Question

How to install stm microscopes and what are their internal setups?

Answer 1

In 1986, Gerd Binnig and Heinrich Rohrer won the Nobel Prize for the development of the scanning tunneling microscope, or STM for short. This new technology pushed the resolution possible down to the range of
angstroms.

STM Design and Construction

The construction of our STM consisted of three major parts: the physical body of the STM, the scanning tip, and the electronics.

• STM BODY

To build the body of the scanning tunneling microscope, we cut two equally sized pieces of metal which would act as the top and bottom of our microscope. To
install the micrometer screws we drilled three holes into the piece of metal that would be acting as the top of the microscope. We placed the micrometer screws
such that two holes were placed in the front in each corner an inch from each side of the metal and one in the middle back. After drilling these holes in the top
of the microscope, the metal was then realigned with the bottom part and we drilled little divots which act as holders for the micrometer screws. To build the arm
crystal beads were glued to the brass cube using very strong non-conductive glue and then the piezo controllers to the crystal beads are glued.

• SCANNING TIP

The most essential part in STM is the tip. The substance used for our tips was tungsten. Tungsten is commonly used because it is quite simple to create extreme sharp tips by only doing a single
etching process, and uses fairly mild chemicals. A drawback is that tungsten is vulnerable to oxidation. The chemicals that are most commonly used
are potassium hydroxide (KOH) or sodium hydroxide (NaOH).

The chemical reaction that occurs is as follows:
Cathode: 6H2O+6e-  3H2(g) +6OH-
Anode: W(s) + 8OH-  WO2-4 + 4H2O + 6e-
Total Reaction: W(s) + 2OH- +2H2O  WO2-4 +3H2(g)

• ELECTRONICS

​​​​​​​The current source put out a constant current which was determined by a specific resistor
in the circuit. This was then fed through an ammeter and finally to the pre-amp. The current input to the pre-amp and voltage output from the pre-amp could
both be read and compared. This was done for several currents from the mA range down to the 0.1 μA range. From here, the current could no longer be reliably
read by the ammeter. However, different resistors were used in the current source to create still smaller currents and the behavior of the pre-amp output
continued to change as expected although the actual input current could not be read.
Once the pre-amp was fully tested and its behavior seemed satisfactory, the final circuit was built.