Synthesis of Carbon-Rich Hafnia Thin Films By Pulsed Laser Deposition

Abstract

Carbon-rich ceramics are an emerging class of materials with attractive high-temperature properties, including resistance to crystallization, dense microstructure, and low porosity. We explored direct synthesis of carbon-rich hafnia, which is known to form as a compact interlayer in the oxide scales of oxidized hafnium carbide. The material was synthesized by pulsed laser deposition, using pure HfO₂ targets in C₂H₂ background gas at low pressures. Stable films up to 700 nm thick and with high molar fractions (∼0.1–0.45) of carbon were obtained. The predominant chemical bonding of Hf and O atoms is that of oxygen-deficient HfO₂, while carbon is present in elemental or hydrogenated forms. Annealing at 600 °C leads to loss of most of the hydrogen from the films, which is accompanied by enhanced sp² bonding of carbon. The films have amorphous, compact, and finely grained microstructure. Carbon molar fractions higher than ∼0.2 inhibit microcrystallinity to at least 600 °C.