Hyperthermal oxidation of graphite and diamond.

Area of Science:

• Materials Science
• Surface Science
• Computational Chemistry

Background:

• Carbon materials like diamond and graphite possess unique properties but are challenging to process due to hardness and inertness.
• Oxidation using atomic oxygen is a key method for processing these carbon materials, enabling applications in etching and functionalization.

Purpose of the Study:

• To theoretically investigate the mechanisms of diamond and graphite oxidation by hyperthermal atomic oxygen.
• To elucidate the reaction pathways and surface modifications occurring during these oxidation processes.

Main Methods:

• Utilized Born-Oppenheimer molecular dynamics with on-the-fly electronic structure calculations (Density Functional Theory and DFT-Tight Binding).
• Simulated collisions of atomic oxygen with diamond and graphite surfaces.
• Compared theoretical findings with experimental molecular-beam scattering data.

Main Results:

• For graphite, revealed mechanisms for CO and CO2 formation via epoxide diffusion to carbonyl-occupied holes, leading to surface hole expansion.
• For diamond (111), observed formation of oxy radicals and ketones, with subsequent CO2 release or graphitization.
• For diamond (100), found limited reactivity, significant inelastic scattering, and formation of O2 or peroxy radicals, with no observed carbon removal mechanism.

Conclusions:

• Theoretical simulations provide detailed insights into the oxidation mechanisms of graphite and diamond surfaces by hyperthermal atomic oxygen.
• The study highlights the differing reactivity of diamond surfaces ((111) vs. (100)) and confirms experimental observations of CO/CO2 formation and preferential etching.