Graphene Films Research Articles

Challenges in Chemical Vapour Deposition of Graphene on Metallurgical Alloys Exemplified for NiTi Shape Memory Alloys

Atomically-thin two-dimensional (2D) materials like graphene have been suggested as ultimately thin corrosion barriers and functional coatings for modern metallurgical alloys. The challenges of chemical vapour deposition (CVD) of such 2D materials, particularly graphene, on modern metallurgical alloys are discussed and reviewed here, focusing on the key problems with the metallurgical alloys’ often limited catalytic activity towards 2D materials growth and the key need to preserve the metallurgical alloys’ bulk properties during the high temperature 2D materials CVD processes. Using graphene CVD on NiTi (Nitinol) shape memory alloys as a case study, we illustrate the constraints arising from low catalytic activity and tendency to form oxides due the Ti in the NiTi alloy in terms of graphene growth results. We show that, by using a scalable low-temperature CVD process at 650 to 750 °C, we can deposit fully covering carbon films on the NiTi, albeit at limited structural quality. Notably, we also demonstrate that our CVD process does not degrade the bulk microstructure of the NiTi during carbon deposition and, importantly, leaves the crystallographic shape memory effect evolution intact. This underscores the potential of CVD for depositing graphene films on NiTi alloys while emphasizing the necessity for further exploration of CVD conditions to achieve high-quality graphene deposits akin to those on prior widely investigated dedicated (often sacrificial) high-purity metal substrates such as Ni.

Research on the Heat Dissipation in Aviation-Integrated Communication Equipment Based on Graphene Films

Aviation-integrated communication equipment is integral to modern aircraft to ensure its performance and safety. The heat dissipation problems of equipment have become increasingly prominent for the high electronic integration and system power consumption. To solve the above problem, the heat dissipation performance of aviation-integrated communication equipment based on graphene films is deeply studied. This paper establishes a three-dimensional model of aviation-integrated communication equipment to simulate the distribution of temperature fields. The influence between aluminum alloy and graphene films on the surface of magnesium alloy on the heat dissipation performance of aviation-integrated communication equipment is studied. The simulation results show that the heat balance time of the equipment using graphene films on the surface of magnesium alloy is reduced from 3600 s to 800 s, representing an approximately 77.78% improvement; the measured equipment exhibited a reduction in its overall thermal equilibrium temperature, decreasing from 68.1 °C to 66.3 °C, representing an improvement of approximately 2.64%.

Study of Morphology Control of Electro-Deposited Silver on Electro-Chemically Exfoliated Graphene Electrode and Its Conductivity.

Solution-processed graphene is beneficial for large-scale, low-cost production. However, its small lateral size, variable layer thickness, and uncontrollable oxidation level still restrict its widespread electronic application. In this study, a newly developed electrochemical exfoliation process was introduced, and a graphene-patched film electrode was fabricated by interfacial self-assembly. We were able to minimize the deterioration of graphene colloids during exfoliation by voltage and electrolyte modulation, but the patched structure of the graphene electrode still showed low conductivity with numerous inter-sheet junctions. Therefore, we determined the optimal conditions for the growth of fully networked silver structures on the multi-stacked graphene film by direct current electro-deposition, and these silver-graphene composite films showed significantly lowered graphene-colloid-patched film surface resistance.

Recovery of Metal Ions (Cd2+, Co2+, and Ni2+) from Nitrate and Sulfate on Laser-Induced Graphene Film Using Applied Voltage and Its Application.

The urgent removal of Cd, Co, and Ni from nitrate and sulfate is essential to mitigate the potential risk of chemical pollution from large volumes of industrial wastewater. In this study, these metal ions were rapidly recovered through applying voltage on nitrate and sulfate, utilizing laser-induced graphene/polyimide (LIG/PI) film as the electrode. Following the application of external voltage, both the pH value and conductivity of the solution undergo changes. Compared to Co2+ and Ni2+, Cd2+ exhibits a lower standard electrode potential and stronger reducibility. Consequently, in both nitrate and sulfate solutions, the reaction sequence follows the order of Cd2+ > Co2+ > Ni2+, with the corresponding electrode adsorption quantities in the order of Cd2+ > Co2+ ~ Ni2+. Additionally, using the recovered Co(OH)2 as the raw material, a LiCoO2 composite was prepared. The assembled battery with this composite exhibited a specific capacity of 122.8 mAh g-1, meeting practical application requirements. This research has significance for fostering green development.

A Stretchable and Tough Graphene Film Enabled by Mechanical Bond.

The pursuit of fabricating high-performance graphene films has aroused considerable attention due to their potential for practical applications. However, developing both stretchable and tough graphene films remains a formidable challenge. To address this issue, we herein introduce mechanical bond to comprehensively improve the mechanical properties of graphene films, utilizing [2]rotaxane as the bridging unit. Under external force, the [2]rotaxane cross-link undergoes intramolecular motion, releasing hidden chain and increasing the interlayer slip distance between graphene nanosheets. Compared with graphene films without [2]rotaxane cross-linking, the presence of mechanical bond not only boosted the strength of graphene films (247.3 vs 74.8 MPa) but also markedly promoted the tensile strain (23.6 vs 10.2 %) and toughness (23.9 vs 4.0 MJ/m3). Notably, the achieved tensile strain sets a record high and the toughness surpasses most reported results, rendering the graphene films suitable for applications as flexible electrodes. Even when the films were stretched within a 20 % strain and repeatedly bent vertically, the light-emitting diodes maintained an on-state with little changes in brightness. Additionally, the film electrodes effectively actuated mechanical joints, enabling uninterrupted grasping movements. Therefore, the study holds promise for expanding the application of graphene films and simultaneously inspiring the development of other high-performance two-dimensional films.

A Stretchable and Tough Graphene Film Enabled by Mechanical Bond

AbstractThe pursuit of fabricating high‐performance graphene films has aroused considerable attention due to their potential for practical applications. However, developing both stretchable and tough graphene films remains a formidable challenge. To address this issue, we herein introduce mechanical bond to comprehensively improve the mechanical properties of graphene films, utilizing [2]rotaxane as the bridging unit. Under external force, the [2]rotaxane cross‐link undergoes intramolecular motion, releasing hidden chain and increasing the interlayer slip distance between graphene nanosheets. Compared with graphene films without [2]rotaxane cross‐linking, the presence of mechanical bond not only boosted the strength of graphene films (247.3 vs 74.8 MPa) but also markedly promoted the tensile strain (23.6 vs 10.2 %) and toughness (23.9 vs 4.0 MJ/m3). Notably, the achieved tensile strain sets a record high and the toughness surpasses most reported results, rendering the graphene films suitable for applications as flexible electrodes. Even when the films were stretched within a 20 % strain and repeatedly bent vertically, the light‐emitting diodes maintained an on‐state with little changes in brightness. Additionally, the film electrodes effectively actuated mechanical joints, enabling uninterrupted grasping movements. Therefore, the study holds promise for expanding the application of graphene films and simultaneously inspiring the development of other high‐performance two‐dimensional films.

Direct Growth Graphene Via Atmospheric Pressure Chemical Vapour Deposition

The integration of graphene in field-effect transistor (FET) has aroused tremendous attention in the field of sensor technology, particularly for electronic biosensors. However, transferring graphene from metal substrates has destructive effects on the electrical characteristics of the graphene film, leading to severe impurities and defects. Here, we investigated a new approach of technique to synthesis direct- growth semiconducting graphene via atmospheric pressure chemical vapour deposition (APCVD) method. In this study we observe the effects of different reaction times, carbon concentrations and temperatures on the carbon arrangement in graphene. The synthesised graphene was characterised by Raman spectroscopy and field emission scanning electron microscopy (FESEM) to observe the quality of graphene formation. From the Raman analysis, the I2D/IG ratio < 1 indicates the formation of graphene in multiple layers. The ID /IG ratio < 1 was also observed, indicating that the graphene has less disorder of defects. Based on the electrical measurement of the material at estimated distance of 250 μm, a higher I2D/IG ratio leads to a higher resistance. Full width at half maximum (FWHM) of 2D band shows graphene with the highest I2D/IG ratio has the lowest value of FWHM. As the conclusion, these directly grown semiconducting graphene layers can be efficiently integrated into biosensors without any complex post-treatment process.

Bidirectional large strain monitoring using a novel graphene film-based patch antenna sensor

This study proposes a rectangular microstrip patch antenna sensor based on a high-conductivity graphene film for bidirectional strain detection in structural health monitoring (SHM). By using a highly conductive graphene film instead of traditional metal foil to produce a patch antenna, the antenna possesses a higher flexibility and a larger sensing range. The mechanical, electromagnetic, and radiative properties were investigated. The strain sensing principle based on the resonant frequency offset of the graphene film antenna was proposed. The relationships between the resonant frequency shift and structural strain were quantitatively explored through theoretical deductions, finite element simulations, and experiments. According to the experimental results, the shift in the resonant frequency was linearly related to the lateral and longitudinal strains. The sensitivity coefficients for the lateral and longitudinal strains were 2.2037 kHz/μϵ and 3.6198 kHz/μϵ, respectively. The thermal strain can be distinguished based on the linear resonant frequency-temperature relationship. The results demonstrated the advantages and prospects of the proposed novel patch antenna for SHM.

Anomalous size effects of ultra-small graphene sheets on the thermal properties of macroscopic films

Graphene films assembled from graphene nanosheets have achieved a wide range of applications in thermal management due to their ultra-high thermal conductivity. Although it is well established in the micron range that increasing the lateral size of graphene sheets enhances the thermal conductivity of graphene films. However, the preparation of large-size graphene sheets and their assembly into ordered film structures remain challenging, which impedes the development of high-performance thermally conductive graphene films. Herein, by unifying the properties of graphene sheets and preparation processes, we correlate the thermal conductivity of graphene films and the lateral size of starting sheets ranging from 0.32 to 20.32 μm and probe the underlying mechanism from the perspectives of macroscopic and microscopic structural defects. Surprisingly, decreasing lateral size to 0.32 μm achieved as high in-plane thermal conductivity (K//, 1550.06 ± 12.99 W/mK) and significantly higher through-plane thermal conductivity (K⊥, 8.11 ± 0.08 W/mK) of graphene films as the case of 20.32 μm. Besides, the commonly overlooked size effect of K⊥ shows an unexpected negative correlation, and the size effect of K// is also not monotonically increasing. These phenomena are correlated with micro-structure defects and lattice defects. Mechanism analysis reveals that thermally induced gas generation and the complex gas-sheet interactions during micro-structure evolution play a critical role in the size effect and may explain the unexpected negative size effect in the sub-micro range. These findings in size effects provide theoretical guidance for the selection of raw materials in fabricating highly thermally conductive graphene films.

Enhancing Thermal Conductivity of Graphene Films via Secondary Graphitization under a Direct Current Arc

Enhancing Thermal Conductivity of Graphene Films via Secondary Graphitization under a Direct Current Arc

Crosslinking Strategy for Constraining the Structural Expansion of Graphene Films during Carbonization: Implications for Thermal Management

Crosslinking Strategy for Constraining the Structural Expansion of Graphene Films during Carbonization: Implications for Thermal Management

ISCOPEM2D V1.0: An In Situ Method to Characterize and Compare Chemical Vapor Deposition Graphene Films Using Quality Matrix Approaches

ISCOPEM2D V1.0: An In Situ Method to Characterize and Compare Chemical Vapor Deposition Graphene Films Using Quality Matrix Approaches

Atomic Layer Deposition Growth and Characterization of Al2O3 Layers on Cu-Supported CVD Graphene

The deposition of thin uniform dielectric layers on graphene is important for its successful integration into electronic devices. We report on the atomic layer deposition (ALD) of Al2O3 nanofilms onto graphene grown by chemical vapor deposition onto copper foil. A pretreatment with deionized water (DI H2O) for graphene functionalization was carried out, and, subsequently, trimethylaluminum and DI H2O were used as precursors for the Al2O3 deposition process. The proper temperature regime for this process was adjusted by means of the ALD temperature window for Al2O3 deposition onto a Si substrate. The obtained Al2O3/graphene heterostructures were characterized by Raman and X-ray photoelectron spectroscopy, ellipsometry and atomic force and scanning electron microscopy. Samples of these heterostructures were transferred onto glass substrates by standard methods, with the Al2O3 coating serving as a protective layer during the transfer. Raman monitoring at every stage of the sample preparation and after the transfer enabled us to characterize the influence of the Al2O3 coating on the graphene film.

Improving strength and toughness of graphene film through metal ion bridging

The fangs, jaws, and mandibles of marine invertebrates such as Chiton and Glycera show excellent mechanical properties, which are mostly contributed to the interactions between metal (Fe, Cu, Zn, etc.) and oxygen-containing functional groups in proteins. Inspired by these load-bearing skeletal biomaterials, we improved tensile strength and toughness of graphene films through bridging graphene oxide (GO) nanosheets by metal ions. By optimizing the metal coordination form and density of cross-linking network. We revealed the relationship between mechanical properties and the unique spatial geometry of the GO nanosheets bridged by different valence metal ions. The results demonstrated that the divalent metal ions form tetrahedral geometry with carboxylate groups on the edges of the GO nanosheets, and the bond energy is relatively low, which is helpful for improving the toughness of resultant graphene films. While the trivalent metal ions are easily to form octahedral geometry with the GO nanosheets with higher bond energy, which is better for enhancing the tensile strength of graphene films. After reduction, the reduced GO (rGO) film bridged by divalent metal ions shows 43% improvement in toughness, while the rGO film bridged by trivalent metal ions shows 64% improvement in tensile strength. Our work reveals the mechanism of metal coordination bond energy and spatial geometry to improve the mechanical properties of graphene films, which lays a theoretical foundation for improving the tensile strength and toughness of resultant graphene films, and provides an avenue for fabricating high-performance graphene films and other two-dimensional nanocomposites.

Tuning the water interlayer spacer of microwave-synthesized holey graphene films towards high performance supercapacitor application

Abstract Graphene-based electrodes have been extensively investigated for supercapacitor applications. However, their ion diffusion efficiency is often hindered by the graphene restacking phenomenon. Even though holey graphene (hG) is fabricated to address this issue by providing ion transport channels, those channels could still be blocked by densely stacked graphene nanosheets. To tackle this challenge, this research aims at improving the ion diffusion efficiency of microwave-synthesized hG films by tuning the water interlayer spacer towards the improved supercapacitor performance. By controlling the vacuum filtration during graphene-based electrode fabrication, we obtain dry films with dense packing and wet films with sparse packing. The SEM images reveal that 20 times larger interlayer distance is constructed in the wet film compared to that in the dry counterpart. The hG wet film delivers a specific capacitance of 239 F g−1, ∼82% enhancement over the dry film (131 F g−1). By an integrated experimental and computational study, we quantitatively show that the interlayer spacing in combination with the nanoholes in the basal plane dominates the ion diffusion rate in hG-based electrodes. Our study concludes that novel hierarchical structures should be further considered even in hG thin films to fully exploit the superior advantages of graphene-based supercapacitors.

Electrochemical-repaired porous graphene membranes for precise ion-ion separation

The preparation of atom-thick porous lattice hosting Å-scale pores is attractive to achieve a large ion-ion selectivity in combination with a large ion flux. Graphene film is an ideal selective layer for this if high-precision pores can be incorporated, however, it is challenging to avoid larger non-selective pores at the tail-end of the pore size distribution which reduces ion-ion selectivity. Herein, we develop a strategy to overcome this challenge using an electrochemical repair strategy that successfully masks larger pores in large-area graphene. 10-nm-thick electropolymerized conjugated microporous polymer (CMP) layer is successfully deposited on graphene, thanks to a strong π-π interaction in these two materials. While the CMP layer itself is not selective, it effectively masks graphene pores, leading to a large Li+/Mg2+ selectivity from zero-dimensional pores reaching 300 with a high Li+ ion permeation rate surpassing the performance of reported materials for ion-ion separation. Overall, this scalable repair strategy enables the fabrication of monolayer graphene membranes with customizable pore sizes, limiting the contribution of nonselective pores, and offering graphene membranes a versatile platform for a broad spectrum of challenging separations.

Conformal growth of B/N modified graphene on metal strings by chemical vapor deposition for robust protection

For string-plucked instruments, the metal strings are always subjected to sweating corrosion and ambient oxidation during the daily use. A specifically thin protection coating, which will not alter its timbre and tone, is highly desirable. In this study, a two-dimensional (2D) coating of B/N-modified graphene (BNG) films is proposed to deposit on the surface of Cu alloy strings via chemical vapor deposition (CVD) as a corrosion barrier. Through providing appropriate amount of B/N dopant, conformal growth of BNG films on Cu alloy string substrate with sharp step-terraces topography can be optimized, and largely improving its robust anti-corrosion performance in both short-term electrochemical and long-term ambient corrosion tests for evaluation. On one hand, the conformal coupling between in-situ grown BNG and Cu alloy string can form a strong interaction which limits the interfacial diffusion of corrosive species. On the other hand, once the defects oxidation is initialized, B/N modified graphene can reduce its conductivity, then suppressing the electrochemical corrosion in the long-term protection. With the insights and understanding of in-situ coating method and the enhanced anti-corrosion mechanisms, this work will extend the potential applications of 2D materials as an atomic-thick protectioncoating for some special devices and instruments.

Selective SERS Detection of TATB Explosives Based on Hydroxy-Terminal Nanodiamond-Multilayer Graphene Substrate.

Selective surface-enhanced Raman scattering (SERS) detection of target explosives with good reproducibility is very important for monitoring soldiers' health and ecological environment. Here, the specific charge transfer pathway was constructed between a stable nanodiamond-multilayer graphene (MGD) film substrate and the target explosives. Two-step wet chemical oxidation methods of H2O2 (30%) and HNO3 (65%) solutions were used to regulate the terminal structure of MGD films. The experimental results showed that the hydroxyl (-OH) functional groups are successfully modified on the surface of MGD thin films, and the MGD-OH substrates having good selectivity for 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) explosive in mixed solutions of the TATB, 2,2-dinitroethene-1,1-diamine, 2,4,6-trinitrotoluene, and 1,3,5-trinitroperhydro-1,3,5-triazine explosives compared with MGD substrates were demonstrated. Finally, first-principles density functional theory simulations revealed that the SERS enhancement of the MGD-OH substrate is mainly attributed to the transferred electrons between the -NO2 groups of TATB and the -OH groups of the MGD-OH substrate.

Photonic quasi-crystal fiber electro-optical modulator

The integration of graphene with optical fiber is considered to be a new interdisciplinary research hotspot for functional fiber. In this paper, an electro-optical modulator based on a six-fold Stampfli-type photonic quasi-crystal fiber (PQF) is theoretically proposed with a sandwiched graphene/hexagonal boron nitride/graphene (Gr/hBN/Gr) film covering all the hole walls. This design exhibits a strong light-graphene interaction with an excellent modulation depth of ∼64 dB mm−1 at 1550 nm by applying an external bias voltage (below 30 V) on both graphene layers. As the Fermi level of the graphene changes with voltage, the fiber shows ‘On’ and ‘Off’ states, serving well as a light-switch. For the modulator performance, the dependence of modulation depth on multiple factors is studied in terms of the layer numbers of graphene and hBN films, the incident wavelength, and the structure parameters. Interestingly, an attenuation peak occurs due to the epsilon-near-zero effect in graphene and shows a linear relationship between the wavelength and the Fermi level. This design provides a guidance for the integration of PQF and graphene, and holds great promise for future all-fiber systems.

Observation of reversible and irreversible charge transfer processes in dye-monolayer graphene systems using Raman spectroscopy as a tool

Herein, we report the Raman spectroscopy of crystal violet (CV) and IR-780 Iodide molecules dispersed on the monolayer graphene film (MGF). In the CV-MGF system, the enhancement in the Raman scattering of CV molecules is observed irrespective of the location probed during the spectral measurements. This enhancement is due to the charge transfer from the MGF to CV molecules. However, in the case of the IR-780 Iodide – MGF system, the enhancement of Raman scattering of dye molecules or MGF is observed strongly depending upon the probed location. These observations indicate that the charge transfer is irreversible and reversible in the CV-MGF and IR-780 Iodide–MGF systems, respectively. Importantly, for the first time, this experimental study revealed that enhancing the Raman scattering of MGF is possible through the “chemical mechanism” with suitable dye molecules apart from the “electromagnetic mechanism” with plasmonic hot spots of the metal nanoparticles and photonic nanojets of single dielectric microparticles.