Germanene Monolayers Research Articles

Adsorption characteristics of amino acids on graphene and germanene using dispersion-corrected density functional theory

In the present study, we have explored the interaction of five distinct kinds of amino acid molecules namely, arginine (Arg), aspartic acid (Asp), alanine (Ala), asparagine (Asn) and histidine (His) with graphene and germanene monolayers employing dispersion-corrected density functional theory . The dispersion correction incorporated in the computational methodology improves the accuracy of the results by taking into account the long range van der Waals interactions between the adsorbent and adsorbate. Using this method, the equilibrium configuration, energetic , electronic and optical properties of amino acids adsorbed on substrate have systematically been found. It is also found that arginine makes the most stable complexes with graphene and germanene in comparison to the other amino acids used in this study. Compared to graphene, germanene shows higher sensitivity to amino acids indicating that germanene monolayers can be useful for bio-integrated electronic devices. • A DFT –D2 study on the adsorption of five amino acids on graphene and germanene. • The electronic and optical properties of different complexes have been investigated. • The interaction strength of amino acids with graphene and germanene is different. • Compared to graphene, germanene shows higher sensitivity to amino acids. • A large dipole moment between the amino acid and germanene is generated.

Interaction of Ge with single layer GaAs: From Ge-island nucleation to formation of novel stable monolayers

In this study, reactivity of single-layer GaAs against Ge atoms is studied by means of ab initio density functional theory calculations. Firstly, it is shown that Ge atoms interact quite strongly with the GaAs layer which allows the formation of Ge islands while it hinders the growth of detached germanene monolayers. It is also predicted that adsorption of Ge atoms on GaAs single-layer lead to formation of two novel stable single-layer crystal structures, namely 1H-GaGeAs and 1HA-GaGeAs. Both the total energy optimizations and the calculated vibrational spectra indicate the dynamical stability of both single layer structures. Moreover, although both structures crystallize in 1H phase, 1H-GaGeAs and 1HA-GaGeAs exhibit distinctive vibrational features in their Raman spectra which is quite important for distinguishing the structures. In contrast to the semiconducting nature of single-layer GaAs, both polytypes of GaGeAs exhibit metallic behavior confirmed by the electronic band dispersions. Furthermore, the linear-elastic constants, in-plane stiffness and Poisson ratio, reveal the ultra-soft nature of the GaAs and GaGeAs structures and the rigidity of GaAs is found to be slightly enhanced via Ge adsorption. With their stable, ultra-thin and metallic properties, predicted single-layer GaGeAs structures can be promising candidates for nanoscale electronic and mechanical applications.

A DFT perspective analysis of optical properties of defected germanene mono-layer

Abstract Germanene, germanium version of graphene, is a novel member in the two-dimensional (2D) materials family. In this present study, a theoretical analysis involving optical properties of defected free standing (FS) germanene layer has been performed within density functional theory (DFT) framework. FS buckled germanene exhibits many fascinating and unconventional optical properties due to introductions of adatoms and voids. Arsenic (As), gallium (Ga) and beryllium (Be) are chosen as doping elements. Doping sites (same or different sub-lattice positions) play a crucial role to improve various optical properties. While Be doping, concentrations of Be are increased up to 18.75 % and void concentrations are increased up to 15.62 % (keeping fixed 3.12 % Be concentration). Emergence of several plasma frequencies occur in case of both parallel and perpendicular polarizations for defected germanene layers. Energy positions of peaks corresponding to maximum of imaginary parts of dielectric constants are red shifted for some As and Ga incorporated systems compared to pristine germanene. Absorption spectra peaks are more prominent for Be doped systems rather than void added systems. In addition, conductivity in infrared (IR) region is very high for the Be doped configurations in case of parallel polarization. Along with these, changes in other optical properties like refractive index, reflectivity, electron energy loss spectroscopy etc. are also analyzed briefly in this present study. We hope, this theoretical investigation may be regarded as an important tool to design novel opto-electronic tuning devices involving germanene in near future.

Adsorption characteristics of DNA nucleobases, aromatic amino acids and heterocyclic molecules on silicene and germanene monolayers

Binding of DNA/RNA nucleobases, aromatic amino acids and heterocyclic molecules on two-dimensional silicene and germanene sheets have been investigated for the application of sensing of biomolecules using first principle density functional theory calculations. Binding energy range for nucleobases, amino acids and heterocyclic molecules with both the sheets have been found to be (0.43–1.16 eV), (0.70–1.58 eV) and (0.22–0.96 eV) respectively, which along with the binding distances show that these molecules bind to both sheets by physisorption and chemisorption process. The exchange of electric charges between the monolayers and the incident molecules has been examined by means of Bader charge analysis. It has been observed that the introduction of DNA/RNA nucleobases, aromatic amino acids and heterocyclic molecules alters the electronic properties of both silicene and germanene nano sheets as studied by plotting the total (TDOS) and partial (PDOS) density of states. The DOS plots reveal the variation in the band gaps of both silicene and germanene caused by the introduction of studied molecules. Based on the obtained results we suggest that both silicene and germanene monolayers in their pristine form could be useful for sensing of biomolecules.

Tuning electronic, magnetic and optical properties of germanene nanosheet with site dependent adatoms arsenic and gallium: A first principles study

A first principles based density functional theory (DFT) has been employed to doped free standing (FS) germanene mono-layer by arsenic (As) and gallium (Ga). It has been revealed that electronic, magnetic and optical properties can be tailored by either (a) type, (b) concentration and (c) choosing specific sites of substitutional doping elements or suitable combinations of them. As a result, one can tune the splitting of Dirac cones at or near Dirac K point by proper doping. In particular, similar type doped structures indicate transition from semi-metallic to metallic region. Besides, induced magnetism for double doping in FS germanene can be traced back to the 4p level electrons in spin-polarized projected density of states. Optical property analysis predicts that values of static dielectric constant (ε1(0)) and refractive index (n(0)) are enhanced significantly than pristine layer by proper doping in case of parallel polarization. Optical conductivity study elucidates the fact that, height of maximum peak is amplified by 5.50% than pristine system for double Ga doping at non-equivalent site. We strongly believe that this investigation of electronic, optical and magnetic properties of doped germanene nanosheet might be useful as a powerful tool for next generation germanene based nano-technology.

Floquet edge states in germanene nanoribbons.

We theoretically demonstrate versatile electronic properties of germanene monolayers under circularly, linearly, and elliptically polarized light. We show for the high frequency regime that the edge states can be controlled by tuning the amplitude of the light and by applying a static electric field. For circularly polarized light the band gap in one valley is reduced and in the other enhanced, enabling single valley edge states. For linearly polarized light spin-split states are found for both valleys, being connected by time reversal symmetry. The effects of elliptically polarized light are similar to those of circularly polarized light. The transport properties of zigzag nanoribbons in the presence of disorder confirm a nontrivial nature of the edge states under circularly and elliptically polarized light.

Germanene: a new electronic gas sensing material

The structural stability and electronic properties of the adsorption characteristics of several toxic gas molecules (NH3, SO2and NO2) on a germanene monolayer were investigated using density functional theory (DFT) based on anab initiomethod.

First-principles electronic functionalization of silicene and germanene by adatom chemisorption

This study presents first-principles results on the electronic functionalization of silicene and germanene monolayers by means of chemisorption of adatom species H, Li, F, Sc, Ti, V. Three general adatom-monolayer configurations are considered, each having its distinct effect on the electronic structure, yielding metallic or semiconducting dispersions depending on the adatom species and configuration. The induced bandgap is a (in)direct Γ gap ranging from 0.2 to 2.3eV for both silicene and germanene. In general the alternating configuration was found to be the most energetically stable. The boatlike and chairlike conformers are degenerate with the former having anisotropic effective carrier masses. The top configuration leads to the planar monolayer and predominately to a gapped dispersion. The hollow configuration with V adatoms retains the Dirac cone, but with strong orbital planar hybridization at the Fermi level. We also observe a planar surface state the Fermi level for the latter systems.

Spin transport in silicene and germanene

In this article, we have investigated spin polarized electronic transport in two dimensional sheet materials of silicon and germanium, such as, monolayer silicene and germanene, using semi-classical Monte-Carlo approach. Monte-Carlo simulations are used to model spin transport along with spin density matrix calculations in the devices. Dephasing of the spin vectors in silicene and germanene are due to primarily D'yakonov–Perel (DP) and Elliott–Yafet (EY) relaxation mechanisms. But, as silicene and germanene has high carrier mobility the latter one is not the dominant relaxation mechanism. In this work, we studied spin polarized transport along the length of the planar monolayer silicene, buckled monolayer silicene and germanene monolayer structure and the spin dephasing length is estimated to be in the range of 0.5 μm for silicene and 1.5 μm for germanene. We also investigated the ensemble averaged spin vector variation along the length of the planar and buckled monolayer silicene and germanene with varying temperature. Finally, we studied the effect of variation of vertical electric field (Ez) on spin dephasing length in silicene buckled monolayer structure. Silicene and germanene show significant potential for future nanoelectronics devices.