Graphene Nanoribbons Research Articles

Effect of Voids on the Percolation Conductivity of Carbon Nanotube Networks

Two-dimensional (2D) networks consisting of one-dimensional (1D) wires, such as carbon nanotubes, metal nanowires, and graphene nanoribbons, are promising candidates for next-generation flexible transparent conducting electrodes in devices such as organic light-emitting diodes (OLEDs), solar cells, touch screens, smart windows, transparent heaters, and liquid crystal displays. Nanotube networks also have broad application potential in flexible electronics, such as thin film transistors, wearables, electronic skin, and internet of things (IoT) sensors.The electrical conductivity of carbon nanotube networks is governed by percolation, which deals with the formation of long-range connectivity in random networks. As a result, Monte Carlo simulations need to be employed in order to compute the electrical properties of these networks [1,2]. Understanding the impact of voids, which could be present due to lack of control in the deposition process or introduced intentionally, on the percolation conductivity of carbon nanotube networks is critical for applications such as transparent conductive electrodes, thin film transistors, sensing, and hardware security.In this work, we generate two-dimensional square carbon nanotube networks with square voids located at the center of the nanotube network. We define the relative void size as the ratio of the length of the side of the void to the length of the side of the nanotube network. We first study the impact of voids on networks consisting of randomly oriented and straight nanotubes. We compute the percolation probability in these networks as a function of nanotube density for different relative void sizes ranging from 0 (no void) to 0.8. Assuming a Gaussian percolation probability density function (PDF), we find that both the mean and standard deviation of the PDF increase with increasing relative void size. We then compute the relative conductivity change as a function of nanotube density for different relative void sizes and find that it increases approximately linearly with relative void size.According to percolation theory, the conductivity of a nanotube network has a power-law dependence on nanotube density. Next, we extract the local power-law critical exponent as a function of nanotube density for different relative void sizes. We find that the critical exponent approaches 2 at high density for all relative void sizes, in agreement with previous observations for junction-resistance dominated networks without voids [1,3].Furthermore, we generate curvy carbon nanotubes using third order Bezier curves characterized by the curviness angle and aligned nanotubes using an orientation characterized by the alignment angle [1,2]. Using the same procedure as randomly oriented and straight nanotubes, we then investigate the impact of voids on the electronic properties of networks consisting of curvy and aligned nanotubes, including percolation probability, mean and standard deviation of the PDF, relative conductivity change, and nanotube density critical exponent.Our results demonstrate the impact voids have on the percolation conductivity of two-dimensional networks consisting of one-dimensional wires such as carbon nanotubes. These results also show that Monte Carlo simulations are an essential predictive tool for providing insights into the electronic properties of nanotube and nanowire networks, which are promising candidates for a wide range of applications such as flexible transparent conductors, thin film transistors, and resistive switching memory.

Artificial Graphene Nanoribbons with Tailored Topological States

Low-dimensional materials functioning at the nanoscale are a critical component for a variety of current and future technologies. From the optimization of light harvesting solar technologies to novel electronic and magnetic device architectures, key physical phenomena are occurring at the nanometer and atomic length-scales and predominately at interfaces. In this presentation, I will discuss low-dimensional material research occurring in the Quantum and Energy Materials (QEM) group at the Center for Nanoscale Materials. Specifically, the synthesis of artificial graphene nanoribbons by positioning carbon monoxide molecules on a copper surface to confine its surface state electrons into artificial atoms positioned to emulate the low-energy electronic structure of graphene derivatives. We demonstrate that the dimensionality of artificial graphene can be reduced to one dimension with proper “edge” passivation, with the emergence of an effectively-gapped one-dimensional nanoribbon structure. Remarkably, these one-dimensional structures show evidence of topological effects analogous to graphene nanoribbons. Guided by first-principles calculations, we spatially explore robust, zero-dimensional topological states by altering the topological invariants of quasi-one-dimensional artificial graphene nanostructures. The robustness and flexibility of our platform allows us to toggle the topological invariants between trivial and non-trivial on the same nanostructure. Our atomic synthesis gives access to nanoribbon geometries beyond the current reach of synthetic chemistry, and thus provides an ideal platform for the design and study of novel topological and quantum states of matter. Figure 1

On-Surface Synthesis of Open-Shell Nanographenes through the π-Extension of Dibenzo[Hi,St]Ovalene

Graphene nanostructures are attracting attentions for their intriguing optical, electronic, and magnetic properties that are critically dependent on their chemical structures. Whereas it is challenging to obtain atomically precise structures by typical top-down fabrication methods, such as lithographic patterning of graphene and unzipping of carbon nanotubes, bottom-up synthesis enables the preparation of molecular nanographenes and graphene nanoribbons (GNRs) with pre-designed structures. In addition to the solution synthesis based on the methods of synthetic organic chemistry, such graphene nanostructures can also be synthesized on metal surfaces under ultrahigh vacuum conditions and directly visualized by atomic resolution scanning probe microscopy (SPM) [1]. Using carefully designed and solution-synthesized molecular precursors, this on-surface synthesis method can provide various nanographenes, including the structures that are highly unstable under ambient conditions. We have previously developed the solution synthesis of dibenzo[hi,st]ovalene (DBOV) with strong red fluorescence [2], and achieved its π-extension to circumpyrene [3]. Following the successful synthesis of rhombus-shaped nanographenes with four zigzag edges, showing a closed-shell or an open-shell depending on the size [4], we functionalized DBOV and circumpyrene with two 2,6-dimethylphenyl groups for their on-surface π-extension to unprecedented zigzag-edged nanographenes. The resulting structures were clearly visualized by scanning tunneling microcopy and their open-shell characters were indicated by theoretical and experimental investigations, revealing large magnetic exchange couplings of up to 190 meV [5]. We have more recently also achieved further π-extension of these open-shell nanographenes on surface and obtained initial results for their polymerization.[1] Chen, Z.; Narita, A.; Müllen, K.; Adv. Mater. 2020, 32, 2001893.[2] Paternò, G. M.; Chen, Q.; Wang, X.-Y.; Liu, J.; Motti, S. G.; Petrozza, A.; Feng, X.; Lanzani, G.; Müllen, K.; Narita, A.; Scotognella, F., Angew. Chem. Int. Ed. 2017, 56, 6753–6757.[3] Chen, Q.; Schollmeyer, D.; Müllen, K.; Narita, A., J. Am. Chem. Soc. 2019, 141, 19994–19999.[4] Mishra, S.; Yao, X.; Chen, Q.; Eimre, K.; Gröning, O.; Ortiz, R.; Di Giovannantonio, M.; Sancho-García, J. C.; Fernández-Rossier, J.; Pignedoli, C. A.; Müllen, K.; Ruffieux, P.; Narita, A.; Fasel, R.; Nat. Chem. 2021, 13, 581.[5] Biswas, K.; Soler, D.; Mishra, S.; Chen, Q.; Yao, X.; Sánchez-Grande, A.; Eimre, K.; Mutombo, P.; Martín-Fuentes, C.; Lauwaet, K.; Gallego, J. M.; Ruffieux, P.; Pignedoli, C. A.; Müllen, K.; Miranda, R.; Urgel, J. I.; Narita, A.; Fasel, R.; Jelínek, P.; Écija, D. J. Am. Chem. Soc. 2023, 145, 2968–2974.

Syntheses of Heteroatom-Substituted and Three-Dimensional Nanocarbon Materials on Surfaces

I will present our recent studies on on-surface chemistry with high-resolution scanning probe microscopy operating at low temperature under ultra-high vacuum. We synthesized three-dimensional organometallic compound and graphene nanoribbon by coupling hexabromo substituted-propellane molecules on Au(111) and Ag(111).[1] In the structure, the C-Br bonds distant from the surface remained intact even after the reaction. The radical species were formed by tip-induced debromination and were also stabilized by either tip-manipulated Br atom or fullerene molecule. We also demonstrate systematic tip-induced isomerization via embedding a text of “NIMS” by following binary and ternary ascii cords, in which two chiral dehydroazulene and diradical units were used.[2] Among the three states, the diradical unit showed the spin coupling of 90 meV. For heteroatom substitution, we developed an on-surface reaction, which can synthesize graphene nanoribbon and covalent organic frameworks with silabenzene units by coupling Si atom and Br-substituted molecule.[3] The heavier congeners of cyclic aromatic compounds have been studied as an elusive target product for organic synthesis due to their high reactivity at ambient temperature and difficult isolation. Thus, this result shows the advantage of on-surface synthesis.Reference[1] S. Kawai, et al Sci. Adv. 6, eaay8913 (2020).[2] S. Kawai, et al Nat. Commun. 14, 7741 (2023).[3] K. Sun et al, Nat. Chem. 15, 136 (2023).

(Invited) Electrochemistry of the 1,1,N,N-Tetramethyl[N](2,11)Teropyrenophanes

Polycyclic aromatic hydrocarbons (PAH) have been of broad interest for many decades. This is due largely to their extended π systems, which imbue them with optical and electronic properties that can be exploited in a variety of organic electronic devices. A current trend in PAH chemistry is the construction of ever-larger and more elaborate aromatic systems. A major challenge associated with this work is to maintain solubility. For innately planar PAH, the standard tactic is to append multiple solubilizing groups to the periphery of the aromatic system. The drawbacks to this are that 1) the mass of solubilizing groups can outweigh that of the PAH, 2) the presence of the solubilizing groups severely limits or rules out doing chemistry on the periphery and 3) the tactic becomes less and less effective as the size of the PAH becomes very large. An alternative and very effective way to boost solubility is to bring about nonplanarity in a PAH. This can be achieved through the presence of nonbonded interactions (as in helicenes), the presence of non-6-membered rings (as in corannulene) and by bridging the aromatic system (i.e. incorporating it into a cyclophane).Cyclophanes constitute a very large and diverse class of compounds. The simplest cyclophanes (the [n]cyclophanes) consist of just one aromatic system and one aliphatic bridge. These cyclophanes are especially interesting because the structure of the aromatic system can be changed by varying the length of the bridge. This enables the study of how the chemical and physical properties of a particular PAH are affected by incremental changes in structure without any complications arising from intramolecular π-π interactions or changes in the character or position of the substituents (the bridge). Understanding the relationships between structure and properties can underpin efforts to tailor properties of organic compounds for use as materials in devices. Very few [n]cyclophanes that have a large PAH are known, so there is plenty of room for exploration in this area.The PAH of interest in this work is teropyrene. It is a member of the ropyrene series of aromatic compounds, which evolve into armchair-edged graphene nanoribbons (GNR) as they propagate. Teropyrene has 10 6-membered rings, 36 carbon atoms and vanishingly low solubility. Only a handful of teropyrene derivatives are known. We have developed a synthetic route to a series of 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes (n = 7-10), which feature a teropyrene system with an end-to-end bend ranging from 145° (n = 10) to 178° (n = 7) and have very good solubility in a variety of organic solvents. Details of the redox behaviour of these teropyrenophanes will be presented. Figure 1

Effect of Functionalized Carbon Nanotubes and Graphene Oxide Nanoribbons on the Supercapacitive Behavior of Zr-Based Metal-Organic Frameworks in Acid Media

Metal-organic frameworks (MOFs) as a kind of crystalline porous materials have attracted much attention due to their high surface area and high electrochemical performance as electrode materials in supercapacitors 1. Recently, there has been a lot of interest in functionalized multiwalled carbon nanotubes (F-MWCNTs) based materials and especially graphene oxide nanoribbons (GONRs), which have unusual characteristics of ultrathin two-dimensional structures and, as promising materials for supercapacitors and other electrochemical energy storage devices. The F-MWCNTs and GONRs' high electrical conductivity, highly changeable surface area, strong chemical stability, excellent mechanical behavior, and capacity to modify attributes for the desired application are behind the reasons for choosing to make a composite of these materials with Zr-MOF 2.In this work, Zr-MOF was synthesized using the solvothermal method 3, MWCNTs were functionalized using acid washing (3 M H2SO4: 1 M HNO3), and GONRs were fabricated using the oxidative unzipping method 4. The Zr-MOF/F-MWCNTs and Zr-MOF/GONRs composites were prepared through physical mixing. The physical and chemical structures of the synthesized Zr-MOF, F-MWCNTs, and GONRs were evaluated using XRD, SEM, TEM, FT-IR, Raman spectroscopy, and XPS. The supercapactive behavior of the prepared composites was evaluated in comparison to their components (Zr-MOF, F-MWCNTs, and GONRs) in 1M H2SO4 utilizing various evaluation systems (three and two-electrode systems). Zr-MOFs showed a high specific capacitance (248 F/g at 1 A/g), making it a promising supercapacitor electrode material. That performance is dramatically improved by the addition of the nanocarbon materials (F-MWCNTs and GONRs). Zr-MOF-GONRs showed the highest specific capacitance (448 F/g at 1 A/g), with a large potential window (1.7 V) in the three-electrode system extended to (2V) in the two-electrode system, and good stability over 10,000 cycles at a high current density of 10 A/g. Reference: (1) Tan, Y.; Zhang, W.; Gao, Y.; Wu, J.; Tang, B. Facile Synthesis and Supercapacitive Properties of Zr-Metal Organic Frameworks (UiO-66). RSC Adv. 2015, 5 (23), 17601–17605. https://doi.org/10.1039/c4ra11896k.(2) Shrivastav, V.; Sundriyal, S.; Tiwari, U. K.; Kim, K. H.; Deep, A. Metal-Organic Framework Derived Zirconium Oxide/Carbon Composite as an Improved Supercapacitor Electrode. Energy 2021, 235, 121351. https://doi.org/10.1016/j.energy.2021.121351.(3) Abdelhamid, H. N. UiO-66 as a Catalyst for Hydrogen Production: Via the Hydrolysis of Sodium Borohydride. Dalton Trans. 2020, 49 (31), 10851–10857. https://doi.org/10.1039/d0dt01688h.(4) Kosynkin, D. V.; Higginbotham, A. L.; Sinitskii, A.; Lomeda, J. R.; Dimiev, A.; Price, B. K.; Tour, J. M. Longitudinal Unzipping of Carbon Nanotubes to Form Graphene Nanoribbons. Nature 2009, 458 (7240), 872–876. https://doi.org/10.1038/nature07872.

Exploring New Carbon Allotropes and Nanographenes on Surfaces

The quest for planar sp2-hybridized carbon allotropes other than graphene has stimulated substantial research efforts because of their predicted unique mechanical, electronic, and transport properties. However, the syntheses of these nonbenzenoid networks remain challenging due to the lack of reliable protocols for generating nonhexagonal rings. We have developed various on-surface synthesis strategies by which straight polymer chains are linked to form the nonbenzenoid carbon networks. In this way, we synthesized biphenylene network, a new carbon allotrope with 4-6-8-membered rings, which is metallic already at very small dimensions. Similarly, we generated phagraphene nanoribbons, which are based on 5-6-7-membered rings.Acenes are another interesting class of carbon materials that have fascinated chemists and physicists due to their potential for use in organic electronic applications. We show the synthesis of tridecacene (13ac) and pentadecacene (15ac), the longest acenes known to date, via multistep single-molecule manipulation of suitable precursor molecules on Au(111). We find antiferromagnetic open-shell ground state electron configurations for both acenes. 15ac shows a low-bias spin-excitation feature, indicating a singlet-triplet gap of around 124 meV. Investigation of 15ac complexes with up to 6 gold atoms suggest considerable multiradical contributions to the electronic ground state of 15ac.Altering the electronic and magnetic properties of carbon-based nanomaterials can also be achieved by doping with heteroatoms. We present an access to a variety of nitrogen-containing 0D and 1D carbon nanostructures including planar and curved cycloarenes with different cavities as well as N-doped graphene nanoribbons.

Synergy of Silicon-Graphene Anodes and Polymer-Ceramic Hybrid Separators for High Rate-Capable Lithium-Ion Batteries

With more and more electric vehicles (EV) hitting the market, the need for better and more robust energy storage system increases, and silicon has been a promising candidate for the next generation anode material to satisfy the high energy density and high-power requirements for electric vehicles because of its extremely high theoretical capacity. This has allowed the design of thinner electrodes to reduce the diffusion time scales and deliver a fast charge. However, at high charge and discharge rates, low electrical conductivity (~1.12 eV) of silicon hampers the battery performance. As a result, a lot of research has been conducted to improve the performance of silicon anodes using nanoscale carbon to increase the electrical conductivity. Graphene has been used to synthesize Si/Gr hybrid anodes due to its high conductivity.Graphene nanoribbons (GNRs) , a part of the graphene family, are one-dimensional graphene nanostructures which tune its electrical properties based on dimensional confinement. GNR has a higher conductivity than Graphene. It also has high aspect ratio and surface area to provide a strong conductive path along with mechanical strength to support the silicon anode. Due to presence of GNR, lithium-ion transport into silicon nanostructures was enhanced. As a result, 50% of graphene was replaced by 50% GNR with silicon nanoparticles to form anodes. Due to the highly conducting structure of GNR, capacity at high rates was significantly improved because of the improved silicon utilization. Since GNR’s dimensions are in nanometer range, connection with silicon nanoparticles is better. It not only improves silicon to silicon conductivity, but it also acts as a filler for better connection of graphene with silicon nanoparticles.Addition of graphene nanoribbons can improve the lithium-ion transport within the anode but to enhance the high charge transfer rate further, Si/GNR/Gr hybrid, high rate-capable anodes were paired with Polyimide (PI)/Polysilsesquioxane (PSSQ) hybrid separators which also shown to exhibit an improved charge transfer rate. At high rates such as 3C and 5C, the effect of separator on the cell performance becomes more prominent. While Celgard’s performance was very unstable at both 3C and 5C, at 3C, the cycling of hybrid separators did not get impacted, despite the relatively harsher conditions. This synergistic combination of high-rate capable silicon/graphene anode and hybrid separator outperformed the commercially used separator especially at high-rate cycling. Cells with Si/GNR/Gr anode paired with the PI/PSSQ separator delivered an impressive capacity of 1,000 mAh/g at high charge/discharge rates of 5C/5C.

Effects of nanocutting environments on the electronic structure of armchair-type graphene nanoribbons: the first-principles study

In order to investigate the effect of nanocutting environment on the electronic structure of armchair-type graphene nanoribbons, this paper adopts a first-principle computational approach to study the effect of different substrates and solutions, such as on the motion of electrons in the middle and outer orbitals of graphene nanoribbons, by observing the energy band structure, the value of the band gap, and the density of the split-wave states. The results show that the adsorption of Si and C atoms at the edge of the nanoribbon leads to a decrease in the band gap value. The adsorption of Al and O atoms at the edges of graphene nanoribbons leads to a decrease in the nanoribbon band gap value to 0 eV. Different substrate atoms mainly affect the p-orbital electron motion in the nanobelt. Bare-edge graphene nanoribbons are indirect bandgap structures, and graphene nanoribbons with H, O and OH atoms adsorbed at the edges of the nanoribbons are direct bandgap structures. Edge O-isation leads to a nanobelt band gap of 0, which exhibits metallic properties. The edge H-isation nanoribbon band gap is higher than the bare edge nanoribbon band gap. Nanoribbon edge OH-isation reduces the nanoribbon band gap value. Nanoribbon edge adsorption of atoms in solution affects p-orbital electron motion. The formation energy of five-ring defects and seven-ring defects is low, and the defects are easier to form. The edges containing defects all reduce the band gap values of graphene nanoribbons. The defects mainly affect the p-orbital electron motion, leading to differences in the band gap values. The bandgap decreases with increasing nanobelt width, and the bandgap value conforms to 3 N+2<3 N<3 N+1, with regular fluctuations in the curve with period 3. The larger the band gap, the smaller the curvature of the curve at the extremes, and the sparser the curve. In this paper, the electronic structures of different edge structures are analysed from a quantum mechanical point of view, and the synthesis of these results will provide theoretical guidance for obtaining high-quality semiconductor nanoribbons by mechanochemical nanocutting.

Length and torsion dependence of thermal conductivity in twisted graphene nanoribbons

Length and torsion dependence of thermal conductivity in twisted graphene nanoribbons

Influence of nano graphene filler on hardness, impact strength and density of glass epoxy composites

AbstractThis study investigates the effects of graphene reinforcement on the hardness and impact strength of glass epoxy composites. Four different materials were examined: pure epoxy (EP), glass epoxy (GE), glass epoxy with 1 wt.% graphene (GE1), and glass epoxy with 2 wt.% graphene (GE2). The results show that the incorporation of graphene significantly enhances the hardness of the composites. Pure epoxy (EP) exhibited a Shore D hardness of 60 and an impact strength of 0.09 J/m2. The glass epoxy (GE) showed a reduction in hardness to 56 but an increased impact strength of 0.15 J/m2 due to the inclusion of 33 wt.% glass fiber. Further addition of graphene in GE1 and GE2 led to notable improvements in hardness, reaching 68 and 74 Shore D, respectively. However, the impact strength displayed a decrease with the inclusion of graphene, with GE1 and GE2 showing values of 0.13 and 0.11 J/m2, respectively. When transitioning from pure epoxy (EP) to glass epoxy (GE), there is a 6.67% decrease in hardness, while the impact strength increases by 66.67%. Introducing 1 wt.% of graphene to the glass epoxy (GE1) results in a 21.43% increase in hardness but a 13.33% decrease in impact strength. Further adding 2 wt.% of graphene (GE2) leads to an additional 8.82% increase in hardness, though the impact strength decreases by 15.38%. X‐ray diffraction (XRD) analysis has revealed nano graphene presence and distribution, while fractography has revealed its effectiveness in enhancing interfacial adhesion and toughening mechanisms. Furthermore, XRD identifies potential changes in crystallinity or phase composition induced by nano graphene incorporation, further elucidating the composite's structure and properties. The study highlights the novel and significant trade‐offs encountered in optimizing the mechanical properties of epoxy‐based composites by incorporating graphene and glass fiber.

An experimental investigation of nano clay and functionalized nano graphene oxide effects on ablation of carbon/phenolic nanocomposites

This work aims to study thermal stability and ablative behaviors of Carbon/Phenolic composites containing nano clay, nano graphene oxide and hybrid additives. To this end a detailed explained and illustrated process is involved to synthesize factionalized graphene oxide based on Hummers method. The XRD test result shows a major shift in basal plane reflection to below 2θ = 20° in the provided spectrum, which indicates achievement in the functionalization process. Prepared nanoparticles suspensions are then mixed by resol resin with desire wt% to outcome nanocomposites. An in-depth analysis of SEM images with focus on the dispersion, morphology, and interaction of the nanofillers with the resin matrix reveals that nanoparticles are dispersed properly with no agglomeration. 200 gr/m2 carbon woven fabric is then impregnated with prepared nanocomposites employing an own made prepreg machine to use to construct standard flexural as well as oxy acetylene test specimens. Using bending test, thermogravimetric analysis and oxyacetylene torch test, effects of different percentages of considered nanoparticles on the mechanical properties, thermal stability and ablative of carbon/phenolic composites are assessed and the results are reported. According to the results, adding only 0.1 wt% of nano graphene oxide increases char yield around 5% and remain back surface temperature under 100°C during flame test. Moreover samples with 0.2 wt% of nano clay and hybrid (0.05 wt% nano graphene oxide and 0.1 wt% nano clay) additives provides best reaming amount of solid.

Enhanced thermoelectric properties in hybrid graphane/graphene nanoribbons

The thermoelectric properties of hybrid graphane and graphene nanoribbons (GGNRs) are studied by the Landauer formula within the atomistic non-equilibrium Green's function. It is shown that hybrid GGNRs present the tunable band gap depending upon the width ratio of their components. Modulation of hybrid GGNRs can give rise to the lower thermal conductance of phonons and the better thermoelectric properties compared to pure graphene nanoribbons and graphane nanoribbons. Introducing the hydrogen defects can enhance the maximum of ZT (ZTmax) in both armchair GGNRs (AGGNRs) and zigzag GGNRs (ZGGNRs). Such the enhancement of ZTmax sensitively depends upon the defect concentrations. Among different defect concentrations, ZTmax for the 20 % defect concentration has the highest value, which can be enhanced to 0.42 and 0.24 at T = 300 K in AGGNRs and ZGGNRs, respectively. A laconic analysis of these results is given.

Energetics and electronic structure of graphene nanoscrolls

Geometric structures and electronic properties of graphene nanoscrolls have been investigated using the density functional theory. A graphene nanoribbon with a width of 21.37 nm, corresponding to a zigzag ribbon with 100 zigzag C chains, prefers scrolled structures until the innermost shell radius of 0.6 nm, because of the competition between the energy gain by the inter-shell van der Waals interaction and the energy cost by the structural strain derived from curvature. The most preferable innermost shell radiuses are 1.3–1.5 nm for the ribbon studied here. The electronic structure of graphene nanoscrolls shows strong position dependence that is sensitive to the shape of nanoscrolls owing to the electrostatic potential modulation by their multi-shell structures.

Interfacial Electrochemistry of Catalyst-Coordinated Graphene Nanoribbons.

The immobilization of molecular electrocatalysts on conductive electrodes is an appealing strategy for enhancing their overall activity relative to those of analogous molecular compounds. In this study, we report on the interfacial electrochemistry of self-assembled two-dimensional nanosheets of graphene nanoribbons (GNR-2DNS) and analogs containing a Rh-based hydrogen evolution reaction (HER) catalyst (RhGNR-2DNS) immobilized on conductive electrodes. Proton-coupled electron transfer (PCET) taking place at N-centers of the nanoribbons was utilized as an indirect reporter of the interfacial electric fields experienced by the monolayer nanosheet located within the electric double layer. The experimental Pourbaix diagrams were compared with a theoretical model, which derives the experimental Pourbaix slopes as a function of parameter f, a fraction of the interfacial potential drop experienced by the redox-active group. Interestingly, our study revealed that GNR-2DNS was strongly coupled to glassy carbon electrodes (f = 1), while RhGNR-2DNS was not (f = 0.15). We further investigated the HER mechanism by RhGNR-2DNS using electrochemical and X-ray absorption spectroelectrochemical methods and compared it to homogeneous molecular model compounds. RhGNR-2DNS was found to be an active HER electrocatalyst over a broader set of aqueous pH conditions than its molecular analogs. We find that the improved HER performance in the immobilized catalyst arises due to two factors. First, redox-active bipyrimidine-based ligands were shown to dramatically alter the activity of Rh sites by increasing the electron density at the active Rh center and providing RhGNR-2DNS with improved catalysis. Second, catalyst immobilization was found to prevent catalyst aggregation that was found to occur for the molecular analog in the basic pH. Overall, this study provides valuable insights into the mechanism by which catalyst immobilization can affect the overall electrocatalytic performance.

Quantized perfect transmission in graphene nanoribbons with random hollow adsorbates

Quantized perfect transmission in graphene nanoribbons with random hollow adsorbates

Adsorption and diffusion behavior of lithium atom on boron-doped armchair graphene nanoribbon- A dispersion-corrected DFT study

In this paper, we study the relevance of considering dispersion interactions in DFT calculations to determine the adsorption behavior of lithium atom(s) on boron-doped armchair graphene nanoribbons. Our findings suggest that substitutional doping with boron atoms makes the AGNR electron-deficient which results in charge transfer from Li to the AGNR. Li atom binds more strongly to B-doped AGNR than pristine AGNR. A stronger Li-C interaction prevents the clustering of Li atoms, thus, inhibiting dendrite growth. The maximum storage capacity of B-doped AGNR reaches to 1261 mAh/g. B-doped AGNR offers a lower diffusion barrier of 0.19 eV to Li atom as compared to pristine AGNR. From the analysis of density of states, it is observed that the semiconducting nature of both pristine and B-doped AGNRs turns into metallic after the adsorption of lithium atom. Our results show that B-doped AGNR can be used as a potential anode material of lithium-ion batteries.

Modeling and analysis of crosstalk induced effects in graphene-carbon nanotube composite interconnects

This paper proposes an equivalent circuit model for two-line coupled multilayer graphene nanoribbon - single-wall carbon nanotube (MLGNR-SWCNT) composite interconnects (MSCs), incorporating the effects of coupling capacitance and mutual inductance. We also examine the temperature-dependent crosstalk effect on the victim line of MSCs in the time domain using decoupling techniques and the ABCD parameter matrix approach. This analysis is conducted at the global level of 7 nm, 14 nm, and 22 nm technology nodes, comparing the performance of MSCs with MLGNR, SWCNT, and copper (Cu) interconnects, validated through HSPICE simulations. Our results reveal that the crosstalk delay of all interconnects induced by dynamic crosstalk exhibits superior performance in the in-phase crosstalk mode compared to the out-of-phase mode at room temperature. In particular, MSCs demonstrate less crosstalk delay in both crosstalk modes compared to SWCNT and Cu interconnects. In addition, we analyze the crosstalk delay of the victim line for two-line coupled MSCs at varying temperatures in out-of-phase crosstalk mode, comparing them with MLGNR, SWCNT, and Cu interconnects. Simulation results indicate that the crosstalk delay is temperature-dependent, increasing with rising temperatures, and the crosstalk delay of MSCs is the least of all interconnects. Furthermore, we investigate the crosstalk noise of MSCs induced by functional crosstalk at different temperatures, comparing it with MLGNR, SWCNT, and Cu interconnects. It is observed that the crosstalk noise peak remains constant with temperature changes across all interconnects; however, the holding time and width of crosstalk noise increases with rising temperatures and MSCs have the least crosstalk noise peak and crosstalk noise width of all interconnects. Also, numerical results exhibit that reducing interconnect temperature, SWCNT diameter, and edge roughness of MLGNR are effective strategies to diminish the crosstalk delay of MSCs. In addition, increasing line spacing is identified as an effective method to reduce crosstalk noise peak of MSCs of different lengths. The proposed model results show excellent agreement with HSPICE simulation data. Therefore, our analysis of crosstalk effect manifests that MLGNR-SWCNT composite can be a promising material to replace SWCNT and copper as an ideal material for global interconnect applications in thermally variable environments.

Twisting Between Topological Phases in 1D Conjugated Polymers via a Multiradical Transition State

AbstractIn recent years, it has become possible via on‐surface bottom‐up synthesis to engineer the topological character of carbon nanostructures. Graphene nanoribbons and 1D conjugated polymers (1DCPs) have thus tailored so as to host either topologically trivial or non‐trivial phases. Molecular design is the primary means to set the topological class of these nanomaterials. However, external control over topology is also demonstrated via electric fields or top‐down hydrogenation. Inspired by the connection between topology and π‐conjugation, here it is demonstrated via first‐principles calculations that aryl ring twist angles also serve as topological knobs. Focusing on rationally designed 1DCPs composed of triarylmethyl (TAM) units, it is shown that rotation of certain aryl rings enables a transition from the trivial to the topologically non‐trivial phase. Accordingly, fixing a particular twist angle configuration (e.g., via chemical functionalization) is equivalent to robustly setting a targeted topological phase. It is also found that in considered 1DCPs, the quantum phase transition occurs without the electronic band gap closing, due to a multiradical antiferromagnetic phase emerging at the transition point. All in all, this study highlights the potential of aryl ring twisting for engineering topological properties in carbon nanomaterials and establishes TAM 1DCPs as exotic topological 1D systems.

Heteroatom‐Doped Graphene Nanoribbons: Precision Synthesis and Emerging Properties†

Comprehensive SummaryGraphene nanoribbons (GNRs), which can be considered as a special type of conjugated polymers, are quasi‐one‐dimensional graphene cutouts with an opened band gap, revealing great potential as functional materials in optoelectronic, spintronic, and energy‐related applications. An effective strategy to modulate the properties of GNRs is doping heteroatoms into the π‐skeleton. Thanks to the bottom‐up synthetic approach, a number of heteroatom‐doped GNRs with precise structures have been reported, exhibiting intriguing properties. Nevertheless, a comprehensive summary of the progress of this field has remained elusive. In this review, we summarize the history and advances in bottom‐up synthesized heteroatom‐doped GNRs, including their synthetic routes, electronic properties, and promising applications. We hope to establish the reliable structure–property relationship, and provide guidance for the molecular design of heteroatom‐doped GNRs in the future.