Thiol Diffusion and the Role of Humidity in “Dip Pen Nanolithography”

The radii of octadecanethiol spots deposited by an atomic force microscope tip onto a gold surface were studied as a function of contact time and humidity. The deposition is well described by two-dimensional diffusion from an annular source of constant concentration, with a surface diffusion coefficient of $8400{\mathrm{nm}}^2{s}^{-1\mathrm{}}$, independent of humidity. Facile transfer is observed even after near continuous deposition for more than 24 h in a dry $N_2$ environment, indicating that a water meniscus is not required.