Multiphoton Lithography of Nanocrystalline Platinum and Palladium for Site-Specific Catalysis in 3D Microenvironments
Original Entry by Cheng Wang, AP225, Fall 2012
Authors: Lauren D. Zarzar, B. S. Swartzentruber, Jason C. Harper, Darren R. Dunphy, C. Jeffrey Brinker, Joanna Aizenberg, and Bryan Kaehr
Publication: Zarzar et al., "Multiphoton Lithography of Nanocrystalline Platinum and Palladium for Site-Specific Catalysis in 3D Microenvironments", Journal of American Chemical Society (2012) 134: 4007-4010
Keywords: Multiphoton Lithography (MPL), catalyst, nanocrystalline, micropattern
Platinum and palladium catalysts are crucial for a broad range of existing and emerging chemical, biological, and technological applications. Abilities to dictate catalysis within microfluidic systems are crucial for the emerging applications of lab on chip devices. This paper reported arbitrarily written micropatterned Pt and Pd structures within 3D fluidic architectures using multiphoton lithography (MPL). The MPL-deposited Pt and Pd materials are composed of polycrystalline metallic nanoparticles.
In the printing approach, support matrix paper is embedded with (NH4)2[PtCl4] or (NH4)2[PdCl4] and (NH4)3[Fe(C2O4)3]. When exposed to UV light, [Fe(C2O4)3]3- iron is reduced to [Fe(C2O4)2]2- and then react with [PtCl4]2- iron to form Pt polycrystallined structures. The micropattern of Pt and Pd is realized by a scanning laser and a dynamic mask-based approach. The fabrication process and EDS, bright-field optical microscopic, backscatter SEM pictures are shown in Fig. 1.
High-resolution SEMs (Fig. 2) show that metallic patterns are comprised of small metal granules and that the glass/metal interface is solidified due to thermal melting/annealing by light absorption. Resulting minimum line width is around 2um, whereas gap width resolution is around 200nm. Characterized electrical resistivities for Pt and Pd are approximately 1 order of magnitude higher than those for bulk metals. TEM analysis shows that the MPL-deposited Pt clusters ranges in diameter from 4-8nm.
The MPL-deposited Pt pattern is used to generate oxygen flow by H2O2 decomposition. This oxygen flow is 3-D directed within microchambers and channels, which are formed by photocross-linked protein. This protein chambers and channels are easy for H2O2 molecules to penetrate, thus to keep the gas flow constant. Using different channels, different types of gas flows and directions can be created (Fig. 3).
The adsorption of molecules on certain catalytic materials (here Pt and Pd) can achieve or accelerate certain chemical reactions. Nanocrystallined structures can greatly increase the surface area so that to enhance chemical reactions by orders. This paper introduced the use of MPL to generate arbitrary micropatterns of nanocrystallined catalysts and demonstrated the possibility to control the flow of chemical output by certain microenvironments.