Graphene Interface Research Articles

A Study on Dislocation Mechanisms of Toughening in Cu-Graphene Nanolayered Composite.

We investigated the role of graphene interfaces in strengthening and toughening of the Cu-graphene nanocomposite by a combination of in situ transmission electron microscopy (TEM) deformation and molecular dynamics (MD) simulations. In situ TEM directly showed that dislocation plasticity is strongly confined within single Cu grains by the graphene interfaces and grain boundaries. The weak Cu-graphene interfacial bonding induces stress decoupling, which results in independent plastic deformation of each Cu layer. As confirmed by the MD simulation, the localized deformation made by such constrained dislocation plasticity results in the nucleation and growth of voids at the graphene interface, which acts as a precursor for crack. The graphene interfaces also effectively block crack propagation promoted by easy delamination of Cu layers dissipating the elastic strain energy. The toughening mechanisms revealed by the present study will provide valuable insights into the optimization of the mechanical properties of metal-graphene nanolayered composites.

A promising ZnO/Graphene van der Waals heterojunction as solar cell devices: A first-principles study

The electronic structure of two-dimensional (2D) materials in van der Waals heterojunctions also appears extensive theoretical research, we use DFT-D2 theory to calculate the energy band, density of states, formation energy, work function, charge density difference, optical properties, and our theoretical calculations show that there is no electrons and holes redistribution at the intrinsic ZnO composite graphene interface, ZnO vacancy defects and doping not only make electron–hole good separation, but also a significant increase in the UV absorption intensity and range. We analyze the effects of the electron–hole pair separation at the heterogeneous junction interface by combining the work function and the movement of the Dirac point. We found that when defected ZnO composite graphene, there is the maximum formation energy, the value is 5.4eV,the largest moving distance of the Fermi level, 0.73eV, and the maximum absorption strength and range of UV light. This 2D van der Waals heterojunction provides a promising prospect for electrons, photovoltaic, solar cell.

Preferred orientation at the Al/graphene interface: First-principles calculations and experimental observation

Orientation relationship at the Al/graphene interface was investigated through first-principles calculations and high-resolution transmission electron microscope (HRTEM). Calculations revealed the preferred orientation of Al(211)/graphene(0001) for the first time. Interface energy of Al(211)/graphene(0001) was much lower than that of published Al(111)/graphene(0001), Al(110)/graphene(0001) and Al(100)/graphene(0001), which was confirmed by HRTEM observation on the orientation of graphene(0001)//Al(21̅1). Further calculations revealed that interplanar spacing of Al slabs increased in Al(211)/graphene(0001) and calculation angle between graphene and Al slabs was in excellent agreement with HRTEM investigations. The findings of most stable Al(211)/graphene(0001) interface threw new lights for researches on Al/graphene interface.

N‐Doped and P‐Doped Graphene on MgO (111): A First‐Principles Study

Herein, first‐principles density functional theory is used to investigate the atomic structure and electrical properties of the contact between primitive graphene, N‐doped graphene, P‐doped graphene, and MgO (111) surface. It has been found that the energy band of the graphene/Mg‐terminated MgO (111) interface exhibits p‐type characteristics, and the energy band of the graphene/O‐terminated MgO (111) interface exhibits n‐type characteristics. N‐doped or P‐doped can control the energy band structure of the interface. The interaction between the graphene and Mg‐terminated MgO (111) interface is a weak physical interaction, and the interaction between the graphene and O‐terminated MgO (111) surface is a strong chemical interaction. N‐doped or P‐doped can promote the charge transfer between the interfaces, and further enhancing the interfacial coupling strength. This result is helpful to understand the interaction between graphene and MgO interface and provides theoretical guidance for the practical application of graphene/MgO interface‐based devices.

Exploring Interfacial Graphene Oxide Reduction by Liquid Metals: Application in Selective Biosensing.

Liquid metals (LMs) are electronic liquid with enigmatic interfacial chemistry and physics. These features make them promising materials for driving chemical reactions on their surfaces for designing nanoarchitectonic systems. Herein, we showed the interfacial interaction between eutectic gallium-indium (EGaIn) liquid metal and graphene oxide (GO) for the reduction of both substrate-based and free-standing GO. NanoIR surface mapping indicated the successful removal of carbonyl groups. Based on the gained knowledge, a composite consisting of assembled reduced GO sheets on LM microdroplets (LM-rGO) was developed. The LM enforced Ga3+ coordination within the rGO assembly found to modify the electrochemical interface for selective dopamine sensing by separating the peaks of interfering biologicals. Subsequently, paper-based electrodes were developed and modified with the LM-rGO that presented the compatibility of the assembly with low-cost commercial technologies. The observed interfacial interaction, imparted by LM's interfaces, and electrochemical performance observed for LM-rGO will lead to effective functional materials and electrode modifiers.

Role of transferred graphene on atomic interaction of GaAs for remote epitaxy

Remote epitaxy is a recently discovered type of epitaxy, wherein single-crystalline thin films can be grown on graphene-coated substrates following the crystallinity of the substrate via remote interaction through graphene. Although remote epitaxy provides a pathway to form freestanding membranes by controlled exfoliation of grown film at the graphene interface, implementing remote epitaxy is not straightforward because atomically precise control of interface is required. Here, we unveil the role of the graphene–substrate interface on the remote epitaxy of GaAs by investigating the interface at the atomic scale. By comparing remote epitaxy on wet-transferred and dry-transferred graphene, we show that interfacial oxide layer formed at the graphene–substrate interface hinders remote interaction through graphene when wet-transferred graphene is employed, which is confirmed by an increase of interatomic distance through graphene and also by the formation of polycrystalline films on graphene. On the other hand, when dry-transferred graphene is employed, the interface is free of native oxide, and single-crystalline remote epitaxial films are formed on graphene, with the interatomic distance between the epilayer and the substrate matching with the theoretically predicted value. The first atomic layer of the grown film on graphene is vertically aligned with the top layer of the substrate with these atoms having different polarities, substantiating the remote interaction of adatoms with the substrate through graphene. These results directly show the impact of interface properties formed by different graphene transfer methods on remote epitaxy.

Robust networks of interfacial localized graphene in cocontinuous polymer blends

Conductive polymer composites enjoy specialized applications such as electrostatic discharge protection. In this work, we create interfacially localized graphene nanoplatelets (GNPs) in a cocontinuous polymer blend of polylactide (PLA) and poly(ethylene-co-vinyl acetate) (EVA). Based on the wetting coefficient analysis, GNPs favor localization in the EVA phase. A two-step compounding sequence is designed such that a PLA/GNP masterbatch is first prepared via solution blending, and then melt compounded with the EVA. In the second step, GNPs transfer from the PLA phase to the EVA phase but become kinetically trapped at the interface, as confirmed by electron microscopy. We achieve an ultralow percolation threshold of 0.048 wt. % GNPs and obtain blends with electrical conductivities of ∼10−5 S/cm at 0.5 wt. % GNP concentration. We systematically study the shear and extensional rheology of the ternary composite system. Cocontinuous blends with interfacial GNPs exhibit higher shear and extensional viscosities compared to samples with GNPs localized entirely within the EVA phase. Rheology, in situ dielectric measurements, and transmission electron microscopic imaging after nonlinear deformations all show the interfacial GNP network undergoes structure recovery and largely remains at the PLA/EVA interface. Moreover, high electrical conductivity is maintained during 2–10 min melt compounding and conductivity recovers with annealing after nonlinear deformations. These results suggest that these robust GNP networks preserve their bulk electrical conductivity during subsequent melt processing.

Reducing Kapitza resistance between graphene/water interface via interfacial superlattice structure

The control of thermal transport across solid/liquid interface has attracted great interests for efficient thermal management in the integrated devices. Based on molecular dynamics simulations, we study the effect of interfacial superlattice structure on the Kapitza resistance between graphene/water interface. Compared to the original interface, introducing interfacial superlattice structure can result in an obvious reduction of Kapitza resistance by as large as 40%, exhibiting a decreasing trend of Kapitza resistance with the decrease of superlattice period. Surprisingly, by analyzing the structure of water block and atomic vibration characteristics on both sides of the interface, we find the interfacial superlattice structure has a minor effect on the water structure and overlap in the vibrational spectrum, suggesting that the improved interfacial heat transfer is not mainly originated from the liquid block. Instead, the spectral energy density analysis reveals that phonon scattering rate in the interfacial graphene layer is significantly enhanced after superlattice decoration, giving rise to the increased thermal resistance between the interfacial graphene layer and its nearest neighboring layer. As this thermal resistance is coupled to the Kapitza resistance due to the local nature of interfacial superlattice decoration, the enhanced thermal resistance in the solid segment indirectly reduces the Kapitza resistance between graphene/water interface, which is supported by the enhancement of the spectral interfacial thermal conductance upon superlattce decoration at microscopic level. Our study uncovers the physical mechanism for controlling heat transfer across solid/liquid interface via interfacial superlattice structure, which might provide valuable insights for designing efficient thermal interfaces.

Modular modification of the two-dimensional electronic properties of graphene by bio-inspired functionalization

Graphene is emerging as a promising 2D material in a variety of advanced electronic and optoelectronic devices. For optimization of the performance of the devices, tuning the work function of the graphene is crucial. This work presents a modular yet straightforward way to modulate the work function of single-layer graphene using specifically designed peptides with varied amounts of amine and indole groups assembled from an aqueous solution. Molecular doping of the graphene layer and the formation of a permanent dipole at the graphene interface led to either decreasing or increasing the work function, depending on the peptide sequence. Overall, the peptide modification increases the conductivity of the graphene layer with hardly compromising its transparency. Consequently, the modification of graphene by peptides emerges as a powerful low-cost and environmentally friendly tool to control 2D materials’ electronic properties. The modularity of peptides provides a simple way to tune the electronic properties by peptide design.

Gyroidal graphene for exciting tamm plasmon polariton as refractive index sensor: Theoretical study

In this work, we design a novel refractive index sensor in the terahertz region. The proposed structure is (PSi1/PSi2)N/Sample/Gyroidal Graphene/substrate. PSi1 and PSi2 are porous silicon with porosity of 80% and 30%, respectively. This sensor based on the Tamm plasmon polariton at the porous silicon interface of photonic bandgap and gyroidal graphene. The appearance of Tamm plasmon polariton at the interface is because of the plasmonic behavior of gyroidal graphene and the controlled porosity of silicon layers. Porous silicon is used due to its refractive index controllable by the porosity, pore size, and sample material filling pores. Tamm plasmon polariton is highly sensitive to the change in the refractive index of the sample material in the order of air index. The effects of the different variables such as gyroidal graphene volume fraction, sample index, the thickness of the gyroidal graphene layer, and the number of periods are studied. The optimizations are performed to improve the performance of the sensor. The high sensitivity of 18.6 THz/RIU is achieved with better FoM 126,835 RIU−1 and Q-factor 26,300. The investigated sensor using gyroidal graphene records performance more than quadrupled comparing with the same structure with graphene sheets. This sensor can be useful in several fields such as gas sensing, environmental monitoring, and biosensing.

Van der Waals heterostructure of graphene Defected&Doped X(X = Au, N) composite ZnO monolayer: A First Principle study

GGA + U(Zn 3d = 10eV, O 2p = 7eV) and van der Waals correction methods (DFT-D2) were used to calculate the surface structural, electronic and optical properties of ZnO composite graphene (Z-G) system via first-principles. The binding energy and Bader charge transfer are calculated. When the composite site is at the top site and the interlayer distance is 2 Å, the ZnO composite graphene (Z-G) interface is the most stable, the energy value is 2.86eV. The Dirac point remained unchanged after intrinsic graphene composite ZnO, indicating that the interaction between intrinsic graphene and ZnO did not affect the excellent electrical conductivity of graphene. By studying the energy band, density of states, and optical properties of ZnO in graphene (ZGC-V) composite ZnO, Au and N doped graphene (ZGC-Au and ZGC-N) composite ZnO. It is found that doped and defected graphene composite ZnO the Dirac points disappeared, the bandgap value is 0.441eV, 0.831eV and 0.203eV, respectively. Electron-hole pair is well separated at the interface of doped and defected graphene composite ZnO. The defected and doped graphene composite ZnO lead to the blue shift phenomenon of light absorption peak, defected graphene composite ZnO absorption peak movement was the maximum of 1.64eV. The change of band gap and optical properties provides a theoretical explanation for the excellent performance of ZnO composite graphene (Z-G) in photocatalysts and ultraviolet light-emitting devices.

Electrochemically Driven Specific Alkaline Metal Cation Adsorption on a Graphene Interface

Electrochemically Driven Specific Alkaline Metal Cation Adsorption on a Graphene Interface

Realizing Long-life Zn Anode by Few-layer Graphene Ion-oriented Interface

Inspired by the nanostructured graphene-based membranes for ionic sieving, an ion-oriented interface of few-layer graphene (FLG) was rationally constructed to achieve long-life zinc (Zn) metal anode. The ion-oriented interface increased the nucleation sites and inhibited localized dendrite growth, which aided the uniform transmission of Zn ions. Moreover, the fewer oxygen-containing functional groups on the FLG surface demonstrated a lower energy barrier of ion transport and a stronger Zn ion-regulating function. The FLG@Zn anode exhibited a much larger capacity with significant stability in the cycling behavior against MnO2 cathode compared to the pristine Zn anode. Specifically, a nearly 97% capacity retention was achieved for FLG@Zn/MnO2 battery after 5000 cycles at 10 A·g–1. Our work provides a novel approach to the fabrication of high-performance Zn anode for ultra-stable aqueous batteries.

Interfacial structures and strengthening mechanisms of in situ synthesized TiC reinforced Ti6Al4V composites by selective laser melting

The in-situ nanoscale TiC particles reinforced Ti6Al4V composites was prepared by selective laser melting (SLM) from the mixture of Ti6Al4V alloy powders and graphene powders, the microstructure and interface bonding of the composites were studied. The composites were mainly composed of α, α' martensite and α+β structures. More TiC were formed in the overlapping regions than that in the molten pool, the solidification rate in overlapping regions was slow, which was beneficial to TiC nucleation and growth. The TiC and Ti matrix displayed following orientation relationships: axis [0 0 1]β-Ti∥[-1 -1 1]TiC∥[0 -1 1 0 ]α-Ti, lattice plane (2 2 2)TiC //(0 0 0 2)α-Ti, lattice plane (1 1 1)TiC//(0 0 0 2)α-Ti, lattice plane (1 1 1)TiC//(1 0 -1 0)α-Ti. The TiC and Ti matrix have a small degree (6.2%) of mismatch between (1 1 1)TiC and (0 0 0 2)α-Ti, and the semi-coherent interface was occurred. TiC preferentially nucleated and grew up along its (1 1 1) plane. The situ synthesized TiC was added into the Ti6Al4V alloy, refined the grains, and increased the microhardness of the alloy. The microhardness of the composites was 13.6% higher than that of Ti6Al4V alloy. The TiC effectively pinned the dislocations and grain boundaries were responsible for the enhanced mechanical properties of the composites.

High-performance, multi-functional and well-dispersed graphene/epoxy nanocomposites via internal antiplasticization and π-πF interactions

It is a longstanding challenge for epoxy-based nanocomposites to optimize the dispersity of graphene so as to improve the mechanical properties and endow more functions. Non-covalent functionalization of graphene via dispersants is a crucial strategy to achieve well-dispersion, which can maintain the original physical/chemical properties. However, the reported dispersants significantly reduce mechanical properties of matrix and their stable graphene concentration is limited. Herein, 2,3,5,6-tetrafluorobenzyloxyglycidyl ether (TFGE) is synthesized and used as a dispersant to realize non-covalent functionalization of graphene, which can further improve the interface, dispersity and loading of graphene via π-πF interactions between tetrafluorophenyl and graphene, compared with π-π interactions. Moreover, TFGE can simultaneously reinforce and toughen the matrix via internal antiplasticization. The well-designed epoxy-based nanocomposite with ultralow graphene loading (less than 0.03 wt%) shows outstanding mechanical and thermomechanical properties, photo/thermochromic ability, light absorption, flame resistance as well as adhesive strength. This facile strategy provides an efficient guideline for better design and large-scale preparation of high-performance and multi-functional graphene/epoxy nanocomposites applied in adhesive, coating, anti-fake and structural materials.

Interfacial Photogating Effect for Hybrid Graphene-Based Photodetectors

Ultrafast and high-sensitive photodetectors operating from the deep-ultraviolet to near-infrared region at room temperature are essential for many applications such as analytical chemistry, optical positioning, biomedical imaging, and remote sensing. Toward high-performance photodetectors, hybrid colloid quantum dots/graphene photodetectors based on the photogating mechanism have been intensively studied. An ultrahigh sensitivity has been obtained in the range from 105 to 109 A/W but the major challenge of these configurations is the slow operating speed on the millisecond to second time scale. Manipulating the transferring of carriers at the interface of semiconductor nanostructures and graphene is an essential key to optimize the interfacial photogating effect. Here, we grow an absorber layer directly on graphene by e-beam evaporation to obtain a fast photoresponse time of the detectors. Thus, the gap between the high responsivity and fast response time can be bridged. The photodetectors indicate a high photoresponsivity of ∼2.5 × 106 A/W at low incident intensity on the order of femto-watts, a specific detectivity of ∼8.5 × 1011 Jones, and a fast response process of ∼20 ns together with a slow component of ∼850 ns (response time of <1 μs) under a drain-to-source bias of 100 mV. The study has provided a method to obtain high-performance photodetectors based on graphene with high responsivity and fast response time.

High-performance terahertz refractive index sensor based on a hybrid graphene Tamm structure

In recent years, the research on tunable and high-performance terahertz devices has attracted widespread attention. In this paper, we propose a novel refractive index sensor consisting of monolayer graphene and multilayer photonic crystal with a defect layer. It is found that Tamm plasmon polaritons can be excited at the top graphene interface, which can strongly interact with the defect mode in this coupled structure. The results of numerical simulation demonstrate that the coupling can be either tuned by adjusting the geometric parameters or actively controlled by the chemical potential in graphene as well as the incident angle of light, allowing for tunable dual-band perfect absorption with strong interaction. Moreover, the resonance frequency of the defect mode is sensitive to the changes of the ambient refractive index. The sensitivity and figure of merit of this device as a sensor can reach 1.01 THz per refractive index unit (THz/RIU) and 631.2 R I U − 1 , respectively. In addition to high performance, the sensor does not require phase- or polarization-matching devices, paving the way for the research of optical devices.

Hydrogen-promoted graphene growth on Pt(111) via CVD methods

Hydrogen has a substantial effect on the growth of graphene by metal-based chemical vapor deposition (CVD). However, the specific role of hydrogen under different preparation conditions is difficult to elucidate. Herein, graphene with high coverage was prepared by CVD method on Pt(111). It was found that a certain proportion of hydrogen can accelerate the growth of graphene at 900 K and promote the quality of graphene, as compared to conditions without hydrogen. In situ low-energy electron microscopy revealed that hydrogen entered the interface of graphene and Pt, weakening overlayer-substrate interaction, which was deduced to be the reason for promoting the growth of graphene. This work provides more deep insights into the controllable growth of graphene, owing to the presence of hydrogen.

In situ electrochemical synthesis of graphene-poly(arginine) composite for p-nitrophenol monitoring

Para-Nitrophenol (p-nitrophenol) is a common industrial pollutant occurring widely in water bodies, yet actual monitoring methods are limited. Herein we proposed a fully electrochemically in situ synthesized graphene-polyarginine composite functionalized screen printed electrode, as a novel p-nitrophenol sensing platform. The electrode was characterized by morphologic, spectrometric and electrochemical techniques. p-nitrophenol in both pure aqueous solution and real water samples was tested. Results show a detection limit as low as the nanomolar level, and display a linear response and high selectivity in the range of 0.5–1250 μM. Molecular simulation reveals a detailed synergy between graphene and poly-arginine. The preferable orientation of nitrophenol molecules on the graphene interface in the presence of poly-arginine induces H- and ionic binding. This sensor is an ideal prototype for p-nitrophenol quantification in real waters.

Bandwidth Enhancement of Graphene–Organic Hybrid Photoconductors by Accelerating Electron Transfer Processes at Graphene Interface

AbstractPhotodetectors based on a heterojunction between graphene and photoactive layers have attractive features such as high responsivity and spectral sensitivity, but their narrow bandwidth originating from charge trapping is a major drawback. Here, it is demonstrated that the bandwidth of a graphene–organic hybrid photoconductor, where a planar bilayer of fullerene (C60) and zinc phthalocyanine (ZnPc) is in contact with the graphene layer, can be significantly increased by doping the C60 layer with ZnPc. The bandwidth, which increases with the doping concentration, is found to be more than two orders of magnitude higher at 40 vol% doping than that of the undoped device. Consequently, the 40%‐doped device has a fall time of the photocurrent transient of 19 μs, which is ≈300 times smaller than that of the undoped device (5.8 ms). Based on the model developed to analyze the electron transfer processes between the graphene and C60 layers, the increased bandwidth is attributed to the reduced electron lifetime in the C60 trap state by recombination with holes photogenerated in the ZnPc domains in the C60 layer.