In the two-dimensional (2D) crystal under test, the local indentation of the AFM tip can result in extremely inhomogeneous stress and strain fields, making it challenging to derive intrinsic mechanical characteristics from experimental observations. Furthermore, nanoindentation experiments do not allow for the visualization of dynamic fracture processes. Alfa Chemistry has devised and developed a number of micro/nanomechanical test equipment that can provide homogeneous in-plane loading on 2D crystal films.
We provide a professional service for 2D material tensile testing to our customers. SEM and TEM may be used to perform in-situ tensile testing, which helps to see the fracture process and evaluate the fracture behavior of 2D crystals. Please get in touch with us as soon as possible so we can help you with your 2D material testing.
Tensile Testing Equipment and Technology
Micromechanical Devices Category
| Thermally driven micromechanical devices | There are two types of actuators in the device: thermal and electrostatic actuators. The thermally driven microelectromechanical systems (MEMS) platform facilitates in-situ SEM and TEM tensile testing. Thermally driven micromechanical devices allow stronger materials like thin films and nanowires with greater dimensions to be tested. Flexible structures, such as carbon nanotubes and nanowires with lower diameters, are well suited to electrostatic actuators. |
| Micromechanical devices with push-pull mechanisms | Tensile testing and pulling tests are possible with this instrument. The microdevice is made up of three moving shuttles connected by slanted independent beams and operates on a spring-like "push-pull" mechanism. Mechanical testing on graphene and other 2D crystals are now possible because of advancements in microdevices. |
Fig 1. Thermal-actuated micromechanical devices. (Karrar K, et al. 2020)
"Dry-Transfer" Technique
The transfer of atomic films to the sample stage is an important step in the mechanical testing of 2D materials. We adopt a novel graphene "dry transfer" approach to solve the problem that liquids are not favorable to the suspension of Si working layers on the stage.
The graphene is generated and then coated with polymethylmethacrylate (PMMA) before being connected to a polydimethylsiloxane (PDMS) block. The heat treatment permits the PMMA/graphene film to cling smoothly and firmly to the device's suspended Si layer, preventing the graphene film from folding. With the tip of tweezers, the graphene/PMMA film was gently sliced along the open window profile of the PDMS block, then the sample stage and the transparent graphene/PMMA film were clamped. After calcination in the air to decompose PMMA, suspended films of graphene were obtained over the entire device.
Fig 2. Dry transfer of 2D crystals. (a-f) Sequential steps of dry transfer. (g) Schematic illustration of MoSe2 transfer. (Karrar K, et al. 2020)
The "dry transfer" approach described above is appropriate for thin-film samples but not for discontinuous crystals. Individual crystals are transferred using another excellent "dry transfer" approach.
The 2D crystals and the substrate are spin-coated with a layer of PMMA and heated to guarantee that the crystals and the PMMA are bonded together. To remove the copper, the substrate was etched with NaOH solution, FeCl3, and Si/SiO2. To remove the floating film from the etchant, use a copper TEM grid. Under an optical microscope, the required portion of the PMMA-coated 2D crystal is sliced with a probe, and the 2D material is carefully put into the test section of the micromechanical device. After that, the PMMA is annealed in a CVD tube furnace.
Suspended monolayer 2D crystals may be easily created using an excellent "dry transfer" process. Furthermore, the different crystals may be stacked in a regulated arrangement.
Tensile Testing Capabilities for 2D Materials
| Graphene Mechanical Testing | We perform in situ quantitative tensile testing of freestanding CVD-grown monolayer graphene using a micromechanical device in a scanning electron microscope. |
| Steel-Reinforced Graphene Mechanical Testing | We free-suspended reinforced graphene on a micromechanical device. Tensile tests were performed within the SEM. |
| MoSe2 Mechanical Testing | We transferred monolayers of MoSe2 to the micromechanical device to quantify its fracture strength and elastic modulus and to study the effect of defects on the mechanical properties of MoSe2. All tests were performed in SEM by real-time observation. |
| Titanium Carbide MXenes Mechanical Testing | We investigated the in-plane mechanical behavior of stacks formed by titanium carbide MXenes (Ti2CTx, Ti3C2Tx ) using in situ SEM nanoindentation and push-press microscale uniaxial tensile experiments |
Reference
- 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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