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How good is the AFM (Atomic Force Microscope)?


1. Principles

Atomic Force Microscope (AFM). AFM is an analytical instrument that can be used to study the surface structure of solid materials, including insulators. It investigates the surface structure and properties of substances by detecting the very weak interatomic interaction forces between the surface of the sample to be measured and a miniature force-sensitive element.

2. Models

Asylum MFP-3D infinity

Figure 1. Asylum MFP-3D infinity

Bruker Multimode 8

Figure 2. Bruker Multimode 8

3. Test items

Surface morphology/roughness

AFM can study the surface morphology, nanostructure and chain conformation of the sample to obtain information on nanoparticle size, pore size, material surface roughness, material surface defects, etc., and also do surface structure morphology tracking (with time, temperature and other conditions). It is also possible to display a rich 3D simulation of the morphology of the sample, making the image more suitable for human intuitive vision. The following figure characterizes the 2D geometric topography, 3D height topography, and roughness of the nanoparticles.

Figure 3. Surface Topography/Roughness

Thickness (nanosheet thickness/step height): pinpointing

It's the place where you need to spend a little bit of time to find this. During semiconductor processing it is often necessary to measure high aspect ratio structures, like trenches and steps, to determine the depth and width of the etch. These can only be measured by cutting the sample along a cross-section under SEM, but can be measured non-destructively by AFM, which has a resolution of about 0.1 nm in the vertical direction, making it ideal for characterizing nanosheet thickness. The following figure characterizes the step height and nanosheet thickness plots.

Figure 4. Thickness (nanosheet thickness/step height)

Phase Diagram

An important extension of the tap mode technique, the phase mode is imaged by detecting the change in the difference between the phase angle of the signal source driving the vibration of the microcantilever probe and the phase angle of the actual vibration of the microcantilever probe (i.e., the phase shift between the two). There are many factors that can cause this phase shift, such as the sample's composition, hardness, viscoelastic properties, modulus, etc. Simply put, if two materials have less contrast in terms of AFM morphology, but you are very interested in illustrating what kind of film this is growing the other, this is a good time to utilize a 2D morphology map + a phase diagram to illustrate this (provided that the two materials have more different physical properties, and the phase diagrams have a clear contrasting signal to be able to do so).

Figure 5. Phase Diagram

Special Modes

PFM (Piezoelectric Force Microscope); EFM (Electrostatic Force Microscope); KPFM (Surface Potential); MFM (Magnetic Force Microscope); C-AFM/PeakForceTUNA (Conductivity Force Microscope); Young's Modulus/Modulus Distribution; Force Curve; Special Modes such as Submerged, Variable Temperature.

4. Sample status

  1. Powder, lump/film and liquid samples can be tested;

  2. Powder samples: particles generally do not exceed 5 microns, provide 20mg;

  3. Block/film samples: length and width between 0.5 ~ 3 cm, thickness between 0.1 ~ 1 cm, surface roughness not more than 5 um;

  4. Liquid sample: liquid not less than 1ml. (Remarks: ultrasonic is generally 5min by default.)