Zigzag Edges Research Articles

Several distance and degree-based molecular structural attributes of cove-edged graphene nanoribbons

A carbon-based material with a broad scope of favourable developments is called graphene. Recently, a graphene nanoribbon with cove-edged was integrated by utilizing a bottom-up liquid-phase procedure, and it can be geometrically viewed as a hybrid of the armchair and the zigzag edges. It is indeed a type of nanoribbon containing asymmetric edges made up of sequential hexagons with impressive mechanical and electrical characteristics. Topological indices are numerical values associated with the structure of a chemical graph and are used to predict various physical, chemical, and biological properties of molecules. They are derived from the graph representation of molecules, where atoms are represented as vertices and bonds as edges. In this article, we derived the exact topological expressions of cove-edged graphene nanoribbons based on the graph-theoretical structural measures that help reduce the number of repetitive laboratory tasks necessary for studying the physicochemical characteristics of graphene nanoribbons with curved edges.

Schottky barrier diode and photoelectric device based on two dimensional noble transition-metal sulfides vertical heterojunction

In this work, we use first-principles method to investigate the properties of two-dimensional noble transition-metal sulfides MS2 (M = Ni, Pd, Pt) and the electronic and optoelectronic applications of their vertical heterojunctions. The vertically bilayer or trilayer stacking can modulate the band structures and optical absorption spectra of MS2 (M = Ni, Pd, Pt) obviously. Therefore, we create the atomically thin Schottky barrier diodes (SBD) by vertically stacking the MS2 (M = Ni, Pd, Pt) on monolayer MS2 (M = Ni, Pd, Pt). All SBDs reveal more excellent current rectification behavior along the armchair edge (AE) transport direction than that along the zigzag edge (ZE) transport direction. SBD based on PdS2 bilayer and monolayer heterojunction has the high current value and the significant rectification ratio (exceeding 105) along AE transport direction. The total photocurrent densities of all SBDs along the ZE transport direction are bigger than that along the AE transport direction. SBD based on PdS2 bilayer and monolayer heterojunction has the largest total photocurrent density (1208.07 μA/mm2) along the ZE transport direction. Our work provides foundations for the application of two-dimensional noble transition-metal sulfides in rectification and optoelectronics.

Thermodynamics and electronic structure of edges in monolayer MoSi2N4

MoSi2N4 is a two-dimensional ternary nitride semiconductor that has attracted attention for its excellent mechanical and thermal properties. Theoretical studies predict that zigzag edges of this material can host magnetic edge states and Dirac fermions, but the stability of such edges has not been examined. Here, we present a density functional theory study of the electronic and thermodynamic properties of MoSi2N4 edges. We develop a (partial) ternary phase diagram that identifies a region of chemical potentials within which MoSi2N4 is stable over competing elemental or binary phases. Based on this phase diagram, we determine the thermodynamic stability of several armchair and zigzag edges and elucidate their electronic structures. Bare zigzag edges, predicted to host exotic electronic states, are found to be substantially higher in energy than armchair edges and, thus, unlikely to occur in practice. However, with hydrogen passivation, these zigzag edges can be stabilized relative to their armchair counterparts while retaining metallicity and magnetic order. Our analysis provides a solid thermodynamic basis for further exploration of MoSi2N4 in nanoscale electronics and spintronics.

Edge-dependent Majorana corner modes in an s-wave superconductor

In contrast to Majorana edge modes in first-order topological superconductors, Majorana corner modes are usually related to spatial symmetries and further rely on specific corner of the sample. In this paper, we study Majorana corner modes in an extended Kane-Mele model with arbitrary phase. Majorana corner mode exists at both corner between zigzag edge and armchair edge and corner between zigzag edge and zigzag edge for the phase at π/2. However, while the Majorana corner mode at the corner between zigzag edge and armchair edge remains as the phase deviates from π/2, Majorana mode at the corner between zigzag edge and armchair edge disappears. These Majorana corner modes are edge dependent and originate from the sign change of Dirac mass or Dirac velocity for edge states at adjacent edges tuned by the phase.

Development of an active agar aerogel with dual antioxidant and UV-blocking activities using chlorine-doped graphene quantum dots

Active packaging is of great interest in the modern food industry due to increasing shelf life and enhancing food quality. The importance of this technology increases when natural polymers are used in the construction of active packages. Development of a natural, biodegradable, and dual-active film was aimed in this study. So, agar aerogel containing different amounts of chlorine-doped graphene quantum dots (Cl-GQDs) was prepared. Cl-GQDs had excitation-dependent fluorimetry behavior due to the zigzag edges of graphene. The mean diameter of spherical nanoparticles of Cl-GQDs was about 12 nm, according to HR-TEM images. The results of Raman and ATR-FTIR confirmed that chlorine was well-doped on the GQD structure. Cl-GQDs showed high UV-absorption capability and very strong antioxidant activity (94.31 %), which maintained these activities after incorporation into the agar aerogel. The doped chlorine was responsible for the capacity to charge transfer of GQDs. BET and SEM results showed that adding Cl-GQDs to agar caused a porous structure. Finally, different types of agar aerogels containing Cl-GQDs can be used considering the intended application of aerogel. Agar aerogel containing 20 % Cl-GQDs is suggested if a porous aerogel with good thermal insulation properties is considered. However, agar aerogel containing 1 % Cl-GQDs is suitable as an active film. In conclusion, while Cl-GQDs hold promise as sustainable and multifunctional food packaging materials, their potential toxic effects must be thoroughly evaluated. Future studies should explore migration, potential interactions with specific food matrices, and long-term safety to ensure consumer protection.

Bisindeno Fusion on the Zigzag Edge of Bis(benzooxa)-2,6-anthraquinodimethane: Effect on Diradical Character, Photostability, and Redox Properties.

We report the synthesis of the bis(benzooxa)-2,6-anthraquinodimethane (BAQ) derivative and its bisindeno fused analogue BIBAQ. We found bisindeno fusion on the quinoidal zigzag edge of BAQ results in decreased diradical character and corresponding increased photostability. Furthermore, BAQ could only be oxidized into its cationic species, while BIBAQ showed balanced redox properties.

Electric-field-controlled electronic structures and quantum transport in monolayer InSe nanoribbons

Electronic structures and quantum transport properties of the monolayer InSe nanoribbons are studied by adopting the tight-binding model in combination with the lattice Green function method. Besides the normal bulk and edge electronic states, a unique electronic state dubbed as edge-surface is found in the InSe nanoribbon with zigzag edge type. In contrast to the zigzag InSe nanoribbon, a singular electronic state termed as bulk-surface is observed along with the normal bulk and edge electronic states in the armchair InSe nanoribbons. Moreover, the band gap, the transversal electron probability distributions in the two sublayers, and the electronic state of the topmost valence subband can be manipulated by adding a perpendicular electric field to the InSe nanoribbon. Further study shows that the charge conductance of the two-terminal monolayer InSe nanoribbons can be switched on or off by varying the electric field strength. In addition, the transport of the bulk electronic state is delicate to even a weak disorder strength, however, that of the edge and edge-surface electronic states shows a strong robustness against to the disorders. These findings may be helpful to understand the electronic characteristics of the InSe nanostructures and broaden their potential applications in two-dimensional nanoelectronic devices as well.

Hexabenzoheptacene: A Longitudinally Multihelicene Nanocarbon with Local Aromaticity and Enhanced Stability

AbstractWe report the synthesis of a longitudinally helical molecular nanocarbon, hexabenzoheptacene (HBH), along with its dimethylated derivative (HBH‐Me), which are composed of six benzene rings periodically benzannulated to both zigzag edges of a heptacene core. This benzannulation pattern endows the resulting nanocarbons with a helical heptacene core and local aromaticity, imparting enhanced solubility and stability to the system. The chiral HBH‐Me adopts a more highly twisted conformation with an end‐to‐end twist angle of 95°, enabling the separation of the enantiomers. Both HBH and HBH‐Me can be facilely oxidized into their corresponding dications, which exhibit enhanced planarity and aromaticity upon loss of electrons. Notably, both longitudinally helical nanocarbons readily promote solid state packing into two‐dimensional (2D) arrangement. Single‐crystal microbelts of HBH‐Me show hole mobility up to 0.62 cm2 V−1 s−1, illustrating the promising potential of these longitudinally helical molecules for organic electronic devices.

Hexabenzoheptacene: A Longitudinally Multihelicene Nanocarbon with Local Aromaticity and Enhanced Stability.

We report the synthesis of a longitudinally helical molecular nanocarbon, hexabenzoheptacene (HBH), along with its dimethylated derivative (HBH-Me), which are composed of six benzene rings periodically benzannulated to both zigzag edges of a heptacene core. This benzannulation pattern endows the resulting nanocarbons with a helical heptacene core and local aromaticity, imparting enhanced solubility and stability to the system. The chiral HBH-Me adopts a more highly twisted conformation with an end-to-end twist angle of 95°, enabling the separation of the enantiomers. Both HBH and HBH-Me can be facilely oxidized into their corresponding dications, which exhibit enhanced planarity and aromaticity upon loss of electrons. Notably, both longitudinally helical nanocarbons readily promote solid state packing into two-dimensional (2D) arrangement. Single-crystal microbelts of HBH-Me show hole mobility up to 0.62 cm2 V-1 s-1, illustrating the promising potential of these longitudinally helical molecules for organic electronic devices.

Formation of Supernarrow Borophene Nanoribbons

AbstractBorophenes have sparked considerable interest owing to their fascinating physical characteristics and diverse polymorphism. However, borophene nanoribbons (BNRs) with widths less than 2 nm have not been achieved. Herein, we report the experimental realization of supernarrow BNRs. Combining scanning tunneling microscopy imaging with density functional theory modeling and ab initio molecular dynamics simulations, we demonstrate that, under the applied growth conditions, boron atoms can penetrate the outermost layer of Au(111) and form BNRs composed of a pair of zigzag (2,2) boron rows. The BNRs have a width self‐contained to ∼1 nm and dipoles at the edges to keep them separated. They are embedded in the outermost Au layer and shielded on top by the evacuated Au atoms, free of the need for post‐passivation. Scanning tunneling spectroscopy reveals distinct edge states, primarily attributed to the localized spin at the BNRs’ zigzag edges. This work adds a new member to the boron material family and introduces a new physical feature to borophenes.

Formation of Supernarrow Borophene Nanoribbons.

Borophenes have sparked considerable interest owing to their fascinating physical characteristics and diverse polymorphism. However, borophene nanoribbons (BNRs) with widths less than 2 nm have not been achieved. Herein, we report the experimental realization of supernarrow BNRs. Combining scanning tunneling microscopy imaging with density functional theory modeling and ab initio molecular dynamics simulations, we demonstrate that, under the applied growth conditions, boron atoms can penetrate the outermost layer of Au(111) and form BNRs composed of a pair of zigzag (2,2) boron rows. The BNRs have a width self-contained to ∼1 nm and dipoles at the edges to keep them separated. They are embedded in the outermost Au layer and shielded on top by the evacuated Au atoms, free of the need for post-passivation. Scanning tunneling spectroscopy reveals distinct edge states, primarily attributed to the localized spin at the BNRs' zigzag edges. This work adds a new member to the boron material family and introduces a new physical feature to borophenes.

Theoretical insights into the activity of the N doped graphene quantum dots for oxygen reduction reaction as a function of the shape and edge terminations

We have investigated the possible activity of the N-doped graphene quantum dots (N-GQD) toward the oxygen reduction reaction (ORR) using density functional theory (DFT) method. The effect of the shape (triangular (N-GQDT), rhombohedral (N-GQDR) and hexagonal (N-GQDH)), connected both with the zigzag (zz) and armchair (ac) edge terminations of the GQD and with the location of the N atom across the sheets are investigated. The activity of part of the studied N-GQDTac, GQDRac, N-GQDHac and N-GQDHzz structures improves significantly compared to the similar pristine structures. On the other hand, no matter on the location of the N in the N-GQDTzz and in the N-GQDRzz, their activity gets worsen, when compared with the activity of the pristine structures or with the activity of the other four investigated structures. N-GQDTac and N-GQDRac are the structures with the most possible locations of N, that generates active sites. CN bond breaking takes place in the triangular shapes (N-GQDTzz and N-GQDTac) when oxygen adsorption takes place. These bonds are less likely to regenerate and new reaction sites are created. The new reaction site created on the N-GQDTzz represents a possible active site compared to the site generated on the N-GQDTac, that is highly inactive.

Homoepitaxy of Boron Nitride on Exfoliated Hexagonal Boron Nitride Flakes.

Although large efforts have been made to improve the growth of hexagonal boron nitride (hBN) by heteroepitaxy, the non-native substrates remain a fundamental factor that limits the quality. This problem can be solved by homoepitaxy, which is the growth of hBN on hBN substrates. In this report, we demonstrate the homoepitaxial growth of triangular BN grains on exfoliated hBN flakes by Metal-Organic Vapor Phase Epitaxy and show by atomic force microscopy and photoluminescence that the stacking of these triangular islands can deviate from the AA' stacking of hBN. We show that the stacking order is enforced by the crystallographic direction of the edge of the exfoliated hBN flakes, with armchair edges allowing for centrosymmetric stacking, whereas zigzag edges lead to the growth of noncentrosymmetric BN polytypes. Our results indicate pathways to grow homoepitaxial BN with tunable layer stacking, which is required to induce piezoelectricity or ferroelectricity.

Theoretical insight into NO formation and reduction at biochar N-sites: Influence of different oxygen-containing functional groups

Biochar is a cost-efficient and promising porous carbonaceous material for the efficient removal of flue gas NOx. The N-site located at the edge of biochar can be a crucial gateway for NO reduction to N2 or for NO formation by oxidation, which can be significantly affected by the oxygen-containing functional groups (OFGs) on the biochar edge. However, the roles of different OFGs in N-site-involved reactions remain elusive. Based on the biochar characterization results, reasonable theoretical models of biochar with different N-sites and OFGs were constructed. Subsequently, the effects of distinct OFGs on the interaction between NO and N-sites as well as the NO liberation from N-sites were elucidated, by employing density functional theory (DFT) and electronic structure analysis. The results reveal that all OFGs, encompassing -CHO, -COOH, and -OH, manifest their roles through the direct inherent electrostatic properties of O/H in OFGs (O*/H*) or altering the reactivity of edge atoms indirectly. For pyridinic nitrogen (N-6) at the zigzag edge, unsaturated (-CHO, -COOH)/saturated (-OH) OFGs inhibit/enhance NO reduction with N-6 by electrostatic properties of O*/H*, and all OFGs inhibit NO generation from N-6. Besides, all OFGs enhance the NO reduction with pyrrolic nitrogen (N-5) at the armchair edge while inhibiting the release of NO, by influencing the edge activity. The present study gives a mechanism insight into the roles of distinct OFGs in reactions involving biochar N-sites.

Chlorinated graphene and graphene nanoribbons: A density functional theory study

Functional groups based on halides, such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), are crucial for understanding the chemical reactivity of graphitic nanomaterials. Except for I, halogens exhibit electronegativity greater than carbon (C); therefore, charge transfer from carbon to halogen is expected. First-principles density functional theory calculations were performed to determine the role of different Cl-functional groups (methyl-trichloride, ethyl-trichloride, chloride, acyl-chloride, vinyl-chloride, acetyl hypochlorite, chloramines, sulfonyl chloride, and more) on the electronic properties of graphene and graphene nanoribbons (GNRs). GNRs with zigzag edges (ZGNRs) and armchair edges (AGNRs) were studied. We analyzed the optimized structures, band structure, density of states, cohesive energy, and band gap. Our results revealed that the based-Cl functional groups can provide an alternative route to activate the borders and surfaces of sp2 carbon materials. Methyl-trichloride and acyl-chloride can induce magnetism and metallicity. Chloride and acyl-chloride are the most energetically stable functional groups attached to the edges. Surprisingly, methyl-trichloride or acyl-chloride functionalizing the surface of the AGNRs showed a direct (indirect) band gap for states with spin-up (spin-down). The results of aromatic (chlorobenzene- and dichlorobenzene-like structures) functionalization considering F, Cl, Br, and I are also shown. Finally, –F2 and –ClF functionalization cases are discussed.

Valley filtering using magnetic proximity effect in monolayer WS[formula omitted]

A quantum system implanted with monolayer transition metal dichalcogenide (TMDC) is proposed as a valley filter based on a ballistic point contact with zigzag edges. A quantum point contact (QPC) structure is formed in the middle of scattering region and the geometrical size of the QPC is varied by electrostatic gate potentials. The energy band structures and electronic transport properties are investigated using a two-bands k⋅p Hamiltonian by using parameters from the density functional theory (DFT) calculations. The magnetic proximity effect from an Eu-terminated ferromagnetic substrate (EuS) generates a giant valley splitting in the energy of the monolayer WS2 nanoribbon. The conductance is limited by reducing the width and by increasing the length of the QPC because conductance is strongly related to the number of transmission channels and the amounts of back scatterings at the QPC. The polarity of valley current can be manipulated by applying a local gate potential in the QPC region, where the manipulated polarity is limited to well defined K′ polarization only. The lateral hetero materials on both sides of the QPC or lateral hetero ferromagnetic substrate is necessary to have desired valley and spin polarities of current by manipulating the local gate potential. The experimental realization of this quantum system will make it possible to control the valley degree of freedom in addition to controlling charge and spin degree of freedom of carriers in future electronic devices.

Spin and charge interactions between nanographene host and ferrocene.

Ferrocene (FeCp2) was introduced as a non-magnetic guest molecule to activated carbon fibers (ACFs) as a nanographene-based host having localized spins originating from zigzag edges of graphene. The introduction of the guest molecule was confirmed by FTIR for ACFs-FeCp2 introduced at 55 (150) °C (FeCp2-ACFs-55(150)). The appearance of satellite Fe2p peaks and the increase in shake-up peak intensity of the C1s in the XPS spectrum proved the emergence of charge-transfer host-guest interaction in FeCp2-ACFs-150, supported by the red-shift of the G-band in the Raman spectrum. The six-times enhancement in the spin concentration in FeCp2-ACFs-150 compared with ACFs indicates the spin magnetism of the non-magnetic guest FeCp2+ molecule induced by a charge-transfer host-guest interaction in the nanographene host. The larger ESR linewidth than that expected from the dipolar interaction estimated by the localized spin concentration suggests the exchange interaction between the nanographene and FeCp2 spins. The narrowing of the ESR linewidth of FeCp2-ACFs-55 upon higher excitation microwave power suggests the inhomogeneity of the environment for FeCp2+ molecules in the nanographene host. The observed induction of spin magnetism by the interfacial interactions between the nanographene host and the guest molecules will be a promising strategy for developing a new class of molecular magnets.

Exploring edge states in square–octagon moiré lattice

Moiré lattices, achieved by the superposition of two or more twisted identical periodic lattices, are of interest to various fields because they provide additional degrees of freedom. Here, we theoretically and experimentally study the edge states in a square–octagon moiré lattice. This moiré lattice is created by superimposing two identical square sublattices with an antiphase and a special twist angle. Five different edges, named type-I zigzag edge, type-II zigzag edge, type-I bearded edge, type-II bearded edge, and armchair edge, are explored. Through band structure analysis and numerical simulation of edge excitation, we find that all five edges support edge states. The topological property of the type-I edge states is verified by calculating the 2D polarization of the lattice. Furthermore, the edge mode distribution manifests that multiple bands support identical edge states at the armchair and type-II bearded edges. In the experiment, the moiré lattice is generated by the CW-laser-writing technique, thereby observing all the edge states with corresponding edge excitations. This study broadens the understanding of edge states in the coupled moiré photonic lattices and provides a new platform for exploring topological physics.

Magneto-plasmon of AA-stacked bilayer graphene nanoribbons at finite temperature

Magneto-band structures of AA-stacked bilayer graphene nanoribbons with armchair and zigzag (BLAGNR and BLZGNR) edges are calculated by the pz-orbital tight-binding model. At zero field, BLAGNR is a semiconductor or metal determined by its width. Magnetic field can reduce band-gap and exhibit crossing bands. For metallic BLZGNRs, crossing bands shift and parabolic bands are separated more widely with magnetic field; however, partial flat bands keep unchanged. Temperature significantly increases plasmon frequency and strength for semiconducting BLAGNRs, but slightly affects those of metallic BLAGNRs and BLZGNRs. Magnetic field, for gapped BLAGNRs, can effectively reduce the threshold temperature for inducing plasmon. Whether magneto-plasmon frequency and critical momentum of dispersion relation increase or decrease is strongly sensitive to nanoribbon’s geometry. Field-modulated plasmons with a wide range of frequency could provide potential applications in waveguides and optical sensors.

Enhancing the 3D printing fidelity of vat photopolymerization with machine learning-driven boundary prediction

Like many pixel-based additive manufacturing (AM) techniques, digital light processing (DLP) based vat photopolymerization faces the challenge that the square pixel based processing strategy can lead to zigzag edges especially when feature sizes come close to single-pixel levels. Introducing greyscale pixels has been a strategy to smoothen such edges, but it is a challenging task to understand which of the many permutations of projected pixels would give the optimal 3D printing performance. To address this challenge, a novel data acquisition strategy based on machine learning (ML) principles is proposed, and a training routine is implemented to reproduce the smallest shape of an intended 3D printed object. Through this approach, a chessboard patterning strategy is developed along with an automated data refining and augmentation workflow, demonstrating its efficiency and effectiveness by reducing the deviation by around 30%.