Irradiation of the mask in contact with the substrate produces lines in positive photoresist and trenches in negative photoresist that can be significantly thinner than the broadband, incoherent light source used for irradiation. Resolution of 50 nm has been demonstrated.174,175 For a detailed quantitative description of the mechanism of the process, see the work by Li et al.,30 Rogers et al.,33 and Paul et al.173

Patterns in photoresist produced by this simple and inexpensive technique can be transferred to the substrate using RIE or to thin films using typical liftoff procedures. To date, the patterns formed by phase-shifting edge lithography have been used to fabricate several structures: single-crystalline nanowires of Si,176 gold, and silica nanowires on planar33 and nonplanar substrates,32 aperture elements for mid-infrared frequency-selective surfaces,177 and single-crystalline nanowires of silicon.176 In combination with etching, physical vapor deposition, and liftoff, phase-shifting photolithography has been employed by Odom and co-workers for the fabrication of mesoscale pyramids with plasmonic properties,178,179 or combined with controlled undercutting to produce other periodic arrays of structures.103