Experts hold 'great optimism' with caution against hype; niche markets to be addressed first

Chairs Frank Koppens and Nathalie Vermeulen open a workshop
featuring graphene research and industry leaders at SPIE Photonics Europe.

BRUSSELS, Belgium and BELLINGHAM, Washington, USA -- The unique and promising properties of graphene -- a one-atom-thick sheet of carbon atoms arranged in a honeycomb-shaped lattice -- and its game-changing potential in numerous applications were explored in a well-attended and highly interactive daylong workshop on 5 April during SPIE Photonics Europe 2016 in Brussels.

At the end of the day, the consensus was that the most promising nearer-term applications are in communications.

Workshop chairs were Frank Koppens of ICFO -- Institute of Photonic Sciences, and Nathalie Vermeulen of B-PHOT -- Brussels Photonics Team, Vrije Universiteit Brussel.

"The workshop clearly showed that bridges are being built between scientists, companies working on applications, and institutions developing the production processes," Koppens said. "In general, great optimism was expressed on the expectations that graphene-based applications will make it to the market. But there was also a warning for too much hype creation, and acknowledgement that niche markets will be addressed first."

The opening session focused on graphene's role in integrated photonics devices for data communications, with speakers Marco Romagnoli (National Laboratory for Photonics Networks, CNIT), Wolfgang Templ (Alcatel-Lucent Bell Labs), Tingyi Gu (Princeton University), and Klaas-Jan Tielrooij, ICFO.

Among graphene's intriguing properties for data communications are its excellent electrical conductivity, capability for strong light-matter interactions, and high optical nonlinearity. These allow all-optical signal processing, avoiding the need for conversion of the optical signal to the electrical, and consequently the need to design high-speed interfaces between optical and electronic parts.

The optical and electrical properties are tunable, making graphene an attractive candidate to complement silicon photonics in the near future, potentially transforming the future of data communication devices.

This is well worth study, speakers agreed, in the face of exponentially growing consumer demand for bandwidth, higher performance, and faster delivery of content as well as the increasing importance of energy efficiency.

"We already have suitable technologies for datacoms systems. Integrated photonics is a promising technology for improving communications as data rates rise," Romagnoli said. "There is the simultaneous need for reduced power and costs."

In the second session, Hartmut Roskos (Physikalisches Institut, Goethe-Universität), Alan Colli(Nokia Technologies), Valerio Pruneri (ICFO), Tom Constant (University of Exeter), and Ilya Goykhman (Cambridge Graphene Centre, University of Cambridge) focused on infrared and terahertz applications in detection and sensing.

Applications such as metal detection, quality assurance, medical spectroscopy, integrity checks, breath-gas analysis, temperature sensing, and biosensing require very sensitive technologies. Much progress has been made with terahertz and infrared sensors, each of which employ physical effects -- thermoelectrics in semiconductors and plasmonics in noble metals such as gold and silver. Performance is limited by unfavorable physical properties of the sensor materials, and cost and scalability remain challenging.

Graphene, however, excels in both of these physical effects. Current technologies would benefit from combination with graphene, making the outlook of creating a highly scalable and cost-effective device very promising.

The third session, on wafer scale processing and integration, featured talks by Grzegorz Lupina (IHP, Leibniz-Institut für innovative Mikroelektronik), Cedric Huyghebaert (IMEC), and Christoph Stampfer(RWTH Aachen University).

Graphene has become more popular in integrated electronics and photonics, where mass manufacturability is key. However, the traditional exfoliation process using cellophane tape is not suitable for mass production.

New methods to grow graphene on a large scale have emerged, of which chemical vapor deposition on copper is by far the most popular. A wet transfer technique is used to deposit graphene on electronic or photonic chips. However, this results in graphene sheets of relatively low quality.

In principle, the use of a single-crystal copper substrate and a dry transfer technique can tackle these issues, but has not been widely applied because of the difficulty of harvesting graphene from the copper substrate. Defects can be avoided by growing graphene on other substrate materials such as boron nitride, which yield perfectly flat substrate surfaces.

These new substrate materials are expected to pave the way for mass fabrication of graphene sheets with the same excellent quality as the exfoliated graphene sheets.

The day's final session targeted the bottom line in brief presentations followed by lively discussion on next steps and challenges in commercialization. Broadband light detectors, gas sensors, and EUV pellicles could be among the first devices made from graphene, the panel agreed.

Rapid presentation participants and panelists were:

• Stijn Goossens, ICFO
• Cedric Huygebaert, IMEC
• Bjarke Jørgensen, Newtec
• Daniel Neumaier, AMO GmbH
• Paul Hedges, Applied Nanolayers
• Richard van Rijn, Applied Nanolayers
• Wolfgang Templ, Alcatel.