Nazim Mamedov

All-dielectric shallow silicon subwavelength gratings (SWGs) are demonstrated as a powerful platform for overcoming the fundamental waveguiding cutoffs of conventional bound transverse-magnetic (TM) modes, enabling strong light-matter interactions directly at the SWG-ambient interface. By leveraging laser interference lithography to fabricate ultrashallow silicon profiles, this work uncovers a unique regime where angle-dependent resonant anomalies emerge not from core-confined guided modes, but from the deliberate excitation of polarization-sensitive surface leaky modes operating strictly at the Wood–Rayleigh diffraction threshold. Finite Element Method (FEM) simulations validate that this threshold configuration can act as a giant electromagnetic energy concentrator at the interface, driving asymmetric Fano resonances and producing an exceptional enhancement of the local density of optical states along the grating ridges. Under p-polarized ultraviolet excitation, this localized field distribution triggers a dramatic Purcell acceleration of radiative decay pathways, enabling the detection of intense room-temperature photoluminescence from submonolayer organic residues with a giant ∼2 eV Stokes shift, resulting in an emission that is entirely quenched on unpatterned bulk silicon. These findings elucidate the physical mechanism of threshold-driven field localization in open dielectric nanostructures and highlight their transformative potential for ultrasensitive, label-free biomolecular optical detection.

MoS₂ is a two-dimensional layered transition metal dichalcogenide with unique electronic and optical properties. The fabrication of ultrathin MoS₂ is vitally important, since interlayer interactions in its ultrathin varieties will become thickness-dependent, providing thickness-governed tunability and diverse applications of those properties. Unlike with a number of studies that have reported detailed information on direct bandgap emission from MoS₂ monolayers, reliable experimental evidence for thickness-induced evolution or transformation of the indirect bandgap remains scarce. Here, the sulfurization of MoO₃ thin films with nominal thicknesses of 30 nm, 5 nm and 3 nm was performed. All sulfurized samples were examined at room temperature with spectroscopic ellipsometry and photoluminescence spectroscopy to obtain information about their dielectric function and edge emission spectra. This investigation unveiled an indirect-to-indirect crossover between the transitions, associated with two different Λ and K valleys of the MoS₂ conduction band, by thinning its thickness down to a few layers.

An Erratum to this paper has been published: https://doi.org/10.1134/S0021364022380039

Vibrational properties of TlFeS₂ and TlFeSe₂ crystal lattices have been investigated experimentally using Raman scattering (RS) and infrared reflection (IR) of light, as well as theoretically, using density functional theory (DFT). Full vibrational representation, compiled on the basis of the analysis of factor symmetry groups, contains 12 RS active modes and 9 IR active modes. Of these, six active RS modes and three IR active modes have been experimentally detected and identified for TlFeS₂, as well as four RS active modes and three IR active modes for TlFeSe₂.