A scanning tunneling microscope (STM) is a non-optical microscope that works by scanning an electrical probe tip over the surface of a sample at a constant spacing. This allows for a 3D picture of the surface to be created.
How STM Works
The STM sample must conduct electricity for the process to work. The STM uses a tip that ends in a single atom and a voltage is passed though the tip and the sample. Electrons use a quantum mechanical effect to ‘tunnel’ from the tip to the sample or vice versa. The current that results depends upon the distance between probe tip and sample surface. The tip is attached to a piezoelectric tube and voltage applied to the piezo rod is altered to maintain a constant distance for the tip from the surface. Changes in this voltage allows a three dimensional picture of the material surface to be built up as the tip is scanned back and forth across the sample.
Figure 1. STM tip
An STM can have a resolution down to 0.2nm, small enough to resolve individual atoms.
Due to the remarkable detail and STM can give about the surface of a material, they are very useful for studying friction, surface roughness, defects and surface reactions in materials like catalysts. STMs are also very important tools in research surrounding semiconductors and microelectronics.