Congratulations to New ICFO PhD Graduate

We congratulate Dr Monserrat Alvarez Ortiz who defended her thesis today in ICFO’s auditorium.

Dr Alvarez Ortiz obtained her MSc in Physics from the Universidad Nacional Autónoma de México. She joined the Molecular Nanophotonics research group at ICFO led by ICREA Prof Dr Niek van Hulst as a PhD student. Dr Alvarez Ortiz thesis entitled ‘Controlling the strong interaction between quantum emitters and plasmonic rod-dimers’ was supervised by ICREA Prof Dr Niek van Hulst and Dr Pawel Wozniak.

ABSTRACT:

The growth of technology and climate change have increased the need for more efficient, biodegradable and ecologically sustainable electronic devices. With this in mind, different methods have emerged to improve the performance of organic materials. In particular, the union of plasmonic nanostructures with quantum emitters marked a new line of device research. The interaction between plasmons and quantum emitters led to the modification of the chemical properties of quantum emitters, which helped improve the absorption and emission capabilities of molecules. However, despite the efforts employed, reliable platforms to study the interaction between plasmons and molecules reproducibly have not yet been developed. This thesis aims to increase the interaction strength between plasmonic structures and organic molecules in a reproducible fashion by varying the optical properties of metallic structures. A  fluorescent dye and a protein belonging to a photosynthetic bacterium were chosen as the systems to study. Consequently, the properties of the structures were tailored to obtain the desired optical response that matched the molecules/protein of interest. Mainly, the plasmonic structures' material, shape and size served to modify the resonance frequency and intensity of the near-field of the plasmon. In particular, this thesis investigated the plasmon interaction volume's effect on achieving and increasing the coupling strength. Fabrication of antennas by lithography, thermal evaporation, and helium ion milling allowed these properties to be modified. Nanorod dimer fabrication decreased the modal volume to less than 10 nm resolution. Characterising the structures was very important since the fine-tuning of the dimers led to different results. Here, darkfield confocal microscopy was used to analyse the plasmonic dimers' spectral response. In addition, finite difference time domain (FDTD) simulations provided information on the near-field strength in the dimer feeding space. Later, the molecules to the nanoantennas extended the study to coupled systems. Some systems showed a strong interaction between the dimers and the molecules/protein, which was identified by the mode splitting of the scattering spectra, the dispersion relation, and a comparison between coupling strength and individual system losses.

Thesis Committee:

Prof Dr María García-Parajo, ICFO

Dr Katja Hoeflich, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

Dr Mathieu Mivelle, Institut des NanoSciences de Paris