Mechanical Properties of Single-Layer MoS2 Nanoribbons Explored with New Measurement Method

Scientists from Japan and China have conducted a study on the mechanical properties of single-layer molybdenum disulfide (MoS2) nanoribbons with armchair edges. The team used in situ transmission electron microscopy to investigate the nanoribbons’ Young’s modulus as a function of their width.

The researchers found that the Young’s modulus of the nanoribbons varied inversely with their width, with a higher bond stiffness observed for the armchair edges. Their findings, published in the journal Advanced Science, contribute to a better understanding of the nanoribbons’ mechanical response, which is crucial for their application in electronic devices, sensors, and catalysts.

Traditionally, quartz crystals have been used as mechanical resonators in sensor technology. However, there is growing interest in advanced nanomaterials like single-layer MoS2 nanoribbons for their potential as thin resonators. Understanding the physical and chemical properties of nanoribbon edges is key to their practical implementation in these devices.

To measure the mechanical properties of the nanoribbons, the researchers developed a novel micromechanical measurement method that incorporated a quartz-based length extension resonator (LER) in an in situ transmission electron microscopy (TEM) holder. This method allowed for high-precision measurements by estimating the equivalent spring constant of the nanoribbons based on changes in the LER’s resonance frequency.

By peeling off the outermost layer of an MoS2 multilayer using a tungsten tip, the researchers obtained a single-layer MoS2 nanoribbon with an armchair edge structure. They determined the width and length of the nanoribbon from TEM images and used the frequency shift of the LER to calculate the Young’s modulus.

The study revealed that the Young’s modulus of the nanoribbons varied depending on their width. For wider ribbons, the modulus remained constant, while for narrower ribbons below 3nm in width, it increased as the width decreased. The researchers attributed this to a higher bond stiffness at the edges compared to the interior.

Density functional theory calculations supported their observations, indicating that the armchair edge structure of the nanoribbons resulted in increased edge strength due to buckling of the Mo atoms and electron transfer to the S atoms.

Understanding the mechanical properties of MoS2 nanoribbons has important implications for the design of nanoscale, ultra-thin mechanical resonators. These findings could pave the way for the development of nanosensors integrated into everyday devices, such as smartphones and watches, enabling real-time monitoring of the environment and providing numerical values for the sense of taste and smell.

Source: Chunmeng Liu et al, Stiffer Bonding of Armchair Edge in Single‐Layer Molybdenum Disulfide Nanoribbons, Advanced Science (2023). DOI: 10.1002/advs.202303477