Multilayer Graphene Research Articles

Competition between fractional quantum Hall liquid and electron solid phases in the Landau levels of multilayer graphene

Competition between fractional quantum Hall liquid and electron solid phases in the Landau levels of multilayer graphene

Room‐Temperature Ferromagnetism and Fermi Level Pinning in Multilayer Graphene Films Derived from Ferrocene

AbstractSpin polarization is a very important condition for spintronics applications which can easily be achieved by using ferromagnetic materials. Graphene‐based magnetic materials, which have long spin lifetime and diffusion length, are very promising as spin channel materials. In this work, Ferrocene molecules are chosen as the precursor carbon source using the chemical vapor deposition method, facilitating the synthesis of multilayer graphene films decorated with magnetic nanoclusters. This resultant material manifested planar ferromagnetism with a Curie temperature exceeding room temperature (≥300 K) and a saturation magnetization as high as 4.1 × 10−7 emu mm−2. The robust ferromagnetic coupling can plausibly be attributed to the presence of magnetic nanoclusters interspersed within the synthesized graphene, enhancing the localized magnetic moment and promoting ferromagnetic long‐range ordering. Furthermore, the Fermi level pinning at the Dirac point is observed and predominantly ascribed to the pervasive defects in the graphene derived from ferrocene. The oxygen functional groups within these defects act as charge traps, effectively anchoring the Fermi level to the Dirac point, intrinsically suppressing the ambipolar behavior of graphene. This work sheds light on potential avenues for the exploration of novel, high‐performance carbonaceous spintronics materials with economic feasibility.

The effect of surface energy on the wettability of graphene-coated copper: A comparison of different single and multilayer graphene

The present research investigated the effect of different types of graphene layers including a slow cooling rate single-layer graphene (SSLG), a high cooling rate single-layer graphene (HSLG), and a multilayer graphene (MLG) on the wettability and surface energy of the copper substrate, which was synthesized using a chemical vapor deposition (CVD) process. Results revealed an increasing trend in surface roughness of the substrate by applying the graphene layer which is mostly due to the formation of step bunches (SBs) during the synthesis process, and the highest surface roughness is obtained for the MLG. Moreover, despite the expectations the results of surface energy indicated that applying the graphene layer in all cases has increased the surface energy. However, the lowest surface energy is related to SSLG among the coated samples. On the contrary, the wettability of the coated-samples was diminished and the lowest wettability was obtained for the SSLG.

Optimization for Current-Enhanced Solid-Phase Deposition of Multi-Layer Graphene with High Crystallinity and Uniformity

Solid-phase deposition (SPD) is a preferable method to fabricate multi-layer graphene (MLG) for device applications since MLG can be deposited directly on substrates without transfer. Previously, we reported that current application during SPD enhances the MLG growth. In this study, we investigated the effects of applied current and heating rate on the crystallinity and uniformity of MLG precipitated from carbon (C) / nickel (Ni) structures. It was found that higher current and slower heating rate lead to improve the MLG crystallinity. Moreover, the uniformity was improved by the optimization of Ni and C thickness which could control the nucleation and growth of MLG during SPD. As a result, a uniform MLG with a high G/D ratio of 5.5 was obtained at a low temperature of 365 °C.

In-situ fracture toughness measurement of multilayer graphene

Understanding the fracture and failure properties of graphene is a critical step towards integrating graphene into electromechanical devices and flexible electronics. However, the exact fracture properties of graphene are hard to measure due to the atomic level thickness of graphene and its brittle nature which tends to cause it to break before accurate measurements of its properties can be made. In this paper, a method is presented for measuring the fracture properties of graphene with varying number of layers. This method utilizes a custom designed MEMS tensile tester and an effective and repeatable graphene transfer process that enables the transfer of patterned graphene structures onto MEMS devices. The fracture properties of graphene samples with different numbers of graphene layers were tested and the critical strain energy release rate of fracture was measured to be 22 J/m2, 71.3 J/m2, and 145 J/m2 for ∼ 7 layer, ∼12 layer, and ∼ 15 layer graphene, respectively. These results show that the fracture toughness of the graphene increases as the number of layers increases. This is likely due to the need for brittle cracks to propagate through multiple, weakly connected layers of the graphene for ultimate failure to occur in the graphene.

Enhancement on Lubrication Performances of Water Lubricants by Multilayer Graphene

Enhancement on Lubrication Performances of Water Lubricants by Multilayer Graphene

Improved Stability of Graphene-Coated CMOS ISFETs for Biosensing.

A polymer-assisted graphene transfer method is used to transfer sheets of monolayer and multilayer graphene onto the passivation layer of ion-sensitive field effect transistor arrays. The arrays are fabricated using commercial 0.35 μm complementary metal-oxide-semiconductor (CMOS) technology and contain 3874 pixels sensitive to pH changes on the top silicon nitride surface. By inhibiting dispersive ion transport and hydration of this underlying nitride layer, the transferred graphene sheets help address non-idealities in the sensor response while retaining some pH sensitivity due to the presence of ion adsorption sites. Improvements in hydrophilicity and electrical conductivity of the sensing surface after graphene transfer, as well as in-plane molecular diffusion along the graphene-nitride interface, also greatly improve spatial consistency across an array, allowing for ∼20% more pixels to remain within operating range and enhancing sensor reliability. Multilayer graphene offers a better performance trade-off than monolayer graphene, reducing drift rate by ∼25% and drift amplitude by ∼59% with minimal reduction in pH sensitivity. Monolayer graphene offers slightly better temporal and spatial uniformity in performance of a sensing array, which is associated with the consistency in layer thickness and a lower defect density.

Gate-tunable anomalous Hall effect in Bernal tetralayer graphene

Large spin-orbit coupling is often thought to be critical in realizing magnetic order-locked charge transport such as the anomalous Hall effect (AHE). Recently, artificial stacks of two-dimensional materials, e.g., magic-angle twisted bilayer graphene on hexagonal boron-nitride heterostructures and dual-gated rhombohedral trilayer graphene, have become platforms for realizing AHE without spin-orbit coupling. However, these stacking arrangements are not energetically favorable, impeding experiments and further device engineering. Here we report an anomalous Hall effect in Bernal-stacked tetralayer graphene devices (BTG), the most stable configuration of four-layer graphene. BTG AHE is switched on by a displacement field and is most pronounced at low carrier densities. The onset of AHE occurs in tandem with a full metal to a broken isospin transition indicating an orbital origin of the itinerant ferromagnetism. At lowest densities, BTG exhibits an unconventional hysteresis with step-like anomalous Hall plateaus. Persisting to several tens of kelvin, AHE in BTG demonstrates the ubiquity and robustness of magnetic order in readily available and stable multilayer Bernal graphene stacks—a new venue for intrinsic non-reciprocal responses.

Highly Selective NO2 Sensors Based on Electrolytically Exfoliated Graphene/Flame-made WO3 Composite Films

Gas sensors based on flame-synthesized WO3 nanoparticles loaded with 0.2-5 wt% electrochemically exfoliated graphene were evaluated for NO2 detection at ppb levels. The characterizations by X-Ray diffraction, nitrogen adsorption, electron microscopy and Raman spectrometry verified that multi-layer graphene sheets were well dispersed within spheroidal WO3 nanoparticles. Sensing layers fabricated with different graphene loading levels were tested towards 50-5000 ppb NO2 with varying operating temperatures from 100 to 350 °C in dry air. From the test results, the graphene-loaded WO3 nanoparticles with the optimal graphene content of 2 wt% exhibited the highest sensor response of ~ 5061 to 5000 ppb NO2 at the optimum working temperature of 150 °C. Furthermore, the sensor based on graphene/WO3 composites displayed high NO2 selectivity against various environmental gases and volatile organic compounds at 150 °C. The mechanistic roles of graphene on NO2 gas-sensing performances were described based on reactive ohmic M-S heterointerfaces. Therefore, the combination of electrochemically exfoliated graphene and flame-made WO3 nanoparticles could be an attractive mean to achieve highly sensitive and selective NO2 sensors.

Amorphous Fe2O3 Porous Films Grown on Multilayer Graphene for High-Performance LIB Anodes

Amorphous Fe2O3 has special high electrochemical performance as anode materials of LIBs due to its disorderly arranged atoms. However, the issue of its low intrinsic electric conductivity should be solved rationally and facilely. In this work, amorphous Fe2O3 porous films are chemically deposited on the mechanically exfoliated multilayer graphene (MLG) nanosheets, forming a Fe2O3/MLG/Fe2O3 sandwich nanostructure. The addition of 10[Formula: see text]mg of EDTA-2Na is crucial for the formation of amorphous nature and holes in Fe2O3 films on MLG. This composite exhibits better electrochemical performance as LIB anodes than well-crystallized Fe2O3 nanoparticles, amorphous Fe2O3 films without holes and amorphous Fe2O3 isolated nanoparticles on MLG, which are prepared using 0[Formula: see text]mg, 5[Formula: see text]mg, 20[Formula: see text]mg of EDTA-2Na, respectively. The optimized composite delivers a reversible discharge capacity of 1067[Formula: see text]mAh g[Formula: see text] at 100[Formula: see text]mA g[Formula: see text] after 100 cycles. Moreover, a capacity of 522 mAh g[Formula: see text] is delivered at a high current density of 2[Formula: see text]A g[Formula: see text]. The high electrochemical performance of the composite is attributed to the amorphous nature and porous film structure of Fe2O3, and well combination of Fe2O3 and highly conductive MLG substrate.

3D Printed Design‐Assisted Multilayered Graphene Oxide‐Modified Polymer Glucose Sensor

This work investigates the capabilities of a platform for nonenzymatic glucose sensing employing a novel 3D printed three‐electrode mask‐embedded design. A reservoir‐on‐mask has been fabricated for smart sample insertion to avoid spillage. Working and counter silver electrodes are modified with three different material combinations such as graphene oxide (GO), poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and GO + PEDOT:PSS, and their performance comparison is demonstrated. It is observed that the GO + PEDOT:PSS modification shows 94.57 and 71.01% higher sensitivity than GO and PEDOT:PSS, respectively, including a higher linearity compared to its counterparts. Glucose concentrations ranging from 50 to 300 mg dL−1 are detected by employing cyclic voltammetry and electrical impedance spectroscopic technique. Herein, a significantly high sensitivity of 18.8 μAmM−1 cm−2 and low limit of detection ≈ 0.4 mM has been achieved for the proposed sensor. The 3D printed mask structure provides 75% higher sample retention ability, greater reliability in terms of sample placement in the sensor and improved test performances. The proposed sensor can provide a stable and large‐scale deployable solution to future biosensing platforms.

Bending and twisting behavior of multilayer graphene

In this work, multilayer graphene was chosen and modeled in ANSYS software. In the software, it was subjected to bending forces through various bend angles. In order to test for bending, the model is subjected to rigid support on the base side. Then a force is applied on the side on which the angle is provided to simulate Bending. Stress–strain plots were analyzed for various bending angles. The graphene sheet was also subjected to twist forces within the software. In order to test for torsion, the model is subjected to rigid support on both sides. Then a couple is applied on the opposite sides to simulate torsion. Torsional stress and strain measurements were analyzed. The trends were studied and correlations with the material properties of graphene were established. The quest is to identify a magic angle for bend and twist.

Multilayer graphene and black phosphorus thin-film frequency doublers using direct-current bias

Multilayer graphene and black phosphorus films exhibit strong nonlinearity under voltage modulation. In this paper, according to the nonlinear characteristics of graphene and black phosphorus, the frequency doubling characteristics of graphene and black phosphorus are introduced, and the nonlinear SDD model of graphene is established in EDA, and the simulation results are basically consistent with the measured results. Under the regulation of DC bias voltage, the second harmonic output power of both graphene frequency doubler and black phosphorus frequency doubler is larger than their third harmonic output power when the operating frequency is 800–1100 MHz. The experimental results show that the minimum conversion loss of the black phosphorus multiplier is 24.22 dB when the input voltage is 0.9 V and the input power is 12 dBm, and the minimum conversion loss of the graphene multiplier is 32.15 dB when the input voltage is 1.6 V. The experimental results show that the conversion loss of the black phosphorus multiplier is better than that of the graphene multiplier, and the conversion efficiency is higher.

Spontaneous broken-symmetry insulator and metals in tetralayer rhombohedral graphene.

Interactions among charge carriers in graphene can lead to the spontaneous breaking of multiple degeneracies. When increasing the number of graphene layers following rhombohedral stacking, the dominant role of Coulomb interactions becomes pronounced due to the significant reduction in kinetic energy. In this study, we employ phonon-polariton-assisted near-field infrared imaging to determine the stacking orders of tetralayer graphene devices. Through quantum transport measurements, we observe a range of spontaneous broken-symmetry states and their transitions, which can be finely tuned by carrier density n and electric displacement field D. Specifically, we observe a layer-antiferromagnetic insulator at n = D = 0 with a gap of approximately 15 meV. Increasing D allows for a continuous phase transition from a layer-antiferromagnetic insulator to a layer-polarized insulator. By simultaneously tuning n and D, we observe isospin-polarized metals, including spin-valley-polarized and spin-polarized metals. These transitions are associated with changes in the Fermi surface topology and are consistent with the Stoner criteria. Our findings highlight the efficient fabrication of specially stacked multilayer graphene devices and demonstrate that crystalline multilayer graphene is an ideal platform for investigating a wide range of broken symmetries driven by Coulomb interactions.

Investigation of Hybrid Wires Combining Superconductive MgB2 and Ultra-conductive Graphene/Cu sheath

In our study, hybrid wires with ultra-conductive Graphene/Copper(GCu) sheath and superconducting MgB2 core were produced and experimentally examined. Cu tubes with outer/inner diameters of 15/12 mm were first coated with multi-layered graphene by chemical vapour deposition (CVD) method. Then, the ultra-conductive G/Cu tubes were filled with Mg+2B powder and they were gradually drawn into wires with a diameter of 1.94 mm. According the analysis results, the graphene coating process was successfully completed and the hybrid wires were produced by achieving MgB2 superconducting phase formation after annealing at 650∘C for 1 h. In this study, a graphene-coated copper tube with a CVD process was used for the first time to manufacture a superconducting wire. The ampacity value of industrial G/Cu sample has been improved in hybrid wires about 75% despite Cu exposed to mechanical deformations throughout the wire production process after graphene coating.

Atomically engineered, high-speed non-volatile flash memory device exhibiting multibit data storage operations

Non-volatile memory devices, which offer large capacity and mechanical dependability as a mainstream technology, have played a key role in fostering innovation in modern electronics. Despite the advantages of non-volatile memory devices, their low ON/OFF ratio and slow operational speed have limited their performance compared to their volatile counterparts. In this study, we present a non-volatile floating-gate memory device based on van der Waals heterostructures, which exhibits ultrahigh-speed memory operations in the range of a hundred nanoseconds with an extinction ratio of up to 106. The device consists of atomically sharp interfaces between different functional elements, including atomically thin sheet of multilayer Graphene (MGr) as a floating gate, hexagonal boron nitride (h-BN) as a tunnel barrier, and two-dimensional (2D) semiconductor tin di-selenide (SnSe2) as a channel material. The memory device exhibits excellent endurance performance with stable and dependable behavior across numerous program/erase cycles, comparable to commercial volatile dynamic random access memory technology. In addition, we demonstrate the ability of the device to store multiple bits per memory cell, which offers promising potential for ultrahigh-density information storage. Our findings provide important implications for memory storage, data processing, and electronic device development, and offer new opportunities in the field of emerging 2D materials with optimal device engineering.

Novel top-down kg-scale processing of 2D multi-layered graphene powder and its application as excellent lubricating additives in commercial engine oils

Multi-layered graphene (MLG) powder is prepared on a kg-scale using a novel fluid-assisted processing of exfoliated graphite. Each MLG particle is a few μm laterally and is constituted by a few graphene layers. When MLG-dispersed commercial engine oil was used as a lubricant, the tribological properties (i.e., friction and resistance to wear) of the contacting metal surfaces were significantly enhanced. The average coefficient of friction (CoF) at room temperature and 75 °C was reduced by ~25.5 % and ~ 16 %, respectively, while the wear resistance at room temperature and 75 °C was improved by ~13 % and ~ 16 %, respectively. MLG-dispersed engine oil forms a protective tribo-film adhering to the contacting metal surfaces, resulting in ultra-low interface friction. The MLG-dispersed engine oil (acting as a tribo-film) diminishes the effective direct metal-to-metal contact area, minimizing the wear.

Study of the Chemical Vapor Deposition of Nano-Sized Carbon Phases on {001} Silicon.

Different nano-sized phases were synthesized using chemical vapor deposition (CVD) processes. The deposition took place on {001} Si substrates at about 1150-1160 °C. The carbon source was thermally decomposed acetone (CH3)2CO in a main gas flow of argon. We performed experiments at two ((CH3)2CO + Ar)/Ar) ratios and observed that two visually distinct types of layers were deposited after a one-hour deposition process. The first layer type, which appears more inhomogeneous, has areas of SiO2 (about 5% of the surface area substrates) beside shiny bright and rough paths, and its Raman spectrum corresponds to diamond-like carbon, was deposited at a (CH3)2CO+Ar)/Ar = 1/5 ratio. The second layer type, deposited at (CH3)2CO + Ar)/Ar = a 1/0 ratio, appears homogeneous and is very dark brown or black in color and its Raman spectrum pointed to defect-rich multilayered graphene. The performed structural studies reveal the presence of diamond and diamond polytypes and seldom SiC nanocrystals, as well as some non-continuously mixed SiC and graphene-like films. The performed molecular dynamics simulations show that there is no possibility of deposition of sp3-hybridized on sp2-hybridized carbon, but there are completely realistic possibilities of deposition of sp2- on sp2- and sp3- on sp3-hybridized carbon under different scenarios.

Tunable Optical Display of Multilayer Graphene through Lithium Intercalation.

The tunable optical display is vital for many application fields in telecommunications, sensors, and military devices. However, most optical materials have a strong wavelength dependence, which limits their spectral operation range. In this work, we develop an electrically reconfigurable optical medium based on graphene, demonstrating a cycle-controlled display covering the electromagnetic spectrum from the visible to the infrared wavelength. Through an electro-intercalation method, the graphene-based surface enables rich colors from gray to dark blue to dark red to yellow, and the response time is about 1 min from the start gray color to the final yellow color. Simultaneously, it exhibits a remarkable change in infrared emissivity (from 0.63 to 0.80 reduction to 0.20) with a response time of 1 s. This modification of optical properties of lithiated multilayer graphene (MLG) is the increase of Fermi energy (Ef) due to the charge transfer from lithium (Li) to graphene layers, which causes changes in interband and intraband electronic transitions. Our findings imply potential value in fabricating multispectral optical materials with high tunability.

Mirror symmetry decomposition in double-twisted multilayer graphene systems

Mirror symmetry decomposition in double-twisted multilayer graphene systems