CHIMERA · Characterising Heterostructures and Integrated Methodologies for Electronic Real-time Analysis in 2D Materials

Characterising Heterostructures and Integrated Methodologies for Electronic Real-time Analysis in 2D Materials

The continued scaling of silicon-based electronics is approaching fundamental physical limits in terms of power dissipation, leakage currents, and device miniaturisation. As outlined in the European Chips Act and the broader Digital Europe programme, securing technological sovereignty in advanced semiconductor technologies is a strategic priority for the European Union. Within this landscape, two-dimensional (2D) transition metal dichalcogenides (TMDCs), and MoS2 in particular, have emerged as one of the most promising material classes for next-generation nanoelectronics. Their atomically thin geometry, tunable band gap, and compatibility with flexible substrates make them attractive candidates for ultra-low-power field-effect transistors (FETs), optoelectronic devices, and sensor architectures. Despite remarkable progress in the synthesis and device integration of 2D materials, a critical bottleneck persists: the absence of experimental methodologies capable of probing the electronic structure of a working device in real time. Standard characterisation techniques such as photoemission spectroscopy, transport measurements, and electron microscopy either operate under conditions incompatible with device operation or provide only indirect information on the electronic states that govern charge transport. This gap between materials characterisation and device-level understanding limits our ability to rationally optimise 2D transistors and, ultimately, to translate laboratory-scale results into industrially relevant technology. The CHIMERA project (Characterising Heterostructures and Integrated Methodologies for Electronic Real-time Analysis in 2D Materials) was conceived to bridge precisely this gap. Its overarching goal was to establish a synchrotron-based, in-operando spectroscopic methodology that would enable the direct correlation between the electronic structure of MoS2 thin films and the electrical performance of FET devices built from them. The project was structured around three interconnected scientific objectives. Objective O1: addressing the materials foundation of the project. Any meaningful in-operando study requires films whose structural quality and electronic properties are well understood and reproducible. IJD was chosen as the primary deposition technique because of its unique advantages: it operates at room temperature, preserves the stoichiometry of the target material, and is inherently scalable to large areas. These are features that distinguish IJD from conventional chemical vapour deposition (CVD), which requires high substrate temperatures, and from mechanical exfoliation, which yields only micron-scale flakes. The scientific challenge was to demonstrate that IJD-grown MoS2 films, after moderate thermal processing, can attain the electronic quality of their CVD-grown or exfoliated counterparts. Soft X-ray absorption spectroscopy (XAS) at the S L2,₃ and Mo M2,₃ edges was selected as the primary characterisation tool, since these edges directly probe the S 3p–Mo 4d hybridised states that define the conduction band of MoS2 and are exquisitely sensitive to crystallinity, dimensionality, and defect density. Objective O2: quantifying 2D-FET performance via in-operando synchrotron spectroscopy. The second objective represented the methodological core of CHIMERA. The idea was to apply photon-in / photon-out spectroscopic techniques — specifically X-ray excited optical luminescence (XEOL) and soft X-ray reflectivity — to MoS2-based FETs while the transistors were electrically biased, thereby tracking changes in the electronic structure as the device switches between ON and OFF states. This approach exploits the element specificity of synchrotron radiation (allowing one to isolate, for example, the Mo 4d conduction band contribution) and the non-destructive character of photon-based probes, which unlike electron-based techniques do not induce charging artefacts in insulating device stacks. The experiments were designed for the BEAR beamline at Elettra, which provides tunable soft X-ray radiation combined with an ultra-high-vacuum experimental chamber equipped with reflectometry, luminescence detection, and electrical feedthroughs for simultaneous device biasing. Objective O3: engineering logic gates with ultra-low energy dissipation. The third objective was planned to build on the knowledge acquired in the first two phases by fabricating and characterising elementary logic circuits (inverters) based on optimised MoS2 FETs, with the ultimate aim of demonstrating measurable reductions in switching energy. The project sits at the intersection of two major European policy priorities. First, it contributes to the objectives of the European Green Deal by advancing the development of energy-efficient electronic devices based on 2D materials, which promise switching energies orders of magnitude lower than conventional silicon CMOS at equivalent gate lengths. The ultra-thin body of 2D channels virtually eliminates short-channel effects, one of the primary sources of standby power dissipation in scaled transistors. Second, the project aligns with the Europe for the Digital Age strategy and the European Chips Act by strengthening the knowledge base in advanced semiconductor technologies within European research institutions and by developing characterisation tools that are directly applicable to the quality control and process optimisation of next-generation semiconductor materials. The global market for 2D materials is projected to grow substantially in the coming decade, driven by applications in flexible electronics, sensing, and energy storage. Within this landscape, Europe holds a strong position in fundamental materials science and synchrotron-based characterisation infrastructure (with facilities such as Elettra, ESRF, DESY, Diamond, and SOLEIL), but faces a persistent challenge in translating laboratory discoveries into scalable manufacturing processes. CHIMERA addressed this translation challenge directly: by combining a scalable deposition technique (IJD) with an advanced, non-destructive characterisation methodology (in-operando synchrotron spectroscopy), the project aimed to create a feedback loop between process optimisation and device-level electronic structure understanding that is essential for rational materials engineering. The collaborative network established during the project, spanning UNIMORE, CNR-IOM (Trieste), Charles University (Prague), Humboldt-Universität zu Berlin, CNR-IMEM (Parma and Trento), the University of Rochester, the Université Libre de Bruxelles, and the University of Genova, further amplifies the potential for long-term impact by embedding the project’s methodological advances within a broad, interdisciplinary European and international research ecosystem. The scientific results are being disseminated through peer-reviewed open-access publications and will continue to generate follow-up studies (notably on in-operando reflectivity and spectroscopic ellipsometry of MoS2 FETs) beyond the formal duration of the fellowship, ensuring a sustained pathway from fundamental insight to technological application.

Data: CORDIS, © European Union