Traditional tensile and bending techniques are challenging to use for investigating the mechanical properties of two-dimensional (2D) materials. This is due to the tiny grain size and unique thickness of 2D materials, which makes applying correct strain shocks to them challenging. Probe microscopy is a useful method for measuring and manipulating low-dimensional materials at the nanoscale. By monitoring the deformation of cantilevers, this approach may be used to analyze the deformation of 2D materials at the sub-nanometer scale.
Nanoindentation on films by transverse loading has recently been used to characterize the mechanical response of 2D materials to external forces. Alfa Chemistry provides specialist nanoindentation testing of 2D materials to aid in the understanding and quantification of their mechanical characteristics. Please contact us as soon as possible so that we can assist you with your 2D material testing!
Nanoindentation Testing Methods
Fabrication of free-suspended 2D materials
We produced free-suspended 2D materials using the following two strategies in order to assess the mechanical characteristics of 2D materials using nanoindentation studies.
- Transferring - The 2D material is transferred to a pre-patterned substrate with a series of holes or trenches.
- Depositing followed by etching - This process involves depositing 2D material onto a smooth substrate and then etching a portion of the substrate beneath the sample.
Fig 1. Schematic illustration of the fabrication of freely suspended 2D material. A, Freely suspended circular drum model. B, Freely suspended doubly-clamped beam model. (Jiang H, et al. 2020)
AFM-Enabled Nanoindentation
AFM nanoindentation is an effective tool for characterizing the mechanical properties of 2D nanostructures. AFM belongs to the scanning probe microscope family, which has a resolution of a fraction of a nanometer. Mechanical probes "feel" or "touch" a sample's surface to get information about it. Individual atoms may also be located using AFM in ambient settings, allowing future nanoscale gadgets to be built. The following are some of the key advantages of employing AFM to collect images:
(i) The capacity to create 2D and 3D pictures using lighting and exact viewing angles.
(ii) The imaged sample's electrical conductivity is not necessary. With complete atomic resolution, both conductive and insulating materials may be scanned.
In-Situ Indentation in SEM
In-situ indentation in SEM has the benefit of allowing exact control of the tip location on the film as well as visualization of fractures throughout the indentation process. To supplement AFM-enabled nanoindentation testing, we employ in-situ indentation in the SEM.
Fig 2. AFM image of the surface of a Faraday plate. (Karrar K, et al. 2020)
Mechanical Testing Capability of 2D Materials
Continuum elasticity theory may be used to describe the mechanical behavior of 2D materials at a macroscale. Our AFM-assisted nanoindentation approach is particularly adapted to measuring the macroscopic mechanical characteristics of 2D materials and has been widely used for graphene, MoS2, h-BN, and other materials.
| Graphene Mechanical Testing | Indentation on single and polycrystalline graphene;
Fabrication and indentation testing of suspended graphene;
Crack paths after nanoindentation;
Indentation and mechanical properties of defective graphene. |
| Graphene Oxide (GO) Mechanical Testing | We have examined the mechanical characteristics of GO and reduced GO (rGO) experimentally and theoretically, such as determining the effective Young's modulus and prestress of monolayer and multilayer GO films using AFM contact mode. |
| MoS2 Mechanical Testing | Since AFM-enabled indentations have been used to characterize the mechanical properties of graphene, GO and rGO, we used the same technique to investigate the mechanical properties of MoS2. |
| WSe2 Mechanical Testing | We performed mechanical tests on films with different layers to obtain their elastic constants. The elastic moduli were 170.3 ± 6.7 GPa, 166.3 ± 6.1 GPa, 167.9 ± 7.2, and 164.8 ± 5.7 GPa for samples with 5, 6, 12, and 14 layers, respectively. These results indicate that Young's modulus of WSe2 is independent of its thickness. |
| h-BN Mechanical Testing | We can measure the elastic constants of multilayer h-BN using AFM nanoindentation. |
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References
- Jiang H, et al. (2020). "Two-Dimensional Materials: From Mechanical Properties to Flexible Mechanical Sensors." Info Mat. 2(6): 1077-1094.
- Karrar K, et al. (2020). "Mechanical Testing of Two-Dimensional Materials: A Brief Review." International Journal of Smart and Nano Materials. 11(3): 207-246.
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