Optical Properties of Stanene-like Nanosheets on Al₂O₃(0001): Implications for Xene Photonics

Abstract

Stanene is one of the most intriguing two-dimensional (2D) materials because of its nontrivial topological properties. Here, the optical properties from THz to UV of molecular beam deposited tin nanosheets on Al 2 O 3 (0001) are reported. The experimental absorption coefficient cannot be described in terms of metallic tin or tin oxides. Nonetheless, a similar optical behavior was predicted by theory for freestanding stanene, thus suggesting the formation of the 2D tin nanosheets with stanene-like properties. These findings show that 2D tin bears appealing optical properties in a broad range of the electromagnetic spectrum, thus paving the way to Xenes-based nanophotonics.

The Rise of the Xenes: From the Synthesis to the Integration Processes for Electronics and Photonics

“…Furthermore, the deposited silicon, up to a maximum thickness of 7 nm, showed an anomalous optical behavior characterized by the absence of an optical bandgap at variance with amorphous or crystalline silicon. Similar investigations revealed that the optical response of tin atomically thin nanosheets does not match with that of conventional tin, either in the metallic or oxide fashion, but the absorption spectra showed spectral signatures compatible with calculated spectra of freestanding stanene considering spin-orbit coupling as reported in Figure 3b [17,57,58]. [14].…”

“…On the other hand, it is intriguing that many of these Xenes were also disclosed on other substrates thus making their existence not linked to a specific template and moreover with other growth techniques out of MBE such as chemical vapor deposition/transport (CVD/T) or even exfoliation (Figure 1c). Silicene was proved to host Dirac fermions when grown onto an insulating substrate such as Al 2 O 3 (0001) [14], stanene was deposited onto the topological insulator Bi 2 Te 3 [15], Cu(111) [16] or Al 2 O 3 (0001) as well [17], and finally antimonene was realized also on conventional semiconductors such as Ge(111) with different growth techniques [18,19]. The choice of the substrates is of paramount importance as it can determine the properties of the deposited Xene, especially via chemical interaction between the X atoms and the substrate.…”

“…The calculated optical properties of the isolated 2D silicene have revealed peculiar spectral features similar to the graphene case, in terms of absorbance, due to the linear bands and Dirac cones at low optical frequencies, while for higher photon energies interband transitions near critical points have been predicted to dominate the optical response [59]. Paradigmatic cases are the growths of 2D silicon and tin nanosheets on transparent c-Al 2 O 3 , namely (0001)-terminated Al 2 O 3 , by MBE deposition [14,17].…”

How Oxygen Absorption Affects the Al2O3‐Encapsulated Blue Phosphorene–Au Alloy

“…The O 1s core level shape progressively becomes asymmetric with a tail at higher binding energy (Figure 4a), which can be associated with hydroxyl groups (─OH) adsorption. [27] Conversely, the Al 2s core level shows a tail at lower binding energy (see Figure 4b) that is related to a residual metallic component caused by the Al 2 O 3 deposition process, which consists of a predeposition of a first Al layer to prevent oxidation of the underlying Xene. [16,19] After 3 days' exposure, both O 1s and Al 2s core levels are shifted to lower binding energy (of 0.5 and 0.6 eV, respectively; see Figure 4) and their binding energy does not change after the 20 day long exposure.…”

Dynamics of Two Distinct Exciton Populations in Methyl-Functionalized Germanane

“…Two-dimensional (2D) materials are presently one of the most actively explored platforms for the development of nanoscaled (opto)­electronic devices. − Monoelemental 2D materials (Xenes) and their substituted counterparts (Xanes, e.g., GeH or GeCH 3 ) are rapidly emerging alongside the much more well-studied transition metal dichalcogenide semiconductors because of high electron mobility, a wide range of band gaps, and the possible tuning of their morphology and physical properties. − Germanane has been proposed recently as a novel active material for optoelectronics, photoelectrocatalysis, antibacterial coating, and biosensors, with the specific performances determined by the functional groups. − …”