Periodic Reporting for period 2 - LACRYMOSA (Designing Multifunctional Self-Limiting Assembled Nanocrystal Superstructures and Monitoring their Self-Assembly at High Spatiotemporal Resolution)
Période du rapport: 2019-10-01 au 2020-09-30
The project LACRYMOSA investigates the self-assembly of colloidal nanocrystals in order to obtain multifunctional assemblies of original geometries in aqueous solution. One of the big challenges in the field of nanomaterial self-assembly is the design of nanostructures of increasing complexity. Among the class of material candidates, colloidal nanocrystals (NCs) are receiving increasing attention because of their potential for many applications ranging from optoelectronics to energy storage and drug delivery. The design of hierarchical assemblies through a self-limited self-assembly, that involves inorganic particles assembling in highly ordered terminal structures, is still challenging but offers many perspectives for templating multifunctional structures of desired shape and size. In this project, the objectives are to design colloidal systems in which chiral micron-sized particles can be chemically synthesized from small nanoparticles by self-assembly. While linear optical properties of similar particles are being a current topic of interest, this project look into the nonlinear optical properties of such particles. Such nonlinear chiroptical colloids could offer perspectives for multimodal two-photon imaging, in situ single-particle motion tracking and target-specific real-time monitoring with efficient background noise suppression.
During the first period of the project, the fellow carried out chemical synthesis of nanoparticles and assemblies of nanoparticles from different material composition, but the helical structures made up of semiconductor quantum dots which were already designed in the group (results also published in 2017, few months before the start date of the project) were found to be promising because of their nonlinear optical properties. More specifically, it was found that these helices exhibit second-harmonic generation (SHG), a feature of nonlinear optics. This result raised many more interesting questions about the origin of this SHG. It was found that this direction was promising and worth deeper investigation. In this aspect, measurements were done using microscopes within the facilities of the University of Michigan. A two-photon microscope located within the Microscopy Center was extensively used. The fellow spent his last 7 months at the University to collect microscopic images, optimize sample and imaging conditions and calibrate the apparatus for power measurements. Quantitative measurements were also obtained from power measurements. However, it was found that spectroscopic measurements were needed to supplement the data. In this context, a collaboration started with the group of Prof. Valev in the University of Bath (U.K). Prof. Valev is a specialist in nonlinear optics and focused on nonlinear chiroptical activity over the past 10 years. His group developed a setup that would allow spectroscopic data combined with microscopic data as well. At the end of the first period at the University of Michigan, the fellow sent samples to collaborators in U.K (University of Bath, group of Prof. Valev).
At the Utrecht University, the fellow is focusing on the stabilization of such colloids for investigation of their second-order nonlinear scattering effects in solution. Such new samples to the group Prof. Valev will be sent again to obtain supplementary results.
The system studied could have potential in the fields of optoelectronics and telecommunications because of its optical properties and could interest industries in this field. However, the first interest is more fundamental as it is not well-known yet which aspect is really contributing to the nonlinear optical activity: What are the contribution of the chirality and the electronic material properties? What are the contribution of the bulk material and the material/environment interface? Besides, this studied system differs from previous systems reported in the same research field: it can be dispersed in solution, making potential use in more diverse fields of chemistry (electrochemistry, photochemistry, colloidal chemistry, …)
The system studied could have potential in the fields of optoelectronics and telecommunications because of its optical properties and could interest industries in this field. However, the first interest is more fundamental as it is not well-known yet which aspect is really contributing to the nonlinear optical activity: What are the contribution of the chirality and the electronic material properties? What are the contribution of the bulk material and the material/environment interface? Besides, this studied system differs from previous systems reported in the same research field: it can be dispersed in solution, making potential use in more diverse fields of chemistry (electrochemistry, photochemistry, colloidal chemistry, …)