A team of researchers has developed a novel technique that enabled them to listen to the avalanches of atoms in crystals at the nanoscale level. This discovery can provide new insight regarding the behavior of materials under stress and give a better understanding of the development of new materials.
What are Nanoscale Avalanches?
When a crystal is subject to stress, the atoms within it rearrange themselves in a process called plastic deformation. This leads to the formation of nanoscale avalanches where groups of atoms move together synchronously.
The motion of atoms during deformation leads to sound emission in the form of a crackling noise. This noise is a scale-invariant event observed in different materials as a response to external stimuli such as force or external fields. A similar principle applies to many other systems, such as crumpling paper and the deformation of porous materials.
The jerky movements of materials in the form of avalanches can extend to many orders of magnitude in size and observe universal scaling rules described by power laws. This concept was originally described as Barkhausen noise in magnetic materials. Today, it is used in a wide range of applications, from earthquake research, monitoring of building materials, and basic research involving phase transformations and neural networks.
Listening to Nanoscale Earthquakes
It is believed that the nanoscale avalanches can have a crucial impact on the mechanical properties of a material, but these properties are difficult to study. Researchers at the University of New South Wales and the University of Cambridge developed a method based on scanning probe microscopy (SPM) nanoindentation to measure nanoscale crackling noise. Indentation refers to producing crackling noise in materials in addition to compression and bending.
In structures such as domain walls in ferroelectrics, atom avalanches differ when the material deforms. According to lead author Dr. Cam Phu Nguyen, their new method allows them to study the crackling noise of individual features of materials at nanoscale levels. One of the unique aspects of this method is that individual nanoscale features can be determined by imaging the material surface before it is indented. Such differentiation allows the conduct of new studies that were previously thought to be impossible.
In the first application of the novel technology, the UNSW researchers used the method to investigate the disruptions in domain walls. These ordered materials are highly attractive due to their potential as building blocks for post-Moore's law electronics. In this study, the researchers showed the alterations of critical exponents for avalanches at the nanoscale features. It leads to a suppression of mixed-criticality otherwise present in domains.
The validity of the measurement concept used by the scientists was tested by comparing it with those of viscoelastic materials that creep, such as polymer materials, which deform continually as long as the stress is present. The study results suggest that the jerks are only observed when the indentation time is long enough to distinguish between the individual jerks.
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