Building molecular surface gradients with electron beam lithography

We present a strategy for patterning self-assembled monolayers with control of the area density of the molecules on the surface in a continuous and tunable fashion. Variation of the electron beam lithography parameters on patterning an amino-terminated silane layer on silicon allows control of the effective area density of the silane molecules. Gold nanoparticles are used as labels to visualize the area density of the amino groups in scanning electron microscopy images. The ability to continuously vary the density of functional molecules on surfaces and prepare molecular gradients is of wide interest in the fields of electronics, sensing and biology.