AFM Tutorial

AFM Tutorial Within the past decade, a family of powerful surface imaging techniques, known collectively as scanned probe microscopy (SPM), has developed in the wake of the invention of the scanning tunneling microscope (STM). Each scanned probe technique relies on a very sharp probe positioned within a few nanometers above the surface of interest. Some combination of probe and/or substrate positioning is required to provide sub-nm-resolution, three-dimensional motion of the probe relative to the substrate. When the probe translates laterally (horizontally) relative to the sample, any change in the height of the surface causes the detected probe signal to change. In general, if the probe signal decreases, this means that the point on the surface directly beneath the probe is farther from the probe than the previous point was. Conversely, if the probe signal increases, then the point on the surface is closer to the probe than the previous point. The electronic circuit that controls the vertical position of the probe relative to the sample uses these changes in the probe signal as sensory feedback to decide which direction (up or down) to move the probe to maintain a constant probe signal. When the probe signal decreases, the circuit realizes that the surface is now farther away, so it moves the probe down until the signal increases to the same level that was measured at the previous point. Similarly, the circuit responds to increases in probe signal ...