A method includes forming a semiconducting region including polyaromatic molecules on a surface of a substrate. The method also includes forming over the region a substantially oxygen impermeable dielectric layer. The act of forming a semiconducting region includes exposing the molecules to oxygen while exposing the molecules to visible or ultraviolet light.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of contract No. DE-FG02-04ER46118 awarded by the Department of Energy.