US researchers have developed a method to track nanoparticle self-assembly by incorporating fluorine-labelled ligands into the nanoparticle shells.

Chemically self-assembling nanoparticles could be a way to make smaller electronic devices than are currently accessible by lithography. However, depositing them uniformly and reproducibly is difficult and there aren't simple ways to characterise them, says Arthur Snow at the Naval Research Laboratory in Washington DC.

Fluorine-labelled thiols enable tracking of nanoparticle self-assembly

Snow and colleagues devised their own cheap and easy-to-use analytical method to characterise large numbers of nanoparticle assemblies. They attached a fluorine atom to an oxyethylene chain to make a fluorine-labelled ligand, which they substituted into the shells of gold nanoparticles. They then showed they could use the fluorine tag to track the particles' self-assembly on surfaces with X-ray photoelectron spectroscopy.

Although proximal probes techniques, such as atomic force microscopy, and analytical techniques, such as scanning and transmission electron microscopies, can provide excellent detail of isolated assemblies, they are not easily adapted to the large numbers of assemblies needed to manufacture nanoelectronic devices, explains Snow. 'Any technology that allows reliable engineering design from device to device throughout development will lead to significantly smaller, faster, lower power and less expensive electronics,' he says.

James Whitten, an expert in organic electronics at the University of Massachusetts Lowell, US, is impressed by the work, commenting that it is 'a difficult problem analytically since both the surface and attached particles contain gold, thiol groups, and hydrocarbons'.

Snow says that he hopes this work will highlight the need for more versatile characterisation tools, which could ultimately lead to improved nanoelectronics manufacturing.

Janet Crombie

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