An actual physical probe that scans the specimen is used in scanning probe microscopy (SPM) to create pictures of surfaces. The scanning tunnelling microscope, a device for capturing atomic-scale images of surfaces, was developed in 1981, the same year that SPM was established. Gerd Binnig and Heinrich Rohrer carried out the initial productive scanning tunnelling microscope experiment. Using a feedback loop to control the spacing between the sample and the probe was crucial to their success. Multiple interactions can be imaged concurrently using a variety of scanning probe microscopes. In general, a mode is the way in which these interactions are used to produce a picture. While resolution varies slightly between approaches, certain probing techniques manage to achieve an atomic resolution that is rather amazing. This is partly because piezoelectric actuators can carry out motions on electronic command with precision and accuracy at the atomic level or better. The term "piezoelectric techniques" can be used to describe this group of methods. The data are commonly collected as a two-dimensional grid of data points, displayed in false colour as a computer picture. This is the second thing they have in common.