Process-Structure Map for Diamond-Like Carbon Fibers from Ethene at Hyperbaric Pressures

Abstract

High-pressure laser chemical vapor deposition (HP-LCVD) is a powerful tool for growing complex microstructures at rapid rates. Not only is it possible to deposit functionally graded materials, but new metastable phases, alloys, and composite materials may be realized. In this paper, the diversity of microstructures that may be obtained through HP-LCVD is demonstrated, including the growth of metastable materials, e.g., diamond-like carbon (DLC). For the first time, a pressure–temperature (P–T) phase diagram has been created for HP-LCVD, identifying nine distinct material phases of carbon from ethene. Regions of high sp3 content are identified via Raman spectroscopy. The kinetics, rate limitations, and thermodynamics of the process are also characterized at hyperbaric pressures, creating a first-ever process-rate map—covering the entire useful pressure range for ethene. Thermodynamically enhanced growth is also documented for the first time, where the contribution of the heat of reaction is much greater than the incident laser power—demonstrating a quasi-self-sustaining reaction. Finally, sufficient information is provided to reconstruct specific fiber geometries, structures, and growth rates for potential industrial production of carbon fibers from the gas phase.