The spin-dependent transport properties of zigzag α-graphyne nanoribbons and new device design

Graphyne and graphdiyne nanoribbons: from their structures and properties to potential applications

Graphyne (GY) and graphdiyne (GDY) have properties including unique sp- and sp2-hybrid carbon atomic structures, natural non-zero band gaps, and highly conjugated π electrons. GY and GDY have good application prospects in many fields, including catalysis, solar cells, sensors, and modulators. Under the influence of the boundary effect and quantum size effect, quasi-one-dimensional graphyne nanoribbons (GYNRs) and graphdiyne nanoribbons (GDYNRs) show novel physical properties. The various structures available give GYNRs and GDYNRs greater band structure and electronic properties, and their excellent physical and chemical properties differ from those of two-dimensional GY and GDY. However, the development of GYNRs and GDYNRs still faces problems, including issues with accurate synthesis, advanced structural characterization, the structure-performance correlation of materials, and potential applications. In this review, the structures and physical properties of quasi-one-dimensional GYNRs and GDYNRs are reviewed, their advantages and disadvantages are summarized, and their potential applications are highlighted. This review provides a meaningful basis and research foundation for the design and development of high-performance materials and devices based on GYNRs and GDYNRs in the field of energy.

The Strain-Tuned Spin Seebeck Effect, Spin Polarization, and Giant Magnetoresistance of a Graphene Nanobubble in Zigzag Graphene Nanoribbons

By using first-principle calculations combined with the non-equilibrium Green's function approach, we studied the spin caloritronic properties of zigzag graphene nanoribbons with a nanobubble at the edge (NB-ZGNRs). The thermal spin-polarized currents can be induced by a temperature difference, and the spin Seebeck effect is found in the nanoribbon. The spin polarization, magnetoresistance, and Seebeck coefficients are discussed, which are strongly affected and can be tuned by the geometrical strain. Moreover, some novel spin caloritronic devices are designed, such as a device that generates bidirectional perfect spin currents and thermally induced giant magnetoresistances. Our results open up the possibility of tuning the spin caloritronic properties of the NB-ZGNR-based devices by changing the elastic strain on the graphene nanobubble.

Strain Investigation on Spin-Dependent Transport Properties of γ-Graphyne Nanoribbon Between Gold Electrodes

Strain engineering has become one of the effective methods to tune the electronic structures of materials, which can be introduced into the molecular junction to induce some unique physical effects. The various γ-graphyne nanoribbons (γ-GYNRs) embedded between gold (Au) electrodes with strain controlling have been designed, involving the calculation of the spin-dependent transport properties by employing the density functional theory. Our calculated results exhibit that the presence of strain has a great effect on transport properties of molecular junctions, which can obviously enhance the coupling between the γ-GYNR and Au electrodes. We find that the current flowing through the strained nanojunction is larger than that of the unstrained one. What is more, the length and strained shape of the γ-GYNR serves as the important factors which affect the transport properties of molecular junctions. Simultaneously, the phenomenon of spin-splitting occurs after introducing strain into nanojunction, implying that strain engineering may be a new means to regulate the electron spin. Our work can provide theoretical basis for designing of high performance graphyne-based devices in the future.

Giant magnetoresistance and dual spin filtering effect in ferromagnetic 6,6,12/γ-graphyne zigzag nanoribbon lateral heterojunction

Based on non-equilibrium Green's function combined with density functional theory (NEGF-DFT), we investigate the spin dependent transport in the ferromagnetic 6,6,12/γ-graphyne zigzag nanoribbon (GYZNR) heterojunction under different magnetic configurations. It is found that, at low bias ([-0.05, 0.1] V), the junction presents metallic transport with negligible spin polarization in parallel configuration (PC) while it behaves as an insulator in anti-parallel configuration (APC), which results in giant magnetoresistance. Interestingly, when we increase the bias voltage beyond [-0.05, 0.1] V, dual spin filtering characterized by electron transport of different spin channels under different polarity of bias is observed in APC but not in PC. All these findings are understood from the symmetry matching of wave functions in two nanoribbons at equilibrium or finite bias. Furthermore, dual spin filtering can also be achieved in PC by applying a gate voltage on the central interface region, which arises from the shift of different single spin channel of the central gate region into the bias window at a different polarity of the gate voltage. Thus, our work demonstrates the great potential of the 6,6,12/γ-GYZNR heterojunction as a multi-functional device and its great perspectives in carbon-based nanoelectronics and spintronics.

Graphyne and Its Family: Recent Theoretical Advances

Graphyne and its family are new carbon allotropes in 2D form with both sp and sp² hybridization. Recently, the graphyne with different structures have attracted great attentions from both experimental and theoretical communities, especially because the first successful synthesis of graphdiyne, which is a typical member of the graphyne family. In this review, recent theoretical progresses in the research of the graphyne family are summarized. More specifically, we systematically introduce the structural, mechanical, band, electronic transport, and thermal properties of graphyne and its family, as well as their possible applications, such as gas separation, water desalination and purification, anode material for ion battery, H₂ storage, and catalysis application. Several related theoretical methods are also reviewed. The coexistence of sp and sp² hybridization and the unique atom arrangement of the graphyne family members bring many novel properties and make them promising materials for many potential applications.

Negative differential resistance, perfect spin-filtering effect and tunnel magnetoresistance in vanadium-doped zigzag blue phosphorus nanoribbons

We investigate the electronic and transport properties of vanadium-doped zigzag blue phosphorus nanoribbons by first-principles quantum transport calculations. We study the spin-dependent transport properties and obtain current-voltage curves showing obvious spin polarization and negative differential behaviors. These interesting transport behaviors can be explained by the band structure of the vanadium-doped zigzag blue phosphorus nanoribbons. The tunnel magnetoresistance and spin-filtering effects under different magnetic configurations originate predominately from the symmetry matching between the band structures of the electrodes. According to our results, vanadium-doped zigzag blue phosphorus nanoribbons can be used as a perfect spin filter with a large tunnel magnetoresistance. This also indicates that blue phosphorus nanoribbons are a promising candidate for their future application in spintronics.

Existence of multi-radical and closed-shell semiconducting states in post-graphene organic Dirac materials

Post-graphene organic Dirac (PGOD) materials are ordered two-dimensional networks of triply bonded sp 2 carbon nodes spaced by π-conjugated linkers. PGOD materials are natural chemical extensions of graphene that promise to have an enhanced range of properties and applications. Experimentally realised molecules based on two PGOD nodes exhibit a bi-stable closed-shell/multi-radical character that can be understood through competing Lewis resonance forms. Here, following the same rationale, we predict that similar states should be accessible in PGOD materials, which we confirm using accurate density functional theory calculations. Although for graphene the semimetallic state is always dominant, for PGOD materials this state becomes marginally meta-stable relative to open-shell multi-radical and/or closed-shell states that are stabilised through symmetry breaking, in line with analogous molecular systems. These latter states are semiconducting, increasing the potential use of PGOD materials as highly tuneable platforms for future organic nano-electronics and spintronics.

Modulation of electronic transport properties in armchair phosphorene nanoribbons by doping and edge passivation

The electronic structures and transport properties of group IV atoms (C, Si, Ge)-doped armchair phosphorene nanoribbons (APNRs) are investigated using first-principles calculations, considering different edge passivation. The results show that the C, Si, Ge dopants can induce the transition occur from semiconductor to metal in the APNRs. The negative differential resistance (NDR) behavior in the doped APNR system is robust with respect to the doping concentration and edge passivation type. However, their current peak positions and peak-to-valley ratio (PVR) values are correlated with doping concentration and edge passivation type. In particular, for the C, Si-doped APNRs, the low bias NDR behavior with the PVR (10⁵–10⁸) can be observed when doping concentration is low in the APNRs with the F and H edge passivation. These results may play an important role for the fabrication of future low power consumption nano-electronic devices.

Density functional theory investigation of negative differential resistance and efficient spin filtering in niobium-doped armchair graphene nanoribbons

A niobium-doped AGNR for efficient negative differential resistance and spin filtering applications.