Domenico De Fazio

Researchers from Ca’ Foscari University of Venice, working within the SUPERVenice research unit, have developed a new type of flexible, skin-compatible photodetector that can sense light across a broad range of wavelengths while operating at low voltage and remaining safe for direct contact with human skin. The device, reported in Advanced Functional Materials, combines graphene with specially engineered carbon dots on a plastic substrate, creating a lightweight and bendable photodetector suitable for wearable electronics and on-skin sensing applications. Addressing a key challenge in wearable optoelectronics Photodetectors—devices that convert light into electrical signals—are essential components in technologies ranging from cameras and optical communications to medical sensors. Conventional photodetectors, often based on rigid silicon electronics, perform well but are poorly suited for wearable or skin-integrated systems, where flexibility, low power consumption and biocompatibility are crucial. Many flexible photodetectors reported to date compromise on at least one of these requirements. Some offer high sensitivity but rely on toxic materials such as lead- or cadmium-based quantum dots; others are flexible but operate over a narrow spectral range or lack evidence of skin safety. The new work addresses these limitations by combining broadband optical response, mechanical flexibility and verified skin compatibility within a single device architecture. Carbon dots and graphene: complementary roles The photodetector is built by integrating hydrothermally synthesized carbon dots with single-layer graphene transferred onto a polyethylene terephthalate (PET) substrate. The carbon dots act as the light-absorbing element, while graphene provides an efficient, high-mobility pathway for charge transport. Unlike conventional quantum dots, the carbon dots used in this study are metal-free, environmentally benign and inherently biocompatible. By carefully tuning their synthesis conditions, the researchers engineered the dots to absorb light not only in the ultraviolet but also across the visible and near-infrared range, extending roughly from 400 to 800 nanometers. Graphene alone absorbs only a small fraction of incoming light, but when coupled to the carbon dots it efficiently collects photogenerated charge carriers, enabling a measurable electrical response across the full spectral window. Low-voltage operation with a biopolymer gate To control the device electronically, the team used a chitosan–glycerol biopolymer electrolyte as a gate dielectric. Chitosan, derived from natural sources such as chitin, is non-toxic and widely used in biomedical applications. This electrolyte enables strong electrostatic gating at very low operating voltages, with optimal performance reached at around 0.5 V, well below the levels typically required by flexible photodetectors. Under illumination, the device shows a gate-dependent photoresponse that can be tuned between different operating regimes, with peak responsivities of approximately 0.19 A/W at 406 nm, 0.32 A/W at 642 nm, and 0.18 A/W at 785 nm. Performance under bending and repeated use Mechanical flexibility is a key requirement for wearable electronics, and the researchers subjected their devices to extensive bending tests. The photodetectors maintained stable operation at bending radii as small as 0.8 cm and showed no significant degradation after up to 1000 bending cycles. The response times, on the order of one second, are compatible with many wearable sensing applications, including biometric monitoring and environmental light sensing. Demonstrated skin compatibility Beyond electrical and mechanical performance, the study directly addresses skin safety, an aspect often assumed rather than tested in wearable optoelectronics. Using reconstructed human epidermis models and fibroblast cultures, the researchers showed that neither the complete device nor its individual components caused skin irritation or cytotoxic effects. Importantly, illumination under realistic operating conditions did not induce detectable reactive oxygen species (ROS) generation, indicating that the device is photo-safe for on-skin use. Toward practical wearable photonics While the device is presented as a proof of concept, the authors emphasize that the materials and fabrication steps are compatible with scalable, low-cost processing. Future work will focus on improving detectivity, optimizing large-area uniformity, and integrating the photodetectors into functional wearable platforms. By combining metal-free light absorbers, graphene electronics, biopolymer gating and direct biological testing, the study outlines a practical route toward next-generation photodetectors designed from the outset for safe, wearable operation. The full study is published in Advanced Functional Materials and is available at https://doi.org/10.1002/adfm.202523076

In a study just published in ACS Nano, the team investigated what happens when monolayer MoS₂ — a direct-gap semiconductor just three atoms thick — is stacked with graphene. This combination of two-dimensional (2D) materials reveals a subtle but powerful mechanism: electrical control over light emission without relying on high levels of doping. By carefully tuning the interaction between MoS₂ and graphene, the researchers observed a dramatic suppression of photoluminescence (light emission) from specific exciton species (bound electron-hole pairs), depending on whether the material was isolated or part of a stacked heterostructure. The introduction of graphene changes the game: it enables efficient, voltage-controlled charge transfer, preventing the accumulation of excess carriers in MoS₂ and thus keeping the optical response stable and predictable. The most striking insight? In pristine MoS₂, high doping leads to a superlinear increase in light emission — a kind of optical “amplification” that stops once the system is saturated. This effect disappears completely in the MoS₂/graphene stack, showing that graphene acts as a natural “exciton regulator,” draining away excess charge and suppressing this nonlinearity. Even B-type excitons — typically unaffected by doping due to their ultrafast decay — are modulated by this setup, revealing that charge transfer occurs before excitons can recombine internally. This suggests the presence of a hot-electron transfer channel, a new dimension to 2D material photophysics. Why it matters This work opens the door to more precise control over how atomically thin materials emit light, essential for developing efficient LEDs, photodetectors, and quantum light sources. The use of layered 2D materials to achieve such control, without chemical treatment or structural modification, marks a significant leap forward in optoelectronics and nanophotonics. The SUPERVenice perspective This discovery strengthens Venice’s growing role in frontier materials research. The participation of Ca’ Foscari University through Prof. Domenico De Fazio, member of SUPERVenice, highlights the impact of collaborative, interdisciplinary science rooted in fundamental physics with clear technological implications. The full paper, “Tunable Exciton Modulation and Efficient Charge Transfer in MoS₂/Graphene van der Waals Heterostructures”, is available open-access in ACS Nano. 🔬 Read the paper: ACS Nano DOI

  Hydrogen-rich materials are paving the way for breakthroughs in superconductivity, but the path to efficiently incorporating hydrogen into these materials has been fraught with challenges. Our recent study, published in the Journal of Molecular Liquids, unveils a transformative method for hydrogen loading using deep eutectic solvents (DES), which promises to revolutionise this field. Led by a collaborative team of researchers from Politecnico di Torino, the Ca’ Foscari University of Venice and other institutions, the study demonstrates how a simple mixture of choline chloride and glycerol can replace the traditionally used ionic liquids for hydrogen incorporation. This innovative approach addresses key issues such as cost, toxicity, and environmental impact while achieving hydrogen concentrations high enough to induce superconductivity in palladium. The concept hinges on ionic gating-induced protonation (IGP), a technique that uses an electric field to drive hydrogen ions into materials. By leveraging the unique properties of DES—low viscosity, biodegradability, and cost-effectiveness—the researchers successfully injected hydrogen into palladium bulk foils and thin films, achieving a stoichiometry of up to PdH₀.₈₉. While partial superconducting transitions were observed in thin films, the study underscores the need for further refinement to ensure a uniform hydrogen distribution within materials. Beyond Palladium: A Vision for the FutureThough the research focuses on palladium as a model system, its implications extend far beyond. The DES-based IGP method could be adapted for a wide range of materials, offering promising applications in hydrogen storage, spintronics, and quantum technologies. This breakthrough aligns with global efforts to develop more sustainable and accessible superconducting technologies at practical pressures and temperatures. This groundbreaking study represents a significant leap forward in material science, potentially heralding a new era of innovation. For more details, you can access the full article in the Journal of Molecular Liquids: https://doi.org/10.1016/j.molliq.2024.126826.  

Graphene, the wonder two-dimensional material, has shown exceptional electronic properties, making it a sought-after candidate for various advanced technologies. However, maintaining high carrier mobility in practical device applications has been a challenge, with the choice of substrate and encapsulation playing a pivotal role. A team of researchers, including Dr Domenico De Fazio at the Ca’ Foscari University of Venice, has made a breakthrough in this domain by successfully encapsulating graphene in tungsten disulfide (WS2). This achievement, detailed in a recent paper, offers an alternative to the commonly used hexagonal boron nitride (hBN) encapsulation method. The researchers applied a chemical treatment involving a super-acid, bis(trifluoromethane) sulfonimide (TFSI), to overcome the hysteresis and enhance the mobility of graphene encapsulated in WS2. High mobility, a key requirement for electronic devices, was achieved through WS2 encapsulation, presenting numerous advantages. The study revealed a significant reduction in hysteresis, making WS2-encapsulated graphene a compelling alternative to hBN. This breakthrough has far-reaching implications for various electronic applications, including field-effect transistors, modulators, photodetectors, and sensors. With hBN’s limitations addressed by WS2, the world of graphene-based electronics may soon see significant improvements in performance and scalability, paving the way for more efficient and powerful devices. The full article is available at the following link: https://doi.org/10.1063/5.0151273