Scanning Tunneling Microscopy
In a Scanning Tunneling Microscope (STM), a metallic, atomically sharp tip gets extremely close to a sample, allowing electrons to quantum mechanically tunnel from the sample to the tip or vice versa. This tunneling decreases exponentially with distance, giving STM its unparalleled spatial resolution. Due to the quantum mechanical nature of the tunneling, STM is able gain information about how electronic states vary with energy and position; a quantity known as the local density of states. Since electrons can tunnel from the sample to the tip and from the tip to sample, STM can study the unoccupied states of a material. The high resolution access to the local density of states and the ability to probe both occupied and unoccupied states makes STM an indispensable tool in the study of quantum materials.