The goal of our project is to develop new and improve existing methods used for the analysis of the optical properties of nanoparticle aggregates trapped in the electrodynamic traps. Particularly, we aim to develop light spectroscopy of single aggregates, improve static light scattering techniques (including rainbow scattering) and interferometric methods e.g. whispering gallery modes analysis. Additionally we plan to analyze aggregated structures with optical, electron (SEM and TEM) and atomic force microcopies after their deposition (soft-landing). Aggregates of nanoparticles are generated in our experimental setup by means of the self-organization and evaporation-driven aggregation phenomena in evaporating microdroplets of suspensions.
In the framework of this project we aim to build a system to characterize aggregates with light spectroscopy. We want also to improve our experimental setup to enable scattering analysis around the rainbow angle. Optical spectroscopy will provide us a possibility to observe spectra of the aggregating structures, which is particularly important when plasmonics inclusions are used. Scattering around the rainbow angle will be beneficial to determine the refractive index of unknown liquids.

The principle of the optical spectroscopy of single aggregates is to measure scattering cross section (for the certain range of scattering angles) of particles illuminated by a polychromatic light beam. As a light source we will use a high class halogen-deuterium lamp, to record spectra: a wide-bandwidth and high-sensitivity spectrometer. The outline of experimental setup is shown in Fig. 1. As an additional measurement method we will apply our library-based method utilizing static light scattering around the right angle (particularly for the range 29° – 61°) as well for the angles between 129° – 161°, i.e. around the so called rainbow angle.

In the numerical part of our work we aim to use and develop also an interferometric method based on the so called whispering gallery modes analysis. We intend also to apply different numerical approaches such as T-Matrix or DDScat. To perform reference analysis we will rebuild and use also the second trap with linear alignment of the electrodes. It will allow us not only observation of the aggregating structures but also their deposition onto substrates. Afterwards, it will be possible to investigate generated metamaterials with optical and electron microscopies (SEM and TEM) as well as atomic force microscopy.

A part of this project will be completed in cooperation with research group of professor Onofri from IUSTI laboratory at Aix-Marseille University in France. Due to the complementary character of the researches carried out and experimental facilities of both laboratories we will be able to study droplet evaporation and self-assembly processes for droplet sizes varying by nearly 3 orders of magnitude.

Aggregates of nanoparticles generated during the evaporation driven aggregation in microdroplets of suspensions, particularly the ones containing plasmonic inclusions, exhibit unique optical properties. Even single gold nanoparticles or their 2-dimensional matrixes characterize very strong enhancement of the scattering field for given frequencies. The 3-dimensional layout of the nanoparticles (that can be adjusted be dielectric particles) will allow us controlling and tailoring of the optical properties of generated aggregates. Thus, they could serve as the optical kernels imposing specific optical properties into metafluids, liquids, glasses or plastics. Additionally, it would be possible to strongly benefit from their independency of nanostructure orientation in 3-dimensional space.

Publications

1. J. Archer, M. Kolwas, G. Derkachov, M. Woźniak, D. Jakubczyk, K. Kolwas, Optical diagnostics of surfaces of single evaporating liquid microdroplet of solutions and suspensions, Proc. SPIE 9884, Nanophotonics VI, 988427 (April 19, 2016); DOI:10.1117/12.2225786 

1. M. Woźniak, G. Derkachov, K. Kolwas, J. Archer, T. T. Wojciechowski, D. Jakubczyk and M. Kolwas, Formation of highly ordered spherical aggregates from drying microdroplets of colloidal suspension, Langmuir, 31, 7860-7868 (2015), DOI: 10.1021/acs.langmuir.5b01621
    
2. M. Kolwas, K. Kolwas, G. Derkachov, D. Jakubczyk, Surface Diagnostics of Evaporating Droplet of Nanospheres Suspension; Fano Interference and Surface Pressure, Phys. Chem. Chem. Phys., 17, 6881-6888 (2015),  DOI: 10.1039/C5CP00013K
   

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