Abstract
A test method for evaluating the quality of graphene flakes, such as reduced graphene oxide (rGO) and graphene nanopowder (GNP), was developed in this study. The pelletizer was selected for a sampling tool, which enables us to formulate the flake sample as a measurable sample. Various parameters were measured from the pelletized sample in order to elucidate the best parameter for representing the quality of the graphene flakes in terms of their electrical properties. Based on the analysis of 4-probe measurement data on the pelletized sample, the best intrinsic parameter is volume resistivity (or volume conductivity) rather than resistivity (or conductivity). Additionally, the possible modification of a sample before and after the pressurization was investigated by electron microscopy and Raman spectroscopy. No significant modification was observed. The volume conductivity in the two types of the graphene was different from their individual conductivities by one order of magnitude. Based on the results of X-ray photoelectron spectroscopy and Raman spectroscopy measurements, the volume conductivity of the graphene flake samples was governed by the oxygen content in the sample. Our achievements will promote the effective use of powder-type graphene products for further applications.
Highlights
Graphene has attracted much attention due to its extremely high mobility and ballistic transport of electrons, which enable its utilization as a next-generation electronic material[1,2]
Three types of graphene flakes were used in this study, namely, i) two commercialized brands labelled as reduced graphene oxide (rGO) by their manufacturers and ii) graphene nanopowder (GNP) which is commercially available
Since the number of layers, which is indicated by the thickness, is a key parameter of a graphene product, the thickness data provided in the material specifications of these products were confirmed by transmission electron microscopy (TEM)
Summary
Graphene has attracted much attention due to its extremely high mobility and ballistic transport of electrons, which enable its utilization as a next-generation electronic material[1,2]. The powder-type graphene that is mainly produced by reduction of graphite oxide monolayer is the other type of graphene that may enable more practical applications, for example serving as an energy material with a high density as well as an outstanding electrical conductivity[8,9,10]. Technical obstacles must still be overcome to enable the economically viable use of film-type graphene as a transparent conducting electrode in display industry because currently, homogeneous electrical conductivity cannot be obtained over the entire surface[13,14]. Since the resistivity or the conductivity of a sample is an intrinsic property, it should be equal or close to that of the CVD–grown graphene Another candidate parameter to should be considered is volume resistivity or volume conductivity which is a function of the given pressure[26]. Based on a systematic review of the results for these three parameters obtained for different types of graphene samples, the best parameter for the characterization was determined
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