New imaging technique at nanometer scale is based on ultrasound

Existing methods of non-destructive imaging for nanoelectronics, such as optical and

electron microscopy, not accurate enough and notapplicable to deeper structures. A well-known three-dimensional technique at the macro level is ultrasound. Its advantage is that it works for every sample. This makes ultrasound a great way to map 3D structures. Yet ultrasonic technology at the nanoscale has not yet existed. Indeed, the resolution of ultrasound imaging is largely determined by the wavelength of the sound used and is usually around a millimeter. In turn, nanoscale assumes a particle size range of 1 to 100 nm. Moreover, a nanometer is equal to one billionth of a meter, and a millimeter is one thousandth.

Today ultrasound is already integrated intoatomic force microscope (AFM). AFM is a technique that allows surfaces to be scanned and mapped very accurately using a tiny needle. The advantage here is that it is not the wavelength but the size of the AFM tip that determines the resolution. Unfortunately, the frequencies used so far (1-10 MHz) are insufficient. “We do see something, but it's not clear what exactly. Therefore, the frequency of the sound used had to be further increased to the GHz range. That's what we did, ”explains Gerard Verbiest of TU Delft.

Increasing the frequency has only recently become possible.The use of photoacoustics helped. The use of the photoacoustic effect generates extremely short sound pulses. Scientists have succeeded in integrating this technique into AFM. Using the AFM tip, the scientists managed to focus the signal. The installation has already passed preliminary tests.

As mentioned, the new method especiallyinteresting for nanoelectronics. In the future, this will help to make even smaller chips with fine patterns. For example, so that you can place two layers on top of each other with nanometer precision.

There are also potential applications foroutside of electronics. For example, in cell biology to create a detailed three-dimensional image of an individual living cell. This will allow you to see how mitochondria fold in the cell. In materials science, the development will be useful for studying the process of heat transfer in graphene.

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