Researchers model material that switches between insulator and semiconductor

Aug. 27, 2014, 12:59 p.m.

Researchers at the Stanford University Materials Computation and Theory Group have successfully modeled a new material, three atoms thick, that switches between being an insulator and a semiconductor when tugged.

While it is difficult to find materials that can be worked down to the thickness of a few atoms without disintegrating, it is possible. The resulting materials, only a few atoms thick, are called two-dimensional (2-D) materials, and they have their own unique properties.

Since 2-D materials switch from being a metal to being a semiconductor, their potential uses are extensive. They are also virtually transparent and may be coated onto other materials, such as windows or paper, to make them electronically interactive.

“A key motivation for studying these materials is that they are light, extremely strong and extremely flexible,” said Karel-Alexander Duerloo M.S. ’13, one of the main authors of the study. “Perhaps the most exciting area of potential application is smart clothing – like a smartphone built into a sweater – where this ultra thin and flexible switching material is woven into regular textiles.”

The potential material discussed in the researchers’ paper also has the unique feature of having two stable, relevant crystal structures instead of just one like most solids do.

Molybdenum ditelluride, the main component of the material, has two crystal structures that are not very different in terms of their total energy. Therefore, the switch between being a semiconductor and a metal is relatively simple when the metallic crystal structure is forcibly changed via tugging or stretching. According to Duerloo, the process is much like flicking a light switch.

“Nature provides few materials that can be controllably switched between multiple atomic structures. [These are] called phase change materials,” said Evan Reed, assistant professor in Stanford’s Department of Materials Science and Engineering. “These properties play critical roles in energy and electronic applications, like re-writable optical discs.”

Duerloo also explained that the new material may be used to make electronics even thinner than they are now. Manufacturers are currently having problems with the leakage of current in chips that are already approaching being too thin. This new material may fix that.

Computer simulations of the new material have run smoothly, and researchers are optimistic about its physical production. While the possibility of production on an industrial scale remains to be seen, materials with a similar three-atom thickness, such as molybdenum disulfide, have been made with relatively little hassle through a commercially viable process called chemical vapor deposition (CVD).

“You can already buy commercial CVD-grown molybdenum ditelluride – the material that we found to be promising – as a thick crystal,” Duerloo said. “The challenge right now is to get it to only three atoms thick and to ensure that it doesn’t oxidize when exposed to the environment.”

Physical production of the new material is projected to begin soon, although a particular date has not yet been specified.

“We are very excited about this research and its potential technological impact,” Duerloo said. “The next step for us is to work with world-leading experimental teams who have the know-how to build this material and conduct experiments.”


Contact Helen Wong at helen ‘dot’ wong ‘at’ saratogafalcon ‘dot’ org.

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