Conductive graphitic layers induced in diamond by multi-species focused ion beam

Irradiation of diamond surface by energetic ion beams has represented a useful and flexible technique to modify the material properties in order to comply with quantum technology needs. For instance, ion implantation is a reliable process to create color centers (CCs) in diamond, due to its ability to define their concentration and three dimensional location1, where the ion kinetic energy defines the depth of the implanted species whereas a nanometric lithography can define the lateral positioning. Besides that, ion implantation can also permanently modify the crystallographic phase of diamond. Indeed, if the ion fluence is able to completely amorphize volume of diamond, the hybridized sp3 bonds of diamond are converted to the sp2 configuration and subsequent thermal annealing can only convert the irradiated areas to graphite in an irreversible way2. This effect, clearly detrimental to the formation of CCs, can be useful considering that the graphitic layers are electrically conductive. Therefore, they can be exploited to create integrated or buried conductive layers3, supporting electrical driving of CCs or even creating electrodes for photocurrent detection of magnetic resonance4. In this work, we report a systematic experiment carried out to produce graphitic layers on ‘electronic grade’ diamonds using a multi-species focused ion beam (FIB) equipment. The lateral resolution of the latter allows to directly write conductive paths on the diamond surface. The installed liquid metal alloy ion source (LMAIS)5 allows to implant Au++, Ge++ and Si++ species with kinetic energy of 70 keV or below. The combination of ion species and implant energies makes possible to tune the graphitic thicknesses. For instance, for 70 keV irradiations graphite thicknesses ranged from 40 to 90 nm. During the experiment, process window was defined for each ion species in terms of ion fluence and thermal annealing, identifying the carbon phases by Raman spectroscopy and measuring by atomic force microscopy the surface swelling after ion irradiation and the removed thicknesses after a selective wet etching. Finally, implications about the possibility of create also CCs during the graphitization itself will be discussed, with particular reference to group IV-vacancy CCs like SiV and GeV6. References 1. S. Pezzagna, et al. New Journal of Physics 13(3) (2011), 035024. 2. C. Uzan‐Saguy, et al. Appl. Phys. Lett. 67(9) (1995), 1194. 3. F. Picollo, et al. New Journal of Physics 14(5) (2012), 053011. 4. G. Villaret, et al. Appl. Phys. Lett. 122(19) (2023), 194001. 5. L. Bischoff, et al. Appl. Phys. Rev. 3(2) (2016), 021101. 6. C. Bradac, et al. Nat. Comm. 10(1), (2019), 5625.