Scanning Tunneling Microscope

A scanning tunneling microscope is one type of electron microscope that is specifically designed to produce three-dimensional images of a sample. In an STM, as it is called, the sample’s surface structure is studied with the use of a stylus that scans over it from a fixed distance.

An STM is capable of achieving resolutions of up to 0.1 nm lateral and 0.01 nm depth. At this level, the individual atoms within the materials can be captured. An STM can also be used in various conditions, such as ultra-high vacuum, air, water, liquid or gas, and even at extreme hot and cold temperatures nearing zero kelvin to a more than a hundred degrees Celsius.

How It Works

A scanning tunneling microscope makes use of an extremely fine conducting probe that is positioned near the sample. The electrons then tunnel between the surface of the sample and the stylus, creating an electrical signal. Since the stylus is very sharp, its tip is just the same size as a single atom. This signal scans the surface of the sample from a distance that’s just as small as an atom’s diameter. If the sample surface is uneven, the stylus has to be raised and lowered to keep the distance consistent and to follow the tiniest details of the surface being scanned. After the scan, an image of the surface is produced in the form of a contour map that is generated by a computer. This scanning technique is most ideal for conducting materials, but can also be used on organic molecules; in fact, it has already been used in studying DNA molecules in the past.

A scanning tunneling microscope is now widely used in the sciences, especially in physics, where the study of surfaces is very important. More particularly, it is used in microelectronics and in semiconductor physics. It is also used to study surface reactions in chemistry.

STM, however, requires some skill during operation, which can be challenging. Nevertheless, it is one of the few electron microscopes that can be built in a DIY manner; in fact, many hobbyists have built and thus own scanning tunneling microscopes, which are more accessible than other types of electronic microscopes.

A Brief History

The scanning tunneling microscope was developed in 1981 by Gerd Binnig and Heinrich Rohrer, both of whom won the Nobel Prize in Physics back in 1986. The STM was developed based on the quantum tunneling concept.