PtSe_{2} is a van der Waals material transitioning from an indirect band gap semiconductor to a semimetal with increasing thickness. Its absorption threshold has been conjectured to originate from interband indirect transitions. By quantitative comparison between broadband (0.8-3.0 eV) optical absorption of high-quality exfoliated crystals and DFT ab initio simulations, we prove instead that the optical absorption arises only from direct transitions. This understanding allows us to shed light on the semiconductor-to-semimetal transition in an emblematic strongly thickness-dependent 2D material, and to explore the effect of stacking and excitons on the optical absorption.

Raman spectroscopy is widely used to assess the quality of 2D materials thin films. This report focuses on P t S e 2 , a noble transition metal dichalcogenide which has the remarkable property to transit from a semi-conductor to a semi-metal with increasing layer number. While polycrystalline P t S e 2 can be grown with various crystalline qualities, getting insight into the monocrystalline intrinsic properties remains challenging. We report on the study of exfoliated 1–10 layers P t S e 2 by Raman spectroscopy, featuring record linewidth. The clear Raman signatures allow layer-thickness identification and provides a reference metrics to assess crystal quality of grown films.

Raman thermometry is a powerful technique for sub-microscale thermal measurements on semiconductor-based devices, provided that the active region remains accessible and is not obscured by metallization. Since pure metals do not exhibit Raman scattering, traditional Raman thermometry becomes ineffective in such cases. To overcome this limitation, we propose the use of atomically thin Two-Dimensional materials as local temperature sensors. These materials generate Raman spectra at the nanoscale, enabling highly precise absolute surface temperature measurements. In this study, we investigate the feasibility and effectiveness of this approach by applying it to power devices, including a calibrated gold resistor and an SiC Junction Barrier Schottky (JBS) diode. We assess the processing challenges and measurement reliability of 2D materials for thermal characterization. To validate our findings, we complement Raman thermometry with thermoreflectance measurements, which are well suited for metallized surfaces. For example, on the serpentine resistor, Raman thermometry applied to the 2D material yielded a thermal resistance of 22.099 °C/W, while thermoreflectance on the metallic surface measured 21.898 °C/W. This close agreement suggests good thermal conductance at the metal/2D material interface. The results demonstrate the potential of integrating 2D materials as effective nanoscale temperature probes, offering new insights into thermal management strategies for advanced electronic components. Additionally, thermal simulations are conducted to further analyze the thermal response of these devices under operational conditions. Furthermore, we investigate two 2D material integration methods, transfer and direct growth, and evaluate them through measured thermal resistances for the SiC JBS diode, highlighting the influence of the deposition technique on thermal performance.

Layered platinum diselenide (PtSe₂) grown by molecular beam epitaxy provides a reliable and reproducible alternative to mechanical exfoliation, making it suitable for scalable device integration. In this work, we thoroughly investigate the in-plane thermal conductivity of multilayer suspended PtSe ₂ membranes. For this study, we first achieved the transfer of large-scale epitaxially grown PtSe ₂ and demonstrate a highly efficient process that enables the fabrication of multiple suspended membranes in a single transfer while maintaining the structural quality of the material. Optothermal Raman Technique is then used to investigate the in-plane thermal conductivity of the suspended PtSe₂ membranes. This approach leverages millimeter-scale transfer to conduct systematic ORT measurements, enabling statistical refined thermal conductivity of 11.92 ± 1.78 W·m ⁻¹ ·K ⁻¹ , with negligible dependence on vacuum/air environments. Finally, our results are supported by numerical simulations using a COMSOL model. This work provides significant insights into the thermal properties of PtSe₂, paving the way for the design of high-performance electronic devices with enhanced thermal management capabilities.