From optical response to thermal properties: investigating Xenes and their heterostructures

The dimensional reduction enabled by the advent of 2D materials has opened new routes in materials science and nanotechnology. Among these, group IV Xenes - graphene-like monoelemental lattices - have attracted considerable attention due to their unique properties [1] and inherent compatibility with existing semiconductor technology. However, their high chemical reactivity and strong hybridization with native substrates have posed substantial challenges to their integration, as exemplified by silicene on Ag and stanene on Al2O3. While the metallic nature of Ag leads to pronounced hybridization effects in silicene [2], the chemical reactivity of tin on Al2O3 results in oxidation [3]. For these reasons, the concept of Xene-based heterostructures gains a certain relevance [4]. Vertical stacking of atomically thin crystals offers a promising strategy to create novel architectures with tunable electronic properties, analogous to van der Waals heterostructures. Such stacks provide unprecedented freedom for exploring new functionalities. Here, we investigate the optical properties of Xene-based configurations, including silicene-stanene on Ag(111) and stanene-graphene on Al2O3(0001), through optical and Raman spectroscopy. Our results reveal the critical role of interlayers in electronically and chemically decoupling Xenes from their native substrates, enabling unique responses when layers are combined. For stanene on graphene, X-ray photoelectron spectroscopy demonstrates the ability of graphene to prevent tin oxidation, while optical analysis reveals a distinct optical response compared to direct stanene growth on Al2O3 [5]. In the case of silicene on stanene, opto-thermal Raman studies highlight differences in heat transport between individual Xenes and their heterostructures [6]. Additionally, this approach allows us to extract effective values for the thermal conductivity and interfacial thermal conductance of silicene, which are crucial parameters for thermal management in integrated circuits [7]. [1] A. Molle et al., Nat. Mater., 2017, 16, 163–169. [2] E. Cinquanta et al., Phys. Rev. B - Condens. Matter Mater. Phys., 2015, 92, 165427. [3] C. Grazianetti et al., ACS Appl. Nano Mater., 2021, 4, 2351–2356. [4] D. S. Dhungana, et al., Adv. Funct. Mater., 2021, 31, 2102797. [5] E. Bonaventura et al., 2024, Nanotechnology 35 23LT01 [6] E. Bonaventura et al., Nanoscale Horiz., 2022,7, 924-930. [7] E. Bonaventura, et al., Adv. Opt. Mat., 2024, 12.33: 2401466.