The Scanning Tunneling Microscope (STM) uses quantum tunneling to view surfaces, achieving higher resolutions than electron microscopes. It operates in various environments but requires a clean surface and sharp tip. Carbon nanotubes are being explored as tips. The STM is driven by a piezoelectric crystal and requires advanced vibration damping. A high school student created a crude one using $100 worth of materials.
A tunneling microscope (STM) is an innovative type of microscope that, instead of using reflecting light like conventional light microscopes, uses quantum tunneling between a sample and a probe tip to view the surface. The resolutions obtained from an STM can reach a lateral resolution of 0.1 nm and a depth resolution of 0.01 nm. This is several times higher than the resolutions achievable using the best electron microscopes.
An STM can operate in a variety of environments: in addition to ultra-high vacuum, it also operates in environments saturated with water, air, etc. This makes the microscope very flexible. However, the surface must be very clean and the STM tip very sharp, causing practical problems in imaging. The STM was developed by Gerd Binnig and Heinrich Rohrer in 1981. In 1986 they won a Nobel Prize in Physics for their work on STDs.
An STM tip is so sharp that it consists of only one atom. When the tip is ‘blunt’ and consists of two atoms instead of one, this leads to blurrier images. The challenge of making tips sharp enough has led researchers to explore the use of carbon nanotubes as STM tips, as they are very stiff and easy to manufacture. The tip is sometimes called a “stylus,” and a platinum-iridium combination is among the most commonly used tip materials.
Like many other microscopes, advanced vibration damping is often required to create a useful STM. Magnetic levitation schemes were used in early systems, although spring-loaded systems are the most popular today. Shortly after STMs entered the public domain, a high school student was able to create a crude one using only about $100 US dollars (USD) worth of materials. An oscilloscope was used as the imaging screen.
The tip of an STM is driven by a “piezo,” or piezoelectric crystal, which bends in small but very predictable ways in response to an electric field. In an STM, the movement of the tip is completely computer controlled.
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