Abstract
Graphene, a two-dimensional nanosheet, is composed of carbon species (sp2 hybridized carbon atoms) and is the center of attention for researchers due to its extraordinary physicochemical (e.g., optical transparency, electrical, thermal conductivity, and mechanical) properties. Graphene can be synthesized using top-down or bottom-up approaches and is used in the electronics and medical (e.g., drug delivery, tissue engineering, biosensors) fields as well as in photovoltaic systems. However, the mass production of graphene and the means of transferring monolayer graphene for commercial purposes are still under investigation. When graphene layers are stacked as flakes, they have substantial impacts on the properties of graphene-based materials, and the layering of graphene obtained using different approaches varies. The determination of number of graphene layers is very important since the properties exhibited by monolayer graphene decrease as the number of graphene layer per flake increases to 5 as few-layer graphene, 10 as multilayer graphene, and more than 10 layers, when it behaves like bulk graphite. Thus, this review summarizes graphene developments and production. In addition, the efficacies of determining the number of graphene layers using various characterization methods (e.g., transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and mapping, and spin hall effect-based methods) are compared. Among these methods, TEM and Raman spectra were found to be most promising to determine number of graphene layers and their stacking order.
Highlights
The 6th element of the periodic table is truly fascinating [1]
We focus on the techniques that are commonly used to determine the number of graphene layers
Monolayer graphene can be produced in various ways, but is usually produced by micromechanical cleavage or liquid phase exfoliation, or using chemical vapor deposition: (a) Micromechanical cleavage (MMC): MMC has been used for decades to synthesize graphene (Figure 1)
Summary
The 6th element of the periodic table is truly fascinating [1]. From the perspective of graphene chemistry, carbon has several allotropes and, when combined with various organic and inorganic molecules, can form an almost infinite number of hybrids. Graphene is perhaps the most interesting carbon allotrope from the viewpoint of research and potential applications due to its fascinating properties [4,5]. Graphene (or “2D graphite”) was considered for 60 years [9,10,11] and was used to describe the properties of various carbonbased materials. 2004, it was synthesized by exfoliation of HOPG using adhesive tape This innovation has since fueled a great number of investigations aimed at understanding the unique electronic structure of graphene. Several studies have been performed to produce graphene flakes with different numbers of layers. Regardless of the method used, the number of graphene layers per flake, importantly, determines the properties of the produced materials. We focus on the techniques that are commonly used to determine the number of graphene layers. Yu et al demonstrate the role of oxygen containing functional groups in performing water purification for graphene-oxide-based membranes [32]
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