AFM tips: how sharp are they?

Area of Science:

• Materials Science
• Biophysics
• Nanotechnology

Background:

• Atomic Force Microscopy (AFM) is crucial for high-resolution imaging of biological materials.
• The sharpness of AFM tips, particularly silicon nitride (Si$_{3}$N$_{4}$) cantilevers, is often considered a limiting factor for resolution.
• Previous estimations of tip geometry may not fully represent their capabilities.

Purpose of the Study:

• To accurately determine the geometric parameters of Si$_{3}$N$_{4}$ AFM tips.
• To assess the suitability of commercially available cantilevers for high-resolution biological imaging.
• To identify potential reasons for suboptimal resolution in routine AFM applications.

Main Methods:

• Utilizing simple geometric estimations.
• Performing 'blind' reconstruction analysis on cryo-AFM images of filamentous actin.
• Analyzing the radius of curvature and conical angle of Si$_{3}$N$_{4}$ tips.

Main Results:

• The radius of curvature at the apex of Si$_{3}$N$_{4}$ tips can be as small as 1 nm.
• The conical angle of these tips falls within the range of 30-40 degrees.
• These findings reveal a significantly higher aspect ratio than previously anticipated.

Conclusions:

• Commercially available Si$_{3}$N$_{4}$ cantilevers are frequently sharp enough for routine high-resolution imaging of biological samples.
• The inherent sharpness of the AFM tip is likely not the primary cause of poor resolution in many cases.
• Other factors, such as sample preparation or environmental conditions, may be more critical for achieving optimal AFM imaging resolution.