Synthesis of Vertically Oriented Graphene Sheets or Carbon Nanowalls-Review and Challenges

Abstract

The paper presents a review on the current methods for deposition of vertically oriented multilayer graphene sheets (often called carbon nanowalls-CNWs) on solid substrates. Thin films of CNWs are among the most promising materials for future applications in capacitors, batteries, electrochemical devices, and photovoltaics, but their application is currently limited by slow deposition rates and difficulties in providing materials of a desired structure and morphology. The review paper analyzes results obtained by various groups and draws correlations between the reported experimental conditions and obtained results. Challenges in this scientific field are presented and technological problems stressed. The key scientific challenge is providing the growth rate as well as morphological and structural properties of CNWs thin films versus plasma parameters, in particular versus the fluxes of reactive plasma species onto the substrate surface. The technological challenge is upgrading of deposition techniques to large surfaces and fast deposition rates, and development of a system for deposition of CNWs in the continuous mode.

Keywords: carbon nanowalls; deposition parameters; deposition speed; deposition temperature; growth mechanism; plasma synthesis.

Figure 1

Number of publications per year regarding carbon nanotube (CNT) synthesis (a) and carbon nanowall (CNW) synthesis (b). Source: Web of Science.

Figure 2

An example of carbon nanowalls grown on the surface of a titanium foil.

Figure 3

Schematic presentation of CNWs growth mechanism as suggested by Hiramatsu [9].

Figure 4

The growth rate versus the temperature as reported in literature shown in Table 1. The dots represent results in the cases when the authors performed experiments at a constant temperature. Some authors reported a range of temperatures during deposition—these results are represented with longitudinal bars.

Figure 5

The growth rate for different types of discharges as reported in literature shown in Table 1. The height of the bars indicates the range of growth rates found in the literature.

Figure 6

The growth rate for different gases as reported in literature shown in Table 1. The height of the bars indicates the range of growth rates found in the literature.