Shape restoration effect in Ag−SiO2 core−shell nanowires.

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“Nanotechnologies have long become part of our day-to-day life. From mobile phones and computers to cosmetics and foods, we are surrounded by objects that benefit from or are based on ‘nano’ effects, and many more are round the corner. However, few people know the magic behind nanotechnology, which goes far beyond merely making things smaller. The “miracle” of nanotechnology, and the reason why it is of enormous scientific and technological interest, can be explained by the fact that the properties and behaviour of materials at the nanoscale can be very different from those at the micro- and macro-scale. The properties include melting point, electrical and thermal conductivity, mechanical strength and many other essential characteristics of materials. These differences are exploited in many unique applications of nanotechnology.

To get the most out of nanomaterials, it is essential to study individual nanostructures and measure their properties and behaviour. However, measuring on such a small scale is tricky and requires extremely fine and sensitive tools. Researchers at Institute Solid State Physics, University of Latvia in collaboration with colleagues from Institute of Physics, University of Tartu (IPUT) developed fine measurements technique for mechanical testing of nanostructures inside a scanning electron microscope. Experiments consist of controllable manipulation (dragging, pushing, bending etc) of nanostructure with simultaneous force registration. Number of different nanostructures were investigated and lot of useful data was extracted. However, most intriguing phenomena was discovered recently when they demonstrated, that combination of two different materials in a single core-shell heterostructure can lead to significantly enhanced and even completely novel properties. Nanomanipulation team studied mechanical properties of Ag/SiO₂ core-shell nanowires, which are several hundred times thinner than human hair (figure 1), and found that such material can withstand severe deformations (can be bent into the loop) without fracture in contrast to uncoated silver nanowires. Moreover, they discovered, that plastically deformed Ag/SiO₂ nanowires can restore their initial straight profile when irradiated with electron beam (figure 2, 3). The reasons behind such shape memory effect are completely different from those that are responsible for the shape restoration in well-known shape-memory alloys.

 

Discovered phenomena is interesting not only from fundamental point of view, but can be very useful in practical applications. For example, it is known, than silver nanowires can trap and guide light in desired direction without losses. Whereas wavelength of confined light can be bigger than diameter of the nanowire, which is impossible in the frameworks of classical physics. A significant degree of bending is often required in waveguide applications. Any cracks introduced by bending will prevent lossless propagation of light inside the nanowire. Therefore, improvement of mechanical properties achieved via composite core-shell nanostructure is essential for performance and reliability of nanowaveguids. Moreover, ability to restore its profile in a controlled manner opens new opportunities in construction and functioning of nanoscale devices such as nanoswithces, nanoresonators etc. Potential applications can include also nanosensor of beta radiation (fast electrons).

Results of the study are published in Nano Letters – one of the most cited and reputable journal in the field of nanotechnology. [1]”
ACS Publications. Shape restoration effect in Ag−SiO2 core−shell nanowires.