| AVS 66th International Symposium & Exhibition | |
| Spectroscopic Ellipsometry Focus Topic | Thursday Sessions |
| Session EL-ThA |
| Session: | Spectroscopic Ellipsometry Late News Session |
| Presenter: | Ufuk Kilic, University of Nebraska-Lincoln |
| Authors: | U. Kilic, University of Nebraska-Lincoln M. Hilfiker, University of Nebraska-Lincoln R. Feder, The Fraunhofer Institute for Microstructure of Materials and Systems (IMWS), Germany R. Korlacki, University of Nebraska-Lincoln E. Schubert, University of Nebraska-Lincoln C. Argyropoulos, University of Nebraska-Lincoln M. Schubert, University of Nebraska-Lincoln |
| Correspondent: | Click to Email |
The differential absorption of left-and right-handed circularly polarized light so-called circular dichroism (CD) has recently gained enormous interest in optics, chemistry, pharmacology and biotechnology fields. [1] Particularly, the subwavelength scale periodic arrangement of nano-plasmonic structures is predicted to be a facile enhancement method of CD response and offers a great potential for chiral opto-electronics. [2,3]
In this study, by using the ultra-high vacuum, electron beam evaporated glancing angle deposition system, we successfully fabricated optically active, spatially coherent, and highly porous chiral hetero-structures (CHS).
Subsequent and repeated depositions of silicon (Si) and gold (Au)/silver (Ag) lead to nanometer-dimension sub-chiral segments which enables to tailor the circular dichroism induced by size, shape and material choice.
The incorporation of transmission mode Mueller matrix spectroscopic ellipsometry technique with finite element modeling(FEM) provides an excellent framework for optical characterization of this new type plasmonic metamaterials within the spectral range from 0.6 eV to 4.5 eV. We systematically studied the influence of geometrical parameters (such as handedness of the structure (left or right), pitch size, minor and major radius of fabricated CHS, and also number of turns) on CD phenomenon.
Interestingly, Au/Ag sub-chiral segments in CHS result in the emergence of multiple plasmonic modes which can be tunable depending on the Au/Ag-Si ratio in a single turn. In addition, the effects of both azimuthal rotation and angle of incidence on CD are also investigated as a part of this study. According to the FEM calculations, as compared with Si chiral structures, we observed a significant enhancement in the circular dichroism of Si-Au/Ag CHS which can be attributed to plasmonic resonance effect [2]. We also calculated Kuhn's dis-symmetry (g) factor (g≈(A+-A-)/(A++A-), where A-, A+ are the absorbance coefficients for left and right circularly polarized light, respectively), which is useful for quantitative comparisons of chiro-optical properties of different structures. Unlike the other studies [4,5] which employs periodic nanostructures made up of single type material, we observed a very pronounced g-factor in our fabricated CHSs around 3-4 eV range.
References:
[1] de Dios, Carolina, et al. Optics Express 27.15, 21142-21152, (2019).
[2] Kneer, Luisa M., et al., ACS nano 12.9 :9110-9115(2018).
[3] Hentschel, Mario, et al., Science advances3.5, e1602735, (2017).
[4] Schulz, Matthias, et al., Nature communications 9.1, 2413, (2018).
[5] Lee, Hye-Eun, et al., Nature 556.7701, 360, (2018).