The scanning tunneling microscope is a high-resolution non-optical microscope which employs principles of quantum mechanics. A fine needle is moved over the probe, and a voltage is applied between probe and needle. Occasionally, electrons will jump from the needle to the probe (this is a quantum-mechanical effect called "tunneling"), resulting in a weak electric current. The size of this current is highly dependent on the distance between probe and needle. By scanning the needle over the probe and measuring the current, one can thus reconstruct the surface structure of the probe. Adjustments of the distance between needle and probe are done using a servo loop and converse piezoelectricity. It is even possible to move and position individual atoms, which makes the scanning tunneling microscope an important tool in nanotechnology.