There is currently considerable interest in preparing materials with gradients in their surface chemistries. Here we explore what we believe is a new approach to this end. Surface modified glass slides are sandwiched together along two opposite edges using an adhesive film of known thickness, e.g., 50 microns. This structure is then placed in an oxygen plasma. Diffusion of the plasma species up the gaps leads to gradient surface modification along the axis of the structure. Gradient formation is studied as a function of gap thickness and reaction time. Gradient surface modification is confirmed by small spot X-ray photoelectron spectroscopy, wetting, and time-of-flight secondary ion mass spectrometry. Force-distance curves from adhesive measurements and surface modification using fluorescent reagents further confirms gradient formation in these devices. Mathematical modeling of this diffusion process is also presented.