Ultrafast laser lithography using self-assembled monolayers (SAMs)

Standard positive photoresist techniques were adapted to generate micropatterns of gold substrate using self-assembled monolayers (SAMs) and ultrafast laser. SAMs formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists. The process underlying photopatterning of SAMs on gold is well- known at the phenomenological level. Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200nm is necessary for oxidation to occur. In this study, ultrafast laser of wavelength 800nm is applied for photolithography. Results show that ultrafast laser of visible range wavelength can replace deep UV laser source for photo patterning using thin organic films. The essential basis of our approach is the photochemical excitation of specific reactions in a particular functional group (in this case a thiolate sulfur atom) distributed with monolayer coverage on a solid surface. By using the photo-chemical process with ultrafast laser, micro-patterns with sub-micrometer width and depth on surfaces of Au could be fabricated.