Secondly, we recognize that the previous mechanism does not account for the closely packed template of the layers. Inspired by the micropancake topography shown in Figure , typically found in the field of surface nanobubbles , we hypothesize that a hydrogen nanobubble template could result in the observed columnar growth. Electrodeposition on bubbles has been demonstrated in the past , even resulting in similar nanowire morphologies . We further note that this is consistent with some of the columns appearing open/hollow (Figure , SI-1, and SI-8), and the template being volatile and therefore not observed in ex-situ AFM.