Dielectric screening versus geometry deformation in two-dimensional allotropes of silicon and germanium

Abstract

The search for connections between electronic and structural features is a key factor in the synthesis of artificial materials for on-demand applications, with graphene and analogous elemental semimetals playing a distinguished role as building blocks of photonic and plasmonic systems. In particular, a diversity of arrangements and electronic-state dispersions is offered by currently synthesized two-dimensional allotropes of silicon and germanium, respectively known as silicene and germanene. These monolayers make the ideal playground to understand how their collective and single-particle electronic states, excited by electron or light beams, may be controlled by geometry rather than doping or gating. Here, we provide such a study using time-dependent density-functional theory, in the random-phase approximation, to identify the structural dependent properties of charge-density plasmon oscillations and optical absorption in flat to buckled silicene and germanene lattices. We further single out flat germanene as an unprecedented two-dimensional conductor, hosting Dirac cone fermions in parallel with metal-like charge carriers, which contribute to strong intraband plasmon modes and one-electron excitations in the far-infrared limit. Finally, we show how this atypical scenario can be tuned by external stress or strain.

Modeling Plasmonics and Electronics in Semiconducting Graphene Nanostrips

“…Instead, we aim to demonstrate the agreement of the refined modeling approach (see Figure 1) based now on the GW approximation with selected experimental observations. By doing so, we aim to establish its potential as an initial step in the theoretical characterization of more complex or similar systems [24][25][26].…”

Local Coordination Modulates the Reflectivity of Liquefied Si–Ge Alloys

“…Group IV-based materials constitute intriguing type of systems since they manifest a variety of crystal structures, allotropes, and polytypes with a consequent richness of related electrooptical properties. − The aforementioned abundance in structures extends to the liquid states of this class of materials; however, the high temperatures needed for accurate measurements make these liquids difficult to be analyzed experimentally, and from the modeling perspective, they exhibit complex bonding regimes that are also challenging to be handled. − It is well-known that the study of these systems has a technological relapse: Si is a mainstream material for microelectronics and photovoltaics. To diversify and enrich their properties, Ge and Si–Ge alloys are nowadays employed in many domains, enabling them to modify strain, carrier mobility, and optical band gaps, as Ge has a higher hole mobility, a smaller band gap, and a larger lattice parameter than Si. − Understanding the complete range of physical properties exhibited by the Si–Ge binary system is particularly important for technological applications.…”

THz Surface Plasmons in Wide and Freestanding Graphene Nanoribbon Arrays

“…Interestingly enough, only the SP demonstrated tunability from the THz frequencies, which, in fact, is the range of the largest number of plasmonic applications. From the theoretical side, SPs in graphene and GNRs have been explored, principally, via time-dependent density functional theory (TD-DFT) plus random phase approximation (RPA) [22][23][24]. Nevertheless, this ab initio method cannot be adapted to switch a large number of carbons in wide GNRs (≥5 nm wide) as well as for the study of related electronic and plasmonic properties.…”