Domenico De Fazio

Researchers at SUPERVenice have shown that stacking two ultrathin materials can make an atomically thin semiconductor emit six times more light at room temperature. What happens when two crystals, each only a few atoms thick, are placed on top of one another? They do not simply retain their individual properties. Their electrons begin to interact across the interface, and the resulting structure can behave in ways that neither material would on its own. Researchers of SUPERVenice at Ca’ Foscari University of Venice, have used this principle to substantially improve light emission from molybdenum diselenide (MoSe₂), one of the most widely studied two-dimensional semiconductors. The team combined a single layer of MoSe₂ with a thin crystal of palladium diselenide, PdSe₂. When illuminated with green light, the resulting heterostructure emitted approximately six times more light than MoSe₂ alone. The work has now been published in Nano Letters. Helping excitons find the bright path When a semiconductor absorbs light, it creates temporary electron–hole pairs known as excitons. These excitons can recombine and release their energy as light, but they can also lose it through other processes, producing heat instead of photons. The challenge is therefore not only to create excitons, but also to guide them towards the pathways that produce light. This is what the PdSe₂ layer appears to do. Although it is not itself a strong light emitter, its electronic interaction with MoSe₂ changes the way excitons relax inside the material. Energy that would otherwise be lost is redirected towards the bright excitonic state responsible for light emission. The result is an estimated photoluminescence quantum yield of about 6%, compared with approximately 1% for an untreated MoSe₂ monolayer. The effect works across a broad range of excitation wavelengths and does not require chemical treatments or significant mechanical strain. The properties of the MoSe₂ layer are improved simply through its interaction with the material placed beneath it. More than brighter emission Two-dimensional semiconductors are promising candidates for future LEDs, lasers, optical sensors and quantum technologies. Their extreme thinness makes them compact and highly responsive, but their light emission is often limited by processes that waste the absorbed energy. The new results show that these losses can be controlled by carefully selecting which materials are stacked together. Not every combination works. When the researchers replaced MoSe₂ with the closely related semiconductor MoS₂, the same enhancement was not observed. The electronic structure and energy alignment of the two materials must therefore match in the right way. This turns the experiment into something more useful than a single bright heterostructure: it provides a possible design principle for engineering other two-dimensional materials with improved light-emission properties. A study led from Venice The research was led by the LION team at Ca’ Foscari University of Venice. Petr Rozhin, first author of the study, is a postdoctoral researcher in the LION group. The work brought together experimental and theoretical expertise from Ca’ Foscari University of Venice, Friedrich Schiller University Jena, the University of Crete and FORTH, Politecnico di Milano, the University of Chemistry and Technology Prague, and the National Institute for Materials Science in Japan. The article, “Highly Efficient Exciton Modulation in MoSe₂/PdSe₂ Heterostructures,” is available open access in Nano Letters. Read the full paper

A new study published in ACS Photonics, led by SUPERVenice researcher Domenico De Fazio, shows that scalable graphene can host coherent acoustic plasmon resonances and use them to enhance terahertz detection. Terahertz radiation sits between microwaves and infrared light in the electromagnetic spectrum. It can pass through many common materials, interact with molecular vibrations, and carry information at high frequency, making it promising for imaging, sensing, security screening, and future wireless communications. Yet detecting terahertz light efficiently, especially in compact devices, remains a major technological challenge. This study reports an advance in this direction using one of the thinnest possible materials: graphene. It demonstrates that chemical-vapor-deposited graphene — a scalable form of graphene compatible with larger-area fabrication — can support coherent acoustic plasmon resonances at terahertz frequencies under the right conditions. In simple terms, the researchers show that tiny waves of charge in graphene can be made to bounce back and forth inside a microscopic cavity, producing a measurable enhancement in the terahertz photoresponse. Turning graphene into a tiny terahertz resonator Graphene is only one atom thick, but its electrons can respond strongly to electromagnetic radiation. When terahertz light hits a graphene device, it can heat the electrons and generate a voltage through the photothermoelectric effect. This makes graphene attractive for terahertz photodetectors. However, because graphene is atomically thin, it normally absorbs only a small fraction of incoming light. To overcome this limitation, the team designed a device in which the metallic gates also act as a terahertz antenna. These gates concentrate the incoming terahertz field into the graphene channel and launch acoustic graphene plasmons — collective oscillations of electrons coupled to the electromagnetic field. At cryogenic temperatures, where electronic losses are strongly reduced, these plasmons become coherent enough to form standing waves. “By cooling the device down, the system becomes quiet enough for us to see the plasmons bouncing back and forth inside the graphene cavity,” explains De Fazio. “It is a bit like watching waves resonate in a tiny box, except that here the box is a graphene channel only a few micrometres long, and the waves are charge oscillations driven by terahertz light.” A full cavity — or only half of it One of the key results of the study is that the plasmon cavity can be reconfigured electrically. By changing the voltages applied to the two gates, the researchers can modify the carrier density profile inside the graphene channel. In one configuration, the plasmon resonance extends across the full graphene channel. In another, the device behaves as if only half of the channel forms the resonant cavity. This “half-cavity” behaviour occurs because the gate-defined conductivity landscape creates an internal reflection point for the plasmons. This gate-controlled behaviour gives direct evidence that the observed peaks in the terahertz photoresponse arise from acoustic plasmon Fabry–Pérot-like cavity modes, rather than from a simple background heating effect. The paper reports that the resonances modulate the photothermoelectric response by up to about 40% at low temperature, with the modes disappearing as the device is warmed due to increased plasmon damping. Why this matters The result is important because it shows that coherent acoustic plasmon cavity modes are not limited to the highest-quality exfoliated graphene devices. Here, the team uses CVD graphene, a form of graphene that is more suitable for scalable fabrication. This opens a route toward compact, frequency-selective terahertz detectors based on engineered graphene cavities. Such devices could eventually contribute to terahertz imaging, spectroscopy, on-chip sensing, and next-generation communication technologies. The work also highlights the broader potential of polaritonic engineering: instead of detecting terahertz light only through direct absorption, the device uses strongly confined light–matter waves to concentrate energy into nanoscale regions and convert it into an electrical signal. Collaboration and visualisation The study was carried out by an international team including researchers from Ca’ Foscari University of Venice, ICFO, the University of Ioannina, Queen Mary University of London, the University of Manchester, INMA-CSIC/University of Zaragoza and other collaborators. The visual concept accompanying the work was created by David Alcaraz Iranzo, who represented the acoustic plasmons as colourful waves bouncing through a graphene cavity, helping translate a highly nanoscale physical process into an intuitive image. For SUPERVenice, the publication reflects the hub’s mission to connect advanced materials, photonics and emerging device concepts, bringing fundamental discoveries closer to future technologies. The full article can be found at the following link: https://pubs.acs.org/doi/10.1021/acsphotonics.6c00272

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