Width Of Graphene Nanoribbons Research Articles

Area-energy optimized ternary multiplier usingefficient design approaches in GNRFET technology

The semiconductor industry has long benefited from CMOS transistors in realizing advanced VLSI circuits. However, achieving area-energy optimization in CMOS-based VLSI circuits has become increasingly challenging due to short-channel effects. Another obstacle in manufacturing these transistors is the adoption of body-biasing techniques to adjust the threshold voltage (Vth) for developing ternary logic-based circuits. Researchers are now exploring emerging devices like graphene nanoribbon field-effect transistors (GNRFET) as potential candidates for future electronics. GNRFET devices not only leverage graphene’s remarkable properties but also benefit from the ability to achieve distinct Vth through tuning the width of graphene nanoribbons. This paper focuses on using tri-state 32-nm GNRFET devices to implement a novel area-energy optimized ternary multiplier circuit. To attain a logic ‘1′ in the proposed circuit, a power-efficient voltage division technique is employed. Additionally, efficient design approaches are used to reduce the critical path length and decrease the number of necessary transistors. Simulation results using HSPICE demonstrate that the proposed design reduces energy consumption by a minimum of 6.75% and up to 37.50% compared to other state-of-the-art 32-nm GNRFET-based TMUL circuits. Furthermore, the proposed design decreases both the area and complexity by utilizing a single-VDD and incorporating 24 transistors.

Quasiballistic thermal transport in submicron-scale graphene nanoribbons at room-temperature.

Phonon transport in two-dimensional materials has been the subject of intensive studies both theoretically and experimentally. Recently observed unique phenomena such as Poiseuille flow at low temperature in graphene nanoribbons (GNRs) initiated strong interest in similar effects at higher temperatures. Here, we carry out massive molecular dynamics simulations to examine thermal transport in GNRs at room temperature (RT) and demonstrate that non-diffusive behaviors including Poiseuille-like local thermal conductivity and second sound are obtained, indicating quasiballistic thermal transport. For narrow GNRs, a Poiseuille-like thermal conductivity profile develops across the nanoribbon width, and wider GNRs exhibit a mixed nature of phonon transport in that diffusive transport is dominant in the middle region whereas non-uniform behavior is observed near lateral GNR boundaries. In addition, transient heating simulations reveal that the driftless second sound can propagate through GNRs regardless of the GNR width. By decomposing the atomic motion into out-of-plane and in-plane modes, it is further shown that the observed quasiballistic thermal transport is primarily contributed by the out-of-plane motion of C atoms in GNRs.

Visualizing Ribbon‐to‐Ribbon Heterogeneity of Chemically Unzipped Wide Graphene Nanoribbons by Silver Nanowire‐Based Tip‐Enhanced Raman Scattering Microscopy (Small 3/2024)

Visualizing Ribbon‐to‐Ribbon Heterogeneity of Chemically Unzipped Wide Graphene Nanoribbons by Silver Nanowire‐Based Tip‐Enhanced Raman Scattering Microscopy (Small 3/2024)

Design of three-dimensional B-C-N structures via tailoring GNRs and BNNRs

A series of porous 3D Cx(BN)y crystal structures with full sp2 hybridization are obtained by polymerizing edge-functionalized graphene nanoribbons (GNRs) and boron nitride nanoribbons(BNNRs). Herein, the crystal structure and properties of Cx(BN)y are systematically and comprehensively investigated by first-principles calculations, deriving that it is feasible to achieve performance tuning by controlling the nanoribbon width. Thermodynamic stability, these structures have energy advantages with respect to the previously proposed B-C-N structures, and the thermodynamic stability of the structures deteriorates with the increase of the carbon content. Electrical properties, the bandgap value is tunable between 0.1 and 1.1 eV, and the bandgap value increases with the width of BNNRs at the same width of GNRs. Mechanical properties, these structures are mechanically stable, and exhibit unexpected superstretching properties, with tensile lengths up to 2.4 times the original length, bulk modulus tunable between 137-167GPa, shear modulus tunable between 81-115GPa, and the incompressibility of the structure decreases as the nanoribbon width increases.

Tunable Tail Swing of Nanomillipedes.

The physical properties of graphene nanoribbons (GNRs) are closely related to their morphology; meanwhile GNRs can easily slide on surfaces (e.g., superlubricity), which may largely affect the configuration and hence the properties. However, the morphological evolution of GNRs during sliding remain elusive. We explore the intriguing tail swing behavior of GNRs under various sliding configurations on Au substrate. Two distinct modes of tail swing emerge, characterized by regular and irregular swings, depending on the GNR width and initial position relative to the substrate. The mechanism can be explained by the moiré effect, presenting both symmetric and asymmetric patterns, resembling a mesmerizing nanomillipede. We reveal a compelling correlation between the tail swing mode and the edge wrinkle patterns of GNRs induced by the moiré effect. These findings provide fundamental understanding of how edge effects influence the tribomorphological responses of GNRs, offering valuable insights for precise manipulation and operation of GNRs.

An unbalanced ternary multiplier cell based on graphene nanoribbon field-effect transistors for PVT-tolerant low-energy portable applications

The potential benefits of using multiple-valued logic (MVL), especially ternary logic, which includes less interconnections, quicker response times, and smaller chip sizes, has gained the interest of designers of digital systems. A practical solution for achieving circuits with multiple thresholds in an efficient manner is through using graphene nanoribbon field-effect transistors (GNRFETs) that have modifiable threshold voltage values by adjusting the width of graphene nanoribbon. This article leverages the unique characteristics of GNRFETs and proposes a new design for a single-trit ternary multiplier (TMUL) circuit. The proposed TMUL uses two supply voltages to block direct current paths from high-to-low voltage levels, resulting in power and energy savings. Additionally, unary operators such as negative and positive ternary inverters and the complement of decisive literal are used to reduce transistor count and improve circuit performance. To thoroughly evaluate the performance of the proposed GNRFET-based TMUL circuit, extensive simulations are performed using Synopsis HSPICE tool and 32-nm channel length GNRFET devices, while taking into account the influences of process-voltage-temperature variations (PVT). The simulation results confirm the robustness and reliability of the proposed design, exhibiting reductions in power consumption by 71.18% to 76.36%, and energy consumption by 67.78% to 86.54%, when compared to other state-of-the-art TMUL circuits available in literature. Moreover, Monte-Carlo simulations have been performed to demonstrate that the suggested design exhibits reduced sensitivity towards significant process variations. As a result, the presented TMUL design can be a good choice for use in low-energy battery-operated portable multimedia device.

Visualizing Ribbon-to-Ribbon Heterogeneity of Chemically Unzipped Wide Graphene Nanoribbons by Silver Nanowire-Based Tip-Enhanced Raman Scattering Microscopy.

Graphene nanoribbons (GNRs), a quasi-one-dimensional form of graphene, have gained tremendous attention due to their potential for next-generation nanoelectronic devices. The chemical unzipping of carbon nanotubes is one of the attractive fabrication methods to obtain single-layered GNRs (sGNRs) with simple and large-scale production. The authors recently found that unzipping from double-walled carbon nanotubes (DWNTs), rather than single- or multi-walled, results in high-yield production of crystalline sGNRs. However, details of the resultant GNR structure, as well as the reaction mechanism, are not fully understood due to the necessity of nanoscale spectroscopy. In this regard, silver nanowire-based tip-enhanced Raman spectroscopy (TERS) is applied for single GNR analysis and investigated ribbon-to-ribbon heterogeneity in terms of defect density and edge structure generated through the unzipping process. The authors found that sGNRs originated from the inner walls of DWNTs showed lower defect densities than those from the outer walls. Furthermore, TERS spectra of sGNRs exhibit a large variety in graphitic Raman parameters, indicating a large variation in edge structures. This work at the single GNR level reveals, for the first time, ribbon-to-ribbon heterogeneity that can never be observed by diffraction-limited techniques and provides deeper insights into unzipped GNR structure as well as the DWNT unzipping reaction mechanism.

Measuring epitaxial graphene nanoribbons with low-frequency alternating current

We have demonstrated the fabrication of both armchair and zigzag epitaxial graphene nanoribbon (GNR) devices on 4H–SiC using a polymer-assisted sublimation growth method. The phenomenon of terrace step formation has traditionally introduced the risk of GNR deformation along sidewalls, but a polymer-assisted sublimation method helps mitigate this risk. Each type of 50 nm wide GNR is examined electrically and optically (armchair and zigzag), with the latter method being a check on the quality of the GNR devices and the former using alternating current to investigate resistance attenuation from frequencies above 100 Hz. Rates of attenuation are determined for each type of GNR device, revealing subtle suggested differences between armchair and zigzag GNRs.

Molecular Bridge Engineering for Tuning Quantum Electronic Transport and Anisotropy in Nanoporous Graphene

Recent advances on surface-assisted synthesis have demonstrated that arrays of nanometer wide graphene nanoribbons can be laterally coupled with atomic precision to give rise to a highly anisotropic nanoporous graphene structure. Electronically, this graphene nanoarchitecture can be conceived as a set of weakly coupled semiconducting 1D nanochannels with electron propagation characterized by substantial interchannel quantum interferences. Here, we report the synthesis of a new nanoporous graphene structure where the interribbon electronic coupling can be controlled by the different degrees of freedom provided by phenylene bridges that couple the conducting channels. This versatility arises from the multiplicity of phenylene cross-coupling configurations, which provides a robust chemical knob, and from the interphenyl twist angle that acts as a fine-tunable knob. The twist angle is significantly altered by the interaction with the substrate, as confirmed by a combined bond-resolved scanning tunneling microscopy (STM) and ab initio analysis, and should accordingly be addressable by other external stimuli. Electron propagation simulations demonstrate the capability of either switching on/off or modulating the interribbon coupling by the corresponding use of the chemical or the conformational knob. Molecular bridges therefore emerge as efficient tools to engineer quantum transport and anisotropy in carbon-based 2D nanoarchitectures.

Controlled Preparation and Device Application of Sub-5 nm Graphene Nanoribbons and Graphene Nanoribbon/Carbon Nanotube Intramolecular Heterostructures

Narrow graphene nanoribbons (GNRs) and GNR/single-walled carbon nanotube (SWNT) intramolecular heterojunctions are ideal candidates to construct next-generation electronic and optoelectronic devices. However, the fabrication of high-quality long sub-5 nm wide GNRs and GNR/SWNT heterojunctions is a great challenge. Here, we report a method to produce high-quality sub-5 nm wide GNRs with smooth edges and GNR/SWNT intramolecular heterostructures via palladium-catalyzed full and partial unzipping of SWNTs, respectively. The resulting GNRs could be as narrow as 2.2 nm and had an average length of over 1 μm. By adjusting the unzipping time and the deposited positions of palladium nanoparticles, controlled multiple GNR/SWNT heterostructures were also fabricated on an individual parent SWNT. A GNR field-effect transistor (FET) constructed by a 3.1 nm wide GNR could simultaneously achieve a high on/off current ratio of 1.1 × 104 and a large mobility of 598 cm2 V-1 s-1. The photovoltaic device based on a single GNR (2.4 nm in width)/SWNT (0.8 nm in diameter) heterojunction exhibited a large open-circuit voltage (Voc) of 0.52 V and a high external power conversion efficiency (η) of 4.7% under the 1550 nm wavelength illumination of 931 mW cm-2. Our method provides a pathway to controllably prepare high-quality sub-5 nm GNRs and GNR/SWNT heterojunctions for fundamental studies and practical applications in the electronic and optoelectronic fields.

Unusual constructive quantum interference in isolated armchair graphene nanoribbons

A new and unusual type of Constructive Quantum Interference (CQI) is revealed in selected isolated armchair graphene nanoribbons (AGNRs). CQI, normally encountered in molecular junctions, occurs when two nearly isoenergetic states interfere constructively. Such almost isoenergetic states are identified here as the energy differences between two pairs of topological end states developed in “wider” AGNRs, through topological metal-insulator-like phase transition, which for 13-AGNRS occurs at a critical length L c ≈ 50 Å. At L c a sudden jump in conductivity by a factor ∼2.5 occurs, which persists up to L ≈ 80 Å and is interpreted as a signature of CQI. Such unusual CQI, in which the zigzag region effectively plays the role of “linkers”, is unique for 13-AGNRs. This is due to their aromaticity i.e., resonance between two different aromatic Clar-sextets, and the resulting symmetry and energy separation of the frontier orbitals. The experimental measurements for 13-AGNRs fully support our results. At a critical length L c a multidimensional phase transition occurs in 13-AGNRs associated with two pairs of nearly isoenergetic end-states and discontinuities in bandgaps and conductivity, which suddenly rises by a factor of ~2.5, signifying a region of constructive quantum interference (CQI). • In wider graphene nanoribbons more than one pair of topological end states occur • These end states appear at critical length L c as metal-insulator phase transitions • For 13-armchair nanoribbons only, this leads to constructive quantum interference • Which is ultimately due to resonance between two aromatic Clar sextets • The role of “linkers” is played by the zigzag ends where end-states are localized

Calibration of Fermi Velocity to Explore the Plasmonic Character of Graphene Nanoribbon Arrays by a Semi-Analytical Model.

We present an analysis of the electronic and plasmonic behavior of periodic planar distributions of sufficiently wide graphene nanoribbons, for which a thorough ab initio investigation is practically unfeasible. Our approach is based on a semi-analytical model whose only free parameter is the charge carrier velocity, which we estimate by density-functional theory calculations on graphene. By this approach, we show that the plasmon resonance energies of the scrutinized systems fall in the lower THz band, relevant for optoelectronic and photonic applications. We further observe that these energies critically depend on the charge carrier concentration, ribbon width, electron relaxation rate, and in-plane transferred momentum angle, thus, suggesting a tunability of the associated light-matter modes.

Nanographenes and Graphene Nanoribbons as Multitalents of Present and Future Materials Science.

As cut-outs from a graphene sheet, nanographenes (NGs) and graphene nanoribbons (GNRs) are ideal cases with which to connect the world of molecules with that of bulk carbon materials. While various top-down approaches have been developed to produce such nanostructures in high yields, in the present perspective, precision structural control is emphasized for the length, width, and edge structures of NGs and GNRs achieved by modern solution and on-surface syntheses. Their structural possibilities have been further extended from “flatland” to the three-dimensional world, where chirality and handedness are the jewels in the crown. In addition to properties exhibited at the molecular level, self-assembly and thin-film structures cannot be neglected, which emphasizes the importance of processing techniques. With the rich toolkit of chemistry in hand, NGs and GNRs can be endowed with versatile properties and functions ranging from stimulated emission to spintronics and from bioimaging to energy storage, thus demonstrating their multitalents in present and future materials science.

Contact Effect On Twisted Graphene Based Schottky Transistor

Owing to the exceptional electrical properties of different one dimensional (1D) classifications of graphene structure such as graphene nanoribbon (GNR) and twisted graphene (TWG) led to a revolution in nanoelectronic researche and applications. Thus, these materials have been extensively explored in nanoelectronics science and materials. This paper is focused on GNR and TWG junction as metal-semiconductor-metal (MSM) in the form of a transistor. The wave vectors of TWG and GNR based on the geometrical effects are discussed. By considering 1D potential barrier at the junction of TWG as a semiconducting region and GNR as a metallic region, the transmission probability is calculated. Then, the I–V characteristics of GNR-TWG Schottky transistor based on quantum tunneling effect arepresented and discussed, as well. The performance of GNR-TWG Schottky transistor under variation of gate-source voltage, channel length, number of twists, width of GNR, and temperature are investigated. It is concluded that increment in number of twists and width of GNR lead to increasing the drain current and threshold voltage. Finally, comparison study with graphene nanoscroll (GNS) Schottky transistor, trilayer graphene nanoribbon (TGNR) Schottky transistor, and reported experimental data are performed and results represent that GNR-TWG Schottky transistor has larger drain current than these works.

Terahertz polarizer based on tunable surface plasmon in graphene nanoribbon

Tunable surface plasmon resonance-based graphene nanoribbon (GNR) terahertz (THz) polarizers with adjustable operating frequency are proposed in this work. While conventional THz polarizers lack robustness and tunability, recently reported graphene-based metastructure polarizers have complex fabrication processes and comparatively smaller extinction ratios (ERs). A comprehensive study using finite-difference time-domain (FDTD) simulation technique reveals high ER, broad tunability, near-perfect degree of polarization (DOP), and low insertion loss for our proposed single and double stage GNR polarizers. The operating frequency of these narrow band polarizers can be tuned by varying GNR width, GNR pitch, chemical potential, and substrate material. Our optimized THz polarizer has an ER of 30 dB which is comparable to the commercially available THz polarizers. The maximum insertion losses within the tunable frequency range were found to be 0.24 dB and 1.87 dB for single and double stage GNR polarizers, respectively, which are substantially low. We compared the performance of the proposed structures with recently demonstrated graphene-based metastructure polarizers. The polarizers are promising for the design of photonic devices, integrated photonic circuits, and optoelectronic systems.

Photoluminescent Semiconducting Graphene Nanoribbons via Longitudinally Unzipping Single-Walled Carbon Nanotubes.

The lack of a sizeable band gap has so far prevented graphene from building effective electronic and optoelectronic devices despite its numerous exceptional properties. Intensive theoretical research reveals that a band gap larger than 1 eV can only be achieved in sub-3 nm wide graphene nanoribbons (GNRs), but real fabrication of such ultranarrow GNRs still remains a critical challenge. Herein, we demonstrate an approach for the synthesis of ultranarrow and photoluminescent semiconducting GNRs by longitudinally unzipping single-walled carbon nanotubes. Atomic force microscopy reveals the unzipping process, and the resulting 2.2 nm wide GNRs are found to emit strong and sharp photoluminescence at ∼685 nm, demonstrating a very desirable semiconducting nature. This band gap of 1.8 eV is further confirmed by follow-up photoconductivity measurements, where a considerable photocurrent is generated, as the excitation wavelength becomes shorter than 700 nm. More importantly, our fabricated GNR field-effect transistors (FETs), by employing the hexagonal boron nitride-encapsulated heterostructure to achieve edge-bonded contacts, demonstrate a high current on/off ratio beyond 105 and carrier mobility of 840 cm2/V s, approaching the theoretical scattering limit in semiconducting GNRs at room temperature. Especially, highly aligned GNR bundles with lengths up to a millimeter are also achieved by prepatterning a template, and the fabricated GNR bundle FETs show a high on/off ratio reaching 105, well-defined saturation currents, and strong light-emitting properties. Therefore, GNRs produced by this method open a door for promising applications in graphene-based electronics and optoelectronics.

Energy Gaps in BN/GNRs Planar Heterostructure.

Using the tight-binding approach, we study the band gaps of boron nitride (BN)/ graphene nanoribbon (GNR) planar heterostructures, with GNRs embedded in a BN sheet. The width of BN has little effect on the band gap of a heterostructure. The band gap oscillates and decreases from 2.44 eV to 0.26 eV, as the width of armchair GNRs, , increases from 1 to 20, while the band gap gradually decreases from 3.13 eV to 0.09 eV, as the width of zigzag GNRs, , increases from 1 to 80. For the planar heterojunctions with either armchair-shaped or zigzag-shaped edges, the band gaps can be manipulated by local potentials, leading to a phase transition from semiconductor to metal. In addition, the influence of lattice mismatch on the band gap is also investigated.

Hybrid Films Based on Bilayer Graphene and Single-Walled Carbon Nanotubes: Simulation of Atomic Structure and Study of Electrically Conductive Properties.

One of the urgent problems of materials science is the search for the optimal combination of graphene modifications and carbon nanotubes (CNTs) for the formation of layered hybrid material with specified physical properties. High electrical conductivity and stability are one of the main optimality criteria for a graphene/CNT hybrid structure. This paper presents results of a theoretical and computational study of the peculiarities of the atomic structure and the regularities of current flow in hybrid films based on single-walled carbon nanotubes (SWCNTs) with a diameter of 1.2 nm and bilayer zigzag graphene nanoribbons, where the layers are shifted relative to the other. It is found that the maximum stresses on atoms of hybrid film do not exceed ~0.46 GPa for all considered topological models. It is shown that the electrical conductivity anisotropy takes place in graphene/SWCNT hybrid films at a graphene nanoribbon width of 4 hexagons. In the direction along the extended edge of the graphene nanoribbon, the electrical resistance of graphene/SWCNT hybrid film reaches ~125 kOhm; in the direction along the nanotube axis, the electrical resistance is about 16 kOhm. The prospects for the use of graphene/SWCNT hybrid films in electronics are predicted based on the obtained results.

Thermal conductivity and interfacial thermal conductivity of complex graphene nanoribbons without and with polyethylene molecules

We investigate the thermal conductivity (TC) and interfacial TC (ITC) of complex graphene nanoribbons (GNRs) with homojunctions formed by two monolayer GNR regions (MRs) and one central multi-layer GNR region (CR), as well as the influences of the CR layer number and length, the MR length, the GNR width, and the temperature. We show that the ITC is always smaller than the TC, indicating the entire heat transport performance is fundamentally determined by the interfaces. The GNRs with the two-layer CR show the largest ITC, which is much greater than the GNRs with other CR layer numbers. With increasing the temperature and the CR length, the ITC will increase while the TC will decrease for the GNRs with arbitrary CR layer numbers. However, the TC and ITC show the oscillations around certain values with the increase of the GNR width, and the TC will increase with the increase of the length of the MR. In addition, the TC (ITC) in the left part of the complex GNR changes in the same pace as the TC (ITC) in the right counterpart, while the TC always changes in the pace opposite to the ITC in the left or right part of the complex GNR. Finally, we show that the ITC can be increased by placing polyethylene molecules at the interfaces. This research should be an important reference for understanding the heat transport mechanism and designing the thermal functional materials.

Recent advances in graphene nanoribbons for biosensing and biomedicine.

In recent years, a new type of quasi-one-dimensional graphene-based material, graphene nanoribbons (GNRs), has attracted increasing attention. The limited domain width and rich edge configurations of GNRs endow them with unique properties and wide applications in comparison to two-dimensional graphene. This review article mainly focuses on the electrical, chemical and other properties of GNRs, and further introduces the typical preparation methods of GNRs, including top-down and bottom-up strategies. Then, their biosensing and biomedical applications are highlighted in detail, such as biosensors, photothermal therapy, drug delivery, etc. Finally, the challenges and future prospects in the synthesis and application of functionalized GNRs are discussed. It is expected that GNRs will have significant practical use in biomedical applications in the future.