Researchers find new way to manipulate properties of ultrathin semiconductors

Simple ‘holey’ substrates used to control electronic properties of 2D materials

MINNEAPOLIS / ST. PAUL (12/09/2021) – A team of University of Minnesota Twin Cities researchers has discovered a new way to easily manipulate and control the properties of two-dimensional sheets of an important class of semiconducting materials that could be used to design next-generation electronic devices.

Using a simple “holey” base, called a substrate, the team was able to create periodic structural patterns in ultrathin crystals of molybdenum disulfide (MoS2), a promising material for advanced electronics applications. They found that crystals only a few atoms thick adhered strongly to the substrate and precisely matched its three-dimensional shape. They also found that the crystals were significantly stretched over the holes, much like a drumhead.

This discovery is particularly exciting, because the electronic and optical properties of materials can be tuned and controlled by deforming the structure. Most importantly, the team’s method does not require a continuous supply of energy to sustain the patterns, and the fabrication method does not require any additional materials to control the shapes.

The team, comprised of researchers from the University of Minnesota Department of Chemical Engineering and Materials Science (CEMS), Department of Aerospace Engineering and Mechanics, and the University’s Characterization Facility, detailed their findings in a paper published in the journal ACS Nano, a publication of the American Chemical Society.

Ultrathin MoS2 is structurally similar to graphene—the strongest, thinnest material known to exist—and it is being intensely studied for applications in a wide range of next-generation electronic devices. Its ultrasmall dimensions are especially attractive for incorporation into key components whose size approaches that of individual atoms.

“As you stretch and shear MoS2, the internal electronic structure starts to change,” explained Yichao Zhang, co-lead author on the paper and recent Ph.D. graduate from the University of Minnesota’s materials science program who also is a recipient of the Louise T. Dosdall Fellowship. “This diverse material can be used in a variety of devices, from the monitoring of human vital signs to the manipulation of light. We use electronic devices to vastly improve many aspects of the human enterprise, so coming up with new and clever ways to further advance this structure-function relationship is critically important.”

The team combined a number of tools and methods to create and characterize the patterns, including transmission electron microscopes, atomic force microscopes, and atomistic simulations.

“The patterns Yichao observed under the transmission electron microscope are very striking,” said David Flannigan, the principal investigator and University of Minnesota L.E. Scriven Associate Professor of Chemical Engineering and Materials Science. “By leveraging the incredible facilities and expertise we have on campus, we were able to determine all of the vital aspects of the structures in great detail. The simplicity of the method and the robust nature of the interactions of the flakes with the substrates is remarkable.”

Flannigan is the founder and principal investigator of the Ultrafast Electron Microscopy Lab at the University of Minnesota, a one-of-kind facility devoted to studying chemicals and materials on ultrasmall and ultrafast scales.

In addition to Zhang and Flannigan, other members of the research team include Professor Ellad Tadmor and graduate student and co-lead author Moon-Ki Choi, both from the University of Minnesota Department of Aerospace Engineering and Mechanics; and Greg Haugstad, a principal researcher and the technical director at the University of Minnesota’s Characterization Facility.

This research was supported primarily by the National Science Foundation (NSF) through the University of Minnesota Materials Research Science and Engineering Center (MRSEC).

Read the full research article titled “Holey Substrate-Directed Strain Patterning in Bilayer MoS2” on the ACS Nano website.