Note that the lower kV makes the proximity effect much more pronounced. Specifically, while the wheel that was written at 30 kV has a center exposed area that is only ~200 nm wide where the spokes meet and the spokes do not broaden noticeably where they join together, the wheel shown here that was written at 10 kV has a center area that is over a micron across and the spokes broaden a very significant amount as they approach the center.

Also, at 10 kV, a center dot is seen where the dose was 12 times higher because all 12 spokes started at the same location and at the lower kV of the beam, the dose at this dot was enough to turn the PMMA negative. Also see "Negative PMMA".

In general, the smallest features with the smallest effects from proximity doses will be obtained at the highest available kV of the microscope, see "Wheel #1".