Periodic Reporting for period 1 - FAJANS (Effective fabrication of 2D TMDs with the aid of in-situ microscopy)
Reporting period: 2023-09-01 to 2025-09-30
Janus 2D TMDs (Janus two-dimensional transition metal dichalcogenides) represent an innovative class of 2D materials composed of a single atomic layer in which the chalcogen atoms above and below the central metal layer are different, forming an asymmetric X–M–Y structure (where M is the transition metal, such as Mo or W, and X and Y are chalcogens like S, Se, or Te). This broken out-of-plane mirror symmetry induces an internal perpendicular electric field, resulting in unique properties such as piezoelectric polarization, pyroelectricity, and Rashba spin–orbit coupling, with promising applications in sensors, photodetectors, spintronic devices, and energy conversion systems. The synthesis of these structures involves the selective substitution of one chalcogen layer in conventional TMDs through processes such as controlled sulfurization or selenization, electron beam irradiation, or thermal treatment in reactive atmospheres (such as H2S). These transformations, often influenced by strain, also modulate optical and electronic properties, making Janus materials highly versatile for future applications in nanoelectronics and catalysis.
The main goals of the project include the successful fabrication of Janus 2D TMDs and the identification of their characteristic vibrational and optical signatures. The Raman and PL studies will provide key insights into how structural defects, chalcogen substitution, and thermal processing influence material quality. These findings will help advance the understanding of the physical properties and fabrication mechanisms of Janus TMDs.
The main goals of the project include the successful fabrication of Janus 2D TMDs and the identification of their characteristic vibrational and optical signatures. The Raman and PL studies will provide key insights into how structural defects, chalcogen substitution, and thermal processing influence material quality. These findings will help advance the understanding of the physical properties and fabrication mechanisms of Janus TMDs.
Monolayer and few-layer transition metal dichalcogenides (TMDs), specifically MoSe2 and WSe2, will be prepared using mechanical exfoliation techniques. These materials will serve as the starting point for the fabrication of Janus TMD structures (MoSSe and WSSe), characterized by the presence of different chalcogen atoms on each side of the metal plane. The transformation into Janus structures will be carried out via a controlled sulfurization process using a custom-built chemical vapor deposition (CVD) system capable of delivering H2S gas as the sulfur source.
Process parameters such as temperature, gas flow rate, and reaction time will be carefully optimized to promote the selective replacement of top-layer selenium atoms while preserving the bottom-layer structure. The role of chalcogen vacancies and atomic diffusion kinetics in the transformation process will be studied to better understand the underlying thermodynamic and kinetic mechanisms.
The structural and optical properties of the resulting Janus materials will be characterized using Raman and photoluminescence (PL) spectroscopy. Raman spectroscopy is expected to reveal characteristic vibrational modes associated with Janus configurations, with stronger signals anticipated in few-layer samples compared to monolayers. PL measurements will help identify the effects of chalcogen vacancies and strain, including possible quenching phenomena and the appearance of alloy-like emission features (e.g. W(S₁₋ₓSeₓ)2) at elevated temperatures.
Process parameters such as temperature, gas flow rate, and reaction time will be carefully optimized to promote the selective replacement of top-layer selenium atoms while preserving the bottom-layer structure. The role of chalcogen vacancies and atomic diffusion kinetics in the transformation process will be studied to better understand the underlying thermodynamic and kinetic mechanisms.
The structural and optical properties of the resulting Janus materials will be characterized using Raman and photoluminescence (PL) spectroscopy. Raman spectroscopy is expected to reveal characteristic vibrational modes associated with Janus configurations, with stronger signals anticipated in few-layer samples compared to monolayers. PL measurements will help identify the effects of chalcogen vacancies and strain, including possible quenching phenomena and the appearance of alloy-like emission features (e.g. W(S₁₋ₓSeₓ)2) at elevated temperatures.
The research is expected to produce significant scientific and technical results in the field of two-dimensional (2D) materials, particularly Janus transition metal dichalcogenides (TMDs). Through the mechanical exfoliation of classical TMD monolayers followed by controlled sulfurization processes, the project will aim to establish a reliable route for fabricating Janus 2D materials, characterized by asymmetry across the vertical axis and an internal electric dipole. These materials offer unique electronic and optical properties arising from broken mirror symmetry and chalcogen substitution. Raman and photoluminescence spectroscopy will be employed to monitor the evolution of structural, vibrational, and excitonic features, allowing the study of strain effects, vacancy formation, and the interaction between defect states and photoelectronic behavior. The outcomes of this work are expected to contribute directly to global’s knowledge base in advanced materials, supporting innovation in nanoelectronics and optoelectronics. To ensure the future uptake and impact of these results, further research will be needed to scale the methods developed, improve material uniformity, and integrate Janus TMDs into device architectures. Access to pilot fabrication facilities, financial support for demonstrators, and collaboration with industry stakeholders will be crucial. Intellectual property protection and alignment with regulatory and standardisation frameworks—especially those linked to material safety and environmental compliance—will also play a vital role in successful technology transfer and commercialisation. Overall, the project will support objectives of scientific excellence, technological innovation, and sustainability.