Feature size dependence on hysteresis due to relative humidity ramping and patterning order in dip-pen nanolithography

The water meniscus that forms between an atomic force microscope (AFM) tip and the substrate has been shown to have variable height and width due to relative humidity (RH) hysteresis. The current study investigates the effect of this variability in meniscus shape due to RH on the feature size of patterns written with mercaptohexadecanoic acid on a gold substrate, using dip-pen nanolithography (DPN). The patterns were written under conditions of increasing and decreasing RH cycles with different tip dwell times. The variation in resulting dot sizes during the RH ramping (up and down) cycles was then measured. DPN patterning was also performed with increasing and decreasing order of dwell times at constant RH, in order to quantify whether the order of patterning has an effect on feature size. Significant differences were observed in dot areas patterned over many RH ramping cycles; whereas the order of patterning was observed to have an effect only for dwell times ≤5 s.