Shape of things to comeExtremely thin sheet exhibits extreme strength

Published 23 July 2007

University of Chicago and Argonne Lab scientists discover amazing strength in a sheet of nanoparticles that measures just 50 atoms in thickness

Scientists at the University of Chicago and Argonne National Laboratory have discovered that a sheet of nanoparticles that measures just 50 atoms in thickness can be surprisingly strong. Even when suspended over a tiny hole and poked with an ultrafine tip, the membrane boasts the equivalent strength of an ultrathin sheet of plexiglass that maintains its structural integrity at relatively high temperatures. The characteristics of the nanoparticles are described in the 22 July issue of the journal Nature Materials in a paper written by Heinrich Jaeger, professor of physics at the University of Chicago, and Xiao-Min Lin, a physicist at Argonne’s Center for Nanoscale Materials, along with Klara Mueggenburg, a graduate student in physics at the University of Chicago, and Rodney Goldsmith, an undergraduate student at Xavier University in New Orleans. The work was funded by the NSF-supported Materials Science and Engineering Center at the University of Chicago. Additional support came from the U.S. Department of Energy.

The material’s characteristics make it a promising candidate for use as a highly sensitive pressure sensor in precision technological applications. “If we use different types of nanoparticles to make the same kind of suspended membrane, we can even imagine using these devices as chemical filters to promote catalytic reactions on a very small length scale,” Lin said. As artificial atoms, the nanoparticles might also serve as building blocks in assembling specially designed nano-objects. “This is the ultimate limit of such a solid. It’s just one layer,” Jaeger said. “What is interesting is that already one layer is so resilient and has these interesting properties.”

Note that the payoff is scientific as well as technological. Scientists had already been familiar with a phenomenon called nano-confinement, that is, that the electronic properties of semiconductor material can change dramatically when its tiniest metallic components are tightly packed between organic molecules. The latest discovery means that not only the electronic properties, but also the mechanical properties can change dramatically. “On a basic science level, that’s why this is exciting,” Jaeger said.

Note also that the Chicago-Argonne experiments focused on two-dimensional sheets, but that there conclusions generally agree with computer simulations on similar three-dimensional assemblies of smaller nanoparticles conducted by Uzi Landman’s team at Georgia Institute of Technology. “The behavior of these systems is sensitive to dimensionality, and this is a subject that should be explored in the future,” said Landman, the Fuller Callaway Chair in Computational Materials Science at the Georgia Institute of Technology. “This actually brings another control parameter into question. Change the dimensionality, you change the properties.”