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 nm² s^-1, independent of humidity. Facile transfer is observed even after near continuous deposition for more than 24 h in a dry N₂ environment, indicating that a water meniscus is not required.