World first for writing silver nanostructures
Image: SEM images of 10 micron planar deposition; silver crystals are 100 nm in size. [HZB/ ACS Applied Materials &Interfaces (2017)]
In a world first, researchers have used electron beam induced deposition to write silver nanostructures onto a substrate.
While the method is well established technique for gold, platinum, copper and further metals, direct electron beam writing of highly reactive silver has remained elusive.
“It took us a lot of time and effort to design a new injection unit and find a suitable silver compound,” explains Dr Katja Höflich from Helmholtz-Zentrum Berlin, Germany.
“Finally, we managed it," she adds. "The compound silver dimethylbutyrate remains stable and dissociates only in the focus of the electron beam.”
Höflich and colleagues from HZB and the Swiss Federal Laboratories for Materials Science and Technology (EMPA) used the EBID method to create sharply defined areas of tiny silver nanocrystals.
They first injected the metal-organic precursor - AgO2Me2Bu - into the vacuum chamber of the SEM, near the surface of the sample using a needle.
As the researchers point out, where the electron beam hits the sample surface, the precursor molecules dissociate and the non-volatile constituents are deposited.
The electron beam is then moved across the substrate to create features.
"Interestingly, the silver deposition was strongly dependent on electron dose; at low doses of 30 nC/μm2 a dominant formation of pure silver crystals was observed, while at higher electron doses around 104 nC/μm2 large carbon contents were measured," highlights Höflich.
The researchers developed a scheme for the enhanced silver deposition under low electron fluxes and went on to fabricate well-defined two-dimensional deposits with maximised silver content approaching 75 at. %.
Silver crystals are 'hot-spots' of extreme brightness under laser illumination. Spectral analysis (Raman spectroscopy) shows that each nanocrystal is surrounded by a skin of carbon. [HZB/ ACS Applied Materials & Interfaces (2017)]
Silver nanostructures have the potential to concentrate visible light at the nanoscale.
Potential applications include sensor design to detect extremely small traces of specific molecules, as well as devices for optical information processing.
Research is published in ACS Applied Materials Interfaces.