A gas cluster ion beam smoothing produces ultrathin silver films and lithographically patterned structures to enhance plasmonic performance.
Plasmonic devices — such as superlenses, hyperlenses and plasmonic waveguides — have exciting potential for research and commercial applications because they permit optical lithography, imaging and waveguiding to be performed at resolutions below the diffraction limit of light.
These devices often require low-loss ultrathin metal films, which are difficult to fabricate using current deposition techniques. Researchers have investigated processes such as seed layer deposition and thermal annealing to reduce the surface roughness and grain-boundary density of these films. To date, however, these processes have not been hugely successful.
Now, Ee Jin Teo and colleagues at the A*STAR Institute of Materials Research and Engineering, Singapore, the University of Hyogo, Japan, and the National University of Singapore have used gas cluster ion beam (GCIB) processing to smooth ultrathin metal films and thereby enhance their properties(1).
A GCIB consists of thousands of gas molecules that are weakly bound by van der Waals forces. Such a beam is able to smooth out surface irregularities and reduce film thickness with nanometer precision. This processing significantly enhances surface plasmon resonance and propagation, and enables the fabrication of ultrathin films with extremely low electrical resistivity and optical loss.
Unlike monomer ion beams used in conventional ion-beam milling and plasma etching, a cluster of nitrogen gas molecules with an energy of 20 kiloelectron volts impinging on a silver film can deliver a high energy density to a relatively small volume: yet the cluster penetrates to a depth of only a few nanometers.
The impact of the beam on the film causes silver atoms in surface peaks to scatter sideways towards valleys, voids and grain boundaries. As well as producing a smoother surface, this processing triples the grain width through the redeposition of atoms at grain boundaries.
The team’s GCIB treatment resulted in up to a four-fold improvement in the electrical and optical properties of films of a thickness of 12 nanometers. “The unique characteristics of GCIB irradiation meant that in a single irradiation step we could reduce scattering losses due to surface roughness, grain boundaries and voids,” notes Teo.
The research team also used the technique to smooth the top surface and sidewalls of lithographically patterned silver-stripe waveguides, increasing the propagation lengths of surface plasmons in these waveguides.
“In the future, we intend to use this technique to improve the colour purity of plasmonic color filters or reflectors, and also to increase the patterned area of superlens nanolithography,” says Teo. “Such developments will bring plasmonic research a step closer to commercialization.”
1. Teo, E. J., Toyoda, N., Yang, C., Wang, B., Zhang, N. et al. Sub-30 nm thick plasmonic films and structures with ultralow loss. Nanoscale 6, 3243–3249 (2014).
Lee Swee Heng | Research SEA News
One in 5 materials chemistry papers may be wrong, study suggests
15.12.2017 | Georgia Institute of Technology
Scientists channel graphene to understand filtration and ion transport into cells
11.12.2017 | National Institute of Standards and Technology (NIST)
DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.
Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...
MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.
Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...
Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...
Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.
To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...
The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.
Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...
11.12.2017 | Event News
08.12.2017 | Event News
07.12.2017 | Event News
15.12.2017 | Power and Electrical Engineering
15.12.2017 | Materials Sciences
15.12.2017 | Life Sciences