We report an original iterative method for fabricating three-dimensional mesoporous structures by independently stacking multiple self-assembled block copolymer films supported by Si membranes. A first layer is formed on the substrate by a self-assembled PS-b-PMMA (polystyrene-block-poly(methyl methacrylate)) film. A porous, permeable Si membrane deposited on top of the first block copolymer film provides mechanical support, preventing pattern collapse during the wet developing used to selectively remove the PMMA component of the PS-b-PMMA film. A second, dense Si membrane is deposited to seal the porous membrane, resulting in an impermeable coating suspended atop the self-assembled mesoporous polystyrene structures. The process can then be iterated using the sealed membrane as the new substrate to support a subsequent self-assembled block copolymer film. This multilayer approach provides a flexible three-dimensional fabrication technique where, in each layer, pattern morphology, domain orientation and degree of ordering can be designed independently. Furthermore, the process is compatible with electron-beam directed assembly, used to achieve regular patterns with feature density multiplication at any level in the stack.

In this study, the capacitances of stainless steel-carbon composite electrodes in 1.0M Na2SO4 were determined as a function of stainless steel loading, sintering temperature, and sintering time (i.e., O. 1-0.5g of stainless steel fiber/lg of carbon fiber, 1323-1423 K, and 2.5-152 min, respectively). Kinetic parameters were determined for stainless steel sintering and catalytic carbon gasification by weight loss measurements and capacitance changes using ac impedance, single potential step methods, and cyclic voltammetry. Apparent activation energies for carbon gasification and sintering were found to be 80 and 200 kJ/mol, respectively. Measured reaction rates and kinetic parameters were used to verify the importance of stainless steel-carbon contacts toward overall electrode capacitance and to successfully predict a maximum capacitance of 45.3 F/g on a total electrode weight basis. This capacitance value yields energy densities of ca. 90 kJ/kg of electrode and does not require pressure for good electrical contact as do electrodes prepared from carbon powders. Capacitance and kinetic measurements demonstrate the ability to control conductivity and active surface area by adjusting: stainless steel to carbon loading, sintering temperature, and sintering time.

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