How Does the STM Work

Scanning tunneling microscope (STM) uses a probe (the tip) to move over the surface of the material being studied.

The tip of the probe, usually composed of tungsten or platinum, is extremely sharp. The tip, which consists of a single atom, is attached to cantilever that looks like a toy diving board with a sharp tip under one end of it.

The tip slowly scans across the surface at a distance of only an atom's diameter. The tip is raised and lowered in order to keep the signal constant and maintain the distance. A small force measures the attraction or repulsion between the tip and the surface ofthe sample during scanning. These forces, causing an up and down movement of the cantilever, are monitored by a laser beam reflecting off the cantilever surface. Recording the up and down movement of the tip makes it possible to study the structure of the surface sample. A profile of the wiggled surface is created, and from that a computer-generated image is produced. The final image is a contour map of the surface showing trenches and valleys. The STM works best with conducting materials, but does not work well with insulators such as rubber.

The STM has many uses and applications in nanotechnology. The STM can image materials from DNA samples and other biological molecules. Another example is that STM has been used to study the surface of operating battery electrodes through which electricity enters or leaves.

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