Picosecond Ultrasonics for Nanoscale Subsurface Structural Characterization
Seeing through metal with sound: new laser technique reveals hidden nanostructures
Physicist Maksym Illienko developed a new technique that can reveal hidden nanostructures using sound waves and ultrafast lasers. The method makes it possible to detect extremely small structures under opaque materials - even when they remain invisible with ordinary microscopes.
The research focuses on so-called picosecond ultrasound, a form of hypersound in which extremely high-frequency sound waves are generated by ultrafast lasers. Whereas light is often blocked by materials such as metal, sound waves can travel through them. That principle forms the basis of the new imaging technique.
Illienko succeeded in detecting and characterizing nanostructures under layers of metal. These structures are smaller than a hundredth of the thickness of a human hair and so small that conventional light cannot distinguish them. According to him, this opens up new possibilities for investigating objects that until now have remained hidden from existing measurement methods.
In addition to the practical demonstration, Illienko also investigated exactly how hypersound is generated and measured with ultrafast lasers. That process proved complex, but a better understanding of it could lead to faster and more accurate measurements at the nanoscale.
The results are of interest to the semiconductor industry. Manufacturers of chips for smartphones, computers and other electronic devices must constantly verify that the internal structures of chips are built correctly during the manufacturing process. As chips become smaller and more complex, so does the need for techniques that can look below the surface without damaging the material.
Traditional optical inspection methods run into limits in this regard because light has difficulty penetrating opaque materials. Instead, the new method uses sound waves, which can penetrate deeper. As a result, the technology could help inspect the next generation of semiconductors and electronic components in the future.
According to Illienko, the technology ultimately offers the prospect of more efficient quality control, more reliable chips and further miniaturization of electronics.
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