Lithographic Fabrication of Model Systems in Heterogeneous Catalysis and Surface Science Studies

Lithographic technologies are applied to fabricate model systems for surface science and heterogeneous catalysis studies. An ordered metal nanocluster array fabricated on oxide substrates is also an ideal model system of supported industrial catalysts. Taking advantage of an ordered nanocluster array fabricated by electron beam lithography, the thermal and chemical stability of supported silver catalysts are examined in both oxidizing and reducing conditions. In reducing conditions, the supported silver nanoparticles are stable up to ∼700 °C. In oxidizing conditions, however, the silver nanoparticles are oxidized below 200 °C, and conglomerate to micrometer-size amorphous clusters ∼400 °C. The supported nanocluster sample can also be adapted to study reactivity of supported metal catalysts, as confirmed by measurement of ethylene hydrogenation turnover rates on platinum nanoparticle samples. Lithographic technologies can also fabricate model systems for other surface science research. A nanometer scale pattern is created on a poly(methyl methacrylate) (PMMA) surface by electron beam lithography. The sample is adapted to test a recent development in nanotribology, in which surface elastic modulus (hardness) is determined by a modified atomic force microscope. In addition, lithographically fabricated supported nanostructures are used to image the AFM tip (thereby determining the radius of curvature of the tip), which is a critical parameter for the quantification of surface mechanical properties such as elastic modulus. Finally, taking advantage of the uniform height profile of lithographically fabricated nanostructures, ion sputtering yield can be determined by the reduction of nanostructure height as a function of ion exposure.