Diamond aerogel could improve optics

Compiled by Photonics Spectra staff

A nanocrystalline diamond aerogel could spell big improvements to optics for applications as large as telescopes or as small as eyeglass lenses. At Lawrence Livermore National Laboratory (LLNL), a laser-heated diamond anvil cell and a standard carbon-based aerogel precursor, combined with high pressure and temperature, were used to produce the diamond aerogel.

A diamond aerogel has been hammered out of a microscopic anvil. Image by Kwei-Yu Chu/LLNL.

Aerogels are a class of materials exhibiting the lowest density, thermal conductivity, refractive index and sound velocity of any bulk solid. Chemists, physicists, astronomers and materials scientists use the properties of aerogels in myriad applications, from a purifier for desalinizing seawater to a meteorite particle collector on a NASA satellite.

A diamond anvil cell comprises two diamonds with the sample compressed between them. It can compress a small piece of material (tens of microns or smaller) to extreme pressures, which can exceed 3 million atmospheres. The device has been used to recreate the pressure existing deep inside planets, creating materials and phases not observed under normal conditions. Because diamonds are transparent, intense laser light also can be focused onto the sample to simultaneously heat it to thousands of degrees.

The new form of diamond has a very low density similar to that of the precursor of around 40 mg per cubic centimeter, which is only about 40 times denser than air.

In creating diamond aerogels, lead researcher Peter Pauzauskie, a former Lawrence fellow now at the University of Washington, infused the pores of a standard carbon-based aerogel with neon, preventing the entire aerogel from collapsing on itself.

The diamond anvil cell is small enough to fit in the palm of a hand, but it can compress a sample to extreme pressures – up to about 3.6 million atmospheres at room temperature. Courtesy of LLNL.

At that point, the team subjected the aerogel sample to tremendous pressures and temperatures (above 200,000 atmospheres and in excess of 2240 °F), forcing the carbon atoms within to shift their arrangement and create crystalline diamonds.

The diamond aerogel could have applications in antireflection coatings, a type of optical coating applied to the surfaces of lenses and other optical devices to reduce reflection. It can be applied to telescopes, binoculars, eyeglasses or any other device that may require reflection reduction. It also has potential applications in enhanced or modified biocompatibility, chemical doping, thermal conduction and electrical field emission.

The success of this work, which was reported in the May 9, 2011, Proceedings of the National Academy of Sciences (doi:10.1073/pnas.1010600108), also leads the team to speculate that additional novel forms of diamond may be obtained by exposing appropriate precursors to the right combination of high pressure and temperature.