Graphene is the first 2D crystal ever isolated by mankind. It consists of a single graphite layer, and its exceptional properties are revolutionizing material science. However, there is still a lack of convenient mass-production methods to obtain defect-free monolayer graphene. In contrast, graphene nanoplatelets, hybrids between graphene and graphite, are already industrially available. Such nanomaterials are attractive, considering their planar structure, light weight, high aspect ratio, electrical conductivity, low cost, and mechanical toughness. These diverse features enable applications ranging from energy harvesting and electronic skin to reinforced plastic materials. This review presents progress in composite materials with graphene nanoplatelets applied, among others, in the field of flexible electronics and motion and structural sensing. Particular emphasis is given to applications such as antennas, flexible electrodes for energy devices, and strain sensors. A separate discussion is included on advanced biodegradable materials reinforced with graphene nanoplatelets. A discussion of the necessary steps for the further spread of graphene nanoplatelets is provided for each revised field.

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Graphene Nanoplatelets-Based Advanced Materials and Recent Progress in Sustainable Applications

Direct ink writing (DIW) of graphite-epoxy composites has gained significant importance in a number of applications in fabricating highly conductive free-standing 3D structures. Processing of the composite inks, which consist of highly loaded graphene nanoplatelets, first involves a detailed understanding of the underlying rheological properties. However, little is known about the effect of processing/print parameters, e.g., print speed has on the orientation of such 2D particles during the printing process and how this subsequently influences the macroscopic properties of the final cured composite. In this work, inks with solid loadings of 7−18 wt% were dispersed into a low viscosity epoxy resin (EPON 862) to form a shear thinning, viscoelastic material. The optimal GNP loading for printing is determined through rheological measurements, and the electrical properties are measured as a function of particle concentration and print speed. The results show a sharp increase in conductivity by a factor of ten as the print speed is increased from 5 to 40 mm/s, and all printed samples had conductivities higher than 10−3 S/cm. We attribute this change in conductivity to the shear stresses generated during the deposition of the ink, resulting in a shift in the orientation of the 2D platelet-like fillers. Such results showcase the ability to tune the electrical properties of a printed structure with a constant loading of filler. The present work helps develop design rules for processing of graphene-based 3D structures with enhanced properties (electrical) using additive manufacturing. We envision the use of such structures in a number of applications such as thermal interface materials, shielding materials for electronic devices, and light-emitting devices, to name a few.

Printability and performance of 3D conductive graphite structures

In this study, we present a facile means of fabricating graphene thin films via layer-by-layer (LbL) assembly of charged graphene nanosheets (GS) based on electrostatic interactions. To this end, graphite oxide (GO) obtained from graphite powder using Hummers method is chemically reduced to carboxylic acid-functionalized GS and amine-functionalized GS to perform an alternate LbL deposition between oppositely charged GSs. Specifically, for successful preparation of positively charged GS, GOs are treated with an intermediate acyl-chlorination reaction by thionyl chloride and a subsequent amidation reaction in pyridine, whereby a stable GO dispersibility can be maintained within the polar reaction solvent. As a result, without the aid of additional hybridization with charged nanomaterials or polyelectrolytes, the oppositely charged graphene nanosheets can be electrostatically assembled to form graphene thin films in an aqueous environment, while obtaining controllability over film thickness and transparency. Finally, the electrical property of the assembled graphene thin films can be enhanced through a thermal treatment process. Notably, the introduction of chloride functions during the acyl-chlorination reaction provides the p-doping effect for the assembled graphene thin films, yielding a sheet resistance of 1.4 kΩ/sq with a light transmittance of 80% after thermal treatment. Since the proposed method allows for large-scale production as well as elaborate manipulation of the physical properties of the graphene thin films, it can be potentially utilized in various applications, such as transparent electrodes, flexible displays and highly sensitive biosensors.

http://ma.ecsdl.org/content/MA2012-01/37/1352.full.pdf

Fabrication of Graphene Thin Films Based on Layer-by-Layer Self-Assembly of Functionalized Graphene Nanosheets

Flexible and Transparent Silver Nanowires Integrated with a Graphene Layer-Doping PEDOT:PSS Film for Detection of Hydrogen Sulfide

Fully solution processed Ag NWs/ZnO TF/ZnO NR composite electrodes with tunable light scattering properties for thin-film solar cells

Effect of hydrofluorocarbon structure of C3H2F6 isomers on high aspect ratio etching of silicon oxide

Graphene nanoplatelets (GNP) have attracted considerable attention due to their high yield and fabrication route that is scalable to enable graphene production. However, the absence of a means of fabricating a transparent and conductive GNP film has been the biggest obstacle to the replacement of pristine graphene. Here, we report on a novel means of fabricating uniform and thin GNP-based high-performance transparent electrodes for flexible and stretchable optoelectronic devices involving the use of an adhesive polymer layer (PMMA) as a GNP layer controller and by forming a hybrid GNP/AgNW electrode embedded on PET or PDMS. Relative to the commercially available indium tin oxide (ITO) film on a PET substrate, a GNP-based electrode composed of hybrid GNP/AgNW on PET exhibits superb optical, physical, and electrical properties: a sheet resistance of 12 Ω sq−1 with 87.4% transmittance, a variable work function from 4.16 to 5.26 eV, an ultra-smooth surface, a rate of resistance increase of only 4.0% after 100 000 bending cycles, stretchability to 50% of tensile strain, and robust stability against oxidation. Moreover, the GNP-based electrode composed of hybrid Cl-doped GNP/AgNW shows outstanding performance in actual organic light-emitting diodes (OLEDs) by exhibiting an increased current efficiency of 29.5% and an increased luminous efficiency of 36.2%, relative to the commercial ITO electrode on PET.

Fabrication of high-performance graphene nanoplatelet-based transparent electrodes via self-interlayer-exfoliation control

The etching properties of C6F6/Ar/O2 in both an inductively coupled plasma (ICP) system and a capacitively coupled plasma (CCP) system were evaluated to investigate the effects of high C/F ratio of perfluorocarbon (PFC) gas on the etch characteristics of SiO2. When the SiO2 masked with ACL was etched with C6F6, for the CCP system, even though the etch selectivity was very high (20 ~ infinite), due to the heavy-ion bombardment possibly caused by the less dissociated high-mass ions from C6F6, tapered SiO2 etch profiles were observed. In the case of the ICP system, due to the higher dissociation of C6F6 and O2 compared to the CCP system, the etching of SiO2 required a much lower ratio of O2/C6F6 (~1.0) while showing a higher maximum SiO2 etch rate (~400 nm/min) and a lower etch selectivity (~6.5) compared with the CCP system. For the ICP etching, even though the etch selectivity was much lower than that by the CCP etching, due to less heavy-mass-ion bombardment in addition to an adequate fluorocarbon layer formation on the substrate caused by heavily dissociated species, highly anisotropic SiO2 etch profiles could be obtained at the optimized condition of the O2/C6F6 ratio (~1.0).

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Investigation of SiO2 Etch Characteristics by C6F6/Ar/O2 Plasmas Generated Using Inductively Coupled Plasma and Capacitively Coupled Plasma

We demonstrate plasma-treated Ag nanowires (NWs) as flexible transparent electrode materials with enhanced long-term stability against oxidation even in a high humidity environment (80% humidity, 20 °C). Through a simple fluorocarbon (C4F8 or C4F6) plasma treatment method, a C x F y protective polymer was sufficiently cross-linked and attached on the surface of the AgNWs strongly and uniformly. Even though C4F8 and C4F6 activate differently on the AgNW surface due to the different dissociated radicals formed in the plasma, it was found that the C x F y protective polymers obtained by both chemicals work similarly as a protective layer for transparent conductive electrodes; a nearly constant sheet resistance ratio (R s/R o) of 1.6 was found for AgNWs treated with C4F8 and C4F6 plasmas, while the AgNWs without the plasma treatment exhibited a ratio of 176.2 after 36 days in a harsh environment. It is believed that the fluorocarbon plasma treatment can be used as a key method for ensuring long-term oxidation stability in numerous electronic applications including flexible solar cells utilizing various types of metallic nanowires.

https://iopscience.iop.org/article/10.1088/1361-6528/ab114c/pdf

Da In Sung

Papers

Effect of hydrofluorocarbon structure of C3H2F6 isomers on high aspect ratio etching of silicon oxide

Fabrication of high-performance graphene nanoplatelet-based transparent electrodes via self-interlayer-exfoliation control

Investigation of SiO2 Etch Characteristics by C6F6/Ar/O2 Plasmas Generated Using Inductively Coupled Plasma and Capacitively Coupled Plasma

Highly oxidation-resistant silver nanowires by C x F y polymers using plasma treatment.