The light lever force sensor had its origins in the work of precision engineers working on surface profilers. In 1932 Smaltz presented a light lever stylus profile that used film to record the movement of a sharp probe as it scanned across a surface. This technique was first applied to AFM by AMER, an IBM scientist. The light lever force sensor is now the standard in AFM designs.
As with the light lever force sensor, vibrating probe instruments were developed first for surface profilers. It was discovered that by vibrating the probe above a surface as it was scanned, lateral forces on the probe were reduced. Although Bennig and Quate discussed vibrating modes in their pioneering paper, it was a team of IBM scientists led by Kumar Wickramsinghe that first applied vibrating techniques to the AFM. They found that they were able to make the technique sensitive enough that they did not have to tap the surface. The AFM Workshop does not recommend tapping the surface in vibrating mode AFM. This is possible using the technology developed by IBM scientists.
The first scanning tunneling microscope developed at IBM in Switzerland utilized analog feedback to control the relationship between the probe and surface while measuring an image. This is very similar to the pioneering work of Young at the NBS. Soon after that pioneers such as A. Lewis built probe microscope instruments with digital feedback in them (Z). However, because of the limitations of ADC and DAC converters the AFM Workshop uses high-fidelity analog feedback circuits to control the Z position of the probe/sample in its microscopes.
In a probe microscope it is often advantageous to store height information while scanning a sample. This stored information can then be used for a following scan to hold the probe at a fixed distance above a sample's surface. This technique was pioneered by University of Texas professor Alan Bard. (X)
For a more complete introduction to Atomic Force Microscopy, we recommend Introduction to Atomic Force Microscopy, by Peter Eaton and Paul West, published by Oxford University Press.