Self-Assembling Nanomaterials Get Complicated

A new method of stacking nanomaterials like a layer cake allows for the self-assembly of complex structures.

Typically, self-assembled nanostructures can form a limited number of different shapes — mainly surface-area-minimizing shapes, such as spheres or hexagonally stacked cylinders, says Kevin Yager, a researcher at the Brookhaven National Laboratory Center for Functional Nanomaterials. Yager and his colleagues were interested in coaxing more complexity out of self-assembled nanostructures for applications like battery electrodes and nanofiltration systems.

Their process uses block copolymer thin films, specifically polystyrene-block-poly(methyl methacrylate) diblock copolymers (PS-b-PMMA), stacked so that each layer acts as a structural component in the final morphology and as a template that guides subsequent self-assembling layers. This approach generates an enormous variety of three-dimensional morphologies.

The key to these layered structures is not destroying one layer during the fabrication of the next. The researchers began with a substrate, in this case silicon. To that, they applied a layer of PS-r-PMMA-OH copolymer by spin-coating. The thin film, just 6 nm thick, provides a chemically neutral layer. Over the neutralized substrate, the researchers used spin-coating and annealing to apply a layer of PS-b-PMMA copolymer...