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Transformed aerogels: From amorphous carbon to nanocrystalline diamond

Transformed aerogels: From amorphous carbon to nanocrystalline diamond

Laser-heated diamond anvil cell allows very large hydrostatic pressure to be applied to amorphous carbon aerogels. Credit: LLNL

Laser-heated diamond anvil cell allows very large hydrostatic pressure to be applied to amorphous carbon aerogels. Cavity dimensions are approximately 100–170 μm wide by 35 μm thick. Credit: LLNL.

While there has been considerable interest in capturing the properties of diamond in a low-density form, converting an amorphous carbon aerogel to a crystalline phase without collapsing the porous network has proven tricky — but not impossible.

In a paper published in the May 9 online edition of the Proceedings of the National Academy of Sciences, a team of Lawrence Livermore researchers describe the successful synthesis of a diamond aerogel from an amorphous carbon aerogel precursor (“Synthesis and characterization of a nanocrystalline diamond aerogel,” doi: 10.1073/pnas.1010600108). The density of the amorphous precursor aerogel in this study is 0.04 g/cm3, which according to a LLNL press release, is about the density of the nanocrystalline diamond aerogel (pure diamond has a density of 3.52 g/cm3).

The team, led by former LLNL fellow, Peter Pauzauskie (now at the University of Washington, Department of Materials Science & Engineering), created an amorphous carbon precursor material using sol-gel processing (see pdf describing details, here) and used a diamond anvil to subject the aerogel to pressures where diamond is the stable phase of carbon. Laser heating was used to overcome the kinetic barriers of the phase transformation to nanocrystalline diamond.

A key goal of the experiment was to maintain the porous structure of the sample. The precursor aerogel is self-supporting, but the researchers note that it is still delicate - finger pressure is enough to crush it. Supercritical neon was used to apply hydrostatic pressures of 21.0 GPa, 22.5 GPa and 25.5 GPa (that’s about 3,000-3,700 ksi), and the samples were laser heated to approximately 1850 oC. The study made no attempt to optimize the pressure and temperature parameters.

Using Raman spectroscopy, the researchers concluded that there was not a superhard graphite phase helping to prevent pore collapse, which had been suggested as a possible mechanism for mesoporous carbon. TEM showed that diamond aerogel is a network of nanocrystals (2.5-100 nm) that appear to be connected by thin surface coatings of graphitic carbon and that the porous morphology seems to have been preserved.

It’s likely a long road from diamond anvil synthesis to a bulk processing method, but the study shows that the phase transformation from amorphous carbon to diamond can be achieved nondestructively while maintaining the porous morphology. Materials of this type are expected to have applications as tunable and optically effficient antireflective coatings, optical quantum bits, and cellular biomarkers. The unique optical, thermal, and chemical properties of a nanocrystalline diamond, porous material will lead quickly to other applications, some novel and some fairly pedestrian (but important), such as  water desalination.

As a proof-of-concept, the study showed that nondestructive phase transformation from amorphous to nanocrystalline morphologies is possible from sol-gel precursor materials, which, the authors note, opens the possibility of producing other highly porous, nanocrystalline materials such as SiO2.

Materials stories that may also be of interest

Check them out:

Role of parallel reformable bonds in the self-healing of cross-linked nanogel particles (also, Nanomaterials with give survive)

Polyelectrolyte functionalized carbon nanotubes as efficient metal-free electrocatalysts for oxygen reduction (also, Cheap fuel cell catalyst made easy: CWRU researchers aim to cut cost of alternative energy)

Iowa State, Ames Lab researcher hunts for green catalysts

How plug-in hybrid cars could be game changers

Errors make some circuits better: A counterintuitive approach could yield smaller, faster, more energy-efficient chips

10 companies to watch for out of ARPA-E

China poised to overhaul US as biggest publisher of scientific papers

Materials stories that may also be of interest

Materials stories that may also be of interest

Worth a look:

‘Rechargeable’ anti-microbial surfaces boost food safety

A University of Massachusetts Amherst food scientist is developing a way to improve food safety by adding a thin anti-microbial layer to food-handling surfaces. Only tens of nanometers thick, it chemically “re-charges” its germ-killing powers every time it’s rinsed with common household bleach.

Overview of NIST’s Polymers Division

Established in 1962, the Polymers Division in the Material Measurement Laboratory of the National Institute of Standards and Technology will soon celebrate its 50th year as a world leader in polymers research.

Moth eye-inspired antireflective material boosts efficiency of solar cells

Researchers at Nagaoka University of Technology (Japan), Mitsubishi Rayon Co. Ltd. and Tokyo Metropolitan University pioneered a way to use anodic porous alumina molds to nanoimprint the microstructure similar to a moth’s eye into acrylic resin. The film could boost solar cell efficiency 5-6 percent.

Torque vectoring gears for smaller, more efficient wind turbines

Gigmag’s Darren Quick reports that investigators at the Technische Universitaet Muenchen “have now adapted this technology to wind turbines, to eliminate the need for converting the alternating current produced by the turbines into direct current and back again before it is fed into the grid.”

Second wave of ‘cleantech’ investing coming?

GigaOM’s Katie Fehrenbacher reports on what may be a renaissance in venture capital firms’ interest in clean and green technologies. What might be guiding their way this time? A) Being more realistic about how long commercialization takes; B) Look for opportunities outside the U.S., such as China, Brazil, India and even Europe.

5 new research sites to be built with $50M in NIST grants

5 new research sites to be built with $50M in NIST grants

Architect’s drawing of the planned Western Institute of Nanotechnology on Green Engineering an
Metrology at UCLA. Credit: Stenfors Associates Architects.

NIST waded through over 100 proposals over the past few months and has now approved proposals and funding for five new scientific research facilities, including two that will concentrate on nano technologies The institute will give a total of $50 million for centers that will construct new labs or expand on existing ones. Each sponsoring institution is matching the NIST dollars with at least 20 percent of the annual project costs.

The facility research centers, locations and funding are as follows:

Michigan’s 63,000 square-feet nano center will focus on several areas including the dynamics of DNA molecules, nanoscale energy conversion, nanomanufacturing and nano/micro electromechanical systems) for medical research and diagnostics. It will also house eight special ultra-low vibration specialized laboratory chambers designed to meet NIST specifications for vibration, air quality, temperature and humidity control. It also plans to have lab dedicated to imaging and optics; biosystems; nanoengineering; micro-bioengineering; materials, mechanics and mechanical testing; microdynamics and nanostructures. Planned research projects for the new facility range from the analysis of single biomolecules to metrology of nanoparticle-based composites to precision nanomanufacturing and assembly.

The UCLA WIN-GEM center is supposed to focus on ”low-dissipation, nonvolatile electronics. One of the particular angles mentioned are low-cost, high-yield, energy-efficient nanoscale semiconductor manufacturing. The facility will also serve as one of DOE’s Energy Frontiers Research Centers that will look at polymer-based solar cells, electrochemical supercapacitors for energy storage and carbon capture. There is supposed to be 35,000 square feet of labs, plus separate facilities for a quantum metrology, microscopy, electron and spintronic transport, and a wet chemistry energy/nano lab.

NIST announced this Construction Grant Program in February. The five winners were selected based on scientific and technical merit of the proposed use of the facility and the need for federal funding; quality of the design of the facility; and adequacy of the construction project management plan.

 

Materials stories that missed the cut this week

At the end of each week, I end up with a list of a bunch of stories I started to write about, or started to investigate or didn’t even get that far even though the topic looked intriguing, but, I had a meeting to go to …

Anyway, it’s Friday, and rather than have these stories evaporate into the ether, I’ve close out each week by providing some raw links to some of these orphan tales. Check ‘em out:

Department of Energy Announces $188 Million for Small Business Technology Commercialization

Nanomaterials in the Construction Industry: A Review of Their Applications and Environmental Health and Safety Considerations

Nanopatterns on the cheap with Shrinky Dinks

Storage system levels energy demands

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