Identifying and Controlling Defects in 2D Metal Dichalcogenides

Semiconducting two-dimensional transition metal dichalcogenides (TMDs) such as MoS₂, MoSe₂, WSe₂, and WS₂ hold great promise for many novel applications, and recent years have witnessed tremendous efforts to manufacture these 2D crystals on a large scale. A long-standing puzzle in the field is the effect of various types of defects on TMDs' electronic, magnetic, catalytic, and optical properties.

Mauricio Terrones presents an overview of TMD defects, defining dimensionalities and various atomic structures of defects, and how these defects could be imaged with novel optical-driven techniques. The presentation covers doping and alloying in monolayers of MoS₂, WS₂, and WSe₂ and describes their implications in magnetism, as well as in electronic transport. He also describes the catalytic effects of edges, vacancies, and local strain observed in Mo_xW₁-_xS₂ monolayers by correlating the hydrogen evolution reaction (HER) with aberration-corrected scanning transmission electron microscopy (AC-HRSTEM).

Findings demonstrate that chalcogenide layers can now be used for the fabrication of more effective catalytic substrates; however, defect control is required to tailor their performance. By studying photoluminescence spectra, atomic structure imaging, and band structure calculations, Terrones and colleagues also demonstrate that the most dominating synthetic defect — sulfur monovacancies in TMDs — is responsible for a new low-temperature excitonic transition peak in photoluminescence 300 meV away from the neutral exciton emission. They further show that these neutral excitons bind to sulfur monovacancies at low temperature, and that the recombination of bound excitons provides a unique spectroscopic signature of sulfur monovacancies. However, at room temperature, this unique spectroscopic signature completely disappears due to thermal dissociation of bound excitons. Also shown are one-dimensional heterointerfaces in TMDs via AC-HRSTEM in conjunction with their nonlinear optical emission, constituting a new way to image 1D defects. Finally, Terrones discusses the electronic effects of C-H defects within TMDs, as p-type doping could be controlled by the presence of C within TMDs.

***This presentation premiered during the 2021 Photonics Spectra Conference Spectroscopy track. For information on upcoming Photonics Media events, see our event calendar here.

About the presenter
Mauricio Terrones, Ph.D., is a tenured professor of physics, chemistry, and materials science and engineering at Penn State. He is also the founder and director of the Center for Two Dimensional and Layered Materials (at Penn State) and the NSF-IUCRC Center for Atomically Thin Multifunctional Coatings (ATOMIC). He has co-authored more than 400 journal articles, and counts more than 28,000 citations to his work (His h-index is 83; Google Scholar h = 91). Terrones has published in Nature, Science, Physical Review Letters, Nano Letters, Nature Nanotechnology, Nature Materials, Nature Communications, Nature Chemistry, ACS Nano, and PNAS, to name a few. He was awarded the Faculty Scholar Medal in Physical Sciences (Penn State) in 2016. Terrones is also associate editor of the following journals: Carbon; 2D Materials; Journal of Materials Research; and Nature Scientific Reports.