Chapter 1 - Carbon Nanoscience

Question 1

Name 3D, 2D, 1D and 0D forms of carbon.

Answer 1

3D: graphite, diamond
2D: graphene
1D: carbon nanotubes
0D: fullerenes

Question 2

What is the electron configuration in carbon, and what is sp3 and sp2-hybridization of orbitals?

Answer 2

C: 1s^2 2s^2 2p^2

sp3 hybridization is when the 3 2p-orbitals and the 2s-orbital combine to form sp3-hybrid orbitals.

sp2 hybdriziation is when 2 2p-orbitals and the 2s-orbital combine to form sp2 hybrid orbitals.

This happens because s and p orbitals are close in energy, and that this sometimes can be energetically favorable.

Question 3

What are conjugated molecules?

Answer 3

They are molecules where the p_z-orbitals experience strong overlap, and the electrons therefore are strongly delocalized.

Question 4

What are conjugated molecules useful for?

Answer 4

• tuneable optical transitions

- charge transport materials

Question 5

What are acenes?

Answer 5

Acenes are sp2-hybridized carbon ringstructures with n number of rings. n = 1 yields benzene.

Question 6

How does the optical gap of acenes depend upon the number of rings? Why?

Answer 6

The more rings, the lower the optical gap. This is because the more rings you have, the more delocalized the π-system is.

Question 7

What provide the curvature of the fullerenes?

Answer 7

The pentagon-rings.

Question 8

From where does the fullerenes have their name?

Answer 8

From the architect Buckminster Fuller.

Question 9

Where are the LUMO located on the buckyball? How many electrons fit into the LUMO of a single buckyball?

Answer 9

They are located at the pentagons. 6 electrons fits in here.

Question 10

What can be said of the symmetry of C60-molecule?

Answer 10

It has a high symmetry. This leads to highly degenerate levels.

Question 11

Give one example of an application where buckyballs can be suitable.

Answer 11

For photovoltaics. This is because it is a potent electron acceptor.

Question 12

What kind of crystal lattice does buckyballs form? What can be said of the interactinos between the molecules?

Answer 12

They crystallize in fcc. The interactions are thought to be weak, so that they freely can rotate around.

Question 13

How is the number of pentagons related to the stability of a fullerene structure?

Answer 13

The less pentagons, the less curvature, and the more strained is the molecule. It is therefore less stable with fewer pentagons.

Question 14

What happens with fullerenes on a surface?

Answer 14

They bond with metal atoms, creating ordered arrays when deposited on the surface.

Question 15

Name some ideas for applications of carbon nanotubes.

Answer 15

• Space elevator
• H2-storage
• Carbon fibers / composite materials (much stronger, and lighter)
• Ultrasharp tips for STM
• Nanoelectronics
• Photonics
• Flexible solar cells

Question 16

What are the electronic properties of carbon nanotubes?

Answer 16

It depends on the helicity and the diameter. Can be both metallic and semiconducting.

For metallic SWCNT there will be no current with a small bias, but then with higher bias we get quantized increase of conductivity.

Question 17

How can the orientation of graphene be seen in a microscope?

Answer 17

We can see the crystal faces and the angles between these.

Question 18

What is a possible reason for the stability of 2D-materials?

Answer 18

They should be thermodynamically unstable. We think they are stable due to rippling of the 2D-structures into more 3D-like structures.

Question 19

How can one realize a vdW vertical heterostructure transistor?

Answer 19

Graphene as gate, source and drain.
h-BN as insulator.
MoS2 as semiconducting channel