SEARCH · Search NASA

Results for “GRAPHENE”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5

All sources NASA NTRS DOE OSTI

DOE OSTI2022

Effects of ion adsorption on graphene oxide films and interfacial water structure: A molecular-scale description

Herein we discuss graphene oxide as a promising, emerging separation material, as it is durable, dispersible in water, and has naturally forming functional groups. Bulk studies using graphene oxide flakes have demonstrated impressive metal adsorption. However, little interfacial information about water and metal organization near graphene oxide is available. A mechanistic understanding of water and ions interactions with graphene oxide films is critical toward advanced separations, including improved sorption efficiency and membrane regeneration. We study metal ion and local water organization near graphene oxide thin films formed at the air/water interface. These films are not typical membranes and allow us to determine nanoscale information about the graphene oxide-water interface. We accomplish this with x-ray reflectivity (XR), x-ray fluorescence near total reflection (XFNTR), and vibrational sum frequency generation spectroscopy (SFG). These interface-specific techniques provide the electron density profile normal to the interface, number of adsorbed ions, and information about the orientational ordering and hydrogen-bonding network of interfacial water, respectively. Via XFNTR and SFG, we find that trivalent yttrium ions preferentially adsorb to graphene oxide and affect its structure, compared to divalent strontium and monovalent cesium ions. Two different interfacial water populations can be described, based on their hydrogen bonding strength, and the adsorbed ions affect these populations differently. These results provide fundamental information about ion and water organization at the interface and help address the large computational-experimental agreement gap for graphene oxide systems. Additionally, they are relevant for improved soft-scaffold graphene oxide membranes and downstream applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Overcoming Secondary Nucleation of Misoriented Domains during Wafer-Scale Epitaxy of Single-Crystal Graphene on Ge(110)

The wafer-scale synthesis of single-crystal graphene on technologically important substrates is a major challenge inhibiting the development of next-generation devices that harness the exceptional electronic, thermal, and mechanical properties of single-crystal graphene. Here, in this work, the factors controlling the domain orientation of graphene grown epitaxially on Ge(110) are elucidated, and this insight is utilized to produce graphene with minimal polycrystallinity. In the early stages of growth, most graphene islands have unidirectionally aligned lattices. However, we discover a secondary nucleation phenomenon in which misoriented graphene domains nucleate near/from the island edges, introducing defective grain boundaries and significantly increasing polycrystallinity throughout growth. We find that secondary nucleation occurs when islands grow over Ge steps, which form because of an interplay between the island growth and Ge surface topography evolution. Strategies for suppressing secondary nucleation are developed, enabling the synthesis of graphene in which the predominant crystal orientation has high coverage >99% and low rotational spread <0.6°. This work overcomes the irreproducibility of graphene epitaxy on Ge(110) reported in the literature, providing a route toward the large-area synthesis of single-crystal graphene on technologically useful semiconductors.

chemical vapor deposition↗

DOE OSTI2022

Deconstructing proton transport through atomically thin monolayer CVD graphene membranes

Selective proton (H + ) permeation through the atomically thin lattice of graphene and other 2D materials offers new opportunities for energy conversion/storage and novel separations. Practical applications necessitate scalable synthesis via approaches such as chemical vapor deposition (CVD) that inevitably introduce sub-nanometer defects, grain boundaries and wrinkles, and understanding their influence on H + transport and selectivity for large-area membranes is imperative but remains elusive. Using electrically driven transport of H + and potassium ions (K + ) we probe the influence of intrinsic sub-nanometer defects in monolayer CVD graphene across length-scales for the first time. At the micron scale, the areal H + conductance of CVD graphene (~4.5-6 mS cm -2 ) is comparable to that of mechanically exfoliated graphene indicating similarly high crystalline quality within a domain, albeit with K + transport (~1.7 mS cm -2 ). However, centimeter-scale Nafion|graphene|Nafion devices with several graphene domains show areal H + conductance of ~339 mS cm -2 and K + conductance of ~23.8 mS cm -2 (graphene conductance for H + is ~1735 mS cm -2 and for K + it is ~47.6 mS cm -2 ). Using a mathematical-transport-model and Nafion filled polycarbonate track etched supports, we systematically deconstruct the observed orders of magnitude increase in H + conductance for centimeter-scale CVD graphene. The mitigation of defects (>1.6 nm), wrinkles and tears via interfacial polymerization results in a conductance of ~1848 mS cm -2 for H + and ~75.3 mS cm -2 for K + (H + /K + selectivity of ~24.5) via intrinsic sub-nanometer proton selective defects in CVD graphene. We demonstrate atomically thin membranes with significantly higher ionic selectivity than state-of-the-art proton exchange membranes while maintaining comparable H + conductance. Our work provides a new framework to assess H + conductance and selectivity of large-area 2D membranes and highlights the role of intrinsic sub-nanometer proton selective defects for practical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2015

Synthesis and Modification of Holey Graphene for Energy Storage

Porous graphene materials have recently drawn significant interest for energy storage applications due to the effective use of the graphitic surface area provided by the pores. Holey graphene is a type of porous graphene with pores in the form of physical through thickness holes. This type of porous graphene provides a unique morphology that allows for effective transport of molecular species through the graphene plane. Therefore, as we recently demonstrated, holey graphene could be advantageous in the preparation of electrodes in supercapacitors with high volumetric performance.1 We have developed methodologies to scalably prepare holey graphene materials with or without the use of catalysts (Figure 1).1,2 In this presentation, we will discuss the choice of synthetic strategies and experimental conditions on the morphology and physical properties of holey graphene (Figure 2) and the effect on their electrochemical properties. We will also present the results on the further modification of holey graphene to study their physical and chemical properties, especially with regard to the stability and chemical reactivity of carbons located around the edges of the holes.

Lin, Yi↗

DOE OSTI2025

Graphene reinforced UHMWPE fibers

Thermoplastic polymers are increasingly used in electric vehicles, hydrogen fuel cell vehicles, and other decarbonization applications due to their lightweight and formability. Higher-strength polymers are needed to supplant metals in the vehicle structure, thereby reducing mass and improving efficiency. Ultra-high molecular weight polyethylene (UHMWPE) fibers possess one of the highest strength-to-weight ratios of technical polymers, and further improvement via reinforcement by nanofillers, such as graphene, will expand their performance envelope. Here, in this work, UHMWPE/graphene nanocomposite fibers were gel spun and characterized for their morphological, microstructural, thermal, and mechanical properties. The addition of a low fraction of graphene improved the tensile strength of the fibers by 25% and tensile modulus by 32%. Differential scanning calorimetry showed an increase in melting temperature and degree of crystallinity, which indicates improved coordination of the molecular chains induced by the addition of graphene. The reinforcement also affected the cross-sectional shape of the fibers; the aspect ratio of the fibers’ elliptical shape declined with increasing graphene content showing the skeletal effect of the graphene nanofillers in the polymer matrix. The reinforcing effect of graphene declined above a threshold concentration, and theoretical modeling was applied to demonstrate that increased agglomerates led to reduced properties. This work demonstrates a simple, effective method to produce graphene-reinforced UHMWPE fibers and lays a foundation for understanding the potential for leveraging graphene to form ultra-high-performance nanocomposite fibers for myriad engineering applications.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Macro copper-graphene composites with enhanced electrical conductivity

Composites demonstrating simultaneously enhanced-electrical conductivity, current density and lowered-temperature coefficient of resistance (TCR) compared to copper have been highly sought after for their advantages in efficient energy transport behavior. While such conductors have been demonstrated in 1D (nanowires) and 2D (films) samples, achieving similar behavior in 3D has been challenging owing to the limitations of the synthesis techniques used. In this paper, novel macro-scale 3D copper conductors were demonstrated with simultaneously increased electrical conductivity and decreased temperature coefficient of resistance (TCR) through the addition of graphene. Hot-extrusion was used to manufacture over 1-m-long, 2-mm-diameter copper-graphene composites with varying graphene content and defect density. Results showed that the electrical conductivity and current density in composites with low defect density graphene increased monotonically as a function of graphene content. They also demonstrated a significant decrease of over 17% in TCR with the addition of only 15 ppm graphene along with over 52% improvement in current density. Comparatively composites with high defect density graphene demonstrated lower electrical conductivity and current density. This study provides first-of-its-kind evidence of 3D metal composites whose bulk electrical performance has been enhanced using graphene additive in minute quantities. Further developments in this area are essential to achieve high performance composite conductors that can improve energy transport efficiency and pave way for industrial adoption of such materials in the future.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Doping of Cr in Graphene Using Electron Beam Manipulation for Functional Defect Engineering

Chromium atoms in graphene have been proposed to exhibit magnetic moments and spin-selective conducting states depending on the local bonding geometry within the graphene structure, which could lead to interesting applications in spintronics. Despite this interest, there are few direct experimental reports of Cr dopants in graphene even though it is theorized to be stable. Here, we demonstrate the introduction of single Cr dopant atoms into the graphene lattice and onto graphene edges through the controlled use of a focused electron beam in a scanning transmission electron microscope. Here, we show local control of doping locations, and when coupled with targeted in situ milling during scanning of the e-beam, these strategies demonstrate an important component of the fabrication of tailored nanostructured devices in the electron microscope. The approach is validated with first-principles calculations to understand synthesis pathways during fabrication and reveal the energetics and local properties of Cr atoms embedded in graphene; for example, Cr doping can convert graphene into a magnetic and semiconducting material, which suggests Cr-doped graphene can be used as a building block for potential electronic devices and a means to construct them.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Trivalent ion overcharging on electrified graphene

We report the structure of the electrical double layer (EDL) formed near graphene in aqueous environments strongly impacts its performance for a plethora of applications, including capacitive deionization. In particular, adsorption and organization of multivalent counterions near the graphene interface can promote nonclassical behaviors of EDL including overcharging followed by co-ion adsorption. In this paper, we characterize the EDL formed near an electrified graphene interface in dilute aqueous YCl 3 solution using in situ high resolution x-ray reflectivity (also known as crystal truncation rod) and resonant anomalous x-ray reflectivity (RAXR). These interface-specific techniques reveal the electron density profiles with molecular-scale resolution. We find that yttrium ions (Y 3+ ) readily adsorb to the negatively charged graphene surface to form an extended ion profile. This ion distribution resembles a classical diffuse layer but with a significantly high ion coverage, i.e., 1 Y 3+ per 11.4 ± 1.6 Å 2 , compared to the value calculated from the capacitance measured by cyclic voltammetry (1 Y 3+ per ~240 Å 2 ). Such overcharging can be explained by co-adsorption of chloride that effectively screens the excess positive charge. The adsorbed Y 3+ profile also shows a molecular-scale gap (≥ 5 Å) from the top graphene surfaces, which is attributed to the presence of intervening water molecules between the adsorbents and adsorbates as well as the lack of inner-sphere surface complexation on chemically inert graphene. We also demonstrate controlled adsorption by varying the applied potential and reveal consistent Y 3+ ion position with respect to the surface and increasing cation coverage with increasing the magnitude of the negative potential. This is the first experimental description of a model graphene-aqueous system with controlled potential and provides important insights into the application of graphene-based systems for enhanced and selective ion separations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2024

Low-cost, high-efficiency III-V photovoltaics enabled by remote epitaxy through graphene (Final Technical Report)

One of the most important outcomes of this project was that the team developed a method to directly grow graphene layer in wafer-scale on III-V substrates. Conventionally, graphene had to be transferred for remote epitaxy, which has imposed significant challenges in scalability, film quality, and substrate recycling, due to the transfer-related issues. The newly developed method of directly forming 2D layers by Metal-Organic Chemical Vapor Deposition (MOCVD) has realized wafer-scale, defect-free graphene formation for remote epitaxy, which has huge implications not only for solar cells but also in expanding the scalability and the possibility for heterointegration with dissimilar material platforms. Another important outcome was on better understanding of remote epitaxy mechanism. The growth of III-V on graphene is vastly different from directly growing films on III-V substrates, because the surface energy of graphene is very small, meaning that the nucleation density on graphene will be much lower than exposed III-V surfaces. Also, the graphene and the interface properties critically affect remote interaction through graphene. With this obtained knowledge regarding III-V remote epitaxy, we were able to achieve wafer-scale single-crystalline remote epitaxy, 100% exfoliation of the remote epitaxial films, as well as multiple times of GaAs wafer reusability demonstration. The general rule of thumbs found during this project will be a stepping stone for the growth and fabrication of various high-performance devices by remote epitaxy. Lastly, because remote epitaxy and 2DLT offer a pathway to isolate single-crystal membranes from the host wafers, the wafer-scale remote epitaxy processes developed in this project could open up pathways for new functionality and multi-functionality by heterointegration of remote epitaxially formed membranes.

14 SOLAR ENERGY↗

DOE OSTI2021

Increasing the Hot‐Electron Driven Hydrogen Evolution Reaction Rate on a Metal‐Free Graphene Electrode

Abstract Recently, it has been shown that a semiconductor–insulator–graphene device can drive the hydrogen evolution reaction (HER) at the graphene surface with a reduced onset potential by injecting hot electrons into graphene. However, the catalytic properties of graphene are limited by the large hydrogen adsorption energy and lack of electrochemically active sites. To address these limitations, a n ‐silicon/insulator/plasma etched graphene device is investigated, where a dry etch process is used to increase the number of active sites on the graphene by creating a greater number of active edge sites, increasing hydrogen adsorption at a given potential. This has been shown to improve the properties of devices with cold electrons. However, here it is shown that this approach can improve the HER rate with hot electrons. The electrons injected into the graphene from the silicon shift the onset potential of HER by as high as ≈0.8 V reaching a current density of 90 mA cm −2 at an overpotential of ‐0.5 V versus RHE. Furthermore, the comparison between device with pristine graphene shows a ≈2X improvement in current density at high overpotentials. This result shows that hot‐electron devices can be improved by modifying the catalytically active sites without metal catalysts.

Chae, Hyun Uk↗

DOE OSTI2022

The structural modification and magnetism of many-layer epitaxial graphene implanted with low-energy light ions

Modifying the properties of graphene has gained wide interest for a plethora of potential applications, including spintronics. One approach has demonstrated that proton irradiation can induce ferromagnetism in graphene as well as in graphite. However, little is known about how the protons interact with graphene, the mechanism that creates the ferromagnetism, or whether the protons remain in the graphene. Here we report an investigation, broadly relevant to graphitic carbon, using low-energy (360–2000 eV) ions of hydrogen, deuterium, and helium implanted into multilayer epitaxial graphene. Complementary x-ray and neutron reflectivity demonstrate that essentially all of the implanted hydrogen remains chemisorbed in graphene. In situ x-ray diffraction reveals significantly different rates of interlayer expansion of the multilayer graphene. Analysis of these data demonstrates that the interlayer expansion arises entirely from the interstitials created by the ions and not from hydrogen that remains in the graphene. The results also establish a quantitative measure of the layer expansion due to carbon interstitials. Magnetometry and x-ray diffraction studies show that the magnetic moment relates to the amount of interstitial carbon rather than the amount of hydrogen, demonstrating that the induced room-temperature ferromagnetism arises directly from the disrupted bonding of the carbon lattice.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Manipulation of electronic property of epitaxial graphene on SiC substrate by Pb intercalation

Manipulating the electronic properties of graphene has been a subject of great interest since it can aid material design to extend the applications of graphene to many different areas. Here, we systematically investigate the effect of lead (Pb) intercalation on the structural and electronic properties of epitaxial graphene on the SiC(0001) substrate. We show that the band structure of Pb-intercalated few-layer graphene can be effectively tuned through changing intercalation conditions, such as coverage, location of Pb, and the initial number of graphene layers. Lead intercalation at the interface between the buffer layer (BL) and the SiC substrate decouples the BL from the substrate and transforms the BL into a p-doped graphene layer. We also show that Pb atoms tend to donate electrons to neighboring layers, leading to an n-doping graphene layer and a small gap in the Dirac cone under a sufficiently high Pb coverage. This paper provides useful guidance for manipulating the electronic properties of graphene layers on the SiC substrate.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Collective Modes in Multilayer Graphene/𝛼−RuCl 3 Heterostructures

Collective modes in multilayer graphene, such as plasmons and phonons, exhibit sensitivity to displacement fields and interlayer coupling, distinguishing them from their counterparts in single-layer graphene. Here, we engineer collective modes in charge-transfer heterostructures composed of multilayer graphene and 𝛼−RuCl 3 . In heterostructures with a single 𝛼−RuCl 3 interface, the charge transfer generates displacement fields up to 7 V/nm at the interface between 𝛼−RuCl 3 and the adjacent graphene layer—the highest value achieved through charge-transfer methods. As a result of the broken inversion symmetry, we discover enhanced nonlinear optical response and modified phonon selection rules. Conversely, we find that multilayer graphene sandwiched between two 𝛼−RuCl 3 flakes causes displacement fields to cancel. There, we achieve carrier densities as high as 8 ×10 13 cm −2 in multilayer graphene and restore the phonon selection rules to their unperturbed state. Meanwhile, we demonstrate that plasmonic properties derive from the depletion of multiple valence bands. As a result of the quasilinear band dispersion, these “Dirac multiband plasmons” are relatively unaffected by displacement fields. On the other hand, the inverted heterostructure sequence—two multilayer graphene sheets encapsulating 𝛼−RuCl 3 —activates significant alteration of the plasmons via interlayer plasmon-plasmon coupling. Hence, multilayer graphene and 𝛼−RuCl 3 heterostructures offer a gate-free platform for engineering collective modes derived from inversion symmetry and interlayer coupling.

Moore, Samuel L. [Columbia University, New York, N↗

DOE OSTI2022

Graphene Nanopattern for Single-Crystal Film Growth, Defect Reduction and Layer Transfer

Thin film heterostructures are key building blocks for advanced electronic and optoelectronic devices. For this, direct heteroepitaxy has been pursued for decades, although it has been challenging to reduce crystal defects stemming from lattice mismatches and thermal mismatches between materials. The layer transfer method has been proposed as an alternative approach, wherein dissimilar materials are separately grown and then hetero-integrated. However, the applicability of layer transfer techniques is limited by several technical challenges, such as controllability, throughput, and damage to the substrate. Remote epitaxy, which is a recently developed method to produce single-crystalline membranes, is a promising approach but cannot be applied to elemental materials such as Si and Ge. In this work, we report graphene nanopattern as a universal template for the growth of single-crystal thin films that can be exfoliated as a freestanding form. This is realized by the chemical inertness of graphene, which allows selective nucleation at the exposed region, followed by lateral overgrowth onto graphene to form a planarized thin film. By employing graphene nanopattern, both group IV and III-V materials are utilized as the substrate as well as the epilayer. The epilayer can be exfoliated at the graphene interface because partially covered graphene effectively weakens the interface, which is corroborated by theoretical analyses of spalling theory. We reveal that graphene nanopattern not only works as a weakened interface for exfoliation, but also allows for dislocation reduction in heteroepitaxial films. This is because of the flexibility and the dangling-bond-free nature of graphene, which provides an additional path for strain relaxation. Therefore, these results represent a meaningful step toward production of high-quality single-crystal membranes that can be hetero-integrated.

Kim, Hyunseok↗

DOE OSTI2022

Graphene Nanopattern for Single-Crystal Film Growth, Defect Reduction and Layer Transfer

Kim, Hyunseok↗

NASA NTRS2018

Nanoscale Fabrication of Microwave Detectors from Commercially-Available CVD-Grown Monolayer Graphene

Using commercially-available monolayer graphene, synthesized by means of chemical vapor deposition, microwave power sensing elements have been nanofabricated and integrated with microwave-grade test structures suitable for on-wafer probing. The graphene, situated on a thermal oxide, was first cleaned of stray contaminants in a forming gas environment briefly held at 250 degrees Celsius using a rapid thermal annealer. Immediately following this step, the graphene was passivated with a protective aluminum oxide layer (approximately S nm in thickness). Micrometer-scale Corbino disc test structures were then fabricated in direct contact with the graphene using a self-aligned process, which relies on the fact that tetramethylammonium hydroxide develops the photoresist while removing the aluminum oxide. Graphene nanoribbons (with widths as small 400 nm) were then fabricated across the Corbino disc gaps using electron-beam writing in conjunction with a negative tone resist. The same developer exposed the majority of the graphene while defining nanometer-scale lines of photoresist stacked upon aluminum oxide. These stacks served as etch-stops while the unprotected graphene was ion-milled in an oxygen plasma. Finally, the photoresist was removed leaving behind passivated graphene nanoribbons. Damage caused by the fabrication was evaluated by comparing the Raman spectra of the grapheme before and after processing.

detectors↗

NASA NTRS2018

Nanomanufacturing of Graphene Nanosheets Through Hole Engineering

Facile and scalable fabrication of highly dense and high quality graphene films and articles is extremely attractive for a range of electronic and mechanical applications. Pristine, high quality graphene with its inherent impermeability poses challenges in fabricating dense films and thick parts with high electrical conductivity due to the difficulty in removing trapped air and/or solvents used in various fabrication methods. To overcome this deficiency, nano-holes were intentionally created in pristine graphene (“holey graphene”) with an average diameter of approximately 15 nm. The holes serve as pathways for the rapid removal of gases or liquids and enable the fabrication of dense holey graphene nanostructures. Subsequently, a high temperature process is applied to effectively repair the nano-holes and recover the high quality graphene conjugated network. Through the creation and repair of the nano-holes, dense graphene articles were created that exhibited an ultrahigh conductivity of 2209 S/cm and a high carrier mobility of 673 cm2V-1s-1. This unique processing methodology enables the facile and scalable fabrication of high quality graphene constructs for a variety of applications.

Yanan Chen↗

NASA NTRSDate not supplied

Solvent-Free Preparation of High Energy, Binder-Free Electrodes Enabled by Dry Compressible Holey Graphene

Graphene is an atomically thick sheet consisting of a graphitic carbon network with excellent mechanical strength, electrical and thermal conductivity, and chemical stability. Holey graphene, a structural derivative of graphene, has an array of through-the-thickness holes across the lateral surface of the nanosheet. The presence of these holes has minimal detrimental effect on the graphene properties and leads to enhanced performance in applications such as electronics, sensors, and energy storage. For example, these holes allow more facile cross-plane ion and gas transport than intact graphene, making holey graphene an ideal electrode material for electrochemical energy storage. This presentation will focus on the ability of holey graphene to be compression molded into robust articles or architectures under solvent-free conditions without the need for potentially parasitic binders. The unique dry compressibility of holey graphene has enabled facile fabrication of high mass loading electrodes with both high density and high porosity, which have found use in supercapacitors and various high-energy battery systems such as lithium-oxygen, lithium-sulfur, and lithium-selenium batteries.

Yi Lin↗