Francesco Bisio

Passive daytime radiative coolers (PDRCs) are physical systems capable, on the Earth's surface, of achieving a net irradiation of energy toward outer space even under direct solar illumination. In order to achieve this amazing feat, PDRCs require tailored photonic properties all the way from the near‐ultraviolet to the mid‐infrared (mid‐IR). In particular, PDRCs require high reflectivity over the solar‐radiation range and selective absorbance (or equivalently emittance) in the mid‐IR atmospheric transparency window. In this study we fabricated PDRCs composed of silica‐loaded poly(4‐methyl‐1‐pentene) thin films hot‐pressed onto Ag‐coated stainless‐steel slabs, and we correlated the photonic response of these systems with their thermodynamic radiative efficiency. We clearly show that the presence of a strong emittance across the mid‐IR range corresponds to a higher radiative power around room temperature, thereby establishing a clear quantitative criterion for PDRC assessment.

We employ Spectroscopic Ellipsometry (SE) in the Kretschmann—Raether (KR) configuration (KRSE) to characterize a DNA‐functionalized platform designed for detecting specific viral oligonucleotide sequences. KRSE merges SE with Surface Plasmon Resonance, improving sensitivity to subtle interfacial phenomena. The sensor consists of a self‐assembled monolayer of thiolated DNA probes mixed with mercaptohexanol (MCH) spacers to promote upright probe orientation. The system is evaluated for its ability to selectively recognize the RdRp‐Helicase sequence of SARS‐CoV‐2, effectively discriminating it from the still circulating SARS‐CoV HKU strain. KRSE spectra exhibit pronounced redshifts (δλ) of the resonance as a function of target concentration. The formation of the probe layer and, in particular, the deposition of MCH, induce a deeper minimum in Ψ vs λ data at resonance. No further variation of the value of Ψ at resonance is observed in sensing/regeneration/sensing cycles. Optical modelling indicates that δλ redshifts are determined by increases in optical thickness of the adsorbed layer, while the Ψ changes at resonance derive from the formation of a sub‐nanometric Au‐thiol interfacial layer. This interface is modelled using a Bruggeman effective medium approximation, following previous standard SE experiments. Analysis of δλ shifts allows to derive a calibration curve with a nanomolar detection limit, and enables precise assessment of sensor specificity, outperforming previous conventional SE measurements on the same system.

Large area monolayer MoS ₂ samples are produced by a simple and reliable innovative exfoliation procedure. The method improves upon conventional processes by allowing the exfoliation of millimetre size flakes on virtually any substrates.

A comprehensive understanding of the relationship between defects concentration, optical properties and mechanical behavior of two-dimensional transition metal dichalcogenides (TMDs) is crucial for their integration as active components in micro- and nanomechanical devices. In this study we characterize the nanoscale contact adhesion and friction of WS₂ flakes grown via chemical vapor deposition. We identify two domains named α and β with distinct mechanical properties, which are not apparent in morphological differences but mirror spatial variations of the optoelectronic properties. The α-domains exhibit high photoluminescence (PL) emission, strong Raman response, higher contact adhesion and lower friction, closely resembling the response of pristine WS₂ flakes prepared by mechanical exfoliation. Conversely, the β-domains display very low PL emission, weak Raman response with blueshifted fingerprint peaks, lower adhesion and up to six-fold higher friction. Based on experimental evidence and general arguments, we attribute the mechanical heterogeneity between the α- and β-domains to the differentiated densities of sulfur and tungsten atomic vacancies, which are known to selectively populate the two domains. Our results indicate that the tungsten vacancies in the β-domains not only mediate non-radiative recombination processes but also drive a prominent friction enhancement, either by increasing the amplitude and disorder of the WS₂ potential energy surface or by impacting the stress distribution within the growing flakes. These findings help identify the type of defects and mechanisms that most significantly affect the properties of TMD monolayer flakes prepared by scalable production routes.

The thermal stability of hyper-doped Ge-on-Si and SiGe-on-Si films featuring carrier concentrations exceeding 5×10¹⁹ cm^–3 obtained by in situ doping and pulsed laser melting has been studied. The deactivation kinetics was systematically analysed through rapid thermal annealing, reflection spectroscopy and electrical characterization. The results demonstrate that while hyper-doped Ge films exhibit rapid deactivation at temperatures above 300 °C, SiGe offers enhanced thermal stability. Surface morphology analysis confirms the preservation of flatness after pulsed laser melting and thermal treatments, suggesting possible exploitation of these materials as substrates for further growths. These findings provide insights into optimizing hyper-doped material platforms for mid-infrared photonic devices and advanced semiconductor applications, emphasizing the trade-offs between the initial carrier concentration and the thermal resilience.

Low-voltage-enabled modulation of the optical response at room temperature in the IR spectral range has been detected by means of in operando spectroscopic ellipsometry in a Al-doped ZnO/BaTiO ₃ bilayer deposited on Nb-doped SrTiO ₃ substrate.

The coupling of nanostructures with emerging 2D semiconductors is gaining significant interest thanks to the unique features of these hybrids systems, which make them key platforms for next‐generation applications in electronics, optoelectronics, and sensing. Top‐down lithographic approaches uniquely enable the fully deterministic high‐resolution fabrication of nanostructures, but some of them, like electron‐beam lithography and focused ion‐beam lithography, employ energetic particles that may damage 2D materials causing an unwanted loss of functionality. Herein thermal scanning probe lithography is applied for the realization of metallic nanoantennas directly on top of exfoliated 2D MoS₂ flakes, showing it can avoid the degradation of this delicate substrate. It is shown that the morphologic and optical features of MoS₂ are fully preserved after the lithography.