NM09.19.01 : Optical Response of Finite-Thickness Ultrathin Plasmonic Films

3:30 PM–3:45 PM Apr 6, 2018

PCC North, 200 Level, Room 231 BC

Igor Bondarev1 Vladimir Shalaev2

1, North Carolina Central University, Durham, North Carolina, United States
2, Purdue University, West Lafayette, Indiana, United States

Current development of nanofabrication techniques makes it possible to produce plasmonic films of precisely controlled thickness down to a few monolayers for a variety of applications in optoelectronics and to probe the fundamentals of the light-matter interactions at the nanoscale [1–3]. As the film thickness decreases, the strong vertical electron confinement can lead to new confinement related and dimensionality related effects [4–6], which require theory development to understand their role in the light-matter interactions and optical response of thin and ultrathin plasmonic films. We develop a quasiclassical theory for the electron confinement effects and their manifestation in the optical response of ultrathin plasmonic films of finite variable thickness [5]. We start with the Coulomb interaction potential in the confined planar geometry to obtain the equations of motion and the conditions for the in-plane collective electron (plasma) motion. The plasma frequency thus obtained, while being constant for relatively thick films, acquires spatial dispersion typical of 2D materials and gradually shifts to the red as the film thickness decreases. As a consequence, the complex-valued dynamical dielectric response function shows the gradual red shift of its epsilon-near-zero point with the dissipative loss decreasing at any fixed frequency and gradually going up at the plasma frequency as it shifts to the red with the film thickness reduction. We argue that these are the universal properties peculiar to all ultrathin plasmonic films and metasurfaces. Our theory explains recent plasma frequency measurements done on ultrathin TiN films of controlled variable thickness [3], offering ways to tune spatial dispersion (and so magnetic permeability [7]) and magneto-optical properties of plasmonic films and metasurfaces — not only by varying their material composition but also by precisely controlling their thickness and by choosing deposition substrates and coating layers appropriately.

Acknowledgements: NSF-ECCS-1306871 (I.B.), NSF-DMR-1506775 (V.S.)

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