Nanostructures can increase the sensitivity of optical sensors enormously - provided that the geometry meets certain conditions and matches the wavelength of the incident light. This is because the electromagnetic field of light can be greatly amplified or reduced by the local nanostructure.
The HZB Young Investigator Group "Nano-SIPPE" headed by Prof. Christiane Becker is working to develop these kinds of nanostructures. Computer simulations are an important tool for this. Dr. Carlo Barth from the Nano-SIPPE team has now identified the most important patterns of field distribution in a nanostructure using machine learning, and has thereby explained the experimental findings very well for the first time (Communication Physics, ("Machine learning classification for field distributions of photonic modes").
The computer simulation shows how the electromagnetic field is distributed in the silicon layer with hole pattern after excitation with a laser. Here, stripes with local field maxima are formed, so that quantum dots shine particularly strongly.
Image: Carlo Barth/HZB
This makes it possible to empirically demonstrate how the laser light interacts with the nanostructure.
"The computer has searched through the approximately 45,000 data records and grouped them into about ten different patterns", he explains.
Finally, Barth and Becker succeeded in identifying three basic patterns among them in which the fields are amplified in various specific areas of the nanoholes.
With the correct geometry and the right excitation by light, the maximum electric field amplification can be generated exactly at the attachment sites of the desired molecules. This would increase the sensitivity of optical sensors for cancer markers to the level of individual molecules, for example.
Helmholtz-Zentrum Berlin für Materialien und Energie. Posted: Sep 28, 2018.