Nanocrystals are typically prepared in a chemical solution using stringy molecules called ligands chemically tethered to their surface. These hydrocarbon-based or organometallic molecules help stabilize the nanocrystal, but also form an undesirable insulating shell around the structure. Efficient and clean removal of these surface ligands is challenging and has eluded researchers for decades.

Now, using Meerwein’s salt — an organic compound also known by the tongue twisting name triethyloxonium tetrafluoroborate — a Berkeley Lab team has stripped away organic ligands tethered to nanocrystals, exposing a bare surface enabling nanocrystals to be used in a variety of applications.

“Our technique basically allows you to take any nanocrystal — metal oxides, metallic, semiconductors — and turn these into dispersions of ligand-free nanocrystal inks for spin or spray coating and even patterning using an ink jet printer,” says Brett Helms, a staff scientist in the Organic and Macromolecular Synthesis Facility at Berkeley Lab’s Molecular Foundry, a nanoscience research center. “What’s more, they retain their structural integrity and exhibit more efficient transport properties in devices.”

“This method is applicable in a truly universal fashion and makes it possible to use nanocrystals in a broad range of applications and in different environments,” said Delia Milliron, director of the Inorganic Nanostructures Facility at the Foundry.

Indeed, Milliron added, several Foundry users are already taking advantage of these nanocrystals for projects on energy storage and supercapacitor materials, which store energy like batteries but can be charged more rapidly.

“Having a robust yet simple procedure to process ‘activated’ nanocrystals from solution over large areas, commensurate with the demands of a manufacturing process, is an important first step to integrating these exciting new materials into next-generation energy-related devices,” Helms said.

Publication date: 01/09/2012