Graphene Boron Nitride Research Articles

Highly confined low-loss light transmission in linear array-enabled hybrid plasmonic waveguides

Deep subwavelength highly confined and long-range optical propagation is vital for photonics integration. However, the performance of the guided mode could be improved by the trade-off between light confinement and loss. Here, we demonstrate a high-performance hybrid waveguide consisting of a high-index nanowire separated from a linear array by a low-index dielectric gap. The array significantly achieves the plasmonic platform optimization based on a linear combination of few-layer graphene (FLG) and hexagonal boron nitride (hBN) layers. Through the hybridization of graphene plasmon polaritons and hyperbolic phonon polaritons mode, the resulting hybrid waveguide shows at least double times larger propagation distance and smaller mode area than the multilayer waveguide. Further, modulated by altering material configuration and geometric effects, the mode properties reveal that it is more flexible to adjust the optical transmission, along with a strong deep-subwavelength mode with low loss. Because of highly confined low-loss propagation, the hybrid waveguide is expected to be an excellent building block for various mid-infrared photonic integrated circuits. The present structure also has the potential to be extended to other FLGs, like magic-angle twisted bilayer graphene and trilayer graphene/hBN moiré superlattice.

64 Effects of Graphene Oxide, Molybdenum Disulfide and Boron Nitride on Human Dendritic Cells

Abstract Graphene oxide and other 2D materials such as molybdenum disulfide and boron nitride have been gaining popularity in various biochemical and industrial applications. Dendritic cells (DCs) are important innate cells that regulate adaptive immune responses and have emerged as the next immune cell of nano-science importance after the commonly published macrophages, as they can also take up nanomaterials. DCs have also been used in nanotechnology to modulate immune response in oncology and autoimmunity and it is crucial to evaluate DC compatibility of common 2D nanomaterials. By using primary human DCs, we show that all materials did not impact DC viability. In terms of cell uptake, BN was mostly located in the cytoplasm while GO was mostly found in phagosomes, and MoS2 was found in both phagosomes and cytoplasm. BN and GO increase DC maturation to different extents, while GO also leads to the release of reactive oxygen species and pro-inflammatory cytokines. BN and MoS2 increased T cell proliferation with and without the presence of DCs. BN exerts minimal toxic effect on DC viability and DC-mediated T cell polarization, although some effects were observed in T cells alone. MoS2 did not have an effect on DC maturation, unlike BN, despite having greater material association with DCs. Overall, materials ranked in term of inherent DC toxicity provided the following trend: GO > BN = MoS2, with GO most cytotoxic. With these, we hope to better shape design of 2D nanomaterials for improved immune compatibility. * H Lin, et al. Small. 2022, 18(20), e2107652.

Umklapp electron-electron scattering in bilayer graphene moiré superlattice

Recent experimental advances have been marked by the observations of ballistic electron transport in moir\'e superlattices in highly aligned heterostructures of graphene and hexagonal boron nitride (hBN). Here, we predict that a high-quality graphene bilayer aligned with an hBN substrate features ${T}^{2}$-dependent resistivity caused by umklapp electron-electron (Uee) scattering from the moir\'e superlattice, that is, a momentum kick by Bragg scattering experienced by a pair of electrons. Substantial Uee scattering appears upon $p$ doping of the bilayer above a characteristic threshold, and its contribution towards the resistivity grows rapidly with hole density, until it reaches a peak value, then falling off by an order of magnitude. This rapid, nonmonotonic dependence of resistivity, in the density range where the system is otherwise highly conductive, suggests the possibility of a nonconventional field-effect transistor operation. We also analyze the influence of an electrostatically induced interlayer asymmetry (and the associated band gap) in the bilayer and trigonal warping on the electron-electron umklapp scattering.

The interplay of intra- and inter-layer interactions in bending rigidity of ultrathin 2D materials

Continuum mechanics break down in bending stiffness calculations of mono- and few-layered two-dimensional (2D) van der Waals crystal sheets, because their layered atomistic structures are uniquely characterized by strong in-plane bonding coupled with weak interlayer interactions. Here, we elucidate how the bending rigidities of pristine mono- and few-layered molybdenum disulfide (MoS2), graphene, and hexagonal boron nitride (hBN) are governed by their structural geometry and intra- and inter-layer bonding interactions. Atomic force microscopy experiments on the self-folded conformations of these 2D materials on flat substrates show that the bending rigidity of MoS2 significantly exceeds those of graphene or hBN of comparable layers, despite its much lower tensile modulus. Even on a per-thickness basis, MoS2 is found to possess similar bending stiffness to hBN and is much stiffer than graphene. Density functional theory calculations suggest that this high bending rigidity of MoS2 is due to its large interlayer thickness and strong interlayer shear, which prevail over its weak in-plane bonding.

In Silico Investigation on the Selective Nanotoxicity of Two-Dimensional Materials to Hen Egg White Lysozyme Protein

Inspired by the urge to determine the underlying mechanism of the induction of toxic effects of state-of-the-art two-dimensional (2D) nanomaterials such as graphene and hexagonal boron nitride (h-BN) toward biomolecules, herein we study the interactions between these nanomaterials with a model protein hen egg white lysozyme (HEWL), employing classical molecular dynamics simulations. It is revealed that the protein gets easily adsorbed on both of the 2D materials, with the interaction energy being much higher in the case of h-BN, suggesting a significantly stronger adsorption affinity. The interactions of aromatic amino acid residues such as tyrosine and tryptophan along with few aliphatic residues such as arginine, lysine, and asparagine with the 2D materials are found to be pronounced, and most of the residues taking part in adsorption are nearly the same for both materials. While the secondary structure of HEWL remains nearly unaltered upon adsorption on graphene, h-BN massively perturbs both the α-helix and β-sheet components through the disruption of intraprotein hydrogen bonds, which are in turn sine quo non for the preservation of the structural integrity. It is demonstrated that the disruption of the secondary structure is due to pronounced thermodynamic preference for the adsorption of the constituent amino acid residues on h-BN compared to their spatial disposition within the proteins. The calculated release times from the adsorbed state are found to be orders of magnitude higher in the case of h-BN compared to graphene, and it is unlikely that the protein would get released in accessible time scales unless dislodged by the application of an external force. The present study contributes to the fundamental understanding of the nanotoxicity of emerging 2D materials toward proteins, thereby aiding experimentalists to design biocompatible 2D materials for nano-biomedical usage and device fabrication.

Area-Specific, Hierarchical Nanowrinkling of Two-Dimensional Materials.

This paper describes an approach to generate hierarchical wrinkles in two-dimensional (2D) electronic materials with spatial control over adjacent wavelengths. A rigid fluoropolymer mold was used to pattern a sacrificial polymer skin layer on monolayer graphene, molybdenum disulfide, and hexagonal boron nitride on prestrained thermoplastic sheets. Strain relief and removal of the polymer layer resulted in 2D-material wrinkles whose wavelengths scaled linearly with the local skin thickness. A second generation of wrinkles could be created on top of the first generation by applying a subsequent cycle of polymer skin coating, strain relief, and polymer removal. This area-specific hierarchical wrinkling is general and will facilitate the engineering of the local properties of various 2D materials and their heterostructures.

Mobile Trions in Electrically Tunable 2D Hybrid Perovskites.

2D hybrid perovskites are currently in the spotlight of material research for light-harvesting and -emitting applications. It remains extremely challenging, however, to externally control their optical response due to the difficulties of introducing electrical doping. Here, an approach of interfacing ultrathin sheets of perovskites with few-layer graphene and hexagonal boron nitride into gate-tunable, hybrid heterostructures, is demonstrated. It allows for bipolar, continuous tuning of light emission and absorption in 2D perovskites by electrically injecting carriers to densities as high as 1012 cm-2 . This reveals the emergence of both negatively and positively charged excitons, or trions, with binding energies up to 46meV, among the highest measured for 2D systems. Trions are shown to dominate light emission and propagate with mobilities reaching 200cm2 V-1 s-1 at elevated temperatures. The findings introduce the physics of interacting mixtures of optical and electrical excitations to the broad family of 2D inorganic-organic nanostructures. The presented strategy to electrically control the optical response of 2D perovskites highlights it as a promising material platform toward electrically modulated light-emitters, externally guided charged exciton currents, and exciton transistors based on layered, hybridsemiconductors.

Boron Nitride-Graphene (BN-G) Bilayer as a Channel of Graphene Based Field Effect Transistor

According to the effect of the interlayer interaction of the boron nitride sheet on electronic properties, especially the energy band gap of the graphene sheet in the boron nitride-graphene (BN-G) bilayer, we propose a gapless graphene-based field effect transistor (FET). It is comprised of a boron nitride layer on top of graphene in the channel region. In this study, we investigate the transfer characteristic and output characteristic of the proposed device for different values of the interlayer distance of (BN-G) bilayer. Also, we compare the output results with simulated bilayer graphene channel FET. We find that the Ion/Ioff ratio in the proposed device shows a significant promotion compared to graphene bilayer channel FET. Our first-principles calculations show that by decreasing the inter-layer distance of (BN-G) bilayer, the energy gap increase which leads to a dipper Ioff current and an increase of Ion/Ioff ratio up to 104 for an inter-layer distance of 2.7 angstroms. Moreover, it is found that the proposed device output characteristic displays a very good saturation due to improved pinch-off of the channel.

Lateral Heterostructures of Graphene and h-BN with Atomic Lattice Coherence and Tunable Rotational Order.

In-plane heterostructures of graphene and hexagonal boron nitride (h-BN)exhibit exceptional properties, which are highly sensitive to the structure of the alternating domains. Nevertheless, achieving accurate control over their structural properties, while keeping a high perfection at the graphene-h-BN boundaries, still remains a challenge. Here, the growth of lateral heterostructures of graphene and h-BN on Rh(110) surfaces is reported. The choice of the 2D material, grown firstly, determines the structural properties of the whole heterostructure layer, allowing to have control over the rotational order of the domains. The atomic-scale observation of the boundaries demonstrates a perfect lateral matching. In-plane heterostructures floating over an oxygen layer have been successfully obtained, enabling to observe intervalley scattering processes in graphene regions. The high tuning capabilities of these heterostructures, along with their good structural quality, even around the boundaries, suggest their usage as test beds for fundamental studies aiming at the development of novel nanomaterials with tailored properties.

Silicone-Based Thermally Conductive Gel Fabrication via Hybridization of Low-Melting-Point Alloy-Hexagonal Boron Nitride-Graphene Oxide.

Thermal contact resistance between the microprocessor chip and the heat sink has long been a focus of thermal management research in electronics. Thermally conductive gel, as a thermal interface material for efficient heat transfer between high-power components and heat sinks, can effectively reduce heat accumulation in electronic components. To reduce the interface thermal resistance of thermally conductive gel, hexagonal boron nitride and graphene oxide were hybridized with a low-melting-point alloy in the presence of a surface modifier, humic acid, to obtain a hybrid filler. The results showed that at the nanoscale, the low-melting-point alloy was homogeneously composited and encapsulated in hexagonal boron nitride and graphene oxide, which reduced its melting range. When the temperature reached the melting point of the low-melting-point alloy, the hybrid powder exhibited surface wettability. The thermal conductivity of the thermally conductive gel prepared with the hybrid filler increased to 2.18 W/(m·K), while the corresponding thermal contact resistance could be as low as 0.024 °C/W. Furthermore, the thermal interface material maintained its excellent electric insulation performance, which is necessary for electronic device applications.

Two Detection Modes of Nanoslit Sensing Based on Planar Heterostructure of Graphene/Hexagonal Boron Nitride

Solid-state nanopore sequencing is now confronted with problems of stochastic pore clogging and too fast speed during the DNA permeation through a nanopore, although this technique is revolutionary with long readability and high efficiency. These two problems are related to controlling molecular transportation during sequencing. To control the DNA motion and identify the four bases, we propose nanoslit sensing based on the planar heterostructure of two-dimensional graphene and hexagonal boron nitride. Molecular dynamics simulations are performed on investigating the motion of DNA molecules on the heterostructure with a nanoslit sensor. Results show that the DNA molecules are confined within the hexagonal boron nitride (HBN) domain of the heterostructure. And the confinement effects of the heterostructure can be optimized by tailoring the stripe length. Besides, there are two ways of DNA permeation through nanoslits: the DNA can cross or translocate the nanoslit under applied voltages along the y and z directions. The two detection modes are named cross-slit and trans-slit, respectively. In both modes, the ionic current drops can be observed when the nanoslit is occupied by the DNA. And the ionic currents and dwell times can be simultaneously detected to identify the four different DNA bases. This study can shed light on the sensing mechanism based on the nanoslit sensor of a planar heterostructure and provide theoretical guidance on designing devices controlling molecular transportation during nanopore sequencing.

Vertically-oriented graphene-boron nitride skeletons using graphene oxide as inorganic adhesives for high-efficiency thermal conduction of polymeric composites with electrical insulation and compressibility

Polymer-based thermal interface materials (TIMs) with high thermal conductivity are in high demand for rapid heat transfer between electronic components. It is still challenging to achieve significant enhancement in thermal conductivity of polymeric composites while maintaining satisfactory electrical insulation and good compressibility. In this work, we have developed a vertically-oriented graphene-boron nitride (GNP-BN) skeleton using graphene oxide (GO) as inorganic adhesives through ice-templating method, and vacuum-infiltrated with polydimethylsiloxane (PDMS) to fabricate GNP-BN/PDMS composites. The 5.2 wt% GNP-BN/PDMS composites exhibited high-efficiency thermal conduction (through-plane thermal conductivity of 1.16 W m−1 K−1 and enhancement efficiency as high as 104.7%), satisfactory electrical insulation (volume resistivity of over 108 Ω cm), and good compressibility (compressive modulus as low as 1.47 MPa). Such high performance is mainly attributed to the high-efficiency heat transfer pathway, low interfacial thermal resistance between components, effective hindrance to long-distance electron transport, and easy deformation of porous skeletons. The GNP-BN/PDMS composites show great potential to be used as high-performance TIMs in the field of electronic devices.

Design optimization of the gallium nitride high electron mobility transistor with graphene and boron nitride heat-spreading elements

The self-heating effect has long been a persistent issue for high electron mobility transistors based on gallium nitride due to their inherently poor heat dissipation capability. Although a wide variety of thermal management solutions has to date been proposed, the problem of the extremely non-uniform heat dissipation at the micrometer scale is still challenging. It has recently been demonstrated, however, that the performance of gallium nitride high electron mobility transistors can be substantially improved by the introduction of various heat-spreading elements based on graphene, boron nitride or diamond. In this paper, using numerical simulation, we carried out a design optimization procedure for a normally-off gallium nitride high electron mobility transistor containing both graphene and cubic boron nitride layers. First, a screening experiment based on a very economical Plackett-Burman design was performed in order to find the most critical geometric parameters that influence the dc characteristics. After that, a full two-level factorial experiment consisting of three factors was implemented and an optimized parameter set was yielded. By applying this set, the output power was increased by 11.35%. The combination of the most significant parameters does not include any factors related to the heat-spreading layers. Keywords: gallium nitride, high electron mobility transistor, optimization, Plackett-Burman design, screening experiment, self-heating.

Theoretical Study on the Conductivity Differences between Graphene and Hexagonal Boron Nitride

Theoretical Study on the Conductivity Differences between Graphene and Hexagonal Boron Nitride

A graphene/h-BN MEMS varactor for sub-THz and THz applications.

Recent development of terahertz systems has created the need for new elements operating in this frequency band, i.e., fast tunable devices such as varactors. Here, we present the process flow and characterization of a novel electronic variable capacitor device that is made with the use of 2D metamaterials such as graphene (GR) or hexagonal boron nitride (h-BN). Comb-like structures are etched into a silicon/silicon nitride substrate and a metal electrode is deposited at the bottom. Next, a PMMA/GR/h-BN layer is placed on top of the sample. As voltage is applied between GR and metal, the PMMA/GR/h-BN layer bends towards the bottom electrode thus decreasing the distance between electrodes and changing the capacitance. The high tunability and complementary metal oxide semiconductor (CMOS)-compatible process flow of the platform for our device and its millimeter size make it promising for applications in future electronics and terahertz technologies. The goal of our research is to integrate our device with dielectric rod waveguides, thus making THz phase shifters.

BN-PVDF/rGO-PVDF Laminate Nanocomposites for Energy Storage Applications.

The increasing demand for high energy storage devices calls for concurrently enhanced dielectric constants and reduced dielectric losses of polymer dielectrics. In this work, we rationally design dielectric composites comprising aligned 2D nanofillers of reduced graphene oxide (rGO) and boron nitride nanosheets (BNNS) in a polyvinylidene fluoride (PVDF) matrix through a novel press-and-fold technique. Both nanofillers play different yet complementary roles: while rGO is designed to enhance the dielectric constant through charge accumulation at the interfaces with polymer, BNNS suppress the dielectric loss by preventing the mobility of free electrons. The microlaminate containing eight layers each of rGO/PVDF and BNNS/PVDF films exhibits remarkable dielectric performance with a dielectric constant of 147 and an ultralow dielectric loss of 0.075, due to the synergistic effect arising from the alternatingly electrically conductive and insulating films. Consequently, a maximum energy density of 3.5 J/cm3-about 18 times the bilayer composite counterpart-is realized. The high thermal conductivities of both nanofillers and their alignment endow the microlaminate with an excellent in-plane thermal conductivity of 6.53 Wm-1K-1, potentially useful for multifunctional applications. This work offers a simple but effective approach to fabricating a composite for high dielectric energy storage using two different 2D nanofillers.

Modeling the Interaction of Anticancer Protein Azurin with the Nanosheets for Medical Applications

AbstractAzurin as an electron transfer protein plays a vital role in the degradation of cancerous cells, but due to the destruction of its structure by stomach acid, finding safe and efficient techniques such as nano material to protect Azurin for drug delivery purposes is in high demand. In the present study, molecular dynamics techniques are exploited to examine the interaction and immobilization of Azurin on the surface of nanosheets such as graphene monoxide, silicon carbide and boron nitride at 310 K. To analyze the simulation results, structural parameters such as root mean square fluctuation (RMSF), root mean square deviation (RMSD), radius of gyration (Rg), the distance between the center of mass of immobilized protein and surface of the considered nanosheets, and surface accessible solvent area (SASA) are measured. Additionally, the interaction energy of the protein with the nanosheet surface is investigated using structural and energetic parameters of the protein and nanosheets including residue polarity, charge density, hydrophilicity, and hydrophobicity. The simulation results exhibit the adsorption and immobilization of Azurin on the targeted surfaces while maintaining its native structure. As an initial step, these results reveal a promising potential application of studied nanosheets in aqueous condition for the smart delivery, medicine and cancer therapy of Azurin.

Adsorption behavior of methylene blue on graphene and hexagonal boron nitride monolayers in aqueous solution: A first-principles treatment

Understanding the adsorption of dye molecules on nanostructured materials is important in regard to innovative potential applications, especially when the corresponding entities are combined. Here, we explore the interaction of methylene blue (MB) with graphene and hexagonal boron-nitride (h-BN) as two-dimensional nanosheets with unique electronic properties and high potential in technological applications. We study these interactions using quantum-based molecular simulations and probe these through the interaction properties and electronic structure of the adsorbed MB on the considered monolayers and especially the specific role of the surrounding environment. We discuss the importance of the findings in view of contaminant removal from wastewater and specifically sensing applications of considered monolayers. Our dispersion-corrected density functional theory (DFT) results show that MB adsorbs strongly on both the graphene and h-BN with interaction energies of −47.454 and −45.072 kcal/mol, respectively, with equilibrium distances of about 3.2 Å between the aromatic rings of adsorbate and substrates. The accuracy of the DFT calculations is validated by the coupled-cluster with single, double (triple) excitations level of theory. The charge density and atom-in-molecule theory analyses reveal the existence of non-covalent and electrostatic interactions between MB and graphene/h-BN surface. The electronic structure analysis shows that the semiconducting graphene becomes metallic after MB adsorption while the h-BN monolayer retains its semiconducting characteristic upon the adsorption. Complementary assays using DFT-based molecular dynamic simulations demonstrate the strong binding of MB to both the graphene and h-BN surfaces in the presence of water molecules as competitive entities. These findings demonstrate the potential applications of graphene and h-BN for the efficient adsorption of dye molecules and for developing promising adsorbents for wastewater treatment and functionalized sensors.

Ultrastable 2D material-wrapped copper nanowires for high-performance flexible and transparent energy devices

Wrapping metallic nanomaterials with two-dimensional (2D) materials can significantly improve the physical properties required for various electronic and catalytic applications. However, synthesizing 2D material-wrapped metal nanowires with highly organized shell morphology is still difficult because of their large surface area and high aspect ratio. We propose a simple and practical method for synthesizing 2D material-wrapped copper nanowires (CuNWs) with highly organized shell morphology by using 2D quantum dot (QD) assembly and flash light irradiation under low temperature and non-vacuum conditions. A uniform and thin layer of QDs comprising 2D material such as graphene or hexagonal boron nitride is constructed on the CuNW by using a solution process. The 2D QD-wrapped CuNW is then subjected to flash light irradiation to realize highly organized shell morphology. Microstructural observations showed that the flash light irradiation reconstructs the shell structure and improves crystal quality without structural deformation. The 2D material-wrapped CuNWs were used to fabricate transparent conducting electrodes (TCEs) exhibited outstanding oxidation stability, chemical stability, and mechanical durability. These TCEs were applied to realize high-performance transparent supercapacitors and heaters. In particular, the transparent supercapacitors based on the graphene-wrapped CuNW TCE demonstrated excellent capacitive behavior under acidic electrolyte conditions. They showed the highest areal capacitance (18.97 mF cm−2) compared to other metal nanowire-based transparent supercapacitors. Finally, a novel method for fabricating carbon and boron nitride nanotubes by wet-etching the core CuNW of the 2D material-wrapped CuNWs was successfully developed.

The Influence of Thermoelectric Properties of Nanomaterial and Applications

To assess the thermoelectric qualities of low-dimensional materials, a nanomaterial was created. Due to its inherent nanoscale structure, a one-dimensional thermoelectric material is predicted to have superior thermoelectric characteristics and low heat conductivity. High efficiency thermoelectric energy conversion devices can be realised by taking use of these better features. Graphene and hexagonal boron nitride (h-BN), two-dimensional nanomaterials, are thermally efficient. Due to the differences in the crystal lattice and electrical structure between graphene and h-BN, a new material with novel thermal properties is created when the two join to produce a planar C-BN hybrid structure or a van der Waals heterostructure. We concentrate on these new qualities while reviewing the two new materials, as their thermal properties affect their structure, size, and number of layers. To assess the thermoelectric qualities of low-dimensional materials, a micro-instrument was created. Due to its inherent nanoscale structure, a one-dimensional thermoelectric material is predicted to have superior thermoelectric characteristics and low heat conductivity. High efficiency thermoelectric energy conversion devices can be realised by taking use of these better features. In this study, we used micromachining to create microdevices to examine the thermoelectric characteristics of low-dimensional materials. The system comprises of a tiny thermocouple with a freely suspended heating element acting as the sensing element. Manipulation was used to place an array of Bi2Te3 nanowires made using the silicon template approach on the microdevice. To show the device’s ability to assess the thermoelectric properties of nanomaterials, measurements of the Bi2Te3 bundle’s electrical, thermal, and Beck coefficients were made. More information about this source text source text necessary for further translation details. We offer a synthetic method for producing Cu2ZnGeSe4 nanocrystals with a limited size range and a predetermined composition. By hot pressing, these nanocrystals were employed to create nanomaterials that were tightly packed. These nanoparticles’ Cu2ZnGeSe4 thermoelectric characteristics have been demonstrated to be very good. A figure of merit of up to 0.55 at 450 °C has already been achieved through early refinement of the nanocrystal composition. The performance of thermoelectric (TE) materials is currently the subject of intense research. One of the suggestions for enhancing their TE performance is nanostructuring. However, a nanomaterial’s shape can have a big impact on how it behaves under tension. In this study, we showed that this action uses a microwave-assisted chemical pathway to create zinc oxide (ZnO) in two distinct forms. The molar ratios of the initial precursors were altered to create nanoparticles (NPs) and nanorods (NRs). According to the results, NRs have better TE properties than NPs, especially at higher temperatures.