MRS Fall 2007: November 2007 Archives

That's all from the 2007 MRS Fall meeting. Check out the organizer's website for details on next year's show.

SabreTube is a bench top CVD tool for developing a range of nanostructures such as CNT forests and nanowires from three-month-old start-up and MRS exhibitor, Absolute Nano.

"We're targeting people who want rapid prototyping," John Hart of Absolute Nano told nanotechweb.org.

The apparatus came out of MIT and boasts fast heating rates (100 degC/sec). An infrared camera measures the temperature of the substrate and you can monitor the film thickness in real time by adding a laser.

For the full specifications, see www.absolutenano.com.

Nanowire phase change memory was up for discussion in symposium JJ. Ritesh Agarwal of the University of Pennsylvania, US, has been putting Ge₂Sb₂Te₅ nanowires through their paces to evaluate the material as a "universal memory" device. The results to-date are impressive with write speeds of less than 50 ns and an estimated data retention of 100,000 years for a wires just 20 nm in diameter.

Alex Zettl of "nano radio" fame was a big hit this morning with his whistlestop tour of nanoelectromechanical systems (NEMS). First up was the use of CNT's to probe biological systems. Coating a CNT with linker molecules, known as mucin mimics, makes the carbon structure compatible with its cell target. Zettl sees CNT probes as a gentler alternative to current biological injection techniques, which can damage or even burst cells.

"The CNT is not used as a hypodermic, instead active molecules are placed on the outside of the probe," Zettl told the audience. "The chemistry has been designed so that the linker molecules will release the active material when they enter the cell."

Switching from cell manipulation to electronics, Zettl moved on to the subject of nanoresonators. He showed some great SEM images of CNTs being "telescoped" in and out of each other to change the structure's resonant frequency, but the best was left until last.

With a broad smile on his face, Zettl played a recording of Eric Clapton's "Layla" as captured by a fully integrated radio receiver made from a single carbon nanotube. The proof of concept opens the door to incredibly compact, low-power wireless communication. For example, between a network of sensors.

Olgica Bakajin and her team from Lawrence Livermore National Laboratory, US, have been putting CNTs to use as a high-performance membrane that could dramatically reduce the amount of energy required to purify water.

The researchers coat their CNT array with Si₃N₄ to fill in the gaps between the tubes and make sure that liquid flows only through the narrow pores. To complete the membrane chip, the scientists shave off the top and the bottom of the coated array and then open up the closed CNT "caps" by adding carboxylic acid groups.

Simulations reveal that the success of the membrane is due to both the hydrophobicity and the atomic smoothness of CNTs. Surprised by just how good the membrane appears to be, the group is now putting its chip though a more rigorous testing program.

When the chair turned to the audience for questions, Bakajin was immediately quizzed about the cost of the device.

"CNTs are expensive, but when you look at how much material is actually used then the membrane's material costs turn out to be low even at today's CNT prices," she explained. "The problem is fabricating the membrane, because at the moment it takes a graduate student three days to make one of these."

Getting fluid to move along nanochannels isn't always straightforward and can present a stumbling block when it comes to lab-on-a-chip technology. One way to get around the issue is to use paramagnetic particles, as Paul Heremans of IMEC, Belgium, pointed out in today's lunchtime symposium.

The paramagnetic beads can be pulled through the stationary fluid by placing microcoils alongside the channel to provide a net magnetic force. Taking this a step further, you could functionalize the movable particles with specific molecules to perform a diagnostic function.

After a decade or more of searching, have CNTs finally found their breakthrough application? Paul Drzaic, Unidym's chief technology officer, presented a compelling case for the use of transparent CNT films in touch screen electronics and emphasized the firm's focus on scalable processing techniques to win over the display makers.

"We are confident that we'll have an ITO replacement that will save manufacturers money," he commented.

In fact, being able to offer a cheaper transparent electrode material is only part of the story. CNTs have a number of advantages over the use of ITO in displays. Firstly, the CNT films are mechanically more robust and should go a long way to improving the lifetime of touch panels.

Drzaic explained that Unidym is working with double-walled CNTs to preserve the film's electrical properties. The thinking is that if a defect develops in the outer tube, the inner tube can act as a shunt and maintain the electrical pathway.

And there's more - CNTs absorb light compared with ITO, which reflects light. This means that CNT-based displays should be more readable under natural light.

"The world's energy problem and what we can do about it" was the theme of Nobel laureate Steven Chu's packed plenary session. Chu has been working for the US department of energy for three years and has thrown his intellectual weight behind creating a more sustainable energy landscape (see - Lighting the way: toward a sustainable energy future).

"We really do need an Apollo program like effort," he told the audience.

Nanotechnology got a mention on the subject of solar cells, but it was the need for better materials that took centre stage. Chu's wishlist includes new metals for use with supercritical steam to help improve the efficiency of coal-fired power stations. Another request was for better insulating materials and better solid-state electronics for stepping up and stepping down power - two barriers to the adoption of a high-voltage DC grid for transporting electricity more efficiently.

On a much lighter note, Chu had an energy problem of his own when his laptop battery ran low during the presentation. Fortunately, a mains lead was found so that the show could go on.

Bharat Bhushan and his team at Ohio State University, US, have been working hard to get to the bottom of nature's most famous superhydrophobic surface - the lotus leaf. Its self-cleaning properties often hit the headlines, but the low friction material is also ideal for reducing drag flow in nanochannels.

SEM images of the leaf reveal micro-sized asperities covered with "nanobumps" that are thought to be due to the dendritic growth of wax. Bushan pointed out that the dual length scale structure allows air molecules to become trapped against the leaf when liquid rolls over the surface, enhancing the water repellent property of the material.

The team is using its analysis to come up with a synthetic version of the wonder material and has started making patterned PMMA structures coated with fluorinated silane to test various designs.

"Sharp edged asperities will pin droplets, which is bad news for fluid flow", Bushan explained. "Ideally, you would like to have round-tipped asperities."

Biomaterials specialist Samuel Stupp had the audience eating out of his hand when he played a video showing the formation of bundled nanofibres with lengths on the order of centimetres. The big news is that his self-assembling peptidic system can be used to align stem cells, which may prove very useful when it comes to generating muscle tissue or forming biological wires.

InGaAs/GaAs self-assembled quantum posts could find their way into future communications technology if the work of Pierre Petroff and his group at UCSB takes off. The researchers form their nanoscale pillars by connecting a seed quantum dot (QD) to a short quantum wire and then capping the MBE-grown structure with another QD.

Petroff sees the structure as the basis for a self-contained exciton memory cell and initial results show that incoming pulses can be stored for hundreds of milliseconds without loss. His sights are set on creating a quantum repeater, although he was quick to temper any excitement with the news that such a device may be "ten years off".

The race is on to bring you the pick of the nanoscale science and technology being unveiled at this year's MRS Fall meeting in Boston, MA, US. nanotechweb.org is registered and ready to go, so stay tuned for updates throughout the week.

Join the nanotechweb.org team at the MRS Fall meeting 2007 from Monday 26 November at the Hynes Convention Center and Sheraton Boston Hotel, Boston, US.