Tailoring Surface Morphology for Characteristic Exciton–Plasmon Resonances in Self-Assembled CuS Nanostructured Films

Abstract

Nanoscale surface corrugation strongly influences the propagation of plasmons and its induced characteristics in self-organized periodic nanostructures. Here, the role of varying surface roughness and thickness in periodic nanostructures of a self-assembled CuS system has been reported. The mixing of surfactants is used to translate the contrary type of clustering processes in a bottom-up fabrication method. X-ray diffraction (XRD) study identifies the improved crystallinity and quantization effects for invariable hexagonal crystal structures. The elaboration of Raman measurements has distinguished the formulated interlayer soft phonon modes from interlayer electron–phonon interactions that gave split-off features in surface enhanced Raman scatterings (SERS). The absorption spectra in linear and diffuse reflectance geometry monitor the scattering of the exciton–plasmon field in terms of defect states, Urbach’s energy, and optical gap. The true nature of periodic energy exchange between exciton–plasmon coupled systems has been derived from the Drude–Lorentz oscillator model fitting to near-normal incidence reflectance spectra. The effects on a dimensionally constrained plasmon’s momentum space and phase velocities are visible in the extraordinary optical behavior of the derived refractive index and dielectric constants. The correlative study on electronic, oxidation, and valence states has been reported using X-ray photoelectron spectroscopy (XPS) measurements. This approach of fabrication and characterization is expected to overcome the major roadblocks for the formation of metamaterials with identical large arrays for photonic devices.

Layer hybridized exciton–plasmon resonances for enhanced dispersion modes in CuS:Al nanostructured films

“…With the increase in doping content, the degeneracy in the E 1 2g mode can be registered in the second and third phonon branches of the transverse and out-of-plane dispersion modes as E ′′(M)TO1 + 2ZA(M) and E ′′(M)TO1 + 3ZA(M) while A 2 1g can split as phonon replicas in the combination of LA(M) + TA(M) and LA(M) + ZA(M) modes towards the higher or lower side of binding energy. 21,26–29 Here, the resulting degeneracy linearly increases with the dopant concentration, as shown in the inset of Fig. 2(b).…”

“…These modes of D 6h crystal symmetry can have degeneracy of 6 optical branches to be distributed as two in-plane longitudinal optical (LO1, LO2), two in-plane transverse optical (TO1-TO2) and two out-of-plane (ZO1 and ZO2) modes. 21,27…”

“…34 The following complex dielectric function is used in non-linear least squares fit to gain insights into their refractive index and dispersive behaviour, where detail on the parameters is given in the ESI† (SI-3 and SI-5).The estimated values from these fittings for both oscillators have been given in Tables S1–S4 of the ESI† (SI-4). In accordance with our last fitting analysis, 11,21 we procure precise values of physical parameters such as ε ∞ , ω o , ω p and ϒ (for Drude oscillator, given in Table 2) to extract genuine behaviour of complex optical dispersions in terms of refractive index and dielectric constants for CuS:Al nanostructured films.…”

“…The initial two substitutions abbreviate the phase velocities (momentum) of plasmon excitations in CuS nanostructures due to structural distortions, which increases their relaxation coefficient to red shift the coupled excitations. 21,33,35 The further increase of dopant concentration might have commenced the UV-Vis region plasmonic excitations of Al that have blue shifted the overall plasmon edge with increased relaxation coefficient (FWHM). Simultaneously, the refractive index obeying these dynamics got tuned towards larger values for which epsilon-near-zero (ENZ) modes in permittivity have been shifted towards longer wavelengths, covering a wide spectral region, as shown in Fig.…”

“…The nanostructure layers were grown on a (2 × 2 cm 2 ) glass substrate using the chemical bath deposition (CBD) technique similar to our previous reports. 11,21 Precursors of analytical grade (Loba Chemie, India), i.e. , copper( i ) chloride (CuCl), copper( ii ) chloride (CuCl 2 ·5H 2 O) and thioacetamide (C 2 H 5 NS), were used as sources of copper and sulfur.…”