Nanomaterials Knowledge-Based Download PDF

Questions

1. 1.

   How does the melting temperature of a metallic nanoparticle change as its particle size decreases below approximately 10 nm, and what thermodynamic factor is primarily responsible for this behavior?

   • A) It increases significantly because the higher surface curvature compresses the crystal core, increasing overall lattice cohesive energy.
   • B) It remains constant because melting point is an intensive thermodynamic property that is fundamentally independent of physical dimensions.
   • C) It increases moderately because enhanced surface tension prevents thermal vibrations from disrupting atomic positions at the boundary.
   • D) It decreases significantly because a large fraction of surface atoms possess lower coordination numbers, reducing the average cohesive energy per atom.
2. 2.

   What physical phenomenon is primarily responsible for the intense, size-dependent optical absorption bands and distinctive vibrant colors exhibited by colloidal suspensions of gold and silver nanoparticles?

   • A) Electron-hole radiative recombination across a widened semiconductor band gap
   • B) Superparamagnetic relaxation caused by thermal fluctuations of magnetic domains
   • C) Raman vibrational scattering enhanced by acoustic phonon confinement
   • D) Localized surface plasmon resonance resulting from collective oscillations of conduction electrons
3. 3.

   In carbon-based nanotechnology, how is the structure of a single-walled carbon nanotube (SWCNT) fundamentally related to graphene?

   • A) An SWCNT is formed by rolling an $sp^3$-hybridized diamond framework into a hollow cylinder.
   • B) An SWCNT is structurally equivalent to a seamless cylinder formed by rolling a single two-dimensional sheet of $sp^2$-hybridized graphene.
   • C) An SWCNT is composed of linear chains of $sp$-hybridized carbon atoms linked by alternating triple bonds.
   • D) An SWCNT is formed by the concentric nesting of spherical fullerene cages along a central axis.
4. 4.

   When the diameter of a semiconductor nanoparticle (quantum dot) is progressively decreased within the quantum confinement regime, how do its electronic band gap and emission wavelength change?

   • A) The band gap decreases, leading to a red shift (longer wavelength) of the emitted light.
   • B) The band gap remains constant, while the emission wavelength decreases due to increased surface scattering.
   • C) The band gap decreases, resulting in a blue shift (shorter wavelength) of the emitted light.
   • D) The band gap increases, leading to a blue shift (shorter wavelength) of the emitted light.
5. 5.

   Which of the following factors primarily accounts for the significantly enhanced catalytic activity of gold nanoparticles compared to chemically inert bulk gold?

   • A) A decrease in the ratio of surface atoms to interior atoms
   • B) A marked increase in the surface-area-to-volume ratio that exposes a high fraction of coordinatively unsaturated surface atoms
   • C) The complete loss of metallic bonding within the crystalline lattice of the nanoparticles
   • D) An increase in the average coordination number of atoms situated at the edges and corners