Values of td were varied slightly between 40, 60, 80, and 100 µs to keep doses the same among the various pressure experiments as the beam current decreased with increasing pressure due to increased scattering. As is evident from the graphs in Figs. , the defect densities exhibit a parabolic trend with increasing pressure, with a maximum around 20 Pa. This trend is the same for all the shot pitch (P = 9.96, 15.39 and 19.92 µm) and dwell time (td = ~40, 60, 80 and 100 µs) values studied. This likely represents two competing phenomena: 1) at low pressures, there is a dearth of species available to create radiolysis products for e-beam chemistry; 2) at higher pressures, the beam is attenuated by the excess of radiolysis species present in the chamber. When the data is replotted in terms of dose (Fig. ) we see that, for a given pressure, only dose matters with respect to the level of defect density in the patterned area up through pressures of 20 Pa. At higher pressures and doses, there is a marked reduction in the defect densities, with a non-monotonic dependence on the electron dose, which we attribute to perturbations and gas currents within the chamber. The pressure-dependence study was also useful to determine the optimal parameters for functionalization such that adjacent graphene remains unaltered. A metric that can be used for this is to compare the ID/IG of the intentionally patterned area [(ID/IG)pattern] to that of the ID/IG of an adjacent area [(ID/IG)skirt] that is intended to remain in a pristine state. This is related to a well-known effect called beamskirting where the scattering of the e-beam with the gaseous species inside the ESEM can cause a reduction of the beam current within the focused area and its redistribution to form a "skirt" around that area. The metric (ID/IG)pattern/(ID/IG)skirt is therefore ideal at ∞. In Fig. we plot this metric as a function of pressure. We note that, with the exception of the 30 Pa value (which we noted in Fig. had instabilities associated with its dose dependence), lower pressures lead to better patterning in terms of prevention of the beamskirt effect and unintentional modification of graphene outside the patterned area. Overall, (ID/IG)pattern/(ID/IG)skirt improved from ~1.5 to ~4 just by lowering the pressure to 5 Pa (the minimum allowed by our instrument in variable pressure mode).