Aluminum oxide nanocardboard is strong yet bendable

Corrugated cardboard is a classic example of a stiff yet lightweight macroscale material. Now, a team at the University of Pennsylvania led by mechanical engineer Igor Bargatin has developed a sandwich structure similar to that of corrugated cardboard, but at the nanoscale (Nat. Commun. 2018, DOI: 10.1038/s41467-018-06818-6). The researchers envision the material, made from an ultrathin aluminum oxide film, being used for a variety of aerospace and microrobotic applications. To make the material, the team started with a silicon template with holes and then coated all its surfaces with aluminum oxide. Then the researchers etched away the silicon from the inner core, leaving a translucent shell with a network of webbing sandwiched between a top and bottom sheet. The “nanocardboard” (shown) is more than 10,000 times as stiff as a solid sheet of aluminum oxide with the same mass, and it can recover its shape after repeated bending.