Writing with liquid using a nanodispenser: spreading dynamics at the sub-micron scale

A nanodispensing technique using specific atomic force microscope tips was used to pattern surfaces with liquids with sub-micron resolution, down to diameter spots of 70 nm. The experimental results revealed that spot sizes and linewidths are ruled by the dynamics of spreading of the liquid on the substrate. The feature size R follows a temporal evolution with two different regimes: it scales as R similar to t(0.26 +/- 0.04) at short times (smaller than 1 s) and then saturates to reach an equilibrium value at longer times. A model considering the spreading of liquid from a source, under constant pressure conditions, was developed. It leads to a R similar to t(1/4) power law for the early stage of spreading which accounts quantitatively for the non-conventional dynamics and for the influence of tip and substrate properties observed in the experiments. This study provides a precise understanding of the nanodispensing mechanism, useful to develop and improve the method. It also shows that this nanodispensing technique is a unique method to study liquid spreading at the sub-micron scale and down to the millisecond timescale.