Molecules adsorbed on a substrate surface can self-assemble into a monolayer. This article models the process of self-assembly guided by an external object. The molecules are electric dipoles, diffusing on the surface at an elevated temperature. Pre-pattern a flat mask with a submonolayer of immobile atoms, which gives rise to a patterned contact potential field. Bring the mask to a small distance above the substrate. The electrostatic interaction transfers the pattern on the mask to a molecular pattern on the substrate. Similarly, one can place above the molecules a charged conducting tip, or a mask that is pre-patterned with a topographic surface. Our model includes the mobile molecular dipoles on the substrate surface, the guiding object, and the electrostatic field in the intervening space. A nonlinear diffusion equation simulates the pattern transfer process. Numerical results are presented when the guiding object is a flat metal, patterned with a submonolayer of immobile atoms. © 2003 American Institute of Physics.