This invention comprises methods for making nanostructured and nanoporous thin film structures of various compositions. These films can be directly patterned. In these methods, precursor films are deposited on a surface and different components of the precursor film are reacted under selected conditions, forming a nanostructured or nanoporous film. Such films can be used in a variety of applications, for example, low k dielectrics, sensors, catalysts, conductors or magnetic films. Nanostructured films can be created: (1) using one precursor component and two reactions, (2) using two or more components based on differential rates of photochemical conversion, (3) using two precursors based on the thermal sensitivity of one precursor and the photochemical sensitivity of the other, and (4) by photochemical reaction of a precursor film and selected removal of a largely unreacted component from the film.