Abstract
Inherent defects, such as grain boundaries (GBs), wrinkles and structural cracks, present on chemical vapor deposition (CVD)-grown graphene are inevitable because of the mechanism used for its synthesis. Because graphene defects are detrimental to electrical transport properties and degrade the performance of graphene-based devices, a defect-healing process is required. We report a simple and effective approach for enhancing the electrical properties of graphene by selective graphene-defect decoration with Pd nanoparticles (Pd NPs) using a wet-chemistry-based galvanic displacement reaction. According to the selective nucleation and growth behaviors of Pd NPs on graphene, several types of defects, such as GBs, wrinkles, graphene regions on Cu fatigue cracks and external edges of multiple graphene layers, were precisely confirmed via spherical aberration correction scanning transmission electron microscopy, field-emission scanning electron microscopy and atomic force microscopy imaging. The resultant Pd-NP-decorated graphene films showed improved sheet resistance. A transparent heater was fabricated using Pd-decorated graphene films and exhibited better heating performance than a heater fabricated using pristine graphene. This simple and novel approach promises the selective decoration of defects in CVD-grown graphene and further exploits the visualization of diverse defects on a graphene surface, which can be a versatile method for improving the properties of graphene. Decorating defects with palladium nanoparticles enhances the electrical properties of chemical vapour deposited graphene. Unlike other methods of synthesizing graphene, chemical vapour deposition can produce large areas of the two-dimensional material, but it also tends to create defects. Han-Bo-Ram Lee from Incheon National University and Taeyoon Lee from Yonsei University in South Korea, together with colleagues across the country, have shown that palladium nanoparticles automatically attach themselves to imperfections in chemical vapour deposited graphene, thereby improving its electrical properties. They chemical vapour deposited graphene on copper and dipped it in a palladium chloride solution. The greater chemical reactivity of defect sites in graphene causes palladium atoms to selectively attach to imperfections such as wrinkles, cracks and grain boundaries, creating nanoparticles at these sites. The researchers anticipate that the method could be used in the manufacture of smart mirrors and displays. Selective decoration of palladium nanoparticles on diverse graphene-defect sites. Graphene grown by chemical vapor deposition method has structural imperfections, such as grain boundaries, wrinkles and topological cracks, which cause reduced graphene-based device performance. Herein, we selectively decorated graphene defects with metal nanoparticles (Pd and Ag) by using a wet-chemistry-based galvanic displacement reaction within a few minutes without generating damage on graphene. The defect-decorated graphene showed a noticeable improvement in electrical characteristics, and defect-decorated graphene-based transparent heater showed better heating performance than a heater fabricated using pristine graphene.
Highlights
Chemical vapor deposition (CVD) has been successfully exploited as a promising method for fabricating graphene for diverse applications in different fields, including high-frequency electronics,[1] energy devices[2] and optoelectronics.[3]
The CVD method is more advantageous for the large-scale fabrication of graphene than other methods, it unavoidably introduces structural defects[4] such as vacancies,[5] grain boundaries (GBs),[6,7,8] wrinkles[4,9,10] and cracks,[11] which result in the deterioration of the physical and electrical properties of graphene
We demonstrate a facile and effective approach for the selective decoration of diverse types of inherent defects present in CVD-grown single-layer graphene (SLG) with palladium nanoparticles (Pd NPs) via a wet-chemistry-based galvanic displacement reaction to enhance the electrical properties of graphene films
Summary
Chemical vapor deposition (CVD) has been successfully exploited as a promising method for fabricating graphene for diverse applications in different fields, including high-frequency electronics,[1] energy devices[2] and optoelectronics.[3]. One-dimensional line defects of GBs and wrinkles are observed on CVD-grown single-layer graphene (SLG) because of its polycrystalline nature and because of the mismatch between the thermal expansion coefficients of graphene and the catalytic metal substrate during the cooling process of the CVD method, respectively.[4,6,7,9] The presence of one-dimensional line defects is detrimental to graphene-based electronic devices. Several groups have reported that the electronic transport properties can be improved by increasing the grain size of graphene via a micrometer-scale growth technique,[12,13] bridging graphene grains using metal nanowires[14] and selectively healing atomic defects in CVD-grown graphene through atomic layer deposition.[15,16,17] despite improved electronic transport properties, these approaches generally require sophisticated treatments, high-cost equipment and a long processing time, which can be disadvantageous for mass production in terms of cost and simplicity. Despite the simplicity of this method, Received 30 October 2015; revised 11 February 2016; accepted 16 February 2016 it did not heal inherent defects of graphene, such as GBs and wrinkles
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