Researchers at the Institute of Electron Microscopy and Nanoanalysis, at Graz University of Technology (TU Graz), and the Graz Centre of Electron Microscopy (ZFE) have been working for more than a decade on manufacturing complex, free-standing 3D architectures – in an attempt to expand the range of applications for optically active nanostructures that can be found in solar cells and biological or chemical sensors.
The team, led by Harald Plank, Verena Reisecker, and David Kuhness, has achieved two breakthroughs. It is now possible to precisely simulate the required shapes and sizes of nanostructures to achieve the desired optical properties, which can then be accurately produced. They have also managed to completely remove chemical impurities incorporated during initial production without negatively impacting the 3D nanoarchitectures.
Until now, 3D nanostructures required a time-consuming trial-and-error process to get the end product with the desired optical properties. According to TU Graz, this effort has finally been eliminated. “The consistency between simulations and real plasmonic resonances of a wide range of nanoarchitectures is very high,” said Harald Plank. “This is a huge step forward. The hard work of the last few years has finally paid off.”
The technology is reportedly the only one in the world that can be used to produce complex 3D structures with individual features smaller than 10 nanometres in a controlled, single-step procedure on almost any surface. For comparison, the smallest viruses are around 20 nanometres in size. “The biggest challenge in recent years was to transfer the 3D architectures into high-purity materials without destroying the morphology,” said Harald Plank. “This development leap enables new optical effects and application concepts thanks to the 3D aspect.”
The researchers use focused electron beam-induced deposition to produce the nanostructures. The relevant surface is exposed to special gases under vacuum conditions. A finely focused electron beam splits the gas molecules, whereupon parts of them change into a solid state and adhere to the desired location. By stacking these nano-volumes on top of each other, 3D structures are constructed. “By precisely controlling beam movements and exposure times, we are able to produce complex nanostructures with lattice- or sheet-like building blocks in a single step”, said Harald Plank.
