Eco-friendly graphene synthesis on Cu foil electroplated by reusing Cu etchants

Influence of chemical and electronic inhomogeneities of graphene/copper on the growth of oxide thin films: the ZnO/graphene/copper case

The interaction of graphene with metal oxides is essential for understanding and controlling new devices' fabrication based on these materials. The growth of metal oxides on graphene/substrate systems constitutes a challenging task due to the graphene surface's hydrophobic nature. In general, different pre-treatments should be performed before deposition to ensure a homogenous growth depending on the deposition technique, the metal oxide, and the surface's specific nature. Among these factors, the initial state and interaction of graphene with its substrate is the most important. Therefore, it is imperative to study the initial local state of graphene and relate it to the early stages of metal oxides' growth characteristics. Taking as initial samples graphene grown by chemical vapor deposition on polycrystalline Cu sheets and then exposed to ambient conditions, this article presents a local study of the inhomogeneities of this air-exposed graphene and how they influence on the subsequent ZnO growth. Firstly, by spatially correlating Raman and x-ray photoemission spectroscopies at the micro and nanoscales, it is shown how chemical species present in air intercalate inhomogeneously between Graphene and Cu. The reason for this is precisely the polycrystalline nature of the Cu support. Moreover, these local inhomogeneities also affect the oxidation level of the uppermost layer of Cu and, consequently, the electronic coupling between graphene and the metallic substrate. In second place, through the same characterization techniques, it is shown how the initial state of graphene/Cu sheets influences the local inhomogeneities of the ZnO deposit during the early stages of growth in terms of both, stoichiometry and morphology. Finally, as a proof of concept, it is shown how altering the initial chemical state and interaction of Graphene with Cu can be used to control the properties of the ZnO deposits.

Pulsed-Plasma Physical Vapor Deposition Approach Toward the Facile Synthesis of Multilayer and Monolayer Graphene for Anticoagulation Applications

We demonstrate the growth of multilayer and single-layer graphene on copper foil using bipolar pulsed direct current (DC) magnetron sputtering of a graphite target in pure argon atmosphere. Single-layer graphene (SG) and few-layer graphene (FLG) films are deposited at temperatures ranging from 700 °C to 920 °C within <30 min. We find that the deposition and post-deposition annealing temperatures influence the layer thickness and quality of the graphene films formed. The films were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and optical transmission spectroscopy techniques. Based on the above studies, a diffusion-controlled mechanism was proposed for the graphene growth. A single-step whole blood assay was used to investigate the anticoagulant activity of graphene surfaces. Platelet adhesion, activation, and morphological changes on the graphene/glass surfaces, compared to bare glass, were analyzed using fluorescence microscopy and SEM techniques. We have found significant suppression of the platelet adhesion, activation, and aggregation on the graphene-covered surfaces, compared to the bare glass, indicating the anticoagulant activity of the deposited graphene films. Our production technique represents an industrially relevant method for the growth of SG and FLG for various applications including the biomedical field.

The electrochemical transfer of CVD-graphene using agarose gel as solid electrolyte and mechanical support layer

An electrochemical method using agarose gel as a solid electrolyte was introduced to realize the eco-friendly transfer of CVD-graphene.