Edges Of Nanoribbons Research Articles

Electronic properties of edge functionalized S-graphene nanoribbons

The structural and electronic properties of edge functionalized S-graphene nanoribbons are studied based on density functional theory. The C atoms of both edges of S-graphene nanoribbons are saturated with –H, –F, –OH, –S, and –Cl groups. It is shown that these edge functionalized nanoribbons are thermally stable. Their electronic properties are strongly dependent on the ribbon width and edge functionalization. The –S and –Cl edge functionalized S-graphene nanoribbons show metallic properties, while S-graphene nanoribbons functionalized by –H, –F, and –OH are semiconductors. Increasing the ribbon width –H, –F, and –OH edge functionalized S-graphene nanoribbons leads to semiconducting-metal transition. Our results indicate that functionalization is a proper way to tune the electronic properties of S-graphene nanoribbons towards various devices and sensing applications.

Spin-thermoelectric transport in nonuniform strained zigzag graphene nanoribbons

We study a nonuniform strain in zigzag graphene nanoribbons for producing the spin-thermoelectric effects, using the mean-field Hubbard approximation and a Green's function approach. Our theoretical results show that a sinusoidal-shaped inhomogeneous strain with electron-electron interaction could induce a different effect on each edge of zigzag nanoribbons and finally generate a spin semiconductor with a tunable spin-dependent band gap. The strength of strain also controls the magnitude of magnetization in each edge. Interestingly, pure spin current and a giant spin Seebeck coefficient can be produced even at low values of strain by applying a thermal gradient and without magnetic elements. These results pave a practical way toward improved design for spin-thermoelectric applications through strain engineering.

Tunable Electronic Properties of Lateral Monolayer Transition Metal Dichalcogenide Superlattice Nanoribbons.

The structural stability and structural and electronic properties of lateral monolayer transition metal chalcogenide superlattice zigzag and armchair nanoribbons have been studied by employing a first-principles method based on the density functional theory. The main focus is to study the effects of varying the width and periodicity of nanoribbon, varying cationic and anionic elements of superlattice parent compounds, biaxial strain, and nanoribbon edge passivation with different elements. The band gap opens up when the (MoS2)3/(WS2)3 and (MoS2)3/(MoTe2)3 armchair nanoribbons are passivated by H, S and O atoms. The H and O co-passivated (MoS2)3/(WS2)3 armchair nanoribbon exhibits higher energy band gap. The band gap with the edge S vacancy connecting to the W atom is much smaller than the S vacancy connecting to the Mo atom. Small band gaps are obtained for both edge and inside Mo vacancies. There is a clear difference in the band gap states between inside and edge Mo vacancies for symmetric nanoribbon structure, while there is only a slight difference for asymmetric structure. The electronic orbitals of atoms around Mo vacancy play an important role in determining the valence band maximum, conduction band minimum, and impurity level in the band gap.

Activated edge of single layered TiO2 nanoribbons through transition metal doping and strain approaches for hydrogen production

The tunable electronic structures and hydrogen evolution reaction ability of single-layered TiO2 nanoribbons were investigated with 3d transition-metal doping and uniaxial strain. Surprisingly, both surface and inner oxygen atoms in nanoribbon can be effectively activated by Cr doping for hydrogen production. Its hydrogen adsorption free energy was reduced to 0.1 eV, much close to that of Pt metal. The binding capacity of inner oxygen with adsorbed hydrogen was related to its py+z band center level. Moreover, the dependence of amendatory hydrogen adsorption ability on the band center level was also proposed to understand the mechanism of strain engineering. These insights provide a potential approach for achieving high hydrogen production activity in oxide nanomaterials.

Термофорез углеродных наночастиц (нанолент и нанотрубок) на плоской многослойной подложке гексагонального нитрида бора (h-BN)

Using the method of molecular dynamics and a 2D chain model, it is shown that thermophoresis of carbon nanoparticles (nanoribbons and nanotubes) on a flat multilayer substrate (on a flat surface of a hexagonal boron nitride crystal) has high efficiency. Placing a nanoparticle on a flat surface of a substrate involved in heat transfer leads to its movement in the direction of the heat flow. The heat flow along the substrate leads to the formation of constant forces acting on the nanoparticle nodes (thermophoresis forces). The main effect of the force is exerted on the edges of graphene nanoribbons, exactly where the main interaction of the nanoribbon with the bending phonons of the substrate occurs. These phonons have a long free path, so the effective transfer of nanoparticles using thermophoresis can occur at sufficiently large distances. The motion of carbon nanoparticles under the action of a heat flow has the form of particle motion in a viscous medium under the action of a constant force. Over time, the nanoparticles always enter the mode of movement at a constant speed. The velocity of the stationary motion is almost the same for all sizes and types of carbon nanoparticles, which is explained by the fact that the thermophoresis force and effective friction have the same source – the interaction of the nanoparticle with the bending thermal vibrations of the substrate layers.

Exploring edge functionalised blue phosphorene nanoribbons as novel photocatalysts for water splitting

1D phosphorene nanoribbon edges activating water molecules under sunlight.

The unique carrier mobility of monolayer Janus MoSSe nanoribbons: a first-principles study.

Charge-carrier mobility is a determining factor of the transport properties of semiconductor materials and is strongly related to the optoelectronic performance of nanoscale devices. Here, we investigate the electronic properties and charge carrier mobility of monolayer Janus MoSSe nanoribbons by means of first-principles simulations coupled with deformation potential theory. These simulations indicate that zigzag nanoribbons are metallic. Conversely, armchair nanoribbons are semiconducting and show oscillations in the calculated band gap as a function of edge-width according to the 3p < 3p + 1 < 3p + 2 rule, with p being the integer number of repeat units along the non-periodic direction of the nanoribbon. Although the charge-carrier mobility of armchair nanoribbons oscillates with the edge-width, its magnitude is comparable to its two-dimensional sheet counterpart. A robust room-temperature carrier mobility is calculated for 3.5 nm armchair nanoribbons with values ranging from 50 cm2 V-1 s-1 to 250 cm2 V-1 s-1 for electrons (e) and holes (h), respectively. A comparison of these values with the results for periodic flat sheet (e: 73.8 cm2 V-1 s-1; h: 157.2 cm2 V-1 s-1) reveals enhanced (suppressed) hole (electron) mobility in the Janus MoSSe nanoribbons. This is in contrast to what was previously found for MoS2 nanoribbons, namely larger mobility for electrons in comparison with holes. These differences are rationalized on the basis of the different structures, edge electronic states and deformation potentials present in the MoSSe nanoribbons. The present results provide the guidelines for the structural and electronic engineering of MoSSe nanoribbon edges towards tailored electron transport properties.

Topological phase transitions driven by topological number change and next-nearest-neighbor hopping in skyrmion crystals

By considering the topological Hall conductivity and the nanoribbon edge states, i.e., the bulk-boundary correspondence of the skyrmion crystal (SkX), this work focused on the relation of the topological properties to the next-nearest-neighbor (nnn) hopping (t′), the exchange coupling strength (J), and the topological number of the skyrmion (Qsk). When the nnn hopping of the electrons coexists with the nearest-neighbor hopping, the flux pattern of the emergent magnetic field traversing the SkX is reshaped giving rise to different topological Hall effect. By increasing t′ from 0 to t, we found the Chern numbers of the electronic bands change from unity to indefinite values demonstrating a phase transition. By continually increasing Qsk from 1 to 2, we found topological phase transitions occur at Qsk=1.3 and 1.7. We also considered the effect of finite J and found the results obtained in the adiabatic limit (J≫t) hold to around J=t.

Electronic structure of graphene nanoribbons under external electric field by density functional tight binding

&lt;sec&gt; In recent years, the rapid development of electronic information technology has brought tremendous convenience to people’s lives, and the devices used have become increasingly miniaturized. However, due to the constraints of the process and the material itself, as the size of the devices made of silicon materials is further reduced, obvious short channel effects and dielectric tunneling effects will appear, which will affect the normal operations of these devices. In order to overcome this development bottleneck, it is urgent to find new materials for the devices that can replace silicon. Carbon has the same outer valence electron structure as silicon. Since 2004, Geim [Novoselov K S, Geim A K, Morozov S V, et al. 2005 &lt;i&gt;Nature&lt;/i&gt; &lt;b&gt;438&lt;/b&gt; 197] prepared two-dimensional graphene with a honeycomb-like planar structure formed by sp&lt;sup&gt;2&lt;/sup&gt; hybridization, graphene has received extensive attention from researchers and industrial circles for its excellent electronic and mechanical properties. However, graphene is not a true semiconductor, and it has no band gap in its natural state. The energy gap can be opened by preparing graphene nanoribbons. On this basis, the electronic structure of the nanoribbons can be further controlled by using an external electric field to destroy the symmetric structure of the nanoribbons. &lt;/sec&gt;&lt;sec&gt;In this paper, the tight-binding method based on density functional theory is used to calculate and study the influence of external transverse electric field on the electronic structure and electron population of un-hydrogenated/hydrogenated armchair graphene nanoribbons. The calculation results show that whether there is hydrogen on the edge of the graphene nanoribbons or not, the energy gap changed at the Г point shows a three-group periodic oscillation decreasing law, and as N increases, the energy gap will disappear. Under the external electric field, the band structure and the density of states of the nanoribbons will change greatly. For un-hydrogenated nanoribbons with semiconducting properties, as the intensity of the external electric field increases, a semiconductor-metal transition occurs. At the same time, the electric field will also have a significant influence on the energy level distribution, resulting in significant changes in the peak height and peak position of the density of states. The external electric field causes the electron population distribution on the atoms in the nanoribbons to break its symmetry. The greater the electric field strength, the more obvious the population asymmetry is. The edge hydrogenation passivation can significantly change the population distribution of atoms in nanoribbons.&lt;/sec&gt;

Enhanced magnetoresistance in hydrogen- and fluorine-passivated zigzag aluminium nitride nano-ribbon

Using density functional theory, we predict junctionless magnetoresistive device (JMD) using edge-passivated zigzag aluminium nitride nano-ribbon (ZAlNNR) for application in magnetoresistive random access memories (MRAMs). The results suggest that the conductivity of ZAlNNR can be modulated by passivating the nano-ribbon edges with hydrogen (H) and fluorine (F) atoms. A semiconducting ZAlNNR results when aluminium (Al) and nitrogen (N) atoms on both the edges of ZAlNNR are passivated by hydrogen or fluorine. A half-metallic nano-ribbon results when the edge consisting of aluminium atoms is passivated by hydrogen or fluorine, whereas a metallic nano-ribbon results when the edge consisting of nitrogen atoms is passivated by hydrogen or fluorine. A junctionless ZAlNNR JMD can thus be formed by selectively passivating the electrodes (half-metallic) and central region (semiconducting). The fluorine-passivated junctionless device offers higher magneto-resistance (MR) and better spin-filtering effect in comparison with hydrogen-passivated device. Smaller device fabrication complexity can also be expected due to a junctionless structure.

Design of a near-infrared plasmonic gas sensor based on graphene nanogratings

In this work, a gas sensor based on the plasmonic double-layer graphene nanograting (GNG) structure with an enhanced figure of merit (FoM) is presented in the near-infrared region. This structure includes double periodic graphene nanoribbon arrays, separated by a dielectric. The wavelength interrogation method is employed to accurately investigate the behavior of the proposed structure for various physical and geometrical parameters, including the array pitch, graphene nanoribbon width, refractive index of the intermediate dielectric between the GNGs, and the chemical potential of the graphene. A sharp dip is achieved by the guided-mode resonance between the two GNG layers, due to their near-field coupling. For the optimized design, obtained sensitivity and FoM are 430.91 nm/RIU and 174.68 R I U − 1 , respectively, when the finite-element method is used for the simulations. The high FoM is a result of the field enhancement at the edges of the graphene nanoribbons, as well as the narrow resonance linewidth achieved by the sharp transmission dip. In addition to the high performance and FoM, the structure is robust to the misalignment of two GNG layers, offering a solution for practical gas sensing applications. To the best of our knowledge, the proposed GNG-based structure enjoys a boosted FoM compared to the previously proposed integrated gas sensors, as well as a practically feasible design for fabrication.

Different noncollinear magnetizations on two edges of zigzag graphene nanoribbons* *Project supported by the National Natural Science Foundation of China (Grant Nos. NSFC11804158, NSFC61974067, NSFC91750112, and NSFC11947101).

Based on density functional theory and non-equilibrium Green’s function method, we studied noncollinear magnetism and spin transport in a 180° domain wall made of zigzag graphene nanoribbon (ZGNR) with different noncollinear magnetic profiles on the top and bottom edges. Our results show that a helical domain wall on the top (bottom) edge and an abrupt domain wall on the bottom (top) edge can survive in the ZGNR. This indicates that such characteristic magnetization distribution can be obtained by some means, e.g., the introduction of impurity on one edge. Compared to a wide ZGNR, a narrow ZGNR presents obvious coupling between the two edges which changes the magnetization and transmission greatly. As for the above-mentioned distinct magnetic profile, the spin transport is blocked in the abrupt domain wall due to strong spin flip scattering while remains unaffected in the helical domain wall due to the spin mixing effect. We deduce a formula of the transmission for various magnetic profiles of the ZGNRs. A new result based on this formula is that the transmission at the Fermi level can be zero, one, and two by tuning the edge magnetization. Our results provide insights into the noncollinear spin transport of the ZGNR-based devices.

How Do the Coadsorbates Affect the Oxygen Reduction Reaction Activity of Undoped and N-Doped Graphene Nanoribbon Edges? A Density Functional Theory Study

Nitrogen-doped graphene represents a good alternative and a promising catalytic structure for the oxygen reduction reaction (ORR) in fuel cell applications compared with the more costly Pt-containi...

The defect impacts of zigzag SiC nanoribbons in the spin devices

In this work, electronic structures and spin transport characteristics of SiC zigzag nanoribbons with defects have been studied by spin-polarized first-principles calculations. It is found that the transport channel of the zigzag SiC nanoribbon device in parallel configurations is located in the edge of nanoribbons. The spin currents can be turned on or off by specific edge defects. As to the antiparallel configuration, all the SiC nanoribbon devices exhibit a perfect dual spin filtering effect, which is immune to the position of defects. By transmission spectra calculations, the corresponding mechanisms of these peculiar effects were explained. The results from this work might indicate a promising pathway for developing spin filters with SiC nanoribbons.

Even\u2013odd conductance effect in graphene nanoribbons induced by edge functionalization with aromatic molecules: basis for novel chemosensors

We theoretically investigate the electron transport in armchair and zigzag graphene nanoribbons (GNRs) chemically functionalized with p-polyphenyl and polyacene groups of increasing length. Our nearest-neighbor tight-binding calculations indicate that, depending on whether the number of aromatic rings in the functional group is even or odd, the resulting conductance at energies matching the energy levels of the corresponding isolated molecule is either unaffected or reduced by exactly one quantum as compared to the pristine GNR, respectively. Such an even–odd effect is shown to originate from a subtle interplay between the electronic states of the guest molecule that are spatially localized on the binding sites and those of the host nanoribbon. We next generalize our findings by employing more accurate tight-binding Hamiltonians along with density-functional theory calculations and critically discuss the robustness of the observed physical effects against the level of theory adopted. Our work offers a comprehensive understanding of the influence of aromatic molecules bound to the edge of graphene nanoribbons on their electronic transport properties, an issue which is instrumental to the prospective realization of graphene-based chemosensors.

First principle insights of NO2 detection via III-V nitride nanoribbons with armchair edges

The development of low-dimensional and robust nano-sensors is an area of potential research and development. In this direction, here, we investigated the sensing of NO2 gas molecules adsorbed on the edges of III-V nitride nanoribbons with armchair edges (AXNNR, X = B/Al/Ga). Five different adsorption sites are considered for the adsorption of NO2 molecules and the adsorption assisted modulation of electronic and transport properties has been observed for detection purpose. Interestingly, a semiconducting to metallic transition has been noticed in considered AXNNR due to NO2 interaction. The selectivity of NO2 with respect to N2 is found to be higher as compared to that of O2. Further, some of the selected structures exhibit an interesting negative differential resistance (NDR) phenomenon which suggest that NO2 adsorbed AXNNR could also be useful for designing of the fast switching devices and oscillators applications.

Thermal energy transport across the graphene/C3N interface

In-plane heterojunctions, obtained by seamless joining two or more nanoribbon edges of isolated two-dimensional atomic crystals such as C3N and graphene, are emerging nanomaterials for the development of future multifunctional devices. The thermal transport behavior at the interface of these heterojunctions plays a pivotal role in determining their thermal conductivity and functional performance. Using molecular dynamics simulations, the interfacial thermal conductance G and effective thermal conductivity keff of C3N/graphene in-plane heterojunctions are investigated. The value of G for the C3N/graphene heterojunction at room temperature is 31.49 GWm−2K−1 when heat transfers from C3N to graphene, which is larger than the value of 28.62 GWm−2K−1in the reverse direction, indicating that thermal rectification exists at the interface. The keff values of the C3N/graphene nanoribbon along the direction from C3N to graphene and the reverse direction are 1183.60 Wm−1K−1 and 1346.51 Wm−1K−1, respectively. In addition, the G and keff of heterojunctions are effectively manipulated by changing the temperature, doping with nitrogen, applying strain and employing a substrate. A vibrational spectral analysis is performed to explore the thermal transport mechanism. The thermal energy transport across C3N/graphene interfaces is enhanced by increasing the size, temperature, nitrogen doping concentration, and compressive strain perpendicular to the heat flux direction or by depositing the materials on an amorphous silicon dioxide substrate. Furthermore, increasing the temperature and compressive strain are efficient methods to increase keff. The results provide valuable insights into the design and application of C3N/graphene-based electronic devices.

Negative differential resistance in nanoscale heterostructures based on zigzag graphene nanoribbons anti-symmetrically decorated with BN

Abstract Nanoscale 2 dimensional (2D) heterostructures based on zigzag graphene nanoribbons (ZGNRs) anti-symmetrically decorated with boron nitride (BN), are proposed as resonant tunneling diodes (RTD). Boron nitride has been utilized to decorate two edges of zigzag graphene nanoribbons in order to create required bandgap difference for constructing double barrier quantum well heterostructure. Nonequilibrium Green's function (NEGF) method including tight-binding (TB) Hamiltonian is employed to obtain transmission versus energy (T-E) curves and current versus bias voltage (I-V) characteristics of proposed heterostructures. Effect of structural parameters on the I-V characteristic is investigated. Proposed RTDs clearly show negative differential resistance (NDR) behavior in their I-V characteristic. Moreover, it is shown that the NDR behavior of proposed heterostructures can be precisely tuned by modulating structural dimensions.

Electronic Properties of the Interface Between Metallic Doped Zigzag Graphene and Pristine Graphene Nanoribbons

The electronic properties of the interface between metallic doped zigzag graphene nanoribbons and perfect graphene nanoribbons are investigated. The density functional based tight-binding approach and a non-equilibrium Green function method are employed for our calculations. The atoms of Ni, Co, and Fe are used as doping atoms. The graphs of current–voltage, density of states, electron density, transmission spectrum, and rectification ratio are obtained. The results show that the bond lengths around the atoms of Ni, Co, and Fe are increased. Moreover, it is observed that for the graphene-based nanodevice the curves of current–voltage are linear and symmetric when no impurity exists and with the effect of impurities the curves are non-linear and asymmetric. While Ni, Co, and Fe impurities are applied into the systems we found that the maximum electron densities are located around the impurities of Ni and the current is decreased. The density of states and transmission spectrum are also examined for different systems. It is found that for certain amount of energies some resonances occur for the current, and the atoms at the edge of nanoribbon are mostly responsible for the transfer of the electrons. The obtained results can be of interest for the construction of nanoelectronic devices and can have practical applications.

Superconductivity on Edge: Evidence of a One-Dimensional Superconducting Channel at the Edges of Single-Layer FeTeSe Antiferromagnetic Nanoribbons.

How superconductivity emerges from antiferromagnetic ordering is an essential question for Fe-based superconductors. Here, we explore the effect of dimensionality on the interplay between antiferromagnetic ordering and superconductivity by investigating nanoribbons of single-layer FeTe1-xSex films grown on SrTiO3(001) substrates by molecular beam epitaxy. Using scanning tunneling microscopy/spectroscopy, we find a one-dimensional (1D) superconducting channel 2 nm wide with a TC of 42 ± 4 K on the edge of FeTe1-xSex (x < 0.1) ribbons, coexisting with a non-superconducting ribbon interior that remains bicollinear antiferromagnetically ordered. Density functional theory calculations indicate that both Se and the presence of the edge destabilize the bicollinear antiferromagnetic magnetic order, resulting in a paramagnetic region near the edge with strong local checkerboard fluctuations that is conducive to superconductivity. Our results represent the highest TC achieved in 1D superconductors and demonstrate an effective route toward stabilizing superconductivity in Fe-based superconductors at reduced dimensions.