Band Gap In Graphene Research Articles

A GRAPHENE-BASED MONOPOLE MICROSTRIP ANTENNA WITH TUNEABLE BANDGAP FOR UWB IMPLEMENTATIONS

Monopole Microstrip Antennas (M-MSAs) are widely used because of their price, ease of manufacturing, and compact size, making them ideal for portable applications. Nowadays, Ultrawide Band (UWB) technology, used in wireless applications, relies on this antenna. The UWB frequency range is 3.1 to 10.6 GHz, allowing low-power wireless applications such as wireless music, personal localization, radio frequency recognition, radar, and HD video dissemination. However, this frequency band's broadness increases interference. This contribution research formulates simulates, and optimises a modified small-square M-MSA that meets UWB technology's huge bandwidth requirements. A square radiated patch, a dielectric material with a thickness of 1 mm and 4.7 relative permittivity, a partly ground plane printed on the patch's face, and a coplanar waveguide feed make up the M-MSA design. The M-MSA design is modified to reduce the patch's bottom corners and change its proportions to enable compatibility with the UWB complete band. A U-shaped aperture on the patch should be etched to produce a bandgap in UWB frequencies, reducing interference. Filling the aperture with graphene allows bandgap tunability. The graphene's bandgap dissipates with DC voltage, but without biassing, its high impedance restricts aperture current flow. The bandgap's effect is seen at 3.87-4.85 GHz. After simulation and tweaking, gain and efficiency improved significantly. The bandgap region, which was chosen to reduce interference from military fixed communications, mobile communications, unmanned aerial vehicles, short-range radio links, satellite communications, and the low band of 5G, also exhibits a significant increase in attenuation and gain degradation.

Theoretical study on structural, electronic, transport and thermoelectric properties of Si/Ge doped graphene

First-principles simulations are used in this study to show the structural, electronic, transport, and thermoelectric features of silicon and germanium-doped monolayer graphene. We employed a supercell of 2 × 2 × 1 graphene that contains 8 C atoms. One C atom was substituted by Si/Ge at a doping concentration of 12.5 %. The results obtained show that the band gap of pure graphene may be effectively opened and converted into a direct bandgap semiconductor material by replacing the C atom with Si/Ge atoms. Phonon dispersion provides a representation of the dynamical stability of all three structures. Graphene's thermal conductivity is also decreased when heteroatoms are added. Additionally, the Seebeck coefficient, the power factor, the electrical conductivity, and the figure of merit of pure, silicon, and germanium-doped graphene were investigated. This study offers a theoretical basis for using a heteroatom-doping process to improve the performance of graphene's electronic, transport, and thermoelectric characteristics.

Electron regulation and gas-sensitivity analysis of hBN-Graphene lateral heterojunctions——First principle study

In this paper, the first-principle calculations of the lateral heterojunction model synthesized by hBN-Graphene were carried out, and it was found that the bandgap of graphene varied with the change in the proportion of hBN, and the bandgap was best regulated with a bandgap of 1.177 eV when the proportion of hBN was 66.67 %. At this time, the adsorption structures of HCN, CO, NH3, and Cl2 were established and energy band calculations were performed on the hBN and Graphene portions of the hBN-Graphene lateral heterojunctions, respectively, and it was found that the adsorption of Cl2 resulted in a significant change in the band gap, which showed a very high electrical sensitivity. To further investigate the adsorption mechanism of Cl2 on the surface of hBN-Graphene lateral heterojunction, the energy band structure, PDOS, charge transfer, adsorption energy, and recovery time of each stabilized adsorption site of Cl2 on the surface of hBN-Graphene lateral heterojunction were calculated. The results show that the adsorption of Cl2 on the surface of hBN-Graphene lateral heterojunction is a stable chemisorption, and the band gap of C-Top1 increases to 1.274 eV, and the band gaps of C-Top3, N-Top1, and N-Top2 decrease to 0.684 eV, 0.376 eV, and 0.398 eV, respectively, and the changes of band gaps are significant and easy to be electrically detection. The recovery time of Cl2 on the surface of hBN-Graphene lateral heterojunction was 7.36 s–2.59 s in visible light and in the temperature interval of 273 K–283 K. The recovery time of Cl2 on the surface of hBN-Graphene lateral heterojunction was 7.36 s–2.59 s in visible light and in the temperature interval of 273 K–283 K. These findings have implications for the research and application of graphene-based Cl2 gas sensors.

Modeling Plasmonics and Electronics in Semiconducting Graphene Nanostrips

In recent decades, both academia and industry have shown noteworthy interest in investigating the semiconducting properties of graphene. Nevertheless, the lack of a suitable bandgap in graphene has restricted its practical applications in the current semiconductor industry. To overcome this limitation, graphene micro/nano-strips have been actively explored. The focus of the present study centers on modeling the electronic and plasmonic characteristics of graphene strips with varying widths: 2.7, 100, 135 nm, and 4 m. This analysis is conducted at ultralow energies (0.3 eV, or ~73 THz). We employ conventional density functional computations to estimate the Fermi velocity of graphene, refining the results via the GW approximation. Utilizing the accurate Fermi velocity, we employ a semi-analytical model to explore the ground state and plasmon properties (frequency and dispersion) of these graphene strips. Notably, this approach effectively replicates the density of states observed in narrow experimental graphene nano-strips (2.7 nm) grown on Ge(001) and, similarly, reproduces the plasmon spectrum found in synthesized graphene microstrips (4 μm) on Si/SiO2. Interestingly, our study also offers insights into the potential application of this approach in comprehending the plasmon frequency and plasmon dispersion of graphene nano-strips (~135 nm) acquired through liquid-phase exfoliation. The outcomes of this investigation present compelling evidence that the properties of graphene-based strips can be customized to fulfill specific requirements and applications. These findings hold significant promise for advancing graphene-based technologies, bridging the gap between fundamental research and tangible applications. Doi: 10.28991/ESJ-2023-07-05-01 Full Text: PDF

Topological band gap in intercalated epitaxial graphene

The study of functional manipulation of graphene is a critical subject, both for fundamental research and practical applications. In this study, we present that the intercalation of 5d transition metals into epitaxial graphene on SiC is a promising strategy for the realization of topologically nontrivial phases with a finite band gap in graphene. Employing first-principles calculations, grounded in density functional theory, we demonstrate that Re- and Ta-intercalated graphene evolve into two-dimensional topological insulators. These exhibit linear Dirac cones and quadratic bands with topological band gaps, respectively. The emergence of these topological states is attributed to the strong spin–orbit coupling strength of the intercalants. We show that the corresponding topological edge states persist within the finite bulk band gap, aligning with the bulk-boundary correspondence. Furthermore, we explore the spin splitting of the band structure, brought about by the inversion symmetry breaking and the spin–orbit coupling. Our study underscores that the intercalation of graphene is an effective and a feasible approach for manipulating the band gap and the topological nature of graphene. Such intercalated graphene systems hold potential utility for spintronics and low-dimensional quantum device applications.

Variation in the bandgap by gradual reduction of GOs with different oxidation degrees: A DFT analysis

The bandgap of two-dimensional graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO) materials is modified by the gradual incorporation and removal of functional groups on the surface of the material. In this work, using Density Functional Theory (DFT) with BIOVIA Materials Studio software, the variation of the bandgap of GO and rGO as a function of the O/C ratio has been studied. The direct relationship between the bandgap and the number of epoxide functional groups in the GO is demonstrated. A gradual increase in the bandgap from 0.211 to 3.58 eV was observed by varying the O/C ratio from 0.06 to 0.50. In the range of O/C ratios from 0.17 to 0.28, the bandgap decreased, estimating the lowest value of 0.0211 eV at O/C = 0.22 despite the increased functional groups in the material. This phenomenon is explained by the balance between the number of sp2 conducting states and the loss of linearity of the sheets due to the incorporation of functional groups. On the other hand, the GOs were reduced by gradually removing their functional groups at different O/C ratios, ranging from 0.50 to the total elimination of the epoxide functional groups. This study showed that the bandgap of the now-called rGOs varies according to two parameters: (i) the number of functional groups to be eliminated in a GO (reduction process) and (ii) the number of functional groups present in the GO to be reduced. This theoretical study has calculated the existence of multiple bandgaps in these materials, finding the most significant difference in the O/C ratio=0.33, estimating bandgaps of 0.50 eV and 1.82 eV, for rGO and GO, respectively, thus raising the need to be more specific in their denomination. Finally, the use of a nomenclature based on subscripts a, b, c, and d, describing the number of layers, the type of functional group, the number of functional groups added (in GO), and the number of functional groups removed in rGO, respectively, has been proposed.

(Invited) Towards Understanding the Competition of Electron and Energy Transfer in Nanographene

Graphene has captured the imagination of researchers around the world due to its groundbreaking chemical and physical properties. Opening a band gap in graphene must be achieved without, however, compromising its exceptional properties as they are of paramount importance for its use in electronic devices. Notable is the fact that the band gap design in graphene is typically carried out by either chemical or physical methodologies. Chemical modification of graphene is mostly centered around “top-down” or “bottom-up” approaches. The earlier alters, nevertheless, the graphene lattice and, as a consequence, poorly defined structures emerge. The latter by means of, for example, organic synthesis offers a wide palette of tools to control sizes as well as geometries of the resulting “molecular” nanographenes with atomic precision. It allows the fabrication of uniform and well-defined molecular structures. Such “molecular” nanographenes are compelling choices for “on demand” molecular electronics, photovoltaic applications, hydrogen storage, and sensing. In recent years, two main strategies have been developed to fabricate “molecular” nanographenes of defined chemical structures. It is, on one hand, oxidative cyclodehydrogenation of custom-made polycyclic aromatic hydrocarbons (PAHs) and, on the other hand, on-surface cyclodehydrogenation, which enabled the preparation of atomically precise “molecular” nanographenes. To this end, the 13 fused-benzene rings of hexa-peri-hexabenzocoronene (HBC), which are arranged in a 2D disk-shaped fashion, render HBCs the smallest “molecular” nanographenes.

(Invited) Modification of Properties of N- and B-Doped Graphene by Heteroatom Functionalization

Since its discovery in 2004, the graphene has attracted great attention owing to its unique chemical bonding structure, which has excellent chemical, thermal, mechanical, electrical and optical properties. Due to the graphene being a zero band-gap material, it has a limited development in the field of nano electronics. Therefore, to broaden its application scope, it is very important to carry out a study on opening the band gap of graphene. One general strategy for achieving this goal is doping graphene with heteroatoms; in this approach, the properties of graphene are controlled by the nature of the dopant elements and by the percentage of doping being N-doped graphene is of n-type doping, while B-doped graphene is of p-type doping. Compared with that of the intrinsic graphene, the Fermi level of N doped graphene moves up 5 eV; on the contrary, the Fermi level of B doped graphene moves down 3 eV.However, it would be convenient to develop additional tools to achieve further control of the electronic properties of graphene materials. In this context, one of the possibilities would be to functionalize those dopant elements on the graphene sheet in such a way that the electron density and electronegativity of the heteroatom are effectively controlled. This objective could, in principle, be achieved by applying concepts from organic chemistry. Organic synthesis offers proven chemical reactions that are applicable to different types of nitrogen and boron compounds.In the work described here, we´ll present our results on the covalent functionalization of the nitrogen atom or boron atom of N-doped and B-doped graphene. In a simple strategy, electron-donating and -withdrawing groups present on aromatic rings can be used to modulate the electronic properties of the material.

Structural, electronic, and transport properties of Ge doped graphene: A DFT study

Using the study of first principles, the structural, electronic, and transport characteristics of a monolayer graphene supercell doped with germanium are investigated. The effect of dopant on the aforementioned properties is examined as the germanium concentration ranges from 12.5% to 25%. It has been observed that hetero atom-like germanium doping can increase the band gap in graphene, enhancing its potential use as a thermoelectric material. We observed the semiconducting and zero band gap semiconducting behaviour of graphene due to variations in doping concentration. It is found that the Seebeck coefficient of pure graphene (C8) is positive, While the doped graphene structures (C7Ge1, C6Ge2) have negative Seebeck coefficients. The ZT of pure graphene is very low, but ZT can be improved by doping the Ge atom to the graphene structure. Also, it is shown that the concentration of doping has a significant impact on the graphene's thermal conductivity.

First-principles study on the electronic structure of siligraphene on a ZnO monolayer

Density functional theory was employed to investigate the electronic structures of atomic bilayer materials that form between graphene (g-C) or graphitic silicon carbide (also known as siligraphene: g-SiC and g-SiC2) and graphitic zinc oxide (g-ZnO). The results indicate that g-C/g-ZnO bilayers have semimetallic properties with an energy band gap of zero like in graphene. For a g-SiC/g-ZnO bilayer, an ensemble of three sp 2-hybridized carbon atoms periodically separated by three silicon atoms on g-ZnO has indirect and direct band gaps of 3.32 and 3.78 eV, respectively, which is suitable for use in light-emitting diode applications. For a g-SiC2/g-ZnO bilayer, an ensemble of four sp 2-hybridized carbon atoms periodically separated by two silicon atoms on g-ZnO has a direct band gap of 1.15 eV, which approaches the optimal value of the band gap (E opt ≃ 1.3 eV) for solar cell applications. The results show that increasing Si content in siligraphene can help to open the band gap of graphene and enhance the band gap of graphitic silicon carbide. The band gaps of siligraphene/g-ZnO bilayers depend on a smaller band gap from the monolayer component. Therefore, adjusting the Si content in siligraphene permits tuning of the band gap, and constructing a bilayer in the presence of a g-ZnO monolayer can slightly decrease the band gap. These results could lead to a new design of heterostructures with tunable band gaps for various applications.

Structural, Electronic and Optical Properties of Some New Trilayer Van de Waals Heterostructures.

Constructing two-dimensional (2D) van der Waals (vdW) heterostructures is an effective strategy for tuning and improving the characters of 2D-material-based devices. Four trilayer vdW heterostructures, BP/BP/MoS2, BlueP/BlueP/MoS2, BP/graphene/MoS2 and BlueP/graphene/MoS2, were designed and simulated using the first-principles calculation. Structural stabilities were confirmed for all these heterostructures, indicating their feasibility in fabrication. BP/BP/MoS2 and BlueP/BlueP/MoS2 lowered the bandgaps further, making them suitable for a greater range of applications, with respect to the bilayers BP/MoS2 and BlueP/MoS2, respectively. Their absorption coefficients were remarkably improved in a wide spectrum, suggesting the better performance of photodetectors working in a wide spectrum from mid-wave (short-wave) infrared to violet. In contrast, the bandgaps in BP/graphene/MoS2 and BlueP/graphene/MoS2 were mostly enlarged, with a specific opening of the graphene bandgap in BP/graphene/MoS2, 0.051 eV, which is much larger than usual and beneficial for optoelectronic applications. Accompanying these bandgap increases, BP/graphene/MoS2 and BlueP/graphene/MoS2 exhibit absorption enhancement in the whole infrared, visible to deep ultraviolet or solar blind ultraviolet ranges, implying that these asymmetrically graphene-sandwiched heterostructures are more suitable as graphene-based 2D optoelectronic devices. The proposed 2D trilayer vdW heterostructures are prospective new optoelectronic devices, possessing higher performance than currently available devices.

Vertical strain engineering of Van der Waals heterostructures

Van der Waals materials and their interfaces play critical roles in defining electrical contacts for nanoelectronics and developing vehicles for mechanoelectrical energy conversion. In this work, we propose a vertical strain engineering approach by enforcing pressure across the heterostructures. First-principles calculations show that the in-plane band structures of 2D materials such as graphene, h-BN, and MoS2 as well as the electronic coupling at their contacts can be significantly modified. For the graphene/h-BN contact, a band gap in graphene is opened, while at the graphene/MoS2 interface, the band gap of MoS2 and the Schottky barrier height at contact diminish. Changes and transitions in the nature of contacts are attributed to localized orbital coupling and analyzed through the redistribution of charge densities, the crystal orbital Hamilton population, and electron localization, which yield consistent measures. These findings offer key insights into the understanding of interfacial interaction between 2D materials as well as the efficiency of electronic transport and energy conversion processes.

Structural, electronic and optical properties of graphene/C2P4 van der Waals heterostructures with direct bandgap and high absorption coefficient

In this paper, we formed two graphene/C2P4 van der Waals (vdW) heterostructures (HSs) by stacking the graphene and the C2P4 monolayer which have been predicted by us. First, we investigated the stability of C2P4 monolayer, and calculated the binding energies and flat average differential charge density of two vdW-HSs. Second, we found that two graphene/C2P4 vdW-HSs are all direct semiconductors with bandgap as 0.051/0.064[Formula: see text]eV and 0.536/0.697[Formula: see text]eV under GGA-PBE/HSE06 functional, respectively, which provides a way to unfold the zero bandgap of graphene or let an indirect monolayer to be a relevant direct semiconductor. Additionally, two graphene/C2P4 vdW-HSs possess high absorption coefficients (16%∼18%) for the visible light and higher absorption coefficients (22%) for the near ultraviolet light, respectively. These admirable properties make two vdW-HSs as novel and potential two-dimensional materials applied on optoelectronic, electronic and photovoltaics devices.

Tiny (ZnO)n clusters supported on graphene for solar energy trapping: A density functional theory study

BackgroundWe propose that tiny (ZnO)n clusters (where n = 1, …, 4) supported on graphene be used as solar energy trapping devices. In order to demonstrate that these (ZnO)n/graphene combinations are appropriate for use, we have checked the stability of their structure, the adsorption energy of each (ZnO)n cluster on graphene and its bonding, as well as their electronic and optical properties. MethodsThese investigations are conducted by applying the density functional theory (DFT) method in every calculation. Then, this DFT is combined with the random phase approximation (RPA) to obtain the real and imaginary parts of the (ZnO)n/graphene dielectric function, which will describe its optical properties. Signiftcant findingsWe discover that all (ZnO)n/graphene structures are stable, with electron sharing among their components generating a strong bond. On the other hand, tiny (ZnO)n clusters open the energy band gap of graphene, with the highest value being 0.062 eV for Zn4O4/graphene. This band gap value is sufficient to allow this Zn4O4/graphene combination to absorb solar energy from the infrared to ultraviolet ranges, with infrared absorption accounting for 93%. In addition, its high dielectric indexes allow it to bend light effectively. Therefore, we recommend Zn4O4/graphene for use in solar energy trapping devices.

Si9C15 monolayer: A silicon carbide allotrope with remarkable physical properties

Zero band gap in graphene and silicene is an important obstacle to their application in nanodevices. Combining carbon and silicon atoms to form a silicon carbide (${\mathrm{Si}}_{x}{\mathrm{C}}_{y}$) sheet is an applicable proposal to solve the band gap issue. Very recently, a large-scale monolayer $\mathrm{Si}{}_{9}\mathrm{C}{}_{15}$ was successfully synthesized and exhibited suitable band gap and environment stability [Gao et al., Adv. Mater. 34, 2204779 (2022)]. Motivated by this recent experiment, we explore the electronic, mechanical, optical, and thermoelectric properties of a $\mathrm{Si}{}_{9}\mathrm{C}{}_{15}$ monolayer using first-principles calculations. Our results reveal that the monolayer is an auxetic material with a negative Poisson ratio of 0.175. The monolayer is a semiconductor with a direct band gap of 2.54 eV calculated by the Heyd-Scuseria-Ernzerhof functional (HSE06) functional. The optical properties of the monolayer are investigated by solving the Bethe-Salpeter equation. It is revealed that the optical band gap of the monolayer is 2.73 eV, and the exciton binding energy is equal to 1.14 eV, indicating a strongly bound bright exciton. Thermoelectric properties of the monolayer are calculated by combining density functional theory and Green's function formalism in the linear response regime. The lattice thermal conductance of the monolayer is 0.85 nW/K at room temperature, and the maximum figure of merit is 1.2 at 800 K, higher than that of other silicon carbide allotropes. High flexibility, a suitable band gap, high mobility, high optical absorption in the UV-visible region, and high thermoelectric efficiency make the $\mathrm{Si}{}_{9}\mathrm{C}{}_{15}$ monolayer a promising candidate for applications in mechanics, optoelectronics, and energy converters.

Ferrotronics for the creation of band gaps in graphene

We experimentally demonstrate a simple graphene/ferrolectric device, termed ferrotronic (electronic effect from ferroelectric) device in which the band structure of single-layer graphene is modified. The device architecture consists of graphene deposited on a ferroelectric substrate which encodes a periodic surface potential achieved through domain engineering. This structure takes advantage of the nature of conduction through graphene to modulate the Fermi velocity of the charge carriers by the variations in surface potential, leading to the emergence of energy minibands and a band gap at the superlattice Brillouin zone boundary. Our work represents a simple route to building circuits whose functionality is controlled by the underlying substrate.

Electric-field-tunable band gap in commensurate twisted bilayer graphene

Bernal bilayer graphene exhibits a band gap that is tunable through the infrared with an electric field. We show that sublattice odd commensurate twisted bilayer graphene (C-TBG) exhibits a band gap that is tunable through the terahertz with an electric field. We show that from the perspective of terahertz optics the sublattice odd and even forms of C-TBG are ``inflated'' versions of Bernal and AA-stacked bilayer graphene, respectively, with energy scales reduced by a factor of 110 for the $21.{79}^{\ensuremath{\circ}}$ commensurate unit cell. This lower energy scale is accompanied by a correspondingly smaller gate voltage, which means that the strong-field regime is more easily accessible than in the Bernal case. Finally, we show that the interlayer coherence energy is a directly accessible experimental quantity through the position of a power-law divergence in the optical conductivity.

Theoretical characterization of codoped bilayer graphene

We studied the structure, stability and electronic propierties of bilayer graphene when both layers are doped with a pair of3p-2pelements. The interlayer interaction energy of codoped bilayer graphene can be fine-tuned by changing the dopants. Al/B codoped bilayer graphene presents the strongest stacking, almost twice the value determined for the undoped materials. In five cases, the interaction is weaker than in bilayer graphene. Interlayer covalent bonds form only in six cases; P/O codoped bilayer graphene presents the largest interlayer distance: 3.97 Å, about 0.72 Å longer than the value determined for undoped-bilayer graphene. In four cases, we observed that a semiconductor-to-metal transition occurs when two layers are stacked. For the remaining cases except P/N codoped bilayer graphene, the band gaps are reduced with respect to the values computed for the codoped monolayers. Controlling the number of layers is an exciting approach to fine-tune the band gap of codoped graphene.

Novel energy bandgap formation of organic solution doped graphene membrane for semiconductor applications

In this work, the electrolyte nano fibrous solution is prepared using corn husk through a chemical process. This study explores the new aspect of producing sizeable and tunable bandgap in graphene by doping organic nanoporous solution as a membrane. The energy bandgap of organic doped graphene membrane varies from 2.313 eV to 2.502 eV. It is noted that the organic nanoporous solution as a membrane also has a bandgap under with (2.665 eV) and without PVA (3.761 eV). The membrane is produced by the phase inversion process. The incorporation of graphene in green solution also exhibits conductive properties like organic nanoporous solution which in terns used as electrolytes to produce electricity. It is the first successful attempt to create a direct graphene bandgap with organic doping but it still requires more research for a better understanding of the properties for future applications. This concept can also be used where bandgap is a very concerning issue. The physical properties of with and without a graphene-based organic membrane are examined by Scanning Electron Microscope Test (SEM), Fourier Transform Infrared Spectroscopy Test (FTIR), and Ultra Violate Test (UV). Sample 4 has a superior surface morphology, which means the particle dispersion is more homogeneous than the others. There are porosities in all the samples.

A review of the synthesis, properties, and applications of 2D transition metal dichalcogenides and their heterostructures

One of the most nascent and universally accepted categories among the 2D materials is the transition metal dichalcogenides (TMDs). The absence of bandgap in graphene fomented the researchers to quest for an alternative semiconducting 2D materials. The aberrant optical and electronic properties helped 2D TMDs to excel in fundamental research and novel device applications. This article overviews the recent advances in the preparation methods, properties, characterization, and novel multifunctional applications of TMDs and their corresponding heterostructures with special emphasis on their biosensing applications. The major portion of the review underlines the TMDs based heterostructures, which find potential applications in optoelectronics, sensors, and photovoltaics, that are devised to boost the functionality and flexibility and there by surmount the existing limitations of monolayered materials. At the end, the advancement and elevation of TMDs as biosensors over other 2D materials are also explored.