Read the following text and answer the following questions on the basis of the same:
Electron Microscope
Electron microscopes use electrons to illuminate a sample. In Transmission Electron Microscopy (TEM), electrons pass through the sample and illuminate film or a digital camera. Resolution in microscopy is limited to about half of the wavelength of the illumination source used to image the sample. Using visible light the best resolution that can be achieved by microscopes is about `-200nm`. Louis de Broglie showed that every particle or matter propagates like a wave. The wavelength of propagating electrons at a given accelerating voltage can be determined by
`l= (h)/(sqrt(2m_(e )v))`. Thus the wavelength of electrons is calculated to be 3.88pm when the microscope is operated at 100keV, 2.74pm at 200keV and 2.24pm at 300keV. However, because the velocities of electrons in an electron microscope reach about 70% the speed of light with an accelerating voltage of 200keV, there are relativistic effects on these electrons. Due to this effect, the wavelength at 100keV, 200keV and 300keV in electron microscopes is 3.70pm, 2.51 pm and 1.96pm, respectively. Anyhow, the wavelength of electrons is much smaller than that of photons (2.5pm at 200keV). Thus if electron wave is used to illuminate the sample, the resolution of an electron microscope theoretically becomes unlimited. Practically, the resolution is limited to `~-0.1`nm due to the objective lens system in electron microscopes. Thus, electron microscopy can resolve subcellular structures that could not be visualized using standard fluorescences microscopy.
In electorn microscope, electron is used

Options

A. to charge the sample
B. to clean the sample
C. to illuminate the sample
D. All of the above

Explanation

**Step-by-Step Solution:**

1. **Understanding the Function of Electron Microscopes:**
- Electron microscopes utilize electrons instead of visible light to illuminate samples. This allows for much higher resolution imaging compared to traditional light microscopes.

2. **Identifying the Type of Microscopy:**
- The specific type of electron microscopy discussed is Transmission Electron Microscopy (TEM). In TEM, electrons pass through the sample and create an image on film or a digital camera.

3. **Resolution Limitations:**
- The resolution in microscopy is fundamentally limited to about half of the wavelength of the illumination source. For visible light, the best resolution achievable is approximately 200 nm.

4. **De Broglie's Hypothesis:**
- Louis de Broglie proposed that particles, including electrons, exhibit wave-like properties. This means that electrons can be treated as waves when used in microscopy.

5. **Calculating Wavelengths:**
- The wavelength of electrons can be calculated using the formula \( \lambda = \frac{h}{\sqrt{2m_e v}} \), where \( h \) is Planck's constant, \( m_e \) is the mass of the electron, and \( v \) is the velocity of the electron. The text provides specific wavelengths for electrons at different accelerating voltages (100 keV, 200 keV, and 300 keV).

6. **Relativistic Effects:**
- At high accelerating voltages (like 200 keV), electrons reach speeds close to the speed of light, which introduces relativistic effects that alter their wavelengths.

7. **Comparing Wavelengths:**
- The wavelengths of electrons at the specified voltages are much smaller than those of photons. For example, at 200 keV, the wavelength of electrons is significantly smaller than that of photons (2.5 pm).

8. **Theoretical vs. Practical Resolution:**
- Theoretically, using electron waves allows for unlimited resolution. However, practical limitations due to the objective lens system in electron microscopes restrict the resolution to about 0.1 nm.

9. **Final Answer to the Question:**
- The question asks what electrons are used for in an electron microscope. Based on the information provided, the correct answer is that electrons are used to illuminate the sample.

**Final Answer:**
In an electron microscope, electrons are used to illuminate the sample.

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