superlens. Srituravanich et al. has developed a mechanically adjustable, hovering plasmonic lens for maskless near-field nanolithography, whereas another maskless approach by Pan et al. uses a "multi-stage plasmonic lens" for progressive coupling. Plasmonic direct writing is a maskless form of photolithography that is based on scanning probe lithography; the method uses localized surface plasmon (LSP) enhancements from embedded plasmonic scanning probes to expose the photoresist. Wang et al. experimentally demonstrated 100 nm field confinement with this method. Kim et al. has developed a ~50 nm resolution scanning probe with a patterning speed of ~10 mm/s. Gold nanoparticles and other plasmonic nanostructures such as nanogaps have been used as masks for lithography; etching in this case can be achieved through either through photomasking principles or enhanced local heating in the vicinity of the nanostructure due to the LSP resonances. Lin et al. also used localized thermal excitations in gold nanoparticles to fabricate two-dimensional structures such as patterned graphene and molybdenum disulfide monolayers in a process termed as "optothermoplasmonic nanolithography." Photochemical effects of LSP resonances were also used as a catalyst in lithographic processes: Saito et al. demonstrated selective etching of silver nanocubes on titanium dioxide substrates by the means of plasmon-induced charge separation. See also Electron-beam lithography Nanoimprint lithography Nanosphere lithography Plasmonic metamaterial References Lithography (microfabrication) Plasmonics