arXiv subjects

Andrea Dellith

Publications and source records attributed to Andrea Dellith.

6 recordsLinked to original sources

arXiv2026

Two-Photon-Induced Direct 3D Printing of Freeform High-Index Phase-Change Sb2S3 Nanostructures

Chalcogenides have recently emerged as an important class of phase-change materials (PCMs) for nanophotonics, owing to their very high refractive index (RI) and low optical loss in the visible to near-infrared range. They exhibit an ultralarge RI change (> 0.7) upon phase transition, which can be triggered by multiple stimuli such as electrical bias, laser illumination or thermal heating. These properties make them highly appealing materials for flat optics and metasurface applications. Current nanophotonic implementations of chalcogenide PCMs mostly rely on two-dimensional (2D) or quasi three-dimensional (3D) thin film patterning based on the coating of chalcogenide materials from a solid-state target. This limits fast prototyping of 3D freeform micro- and nanostructures, thus restricting geometric design freedom and device functionality. Here, we demonstrate a solution-phase direct printing of chalcogenide PCMs into functional structures. The method is based on dip in two photon-induced solidification (DITPS) of a specially synthesized antimony trisulfide (Sb2S3) precursor solution. Direct printing with DITPS is simple, maskless, fast and cost effective, enabling true freeform 3D printing of photonic devices with sub micron resolution. We show direct writing of Sb2S3 helices with different wire cross section profiles on gold and ITO substrates, as well as functional planar Fresnel zone plates (FZPs) and computer generated hologram metasurfaces (CGHMs) in a single printing step. This freeform DITPS approach thus enables rapid 3D prototyping of high index metasurfaces and opens a route to integrating high-index PCMs into existing photonic architectures and device platforms.

physics.optics↗

arXiv2025

Effect of hybrid field coupling in nanostructured surfaces on anisotropic signal detection in nanoscale infrared spectroscopic imaging methods

Anisotropic intensity distributions on nanostructured surfaces and polarization-sensitive spectra have been observed in a number of nanoscale infrared spectroscopic imaging methods, including nano-FTIR [Bakir et al., Molecules, 2020, 25, 4295], photothermal induced resonance (PTIR) [Waeytens et al., Analyst, 2021, 146], tapping AFM-IR [Hondl et al., ACS Meas. Sci. Au, 2025, 5, 469; Luo et al., APL, 2022, 121, 23330], infrared photoinduced force microscopy (PiF-IR) [Anindo et al., JPCC, 2025, 129, 4517; Shcherbakov et al., Rev Methods Primers, 2025, 5, 1; Ali et al., Anal. Chem., 2025, 97, 23914] and peak force infrared microscopy (PFIR) [Xie et al., JPCC, 2022, 126, 8393; Anindo, JPCC, 2025]. A recent work combining modeling and experiment demonstrated that the hybrid field coupling of the IR illumination E0 with a polymer nanosphere and a metallic AFM probe is nearly as strong as the plasmonic coupling in case of a gold nanosphere [Anindo, JPCC, 2025]. For p-polarized illumination, this results in enhanced IR absorption on the surface perpendicular to the propagation of E0 which can explain the observed anisotropic intensity distribution. An additional anisotropy may be introduced by aligned surface molecules with oriented vibrational transition moments [Bakir et al., Molecules, 2020, 25, 4295; Luo, APL, 2022]. PiF-IR is strongly surface sensitive combining an unprecedented spatial resolution < 5 nm with high spectral resolution [Shcherbakov, Rev Methods Primers, 2025; Ali, Anal. Chem., 2025], which allows, for example, to visualize nanoscale chemical variation on the surface of bacteria cells affected by antimicrobial interaction [Ali, Anal. Chem., 2025]. We compare PiF-IR hyperspectra of aligned perylene Langmuir Blodgett monolayers on nanostructured and planar gold substrates and use quantum chemical calculations of the oriented vibrational oscillators to interpret the observations.

cond-mat.mes-hall↗

arXiv2025

Positive-tone Nanolithography of Antimony Trisulfide with Femtosecond Laser Wet-etching

Antimony trisulfide ($Sb_{2}S_{3}$), as an emerging material for integrated photonic devices, has attracted significant attention due to its high index, low loss, and phase-changing property in the optical regime. However, conventional lithography-based fabrication methods involve complex, time-consuming, multistep processes, rendering the photonic application of $Sb_{2}S_{3}$ challenging. Here, we demonstrate that positive-tone fabrication of $Sb_{2}S_{3}$ nanostructures using wet-etch femtosecond laser processing, a straightforward technique for the engraving of micro- and nanoscale structures, can address major fabrication challenges. The patterning mechanism and factors influencing resolution of $Sb_{2}S_{3}$ thin film structures deposited on quartz (transmissive) and gold (reflective) substrates are experimentally investigated and supported by theoretical modelling. Using this approach, the smallest linewidth fabricated is measured at 178 nm. Consequently, multiple test patterns are demonstrated showing versatile functionalities. Functional Fresnel Zone Plates (FZPs) with varying focal length are fabricated and characterized. This study provides a significantly simplified approach for realizing $Sb_{2}S_{3}$ based integrated photonic devices.

physics.optics↗

arXiv2024

Optical characterization of size- and substrate-dependent performance of ultraviolet hybrid plasmonic nanowire lasers

Nanowire-based plasmonic lasers are now established as nano-sources of coherent radiation, appearing as suitable candidates for integration into next-generation nanophotonic circuitry. However, compared to their photonic counterparts, their relatively high losses and large lasing thresholds still pose a burdening constraint on their scalability. In this study, the lasing characteristics of ZnO nanowires on Ag and Al substrates, operating as optically-pumped short-wavelength plasmonic nanolasers, are systematically investigated in combination with the size-dependent performance of the hybrid cavity. A hybrid nanomanipulation-assisted single nanowire optical characterization combined with high-throughput PL spectroscopy enables the correlation of the lasing characteristics to the metal substrate and the nanowire diameter. The results evidence that the coupling between excitons and surface plasmons is closely tied to the relationship between substrate dispersive behavior and nanowire diameter. Such coupling dictates the degree to which the lasing character, be it more plasmonic- or photonic-like, can define the stimulated emission features and, as a result, the device performance.

physics.optics↗

arXiv2024

Grayscale Electron Beam Lithography Direct Patterned Antimony Sulfide

The rise of micro/nanooptics and lab-on-chip devices demands the fabrication of three-dimensional structures with decent resolution. Here, we demonstrate the combination of grayscale electron beam lithography and direct forming methodology to fabricate antimony sulfide structures with free form for the first time. The refractive index of the electron beam patterned structure was calculated based on an optimization algorithm that is combined with genetic algorithm and transfer matrix method. By adopting electron irradiation with variable doses, 4-level Fresnel Zone Plates and metalens were produced and characterized. This method can be used for the fabrication of three-dimensional diffractive optical elements and metasurfaces in a single step manner.

physics.optics↗

arXiv2021

Extremely confined gap plasmon modes: when nonlocality matters

Historically, the field of plasmonics has been relying on the framework of classical electrodynamics, with the local-response approximation of material response being applied even when dealing with nanoscale metallic structures. However, when approaching the atomic-scale confinement of the electromagnetic radiation, mesoscopic effects are anticipated to become observable, e.g., those associated with the nonlocal electrodynamic surface response of the electron gas. We investigate nonlocal effects in propagating gap surface plasmon modes in ultrathin metal--dielectric--metal planar waveguides, exploiting monocrystalline gold flakes separated by atomic-layer-deposited aluminum oxide. We use scanning near-field optical microscopy to directly access the near-field of such confined gap plasmon modes and measure their dispersion relation (via their complex-valued propagation constants). We compare our experimental findings with the predictions of the generalized nonlocal optical response theory to unveil signatures of nonlocal damping, which becomes appreciable for smaller dielectric gaps.

cond-mat.mes-hall↗