When their size changes, their properties also change. This suggests that uniform control over size is critical in order to use them reliably as components in electronics.
Put another way, "if you don't control size, you will have inhomogeneity in performance," says Mark Hersam. "You don't want some of your cell phones to work, and others not."
Hersam, a professor of materials science engineering, chemistry and medicine at Northwestern University, has developed a method to separate nanomaterials by size, therefore providing a consistency in properties otherwise not available. Moreover, the solution came straight from the life sciences—biochemistry, in fact.
The technique, known as density gradient ultracentrifugation, is a decades-old process used to separate biomolecules. The National Science Foundation (NSF)-funded scientist theorized correctly that he could adapt it to separate carbon nanotubes, rolled sheets of graphene (a single atomic layer of hexagonally bonded carbon atoms), long recognized for their potential applications in computers and tablets, smart phones and other portable devices, photovoltaics, batteries and bioimaging.