Explain the differences between chiral zig-zag and armchair

Question

Question 1.

Explain, giving five detailed examples, why nanomaterials are currently important in industry. Describe how you would synthesise three of these nanomaterials and how each could be used in specific applications.

Question 2.

Explain the differences between chiral, zig-zag and armchair carbon nanotubes. How may these structures be described mathematically? What are the predicted electronic properties of (10, 0), (21, -3) and (8, 8) SWNTs?

Question 3.

Discuss the role of defects in influencing the structural properties of carbon nanotubes and how these may be investigated experimentally. What would you expect the band structure of a junction between a (7, 1) and a (8, 0) SWNT to look like?

Question 4.

Using the data given in the accompanying screens for copper and silver, compare the behaviour you would expect for fine dispersions of those metals in Perspex (PMMA) which has a mean refractive index in the visible spectrum of 1.5. How would you expect this to change if the Perspex was replaced by photo resist that has refractive index of 1.7?

Question 5.

Give a detailed explanation, referring to theory where necessary, of the analogy between periodic atomic scale structures (think in terms of Bragg scattering behaviour) and photonic crystals. There are one-dimensional, two-dimensional and three dimensional photonic crystals. Can you think of analagous structures formed by atomic scale materials ?

Question 6.

Assess the effective band-gaps for cubic shaped quantum dots of side 5nm that you would expect for the following semiconductors using the infinite well approximation:

In₂S₃ band gap 1.1eV, m_e = 0.2 m_o, m_h = 1.0 m_o, ε = 6.5ε_o

CdP₂ band gap 1.6eV, m_e = 0.03 m_o, m_h = 0.3 m_o, ε = 12ε_o

ZnO band gap 3.27eV, m_e = 0.24 m_o, m_h = 0.6 m_o, ε = 3.7ε_o

Where m_o is the free electron mass.

Repeat using the Brus formula, and comment on the differences.

Discuss the suitability of these for:

- Application in solar cells as the absorber or the conducting electrode.

- Applications in displays.

Question 7.

The silver particles are now converted to silver sulphide. Estimate the Plasmon frequency of silver sulphide (density of 7300 kgm^-3) assuming that it is a free electron-like semiconductor.

Silver sulphide has a band gap of 0.85eV and a further optical transition at 1200nm. Above this energy the dielectric permittivity varies as:

ε(ω)=1- ωp2ω²

Estimate the absorption energy you would expect for the interface Plasmon energy of silver sulphide embedded in PMMA.

Question 8.

The data below is for silver particles embedded in different dielectrics.

Give a brief explanation of this behaviour. You will need to look up values of the dielectric permittivity for these materials.

Measured optical absorption spectra of 2nm silver clusters embedded in various oxidic embedding materials. For comparison a spectrum of free clusters is added.

Answer 1

In regards of the nano-materials, submit a paper in which you have to answer the following questions in an essay format as per the requisite of the problem. Q1. Describe, giving five thorough illustrations, why nano-materials are presently significant in industry. Illustrate how you would synthesize three of such nano-materials and how each could be employed in particular applications. Q2. Describe the differences between the chiral, zig-zag and armchair carbon nano-tubes. Illustrate how might such structures be explained mathematically? Illustrate what are the predicted electronic properties of (10, 0), (21, -3) and (8, 8) SWNTs? Q3. Illustrate the role of defects in affecting the structural properties of carbon nano-tubes and how such might be investigated experimentally. Explain what would you expect the band structure of a junction between a (7, 1) and a (8, 0) SWNT to look similar to?