High viscosity environments: an unexpected route to obtain true atomic resolution with atomic force microscopy

Area of Science:

• Surface Science
• Nanotechnology
• Physical Chemistry

Background:

• Atomic force microscopy (AFM) is a key technique for imaging solid-liquid interfaces at the atomic level.
• High-viscosity liquids, relevant to energy applications, have been avoided in AFM due to expected signal-to-noise ratio (SNR) degradation from thermal noise.
• Previous assumptions suggested that increased cantilever thermal motion in viscous media inherently reduces AFM performance.

Purpose of the Study:

• To theoretically investigate the thermal noise limitations of dynamic AFM in varying viscosity environments.
• To derive expressions for amplitude, phase, and frequency noise in AFM operation.
• To redefine the performance limits for amplitude, phase, and frequency modulation AFM.

Main Methods:

• Theoretical analysis of thermal noise contributions in dynamic AFM.
• Derivation of noise expressions for cantilever motion in low and high viscosity fluids.
• Experimental validation using highly ordered pyrolytic graphite and mica surfaces.

Main Results:

• Demonstrated that reduced SNR in viscous environments is not an inherent limitation of AFM.
• Achieved SNR values comparable to ultra-high vacuum systems in high viscosity liquids under specific conditions.
• Obtained true atomic resolution images in high viscosity environments.

Conclusions:

• High-resolution AFM imaging is feasible in high viscosity liquids, contrary to prior expectations.
• The study redefines the performance limits of various dynamic AFM modes.
• This opens new avenues for AFM applications in fields utilizing viscous media, such as energy storage and electrochemistry.