The Scanning Tunneling Microscope (STM)

The advantages of Atomic Resolution


A scanning tunneling microscope, or STM, is a microscope commonly used in fundamental and industrial research.

Invented in 1981 by Gerd Binnig and Heinrich Rohrer from IBM's Zurich Research Center in Switzerland, it helped them win the 1986 Nobel Prize in Physics.





High-End Resolution

For an STM, good resolution is 0.1 nm lateral resolution and 0.01 nm depth resolution.

The high resolution of STMs enable researchers to examine surfaces at an atomic level.

The microscopes help scientists get a picture of how the atoms are arranged on a surface, by looking at the electron density of the surface atoms.


Quantum Tunneling

STMs are based on the idea of quantum tunneling, when a conducting tip is brought very close to the surface and a voltage difference between the tip and the surface is applied.

When the voltage difference is applied, electrons can tunnel through the vacuum between the tip and the surface, causing a tunneling current.

Using this principle, STMs work by passing a sharp wire made of metal over the surface that is to be examined.

The tip passes very close to the surface at the same time that the microscope applies an electrical voltage to the tip.

This creates an image that shows miniscule details on an atomic level.


Further Developments

There are several other microscopy techniques that researchers have developed based on the principles used for STMs.

These include:


STM Advantages

STMs are helpful because they can give researchers a three dimensional profile of a surface, which allows researchers to examine a multitude of characteristics, including roughness, surface defects and determining things about the molecules such as size and conformation.

Other advantages of the scanning tunneling microscope include:

  • It is capable of capturing much more detail than lesser microscopes. This helps researchers better understand the subject of their research on a molecular level.
  • STMs are also versatile. They can be used in ultra high vacuum, air, water and other liquids and gasses.
  • They will operate in temperatures as low as zero Kelvin up to a few hundred degrees Celsius.




STM Disadvantages

There are very few disadvantages to using a scanning tunneling microscope.

The two major downsides to using STMs are:

  • STMs can be difficult to use effectively. There is a very specific technique that requires a lot of skill and precision. STMs require very stable and clean surfaces, excellent vibration control and sharp tips.
  • STMs use highly specialized equipment that is fragile and expensive.


Price

The electronics required for an STM are extremely sophisticated as well as very expensive.

Low cost and relatively low quality STMs start at approximately $8,000 but some people have actually built their own amateur STMs for much less than that amount.

However, professional quality STMs can range anywhere from $30,000 to $150,000 depending on the manufacturer and the extra parts included.


Manufacturers

If you are interested in buying a scanning tunneling microscope, there are several reputable manufacturers from which you can make a purchase.

STM manufacturers include:

  • Nanosurf is a company that specializes in manufacturing both AFM and STMs. The company's primary STM is called the Nanosurf easyScan 2 STM. You can also buy upgrades and customize this STM to your specific needs.
  • RHK Technology is another major manufacturer of scanning probe microscopes, including STMs. RHK Technology was founded in 1981 and has since become a leader in SPM manufacturing.


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