Question

To produce high-resolution images, Transmission Electron Microscope uses a high-energy electron beam of typically:

• A. \( 5000 - 10000 \text{ V} \)
• B. \( 1000 - 300 kV \)
• C. \( 50 - 80 \text{ kV} \)
• D. \( 200 - 1000 \text{ kV} \)

Hint:

Remember that high resolution requires fast electrons with high energy. Standard laboratory high-resolution TEMs universally use an accelerating potential sweet-spot of \( 100 \text{ to } 300 \text{ kV} \).

Answer 1

The Correct Option is B

Concept: The resolution limit of a microscope is fundamentally governed by the wavelength of the illumination source used. Transmission Electron Microscopes (TEM) achieve atomic-level imaging resolution by accelerating an electron beam to extreme velocities, which dramatically shrinks the relativistic de Broglie wavelength of the electrons.

Step 1: Examining the wavelength relationship.
The de Broglie wavelength (\( \lambda \)) of an electron accelerated through an electrical potential difference \( V \) can be modeled (ignoring relativistic corrections for simplicity) as: \[ \lambda \approx \frac{1.22}{\sqrt{V}} \text{ nm} \] As the accelerating voltage (\( V \)) increases into the kilovolt (\( \text{kV} \)) range, the wavelength shrinks to less than a few picometers (\( 10^{-12} \text{ m} \)), allowing the microscope to resolve atomic lattices.

Step 2: Matching standard TEM operational energy ranges.
For standard high-performance Transmission Electron Microscopes tasked with penetrating thin sample slices to generate high-resolution sub-nanometer images, the conventional accelerating voltage range used across standard laboratory instruments sits firmly between \( 100 \text{ kV} \) and \( 300 \text{ kV} \) (e.g., common commercial models run at \( 80 \text{ kV}, 120 \text{ kV}, 200 \text{ kV}, \text{ or } 300 \text{ kV} \)).
• Voltages lower than \( 100 \text{ kV} \) lack sufficient specimen penetration capability for high resolution.
• Voltages higher than \( 300 \text{ kV} \) (like \( 400 - 1000 \text{ kV} \)) represent specialized ultra-high voltage instruments that can easily introduce severe radiation beam-damage to biological specimens. Thus, the typical range is \( 100 - 300 \text{ kV} \), corresponding to Option (B).