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From Scotch Tape to Deli Sandwiches: Future 2D Materials

Return to Spotlight Roundtable: "Layer by Layer: The Ascent of Nanoscale Two-Dimensional Materials"

SIDEBAR: From Scotch Tape to Deli Sandwiches: Future 2D Materials

Among the naturally occurring 2D materials is graphite, whose bulk forms are composed of atomically thin sheets of graphene: carbon atoms arranged in chicken-wire sheets, writ nanosmall. Those sheets are shed from pencil “leads” to leave marks on paper, to mention the most familiar application of 2D materials. And it was the Noble-Prize-winning discovery, reported in 2004 by Kostya Novoselov and Andre Geim, that revealed it was possible to successively remove sheets from graphite flakes – using adhesive tape, no less! – all of the way to the logical and physical conclusion: to an atomically-thin graphene sheet.

2D edgeMolybdenum disulfide is a great lubricant because it forms into loose layers that readily slide from one another. Shown here are two views - via optical microscopy on the left (with an overlay of the material’s atomic structure) and via photoluminescence on the right - of a nanoscale MoS2 crystal consisting of two molecular layers with part of one layer broken away. Together, the images reveal the relationship between atomic locations, the number of molecular layers, and the emissive properties of the 2D material. (Credit: Tony Heinz)

Besides the Scotch tape technique to isolate layers of graphene, molybdenum disulfide and other so-called van der Waal solids (a kind of 2D material), researchers have been making other types of 2D materials by deploying vapor or solution phase deposition methods atop substrate surfaces and a dipping procedure. “Nanosheet multilayer assemblies are formed by alternately dipping substrates in colloidal suspensions of charged nano-sheets and in aqueous solutions of polyelectrolytes having the opposite charge,” stated a 22-author review of 2D materials published in the journal ACS Nano. Roundtable participants Joshua Goldberger and Tony Heinz are among the authors.

The emerging ability to precisely engineer the charge environment along the surface area of 2D materials is opening design pathways to, among other things, future-generation microelectronics devices – in arenas with names like spintronics and valleytronics, the latter referring to the energy landscapes of the materials – that do more computing using less energy and even to never-before-seen devices.

Pushing forward into the “deli sandwich” approach of stacking different nanosheets into multilayer films “can lead to improved properties in the areas of supercapacitors, pseudocapacitors, photoconductive materials, and heterojunction photodiodes as new magnetic materials and as magneto-optical components,” according to the ACS Nano review. Additional applications include the following: batteries, magneto-optical materials in which the magnetization is affected by light, photoconductors, high dielectric constant materials, and new types of liquid crystals.

— Ivan Amato (Summer, 2014)