Permittivity acquisition of plasmonic materials at epsilon near zero wavelengths

Abstract

Due to their unique optical properties, plasmonic materials are widely used in nonlinear optics, nanophotonics, optoelectronics, photocatalysis, biosensing, information storage, etc. Researchers usually need to know the detailed permittivity behavior at the vicinity of surface plasmons’ excitation wavelengths, which in turn are located near the zero points of the real part of the permittivity called epsilon-near-zero (ENZ). We hereby introduce a spectral fitting method to quickly obtain the materials' permittivity at the ENZ region and summarize the experiences of selecting dispersion models and optimizing model parameters. Specifically, we have made a detailed description of the optical constant fitting process for a series of plasmonic materials such as heavily doped semiconductors, transparent conductive oxides, organic conductive materials, two-dimensional materials, and sandwiched composites. Hopefully, to provide specific data and theoretical support for researchers in the field of photoelectric properties of plasmonic materials.

Tunable Organic ENZ Materials with Large Optical Nonlinearity

“…Equation suggests that the visible ENZ wavelength in the acid-modified PEDOT is due to the high hole concentration (3.119 × 10 21 cm –3 ). According to our Hall measurement (Table and supplementary Figure b), the carrier mobility μ of EG-modified PEDOT:PSS and acid-modified PEDOT is 5.8 and 4.0 cm 2 /V·s, respectively, which are ∼5 times lower than that of ITO …”

“…X-ray diffraction (XRD) (Supporting Information Figure S2) confirms that dry annealing of the as-deposited film causes PEDOT chains to undergo a change from an amorphous to a polycrystalline state. The increased hole concentration and the improved film crystallinity are considered to manifest a considerable increase in carrier mobility μ. ,, Figure b shows that such a treatment for the PEDOT:PSS film causes the blue shift of the plasma frequency ω P and the ENZ frequency ω ENZ from the mid-infrared to 189 THz (λ ENZ = 1587 nm), which were extrapolated from the reflection spectrum inversion on the basis of the Drude model …”

“…According to our Hall measurement (Table 1 and supplementary Figure 1b), the carrier mobility μ of EG-modified PEDOT:PSS and acid-modified PEDOT is 5.8 and 4.0 cm 2 /V•s, respectively, which are ∼5 times lower than that of ITO. 32 Equations 4 and 5 indicate that the ENZ wavelength could be further shortened, and the loss may be optimized by tailoring the carrier concentration and tuning the mobility. The degree of disorder dictates the conduction mechanism in organic semiconductor polymers.…”

“…(b) Real (solid line) and imaginary (dashed line) parts of permittivity of pristine (blue), EG-modified (red), and acid-modified (green) PEDOT:PSS, which are extrapolated from the reflection spectrum inversion using the Drude−Lorentz model. 32 The EG-modified PEDOT films show an ENZ wavelength at 1587 nm. In general, the free-carrier-related nonlinearity in n-type degenerate ENZ materials is due to the intraband transition of electrons from the conduction band edge.…”

Plasmonics: Enabling functionalities with novel materials

“…Therefore, methods for obtaining the dielectric functions of plasmonic materials in their ENZ regions are important. Zheng et al 7 show how to do this through spectral fitting. Novel combinations of organics and metals in composite films to realize ENZ metamaterials are proposed in Ref.…”