Microscopy of Metal Oxide Surfaces

Area of Science:

• Materials Science
• Surface Science
• Solid State Physics

Background:

• Many technologically important oxides are insulators at room temperature.
• Electrical conductivity is necessary for surface imaging techniques like scanning tunneling microscopy.
• Understanding oxide surface structure and defects is crucial for various applications.

Purpose of the Study:

• To develop and apply high-temperature scanning tunneling microscopy (HT-STM) for imaging electrically insulating oxides.
• To determine the surface structure and identify defects in Nickel Oxide (NiO), Cobalt Oxide (CoO), and Uranium Dioxide (UO(2)).
• To investigate the surface energy ratio of different crystallographic planes in UO(2) using low-voltage scanning electron microscopy (LV-SEM).

Main Methods:

• Utilizing elevated temperature scanning tunneling microscopy (HT-STM) to achieve sufficient electrical conductivity for atomic resolution imaging.
• Performing electronic surface structure modeling to interpret image contrast and identify contributing atomic sites.
• Employing low voltage scanning electron microscopy (LV-SEM) to image equilibrium pores in UO(2) single crystals.

Main Results:

• Atomic resolution images of NiO, CoO, and UO(2) surfaces were successfully obtained using HT-STM.
• Surface structure and defects were identified in the studied oxides.
• Modeling provided insights into the origin of contrast in HT-STM images.
• The surface energy ratio of (111) to (001) surfaces in UO(2) was evaluated.

Conclusions:

• Elevated temperature STM is a viable technique for atomic-resolution surface characterization of oxides that are insulators at ambient temperatures.
• The study provides valuable data on the surface structure and defects of NiO, CoO, and UO(2).
• LV-SEM is effective for evaluating surface energy ratios in UO(2) single crystals.