Tunable Electronic and Topological Properties of Germanene by Functional Group Modification

Abstract

Electronic and topological properties of two-dimensional germanene modified by functional group X (X = H, F, OH, CH3) at full coverage are studied with first-principles calculation. Without considering the effect of spin-orbit coupling (SOC), all functionalized configurations become semiconductors, removing the Dirac cone at K point in pristine germanene. We also find that their band gaps can be especially well tuned by an external strain. When the SOC is switched on, GeX (X = H, CH3) is a normal insulator and strain leads to a phase transition to a topological insulator (TI) phase. However, GeX (X = F, OH) becomes a TI with a large gap of 0.19 eV for X = F and 0.24 eV for X = OH, even without external strains. More interestingly, when all these functionalized monolayers form a bilayer structure, semiconductor-metal states are observed. All these results suggest a possible route of modulating the electronic properties of germanene and promote applications in nanoelectronics.

Electronic Structural and Optical Properties of Multilayer Blue Phosphorus: A First-Principle Study

“…The phonon spectrum is calculated using a supercell approach within the PHONOPY code [30]. From Figure 2, the dynamic stability is confirmed by the phonon spectrum calculated along the highly symmetric directions with zero strain, and the frequencies of all modes are positive over the whole Brillouin zone, indicating the structure is dynamically stable [31][32][33][34][35][36][37][38][39][40].…”

Germanium‐based monoelemental and binary two‐dimensional materials: Theoretical and experimental investigations and promising applications

“…The successful preparation of germanene, GeH, and organic functionalized germanane (GeR) has provided researchers with the opportunity to understand and further study germanene using a combination of experimental data and theoretical calculations. For example, the bandgap of germanene can be tuned by electric field and biaxial strain application, 56,57 foreign element doping, 45,47 atom or molecule adsorption, 48–55 and modification via other functional groups X (X = F, Br, I, OH) 39–44 . The existence of vacancies in germanene affects its band structure as well as optical and magnetic properties 141,142 .…”

Tight–Binding Analysis of Electronic Structure of Germanene Sheet and Nanoribbons Including Stone-Wales Defect

“…Furthermore, the buckled structure causes reduction of electron-phonon coupling strength [7]. The σ and π bonds between atoms of germanene with LB geometry are separately coupled and there is a weak π-π interaction among them [8]. Figure 1 indicates germanene as a honeycomb monolayer of Ge atoms.…”

“…Owing to the buckling, it is easier to open a band gap in germanene than in the planar graphene. Although germanene is a zero-gap semi-metallic, however by applying periodic nanoholes, chemisorption of adatom species, lateral confinement, hydrogenation, introducing uniaxial and biaxial strain, edge functionalization, doping with different impurities, organic molecule adsorption, single-side adsorption of alkali metal (AM) atoms, coupling with a substrate, applying vertical electric field, and defects it is possible to open a band gap in germanene [8][9][10][11][12]. In [3] authors have reported the dependence of the energy band gap of armchair germanene nanoribbon (AGeNR) on width of ribbon and the shape of its edges.…”