Slip avalanches are ubiquitous phenomena occurring in three-dimensional materials under shear strain, and their study has contributed immensely to our understanding of plastic deformation, fragmentation, and earthquakes. Now new research by Blusson QMI scientists published in Nano Letters reports on a world-first observation of shear strain induced avalanches at the atomic scale in two-dimensional (2D) materials.
Shear strain is a type of deformation in materials that occurs when an applied force causes the material’s layers to slide past each other in a parallel manner. In avalanches, shear strain occurs when different layers or sections of snow slide past each other, leading to the rupture or failure of the snowpack. In earthquakes, it refers to the deformation caused by the shearing or sliding motion of rocks along a fault plane.
“In recent years, 2D materials have provided a unique platform for studying new science and technology at the atomic level, but we don’t know much about the effects of shear strain in these materials,” said Blusson QMI Investigator and Assistant Professor in UBC’s Department of Physics and Astronomy Dr. Ziliang Ye.
“In this study, we find that the stacking order in 2D materials can be changed due to the shear strain during the mechanical exfoliation stage. The stacking order determines many important properties of 2D materials, and therefore, it’s significant for us to know what can affect it and how we can control it,” said Dr. Ye.
Mechanical exfoliation is a method used for producing 2D materials where researchers use adhesive tape to chip away a sample from the bulk of the crystal.
Postdoctoral Fellow and the study’s first author Dr. Jing Liang said the emergence of 2D materials from van der Waals (vdW) crystals has turbo-charged atomic-level investigations in various scientific and technological domains.
“These materials exhibit weaker interlayer bonding forces, making them a great platform for studying the effects of in-plane shear strain in two dimensions,” said Dr. Liang.
“Our study focuses on exfoliated rhombohedral MoS2 as this lab-grown material allows us to differentiate between various stacking configurations through interfacial polarization in 3R-MoS2. On the other hand, mechanical exfoliation involves shear strain, making it a promising process to explore the interplay of shear strain and slip avalanches.”
By utilizing advanced surface potential sensitive characterization techniques such as electrical force microscopy (EFM) and Kelvin probe force microscopy (KPFM), the team was able to visualize polarization domains and directly observe a highly abnormal distribution of polarization domain sizes in 3R-MoS2.
“This distribution, following a power-law pattern, indicates the occurrence of interlayer slip avalanches triggered by shear strain near the threshold during the mechanical exfoliation process,” Dr. Liang said.
Dr. Ye said that in the future, the findings could lead to the development of devices that use strain to control the stacking order in 2D materials, which can be read out electrically or optically. This may enable the discovery of new physics or new memory functions for computing.
“This discovery came as a surprise in the lab and the discussion with Prof. Joerg Rottler helped us tremendously to figure out the underlying physics. The phenomenon observed here in 2D Materials is similar to many other naturally occurring phenomena, such as avalanches and earthquakes,” Dr. Ye said. “Such universality is always fascinating to discover for us scientists.”
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