Step-orientation-dependent oxidation: from 1D to 2D oxides.

Area of Science:

• Surface Science
• Materials Science
• Catalysis

Background:

• Understanding the initial stages of metal oxidation is crucial for controlling material properties and reactivity.
• Rhodium (Rh) surfaces, particularly stepped surfaces, are important in catalysis and oxidation studies.
• Step edges on metal surfaces often exhibit unique reactivity compared to terraces.

Purpose of the Study:

• To investigate the initial oxidation process on Rh(111) surfaces with different step structures.
• To elucidate the role of one-dimensional (1D) oxide formation at steps in hindering two-dimensional (2D) oxide growth.
• To understand how step structure influences oxidation kinetics and its implications for nanoparticle oxidation.

Main Methods:

• Scanning Tunneling Microscopy (STM) for atomic-scale imaging of surface structures and oxide formation.
• Density Functional Theory (DFT) calculations to model surface energies, reaction pathways, and oxide structures.
• Comparative studies of oxidation on Rh(111) with {100} and {111} microfaceted steps.

Main Results:

• Initial oxidation on Rh(111) steps forms a one-dimensional (1D) oxide structure.
• This 1D oxide acts as a kinetic barrier, significantly slowing down the formation of a 2D oxide on the adjacent (111) terrace.
• The specific atomic structure of the 1D oxide at the step edge directly controls the rate of subsequent 2D oxide formation.
• Differences in step microfacet ({100} vs. {111}) lead to distinct 1D oxide structures and varying oxidation rates.

Conclusions:

• The initial oxidation pathway on stepped metal surfaces is highly sensitive to step structure.
• One-dimensional oxide formation at step edges can act as a protective layer, controlling further oxidation.
• These findings have significant implications for understanding and controlling the oxidation of supported metal nanoparticles, where step edges are prevalent.