Nanolithographic fabrication and heterogeneous reaction studies of two-dimensional platinum model catalyst systems.

摘要

Electron beam lithography (EBL) has been used to fabricate platinum nanoparticle arrays in the 20-nm size range on oxide thin films of silica and alumina deposited onto silicon wafers. Ethylene hydrogenation reaction studies have been carried out over these platinum nanoarrays and have revealed major differences in turnover rates and activation energies of the different nanostructures when clean and when poisoned with carbon monoxide. The oxide-metal interfaces are implicated as important reaction sites that remain active when the metal sites are poisoned by adsorbed carbon monoxide.; Size-reduction lithography (SRL) and nanoimprint lithography (NIL) have been utilized to produce platinum nanowires in the 20--60-nm size range on planar oxide films of silica, alumina, ceria and zirconia supported on silicon wafers. Ethylene hydrogenation reaction studies have been carried out over the silica and alumina-supported catalysts as a probe reaction and have shown to have comparable turnover rates and activation energies to other platinum catalysts. Nanowire arrays on all four oxide supports have been used as two-dimensional platinum model catalysts to study the effects of support on catalytic activity during the catalytic oxidation of carbon monoxide. A strong support dependence is seen for both reaction turnover frequency and the measured activation energy. The thermal stability of these nanowire arrays has been studied by annealing at 773 K and 973 K in a flow of helium. Upon annealing, substantial silicon migration is seen through the oxide support and a marked decrease in surface platinum is measured.; Using a variation of size-reduction lithography on an EBL-patterned silicon nitride membrane, we have reduced the size of 56-nn features in a silicon nitride membrane, call a stencil, down to 36 nm. Sub-50 nm, uniformly-sized nanoparticles are fabricated by electron beam deposition of Pt through the stencil mask. The particle pattern replicates that of the stencil. Repositioning of the stencil mask in between two consecutive Pt deposition cycles led to a doubling of the original pattern density. A self-assembled monolayer (SAM) of tridecafluoro-1,1,2,2-tetrahydrooctyl-1-trichlorosilane was used to prevent Pt clogging of the nano-sized holes during deposition, as well as to protect the stencil during the post-deposition Pt removal.