How flat is an air-cleaved mica surface?

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Muscovite mica is a standard substrate for biological materials due to its {001} cleavage planes.
• Atomic Force Microscopy (AFM), particularly non-contact mode (NC-AFM), is a key technique for surface characterization.
• Surface charges on mica cleaved in ultra-high vacuum (UHV) hinder NC-AFM imaging.

Purpose of the Study:

• To investigate the surface morphology of muscovite mica using NC-AFM.
• To understand the effect of cleavage environment (air vs. UHV) on mica surface properties.
• To assess the suitability of mica surfaces for high-resolution imaging after UHV treatment.

Main Methods:

• Dynamic atomic force microscopy (AFM) operated in non-contact mode (NC-AFM).
• Experiments conducted under ultra-high vacuum (UHV) conditions.
• Comparison of mica surfaces cleaved in air versus UHV.

Main Results:

• Mica surfaces cleaved in air exhibit significantly less surface charge, enabling NC-AFM imaging.
• Highly resolved NC-AFM images show rough morphology with a high density of nanometre-sized particles.
• Regularly shaped structures indicate the growth of crystallites on the mica surface.
• Contamination layers persist even after degassing and heating at 560 K in UHV, preventing atomically flat surfaces.

Conclusions:

• Cleavage in air is crucial for obtaining NC-AFM-imaged mica surfaces.
• Air-cleaved mica surfaces are characterized by nanoscale particles and crystallites, not atomically flat.
• The persistent contamination layer limits the use of UHV-treated mica as an atomically flat substrate for certain applications.