Researchers at the University of Texas at Austin have developed an all-optical technique based on plasmon-enhanced optothermal effects for on-demand patterning of atomically thin two-dimensional (2D) materials. Unlike expensive and complex photolithography, electron- and ion-beam lithography, and even high-power femtosecond laser patterning, optothermoplasmonic nanolithography (OTNL) is a low-power, submicron, maskless, and high-throughput process whereby graphene, molybdenum sulfide (MoS2), or other 2D materials are transferred onto a thermoplasmonic substrate (such as a porous gold substrate).
When illuminated by a focused 532 nm laser beam, localized surface-plasmon resonances are excited on the gold thermoplasmonic substrate, inducing well-confined, localized thermal hotspots that can reach a maximum temperature of 850 K when heated by a laser with optical intensity of 6.4 mW/µm2. Dynamic interaction between the thermal hot spots and the 2D materials are further achieved by steering the laser beam through a spatial light modulator (SLM) or with a translation stage.
These hotspots ablate or displace the 2D material through sublimation or other material-dependent mechanisms, creating an array of versatile patterns at submicron resolution. For example, 40 × 40 µm nanoribbon structures on graphene have a 600 nm linewidth and 2 µm periodicity, nanohole arrays on MoS2 have a diameter of 1.1 µm, and the word “graphene” patterned on a graphene substrate has a linewidth of 1.5 µm. Reference: L. Lin et al., Adv. Funct. Mater., 1803990 (Aug. 12, 2018); https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201803990.
