Germanene Nanoribbons Research Articles

Tuning the electro-optical properties of germanene nanoribbons by boron atom substitution for application in information transmission

Germanene nanoribbons, a one-dimensional material, have great potential for future technological applications. This research aims to investigate the electro-optical properties of boron-doped germanene nanoribbons with a width of five atoms. The theory used in this study is density functional theory (DFT). The original system is a narrow band gap semiconductor, with a gap size of 0.06[Formula: see text]eV. The doped configurations, which retain the honeycomb hexagonal structure, are stable and metallic in nature. The introduction of B atoms flattens the configuration, leading to a partial charge shift from Ge to B. The absorption peaks in the 3B and 5B configurations occur in the frequency range less than 500[Formula: see text]nm, indicating good absorption of visible light, and suggesting possible applications in light-sensitive components. Notably, the real part of the dielectric function’s 0z component is negative, offering immense potential for optical, microwave and communication applications.

Computational Modeling, Simulation and Tight–Binding Analysis of Electronic Characteristics of Defective Germanene Nanoribbons for Future Applications of High Sensitivity Ge-Based Nanosensors

In this research, the electronic characteristics of germanene sheet and nanoribbons using the computational modeling, simulation and tight binding approximation are investigated. Our analysis is focused on the pristine sheet of germanene as well as defective monolayer. The obtained results show that applying the Stone–Wales defect into the germanene monolayer changes the energy band structure. The E-k curves around the Dirac point are no longer linear, in which a band gap is opened, and the Fermi velocity is reduced. Furthermore, the main parameters such as density of states, carrier concentration in degenerate and non-degenerate limits, carrier effective mass, conductance and AC conductivity of germanene are analytically modeled with the inclusion of the spin–orbit coupling effect, temperature and ribbon width. Obtained results demonstrate that the inclusion of the spin–orbit coupling makes a small splitting of the energy levels and creating a small band gap. Finally, the Tight binding and computational values are compared with our simulation results and available data, and a rational agreement is reported in terms of trend and value. The findings of this study provide theoretical reference for the design of germanene-based nanosensors and optoelectronic devices.

Significant enhancement in thermoelectric performance of S-shaped germanene nanoribbon devices

Due to the advantages including high efficiency and environmental friendliness, the two-dimensional thermoelectric materials have received huge attention. However, the energy conversion efficiency is not high enough for application. In this work, we have theoretically investigated the thermoelectric performance for both zigzag (ZGeNRs) and armchair (AGeNRs) germanene nanoribbons with edge defects by nonequilibrium Green's function method. For perfect germanene nanoribbons (GeNRs), it is shown that with its width increasing, the maximum of ZT values (ZTmax) decreases monotonously while the phononic thermal conductance increases linearly. For both ZGeNRs and AGeNRs, with increasing defect numbers in longitudinal direction, ZTmax increases monotonously while the phononic thermal conductance decreases. In particular, by introducing periodic defects, the ZTmax of both ZGeNRs and AGeNRs has been raised to above 2, which is due to higher Seebeck coefficient and lower thermal conductance. Our findings provide an effective way to enhance thermoelectric performance, which is beneficial for the design of ultra-thin thermoelectric devices.

Potential optoelectronic applications of C and Si-doped germanene nanoribbons

In this study, C and Si atoms were doped into armchair germanene nanoribbons (AGeNRs) to investigate their electro-optical properties for future applications. The method employed for this investigation is Density Functional Theory (DFT). The initial configuration of AGeNRs exhibits a non-planar structure with a buckling of approximately 0.73 Å. Among the eight doping configurations examined, the 1:1 C-doped configuration is the most stable, resulting in a flattened structure, an extended band gap of up to 1.91 eV, and optimal suitability for optoelectronic applications. Additionally, the 1:3 C-doped configuration and all Si-doped configurations exhibit an extended band gap, making them suitable for room-temperature field-transistor applications. The electronic and optical properties, including PDOS, charge density difference, jDOS, refractive index, absorption coefficient, and dielectric function, of the most optimal configurations are also analyzed and compared with the original configuration to determine differences.

Electronic and transport properties of boron and nitrogen doped germanene nanoribbons: A first principles study

We have studied the electronic properties of pristine zigzag germanene nanoribbons (ZGeNRs) using ab initio method. The effect of boron and nitrogen doping on electronic properties of ZGeNRs at two different edge sites is also calculated. It is observed that the H-terminated pristine ZGeNRs exhibit semi-metallic behavior while the ZGeNRs doped with boron and nitrogen shows the metallic behavior. The electron density calculation shows that the density is low in pristine ZGeNRs while it is high in the doped ZGeNRs. The transmission coefficient analysis also suggests the same. As the transmission is sensitive to doping, hence, ZGeNRs have potential application in nanoelectronics devices.

Эластопроводимость германеновых нанолент с изоморфными дефектами замещения

The results of the theoretical study of the impurity germanium nanoribbons piezoresistance are demonstrated in this article. The nanomaterial contains point isomorphic substitution defects of different concentrations of two types of isomorphic atoms of group IV: silicon (Si) and tin (Sn). The functions of the dependence of the longitudinal component of the elastic conductivity tensor on the magnitude of the strain of tension (compression), types and concentrations of defects are presented to study the characteristics of the piezoresistance effect. The results of the calculations show a qualitative agreement of the behavior of the piezoresistance constant of germanene nanoribbons for two types of isomorphic defects and with the literature data. Quantitative analysis allows us to conclude that the longitudinal component is higher in modulus in nanofilms with tin impurities, which indicates a more pronounced piezoresistance of the material. Conclusions are showed, that the impurity germanene with the tin atoms manifested more pronounced piezoresistance properties. It was be explained by high the electron mobility of the valence shell of this element compared to the germanium atom. This shell of the atom turns out to be more sensitive to deformations of the structure. Such material can be more effectively integrated as a basic element of semiconductor electronics devices due to the high susceptibility of its properties to the effects of deformations and the concentration of structural defects in accordance with this factor.

Boron-doped armchair germanene nanoribbons with a width of six atoms in an external field: a DFT study

Density functional theory (DFT)has been used to study the structure and electronic properties of boron-doped armchair germanene nanoribbons materials. The doped configurations are all stable in the electric field by the σ bond and the π bond. The doped structures can be semi-conductive or semi-metallic depending on the doping substitution positions. The doping configuration B:Ge = 1:1 proved to be superior and stable in the electric field, and the doping changed this structure to become planar. With three different directions of electric field, the horizontal electric field has the most influence on the geometric structure, multi-orbit hybridization as well as the spatial charge distribution of the doped systems. The magnetization of the systems changes with the changing direction of an electric field, anti-ferromagnetic structures are found in meta-configuration and ortho-configuration with longitudinal electric fields, and 1-1 configuration with perpendicular electric fields and horizontal electric fields. The ortho-configuration with an electric field of 0.5V/m with an extended band gap of 0.69eV is perfectly applicable in room-temperature field-effect transistors; other configurations have potential in nanoscale applications.

Structural and electronic properties of hydrogen - functionalized armchair germanene nanoribbons: A first-principles study

Structural and electronic properties of armchair germanene nanoribbons functionalized by hydrogen atoms (H-AGeNR) are studied through density functional theory (DFT) method. The DFT quantities for analyzing the structural and electronic properties are fully developed through the DFT calculations, including the functionalization energy, relaxed geometric parameters, orbital- and atom-decomposed energy bands, electronic density of states, charge density, and charge density difference. Under hydrogen functionalization, the functionalization energy is achieved at -2.59 eV, and the structural parameters are slightly distorted. This provides evidence of good structural stability of the functionalized system. Besides, the very strong bonds of H-Ge are created because the electrons are transfered from Ge atoms to H adatoms, which induces hole density in the functionalized system, which is regarded as p-type doping. As a result, the π bonds of 4pz orbitals at low-lying energy are fully terminated by the strong H-Ge covalent bonds, in which the strong hybridizations of H-1s and Ge-(4s, 4px, 4py, and 4pz) orbitals have occurred at deep valence band. The termination of π bonds leads to the opened energy gap of 2.01 eV in the H-functionalized system that belongs to the p-type semiconductor. The enriched properties of the H-functionalized system identify that the H-functionalized system...

Band structures and electronic properties of edge-functionalized germanene nanoribbons

Free-standing germanene is a buckled 2D hexagonal semimetal with an intrinsic carrier mobility more than double that of graphene's. The germanene lattice allows for band gap opening via an applied electric field or adsorption of foreign atoms, enabling the creation of germanene based field-effect devices. While the formation of germanene nanoribbons has been shown to have a band gap, little research has been done on the electronic tunability of Ge nanoribbons. In this study, we analyzed the effect of H, C, P, As, S, Se, Te, F, Cl, Br, and I for edge-functionalization on the physical and electronic properties of germanene armchair (AGeNRs) and zigzag (ZGeNRs) nanoribbons. We found that the band gaps of AGeNRs are tunable through width and edge species, and alternate between semiconducting and semi-metallic. Through these methods the band gap can be tuned to any IR spectral band, while ZGeNRs are shown to be nodal semimetals at small atomic widths but transition to metallic behavior at large widths. This work indicates that the functionalized germanene nanoribbons are promising quantum materials with tunable band structures and electronic properties.

A DFT study of the adsorption of F atoms on germanene nanoribbons

In the paper, we investigate the structure and electronic properties of the pristine germanene nanoribbon and four adsorption configurations of 1F and 2F on the substrate of germanene nanoribbon. We obtained the parameters of the most stable structures of pristine germanene nanoribbon and four adsorption configurations. The band structure and the density of state and the part density of state for each element were also obtained. Findings show the adsorption configuration of 1F-GeNR.bridge has no band structure, while other configurations are semimetals with band gap from 0.175eV to 0.67eV; both four adsorption configurations are chemisorption and non-magnetic. The charge distribution of all configurations also was investigated; it showed that there is a charge shift from Ge atoms towards F atoms due to their electronegativity difference.

Feature-rich structural and electronic properties of halogen-functionalized germanene nanoribbons: A DFT study

Structural and electronic properties of halogen (F, Cl, Br, I, and At)-functionalized armchair germanene nanoribbons (AGeNR) are investigated using the density functional theory (DFT) method. The first-principles quantities are fully developed to determine the studying properties, including the functionalized energies, optimal structural parameters, atom- and orbital-decomposed electronic band structures and density of states, charge density, and charge difference. The halogen-functionalized structures achieve good stability that is determined by the calculated functionalized energies. The pristine AGeNR presents a direct bandgap located at the band-edge states of 0.23 (0.36) eV that opens at 0.76 (1.38) eV under the F-functionalization as calculated by PBE (HSE06) functionals, respectively. The opened bandgaps of 0.73 eV and 0.51 eV are found in the Cl-AGeNR and Br-AGeNR. In contrast, the bandgap is shrunk/destroyed in the I-AGeNR/At-AGeNR, respectively. Besides, a case study of F-functionalized zigzag germanene nanoribbons (F-ZGeNR) is also investigated to compare with the AGeNR case. As a result, the opened bandgap is much larger in the F-AGeNR case than that in the F-ZGeNR case. This indicates that the electronic properties are better enhanced in the AGeNR than that in the ZGeNR. The bandgap-diversified mechanism is due to the termination of free-standing π bonds and complex orbital hybridization in halogen-Ge bonds. Under halogen functionalizations, electrons are transferred from Ge atoms to halogen adatoms that create free holes in the functionalized systems that can be regarded as p-type semiconductors/semimetals. The diverse structural and electronic properties of halogen-functionalized GeNR will be very potential 1D materials for various electronic applications.

Electric field induced pure spin-photo current in zigzag stanene and germanene nanoribbons

The spin-photo current in single layer stanene and germanene under a linearly polarized light is theoretically investigated based on the tight-binding Hamiltonian combined with the nonequilibrium Green’s function at room temperature. The results show that by considering the simultaneous effect of the linear illumination and a vertical external electric field without any magnetic exchange element, pure spin-photo current without charge current is generated in two-dimensional lattices with a large intrinsic spin–orbit coupling. The necessity of enhanced spin life-time for detection of spin polarization can be explained by spin-valley locking concept. Spin-valley locking arises in buckled two-dimensional materials as a result of the large spin–orbit coupling and electric-field reversible valley spin polarization. Equal absorption of the linearly illumination at both valleys with different spin polarization, leads to pure spin-photo current injection. In addition, an acceptable photoresponsivity has been reported in a broad range of photon energy. The numerical results indicate high quantum efficiency with a maximum of nearly 83% and 50% for stanene and germanene, respectively. This work may pave theoretical reference toward design of new spin-optoelectronic devices based on satanene and germanene junctions with high performance.

The Magnetic and Thermally-Induced Spin-Related Transport Features Using Germanene Nanoribbons With Zigzag and Klein Edges

The current work employs the first-principles computations and non-equilibrium Greens function to investigate the magnetic and thermally-induced spin-related transport features using germanene nanoribbons with zigzag and Klein edges (ZKGeNRs). It was demonstrated that the ZKGeNRs with various widths (N) are placed in various spin-resolved electronic states. By increasing the width parameter N from 4 to 9, the ZKGeNRs moves from an indirect-gap bipolar magnetic semiconducting state (BMS) to bipolar spin gapless semiconductor (BSGS), and finally to ferromagnetic metal (FM). Moreover, since the right and the left temperatures of the ZKGeNRs device are different, the spin-up and spin-down currents flow in reverse orientations, demonstrating the spin-dependent Seebeck effect (SDSE). Besides, the threshold temperature decreases as N increases and then disappears, while the spin currents increase as N increases. Simulation results indicated that the ZKGeNRs could be an appropriate choice for spin caloritronic devices and could be utilized in future low-power consumption applications.

Al doping in germanene nanoribbons in the presence of an external electric field

Germanene by description, is a two-dimensional material with many different properties from graphene. Germanene also has a honeycomb hexagonal form but it is not a planar structure. Germanene nanoribbons (GNRs) are created from germanene with edges that have been changed by other atoms; in this study, two of the GNRs’ edges have been modified by hydrogen. The density of states (DOS), energy formation, and band structure of the system are computed, displayed, and studied using density functional theory (DFT). Due to the presence of hydrogen at the two edges, GNRs have a narrow band gap. This research will look into Al doping in GNRs with the system being immersed in a 0.5V/Angstrom external electric field. Two configurations are examined in this section: the top configuration and the valley configuration. The doped configurations do not break up in the electric field, and both configurations become semi-metals with bands crossing the Fermi level. This research lays the groundwork for future applications in nanochip technology

DNA/RNA sequencing using germanene nanoribbons via two dimensional molecular electronic spectroscopy: an ab initio study.

Developing fast, reliable, and cost effective, yet practical DNA/RNA sequencing methods and devices is a must. In this regard, motivated by the recently introduced two-dimensional electronic molecular spectroscopy (2DMES) technique for molecular recognition, and the compatibility of 2D layers of group IV elements with the current technology of manufacturing electronic devices, we investigate the capability of germanene nanoribbons (GeNRs) as a feasible, accurate, and ultra-fast sequencing device under the application of 2DMES. We show that by employing 2DMES, not only can GeNRs unambiguously distinguish different nucleobases to sequence DNA/RNA, they are also capable of recognizing methylated nucleobases that could be related to cancerous cell growth. Our calculations indicate that, compared to frequently used graphene layers, germanene provides more distinct adsorption energies for different nucleobases which implies its better ability to recognize various molecules unambiguously. By calculating the conductance sensitivity of the system for experimental purposes, we also show that the introduced sequencing device possesses a high sensitivity and selectivity characteristic. Thus, our proposed system would be a promising device for next-generation DNA sequencing technologies and would be realizable using the current protocols of fabricating electronic devices.

Magneto-plasmons of germanene nanoribbons

Magneto-band structures of armchair and zigzag germanene nanoribbons (AGeNR and ZGeNR) are calculated by the p z -orbital tight-binding model including the spin–orbit coupling (SOC). Magnetic field induces spin splitting leading to a change in energy dispersion and band-gap. Band-gap decreases with increasing magnetic field for AGeNRs, whereas it increases for ZGeNRs. Low-frequency plasmon is further studied within the random-phase-approximation. At zero field and temperature, plasmon emerges just in small-gapped AGeNRs but is weakened due to Landau damping for sufficiently small or large transferred momentum. With increasing magnetic field, frequency and peak height of plasmon are reduced, showing strongly field-dependent dispersion relations. On the contrary, plasmon frequency of large-gapped AGeNRs rises with increasing magnetic field. Moreover, magneto-plasmons of large-gapped AGeNRs are more sensitive to a change in temperature than small-gapped ones. Regarding ZGeNRs, magnetic field cannot induce low-frequency plasmon at zero temperature. As temperature increases, plasmon frequency increases and dispersion relation exists within a wider range of momentum. While magnetic field increases, changes in energy dispersion and band-gap reduce plasmon frequency. Magneto-plasmons of GeNRs at various temperatures, due to the SOC, exhibit rich features which are also profoundly related to geometric structures. • With increasing field, band-gap decreases for AGeNR but it increases for ZGeNR. • Plasmon frequency decreases (increases) for small (large) gapped AGeNR as field increases. • Magneto-plasmon of large gapped AGeNR is more sensitive to temperature than small gapped ones. • Plasmon of ZGeNR at zero field could be induced by raising temperature. • At finite temperature, plasmon frequency of ZGeNR decreases with increasing field.

Doping two boron atoms in germanene nanoribbons in an external electric field

Germanene is a two-dimensional system made of germanium atoms, its configuration is hexagonal honeycomb. Germanene nanoribbons (GNRs) are one-dimensional systems made from germanene with hydrogen-modified edges. The GNRs configuration studied here consists of 12 germanium atoms and 4 hydrogen atoms per unit cell. This work investigated the doping of two boron atoms into the unit cell of GNRs. Changing the different doping sites produces different configurations, the configurations been studied as meta-configuration, para-configuration, and ortho-configuration. By using density functional theory (DFT), the formation energies, energy band structures, and density of states of the configurations are studied. The ortho-configuration for the formation energy is the smallest, so this configuration is the most stable. The appearance of an external electric field changes the band gap and the energy band structure of the system.

Electrically Induced Dirac Fermions in Graphene Nanoribbons.

Graphene nanoribbons are widely regarded as promising building blocks for next-generation carbon-based devices. A critical issue to their prospective applications is whether their electronic structure can be externally controlled. Here, we combine simple model Hamiltonians with extensive first-principles calculations to investigate the response of armchair graphene nanoribbons to transverse electric fields. Such fields can be achieved either upon laterally gating the nanoribbon or incorporating ambipolar chemical codopants along the edges. We reveal that the field induces a semiconductor-to-semimetal transition with the semimetallic phase featuring zero-energy Dirac fermions that propagate along the armchair edges. The transition occurs at critical fields that scale inversely with the width of the nanoribbons. These findings are universal to group-IV honeycomb lattices, including silicene and germanene nanoribbons, irrespective of the type of edge termination. Overall, our results create new opportunities to electrically engineer Dirac semimetallic phases in otherwise semiconducting graphene-like nanoribbons.

A First-Principles Study of Transport Properties in Armchair Germanene Nanoribbon Field Effect Transistors Subject to Metallic Dopants

Density functional theory (DFT) in combination with non-equilibrium Green’s function (NEGF) formalism are utilized to reveal the transport properties of armchair Germanene nanoribbon field effect transistors (AGeNR-FETs) subject to metallic dopants. Due to the semiconducting nature of p-type and n-type in the AGeNRs in the presence of In and Ag/Au dopants, these atoms are used at the source/drain electrodes to make FETs and Tunneling-FETs (TFETs). The transport properties of these transistors subject to Ag, Au and In atoms are analyzed with the aid of I–VDS, I–VG characteristics and transmission spectrum. It is shown that a negative differential resistance (NDR) is observed for each structure which occurs at low bias voltages. In particular, the maximum NDR with Ip/Iv = 14.78 is observed for the AGeNR-FET. From the transfer characteristics at VDS = 0.7 V it is also observed that depending on the type of impurity and the transistor, the minimum current decreases or increases, Dirac point shifts, and on-state current decreases. In addition, the highest Ion/Ioff ratio in FET is related to Ag-AGeNR structure with the value of 49 while for TFET it is related to In-Ag-AGeNR structure with a value of 6.4.

First principle study of fluorine functionalized germanene based two probe device

The high mobility and velocity of the carriers make germanene and silicene promising materials for future electronic devices like field-effect transistors. The lack of bandgap in these materials has been a prominent hurdle in the development of electronic devices based on them. This work presents a novel method of bandgap creation in zigzag germanene nanoribbons (ZGeNRs) by using fluorine (F) atoms as the functionalizing agent. A combination of density functional theory and non-equilibrium Green's function is employed for all the calculations. Variation of bandgap and effective mass of carriers with the width of the nanoribbons is also presented. Furthermore, a study of the transmission spectrum and transmission Eigen channels substantiates the semiconducting nature of F functionalized ZGeNRs. To assess the stability of F functionalized ZGeNRs, the formation energy of the nanoribbons is evaluated. The formation energy is found to be −1.60 eV/Å. Since the formation energy of F functionalized ZGeNRs is more negative than that of its pristine counterpart, the F functionalized ZGeNR is more stable than its pristine counterpart. Such results are suggestive of the potential of F functionalized ZGeNRs for future nano-scale devices.