Exploring partially reduced CeO   2 (111) surface at the atomic scale using scanning probe microscopy

Area of Science:

• Materials Science
• Surface Science
• Catalysis

Background:

• Cerium dioxide (CeO2) exhibits unique redox properties crucial for catalysis, linked to oxygen vacancies and Ce3+/Ce4+ transitions.
• Identifying Ce3+ species at the atomic level is challenging but vital for understanding catalytic active sites.

Purpose of the Study:

• To develop and apply atomic-resolution techniques for distinguishing Ce3+ from Ce4+ on CeO2 surfaces.
• To investigate the chemical reactivity of Ce3+ sites using force spectroscopy.

Main Methods:

• Simultaneous scanning tunneling microscopy (STM) and atomic force microscopy (AFM) on reduced CeO2 (111) surfaces.
• Force spectroscopy with CO-functionalized probes to probe chemical reactivity.
• Correlating electronic contrast from STM with topographic data from AFM.

Main Results:

• STM revealed electronic modulations indicative of Ce3+ sites, appearing as inhomogeneous shading.
• AFM successfully differentiated these electronic features from true atomic topography.
• Force spectroscopy quantified the distinct chemical reactivity of candidate Ce3+ sites compared to Ce4+ sites.

Conclusions:

• The combined STM-AFM and force spectroscopy approach provides robust atomic-level insights into ceria surface defects.
• This methodology is promising for characterizing the chemistry of active sites in CeO2-based catalysts.