TBA-enabled spin-coating of a percolatively connected GO nanosieve for thru-hole epitaxy: tuning GO flake stacking and coverage to control GaN nucleation
We report a spin-coating-based approach for forming a percolatively connected graphene oxide (GO) nanosieve on SiO$_2$-patterned sapphire substrates, where the addition of tetrabutylammonium (TBA) to the GO solution significantly improves the uniformity of flake coverage and modulates GaN nucleation behavior. Upon thermal annealing of GO, the resulting reduced graphene oxide (rGO) films exhibit spatially varying coverage, leading to three distinct GaN nucleation outcomes: (i) ELOG-like nucleation on exposed substrate regions, (ii) thru-hole epitaxy (THE)-like nucleation through appropriately thin areas, and (iii) complete nucleation suppression on thickly stacked zones. On spin-coated GO films without TBA, all three behaviors coexist, and undesired ELOG- and no-nucleation modes persist due to uneven coverage. Importantly, these issues cannot be resolved by simply adjusting GO flake concentration, as concentration tuning alone fails to eliminate the formation of locally bare and overly thick regions. In contrast, the addition of TBA results in a more uniform, moderately stacked rGO morphology that suppresses both ELOG- and no-nucleation modes while expanding THE-like nucleation regions. This reshaped nucleation landscape confines GaN growth to areas with engineered percolative transport. The approach offers a scalable, lithography-free route for controlling GaN epitaxy using solution-processable 2D material masks.