Fabrication of conductive graphitic layers in diamond by multi-species focused ion beam

Ion beam irradiation of diamond surface is a powerful technique to modify structural, electrical and optical properties to target quantum technology applications. In particular, ion implantation has been proven as a reliable and flexible process to create color centers (CC) in diamond, due to its ability to define their concentration and three dimensional location1. Ion implantation can also act on the crystal structure permanently modifying the phase of the irradiated diamond: once a certain level of lattice damage has been reached, subsequent thermal annealing can only convert the irradiated areas to graphite in an irreversible way2. This effect is clearly detrimental to the formation of CC, since the implanted ion species end up in a not-diamond phase. However, since the graphitic layers are electrically conductive, the effect can be exploited to create integrated or buried conductive layers3, supporting electrical driving of CC or even creating electrodes for photocurrent detection of magnetic resonance4, if the irradiation can be designed using a focused ion beam (FIB) system. Figure 1 – Diagram showing the multispecies FIB process to either create graphitic layers or a nanometric patterning of diamond surface. In this work, we report a systematic study to produce controlled layers of graphite on ‘electronic grade’ diamonds by ion implantation using a multi-species column FIB equipment. The liquid metal alloy ion source (LMAIS)5 allowed to select among Au++, Ge++ and Si++ species with implant energy of 70 keV. In particular, the process window was defined for each ion species in terms of ion fluence and thermal annealing recipe, identifying the carbon phases by Raman spectroscopy and measuring the developed topographies by atomic force microscopy, before and after a selective etching. Due to the mass difference, different graphite thicknesses were achieved, ranging from 40 to 90 nm. Another possibility is to exploit the selective etching coupled to FIB irradiation for a direct patterning of the diamond surface6, a process in principle able to create nanometric structures embedding CC. 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. N. Kawasegi, Noritaka, et al. Diam. Relat. Mater 70 (2016), 159.