STM - Scanning Tunneling Microscopy
The scanning tunneling microscopy is a powerful technique for the microscopy of conducting or semiconducting surfaces at atomic level. A conducting sharp tip is brought very close to the surface. In the close proximity is a certain probability for electrons to tunnel between the electrodes if a bias is applied between tip and surface. If the tunnel current is kept constant and the tip is scanned across the surface the correction of the tip height can be used as measure for the surface density of states. The tip is scanned by piezoelectric ceramic tubes which stretch or contract if a voltage is applied. Optimum resolution can be reached if the tip is extremely clean and sharp.