Carbon nanotubes

2020 vision

The US sees electronics as a leading enabler for nanotechnology's next decade.

Does electronics hold the key to pushing nanotechnology research to the next level? A global sector review due for release this month will suggest that such is the case.

The US National Science Foundation (NSF) and the World Technology Evaluation Centre (WTEC) have prepared Nano2. It follows a similar project a decade ago that convinced President George W. Bush to commit more than $1bn a year to research, largely under the aegis of the National Nanotechnology Initiative (NNI). The NNI celebrates its 10th anniversary in 2011, so it's a good time to take stock - and nudge President Barack Obama's administration on its continued importance.

Like Nano1, the new review is led by Dr Mihail Roco, senior advisor to the NSF for nanotechnology. He thinks for all the investment so far, the task still comes down to basics.

At an NSF-hosted pre-publication hearing on Nano2, Roco said, "There are many things that are still open - even self-assembly. Self-assembly was so promising in 2000, but the first test measurements to see where atoms go and why they go there were done only a year ago - and we need that knowledge to understand fully what we can do.

"And we found that the situation is very similar throughout the world," he said. "We found that sometimes a country's focus was just to take an existing discovery and make a product in five years. That's not bad in itself, but we need the balance where there is some contribution to continuing to develop the fundamentals."

The numbers for nano-incorporated products released support Roco's position. Just six base materials are used in more than 90 per cent, the foremost quartet being carbon nanotubes, titanium dioxide, zinc oxide and silver.

Understanding materials in more depth and adding new ones could, in Roco's view, create a global market worth $1Tr by 2015 and $3Tr by 2020 from approximately $300bn today.

But if the talk is about materials science, why is it that electronics is so important to the project? Part of the solution here lies in Roco's comments about test, another in the potential it offers for re-use and a third in the dominant theme in electronics design today, systems-based thinking.

State of play

Nano2 addresses global, not just US nanotechnology activity, so there are lessons for all. There are also a lot of politicians looking for a return on taxpayers' money that's already been spent. In 2008, the EU led government funding at $1.7bn, followed by the US at $1.6bn and Japan at $950m.

There has been some payback. In the US between 2000 and 2008, related employment grew from 25,000 to 150,000 people, R&D spending from $370m to $3.7bn, and product sales from $13bn to $80bn. An important aspect of those numbers is that that they show private sector investment now exceeding that from the public sector.

However, the products coming to market point to a relative immaturity in our use of nanotechnology. Roco believes we are currently working through two types of design. 'Passive nanostructures' are things like coatings that give us stain-resistant clothing. 'Active nanostructures' help us create more sophisticated items such as 3D transistors, targeted pharmaceuticals and adaptive structures.

The real game changers come in two emerging categories: 'Nanosytems' leading to 'Molecular nanosystems'. In these areas, we would progress from guided high-level assembly to bespoking molecules, from advanced but discrete-by-discipline hierarchical architectures to those that cross multiple disciplines.

Much as in electronics, the world needs to undergo a shift towards system thinking where the application comes first. This is why Roco believes that we still need broader fundamental research and he amplifies that argument by pointing out that we also need the tools to do that job.

"We are still in a formative phase, he said. "We are at the micro level - a shape and size approach, not an internal one. Only last year, did we start to see early measurements made using a direct approach."

TEAM work

"Our periodic table is a bit daft," says Dr Chad Mirkin, another Nano2 contributor and director of the International Institute for Nanotechnology at Northwestern University. "We've defined things by size, shape and composition."

Mirkin's view is that as nanotechnology pushes science beyond spherical particles into such areas as rods, wires, prisms and platonic solids, we need a periodic table that works in multiple dimensions. Thermal, photochemical and electrochemical behaviour also need to be considered.

To do this, sophisticated tools are vital. These are beginning to emerge. One example of the advances taking place was cited by Nano2 contributor, Dawn Bonnell, director of the Centre of Science and Engineering of Nanoscale Systems at the University of Pennsylvania. "Aberration correction is revolutionizing structural imaging in electron microscopy," she said. "It allows atomic-level vision of atoms as light as oxygen."

The Transmission Electron Aberration Correction Microscope (TEAM) project demonstrated equipment capable of resolution of 0.05nm in 2009. It is already being used to explore materials such as graphene, germanium and gold. However, the great promise is that TEAM could go much further as demands upon it inevitably grow.

The smallest feature a microscope can observe is first determined by the wavelength of the light source. The use of high energy electrons implies a potential wavelength as low as 2.0pm (or 0.002nm). However, a further constraint is imposed by the inherent presence of imperfections in the lenses.

The Scherzer Theorem states that two types of aberration, chromatic and spherical, will occur in all static, rotationally-symmetric electron lenses, and they typically limit resolution to about 100 times the wavelength of the electron. TEAM overcomes distortions by using corrective elements that allow them to deviate from rotational symmetry much as we might wear glasses to correct short-sightedness.

The correctors can be made from multipole elements and TEAM has demonstrated that two types, hexapole and quadrupole-octopole, will compensate for spherical aberration. A quadrupole-octopole corrector can then also be the basis for a chromatic aberration corrector.

More resolution gains are made by using techniques that increase the stiffness of the microscope's mechanical column and reduce electromagnetic instabilities by stabilizing fields to an accuracy of about 100 parts per billion. To then reach closer to the resolution limit, a computational iterative mechanical alignment is used.

The TEAM work is being advanced by four US laboratories (the Lawrence Berkeley National Laboratory, the Argonne National Laboratory, the Oak Ridge National Laboratory and the Frederick Seitz Materials Research Laboratory at the University of Illinois, Urbana-Champaign) and two manufacturers, FEI of the US and CEOS of Germany.

Bonnell also cited recent advances in synchroton radiation technology that have allowed observation of attosecond snapshots of electronic disturbances in water produced by diffusing gold ions. That implies improvements in available in brightness ahead of those being achieved in microelectronics under Moore's Law.

The underlying message is clear - to get to the level of knowledge we need, the tools for the job will be primarily electronic.

Making it

Electronics has taken more steps into the world of nanotechnology than any other industry. Inevitably, it is going to be one of the sector's great enablers. Beyond its importance to metrology, Dr James Munday of the University of South Carolina added that it also offers opportunities for reuse, particularly in manufacturing.

"One way to exploit the work of the semiconductor industry is that they leave behind many technologies that have been amortised but which can be coupled now into areas such as healthcare," he said.

But in electronics-specific terms, Dr Jeffrey Welser, director of the Nanoelectronics Research Initiative, offered an intriguing view into how it can also push manufacturing further. For example, as lithography for chip fabrication hits roadblock after roadblock, he suggested that the traditional top down approach could be used down to 10nm but then combined with bottom-up self-assembly to reach 1nm.

However, his main theme was that a 'systems-based' shift in thinking is required if the sector is to exploit much hyped materials and concepts like spintronics and magnetic tunneling.

"We need," he said, "increased focus on utilizing new nanoscale physics for device functionality rather than just fighting those physics to continue current device scaling."

Architectures will change, carbon will play a greater role and the applications driving that system thinking will increasingly move beyond the traditional world of information technology into sensors, energy, medicine and more complex mobile devices. All that then will be enabled by more multi-disciplinary design practices.

"Microelectronics was the economic driver of the last half of the 20th Century; nanoelectronics is poised to drive the first half of the 21st," Welser said.

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