Nanotechnology – Important Questions & Answers

1. List any two differences between SEM and TEM.
   SEM: Scans the surface of a sample with electrons to produce a 3D surface image; operates in a lower vacuum.
   TEM: Electrons pass through a thin sample to form a 2D internal structure image; requires a higher vacuum.
2. Name any two Bottom-up fabrication methods of nanomaterials.
   Sol–Gel method.
   Chemical Vapor Deposition (CVD).
3. What is quantum confinement effect?
   Quantum confinement occurs when the size of a material is reduced to the nanoscale, restricting electron motion and leading to discrete energy levels, thereby altering optical and electrical properties.
4. What is the meaning of CVD?
   CVD stands for Chemical Vapor Deposition, a process used to deposit thin films by reacting gaseous precursors on a heated substrate.
5. Sol–Gel method belongs to which approach?
   The Sol–Gel method belongs to the Bottom-up approach.
6. Distinguish 1-D, 2-D, and 3-D nanomaterials.
   1-D: Confined in two dimensions (nanowires, nanotubes).
   2-D: Confined in one dimension (graphene, thin films).
   3-D: Nanoscale in all dimensions (nanoparticles, quantum dots).
7. Why do nanomaterials show different properties than bulk materials?
   Due to high surface area-to-volume ratio and quantum confinement effects at the nanoscale.
8. Mention the importance of quantum confinement at nanoscale.
   It leads to discrete energy levels and tunable optical and electrical properties, essential for nanoelectronics and optoelectronic devices.
9. What are nanomaterials?
   Nanomaterials are materials with at least one dimension in the range of 1–100 nm, exhibiting unique size-dependent properties.
10. Find the condition for Bragg’s law.
    a) \( n\lambda = 2d \cos 2\theta \)   b) \( n\lambda = 2d \sin 2\theta \)   c) \( n\lambda = 2d \cos \theta \)   d) \( n\lambda = 2d \sin \theta \)
    Correct Answer: d) \( n\lambda = 2d \sin \theta \)
11. Write any two advantages of SEM and TEM.
    SEM: Detailed surface imaging, easier sample preparation.
    TEM: Atomic-scale resolution, internal structure analysis.
12. What is X-ray diffraction? Why does it happen?
    X-ray diffraction is the scattering of X-rays by atoms in a crystal. It occurs because X-ray wavelengths are comparable to interatomic spacing, producing constructive interference.
13. Does interatomic distance change at nanoscale?
    Yes, slight changes occur due to surface effects, lattice strain, and quantum confinement.
14. Which two factors change material properties at nanoscale?
    High surface area-to-volume ratio and quantum confinement effects.
15. Write any four properties of nanomaterials.
    Enhanced electrical conductivity, tunable optical properties, increased chemical reactivity, and improved mechanical strength.
16. Why are X-rays not deflected by electric and magnetic fields?
    X-rays are electromagnetic waves with no electric charge, hence they are not deflected by electric or magnetic fields.