Nano-structured interface of graphene and h-BN for sensing applications

Two-dimensional Cu-doped G/h-BN/G heterostructures for highly sensitive gas detection: an ab initio study

Two-dimensional materials like graphene and h-BN have drawn significant interest for gas sensing applications due to their high surface-to-volume ratio and exceptional physical properties. This study introduces a novel approach involving a 2-D G/h-BN/G heterostructure doped with a Cu atom to develop a highly sensitive gas sensor. The intermediate h-BN layers support the Cu dopant and enhance the electrical sensitivity by constraining the offset current. Density functional theory and non-equilibrium Green's function formalisms are employed to investigate the geometry, stability, and electrical properties of the G/h-BN/G structure with the Cu dopant at various vacancy sites, alongside exploring the adsorption behavior of six different gas molecules (NO2, CO, NH3, PH3, HCN, and HO2). Results reveal that doping Cu in the B vacancy and the Stone-Wales defect yields highly stable structures with promising electrical characteristics for gas sensing applications. Gas molecules exhibit a higher tendency to adsorb onto the Cu-doped structure compared to the pristine G/h-BN/G, demonstrating a stronger impact on current flow. The Cu-doped structures display robust electrical sensitivity toward NO2, CO, NH3, and HCN molecules, and the significant gap in current modulation for each gas indicates the potential for distinguishing different gas molecules. Hence, incorporating the Cu dopant in the G/h-BN/G heterostructures emerges as a promising platform for gas sensing applications.

In-plane graphene/h-BN/graphene heterostructures with nanopores for electrical detection of DNA nucleotides

The in-plane heterostructure of graphene and h-BN has unique physical and electrical characteristics, which can be exploited for single-molecule DNA sequencing. On this account, we propose a nanostructure based on a nanopore in graphene/h-BN/graphene heterostructures as a viable approach for in-plane electrical detection. The insulating h-BN layer changes the charge transport to the quantum tunneling regime, which is very sensitive to the electrostatic interactions induced by nucleotides during their translocation through the nanopore. Density functional theory (DFT) is utilized to study the membrane/nanopore interactions as well as their interactions with different nucleotides (dAMP, dGMP, dCMP, and dTMP). The results indicate that the nucleotides show stronger interactions with nanopores in h-BN rather than nanopores in pristine graphene. For the calculation of electronic transport, non-equilibrium Green's function (NEGF) formalism at the first principles level is employed. The in-plane currents at different applied voltages are calculated in the presence of different nucleotides in the nanopore. The sensitivity of the proposed nanostructure towards different nucleotides is measured based on the current modulation induced by each nucleotide. The graphene/h-BN/graphene heterostructure shows higher sensitivity toward different nucleotides compared to a similar structure consisting of pristine graphene and can be considered as a promising candidate for DNA sequencing applications.

Nanogap-based all-electronic DNA sequencing devices using MoS2 monolayers

The realization of nanopores in atom-thick materials may pave the way towards electrical detection of single biomolecules in a stable and scalable manner. In this work, we theoretically study the potential of different phases of MoS2 nanogaps to act as all-electronic DNA sequencing devices. We carry out simulations based on density functional theory and the non-equilibrium Green's function formalism to investigate the electronic transport across the device. Our results suggest that the 1T'-MoS2 nanogap structure is energetically more favorable than its 2H counterpart. At zero bias, the changes in the conductance of the 1T'-MoS2 device can be well distinguished, making possible the selectivity of the DNA nucleobases. Although the conductance fluctuates around the resonances, the overall results suggest that it is possible to distinguish the four DNA bases for energies close to the Fermi level.

Electrically sensing Hachimoji DNA nucleotides through a hybrid graphene/h-BN nanopore

The feasibility of synthesizing unnatural DNA/RNA has recently been demonstrated, giving rise to new perspectives and challenges in the emerging field of synthetic biology, DNA data storage, and even the search for extraterrestrial life in the universe. In line with this outstanding potential, solid-state nanopores have been extensively explored as promising candidates to pave the way for the next generation of label-free, fast, and low-cost DNA sequencing. In this work, we explore the sensitivity and selectivity of a graphene/h-BN based nanopore architecture towards detection and distinction of synthetic Hachimoji nucleobases. The study is based on a combination of density functional theory and the non-equilibrium Green's function formalism. Our findings show that the artificial nucleobases are weakly binding to the device, indicating a short residence time in the nanopore during translocation. Significant changes in the electron transmission properties of the device are noted depending on which artificial nucleobase resides in the nanopore, leading to a sensitivity in distinction of up to 80%. Our results thus indicate that the proposed nanopore device setup can qualitatively discriminate synthetic nucleobases, thereby opening up the feasibility of sequencing even unnatural DNA/RNA.

Embedded carbon nanowire in black phosphorene and C-doping: the rule to control electronic properties

Tuning the properties of black phosphorene such as structural, electronic and transport are explored via substitutional C-doping. We employed density functional theory calculations in combination with the non-equilibrium Green's function for modeling the systems. Our results revealed that substitutional C-doped phosphorene is energetically favorable and ruled by the exothermic process. We also found that C-doping induces a change of the electric properties, such as a semiconductor-to-metal transition for the most lower concentration and zig-zag C-wire. Furthermore, for an armchair C-wire at the highest concentration, the semiconductor character is kept, meanwhile direct-to-indirect transitions are observed in the band gap nature. The band structures show that there exists a dependence of the electronic charge transport with the directional character of the C-doped configuration. The findings demonstrate that the directional doping could play a key role for the conductance of a 2D platform.

Controlled current confinement in interfaced 2D nanosensor for electrical identification of DNA

The controlled synthesis of hybrid two-dimensional (2D) materials and the development of atomically precise nanopore fabrication techniques have opened up entirely new possibilities for sensing applications via nanoelectronics. Here, we investigate the electronic transport properties of an in-plane hybrid graphene/h-BN device, containing a graphene nanopore, to assess its feasibility to act as a molecular sensor. The results from our calculations based on density functional theory and the non-equilibrium Green's function formalism reveal the capability to confine the electric current pathways to the two carbon wires lining either edge of the nanopore, thereby creating conditions in which the conductance is highly sensitive to any changes in the electrical potential inside the nanopore. We apply this setup to assess whether it is possible to electrically determine the base sequence in a DNA molecule. Indeed, the modulation of the device conductance reveals a characteristic fingerprint of each nucleotide, which manifests itself in a pronounced difference in the sensitivity of the four different nucleotides, thereby allowing electrical discrimination. These findings lead us to propose this device architecture as a promising nanobiosensor. While fabrication in the lab may represent a profound experimental challenge, it should nevertheless in principle be feasible with existing contemporary techniques of hybrid 2D material synthesis, in conjunction with approaches for highly controlled nanopore creation.

Tunable, omnidirectional, and nearly perfect resonant absorptions by a graphene-hBN-based hole array metamaterial

In this paper, we propose an electrically tunable mid-infrared plasmonic-phononic absorber with omnidirectional and polarization insensitive nearly perfect resonant absorption characteristics. The absorber consists of a graphene/hexagonal boron nitride (hBN)/graphene multilayer on top of a gold bottom reflector separated by a dielectric spacer. The graphene/hBN/graphene multilayer is patterned as a hole array in square lattice. We analytically and numerically prove that, due to the support of hybrid plasmon-phonon-polaritons, nearly perfect multi-resonant absorption peaks with high quality factors are obtained both inside and outside of the Reststrahlen band of hBN. As a result of the hybridization of graphene plasmons with the hyperbolic phonon polaritons of hBN, the high quality resonant absorptions of the metamaterial are almost unaffected by decreasing the phenomenological electron relaxation time of graphene. Moreover, the obtained resonances can be effectively tuned in practice due to the continuity of the graphene layers in the hole array metamaterial. These features make the graphene-hBN metamaterial a skeptical design for practical purposes and mid-infrared multi-functional operations such as sensing.

Electron transport in polycyclic aromatic hydrocarbons/boron nitride hybrid structures: density functional theory combined with the nonequilibrium Green's function

We investigate the electronic transport properties of two types of junction based on single polyaromatic hydrocarbons (PAHs) and PAHs embedded in boron nitride (h-BN) nanoribbons, using nonequilibrium Green's functions (NEGF) and density functional theory (DFT). In the PAH junctions, a Fano resonance line shape at the Fermi energy in the transport feature can be clearly seen. In hybrid junctions, structural asymmetries enable interactions between the electronic states, leading to observation of interface-based transport. Our findings reveal that the interface of PAH/h-BN strongly affects the transport properties of the structures.

Probing the local interface properties at a graphene–MoSe2 in-plane lateral heterostructure: an ab initio study

We report a theoretical study of the local interface properties at a graphene–MoSe₂ (G–MoSe₂) in-plane lateral heterostructure.

Prospects of Graphene-hBN Heterostructure Nanogap for DNA Sequencing

Recent advances in solid-state nano-device-based DNA sequencing are at the helm of the development of a new paradigm, commonly referred to as personalized medicines. Paying heed to a timely need for standardizing robust nanodevices for cheap, fast, and scalable DNA detection, in this article, the nanogap formed by the lateral heterostructure of graphene and hexagonal boron nitride (hBN) is explored as a potential architecture. These heterostructures have been realized experimentally, and our study boasts the idea that the passivation of the edge of the graphene electrode with hBN will solve many of practical problems, such as high reactivity of the graphene edge and difficulty in controlled engineering of the graphene edge structure, while retaining the nanogap setup as a useful nanodevice for sensing applications. Employing first-principle density-functional-theory-based nonequilibrium Green's function methods, we identify that the DNA building blocks, nucleobases, uniquely couple with the states of the nanogap, and the resulting induced states can be attributed as leaving a fingerprint of the DNA sequence in the computed current-voltage (I-V) characteristic. Two bias windows are put forward: lower (1-1.2 V) and higher (2.7-3 V), where unique identification of all four bases is possible from the current traces, although higher sensitivity is obtained at the higher voltage window. Our study can be a practical guide for experimentalists toward development of a nanodevice DNA sensor based on graphene-hBN heterostructures.

Electrical detection of nucleotides via nanopores in a hybrid graphene/h-BN sheet

Designing the next generation of solid-state biosensors requires developing detectors which can operate with high precision at the single-molecule level. Nano-scaled architectures created in two-dimensional hybrid materials offer unprecedented advantages in this regard. Here, we propose and explore a novel system comprising a nanopore formed within a hybrid sheet composed of a graphene nanoroad embedded in a sheet of hexagonal boron nitride (h-BN). The sensitive element of this setup is comprised of an electrically conducting carbon chain forming one edge of the nanopore. This design allows detection of DNA nucleotides translocating through the nanopore based on the current modulation signatures induced in the carbon chain. In order to assess whether this approach is feasible to distinguish the four different nucleotides electrically, we have employed density functional theory combined with the non-equilibrium Green's function method. Our findings show that the current localized in the carbon chain running between the nanopore and h-BN is characteristically modulated by the unique dipole moment of each molecule upon insertion into the pore. Through the analysis of a simple model based on the dipole properties of the hydrogen fluoride molecule we are able to explain the obtained findings.