代做CHEM20018 Intermolecular Forces and Materials Chemistry Week 12代写C/C++语言

Tutorial Week 12 20018, 2025.

Intermolecular Forces and Materials Chemistry.

1.  Rationalise the fact that sodium, magnesium, and aluminium are metals but silicon is a metalloid/semiconductor, based on the schematic 3s and 3p band structure shown below:

Atomic  ---------->   Material

 

2.  The following lists the apparent colour of single crystals of a variety of

materials. Decide if they are metals, semiconductors, or insulators. For the semiconductors, estimate the band gap in nm and in eV.

(conversion factor eV = 1240/nm)

HgS: Red

Magnetite: Black

Cadmium sulfide: Yellow

ZnO: Colourless.

3. (a) Pure semiconductors can never be green in colour. Explain this.

(b) Why can plants, however, be green?

(c) How could you explain the green colour of the mineral emerald? (Hint: emerald consists of an insulator, Beryl, doped with chromium)

4.  Which of the following materials would be n-type and which would be p- type? (a) As in Ge, (b) B in Si (c) In in Ge

5.  (a) Describe the major ways that energy is lost or stored when a

semiconductor crystal is irradiated with above-band gap radiation. A drawing is best. What happens to the photon energy that hits a metal?

6.  a) Zinc Oxide has a band gap of 368 nm (3.37 eV). How would you make it into a transparent metal? What would be a suitable dopant?

(b) Estimate the conductivity of n-doped ZnO at 298K if:

Mobility of conduction band electrons, µe = 166 cm2. V-1.s-1 the dopant concentration, ndopant = 2 x 1018 cm-3

7.  For metals and semiconductors, draw a diagram and indicate the following energy levels: band gap, conduction band edge, valence band edge, work function, ionisation potential, Fermi level and electron affinity.

8.  Explain why there is an optimal band gap for solar cell materials in terms of the power produced, P=VI (power = volts x current)