the electrodes and inherent nonlinearities, the motion is calibrated, and voltages needed for independent x, y and z motion applied according to calibration tables. Due to the extreme sensitivity of the tunneling current to the separation of the electrodes, proper vibration isolation or a rigid STM body is imperative for obtaining usable results. In the first STM by Binnig and Rohrer, magnetic levitation was used to keep the STM free from vibrations; now mechanical spring or gas spring systems are often employed. Additionally, mechanisms for vibration damping using eddy currents are sometimes implemented. Microscopes designed for long scans in scanning tunneling spectroscopy need extreme stability and are built in anechoic chambers—dedicated concrete rooms with acoustic and electromagnetic isolation that are themselves floated on vibration isolation devices inside the laboratory. Maintaining the tip position with respect to the sample, scanning the sample and acquiring the data is computer-controlled. Dedicated software for scanning probe microscopies is used for image processing as well as performing quantitative measurements. Some scanning tunneling microscopes are capable of recording images at high frame rates. Videos made of such images can show surface diffusion or track adsorption and reactions on the surface. In video-rate microscopes, frame rates of 80 Hz have been achieved with fully working feedback that adjusts the height of the tip. Principle of operation Quantum tunneling of electrons is a functioning concept of STM that arises from quantum mechanics. Classically, a particle hitting an impenetrable barrier will not pass through. If the barrier is described by a potential acting along z direction, in which an electron of mass me acquires the potential energy U(z), the electron's trajectory will be deterministic and such that the sum E of its kinetic and potential energies is at all times conserved: The electron will have a defined, non-zero momentum p only in regions where the initial energy E is greater than U(z). In quantum physics, however, particles with a very small mass, such as the electron, have discernible wavelike characteristics and are allowed to leak into classically forbidden regions. This is referred to as tunneling. Rectangular barrier model The simplest model of tunneling between the sample and the tip of a scanning tunneling microscope is that of a rectangular potential barrier. An electron of energy E is incident upon an energy barrier of height U, in the region of space of width w. An electron's behavior in the presence