conductivity and graphitic content was assessed.
• A rationale for the different composition of phases obtained in different condition has been found.

Pulsed laser writing of graphitic electrodes in diamond is a promising technique for innovative particle detectors. Although of great relevance in 3D fabrication, the processes involved in sub-bandgap bulk irradiation are still not well understood. In this work, Raman imaging is exploited to correlate resistivity and graphitic content in 5–10 μm-thick electrodes, obtained both in the domains of femtoseconds and of nanoseconds of pulse duration. A wide interval of resistivities (60–900 mΩcm), according to the irradiation technique employed, are correlated with an sp2 content of the modified material ranging over a factor 2.5. The stress distribution (maximum of about 10 GPa) and the presence of nanostructured sp3 material around the graphitic columns have also been studied by Raman spectroscopy, and a rationale for the conductive behavior of the material is presented in terms of the thermodynamics of the process.