Atomic force microscope (AFM) is a very high-resolution type of scanning probe microscopy (SPM) with a verified resolution in the order of nanometer fractions, more than 1,000 times better than optical diffraction. The measurement is made by “feeling” or “touching” the surface with a mechanical probe. Piezoelectric elements, which provide tiny but precise and accurate movement on (electronic) command, allow accurate scanning. The AFM has three main functions: force measurement, topographic imaging, and manipulation. In force measurement, AFMs can be used to measure the forces between the probe and the sample as a function of their mutual distance. This can be used to perform force spectroscopy to measure the mechanical properties of the sample, such as Young’s modulus of the sample, a measure of stiffness. In imaging, the response of the probe to the forces exerted on it by the sample can be used to create an image of the three-dimensional shape (topography) of a sample surface at high resolution. This is achieved by gridding the position of the sample with respect to the tip and recording the height of the probe, which corresponds to a constant interaction between the probe and the sample. In this context, the structure, working principle, sample preparation, and application of the AFM technique are explained in detail in this chapter.