Nanomaterials Knowledge-Based Practice

Questions

1. 1.

   The striking optical absorption observed in colloidal gold and silver nanoparticles arises from the collective oscillation of their conduction-band electrons in resonance with incident electromagnetic radiation. What is this characteristic physical phenomenon termed?

   • A) Quantum size confinement
   • B) Rayleigh backscattering
   • C) Localized surface plasmon resonance
   • D) Magneto-optical Kerr effect
2. 2.

   When the physical dimensions of a semiconductor crystal decrease below its exciton Bohr radius, its effective bandgap energy widens, causing a blue shift in optical absorption and emission spectra. Which phenomenon is primarily responsible for this size-dependent electronic behavior?

   • A) Localized surface plasmon resonance
   • B) Quantum confinement effect
   • C) Superparamagnetic relaxation
   • D) Ostwald ripening
3. 3.

   Which method of nanomaterial synthesis represents a bottom-up approach that builds nanostructures from atomic or molecular precursors?

   • A) High-energy ball milling of bulk metallic powders
   • B) Chemical vapor deposition of carbon precursors onto a substrate
   • C) Laser ablation of a macroscopic solid target
   • D) Mechanical attrition and ultra-fine crushing of coarse grains
4. 4.

   Gold in bulk form is chemically inert, yet gold nanoparticles with diameters below 5 nm exhibit notable catalytic activity for various chemical reactions. What fundamental physical change at the nanoscale primarily accounts for this emergence of catalytic activity?

   • A) An increase in the surface-to-volume ratio that greatly elevates the proportion of coordinatively unsaturated surface atoms
   • B) A substantial increase in the melting point that thermally stabilizes reactive transition states
   • C) A marked increase in the density of the crystal lattice that prevents reactant diffusion into the interior
   • D) A complete transition from metallic bonding to ionic bonding between neighboring gold atoms
5. 5.

   Carbon nanotubes have two dimensions confined to the nanoscale (1–100 nm), allowing electrons to propagate freely along only one dimension. According to the dimensional classification of nanomaterials, into which category are carbon nanotubes classified?

   • A) Zero-dimensional (0D) nanomaterials
   • B) Two-dimensional (2D) nanomaterials
   • C) One-dimensional (1D) nanomaterials
   • D) Three-dimensional (3D) nanomaterials

Answers and step-by-step solutions appear after you finish the test.