Graphene-based crown-cork-like macrostructures

Abstract

In recent years, many attempts have been made to fabricate large and complex three-dimensional carbon structures. The present research demonstrates the formation of novel graphene-based macrostructures having lateral sizes of several tens of micrometers, i.e., crown cork structures consisting of stacks of curved multilayer graphene via a chemical vapor deposition method. Based on the elemental, structural and morphological analyses using Raman spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffraction, their origin and formation mechanism are fully discussed. The carburizing Fe at high temperatures in the presence of CH₄ initially results in the growth of C precipitates on the Fe substrate surface. At this stage, the Fe substrate exhibits a pearlite structure with thin alternating layers of Fe₃C and α-Fe. In contrast, the C precipitates are multilayer graphene with a crystal structure of well crystalline graphite. Providing additional C leads to the continuous growth of graphene flakes extending downward from the periphery of multilayer graphene grains into the bulk direction. This results in a stacked structure comprising curved microcrystals on the Fe surface. Employing a solid-state reaction using Fe as both a catalyst and a substrate, we have found a new growth form in the precipitation process of C in Fe, established a synthesis method, and obtained new hybrid structures that can be used for electromagnetic response substances and long-term anti-corrosion coatings. The fabrication of macrostructures having complex shapes via this technique could allow the design of carbon materials having unique structures with extremely few defects.