Spatially selective, solid state etching of diamond using lithographically patterned FeCoB

Nanocrystalline layers of FeCoB (Fe:Co:B = 60:20:20 at atom ratio) enable spatially selective, microstructurally agnostic removal of diamond through a solid-state diffusion reaction. Lithographically fabricated 100-300 nm thick films of FeCoB are deposited on polycrystalline diamond substrates. Heat treatment at temperatures ranging from 700 degrees C-900 degrees C for 30 min-90 min are used to trigger the conversion of sp(3) to sp(2) carbon at the diamond-transition metal interface. The integrity of the solid-state etchant within the thermal processing window underpins the spatial selectivity with which the diamond is removed. Removal of the reaction products using solvothermal etching in an acid solution enables the recovery of the structured diamond surfaces. FeCoB offers material removal rates, which exceeds that possible with just Fe or Co - pointing to the key role of B. The interaction zone was excised using focused ion beam milling and characterized using electron microscopy. In addition, XRD and Raman spectroscopy were performed to study the phase composition of the interaction zone. The role of the transition metal-diamond interface is key to controlling the material removal; the stability of the interface determines the ability to faithfully replicate the ultrafine features that were lithographically patterned in the FeCoB.