AFM University Introduction to Atomic Force Microscopy by Paul West

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« Foreward
« Chapter 1
 « Chapter 2
 « Chapter 3
 « Chapter 4
 
4.1 Topography Modes
4.1.1 Contact Modes
4.1.2 Vibrating Modes
4.2 Field Modes
4.2.1 Electric Force Microscopy
4.2.2 Magnetic Force Microscopy
4.3 Material Sensing Modes
4.3.1 Lateral Force / Frictional Force
4.3.2. Vibrating Phase
4.4 Electrical Modes
4.4.1 Parametric Testing (I/V and C/V)
4.4.2 SHARK
4.4.3 Ferroelectric / Piezoelectric Testing
4.4.4 Kelvin Probe (SKPM)
4.4.5 Scanning Capacitance
4.5.1 Voltage
4.5.2 Scratching
4.5.3 Chemical Deposition
4.6 Mechanical Measurements
4.6.1 Force / Distance Curves
4.6.2 Nano Indenting
4.6.3 Frictional Measurements
4.7 Thermal Measurements
4.8 Other Modes
4.8.1 Electrochemistry
4.8.2 Scanning Tunneling Microscope
4.8.3 Pulsed Force Mode
4.8.4 Nano-Manipulation
 « Chapter 5
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« Appendix A
« Appendix B
« Appendix C
« Appendix D
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Chapter 4
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(AFM)2, the force between a probe and surface is monitored. Lastly, in the near field optical microscope (NSOM)3 the optical properties of a sample’s surface are monitored.
Soon after the invention of the AFM it was realized that these instruments were capable of measuring far more than surface topography. In fact, it is possible to measure almost any physically observable phenomena at the nanometer scale. The only requirement is that a nanoscopic sensor must be developed for the end of a probe. For example, magnetic fields, electric fields, temperature, and hardness may be measured with the AFM probe. Additionally, it is possible to use the AFM probe to modify surfaces. By definition, an AFM mode is a non-topographical measurement made with an AFM.
For the most part, atomic force microscopes are operated in ambient air. At the surface of samples maintained in ambient air, there is always a contamination layer comprised of water and hydrocarbons. Thus, in an AFM, the probe tip is typically immersed in the contamination layer (see Figure 4-2). Because the contamination layer can vary from one environment to the next, the layer can cause uncertainty in AFM measurements. This is especially true for mode measurements made with AFM.
FIGURE 4-2In ambient air, the AFM probe must pass through a surface contamination layer to touch the surface.
AFM probes contribute a lot of uncertainty of topography and mode measurements. The uncertainty is due to variations in probe geometry. As provided by a vendor4, the typical AFM probe has a diameter of < 15 nm. That is to say it could be 15 or 5 or 10 nm in diameter. The uncertainty goes up when the probe is coated with a thin film of metal or other type of material. Not only are there variations in the probe coating thickness, there can be variations in the integrity of the probe. For example, the coating on an AFM probe may have grains. Figure 4-3 shows an SEM image of a typical AFM probe and an AFM probe coated with a conductive diamond film.

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