Synthesis of carbon-rich hafnia thin films by pulsed laser deposition

摘要

Carbon-rich ceramics are an emerging class of materials with attractive high-temperature properties, including resistance to crystallization, densemicrostructure, and low porosity. We explored direct synthesis of carbon-rich hafnia, which is known to form as a compact interlayer in the oxidescales of oxidized hafnium carbide. The material was synthesized by pulsed laser deposition, using pure Hf02 targets in C_2H_2 background gas atlow pressures. Stable films up to 700 nm thick and with high molar fractions (～0.1-0.45) of carbon were obtained. The predominant chemicalbonding of Hf and 0 atoms is that of oxygen-deficient HfO_2 , while carbon is present in elemental or hydrogenated forms. Annealing at 600 leadsto loss of most of the hydrogen from the films, which is accompanied by enhanced sp~2 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℃.