We report the complex pseudodielectric function of molybdenum disulfide (MoS₂) monolayers for energies from 1.40 to 6.42 eV and temperatures from 35 to 350 K. MoS₂ was grown as a continuous monolayer on a SiO₂/Si substrate in a two zone hot-wall furnace using a catalyst-free chemical vapor growth process. The monolayer was then transferred onto a sapphire substrate. We investigated the optical properties of MoS₂ using a dual-rotating-compensator ellipsometer with the sample in ultrahigh vacuum to prevent degradation and to minimize condensation artifacts in the data at low sample temperatures. Critical-point (CP) energies were determined using numerically calculated second energy derivatives of the spectra. At low temperature, we observed a splitting of A-excitonic peak. This identifies the bound excitonic states, including negatively charged excitons, trion states in monolayer MoS₂. Splitting of the B-excitonic peak is also indicated. Blue shifts of the CP energies and enhanced structures with reduced electron–phonon interaction are observed as the temperature is lowered. The temperature dependences of the CP energies were fit to a phenomenological expression that contains the Bose–Einstein statistical factor and the temperature coefficient.

The dielectric function $${\boldsymbol{\varepsilon }}{\boldsymbol{=}}{{\boldsymbol{\varepsilon }}}_{{\bf{1}}}{\boldsymbol{+}}{\bf{i}}{{\boldsymbol{\varepsilon }}}_{{\bf{2}}}$$ε = ε 1 + i ε 2 of monolayer molybdenum diselenide (MoSe₂) is obtained and analyzed at temperatures from 31 to 300 K and at energies from 0.74 to 6.42 eV. The sample is a large-area, partially discontinuous monolayer (submonolayer) film of MoSe₂ grown on a sapphire substrate by selenization of pulsed laser deposited MoO₃ film. Morphological and optical characterizations verified the excellent quality of the film. The MoSe₂ data were analyzed using the effective medium approximation, which treats the film and bare substrate regions as a single layer. Second derivatives of ε with respect to energy were numerically calculated and analyzed with standard lineshapes to extract accurate critical-point (CP) energies. We find only 6 CPs for monolayer MoSe₂ at room temperature. At cryogenic temperatures 6 additional structures are resolved. The separations in the B- and C-excitonic peaks are also observed. All structures blue-shift and sharpen with decreasing temperature as a result of the reducing lattice constant and electron-phonon interactions. The temperature dependences of the CP energies were determined by fitting the data to the phenomenological expression that contains the Bose-Einstein statistical factor and the temperature coefficient.

We report the temperature dependence of the dielectric function ε = ε₁ + iε₂ and critical point (CP) energies of biaxial α-SnS in the spectral energy region from 0.74 to 6.42 eV and temperatures from 27 to 350 K using spectroscopic ellipsometry. Bulk SnS was grown by temperature gradient method. Dielectric response functions were obtained using multilayer calculations to remove artifacts due to surface roughness. We observe sharpening and blue-shifting of CPs with decreasing temperature. A strong exciton effect is detected only in the armchair direction at low temperature. New CPs are observed at low temperature that cannot be detected at room temperature. The temperature dependences of the CP energies were determined by fitting the data to the phenomenological expression that contains the Bose–Einstein statistical factor and the temperature coefficient for describing the electron–phonon interaction.

We investigate analytically the anisotropic dielectric properties of single-crystal α-SnS near the fundamental absorption edge by considering atomic orbitals. Most striking is the excitonic feature in the armchair- (b-) axis direction, which is particularly prominent at low temperatures. To determine the origin of this anisotropy, we perform first-principles calculations using the GW0 Bethe–Salpeter equation including the electron–hole interaction. The results show that the anisotropic dielectric characteristics are a direct result of the natural anisotropy of p orbitals. In particular, this dominant excitonic feature originates from the p_y orbital at the saddle point in the Γ–Y region.

In this study, we present a novel surface-enhanced Raman scattering (SERS) substrate based on porous silicon microcavities (PSiMCs) decorated with silver nanoparticles (AgNPs) for ultra-sensitive molecule detection. This substrate utilizes a dual enhancement mechanism: the localized surface plasmon resonance (LSPR) of AgNPs and the optical resonance of the PSiMC structure, which together create intense electromagnetic hot spots and prolong photon–molecule interactions. The porous architecture provides a large surface area for uniform nanoparticle distribution and efficient analyte adsorption. The AgNP/PSiMC substrate demonstrates an impressive detection limit of 1.0 × 10⁻¹³ M for rhodamine101 and 1.0 × 10⁻¹⁰ M for methyl parathion, outperforming many previously reported SERS platforms. Furthermore, the substrate exhibits excellent signal uniformity (RSD ≈ 6.14%) and long-term stability, retaining over 50% signal intensity after 28 days. These results underscore the potential of AgNP/PSiMCs as highly efficient, reproducible, and scalable SERS platforms for trace-level chemical and environmental sensing applications.

In spectroscopy, the objective is to obtain information by analyzing spectra that ideally are undistorted and noise-free. In standard Fourier-space filtering, this goal cannot be achieved because of apodization, which forces a trade-off among errors arising from distortion, noise leakage, and Gibbs oscillations. We show that low-order coefficients can be preserved and apodization, and its associated errors eliminated with the corrected maximum-entropy (M-E) filter obtained here. Although the Burg derivation begins as M-E, by making certain assumptions the Burg approach yields a procedure that deconvolves (sharpens) structure in spectra, thereby violating the basic M-E principle of leaving the low-order coefficients intact. The corrected solution preserves these data and projects the trends established by them into the white-noise region in a model-independent way, thereby eliminating apodization and its associated errors. For a single Lorentzian line, the corrected M-E approach has an exact analytic solution, which reveals not only how M-E performs its extension but also why it works particularly well for line shapes resulting from first-order decay processes. The corrected M-E filter is quantitatively superior to any previous filtering method, including recently proposed high-performance linear filters, yet requires only minimal computational effort. Examples, including multiple differentiation, are provided.