Nottingham University and National Physical Laboratory (NPL) scientists have found that stabilizer residue in metal nanoparticle inks inhibits conductivity in 3D printed electronics.
They were able to prove this by making use of Nottingham’s orbiSIMS instrument which allows for label-free 3D chemical imaging of materials with high resolution.
According to The Engineer, inks containing metal nanoparticles (MNP) are among the most commonly used conducive materials for 3D printed electronics.
It is these ink-jetting layers of MNP materials that allow for design flexibility, rapid processing, and 3D printing of devices such as sensors, solar panels, LED displays, transistors and smart textiles.
Inkjet 3D printing of metals usually involves a two-step process: solvent evaporation upon printing (pinning) and subsequent low-temperature consolidation of nanoparticles (sintering).
Low temperature is the norm here as the nanoparticles need to be co-printed with other functional/structural organic materials that are sensitive to higher temperatures.
However, layers produced by inkjet printing of metal nanoparticles have different electrical conductivity between horizontal and vertical directions, reports the Nottingham and NPL team.
This is known as ‘Functional Anisotropy’ and is a long-standing problem for 3D printed electronics.
According to previous research, reduced vertical conductivity was thought to have been caused by shape and physical continuity problems at the interfaces of the constituent nanoparticles at micro and nanoscale.
But this is not the case, as shown by the Nottingham scientists. They made use of silver nanoparticles to show that reduced vertical conductivity is caused by organic chemical residues in the inks.
The nanoparticles were added to the inks to help stabilize the nanomaterials, leading to the formation of low-conducting, thin nanoscale layers which interfere with the electrical conductivity of the printed sample in the vertical direction.
According to lead author Dr Gustavo Trindade, this new insight will enable the development of routes to overcome functional anisotropy in inkjet-based nanoparticles – albeit in an economical and efficient manner.
What’s more, the new approach is also transferable to other nanomaterial-based inks such as graphene and functionalised nanocrystals, enabling development of both 2D and 3D printed electronics.
Image and content: Gustavo Trindade/The Engineer