Graphene Interlayer Research Articles

Bending induced mechanical exfoliation of graphene interlayers in a through thickness Al-GNP functionally graded composite fabricated via novel single-step FSP approach

A novel step grooving approach is proposed for the reinforcement incorporation before FSP, enabling the creation of through-thickness composition gradient with a higher volume fraction of reinforcement near the surface and relatively lower volume fraction in the core by using a single step of FSP. The overall tensile strength of Al-GNP functionally graded composite (FGC) is increased by ∼52% compared to pure aluminium. The localized Young's modulus and yield strength of the core region is increased by ∼12% and ∼54% compared to the surface region of the fabricated composite, respectively. The maximum strain in the core region is also decreased by ∼38% depicting its higher stiffness over the surface region. Contrastingly, the microhardness of the surface region is increased by ∼18% compared to the core region of the fabricated composite. Thus, a combination of higher surface hardness and excellent core tensile strength is achieved with the proposed methodology. The bending of graphene interlayers leading to the mechanical exfoliation of GNP increased the load sharing capability of the Al/GNP interface. The load sharing through interface and coefficient of thermal expansion mismatch between Al and GNP are identified as the dominant strengthening mechanisms in the fabricated composite.

Extrinsic Surface Magnetic Anisotropy Contribution in Pt/Y3Fe5O12Interface in Longitudinal Spin Seebeck Effect by Graphene Interlayer

A recent study found that magnetization curves for Y3Fe5O12 (YIG) slab and thick films (>20 μm thick) differed from bulk system curves by their longitudinal spin Seebeck effect in a Pt/YIG bilayer system. The deviation was due to intrinsic YIG surface magnetic anisotropy, which is difficult to adopt extrinsic surface magnetic anisotropy even when in contact with other materials on the YIG surface. This study experimentally demonstrates evidence for extrinsic YIG surface magnetic anisotropy when in contact with a diamagnetic graphene interlayer by observing the spin Seebeck effect, directly proving intrinsic YIG surface magnetic anisotropy interruption. We show the Pt/YIG bilayer system graphene interlayer role using large area single and multilayered graphenes using the longitudinal spin Seebeck effect at room temperature, and address the presence of surface magnetic anisotropy due to magnetic proximity between graphene and YIG layer. These findings suggest a promising route to understand new physics of spin Seebeck effect in spin transport.

Multifunctional B/N Co‐Doped Graphene Interlayer for Fast and Stable Lithium‐Sulfur Batteries

AbstractA boron (B)/nitrogen (N) co‐doped graphene is synthesized via an two‐steps method and used as an interlayer for lithium‐sulfur (Li−S) batteries. Due to the excellent electronic conductivity and dense sheet constructure of graphene, it can improve the conductive network, reduce the pores of polypropylene (PP) membrane, and consequently inhibit the penetration of polysulfide in Li−S batteries. More importantly, the co‐doped B and N atoms play the role of Lewis acid‐base, which have a strong adsorption capacity to lithium ions and as well as sulfur ions during reactions, and thus inhibit the “shuttle effect” and accelerate the conversion reactions of polysulfides. Based on this multifunctional interlayer, the cells exhibit a high initial capacity of 1448 mAh g−1, and achieve a reversible capacity of 578 mAh g−1 under a large rate of 2 C after 350 cycles with a capacity decay of 0.015 % per cycle. These results demonstrate the enormous potential of the B/N co‐doped graphene as the interlayer for high‐performance Li−S batteries.

Zincophilic Laser‐Scribed Graphene Interlayer for Homogeneous Zinc Deposition and Stable Zinc‐Ion Batteries

Zinc metal is an important anode material for next‐generation energy storage systems. Unfortunately, uncontrollable dendrite growth caused by nonuniform Zn nucleation during the plating process severely restricts their practical applications. Herein, a nitrogen‐doped 3D laser scribed graphene (NLSG) with a large surface area and uniform distribution of nucleation sites is used as the interlayer to control Zn nucleation behavior and suppress Zn dendrite growth. The N‐containing functional groups in the carbon matrix are highly zincophilic, which induces uniform nucleation of Zn and guides homogenous Zn deposition. Meanwhile, the large specific area can effectively decrease the local current density, which is more favorable for highly reversible Zn plating/stripping. Benefiting from superior properties, the NLSG demonstrates improved electrochemical performance with high Coulombic efficiency (99.4%) and enhanced cycling performance (200 h). Compared with the bare Zn anodes, the NLSG‐coated Zn//MnO2 battery demonstrates higher capacity retention (72.3% vs 59.3%) after 1200 cycles.

Enhanced Tensile Strength of Monolithic Epoxy with Highly Dispersed TiO2-Graphene Nanocomposites

The functionalization of graphene has been reported widely, showing special physical and chemical properties. However, due to the lack of surface functional groups, the poor dispersibility of graphene in solvents strongly limits its engineering applications. This paper develops a novel green “in-situ titania intercalation” method to prepare a highly dispersed graphene, which is enabled by the generation of the titania precursor between the layer of graphene at room temperature to yield titania-graphene nanocomposites (TiO2-RGO). The precursor of titania will produce amounts of nano titania between the graphene interlayers, which can effectively resist the interfacial van der Waals force of the interlamination in graphene for improved dispersion state. Such highly dispersed TiO2-RGO nanocomposites were used to modify epoxy resin. Surprisingly, significant enhancement of the mechanical performance of epoxy resin was observed when incorporating the titania-graphene nanocomposites, especially the improvements in tensile strength and elongation at break, with 75.54% and 176.61% increases at optimal usage compared to the pure epoxy, respectively. The approach presented herein is easy and economical for industry production, which can be potentially applied to the research of high mechanical property graphene/epoxy composite system.

Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes

Single-crystalline membranes of functional materials enable the tuning of properties via extreme strain states; however, conventional routes for producing membranes require the use of sacrificial layers and chemical etchants, which can both damage the membrane and limit the ability to make them ultrathin. Here we demonstrate the epitaxial growth of the cubic Heusler compound GdPtSb on graphene-terminated Al2O3 substrates. Despite the presence of the graphene interlayer, the Heusler films have epitaxial registry to the underlying sapphire, as revealed by x-ray diffraction, reflection high energy electron diffraction, and transmission electron microscopy. The weak Van der Waals interactions of graphene enable mechanical exfoliation to yield free-standing GdPtSb membranes, which form ripples when transferred to a flexible polymer handle. Whereas unstrained GdPtSb is antiferromagnetic, measurements on rippled membranes show a spontaneous magnetic moment at room temperature, with a saturation magnetization of 5.2 bohr magneton per Gd. First-principles calculations show that the coupling to homogeneous strain is too small to induce ferromagnetism, suggesting a dominant role for strain gradients. Our membranes provide a novel platform for tuning the magnetic properties of intermetallic compounds via strain (piezomagnetism and magnetostriction) and strain gradients (flexomagnetism).

Fatigue damage tracking and life prediction of fiberglass composites using a laser induced graphene interlayer

Fiberglass-reinforced composite materials are commonly used in engineering structures subjected to dynamic loading, such as wind turbine blades, automobiles, and aircraft, where they experience a wide range of unpredictable operating conditions. The ability to monitor these structures while in operation and predict their remaining structural life without requiring their removal from service has the potential to drastically reduce maintenance costs and improve reliability. This work exploits piezoresistive laser induced graphene (LIG) integrated into fiberglass-reinforced composites for in-situ fatigue damage monitoring and lifespan prediction. The LIG is integrated within fiberglass composites using a transfer-printing process that is scalable with the potential for automation, thus reducing barriers for widespread application. The addition of the conductive LIG within the traditionally insulating fiberglass composites enables direct in-situ damage monitoring through simple passive resistance measurements during tension-tension fatigue loading. The accumulation and propagation of structural damage are detected throughout the fatigue life of the composite through changes to the electrical resistance measurements, and the measurement trends are further used to predict the onset of catastrophic composite failure. Thus, this work results in a scalable and multifunctional composite material with self-sensing capabilities for potential use in high-performing, dynamic, and flexible composite structures.

Hydrous Proton Transfer through Graphene Interlayer: An Extraordinary Mechanism under Magnifier

AbstractBalancing ionic selectivity against permeability in filters made from graphene remains a challenge today. Interlayer distance, as the most important factor, dominates nearly all aspects of the flow inside the channel, from the formation of water molecules to the hydration shell of the ions. Unraveling the effects of the interlayer distance on the proton diffusion process helps lay a foundation for the cutting‐edge proton conduction technology. Here, the reactive molecular dynamics simulations are used to probe the proton flow through a series of hydrated graphene channels with different interlayer distance values. The results show that the proton‐selectivity experiences a sharp increase when the channel height is reduced to values under 8 Å, which is near the end of the hydration radii range of the monovalent and divalent cations. Reducing the interlayer distance also decreases the number of confined water molecules, consequently reducing the proton diffusion rate as the hopping platform fades. This way, spatial hindrance combined with the proton‐selective Grotthuss mechanism provide a proton‐exclusive membrane. The outputs of this work can be used for the optimization of proton‐exclusive nanochannels and to serve affordable proton‐exchange membranes (PEMs) for technological advancement in diverse fields from PEM fuel cells to storing liquid hydrogen.

Understanding acid pretreatment of lotus leaves to prepare hard carbons as anodes for sodium ion batteries

Lotus leaves are pretreated by exposure to hydrochloric acid (HCl) by several methods, including mild (PHT), hydrothermal (HHT), and mild and hydrothermal (PHHT) treatments, and subsequently pyrolyzed to yield hard carbon materials. The hydrothermal pretreatment produces the most substantial impact on the microstructures, surface compositions, and electrochemical performances of the resulting hard carbons. Materials prepared by the HHT pretreatment exhibit carbon microspheres with the largest graphene interlayer spacing, lowest quantities of oxygen functional groups, and no observable inorganic impurities. Moreover, such materials exhibit initial coulombic efficiencies and discharge capacities of 66% and 250 mA h g−1, respectively, at 0.2 C rate and after 100 cycles, which are significantly higher than those of non-treated hard carbons (53% and 162 mA hg−1). Surprisingly, the HHT pretreated materials show a maximum discharge capacity of 58 mA h g−1 at a current density of 20 C, while the non-treated materials show no detectable discharge capacity. The superior charging rates of the HHT-treated materials originate from surface properties that facilitate rapid charging processes. Specifically, these capabilities arise from a less reactive surface and larger pore volume that reduce the resistance of the solid electrolyte interphase (SEI) and enhance the diffusivity of sodium ions.

Fermi Velocity Reduction of Dirac Fermions around the Brillouin Zone Center in In2 Se3 -Bilayer Graphene Heterostructures.

Emergent phenomena such as unconventional superconductivity, Mott-like insulators, and the peculiar quantum Hall effect in graphene-based heterostructures are proposed to stem from the superlattice-induced renormalization of (moiré) Dirac fermions at the graphene Brillouin zone corners. Understanding the corresponding band structure commonly demands photoemission spectroscopy with both sub-meV resolution and large-momentum coverage, beyond the capability of the current state-of-the-art. Here the realization of moiré Dirac cones around the Brillouin zone center in monolayer In2 Se3 /bilayer graphene heterostructure is reported. The renormalization is evidenced by reduced Fermi velocity (≈23%) of the moiré Dirac cones and the reshaped Dirac point at the Γ point where they intersect. While there have been many theoretical predictions and much indirect experimental evidence, the findings here are the first direct observation of Fermi velocity reduction of the moiré Dirac cones. These features suggest strong In2 Se3 /graphene interlayer coupling, which is comparable with that in twisted bilayer graphene. The strategy expands the choice of materials in the heterostructure design and stimulates subsequent broad investigations of emergent physics at the sub-meV energy scale.

Direct Synthesis of Molybdenum Phosphide Nanorods on Silicon Using Graphene at the Heterointerface for Efficient Photoelectrochemical Water Reduction

HighlightsMoP nanorod-array catalysts were directly synthesized on graphene passivated silicon photocathodes without secondary phase.Mo-O-C covalent bondings and energy band bending at heterointerfaces facilitate the electron transfer to the reaction sites.Numerous catalytic sites and drastically enhanced anti-reflectance of MoP nanorods contribute to the high solar energy conversion efficiency.Transition metal phosphides (TMPs) and transition metal dichalcogenides (TMDs) have been widely investigated as photoelectrochemical (PEC) catalysts for hydrogen evolution reaction (HER). Using high-temperature processes to get crystallized compounds with large-area uniformity, it is still challenging to directly synthesize these catalysts on silicon photocathodes due to chemical incompatibility at the heterointerface. Here, a graphene interlayer is applied between p-Si and MoP nanorods to enable fully engineered interfaces without forming a metallic secondary compound that absorbs a parasitic light and provides an inefficient electron path for hydrogen evolution. Furthermore, the graphene facilitates the photogenerated electrons to rapidly transfer by creating Mo-O-C covalent bondings and energetically favorable band bending. With a bridging role of graphene, numerous active sites and anti-reflectance of MoP nanorods lead to significantly improved PEC-HER performance with a high photocurrent density of 21.8 mA cm−2 at 0 V versus RHE and high stability. Besides, low dependence on pH and temperature is observed with MoP nanorods incorporated photocathodes, which is desirable for practical use as a part of PEC cells. These results indicate that the direct synthesis of TMPs and TMDs enabled by graphene interlayer is a new promising way to fabricate Si-based photocathodes with high-quality interfaces and superior HER performance.Graphic

Diffusivity and band offset analysis of a graphene interlayer at the back contact of a copper zinc tin sulphide solar cell.

Cu2ZnSnS4 (CZTS) is a promising 3rd generation solar cell absorber based on earth-abundant and nontoxic elements. However, the formation of detrimental MoS2 in the Mo/CZTS back contact interface hinders the overall performance due to poor band alignment in the back contact and a degraded interface. We propose that graphene can be a suitable candidate for the protective interlayer at the back contact to prevent the formation of amorphous MoS2 by blocking S diffusion. Using first principles calculations, we investigated the kinetics processes of S atom diffusion on and across the graphene plane with various defects considered. It was found that while an S atom can easily diffuse on graphene with a diffusion barrier of 0.355 eV, it is hard to diffuse across the graphene plane with or without defects, with diffusion barriers ranging from 1.19 eV through a double vacancy to 8.66 eV across pristine graphene. In addition, a band offset calculation using a local potential alignment method was performed to understand the role of graphene in hole transport. We discover that the interpolation of Hartree potential data can largely improve the stability of the band offset algorithm, comparable to a core level alignment method. The band offset calculation results show that the Fermi level of graphene is 0.664 eV higher than the valence band maximum of CZTS. Therefore, graphene is a benign interlayer in the back contact that can facilitate hole collection. Our calculations suggest that graphene is a promising protective interlayer.

Luminescence of structured InN deposited on graphene interlayer

Indium nitride epilayers were grown by metalorganic chemical vapour deposition (MOCVD) on graphene/SiC substrates with different terrace widths. Photoluminescence (PL) properties in the epilayers of different thickness and along the epilayer growth direction were studied with spatial resolution using confocal microscopy. The PL properties have been linked with the structure of the epilayers studied by X-ray diffraction, transmission electron microscopy, atomic force microscopy and Raman scattering. It is revealed that InN on graphene/SiC layers with a thickness of up to ~2 μm consists of chaotically oriented nanocrystals of 20 nm in diameter but tends to transform into a more homogeneous multicrystalline layer at longer deposition durations. The PL band in the top part of thick layers is peaked at 0.687 eV, closer to the band gap than in any InN epilayer grown by MOCVD before. This evidences a low density of equilibrium electrons usually deteriorating performance of InN epilayers. The PL band in thin samples or in the lower part of thick samples is shifted by 60 meV predominantly to quantum confinement in the nanocrystals.

Bioinspired ultrathin graphene nanosheets sandwiched between epoxy layers for high performance of anticorrosion coatings

The special “brick-mud” layered micro-nano structure of nacre has undergone millions of years of biological evolution, which can withstand the corrosion of seawater in different environments, and has both high strength and toughness. Inspired by mussels and natural nacre, we successfully designed a bionic epoxy-(graphene-dopamine)n-epoxy sandwich composite coating. Not only does dopamine act as a binder to improve the interfacial compatibility and adhesion between epoxy resin and graphene, but due to the hydrogen bonding and the electrostatic interaction of –COO− and –NH3+, graphene interlayers is parallel to the substrate and arranged between two epoxy coatings. This not only gives full play to the barrier effect of graphene, but also shielding the galvanic corrosion by avoiding direct contacting with the substrate. The results show that the composite coating prepared 10 scanning of dopamine functionalized graphene oxide has a low-frequency impedance of 1.30 × 109 O cm2 after immersion in 3.5 wt% NaCl solution for 90 days, which is three orders of magnitude higher than that of pure coating, revealing remarkable long-term anticorrosion. We consider that our strategy can be readily extended to the self-alignment of a variety of two-dimensional nanofillers to facilitate the development of long-term corrosion resistant coatings.

Linear stimuli-responsive upconversion luminescent nanoprobes coupled with graphene

Abstract Upconversion nanoparticles (UCNPs) have been widely used as powerful bio-probes, but still suffer from low sensitivity and complex nonlinear response. Here, we show that local optical mode and surface scattering and absorption of core-shell UCNPs can be manipulated by coupling to the whispering-gallery modes of glass microfibers with graphene interlayer (a composite nanosystem). Graphene can tune the refraction and scattering of glass microfibers to excitation light, and simultaneously the photon transmission from glass microfibers to upconversion nanoparticles, so that the composite nanosystem with graphene presents different luminescent property from that without graphene. The linear stimuli-responsive upconversion luminescence is indirectly realized via stimuli of graphene in the composite nanosystem since graphene plays a role of ‘light gate’. This composite nanosystem could be used as a linear-response and highly-sensitive luminescent sensor for the detection of methanol with a limit of 0.052 ppm at room temperature.

Nitrogen-doped nanoporous graphene induced by a multiple confinement strategy for membrane separation of rare earth.

SummaryRare earth separation is still a major challenge in membrane science. Nitrogen-doped nanoporous graphene (NDNG) is a promising material for membrane separation, but it has not yet been tested for rare earth separation, and it is limited by multi-complex synthesis. Herein, we developed a one-step, facile, and scalable approach to synthesize NDNG with tunable pore size and controlled nitrogen content using confinement combustion. Nanoporous hydrotalcite from Zn(NO3)2 is formed between layers of graphene oxide (GO) absorbed with phenylalanine via confinement growth, thus preparing the sandwich hydrotalcite/phenylalanine/GO composites. Subsequently, area-confinement combustion of hydrotalcite nanopores is used to etch graphene nanopores, and the hydrotalcite interlayer as a closed flat nanoreactor induces two-dimensional space confinement doping of planar nitrogen into graphene. The membrane prepared by NDNG achieves separation of Sc3+ from the other rare earth ions with excellent selectivity (∼3.7) through selective electrostatic interactions of pyrrolic-N, and separation selectivity of ∼1.7 for Tm3+/Sm3+.

Structure and behavior of ZrO2-graphene-ZrO2 stacks

ZrO2-graphene-ZrO2 layered structures were built and their crystallinity was characterized before resistive switching measurements. Thin nanocrystalline ZrO2 dielectric films were grown by atomic layer deposition on chemical vapor deposited graphene. Graphene was transferred, prior to the growth of the ZrO2 overlayer, to the ZrO2 film pre-grown on titanium nitride. Nucleation and growth of the top ZrO2 layer was improved after growing an amorphous Al2O3 interface layer on graphene at lowered temperatures. Studies on resistive switching in such structures revealed that the exploitation of graphene interlayers could modify the operational voltage ranges and somewhat increase the ratio between high and low resistance states.

Construction of TiO2-pillared multilayer graphene nanocomposites as efficient photocatalysts for ciprofloxacin degradation

We successfully constructed TiO2-pillared multilayer graphene nanocomposites (T-MLGs) via a facile method as follows: dodecanediamine pre-pillaring, ion exchange (Ti4+ pillaring), and interlayer in-situ formation of TiO2 by hydrothermal method. TiO2 nanoparticles were distributed uniformly on the graphene interlayer. The special structure combined the advantages of graphene and TiO2 nanoparticles. As a result, T-MLGs with 64.3wt% TiO2 showed the optimum photodegradation rate and adsorption capabilities toward ciprofloxacin. The photo-degradation rate of T-MLGs with 64.3wt% TiO2 was 78% under light-emitting diode light irradiation for 150 min. Meanwhile, the pseudofirst-order rate constant of T-MLGs with 64.3wt% TiO2 was 3.89 times than that of pristine TiO2. The composites also exhibited high stability and reusability after five consecutive photocatalytic tests. This work provides a facile method to synthesize semiconductor-pillared graphene nanocomposites by replacing TiO2 nanoparticles with other nanoparticles and a feasible means for sustainable utilization of photocatalysts in wastewater control.

Laser induced graphene interlaminar reinforcement for tough carbon fiber/epoxy composites

Poor interlaminar fracture toughness is a critical limitation in the performance of fiber reinforced polymer matrix composites over a wide range of structural applications. Recent efforts to overcome this problem have shown that the introduction of various forms of nanoscale interleaves can yield composites with improved toughness. In this work, it is demonstrated that forests of vertically aligned, laser induced graphene (LIG) can provide significant improvement to the interlaminar properties of carbon fiber reinforced composites. The conductive graphene interlayers are first synthesized using a laser induction process and then transfer printed onto carbon fiber prepregs while maintaining their out-of-plane alignment. The introduced LIG interlayers result in a significantly increased short beam shear toughness, along with a 41% and 69% increase in both initiation Mode I and pre-cracked Mode II fracture toughness of the composites, respectively. In addition, the tensile and viscoelastic properties of the carbon fiber composites are preserved post-treatment. The LIG strengthened interlaminar region exhibit failure modes that provide greater resistance to crack initiation and propagation such as cohesive failure, crack deflection and nanoscale bridging. Therefore, this work provides a simple, fast and convenient method to toughen carbon fiber reinforced composites using transferred LIG interlayers, allowing for the cost-effective and rapid fabrication of simultaneously strong and tough carbon fiber reinforced composite structures.

Moiré diamanes based on the hydrogenated or fluorinated twisted bigraphene: The features of atomic and electronic structures, Raman and infrared spectra

We applied density functional theory to predict the atomic and electronic structures, Raman, and IR spectra of the new diamond-like 2D materials – Moiré diamanes (Dns). They are based on the fully hydrogenated or fluorinated twisted bilayer graphenes (tBG) and are formed by interlayer connection. Due to the twisted structure of Moiré bilayer, graphene interlayer connection significantly different from the connection of AA- or AB-stacked bilayer that dictates their property features. We consider characteristics of hydrogenated and fluorinated Moiré diamanes with the simplest unit cell based on the 21.8° tBG- Dn21.8 and F-Dn21.8, respectively. The calculated band structures of considered twisted diamanes show the band gaps higher than 4 eV exceed the gaps of standard diamanes. The presence of a large number of narrow peaks of densities of states (DOS) connected with flattened minizones provides their applicability in optical and optoelectronic devices. To identify Dn21.8 or F-Dn21.8, we calculate and describe Raman and IR spectral features of both structures, which turned out to be similar. The most active Raman frequencies of these Moiré structures are blue-shifted concerning standard AA or AB-stacked diamanes. In contrast to traditionally stacked arrangements, considered twisted diamanes can interact with the light polarized parallel to the film plane.