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Nanocrystal assembly method could transform photonics devices

08 Jun 2020

Australian scientists develop controllable method to assemble single nanoparticles into advantageous templates.

A new method of nanocrystal assembly developed by Australian scientists could transform a range of photonics-based consumer devices and technologies, including smart phones, tablets and laptop displays, camera lenses, biosensors, solar cells and PICs. The research is led by the ARC Centre of Excellence in Exciton Science at the University of Melbourne.

The ARC Centre of Excellence in Exciton Science is funded by the Australian Research Council to bring together researchers and industry. The Centre is a collaboration between Australian universities and international partners to find better ways to manipulate how light is absorbed and transformed by advanced molecular materials.

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.

The researchers from Exciton Science have demonstrated a highly efficient and controllable method to assemble single nanoparticles directly into a pre-patterned template. The technique is described in Advanced Materials.

By applying an electric field at a certain level of strength, a technique called electrophoretic deposition (EPD), the researchers at the University of Melbourne and Australia’s national science agency, CSIRO, have created a nearly perfect single nanocrystal array using either gold nanospheres or gold nanorods.

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.

Lead author Heyou Zhang, a PhD candidate, commented, “Conventional nanofabrication methods normally produce 2D nanostructures. 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 manufacture nanoscale structures.”

Quantum dot potential

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 already 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 polarization-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: “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.”

The Centre is looking for partners to help scale-up the novel EPD process. Senior author Professor Paul Mulvaney, Director of Exciton Science, commented, "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."

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