Question

Which statement is true for Scanning Tunneling Microscopy:

• A. Tunneling current between the surface and the probe
• B. Alternating current between the surface and the probe
• C. The electromagnetic radiation between the surface and the probe
• D. Direct current between the surface and the probe

Hint:

For STM, the keyword is "tunneling." Both its underlying principle and the quantity it measures are directly related to this quantum effect. STM measures the tunneling current.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
This question asks about the physical quantity that is measured or utilized to generate an image in a Scanning Tunneling Microscope (STM).
Step 2: Detailed Explanation:
As explained in the previous question, the STM operates based on the quantum tunneling of electrons between a sharp probe (tip) and the sample surface. This net flow of electrons across the vacuum gap forms an electrical current. This specific current is called the tunneling current.
The magnitude of the tunneling current is exponentially dependent on the distance between the tip and the surface. The STM's feedback loop maintains this current at a constant value by adjusting the tip's height, or it measures the variation in current at a constant height. In either mode, it is the tunneling current that provides the information about the surface's topography and electronic properties.
Options (B), (C), and (D) are incorrect. While the tunneling current is a type of direct current, the term "Tunneling current" is the most precise and correct description of the phenomenon being measured.
Step 3: Final Answer:
The operation of an STM is based on measuring the tunneling current that flows between the surface and the probe.