Question

The EDX (Energy-Dispersive X-ray) detector used with SEM/TEM provides

• A. Phase contrast images
• B. Diffraction data
• C. Elemental composition via characteristic X-rays
• D. High-temperature imaging

Hint:

Remember:
- EDX/EDS \(\rightarrow\) Elemental composition (uses characteristic X-rays).
- EBSD \(\rightarrow\) Crystallographic orientation and texture (uses electron backscatter diffraction).
- SE (Secondary Electrons) \(\rightarrow\) Topographical surface imaging.
- BSE (Backscattered Electrons) \(\rightarrow\) Atomic number contrast imaging.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
This question asks for the primary function and physical mechanism of the Energy-Dispersive X-ray (EDX or EDS) detector when integrated with a Scanning Electron Microscope (SEM) or Transmission Electron Microscope (TEM).

Step 2: Key Formula or Approach:
The EDX technique is based on Moseley's Law:
\[ \nu = a(Z - \sigma)^2 \]
where:
\( \nu \) is the frequency of the emitted characteristic X-ray.
\( Z \) is the atomic number of the emitting element.
\( a \) and \( \sigma \) are constants.
This law establishes that each element in the periodic table has a unique electronic shell configuration and thus emits X-rays of highly specific, characteristic energies when excited.

Step 3: Detailed Explanation:

• Physical Mechanism of EDX:
- A focused high-energy electron beam hits the sample.
- This beam has enough energy to knock out an inner-shell electron (e.g., from the K or L shell) of an atom, leaving a vacant position.
- An electron from an outer, higher-energy shell drops down to fill this vacancy.
- The difference in energy between the two states is released in the form of an X-ray photon.
- The EDX detector measures the energy and count of these emitted X-rays.

• Elemental Analysis:
- By plotting the intensity of X-ray counts vs. energy, the system generates a spectrum with peaks that identify which elements are present (qualitative) and in what concentrations (quantitative).
- Phase contrast images are obtained by TEM or specific SEM detectors.
- Diffraction data is obtained by EBSD or TEM diffraction patterns.


Step 4: Final Answer:
The EDX detector provides the elemental composition of a sample by capturing and measuring characteristic X-rays.
Therefore, the correct choice is option (C).