Difference-Making Defects

Image of silicon atoms (orange band) in a graphene sheet (grey hexagons). Image courtesy of Dr. Juan C. Idrobo, Oak Ridge National Laboratory

Image of silicon atoms in a graphene sheet.

Sometimes, seeming defects can make surprisingly positive differences. History is full of individuals who suffered great personal anguish, but still created works of incredible value. What's true for humankind may be true for molecules too, based on recent research out of the Office of Science's Oak Ridge National Laboratory (ORNL).

A team of researchers led by ORNL's Dr. Juan C. Idrobo studied intrinsic defects in graphene, a flat material of rising potential. Graphene consists of pure sheets of carbon atoms, arrayed in hexagonal, chicken-wire like rows. It's stronger than steel and more electrically-conductive than copper. The ultra-thin sheets have incredible possibilities, which researchers supported by the DOE Office of Science are striving to work into new applications.

Specifically, the scientists studied point defects on the graphene sheets; the defects are formed by the substitution of silicon atoms for carbon atoms at few atomic sites in the sheets. To the researchers' surprise, these "point defects" locally enhanced the graphene's ability to transform waves of light into electronic signals (for more detail, see Nature Nanotechnology, http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2011.252.html). Sounds complex, but radios do exactly the same thing. Essentially, ORNL researchers had created one of the world's smallest antennas, consisting of just one silicon atom.

Proving their discovery took effort. To that end, the researchers were able to take advantage of a specialized electron microscope at ORNL's Shared Research Equipment User Facility, which is so sensitive that it can analyze properties at the scale of a single atom.

ORNL's atomic antenna can also convert electron waves back into light waves, which makes it a great example of what researchers call a plasmonic device. Researchers believe that plasmonic devices have great potential to improve the performance of electronic devices, and the "why" goes to the "how" of how they work.

Conventional electronics like batteries and light bulbs and computers work by having tiny negatively-charged particles known as electrons flow through them in race-track-like fashion. However, in plasmonic devices, the electrons vibrate in place, sort of like fans in a stadium doing the wave. The vibration tends to dissipate quickly (somewhat like a disorganized wave from disappointed – or dissipated – fans at the stadium), but it also tends to move much faster than electrons, which is why plasmonics is sometimes known as "light on a wire."

The ability to send and even store information via light rather than electrons could be important in future computers, since the performance limits of silicon are being reached. Researchers are investigating how this might be done in the developing field of silicon photonics, and ORNL's new finding may be important in advancing the field. ORNL's results could also be used to make other essential electronic devices smaller and faster, opening the way to a wide range of new applications.

These vast possibilities are coming from tiny, and sometimes, unintentional imperfections. It is as the poetess Alice Carry observed in Nobility, "And sometimes the thing our life misses/Helps more than the thing which it gets." As ORNL researchers showed, seeming defects can make a surprising, signal difference.

For more information about ORNL, please go to: http://www.ornl.gov/.

Charles Rousseaux is a Senior Writer in the Office of Science.