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Making nanostructures

Find out how photonic nanostructures are produced in the lab in this short video.
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This short video will tell you how we make high precision photonic nanostructures. We use a simple grating as an example. We use a process called Electron Beam Lithography, which is a very high precision patterning process. Here you can see Christina mounting the sample on the special holder. This holder is then placed inside the electron beam system and automatically loaded. Because electron beam lithography requires a very high vacuum, you have an antechamber, so that the main machine always stays under good vacuum. Once the sample is loaded, the exposure process can begin. First, you align the beam, which you do by imaging a test pattern, and check a few imaging parameters. Then you expose the pattern.
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This would usually take a couple of hours.
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Once the exposure has finished, you unload the stage and take the sample out.
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Now Alex is going to do the next step, development, whereby you use chemicals to develop the sample similar to a photographic process. You notice that this is done in the clean room and people wear protective clothing. This is mainly to protect the sample from the people, not the other way around. The developer dissolves the part of the resist that has been exposed by the electron beam and leaves the rest untouched. We use a basket to move the sample around in the chemicals and take great care to avoid damage. After the development, the sample is then placed inside a plasma etcher that removes the Silicon or Silicon nitride, where it’s not protected by the resist.
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This is the sample being loaded to the plasma etcher. Here, you can see the plasma glowing in purple. Now Alex removes the sample from the etching machine, and then you can see the finished sample and admire the rainbow colour, thanks to the diffraction The next step is for Donato to inspect the sample in the electron microscope. The sample is again mounted on the special holder and inserted into the machine via an antechamber. Now Donato is zooming in – there you can see the nanostructures. He is able to measure whether the sample has been made according to the specification, before it goes to the biosensor laboratory.

Once a photonic nanostructure has been designed, we need to manufacture it. The process, for the example of a diffraction grating discussed in the previous article, is shown in the video above.

We first use electron-beam lithography to remove unwanted material. As we have seen in the context of electron microscopy, beams of electrons can be focused into tiny spots of nanometre size. We use such focused electron beams to define our structures. The beam of electrons is scanned across the image to expose the pattern sequentially. The sample is coated in a resist that is sensitive to electron exposure and therefore only the desired areas are removed to reveal the design.

The specific function we aim to achieve with these nanostructures requires careful control of their dimensions. For example, some of our gratings operate at a scale of half the wavelength of the light we are intending to use. For visible and near-infrared light of a wavelength less than 1µm, this means that the grating period may be 500 nm or smaller, and the slits may be as small as 100 nm.

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Frontier Physics, Future Technologies

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