arXiv subjects

Tomasz J. Antosiewicz

Publications and source records attributed to Tomasz J. Antosiewicz.

At least 19 recordsLinked to original sources

arXiv2026

Precise one-dimensional nanochannels in transition metal dichalcogenides as building blocks for advanced nanophotonics

Atomically sharp edges are essential for future high-index nanophotonic structures, yet conventional lithography and dry etching methods inevitably introduce edge roughness that limits optical confinement and reproducibility. Recently, anisotropic wet etching of multilayer van der Waals crystals, such as transition metal dichalcogenides (TMDs), has enabled crystallographically defined, atomically sharp zigzag edges, eliminating the edge-roughness problem. However, the process is intrinsically limited to confined geometries such as isolated triangular or hexagonal features dictated by crystal stacking symmetry. Here, we demonstrate a lithography-guided anisotropic etching framework that drives TMDs etching beyond isolated confined geometries by enforcing controlled interaction of neighboring etched nanoholes regions. In multilayer 2H-WS2, merging of anisotropic etch fronts enables sustained long-range propagation of zigzag facets, introducing a previously inaccessible 180-degree edge alignment and a crystallographically defined design space combining 120-degree and 180-degree junctions. Using this approach, we fabricate extended nanophotonic structures with ultrasharp sidewalls, including sub-100-nm-gap one-dimensional gratings, waveguides, defect-engineered photonic cavities, angle programmed photonic lattices, and diffractive zone plates. Back-focal-plane reflection spectroscopy of atomically sharp 1D periodic 2H-WS2 gratings demonstrates their photonic functionality, revealing symmetry-protected bound states in the continuum (SP-BICs) and strong exciton-photon coupling in multilayer WS2. Finally, we fabricate ultrathin, ultranarrow, and ultralong nanoribbons with record-high aspect ratios. Together, these results demonstrate edge merging as a generic route to fabricate edge-defined, atomically sharp nanophotonic and nanoelectronic architectures in layered van der Waals platforms.

physics.optics↗

arXiv2026

Multipole analysis of substrate-supported dielectric nanoresonator arrays with T-matrix method

Substrates, and layered media in general, are ubiquitous, affect the properties of whatever is in their vicinity, and their influence is, in an arbitrary framework, challenging to quantify analytically, especially for large arrays which escape explicit numerical treatment due to the computational burden. In this work, we develop a versatile T-matrix based framework in which we generalize the coupled multipole model towards arbitrarily high multipole orders and substrate-supported arrays. It allows us to study substrate-supported random/amorphous arrays of high index dielectric nanoparticles which are of wide interest due to relatively low losses and a highly tunable optical response, making them promising elements for nanophotonic devices. We discuss how multipole coupling rules evolve in the presence of a substrate in amorphous arrays for three interaction mechanisms: direct coupling between particles, substrate-mediated interparticle coupling and substrate-mediated self-coupling. We show the interplay between array density, distance from the substrate and its refractive in determining the optical response of an array. As an example, we use this framework to analyze refractometric sensing with substrate-supported arrays and demonstrate that the substrate plays a crucial role in determining the array sensitivity.

physics.optics↗

arXiv2026

Raman scattering of phonon polaritons under nanoscale confinement: the role of structure and environment

Strong light-matter coupling gives rise to polaritons -- quasiparticles that combine both photonic and material characteristics. Here, we show that polar nanocrystals exhibit structure- and environment-dependent Raman scattering, enabled by their hybrid phonon polariton nature. Such dispersive behavior enables refractive index sensing in the mid-infrared range via visible-wavelength inelastic spectroscopy and draws parallels with molecular systems under vibrational strong coupling. Crucially, Raman scattering appears only under nanoscale confinement of phonon polaritons. For optimal structures, this leads to self-hybridization between localized phonon modes and surface phonon polaritons hosted by the same nanoparticle.

physics.optics↗

arXiv2024

Nanogap-Engineered Core-Shell-Like Nanostructures for Comprehensive SERS Analysis

Development of fabrication protocols for large-area plasmonic nanostructures with sub-10 nm gaps with a spatially controlled distribution is critical for their real-world applications. In this work, we develop a simple, cleanroom-free protocol for the fabrication of macroscopic-sized plasmonic substrates (>6 cm^2), featuring a tunable multi-resonance optical response and light concentration in sub-10 nm gaps. Critically, these gaps are free to interact with the surrounding medium. This architecture consists of non-periodically distributed dielectric nanospheres coated with a metal multilayer, forming semi-spherical core-shell-like nanostructures (CSLNs) surrounded by a planar film. The sub-10 nm gaps formed between metal caps and the planar film are easily tuned by adjusting fabrication parameters such as multimetal layer thickness, composition, or nanosphere size and density. The excellent structural homogeneity, wide optical tunability, and extreme light confinement in the spatially controlled subwavelength nanogaps make CSLN-based substrates an ideal platform for comprehensive surface-enhanced Raman scattering (SERS) spectroscopy. This is proven through a combination of numerical modeling and iterative fabrication/characterization, leading to the optimized substrates showing cutting-edge spatial uniformity down to 1.9% determined as the relative standard deviation (RSD) of the SERS signal of p-mercaptobenzoic acid for 225 spectra over 3600 μm^2 area. High sensitivity is evidenced by an enhancement factor of ~10^6. The proposed substrates also meet all other demanding criteria, including sufficient signal temporal stability (RSD <4%), high substrate-to-substrate reproducibility (<15%), and SERS activity towards three various analytes. The unique geometry and wide spectral tunability of the CSLN substrates will also be of great value for other plasmon-driven applications.

physics.optics↗

arXiv2024

Humidity-enhanced NO$_2$ gas sensing using atomically sharp edges in multilayer MoS$_2$

Ambient humidity poses a significant challenge in the development of practical room temperature NO$_2$ gas sensors. Here, we employ atomically precise zigzag edges in multilayer MoS$_2$, fabricated using electron beam lithography and anisotropic wet etching, to achieve highly sensitive and selective gas sensing performance that is humidity-tolerant at elevated temperatures and humidity-enhanced at room temperature under ultraviolet illumination. Notably, exposure to 2.5 parts per billion (ppb) NO$_2$ at 70% relative humidity under ultraviolet illumination and at room-temperature resulted in a 33-fold increase in response and a 6-fold faster recovery compared to 0% relative humidity, leading to response values exceeding 1100%. The optimized samples demonstrated a theoretical detection limit ranging from 4 to 400 parts per trillion (ppt) NO$_2$. The enhanced NO$_2$ sensing capabilities of MoS$_2$ edges have been further confirmed through first-principles calculations. Our study expands the applications of nanostructured MoS$_2$ and highlights its potential for detecting NO$_2$ at sub-ppb levels in complex scenarios, such as high humidity conditions.

physics.app-ph↗

arXiv2024

Ultrathin 3R-MoS$_2$ metasurfaces with atomically precise edges for efficient nonlinear nanophotonics

Dielectric metasurfaces that combine high-index materials with optical nonlinearities are widely recognized for their potential in various quantum and classical nanophotonic applications. However, the fabrication of high-quality metasurfaces poses significant material-dependent challenges, as their designs are often susceptible to disorder, defects, and scattering losses, which are particularly prone to occur at the edges of nanostructured features. Additionally, the choice of the material platforms featuring second-order optical nonlinearities, $χ^{(2)}$, is limited to broken-inversion symmetry crystals such as GaAs, GaP, LiNbO$_3$, and various bulk van der Waals materials, including GaSe and NbOCl$_2$. Here, we use a combination of top-down lithography and anisotropic wet etching of a specially stacked van der Waals crystal -- 3R-MoS$_2$, which exhibits both a high refractive index and exceptional $χ^{(2)}$ nonlinearity, to produce metasurfaces consisting of perfect equilateral triangle nanoholes with atomically precise zigzag edges. Due to the geometry of the triangle, the etching process is accompanied by a transition from an in-plane $C_4$ symmetric structure to a broken-in-plane symmetry configuration, thereby allowing for the realization of the quasi-bound-state-in-the-continuum (q-BIC) concept. The resulting ultrathin metasurface ($\sim$ 20-25 nm) demonstrates a remarkable enhancement in second-harmonic generation (SHG) -- over three orders of magnitude at specific wavelengths and linear polarization directions compared to a host flake.

physics.optics↗

arXiv2024

Defect-assisted reversible phase transition in mono- and few-layer ReS$_2$

Transition metal dichalcogenide (TMD) materials have attracted substantial interest due to their remarkable excitonic, optical, electrical, and mechanical properties, which are highly dependent on their crystal structure. Controlling the crystal structure of these materials is essential for fine-tuning their performance, $\textit{e.g.}$, linear and nonlinear optical, as well as charge transport properties. While various phase-switching TMD materials, like molybdenum telluride (MoTe$_2$), are available, their transitions are often irreversible. Here, we investigate the mechanism of a light-induced reversible phase transition in mono- and bilayer flakes of rhenium disulfide (ReS$_2$). Our observations, based on scanning transmission electron microscopy, nonlinear spectroscopy, and density functional theory calculations, reveal a transition from the ground T$''$ (double distorted T) to the metastable H$'$ (distorted H) phase under femtosecond laser irradiation or influence of highly-energetic electrons. We show that the formation of sulfur vacancies facilitates this phenomenon. Our findings pave the way towards actively manipulating the crystal structure of ReS$_2$ and possibly its heterostructures.

physics.optics↗

arXiv2024

Quantum trapping and rotational self-alignment in triangular Casimir microcavities

Casimir torque -- a rotational motion caused by the minimization of the zero-point energy -- is a problem that attracts significant theoretical and experimental interest. Recently, it has been realized using liquid crystal phases and natural anisotropic substrates. However, for natural materials, the torque reaches substantial values only at van der Waals distances of ~10 nm. Here, we employ Casimir self-assembly using templated gold nanostructures of triangular symmetry for the purpose of rotational self-alignment at truly Casimir distances (100 -- 200 nm separation). The joint action of repulsive electrostatic and attractive Casimir potentials leads to the formation of a stable quantum trap, giving rise to a tunable Fabry-Perot microcavity. This cavity self aligns both laterally and rotationally to maximize the overlap area between the templated and floating triangular flakes. The rotational self-alignment is remarkably sensitive to the equilibrium distance between the two triangles as well as their area, which opens possibilities for active control through manipulating the electrostatic screening. Our self-assembled and self-aligned Casimir microcavities could find future use as a versatile and tunable platform for nanophotonic, polaritonic, and optomechanical applications.

cond-mat.mes-hall↗

arXiv2022

Computational Design of Alloy Nanostructures for Optical Sensing of Hydrogen

Pd nanoalloys show great potential as hysteresis-free, reliable hydrogen sensors. Here, a multi-scale modeling approach is employed to determine optimal conditions for optical hydrogen sensing using the Pd-Au-H system. Changes in hydrogen pressure translate to changes in hydrogen content and eventually the optical spectrum. At the single particle level, the shift of the plasmon peak position with hydrogen concentration (i.e., the "optical" sensitivity) is approximately constant at 180 nm/c_H for nanodisk diameters >~ 100 nm. For smaller particles, the optical sensitivity is negative and increases with decreasing diameter, due to the emergence of a second peak originating from coupling between a localized surface plasmon and interband transitions. In addition to tracking peak position, the onset of extinction as well as extinction at fixed wavelengths is considered. We carefully compare the simulation results with experimental data and assess the potential sources for discrepancies. Invariably, the results suggest that there is an upper bound for the optical sensitivity that cannot be overcome by engineering composition and/or geometry. While the alloy composition has a limited impact on optical sensitivity, it can strongly affect H uptake and consequently the "thermodynamic" sensitivity and the detection limit. Here, it is shown how the latter can be improved by compositional engineering and even substantially enhanced via the formation of an ordered phase that can be synthesized at higher hydrogen partial pressures.

cond-mat.mtrl-sci↗

arXiv2022

Local versus bulk circular dichroism enhancement by achiral all-dielectric nanoresonators

Large optical chirality in the vicinity of achiral high index dielectric nanostructures has been recently demonstrated as useful means of enhancing molecular circular dichroism. We theoretically study the spatial dependence of optical chirality enhancement in the vicinity of high index dielectric nanodisks and highlight its importance for the design of nanophotonic platforms for circular dichroism enhancement. Using a T-matrix framework, we demonstrate that depending on disk aspect ratio chirality is enhanced preferentially along different directions. We employ various statistical procedures (including surface, volume and orientation averaging) that are necessary to predict the enhancement of chiroptical effects and show that optimal properties of a nanostructure depend substantially on whether spatial maximum or average chirality enhancement is sought after. Similarly, the optimal choice of the nanostructure is influenced by the presence of substrate, which limits the space available to be occupied by analyte molecules and impacts the optical chirality in the vicinity of the nanostructure.

physics.optics↗

arXiv2022

Optical constants of several multilayer transition metal dichalcogenides measured by spectroscopic ellipsometry in the 300-1700 nm range: high-index, anisotropy, and hyperbolicity

Transition metal dichalcogenides (TMDs) attract significant attention due to their exceptional optical and excitonic properties. It was understood already in the 1960s, and recently rediscovered, that many TMDs possess high refractive index and optical anisotropy, which make them attractive for nanophotonic applications. However, accurate analysis and predictions of nanooptical phenomena require knowledge of dielectric constants along both in- and out-of-plane directions and over a broad spectral range -- information, which is often inaccessible or incomplete. Here, we present an experimental study of optical constants from several exfoliated TMD multilayers obtained using spectroscopic ellipsometry in the broad range of 300--1700 nm. The specific materials studied include semiconducting WS$_2$, WSe$_2$, MoS$_2$, MoSe$_2$, MoTe$_2$, as well as, in-plane anisotropic ReS$_2$, WTe$_2$, and metallic TaS$_2$, TaSe$_2$, and NbSe$_2$. The extracted parameters demonstrate high-index ($n$ up till $\approx 4.84$ for MoTe$_2$), significant anisotropy ($n_{\parallel}-n_{\perp} \approx 1.54$ for MoTe$_2$), and low absorption in the near infrared region. Moreover, metallic TMDs show potential for combined plasmonic-dielectric behavior and hyperbolicity, as their plasma frequency occurs at around $\sim$1000--1300 nm depending on the material. The knowledge of optical constants of these materials opens new experimental and computational possibilities for further development of all-TMD nanophotonics.

physics.optics↗

arXiv2022

Nanostructured transition metal dichalcogenide multilayers for advanced nanophotonics

Transition metal dichalcogenides (TMDs) attract significant attention due to their exceptional optical, excitonic, mechanical, and electronic properties. Nanostructured multilayer TMDs were recently shown to be highly promising for nanophotonic applications, as motivated by their exceptionally high refractive indexes and optical anisotropy. Here, we extend this vision to more sophisticated structures, such as periodic arrays of nanodisks and nanoholes, as well as proof-of-concept waveguides and resonators. We specifically focus on various advanced nanofabrication strategies, including careful selection of resists for electron beam lithography and etching methods. The specific materials studied here include semiconducting WS$_2$, in-plane anisotropic ReS$_2$, and metallic TaSe$_2$, TaS$_2$ and NbSe$_2$. The resulting nanostructures can potentially impact several nanophotonic and optoelectronic areas, including high-index nanophotonics, plasmonics and on-chip optical circuits. The knowledge of TMD material-dependent nanofabrication parameters developed here will help broaden the scope of future applications of these materials in all-TMD nanophotonics.

physics.optics↗

arXiv2021

Polarization-dependent mode coupling in hyperbolic nanospheres

Hyperbolic materials offer a much wider freedom in designing optical properties of nanostructures than ones with isotropic and elliptical dispersion, both metallic or dielectric. Here, we present a detailed theoretical and numerical study of the unique optical properties of spherical nanoantennas composed of such materials. Hyperbolic nanospheres exhibit a rich modal structure that, depending on the polarization and direction of incident light, can exhibit either a full plasmonic-like response with multiple electric resonances, a single, dominant electric dipole or one with mixed magnetic and electric modes with an atypical reversed modal order. We derive resonance conditions for observing these resonances in the dipolar approximation and offer insight into how the modal response evolves with the size, material composition, and illumination. Specifically, the origin of the magnetic dipole mode lies in the hyperbolic dispersion and its existence is determined by two diagonal permittivity components of different sign. Our analysis shows that the origin of this unusual behavior stems from complex coupling between electric and magnetic multipoles, which leads to very strongly scattering or absorbing modes. These observations assert that hyperbolic nanoantennas offer a promising route towards novel light-matter interaction regimes.

physics.optics↗

arXiv2021

Dipolar coupling of nanoparticle-molecule assemblies: An efficient approach for studying strong coupling

Strong light-matter interactions facilitate not only emerging applications in quantum and non-linear optics but also modifications of materials properties. In particular the latter possibility has spurred the development of advanced theoretical techniques that can accurately capture both quantum optical and quantum chemical degrees of freedom. These methods are, however, computationally very demanding, which limits their application range. Here, we demonstrate that the optical spectra of nanoparticle-molecule assemblies, including strong coupling effects, can be predicted with good accuracy using a subsystem approach, in which the response functions of the different units are coupled only at the dipolar level. We demonstrate this approach by comparison with previous time-dependent density functional theory calculations for fully coupled systems of Al nanoparticles and benzene molecules. While the present study only considers few-particle systems, the approach can be readily extended to much larger systems and to include explicit optical-cavity modes.

cond-mat.mes-hall↗

arXiv2020

Strong transient flows generated by thermoplasmonic bubble nucleation

The challenge of inducing and controlling localized fluid flows for generic force actuation and for achieving efficient mass transport in microfluidics is key to the development of next generation miniaturized systems for chemistry and life sciences. Here we demonstrate a methodology for the robust generation and precise quantification of extremely strong flow transients driven by vapor bubble nucleation on spatially isolated plasmonic nanoantennas excited by light. The system is capable of producing peak flow speeds of the order mm/s at modulation rates up to 100 Hz in water, thus allowing for a variety of high-throughput applications. Analysis of flow dynamics and fluid viscosity dependence indicate that the transient originates in the rapid bubble expansion that follows nucleation rather than being strictly thermocapillary in nature.

physics.app-ph↗

arXiv2020

Abundance of cavity-free polaritonic states in resonant materials and nanostructures

Strong coupling between various kinds of material excitations and optical modes has recently shown potential to modify chemical reaction rates in both excited and ground states. The ground-state modification in chemical reaction rates has usually been reported by coupling a vibrational mode of an organic molecule to the vacuum field of an external optical cavity, such as a planar Fabry-Pérot microcavity made of two metallic mirrors. However, using an external cavity to form polaritonic states might: (i) limit the scope of possible applications of such systems, and (ii) be unnecessary. Here we highlight the possibility of using optical modes sustained by materials themselves to self-couple to their own electronic or vibrational resonances. By tracing the roots of the corresponding dispersion relations in the complex frequency plane, we show that electronic and vibrational polaritons are natural eigenstates of bulk and nanostructured resonant materials that require no external cavity. Several concrete examples, such as a slab of excitonic material and a spherical water droplet in vacuum are shown to reach the regime of such cavity-free self-strong coupling. The abundance of cavity-free polaritons in simple and natural structures questions their relevance and potential practical importance for the emerging field of polaritonic chemistry, exciton transport, and modified material properties.

physics.optics↗

arXiv2019

Strong coupling out of the blue: an interplay of quantum emitter hybridization with plasmonic dark and bright modes

Strong coupling between a single quantum emitter and an electromagnetic mode is one of the key effects in quantum optics. In the cavity QED approach to plasmonics, strongly coupled systems are usually understood as single-transition emitters resonantly coupled to a single radiative plasmonic mode. However, plasmonic cavities also support non-radiative (or "dark") modes, which offer much higher coupling strengths. On the other hand, realistic quantum emitters often support multiple electronic transitions of various symmetry, which could overlap with higher order plasmonic transitions -- in the blue or ultraviolet part of the spectrum. Here, we show that vacuum Rabi splitting with a single emitter can be achieved by leveraging dark modes of a plasmonic nanocavity. Specifically, we show that a significantly detuned electronic transition can be hybridized with a dark plasmon pseudomode, resulting in the vacuum Rabi splitting of the bright dipolar plasmon mode. We develop a simple model illustrating the modification of the system response in the "dark" strong coupling regime and demonstrate single photon non-linearity. These results may find important implications in the emerging field of room temperature quantum plasmonics.

quant-ph↗

arXiv2019

Strong plasmon-molecule coupling at the nanoscale revealed by first-principles modeling

Strong light-matter interactions in both the single-emitter and collective strong coupling regimes attract significant attention due to emerging quantum and nonlinear optics applications, as well as opportunities for modifying material-related properties. Further exploration of these phenomena requires an appropriate theoretical methodology, which is demanding since polaritons are at the intersection between quantum optics, solid state physics and quantum chemistry. Fortunately, however, nanoscale polaritons can be realized in small plasmon-molecule systems, which in principle allows treating them using ab initio methods, although this has not been demonstrated to date. Here, we show that time-dependent density-functional theory (TDDFT) calculations can access the physics of nanoscale plasmon-molecule hybrids and predict vacuum Rabi splitting in a system comprising a few-hundred-atom aluminum nanoparticle interacting with one or several benzene molecules. We show that the cavity quantum electrodynamics approach holds down to resonators on the order of a few cubic nanometers, yielding a single-molecule coupling strength exceeding 200 meV due to a massive vacuum field value of 4.5 V/nm. In a broader perspective, our approach enables parameter-free in-depth studies of polaritonic systems, including ground state, chemical and thermodynamic modifications of the molecules in the strong-coupling regime, which may find important use in emerging applications such as cavity enhanced catalysis.

cond-mat.mes-hall↗