Berkeley Lab researchers discover cause of defects in 2D materials used to create electronics

Bruno Schuler/Courtesy

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Discoveries of the causes of defects in transition metal dichalcogenides, or TMDs, by researchers at the Lawrence Berkeley National Laboratory, has brought scientists closer to creating ultra-high efficiency electronics.

Most electronics use silicon because scientists have figured out how to arrange the silicon crystals almost perfectly. Scientists have reached the limit, however, of how small the electronics can be using silicon, according to Bruno Schuler, the study’s co-lead author and a Berkeley Lab postdoctoral researcher. TMDs, however, are only one layer of atoms, and are therefore capable of being used to create much smaller electronics.

“In this respect two-dimensional (2D) materials that are intrinsically only one or a few atoms thick are becoming a real game changer,” Schuler said in an email. “But before we can put them in devices we need to understand what common ‘errors’ in such 2D materials are present such as missing atoms and impurity atoms.”

Schuler and his fellow co-lead author, Sara Barja, a former Berkeley Lab postdoctoral researcher, developed a new microscope that is able to see individual atoms in these 2D materials. As a result, they are able to identify defects and learn what their properties are, according to Schuler.

In their study, Schuler and Barja found that a common defect was not a result of the lack of atoms, as many researchers assumed. Instead, these defects are a result of oxygen atoms, which are in the same chalcogen group as atoms in TMDs and therefore share similar properties, filling in for the sulfur, S, or selenium, Se, atoms in the crystal structure.

“We believe that the oxygen substitutions are a way that nature wants to ‘fix’ missing S/Se sites that can be formed during synthesis,” Schuler said in an email. “It just takes the next best thing that is available in the atmosphere.”

To study the defect caused by the lack of an atom, researchers used a vacuum and heat to “kick out” a sulfur atom to create a vacancy, according to Schuler.

Researchers discovered that the vacancies create spin-orbit coupling, which is when electrons’ orbital path and spin interact, creating hybrid states of electronic structure, according to a Berkeley Lab news release. This has a significant impact on the structure of defect sites in TMDs, according to the release.

According to Schuler, the role defects will play in future electronics is an important discussion happening now in the scientific community, which is why it is so important to understand how these defects form and what they are capable of.

“Traditionally we look at defects in materials as the nemesis of any synthetic materials chemist,” said Kwabena Bediako, a UC Berkeley assistant professor of chemistry, in an email. “These studies show us that the more we understand about precisely what these defects consist of, the better we can manipulate and exploit these defects to do something productive.”

The next steps are to deliberately place specific atoms in the TMD materials, according to Schuler. He added that they will look at how the implanted impurities will affect the electron spin and how that spin can be used to learn more about quantum information, which deals with the state of a quantum system. According to Schuler, this could establish a new branch of quantum information science.

Contact Maria Young at [email protected] and follow her on Twitter at @maria_myoung.