Graphene Ribbons Research Articles

Enhanced terahertz frequency mixing in all-dielectric metamaterial with multiple surface plasmon polaritons resonances

Nonlinear metamaterials hold a promising platform for generating terahertz (THz) waves. In this paper, we present an all-dielectric metamaterial with multiple surface plasmon polariton (SPP) resonances for enhanced THz frequency mixing. The metamaterial is composed of graphene ribbons, a dielectric layer, and a one-dimensional photonic crystal, displaying the multiple absorptions with simultaneous excitation of three SPP resonances. Taking advantage of SPP resonances with high Q factor and strong localized field at the input frequency, the third-order nonlinear processes are remarkably enhanced, including third-harmonic generation and four-wave mixing, producing a variety of frequencies in the THz range. The proposed efficient nonlinear metamaterials offer promising applications for THz frequency synthesis.

Giant enhancement of third harmonic generation in an array of graphene ribbons using amplification of surface plasmon polaritons by optical gain

In this paper, we theoretically study the enhancement of third-harmonic generation in a plasmonic structure composed of an array of trilayer graphene ribbons sandwiched between two CaF2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$CaF_{2}$$\\end{document} layers. In fact, we suggest a new method for more enhancement of nonlinearity in plasmonic structures using incorporation of optical gain into graphene ribbons. As the pump intensity increases, the maximum output intensity of third harmonic generated (THG) wave versus fundamental frequency is blue-shifted while its value enhances. Our analysis indicates that the enhancement factor of THG in our proposed structure is 1.1 × 107 without occurring an electric breakdown compared to case at which an optically pumped trilayer graphene sheet sandwiched between two CaF2 layers. Therefore, only presence of optical gain is not sufficient for significant enhancement of output intensity of THG wave and excitation of SPPs through the structure is also essential. On the other hand, our results demonstrate that the output intensity of THG wave from the proposed structure under optical pumping enhances by 105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{5}$$\\end{document} times compared to the plasmonic structure without optical gain which confirms the role of optical gain for THG enhancement in the plasmonic structure. This is because the gain in graphene ribbons amplifies the SPPs waves leading to the more field enhancement along the graphene ribbons which results in significant enhancement of THG wave in the plasmonic structure in comparison with one without gain. Therefore, we reveal that both SPPs and optical gain contribute to the strong output intensity of THG in our proposed structure compared to the trilayer graphene sheet inserted between two CaF2 layers.

Improving the electrical performances of InSe transistors by interface engineering

InSe has emerged as a promising candidate for next-generation electronics due to its predicted ultrahigh electrical performance. However, the efficacy of the InSe transistor in meeting application requirements is hindered due to its sensitivity to interfaces. In this study, we have achieved notable enhancement in the electrical performance of InSe transistors through interface engineering. We engineered an InSe/h-BN heterostructure, effectively suppressing dielectric layer-induced scattering. Additionally, we successfully established excellent metal–semiconductor contacts using graphene ribbons as a buffer layer. Through a methodical approach to interface engineering, our graphene/InSe/h-BN transistor demonstrates impressive on-state current, field-effect mobility, and on/off ratio at room temperature, reaching values as high as 1.1 mA/μm, 904 cm2⋅V−1⋅s−1, and >106, respectively. Theoretical computations corroborate that the graphene/InSe heterostructure shows significant interlayer charge transfer and weak interlayer interaction, contributing to the enhanced performance of InSe transistors. This research offers a comprehensive strategy to elevate the electrical performance of InSe transistors, paving the way for their utilization in future electronic applications.

Active control of polarization-dependent terahertz surface plasmonic wave excitation using coupled graphene-metal hybrid metasurfaces

Active control of terahertz surface plasmonic wave (SPW) intensity in the propagation direction holds substantial significance for advanced terahertz functional devices. In this study, we propose a graphene-metal hybrid split-ring slit resonator (SRSR) array metasurfaces and employ the concept of electromagnetically induced transparency (EIT) to achieve excitation of asymmetric SPWs under various polarization states. By individually integrating two graphene ribbons into the two split-ring slit gaps and applying different bias voltages, we observed a gradual transition in the excitation behavior of asymmetric terahertz SPWs, ultimately resembling that of a single SRSR. Near-field simulations reveal that this phenomenon is attributed to the short-connection effect of graphene. Our proposed graphene-metal active hybrid metasurface introduces a novel approach to realize active SPWs devices, holding potential applications in terahertz on-chip communication.

Ultrathin Two-dimensional Layered Composite Carbosilicates from in situ Unzipped Carbon Nanotubes and Exfoliated Bulk Silica.

A key task in today's inorganic synthetic chemistry is to develop effective reactions, routes, and associated techniques aiming to create new functional materials with specifically desired multilevel structures and properties. Herein, we report an ultrathin two-dimensional layered composite of graphene ribbon and silicate via a simple and scalable one-pot reaction, which leads to the creation of a novel carbon-metal-silicate hybrid family: carbosilicate. The graphene ribbon is in situ formed by unzipping carbon nanotubes, while the ultrathin silicate is in situ obtained from bulk silica or commercial glass; transition metals (Fe or Ni) oxidized by water act as bridging agent, covalently bonding the two structures. The unprecedented structure combines the superior properties of the silicate and the nanocarbon, which triggers some specific novel properties. All processes during synthesis are complementary to each other. The associated synergistic chemistry could stimulate the discovery of a large class of more interesting, functionalized structures and materials.

Ultrathin Two‐dimensional Layered Composite Carbosilicates from in situ Unzipped Carbon Nanotubes and Exfoliated Bulk Silica

AbstractA key task in today's inorganic synthetic chemistry is to develop effective reactions, routes, and associated techniques aiming to create new functional materials with specifically desired multilevel structures and properties. Herein, we report an ultrathin two‐dimensional layered composite of graphene ribbon and silicate via a simple and scalable one‐pot reaction, which leads to the creation of a novel carbon‐metal‐silicate hybrid family: carbosilicate. The graphene ribbon is in situ formed by unzipping carbon nanotubes, while the ultrathin silicate is in situ obtained from bulk silica or commercial glass; transition metals (Fe or Ni) oxidized by water act as bridging agent, covalently bonding the two structures. The unprecedented structure combines the superior properties of the silicate and the nanocarbon, which triggers some specific novel properties. All processes during synthesis are complementary to each other. The associated synergistic chemistry could stimulate the discovery of a large class of more interesting, functionalized structures and materials.

High fractal-dimensional carbon conductive agent for improving the Li storage performance of Si-based electrode

Constructing stable Si electrodes with high areal capacity is crucial for improving the total energy density of lithium ion batteries (LIBs). However, it remains challenging because the poor intrinsic conductivity and serious pulverization of Si usually lead to the active material falling-off from the conductive network. Herein, we demonstrate novel spatially extended graphene ribbons with a high fractal-dimension structure (HFGR-400), which can construct highly conductive and mechanically reinforced networks when used as the conductive agent for Si electrodes. The HFGR-400 added electrode shows 1.5–3.2 times higher conductivity and 1.4–2.3 times larger peeling strength than those of the commonly used carbon conductive agent added electrodes. Moreover, the flexible HFGR-400 ribbons with appropriate amount of functional groups ensure large contact area and strong interfacial interaction with Si particles, but without blocking the ion transport channels. Therefore, the HFGR-400 added Si electrode exhibits good cycle stability (2051.8 mAh/g after 200 cycles) and high rate performance. Moreover, the high Si mass loading HFGR-400 electrode shows a competitive areal capacity of 3.5 mAh cm−2 after 200 cycles, superior to most of the reported Si-based electrodes. Our work highlights the importance of conductive agents with high fractal-dimension structure for practical Si-based electrodes.

Impact of pyrene orientation on the electronic properties and stability of graphene ribbons

We report a novel synthetic route to a series of fused acene derivatives, in which linear extension of the fully conjugated core proves to be an efficient method to tune optoelectronic properties.

Role of 1D edge in the elasticity and fracture of h-BN doped graphene nanoribbons

Recent achievement of BN-graphene alloy material has enabled the potential of bandgap tuning through both sub-10 nm width control and BN concentration variation. However, its mechanics, which is necessary for prediction of stability in functional applications, is not well studied. Here, molecular dynamics simulation is performed to conduct uniaxial tensile test for BN-doped graphene nanoribbons (BN-GNR) with varying widths and BN atom fractions. Efforts are made to study the constitutive relations for the edges and the whole BN-GNR and explore the fracture mechanisms of the hybrid nanoribbons. The substantial softening effect of the edges induced by wrinkling alters the impact of BN concentration on the stiffness in the sub-20 nm regime deviating from the linear behaviour observed in the bulk case. Fracture properties are unexpectedly independent of BN concentrations unlike in the bulk and the failure behaviour is rather decided by the graphene ribbon edge structure. Here the armchair edges serve as the source of crack nucleation at an early stage leading to weakened strength and reduced stretchability, whereas zigzag edges do not promote early crack nucleation and leads to the size dependence of fracture properties.

Tuning Active Site Flexibility by Defect Engineering of Graphene Ribbon Edge‐hosted Fe−N3 Sites

AbstractNitrogen‐doped, carbon‐supported transition metal catalysts are excellent for several reactions. Structural engineering of M−Nx sites to boost catalytic activity is rarely studied. Here, we demonstrate that the structural flexibility of Fe−N3 site is vital for tuning the electronic structure of Fe atoms and regulating the catalytic transfer hydrogenation (CTH) activity. By introducing carbon defects, we construct Fe−N3 sites with varying Fe−N bond lengths distinguishable by X‐ray absorption spectroscopy. We investigate the CTH activity by density‐functional theory and microkinetic calculations and reveal that the vertical displacement of the Fe atom out of the plane of the support, induced by the Fe−N3 distortion, raises the Fe orbital and strengthens binding. We propose that the activity is controlled by the relaxation of the reconstructed site, which is further affected by Fe−N bond length, an excellent activity descriptor. We elucidate the origin of the CTH activity and principles for high‐performing Fe−N−C catalysts by defect engineering.

Tuning Active Site Flexibility by Defect Engineering of Graphene Ribbon Edge-hosted Fe-N3 Sites.

Nitrogen-doped, carbon-supported transition metal catalysts are excellent for several reactions. Structural engineering of M-Nx sites to boost catalytic activity is rarely studied. Here, we demonstrate that the structural flexibility of Fe-N3 site is vital for tuning the electronic structure of Fe atoms and regulating the catalytic transfer hydrogenation (CTH) activity. By introducing carbon defects, we construct Fe-N3 sites with varying Fe-N bond lengths distinguishable by X-ray absorption spectroscopy. We investigate the CTH activity by density-functional theory and microkinetic calculations and reveal that the vertical displacement of the Fe atom out of the plane of the support, induced by the Fe-N3 distortion, raises the Fe orbital and strengthens binding. We propose that the activity is controlled by the relaxation of the reconstructed site, which is further affected by Fe-N bond length, an excellent activity descriptor. We elucidate the origin of the CTH activity and principles for high-performing Fe-N-C catalysts by defect engineering.

Nonlocal phonon thermal transport in graphene in hydrodynamic regime

The hydrodynamic behavior of phonons is of particular interest and importance owing to the strong demand for highly thermal conductive materials. Thermal transport in hydrodynamic regime becomes essentially nonlocal, which can give rise to a number of new and counterintuitive phenomena. In this work, we present a direct numerical study of nonlocal phonon thermal transport in graphene ribbon with vicinity geometry based on the phonon Boltzmann transport equation with first-principles inputs. We demonstrate the viscosity-dominated hydrodynamic transport behaviors with two abnormal thermal transport phenomena: heat current whirlpools and negative nonlocal effect, which originate from phonon viscosity. Phonon viscosity produces the vorticity of shear flows, leading to the backflow of the heat current and the generation of negative nonlocal vicinity response. The system average temperature and the ribbon width as well as the relative positions of the heat sources play a pivotal role in the occurrence of heat current whirlpools and negative nonlocal temperature response. The present work provides solid evidence for phonon hydrodynamic transport in graphene and a potential avenue for experimental detection in the future.

Adjustable gas adsorption and desorption via a self-shrinking nanoscroll

In a gas adsorption–desorption process, gas desorption consumes energy, as well. Hence, the development of gas adsorption–desorption methods and/or adsorbent materials with low-energy consumption for precisely controlling the reversible process is still an open issue. Taking carbon dioxide as an example, this study proposed a carbon nanospring as a unit of an adsorbent model to control the capacity for gas adsorption (CGA), via expanding for adsorption or self-shrinking for desorption by the nanoscroll made from partly hydrogenated graphene ribbon (H-GR). The numerical results obtained from the molecular dynamics approach demonstrate that the CGA of H-GR can be precisely controlled by changing the deformation of H-GR. The adjustable scope of CGA, called capacity for gas desorption, depends on the gas density and the loading speed. However, the ratio of desorption slightly depends on the gas density, which benefits gas capturing in potential application of the present material model.

Electrical Characteristics of Single Layer Graphene Ribbons in a Wide Temperature Range

This paper provides electrical characterization of single layer graphene ribbon devices defined as back-gated graphene transistors. The two-terminal back-gated graphene ribbon devices were fabricated on a conventional Si substrate covered by a 90 nm-thick thermal SiO2. The chemical vapor deposition process was used for the graphene layer deposition and its quality was checked with optical microscopy, scanning electron microscopy and Raman spectroscopy. For the device fabrication, optical lithography was used for electrode patterns through a mask, and Ti/Au (10 nm/100 nm) metallic contacts were deposited by thermal evaporation. We report low and high field electrical measurements of several devices, under a controlled environment over a wide temperature range, from 77 to 300 K. At 77 K, the drain current decreases, i.e. the resistance of the graphene increases, and the nonlinearity is still present. The maximum influence of the temperature is reached at the charges neutrality point, and we observe that the temperature could influence the position of the charge neutrality point. This indicates that the carriers are thermally activated, which yields a least pronounced current with the increase of the back gate voltage.

Resonant Transducers Consisting of Graphene Ribbons with Attached Proof Masses for NEMS Sensors.

The unique mechanical and electrical properties of graphene make it an exciting material for nanoelectromechanical systems (NEMS). NEMS resonators with graphene springs facilitate studies of graphene's fundamental material characteristics and thus enable innovative device concepts for applications such as sensors. Here, we demonstrate resonant transducers with ribbon-springs made of double-layer graphene and proof masses made of silicon and study their nonlinear mechanics at resonance both in air and in vacuum by laser Doppler vibrometry. Surprisingly, we observe spring-stiffening and spring-softening at resonance, depending on the graphene spring designs. The measured quality factors of the resonators in a vacuum are between 150 and 350. These results pave the way for a class of ultraminiaturized nanomechanical sensors such as accelerometers by contributing to the understanding of the dynamics of transducers based on graphene ribbons with an attached proof mass.

Interlayer Conductance in the Armchair Nanotube - Zigzag Graphene Ribbon Parallel Contact: Theoretical Proposal of Detection of Wavefunction Growing from the Edge to the Center in the Graphene Ribbon

Interlayer Conductance in the Armchair Nanotube - Zigzag Graphene Ribbon Parallel Contact: Theoretical Proposal of Detection of Wavefunction Growing from the Edge to the Center in the Graphene Ribbon

Применение метода тринарной дискретизации для анализа структурного распределения углерода в графеносодержащем шунгите

Using the high-permission raster electron microscopy on nano-level the structure distribution of carbon in natural graphene-containing shungite applied for manufacturing adsorbing surfaces is investigated. The analysis is executed in specimens with specific carbon containing about 80-97% and specific conductivity from 2200 to 8600 Sm/m. The results of measuring were the cards of carbon distribution along the specimen surface. It was investigated four specimens and in each specimen was copied five cards in different its points, as a result – twenty cards. It is found the presence on the cards the graphene packets and long graphene ribbons and also domains without clear graphene-similar structure. For the analysis of local carbon distribution, it is proposed the discretization method which consist of applying on the card plane the grid with square cells and following analysis of regularity graphene layers by each cell. It is found three levels of structure regularization: high, middle and low. For the high level it is typical the regular periodic distribution of graphene layers along the whole square of cell, for middle – explosive character of graphene layers, for low – absence of graphene layers along the whole cell. For individual characteristics of each specimen, it is proposed the concept of order degree which supposed the relative number cells in three levels which is averaged on all its cards. It is found that in typical case the high degree of order presents on 35,4% of card area, middle in 47,3% and low in 17,3% of the same area. By way of possible course of distinction in order level is proposed the specific geological origin of specimens from different depositions.

Применение метода трехуровневой дискретизации для анализа связи между структурой и удельной проводимостью графеносодержащего шунгита

The correlation between structure configuration of carbon distribution of graphene-contained shungite and its specific electrical conductivity is investigated. The four shungite specimens from different natural depositions are investigated. The carbon structure configuration is investigated by high-permission raster electron microscopy. As a result, there was found cards of graphene layers, graphene packets and graphene ribbons along the plane of specimen surface. The specific electrical conductivity was merit be the four-contact method. On each specimen was found five cards in different its points as a whole – twenty cards. For the analysis of carbon local distribution, the descretization by three levels method was used. This method consists of applying on the card plane the grid with square cells and following analysis of regularity graphene layers by each cell. It is found three levels of order regularity structure: high, middle and low which distinguished by the number and length of graphene layers inside of cell. By averaging along all cards of present specimen for each specimen was found the own numerical characteristic which describes the carbon distribution structure. As a most important parameters were selected the averaged meaning of order degree and inversed value of square deflection from this value. It was found that the dependence of inverted value on specimen from the specimen number has the same character as the dependence on specific conductivity form the same number. As a result of investigations, it was proposed that the specific conductivity of shungite specimen may be found from statistical analysis of carbon space distribution cards which are found by the high-permission raster electron microscopy. It was proposed the algorithm of founding conductivity by analysis carbon configuration cards consisted from 16 successive steps which started from the founding the total combination of cards with the aid of electron microscope and finished by obtaining the electric conductivity value.

Graphene-Enabled Tunable Phase Gradient Metasurface for Broadband Dispersion Manipulation of Terahertz Wave.

With the increasing demand for the miniaturization and flexibility of optical devices, graphene-based metasurfaces have emerged as a promising ideal design platform for realizing planar and tunable electromagnetic or optical devices. In this paper, we propose a tunable metasurface with low-dispersion phase gradient characteristics that is composed of an array of double-layer graphene ribbons sandwiched with a thin insulating layer and a polymer substrate layer with a gold ground plane. As two typical proof-of-concept examples, metasurfaces act as a planar prism and a planar lens, respectively, and the corresponding performances of tunable broadband dispersion are demonstrated through full-wave simulation experiments. By changing the Fermi level of each graphene ribbon individually to introduce abrupt phase shifts along the metasurface, the broadband continuous dispersion effect of abnormal reflection and beam focusing is achieved within a terahertz (THz) frequency region from 3.0 THz to 4.0 THz, and the dispersion results can be freely regulated by reconfiguring the sequence of Fermi levels via the bias voltage. The presented graphene metasurface provides an avenue for the dispersion manipulation of a broadband terahertz wave and may have great prospects in the fields of optics, imaging, and wireless communication.

Tunable slow light device based on a graphene metasurface.

Slow light devices have significant applications in memory, switching, and quantum optics. However, the design and fabrication of slow light devices with large tunable group delay are still challenging. Here, a graphene-based slow light device that can electrically modulate the group delay of terahertz (THz) waves is proposed and experimentally demonstrated. The unit cell of the device consists of a U-shaped metal resonator and an Ω-shaped metal resonator, with three graphene ribbons embedded between the two resonators. Under electrical stimuli, a relatively high amplitude modulation depth of 74% is achieved and the maximum transmission amplitude is as high as 0.7 at the transmission peak of 0.6 THz. Most importantly, the maximum group delay variation reaches 5 ps at 0.76 THz and the maximum group delay amplitude is as high as 8.8 ps. The experiment shows good agreement with simulation. This study paves a new way for developing novel switchable nanophotonic devices and slow light devices.