Nanocrystal assembly method developed

Australian scientists, led by the ARC Centre of Excellence in Exciton Science, have pioneered an innovative method of nanocrystal assembly that could benefit applications including smartphones, tablets and laptop displays, camera lenses, biosensing devices, integrated chips and solar photovoltaic cells.

Nanocrystals have a wide range of existing and potential uses, but they are often made with wet chemical methods that present challenges when seeking to incorporate them effectively into devices. Researchers from Exciton Science have now demonstrated a highly efficient and controllable method to assemble single nanoparticles directly into a pre-patterned template, with the results of their work published in the journal Advanced Materials.

By applying an electric field at a certain level of strength, a technique called electrophoretic deposition (EPD), researchers at the University of Melbourne and CSIRO were able to create a nearly perfect single nanocrystal array using either gold nanospheres or gold nanorods. And by tweaking the potential applied to the materials as part of this field, the researchers even discovered they were able to dictate whether the nanocrystals assemble in vertical or horizontal configurations.

“Conventional nanofabrication methods normally produce 2D nanostructures,” said Heyou Zhang, lead author of the study and a PhD candidate at Exciton Science. “With the ability to assemble in both vertical and horizontal directions and with spatial control of the nanoparticles on the surface, this method provides far more opportunities to build and manufacture nanoscale structures.”

Although the manuscript focuses on assembly of gold nanocrystals, the technique has been applied to semiconductor quantum dots, magnetic nanoparticles and organic nanoparticles. The next goal for the research is the creation of a single quantum dot on/off switch, which can form part of a logic gate or memory pixel for high-density information storage; however, there is interest from industry partners in other areas too.

“We can use assembled gold nanocrystals arrays as a plasmonic pixel, which is a colour display unit with high purity and colour saturation,” Heyou said.

“It provides very distinct colour with angle or polarisation-dependent properties, which has potential as a security feature or in medical imaging.”

Heyou feels the approach has great potential as a universal nanomaterial assembly method, saying, “We can use these particles to build up reconfigurable metal lenses, such as the lenses on your phone.

“The thickness of the lens on your phone camera is limited by optical geometries, but with this method you might be able to shrink it down to micrometre size.”

Senior author Professor Paul Mulvaney, Director of Exciton Science, concluded, “Heyou has found a novel approach to large-scale fabrication for nanomaterials. This deposition method solves a fundamental roadblock for nanotechnology and creates a viable pathway for miniaturisation of both optical and electronic devices.”

Exciton Science is now looking for partners to help scale up the novel EPD process.

Image caption: Heyou Zhang.

Please follow us and share on Twitter and Facebook. You can also subscribe for FREE to our weekly newsletter and bimonthly magazine.