Defect Engineering in Atomic-Layer-Deposited Cerium Oxide

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• Atomic Layer Deposition (ALD) is a powerful technique for creating ultrathin films with precise control.
• Defect engineering, particularly controlling oxygen vacancies, is crucial for enhancing catalytic activity in metal oxides.
• Cerium oxide (ceria) is a widely studied material for catalytic applications due to its redox properties.

Purpose of the Study:

• To explore ALD for defect engineering of catalytically active ultrathin cerium oxide deposits.
• To demonstrate tuning of the oxygen/cerium (O/Ce) ratio in ceria films via thermal ALD.
• To investigate the influence of coreactants, substrates, and film thickness on defect formation and film morphology.

Main Methods:

• Thermal Atomic Layer Deposition (ALD) using tris(N, N'-diisopropyl-2-dimethylamido-guanidinato)cerium(III) ([Ce(dpdmg)₃]) precursor.
• Utilized H₂O, O₂, or O₃ as coreactants for growing ceria films on silicon-based or alumina substrates.
• Employed in situ X-ray photoelectron spectroscopy (XPS) to analyze Ce³⁺ concentration (oxygen vacancies).

Main Results:

• Ce³⁺ concentration (oxygen vacancies) strongly depends on oxygen source, substrate, and film thickness.
• Interface formation (silicates, aluminates) significantly impacts early-stage Ce³⁺ fixation.
• For films >5 nm, oxygen vacancies are coreactant-dependent, and morphology is tunable by the oxygen source, enabling nanoisland formation.
• ALD reaction mechanism shifts from ligand exchange (H₂O) to ligand combustion (O₃) with increasing cycles.

Conclusions:

• ALD offers precise control over defect engineering in ultrathin ceria films.
• The O/Ce ratio and oxygen vacancy concentration can be tailored by selecting appropriate ALD parameters (coreactant, substrate, thickness).
• Morphological and chemical tuning via ALD provides pathways for surface functionalization and optimized catalytic performance.