Scanning Tunneling Microscope
The scanning tunneling microscope (STM) is a tool we use to look at the surfaces of conductive samples with atomic resolution. Using a conducting tip that has a point of a single atom, it is brought within less than a nanometer of the surface of the sample we are interested in. The tip uses a phenomenon known as quantum tunneling to sense where the atoms are. Quantum tunneling is the "jumping" of an atom from one location to another: in this case, from the sample to the conducting tip. As the tip moves over the surface, the tunneling increases when the tip is over an atom, and decreases when it is between atoms, giving a picture of the atomic layout of the surface. The STM allows us to learn many electronic properties of materials that other machines are simply unable to do, such as mapping the electronic density of states or directly view the physical structures of atoms in the material.