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NanoSculptors carve atom by atom

Sculpting nanotubes

Electron microscopy is a delicate balancing act between using the highest energy electrons possible in order to obtain the best image, while avoiding destruction of the sample under investigation. The trouble is, the electron beam does not just observe, it also interacts with the structure we observe. This can be critical for “fragile” samples such as nanostructures: the transfer of energy from the electron beam can be sufficient that atoms are knocked right out of the material. In the worst cases the sample is destroyed in front of your eyes.

In the current study we turned this problem to our advantage. The idea was to use a STEM [scanning transmission electron microscope] as a carving tool with nanometric precision, with the added advantage that we can image what we are doing at the same time.
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Mapping surface plasmons

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It is well known that a silver fork reflecting light appears grey, or that a gold ring is golden. Stained-glass church windows exhibit various colours, although they are also made up of gold or silver. The colour difference stems from the different morphologies of the metals: continuous films in the first case, nanoparticles in the second. This effect is known since ancient times, and has been theoretically described since a century: when metal particles have dimensions lower than the wavelength of the light illuminating them (typically, a few hundreds of nanometers), the colour of these particles depends on their size and their shape. To illustrate this effect, we can use the analogy of a vibrating piano string. For a given tension on the string, the note produced by the vibrating string depends on its length: the shorter the string is, the more quickly it vibrates and the sharper the sound produced. For nanoparticles under light illumination, a similar effect occurs. If one sends an electromagnetic wave (the light) on a nanoparticle, the latter will be set in "vibration". These vibrations of the electromagnetic field are called "surface plasmons��. Read more »


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