Using Graphdiyne Nanoribbons for Molecular Electronics Spectroscopy and Nucleobase Identification: A Theoretical Investigation.

In pursuit of fast, cost-effective, and reliable DNA sequencing techniques, a variety of two-dimensional (2D) material-based nanodevices such as solid-state nanopores and nanochannels have been explored and established. Given the promising potential of graphene for the design and fabrication of nanobiosensors, other 2D carbon allotropes such as graphyne and graphdiyne have also attracted a great deal of attention as candidate materials for the development of sequencing technology. Herein, employing the 2D electronic molecular spectroscopy (2DMES) method, we investigate the capability of graphdiyne nanoribbons (GDNRs) as the building blocks of a feasible, precise, and ultrafast sequencing device. Using first-principles calculations, we study the adsorption of four canonical nucleobases (NBs), i.e., adenine (A), cytosine (C), guanine (G), and thymine (T) on an armchair GDNR (AGDNR). Our calculations reveal that compared to graphene, graphdiyne demonstrates more distinct binding energies for different NBs, indicating its more promising ability to unambiguously recognize DNA bases. Utilizing the 2DMES technique, we calculate the differential conductance (Δg) of the studied NB-AGDNR systems and show that the resulting Δg maps, unique for each NB-AGDNR complex, can be used to recognize each individual NB without ambiguity. We also investigate the conductance sensitivity of the proposed nanobiosensor and show that it exhibits high sensitivity and selectivity toward various NBs. Thus, our proposed graphdiyne-based nanodevice would hold promise for next-generation DNA sequencing technology.

Structural, Electronic, and Magnetic Characteristics of Graphitic Carbon Nitride Nanoribbons and Their Applications in Spintronics.

The development of quantum information and quantum computing technology requires special materials to design and manufacture nanosized spintronic devices. Possessing remarkable structural, electronic, and magnetic characteristics, graphitic carbon nitride (g-C3N4) can be a promising candidate as a building block of futuristic nanoelectronics and spintronic systems. Here, using first-principles calculations, we perform a comprehensive study on the structural stability as well as electronic and magnetic properties of triazine-based g-C3N4 nanoribbons (gt-CNRs). Our calculations show that gt-CNRs with different edge conformation exhibit distinct electronic and magnetic characteristics, which can be tuned by the edge H-passivation rate. By investigating gt-CNRs with various possible edge configurations and H-termination rates, we show that while the ferromagnetic (FM) ordering of gt-CNRs stays preserved for all of the studied configurations, half metallicity can only be achieved in nanoribbons with specific edge structure under full H-passivation rate. For spintronic application purposes, we also study spin-transport properties of half-metal gt-CNRs. By determining the suitable gt-CNR configuration, we show the possibility of developing a perfect gt-CNR-based spin filter with a spin filter efficiency (SFE) of 100%. Considering the above-mentioned notable electronic and magnetic characteristics as well as its high thermal stability, we show that gt-CNR would be a remarkable material to fabricate multifunctional spintronic devices.

A high performance N-doped graphene nanoribbon based spintronic device applicable with a wide range of adatoms.

Designing and fabricating nanosize spintronic devices is a crucial task to develop information technology of the future. However, most of the introduced spin filters suffer from several limitations including difficulty in manipulating the spin current, incapability in utilizing a wide range of dopants to provide magnetism, or obstacles in their experimental realization. Here, by employing first principles calculations, we introduce a structurally simple and functionally efficient spin filter device composed of a zigzag graphene nanoribbon (ZGNR) with an embedded nitrogenated divacancy. We show that the proposed system, possessing a robust ferromagnetic (FM) ordering, exhibits perfect half metallic behavior in the absence of frequently used transition metals (TMs). Our calculations also show that the suggested system is compatible with a wide range of adatoms including basic metals, metalloids, and TMs. It means that besides d electron magnetism originating from TMs, p electrons of incorporated elements of the main group can also cause half metallicity in the electronic structure of the introduced system. Our system exploiting the robustness of doping-induced FM ordering would be beneficial for promising multifunctional spin filter devices.

Graphene and Graphene Analogs toward Optical, Electronic, Spintronic, Green-Chemical, Energy-Material, Sensing, and Medical Applications.

This spotlight discusses intriguing properties and diverse applications of graphene (Gr) and Gr analogs. Gr has brought us two-dimensional (2D) chemistry with its exotic 2D features of density of states. Yet, some of the 2D or 2D-like features can be seen on surfaces and at interfaces of bulk materials. The substrate on Gr and functionalization of Gr (including metal decoration, intercalation, doping, and hybridization) modify the unique 2D features of Gr. Despite abundant literature on physical properties and well-known applications of Gr, spotlight works based on the conceptual understanding of the 2D physical and chemical nature of Gr toward vast-ranging applications are hardly found. Here we focus on applications of Gr, based on conceptual understanding of 2D phenomena toward 2D chemistry. Thus, 2D features, defects, edges, and substrate effects of Gr are discussed first. Then, to pattern Gr electronic circuits, insight into differentiating conducting and nonconducting regions is introduced. By utilizing the unique ballistic electron transport properties and edge spin states of Gr, Gr nanoribbons (GNRs) are exploited for the design of ultrasensitive molecular sensing electronic devices (including molecular fingerprinting) and spintronic devices. The highly stable nature of Gr can be utilized for protection of corrosive metals, moisture-sensitive perovskite solar cells, and highly environment-susceptible topological insulators (TIs). Gr analogs have become new types of 2D materials having novel features such as half-metals, TIs, and nonlinear optical properties. The key insights into the functionalized Gr hybrid materials lead to the applications for not only energy storage and electrochemical catalysis, green chemistry, and electronic/spintronic devices but also biosensing and medical applications. All these topics are discussed here with the focus on conceptual understanding. Further possible applications of Gr, GNRs, and Gr analogs are also addressed in a section on outlook and future challenges.

Lower Electric Field-Driven Magnetic Phase Transition and Perfect Spin Filtering in Graphene Nanoribbons by Edge Functionalization.

Perfect spin filtering is an important issue in spintronics. Although such spin filtering showing giant magnetoresistance was suggested using graphene nanoribbons (GNRs) on both ends of which strong magnetic fields were applied, electric field controlled spin filtering is more interesting due to much easier precise control with much less energy consumption. Here we study the magnetic/nonmagnetic behaviors of zigzag GNRs (zGNRs) under a transverse electric field and by edge functionalization. Employing density functional theory (DFT), we show that the threshold electric field to attain either a half-metallic or nonmagnetic feature is drastically reduced by introducing proper functional groups to the edges of the zGNR. From the current-voltage characteristics of the edge-modified zGNR under an in-plane transverse electric field, we find a remarkable perfect spin filtering feature, which can be utilized for a molecular spintronic device. Alteration of magnetic properties by tuning the transverse electric field would be a promising way to construct magnetic/nonmagnetic switches.