From images to interactions: high-resolution phase imaging in tapping-mode atomic force microscopy

Area of Science:

• Surface science
• Nanotechnology
• Biophysics

Background:

• Tapping-mode atomic force microscopy (AFM) utilizes cantilever phase shifts as a signal.
• This phase signal provides material-dependent information complementary to surface topography.
• Understanding the phase signal's origin is crucial for advanced AFM applications.

Purpose of the Study:

• To demonstrate the localization of information within the phase signal in tapping-mode AFM.
• To investigate the relationship between the phase signal and tip-sample interactions.
• To propose a method for extracting interaction information from the phase signal.

Main Methods:

• Utilized tapping-mode atomic force microscopy (AFM).
• Analyzed the phase shift between cantilever excitation and response.
• Investigated purple membrane of Halobacterium salinarum in buffer solution.
• Developed a two-order approximation model for phase signal analysis.

Main Results:

• Achieved 1.4-nm lateral resolution in phase signal localization.
• Demonstrated correlation between phase signal and topography-induced amplitude modulations (first-order approximation).
• Proposed a method to extract tip-sample interaction information from the phase signal (second-order approximation) for rough surfaces.

Conclusions:

• The phase signal in tapping-mode AFM contains localized, material-dependent information.
• The phase signal is influenced by both topography and tip-sample interactions.
• The proposed method allows for enhanced characterization of surface properties and interactions.