A resist medium in which features are lithographically produced by scanning a surface of the medium with an AFM probe positioned in contact therewith. The resist medium comprises a substrate; and a polymer resist layer within which features are produced by mechanical action of the probe. The polymer contains thermally reversible crosslinkages. Also disclosed are methods that generally includes scanning a surface of the polymer resist layer with an AFM probe positioned in contact with the resist layer, wherein heating the probe and a squashing-type mechanical action of the probe produces features in the layer by thermally reversing the crosslinkages.