Earlier attempts at testing 1D nanomaterials have encountered drawbacks such as uncontrollable sample/loading geometry and limited material selectivity. Researchers at Rice University, US, have been trying to establish a universal tensile testing platform for studying different 1D nanomaterials. Their solution, dubbed MMD, was aligned and actuated by a quantitative nanoindenter inside a scanning electron microscope, and can be used to measure the tensile strength of carbon nanotubes, gold and nickel nanowires with different diameters.

In recent work published in the journal Nanotechnology, the team has taken the idea one step further and placed the MMD inside a TEM. The MMD has a footprint of just 2.5 mm × 1.2 mm, which allows it to be inserted into a TEM chamber for in situ mechanical testing. TEM is capable of revealing the internal crystalline (and even atomic) structures of test samples during and after deformation.

The MMD is actuated by a quantitative TEM-nanoindenter (Nanofactory Instruments AB). The unique "push-to-pull" mechanism transforms the indentation loading into uni-axial tensile loading of the specimen, which is pre-clamped on the device. This purely mechanical actuation eliminates the need for complicated electro-mechanical or thermo-mechanical coupling and provides a larger load and displacement capability for a wider range of samples.

Real-time window

The simple design both minimizes the number of error sources and reduces the cost of the device fabrication. Most importantly, the back-side window design allows proper electron beam alignment and transparency for real-time TEM imaging.

Using the device, the team examined the mechanical behaviour of a nickel nanowire, which fractured at an engineering stress of ~1.2 GPa. More interestingly, the dramatic contrast changes within the strained nanowire imaged under bright-field TEM imaging conditions suggested possible local atomic distortions (for example, a dislocation network). The high magnification TEM images of the fracture surfaces verified the brittle fracture mechanism. And in addition, select area diffraction (SAD) analysis – a unique and important capability of TEM – could offer particularly useful insight into the evolution of the crystalline structure.

This preliminary work demonstrates the set-up's strength and potential and the group is now busy exploring the behaviour of a wide variety of one-dimensional nanomaterials.

More information can be found in the journal Nanotechnology.