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May 2016

Molecular Foundry Scientists Discover Surprising New Properties in a 2-D Semiconductor


In the world of semiconductors, impurities and defects can be a good thing. They modify the properties of materials such as silicon, and scientists can exploit these properties to develop better transistors for laptops, smart phones, and solar cells.

Recently, a new class of semiconductor was discovered that is only three atoms thick and which extends in a two-dimensional plane, similar to graphene. These 2-D semiconductors, called Transition Metal Dichalcogenides (TMDs), have exceptional optical characteristics. They can be developed into ultra-sensitive photo detectors, and a single TMD layer emits as much light as a 3-D TMD crystal composed of 10,000 layers.

For the past several years, scientists have wondered if impurities and defects could also modify TMDs’ intrinsic properties, perhaps in ways that improve the semiconductor or lead to new functionalities.

Scientists at the Molecular Foundry, in collaboration with researchers at the ALS, have taken a big step toward answering this question. They found—to their surprise—how substantial linear defects in TMDs create entirely new properties. Some of these properties indicate that defects in TMDs might even mediate superconducting states.

The scientists synthesized three-atom thick, clean layers of molybdenum diselenide, which is a type of TMD, and then studied the material with a microscope that can visualize atoms and their electronic wave functions.

They discovered a linear defect formed by a line of missing selenium atoms. This defect creates one-atom thick metallic wires that cross the otherwise intact semiconductor like veins.

The scientists say this poses a big question: If similar defects could be incorporated in other types of the more than 60 different TMDs, might it be possible to induce a superconducting state in the material at temperatures that are higher than the highest critical temperatures currently reported for superconductors?

Read the full press release.