Understanding the Working of Scanning Tunneling Microscope (STM).
                     Understanding the 
Working of Scanning 
Tunneling Microscope 
(STM)
SCANNING TUNNELING 
MICROSCOPY
• The development of the family of 
scanning probe microscopes started 
with the original invention of the STM in 
1981. 
• Gerd Binnig and Heinrich Rohrer 
developed the first working STM while 
working at IBM Zurich Research 
Laboratories in Switzerland. 
• This instrument would later win Binnig 
and Rohrer the Nobel prize in physics in 
1986.
Source: www.nanoscience.com
THE QUANTUM CORRAL
• The STM shows the direction of 
standing-wave patterns in the local 
density of states of the Cu(111) surface. 
• These spatial oscillations are quantum-
mechanical interference patterns caused 
by scattering of the two-dimensional 
electron gas off the Fe atoms and point 
defects.
Source: www.nanoscience.com
HOW AN STM WORKS?
• The scanning tunneling microscope 
(STM) works by scanning a very sharp 
metal wire tip over a surface. 
• By bringing the tip very close to the 
surface, and by applying an electrical 
voltage to the tip or sample, we can 
image the surface at an extremely small 
scale down to resolving individual 
atoms.
Source: www.nanoscience.com
OPERATING PRINCIPLES
• The STM is based on several principles. 
One is the quantum mechanical effect of 
tunneling. It is this effect that allows us 
to “see” the surface. 
• Another principle is the piezoelectric 
effect. It is this effect that allows us to 
precisely scan the tip with angstrom-
level control. 
Source: www.nanoscience.com
PRINCIPLES CONT.
• Lastly, a feedback loop is required, 
which monitors the tunneling current 
and coordinates the current and the 
positioning of the tip.
Source: www.nanoscience.com
TUNNELING
• Tunneling is a quantum mechanical 
effect. A tunneling current occurs when 
electrons move through a barrier that 
they classically shouldn’t be able to 
move through. In classical terms, if you 
don’t have enough energy to move 
“over” a barrier, you won’t.
Source: www.nanoscience.com
PIEZOELECTRIC EFFECT
• The piezoelectric effect was discovered 
by Pierre Curie in 1880. The effect is 
created by squeezing the sides of 
certain crystals, such as quartz or 
barium titanate. 
• These materials are used to scan the tip 
in an scanning tunneling microscopy 
(STM) and most other scanning probe 
techniques. 
• A typical piezoelectric material used in 
scanning probe microscopy is PZT (lead 
zirconium titanate).
Source: www.nanoscience.com
FEEDBACK LOOP
• Electronics are needed to measure the 
current, scan the tip, and translate this 
information into a form that we can use 
for STM imaging. 
• A feedback loop constantly monitors the 
tunneling current and makes 
adjustments to the tip to maintain a 
constant tunneling current.
Source: www.nanoscience.com
APPLICATIONS
• The STM is used primarily for imaging, 
but there are many other modalities 
that have been explored. 
• The strong electric field between tip and 
sample has been utilized to move atoms 
along the sample surface.
Source: www.britannica.com
RESOLUTION
• An STM can have a lateral resolution of 
up to 0.1nm, and a depth resolution of 
up to 0.01nm, which combined is small 
enough to resolve individual atoms. 
• In recent years, carbon nanotubes have 
been used for constructing these tips, 
allowing for improved resolution and 
reduced error in image reconstruction.
Source: www.azonano.com