Wednesday, January 2, 2019

Scanning Tunneling Microscopy (STM)

Scanning Tunneling Microscopy (STM)

1986 Nobel Prize in Physics: Drs. GerdBinning and Heinrich Rohrer (IBM Zurich) Invention of the STM /Scanning Probe Microscopy
Quantum tunneling

Quantum tunneling
In quantum mechanics, an electron has a non-zero probability of tunneling through a potential barrier

Principle of STM

1. When a conducting tip is very close to a conducting/semiconducting surface and a  bias voltage is applied, there will be a tunneling current flowing between the tip and the surface


2. The tunneling current (~pAnA) is a strong function of the gap between the tip and the surface


3. If the tunneling current is monitored and maintained constant by adjusting the gap, the elevation of the surface can be traced



4. The surface morphology in atomic resolution can be obtained by x-yscan

Very Sharp Tungsten Tip

Drop-off Method


•Electrochemical etching method 
•Average radius curvature < 50nm

Piezoelectric Scanner
Piezoelectric effect


Inverse piezoelectric effect



STM Imaging


Atomic resolution (0.1nm)

Scanning Tunneling Spectroscopy (STS)

By ramping the bias voltage, or distance of the tip from surface, the current signal can reveal the local electronic character of the substrate.
•Conductivity •Bandgap 
•Work function 
•Density of State


Manipulation of Atoms

\manipulation

Atomic Force Microscopy (AFM)




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