Diamond nano-patterning by graphitization induced by ion implantation

Irradiation of diamond surface by energetic ion beams has represented a useful and flexible technique to modify the material properties to comply with quantum technology needs. Ion implantation is a reliable process to create color centers in diamond, due to its ability to define their concentration and three dimensional location1. Besides that, ion implantation can also permanently modify the crystallographic phase of diamond, by damaging the diamond lattice. Thermal annealing can convert the irradiated areas to graphite2. The diamond graphitization via ion implantation combined with a selective etching3 could be a useful approach for diamond surface nano-patterning4, enabled by a lower fluence than direct milling, achieving a high lateral resolution if a focused ion beam (FIB) system is used. We report a systematic experiment to nano-pattern the surface of an ‘electronic-grade’ diamond inducing graphitization using a multi-species FIB and removing the graphite by wet etching. The installed liquid metal alloy ion source (LMAIS)5 enables to implant Au++, Ge++ and Si++ species with maximum energy of 70 keV, allowing the tuning of the graphitic thicknesses and thus the depth of the nanostructures. For instance, for 70 keV irradiations the graphite layer thicknesses ranged from 40-90 nm. The 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 swelling after ion irradiation, the etched thicknesses, and the minimum lateral resolution after the wet etching. Moreover, the fabrication of suspended nano-structure by the formation of buried graphite layer is investigated by exploiting the ions energy distribution in the diamond.