Trilayer Graphene Research Articles

Performance Analysis of Electrochemical Detection Platform for DNA Hybridization Using TGN-Based Nanobiosensor

Trilayer graphene nanoribbon (TGN) has great potential in related biomedical applications such as drug and gene delivery and deoxyribonucleic acid (DNA) sensing. The performance of a biosensor based on a liquid gate TGN field effect transistor (Lg-TGNFET) to different DNA cancentrations and adsorption effect on the sensing parameters are analytically investigated in this research. Also, the energy band structure, density of states, carrier concentration, electrical conductance and caused electrical response on TGN as a detection element are studied considering the spin–orbit coupling effect, in which significant current change of the TGN-based biosensor is observed after exposure to DNA different values. DNA concentration as a function of gate voltage is assumed and sensing factor is defined. The results of this research confirm that the current of the biosensor is decreased and Vg-min is obviously left-shifted by increasing value of DNA concentration, suggesting that DNA molecules n-dopes the TGN film. In order to verify the accuracy of the TGN-based biosensor, it is compared with recent analytical and experimental reports on DNA biosensors. The proposed biosensor with high specificity and sensitivity exposes higher current compared to that of monolayer graphene counterpart for analogous ambient conditions.

Gate-tunable anomalous Hall effect in Bernal tetralayer graphene

Large spin-orbit coupling is often thought to be critical in realizing magnetic order-locked charge transport such as the anomalous Hall effect (AHE). Recently, artificial stacks of two-dimensional materials, e.g., magic-angle twisted bilayer graphene on hexagonal boron-nitride heterostructures and dual-gated rhombohedral trilayer graphene, have become platforms for realizing AHE without spin-orbit coupling. However, these stacking arrangements are not energetically favorable, impeding experiments and further device engineering. Here we report an anomalous Hall effect in Bernal-stacked tetralayer graphene devices (BTG), the most stable configuration of four-layer graphene. BTG AHE is switched on by a displacement field and is most pronounced at low carrier densities. The onset of AHE occurs in tandem with a full metal to a broken isospin transition indicating an orbital origin of the itinerant ferromagnetism. At lowest densities, BTG exhibits an unconventional hysteresis with step-like anomalous Hall plateaus. Persisting to several tens of kelvin, AHE in BTG demonstrates the ubiquity and robustness of magnetic order in readily available and stable multilayer Bernal graphene stacks—a new venue for intrinsic non-reciprocal responses.

Imaging quantum oscillations and millitesla pseudomagnetic fields in graphene

The exceptional control of the electronic energy bands in atomically thin quantum materials has led to the discovery of several emergent phenomena1. However, at present there is no versatile method for mapping the local band structure in advanced two-dimensional materials devices in which the active layer is commonly embedded in the insulating layers and metallic gates. Using a scanning superconducting quantum interference device, here we image the de Haas–van Alphen quantum oscillations in a model system, the Bernal-stacked trilayer graphene with dual gates, which shows several highly tunable bands2–4. By resolving thermodynamic quantum oscillations spanning more than 100 Landau levels in low magnetic fields, we reconstruct the band structure and its evolution with the displacement field with excellent precision and nanoscale spatial resolution. Moreover, by developing Landau-level interferometry, we show shear-strain-induced pseudomagnetic fields and map their spatial dependence. In contrast to artificially induced large strain, which leads to pseudomagnetic fields of hundreds of tesla5–7, we detect naturally occurring pseudomagnetic fields as low as 1 mT corresponding to graphene twisting by 1 millidegree, two orders of magnitude lower than the typical angle disorder in twisted bilayer graphene8–11. This ability to resolve the local band structure and strain at the nanoscale level enables the characterization and use of tunable band engineering in practical van der Waals devices.

Evidencing contributions arising from disorder-rich rhombohedral stacking-order regions in S-doped carbon nanotube buckypapers

The recent observations of superconductive-ordering in carbon-based systems consisting of rhombohedral stacking-faults, trilayer graphene (ABC-stacks) or dislocation-rich interfaces (pyrolytic graphite) have attracted a significant attention. Here we report an unusual nucleation of rhombohedral (ABC) stacking-faults in low-dimensional systems comprising of multiwall carbon nanotube (CNT) buckypapers, in experiments involving doping with sulfur. Interestingly, at low sulfur-concentrations, a broad-band at the Raman shift from 1800 to 2000 cm−1 was frequently identified, evidencing contributions arising from disorder-rich regions with rhombohedral stacking-order (ABC-stacks), as confirmed by X-ray diffraction and Rietveld refinements. These observations were further supported by a broadening in the left-shoulder of the 2D band at higher frequencies. T-ESR in the T range from 300 K to 77 K revealed multiple resonant signal splitting, indicative of paramagnetic contributions arising from the conduction π-electrons of the CNT and from amorphous iron-based-sulfides. Presence of CS bonding was revealed by Raman- and X-ray photoelectron-spectroscopy, evidencing a modification of the CNT. A sulfur-induced collapse within the CNTs-structure was found at high concentrations, as a consequence of a substitutional doping process and investigated through XRD, Rietveld refinements, TEM, HRTEM and magnetometry. ZFC/FC and magnetization vs field acquisitions revealed an interplay of ferromagnetic, paramagnetic and diamagnetic components with the diamagnetic-susceptibility χ being −2.85 ∗ 10−6 (emu/gOe) at T ~ 30 K.

Imaging inter-valley coherent order in magic-angle twisted trilayer graphene.

Magic-angle twisted trilayer graphene (MATTG) exhibits a range of strongly correlated electronic phases that spontaneously break its underlying symmetries1,2. Here we investigate the correlated phases of MATTG using scanning tunnelling microscopy and identify marked signatures of interaction-driven spatial symmetry breaking. In low-strain samples, over a filling range of about two to three electrons or holes per moiré unit cell, we observe atomic-scale reconstruction of the graphene lattice that accompanies a correlated gap in the tunnelling spectrum. This short-scale restructuring appears as a Kekulé supercell-implying spontaneous inter-valley coherence between electrons-and persists in a wide range of magnetic fields and temperatures that coincide with the development of the gap. Large-scale maps covering several moiré unit cells further reveal a slow evolution of the Kekulé pattern, indicating that atomic-scale reconstruction coexists with translation symmetry breaking at a much longer moiré scale. We use auto-correlation and Fourier analyses to extract the intrinsic periodicity of these phases and find that they are consistent with the theoretically proposed incommensurate Kekulé spiral order3,4. Moreover, we find that the wavelength characterizing moiré-scale modulations monotonically decreases with hole doping away from half-filling of the bands and depends weakly on the magnetic field. Our results provide essential insights into the nature of the correlated phases of MATTG in the presence of strain and indicate that superconductivity can emerge from an inter-valley coherent parent state.

New local pseudopotential for multilayer carbon materials and its application in wave packet dynamics

Formerly we created a one-electron local pseudopotential which proved to be successful in studying transport phenomena in various sp2 carbon nanosystems, e.g. graphene grain boundaries and nanotube networks. In this work, we present an extended version of the local pseudopotential which correctly describes the electronic structure of van der Waals stacks of carbon sheets, e.g. AA, AB bi-layer graphene, ABC (rhombohedral) tri-layer graphene, as well as AA, AB, and ABC graphite, etc., even in case of external electric fields. We utilize this potential to study the hopping dynamics of wave packets between the graphene sheets in multilayer systems. The frequency of the hopping is proportional to the band splitting, caused by the interlayer coupling. For the case of AB and ABC graphene there is a backscattering near the Fermi level, causing a Zitterbewegung-like phenomenon, an interference between +kBloch and −kBloch states. For the rhombohedral tri-layer graphene the time dependence of the wave packet probability density is an aperiodic function for the first- and third layer (the two outer layers), but a quasi-periodic function for the second (inner) layer.

Effects of stacking layers and different doping elements on the electronic structures and quantum capacitance of graphene: A DFT study

The influence of boron (B), nitrogen (N), oxygen (O), and sulfur (S) doping on enhancing quantum capacitance were investigated through a series of the surface-doped trilayer graphene structures by using density functional theory (DFT) calculations. The quantum capacitance of monolayer models was enhanced through a single doping, a triple doping, and a vacancy defect. Our calculations suggested that the layer interactions within the trilayer models decreased the quantum capacitance but increased the stability of the doped structures. Interestingly, in the case of sulfur dopants with significantly larger atomic size than carbon, the stacking layers induced a surface distortion that could avoid the steric clashes with stacking layers and enhanced the stability. In conclusion, this work provided more realistic models of modified carbon-based electrodes for supercapacitors with more accurate information from the combined effects of doping and stacking layers.

Magic angle butterfly in twisted trilayer graphene

Magic angle butterfly in twisted trilayer graphene

Halogenated graphene derivatives as an absorber layer for solar cell applications : A DFT study with vdw correction

Due to the flexible nature and high transparency of Graphene (G) in the ultraviolet to infrared spectrum, it is ideal for thin-film solar cell applications. To use graphene for such a purpose, there is a need to tune its band gap at Fermi level, and the most convenient method is chemical functionalization. So, in this study, we will investigate electronic and mechanical properties, along with the structure and stability analysis of halogenated (X) bilayer and trilayer graphene B(T)LG using density functional theory with van der Waals correction (vdw-GGA). These halogenated B(T)LGs are designed by adsorbing the top and bottom surfaces with fluorine (F) and chlorine (Cl) at the maximum possible separation. BLGs are designed as X/graphene/graphene/X with bernal (AB) and non-bernal (AA) stacking. TLGs are designed as X/graphene/graphene/graphene/X as AAA, ABA, and ABC stacking with 50% X termination at the top and 50% on the bottom side. Chlorination results in weak physisorption while fluorination results in chemisorption. Binding energies Eb found quite higher for fluorinated bilayer graphene derivatives. Halogenation of TLG disturbs Dirac cones at Fermi level in case of fluorine adsorption while remaining unaffected under chlorination. Due to repositioning of some states above EF, provide an additional path for intraband transition, made systems more conductive except for fluorinated bilayer graphenes F-BLGs. A small band gap of 0.2 meV and 0.04 eV appeared at Fermi level of fluorinated non-bernal and bernal configuration, respectively. An E-field applied normal to the plane of F-BLGs can further tune the band gap. Due to underestimation of Band gap using GGA, hybrid functionals HSE06 were used for better estimation.

Dispersion consisting entirely of trilayer graphene provides film of high specific capacitance

The excellent electrical conductivity and tunable bandgap make trilayer graphene (TG) an attractive material for energy storage and electronic applications. The variation in electronic properties of graphene with number of layers present, severely limits the utility of scalable and cost-effective electrochemical exfoliation of graphite for TG synthesis, as the produced graphene is layer-polydispersed. The limitation is further accentuated by the oxygen functionalization, high defect density, and smaller sizes of the produced graphene. Here we produce a dispersion consisting entirely of TG through tailored electrochemical exfoliation of graphite to single-stage III graphite bisulfate (GB) particles, enabling subsequent selective cleaving to TG in the dispersion-favorable solvent DMF. A detailed morphological, structural, and chemical analysis revealed large size of flakes (average size: ∼ 96 μm2) with low defect density (ID∕IG ratio < 0.1) and high C/O ratio (26.78), along with excellent optoelectronic properties (transmittance: ∼ 92.2 % and conductivity: ∼ 2.17 × 106 S m−1) comparable to CVD grown TG. The specific capacitance of TG film is ∼ 259 F g−1 indicating its suitability for energy storage applications.

Moiré Superlattice Structure of Pleated Trilayer Graphene Imaged by 4D Scanning Transmission Electron Microscopy.

Moiré superlattices in graphene arise from rotational twists in stacked 2D layers, leading to specific band structures, charge density and interlayer electron and excitonic interactions. The periodicities in bilayer graphene moiré lattices are given by a simple moiré basis vector that describes periodic oscillations in atomic density. The addition of a third layer to form trilayer graphene generates a moiré lattice comprised of multiple harmonics that do not occur in bilayer systems, leading to nontrivial crystal symmetries. Here, we use atomic resolution 4D-scanning transmission electron microscopy to study atomic structure in bilayer and trilayer graphene moiré superlattices and use 4D-STEM to map the electric fields to show subtle variations in the long-range moiré patterns. We show that monolayer graphene folded into an S-bend graphene pleat produces trilayer moiré superlattices with both small (<2°) and larger twist angles (7-30°). Annular in-plane electric field concentrations are detected in high angle bilayers due to overlapping rotated graphene hexagons in each layer. The presence of a third low angle twisted layer in S-bend trilayer graphene, introduces a long-range modulation of the atomic structure so that no real space unit cell is detected. By directly imaging trilayer moiré harmonics that span from picoscale to nanoscale using 4D-STEM, we gain insights into the complex spatial distributions of atomic density and electric fields in trilayer twisted layered materials.

Deep learning extraction of band structure parameters from density of states: A case study on trilayer graphene

Deep learning extraction of band structure parameters from density of states: A case study on trilayer graphene

Magic-angle helical trilayer graphene.

We propose magic-angle helical trilayer graphene (HTG), a helical structure featuring identical rotation angles between three consecutive layers of graphene, as a unique and experimentally accessible platform for realizing exotic correlated topological states of matter. While nominally forming a supermoiré (or moiré-of-moiré) structure, we show that HTG locally relaxes into large regions of a periodic single-moiré structure realizing flat topological bands carrying nontrivial valley Chern number. These bands feature near-ideal quantum geometry and are isolated from remote bands by a very large energy gap, making HTG a promising platform for experimental realization of correlated topological states such as integer and fractional quantum anomalous Hall states.

Role of Local Conductivities in the Plasmon Reflections at the Edges and Stacking Domain Boundaries of Trilayer Graphene.

We employed infrared scattering-type scanning near-field optical microscopy (IR-sSNOM) to study surface plasmon polaritons (SPPs) in trilayer graphene (TLG). Our study reveals systematic differences in near-field IR spectra and SPP wavelengths between Bernal (ABA) and rhombohedral (ABC) TLG domains on SiO2, which can be explained by stacking-dependent intraband conductivities. We also observed that the SPP reflection profiles at ABA-ABC boundaries could be mostly accounted for by an idealized domain boundary defined by the conductivity discontinuity. However, we identified distinct shapes in the SPP profiles at the edges of the ABA and ABC TLG, which cannot be solely attributed to idealized edges with stacking-dependent conductivities. Instead, this can be explained by the presence of various edge structures with local conductivities differing from those of bulk TLGs. Our findings unveil a new structural element that can control SPP, and provide insights into the structures and electronic states of the edges of few-layer graphene.

Magic angles in equal-twist trilayer graphene

Magic angles in equal-twist trilayer graphene

Hofstadter moiré butterfly in twisted trilayer graphene

Hofstadter moiré butterfly in twisted trilayer graphene

Interferometric Imaging of Twisted Trilayer Graphene Moiré Superlattices.

Interferometric Imaging of Twisted Trilayer Graphene Moiré Superlattices.

Magnetic Field-Stabilized Wigner Crystal States in a Graphene Moiré Superlattice.

ABC-stacked trilayer graphene on boron nitride (ABC-TLG/hBN) moiré superlattices provides a tunable platform for exploring Wigner crystal states in which the electron correlation can be controlled by electric and magnetic fields. Here we report the observation of magnetic field-stabilized Wigner crystal states in a ABC-TLG/hBN. We show that correlated insulating states emerge at multiple fractional and integer fillings corresponding to ν = 1/3, 2/3, 1, 4/3, 5/3, and 2 electrons per moiré lattice site under a magnetic field. These correlated insulating states can be attributed to generalized Mott states for the integer fillings and generalized Wigner crystal states for the fractional fillings. The generalized Wigner crystal states are stabilized by a vertical magnetic field and are strongest at one magnetic flux quantum per three moiré superlattices. The ν = 2 insulating state persists up to 30 T, which can be described by a Mott-Hofstadter transition at a high magnetic field.

Recent Advancements in Applications of Graphene to Attain Next-Level Solar Cells

This paper presents an intensive review covering all the versatile applications of graphene and its derivatives in solar photovoltaic technology. To understand the internal working mechanism for the attainment of highly efficient graphene-based solar cells, graphene’s parameters of control, namely its number of layers and doping concentration are thoroughly discussed. The popular graphene synthesis techniques are studied. A detailed review of various possible applications of utilizing graphene’s attractive properties in solar cell technology is conducted. This paper clearly mentions its applications as an efficient transparent conducting electrode, photoactive layer and Schottky junction formation. The paper also covers advancements in the 10 different types of solar cell technologies caused by the incorporation of graphene and its derivatives in solar cell architecture. Graphene-based solar cells are observed to outperform those solar cells with the same configuration but lacking the presence of graphene in them. Various roles that graphene efficiently performs in the individual type of solar cell technology are also explored. Moreover, bi-layer (and sometimes, tri-layer) graphene is shown to have the potential to fairly uplift the solar cell performance appreciably as well as impart maximum stability to solar cells as compared to multi-layered graphene. The current challenges concerning graphene-based solar cells along with the various strategies adopted to resolve the issues are also mentioned. Hence, graphene and its derivatives are demonstrated to provide a viable path towards light-weight, flexible, cost-friendly, eco-friendly, stable and highly efficient solar cell technology.

Chemical Potential Characterization of Symmetry-Breaking Phases in a Rhombohedral Trilayer Graphene.

Rhombohedral trilayer graphene has recently emerged as a natural flat-band platform for studying interaction-driven symmetry-breaking phases. The displacement field (D) can further flatten the band to enhance the density of states, thereby controlling the electronic correlation that tips the energy balance between spin and valley degrees of freedom. To characterize the energy competition, chemical potential measurement─a direct thermodynamic probe of Fermi surfaces─is highly demanding to be conducted under a constant D. In this work, we characterize D-dependent isospin flavor polarization, where electronic states with isospin degeneracies of one and two can be identified. We also developed a method to measure the chemical potential at a fixed D, allowing for the extraction of energy variation during phase transitions. Furthermore, symmetry breaking could also be invoked in Landau levels, manifesting as quantum Hall ferromagnetism. Our work opens more opportunities for the thermodynamic characterization of displacement-field tuned van der Waals heterostructures.