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High-impact MIT research comes to ORNL

MIT doctoral candidate Shengxi Huang.

Two-dimensional nanomaterials may be infinitesimally small, but they are a big deal for the chemists and materials scientists who trek to ORNL to study them. One such user is Shengxi Huang.

Huang is a doctoral candidate at the Massachusetts Institute of Technology working with Mildred Dresselhaus, a noted physicist, engineer, and long-time ORNL collaborator known as “The Queen of Carbon Science.”

Dresselhaus pioneered research in carbon nanotubes, graphene and other carbon nanostructures. When Huang joined the research group shortly after arriving at MIT, Dresselhaus assigned her to work on 2-D materials at ORNL’s Center for Nanophase Materials Sciences, which has the specialized facilities and active research interest necessary for their work, in this case allowing them to apply a technique known as low-frequency Raman spectroscopy.

Huang and Xi Ling, a former group member and current professor of chemistry at Boston University, came to ORNL to study a family of 2-D materials called transition metal dichalcogenides.

These materials are promising semiconductor candidates and exhibit excellent optical properties, such as strong photoluminescence and absorption, that can be applied to next-generation optoelectronic devices.

“I think these materials are potentially quite useful in making ultrathin and flexible devices,” Huang said. “For example, our screens would be less rigid and could be rolled up or folded into a bag. They can be quite unique.”

Working with CNMS researchers including Bobby Sumpter and David Geohegan, the MIT team used low-frequency Raman spectroscopy to characterize the properties of 2-D materials such as molybdenum disulfide and black phosphorus, also known as phosphorene.

Traditional Raman spectroscopy measures and identifies chemical composition and molecular structures using high frequencies. Low-frequency Raman is more advanced and costly, but it is also more powerful and can be used to measure the number of monolayers in a material and gauge the strength of the coupling between layers.

“Besides their unique facilities, ORNL is also staffed by experts in the field who can assist us with our research,” Huang said. “There are people who are really good at maintaining and operating these machines and can make them do what you want and more. They can work unique functions into the spectrometers, which is also an important capability.”

Huang is currently studying gallium telluride, which exhibits superior photoresponsitivity and may be the best known photodetecting 2-D material in existence. She plans on returning to ORNL to study the material’s photoresponse capabilities with the lab’s ultrafast optical spectrometers.

“We want to study the optic dynamics of these materials to help solve some mysteries as to why they have such high photoresponsivity and fast photoresponse times,” she said.

The science of 2-D material physics is largely unexplored and constantly evolving. The continuing partnership between Dresselhaus’s group and ORNL will push the boundaries of the field by combining state-of-the-art facilities, technological innovation, and the seasoned expertise of researchers from both parties.

“Oak Ridge probably has the best facilities in the U.S. for what we do. It is really good that they are open to users, especially in academia, to use their facilities and set up collaborations,” she said. “People at MIT are very interested in exploring new fields, so the collaborations between the two institutions can be quite useful.”

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