One of the applications of cathodoluminescence is studying optical nanoantennas. But what are they exactly? These devices, made usually from noble metals (gold or silver, for example) or from semiconductor materials, are capable of amplifying and manipulating light on the nanoscale.
Dr. Ruggero Verre is one the Delmic’s oldest customers: he is a post-doctoral researcher in the Department of Applied Physics at the Chalmers University of Technology in Gothenburg, Sweden. Optical nanoantennas is the focus of his research group, headed by Prof. Mikael Käll.
One way to study the properties of the antennas and understand how they work is by characterizing them with cathodoluminescence. The group of Ruggero Verre has been using the SPARC cathodoluminescence detector to study them, and they have achieved some interesting results.
At the end of May Dr. Ruggero Verre came to Amsterdam to be a speaker during the cathodoluminescence workshop in AMOLF. He talked with Delmic to share his thoughts about the system and about the work his group has been doing.
Delmic: Why did your group acquire the SPARC system?
Ruggero: We saw the portfolio of the capabilities and possibilities the SPARC was offering, together with the ease of use and flexibility it offered. A particular interesting aspect was that it provided codes for analysis of angle-resolved measurements.
D: For how long have you been using it?
R: We have installed the system in May 2015 and it has been up and running for more than 3 years.
D: For what purposes have you and your group been using the system?
R: Optical microscopy technique cannot resolve the optical antenna´s behavior at the nanoscale due to diffraction principle. However, this is the most valuable information of these kind of object. We hence needed a tool able to experimentally measure where and how light is concentrated and focused and cathodoluminescence was the perfect tool for us.
D: Could you tell me a bit more about the research that you have been doing?
R: We are working with optical nanoantennas, i.e. objects that are able to focus light in extremely small volumes. This capability gives unprecedented control over light-matter interaction, which can be used for many different applications. In our group, we focus on understanding the physical properties of nanostructured materials made either with noble metals or with semiconductor materials. The final aim in our group is to use these structures mainly for biological and sensing applications. The possibility to focus in small volumes allows one to achieve light confinement into volumes which are comparable to many nanoscopic object of interest in biology such as viruses and protein, rendering nanoatennas a perfect toolkit for these studies.
D: Did you manage to get some valuable insight and results?
R: Yes. For example, an important aspect of many molecule is its chirality, which is essential in many biological processes. DNA is an example of a chiral molecule. The possibility of coupling Au antennas with chiral molecules has been discussed largely by scientists, however nobody had previously measured the chiral response with nanometer resolution. We were the first group doing this by inserting optical polarization elements before reaching our detector.
D: Finally, what are the main advantages of the SPARC system?
R: We like the possibility and flexibility of the system, with the possibility of adding optical elements to analyze the response. Other advantages are: 1) the fact that DELMIC is still a small company, trying to develop ad hoc solutions for different needs. 2) Ease of alignment for reproducible and stable signals 3) The fact that DELMIC tries to push the capabilities of CL by developing new methods (angle-resolved imaging, space momentum mapping, time-resolved measurements).