Dip-pen nanolithography: What controls ink transport?

The influence of temperature and humidity on the growth rates of I-octadecanethiol (ODT) and 16-mercaptohexadecanoic acid (MHA) monolayers deposited onto a gold substrate has been systematically studied in the context of dip-pen nanolithography (DPN) experiments. By analyzing a statistically meaningful data set, we conclude that for both inks the deposition rate increases with increasing temperature, and that this temperature dependence is strongly affected by relative humidity, chemical nature of the ink and substrate, and writing speed. We attribute these observations to the different solubilities of the ink molecules in water (both the water in the meniscus and on the cantilever walls). In addition, we report a set of experiments that demonstrate meniscus formation even at 0% relative humidity due to residual water that moves to the point of contact between tip and sample.