Direct Growth of the Oriented Nanocrystals of Gamma-Iron on Graphene Oxide Substrate. The Detailed Analysis of the Factors Affecting Unexpected Formation of the Gamma-Iron Phase

Abstract

In bulk, face-centered gamma-iron exists only at temperatures above 917 ?C, returning back to body-centered alpha-iron upon cooling below this temperature. In this work, we report formation of the gamma-iron phase at temperatures significantly lower than the 917 ?C threshold in the form of nanoparticles. Moreover, the as-grown nanoparticles have specific orientation along the (002) plane as the result of the templating effect of the graphene oxide substrate. Also, we provide a complete account of the factors responsible for the formation of the gamma-phase. Namely, we demonstrate the role of the type of carbon substrate, and the effect of the temperature and time of annealing and the graphene oxide/iron ion ratio. We demonstrate that the gamma-phase is not formed when using three-dimensional forms of carbon, elucidating the "magic" role of graphene oxide in this process.