Apertureless scanning near-field optical lithography Ignacio Falc´ on Casas and Wolfgang Kautek Abstract Optical nanolithography has experienced substantial advances in the last decades. Lithography resolution by optical methods has been historically limited by light diffraction. One potential approach to surpass this barrier is ”apertureless scanning near-field optical lithography”. In this method, a scanning probe micro- scope tip is illuminated by a focused laser beam and the electromagnetic field is strongly enhanced in the vicinity of the tip’s apex. This may generate nanomodifi- cations on a solid surface in close proximity with the tip. In this chapter, we review the thermal effects that allow distinguishing the underlying physical mechanisms: near-field optical enhancement and/or thermal surface modification. Key words: near-field, nanolithography, femtosecond, laser, SNOM, SFM 1 Introduction Since Synge proposed the first near-field microscope idea in 1928 [1], there have been multiple attempts to overcome the diffraction limit of light. In 1984, Pohl [2] and Lewis [3] independently developed the first scanning near-field optical micro- scope (SNOM), a combination of a scanning probe microscope (SPM) with a laser beam channeled into a tapered optical fibre, overcoming the diffraction limit [4–9]. Ignacio Falc´ on Casas Department of Physical Chemistry, Faculty of Chemistry, University of Vienna W¨ ahringer Straße 42, 1090 Vienna, Austria e-mail: ignacio.falcon.casas@univie.ac.at Wolfgang Kautek Department of Physical Chemistry, Faculty of Chemistry, University of Vienna W¨ ahringer Straße 42, 1090 Vienna, Austria e-mail: wolfgang.kautek@univie.ac.at 1 Springer Series in Materials Science 309 (2020) 113-132