Assessment of acid and thermal oxidation treatments for removing sp2 bonded carbon from the surface of boron doped diamond

The presence of sp2 bonded carbon on a diamond or doped diamond surface, as a result of growth or processing, can affect material properties negatively, hence removal processes must be developed. Using boron doped diamond (BDD) we investigate the effectiveness of different removal methods via electrochemistry and transmission electron microscopy. We focus on two BDD surfaces, one processed by ns laser micromachining and the second which contains sp2 bonded carbon as a result of chemical vapour deposition (CVD) growth. After micromachining a layer of ordered graphite sits on the BDD surface, topped by fissured amorphous carbon (total thickness ∼ μm). Oxidative acid treatment at elevated temperature cannot remove all the sp2 bonded carbon and much smaller clusters of perpendicularly-orientated graphite (tens of nm in diameter), capped with a thinner layer of amorphous carbon – that we term “denatured graphite” – remain. In contrast, thermal oxidation in air at 600 °C is capable of all cluster removal, and can also be used to remove sp2 bonded carbon from as-grown CVD BDD. Such understanding is important to any application where sp2 bonded surface carbon resulting from CVD growth or laser processing is detrimental for the intended application, e.g. in diamond quantum technology, photonics and electrochemistry.