Dr. Ayat Bozeya 2023/2024: Nanometric Crystal Structures Quiz
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Questions and Answers

What is the significance of 'magic numbers' in nanometric crystals?

  • They represent clusters with higher stability than others. (correct)
  • They correspond to clusters with lower stability.
  • They are irrelevant in the study of nanometric crystals.
  • They indicate clusters with a random number of atoms.

    • What is the general trend regarding the binding energy (Eb) in a given structure?

  • It is directly proportional to the surface area of the crystal.
  • It can be estimated based on the packing of spheres into certain shapes. (correct)
  • It decreases with an increase in the number of atoms.
  • It grows linearly with the size of the crystal.

    • Why should a structure minimize its surface contribution when considering surface and volume contributions?

  • To decrease the volume contribution.
  • To increase the linear growth of the volume energy.
  • To achieve a spherical shape similar to an icosahedron. (correct)
  • To increase stress within the structure.

    • What happens to the volume contribution compared to the surface energy as the size of a nanocluster grows?

    <p>Volume contribution increases faster than surface energy.</p> Signup and view all the answers

    What kind of nanoclusters are likely to become abundant based on their evaporation rates or binding energies?

    <p>Clusters with low evaporation rates or strong binding energies.</p> Signup and view all the answers

    Which sizes are more abundant among nanoclusters according to the text?

    <p>$N=8, 20, 40, 58, 92$</p> Signup and view all the answers

    What determines the stability, reactivity, and electronic properties of atoms?

    <p>Energy gap between the highest occupied and lowest unoccupied orbital</p> Signup and view all the answers

    What is the minimum number of atoms required for icosahedral structures with fivefold symmetry to appear in clusters?

    <p>13 atoms</p> Signup and view all the answers

    In clusters of atoms, where are the electrons distributed?

    <p>Along the bonds formed by the atoms</p> Signup and view all the answers

    What defines whether a crystal is semiconducting or insulating?

    <p>Overlap between discrete energy levels</p> Signup and view all the answers

    Which metal clusters exhibit fivefold symmetry even in clusters with as few as 6 atoms?

    <p>Gold (Au)</p> Signup and view all the answers

    What type of bonding arises when electrons are delocalized and energy gaps at the Fermi level disappear?

    <p>Metallic bonding</p> Signup and view all the answers

    What is unique about gold clusters compared to other coinage group metals?

    <p>They are chemically inert</p> Signup and view all the answers

    At what number of atoms do Au clusters assume a cage structure according to Dr. Bozeya?

    <p>14–18 atoms</p> Signup and view all the answers

    Which model for a cluster assumes uniform distribution of positive charge and electronic shells for valence electrons?

    <p>Jellium model</p> Signup and view all the answers

    What type of functions are the wave functions of electrons in a spherical potential well according to the text?

    <p><em>Bessel Functions</em></p> Signup and view all the answers

    What is the distinctive feature of Au20 cluster structure?

    <p>(111) surface mimicry</p> Signup and view all the answers

    What effect is attributed to the sharp departure of Au cluster geometries from other monovalent simple metal atoms?

    <p>Relativistic effects on electronic structure</p> Signup and view all the answers

    What type of structure is formed by Au clusters containing 14–18 atoms?

    <p>Hollow cage structures</p> Signup and view all the answers

    What structure do Al clusters show during growth?

    <p>Icosahedric growth</p> Signup and view all the answers

    At what size do Au clusters switch from a planar structure to a hollow cage structure?

    <p>20 atoms</p> Signup and view all the answers

    How do the properties of Al clusters compare to those of Au clusters?

    <p>Al clusters exhibit icosahedric growth, while Au clusters show pyramidal growth</p> Signup and view all the answers

    When does the Si crystal structure mimic the cage structures discussed?

    <p>Around 70 atoms</p> Signup and view all the answers

    What is a common characteristic of heteroatomic clusters involving two metals like Au and Al?

    <p>Behaving as simple metals</p> Signup and view all the answers

    What is the total spin angular momentum, S, for an individual iron atom?

    <p>3/2</p> Signup and view all the answers

    What is the typical material size for the ferromagnetic to para-magnet phase transition to occur in nanocrystals?

    <p>3-50 nm</p> Signup and view all the answers

    What happens to the ferromagnetic material when its size is reduced significantly?

    <p>It becomes paramagnetic</p> Signup and view all the answers

    What is the valence electron configuration of iron in the bcc structure?

    <p>3d^7 4s^1</p> Signup and view all the answers

    What happens to the spin moments of neighboring atoms in the bcc structure of iron metal?

    <p>All of the above</p> Signup and view all the answers

    Which of the following materials are used to create monodisperse semiconductor nanocrystals?

    <p>Sufides and Selenides of cadmium</p> Signup and view all the answers

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