2024 Nanotech L4

Why was the discovery of graphene surprising?

• Due to Merlin-Werner theory.
• Since 2D crystals should not be stable at finite temperature.
• Since the strong sp2 bonds does not allow remove one layer
• Since it was difficult to see it.

Graphene can be created

• by exfoliation, which is a slow process resulting in nm-scale flakes.
• by CVD, which is good for mass production.
• by liquid phase exfoliation, which produces the largest crystals.
• only in lab conditions, no way for mass production.

Graphene is ideal for composites, since

• van der Waals interaction creates strong bonds.
• it can be streached up to 10% inelastically.
• it is light and strong.
• it can be mixed with plastics.

Graphene is promising for optical applications, since

• it is completely transparent for visible light.
• it conducts and allows 97% of visible light through.
• it has small band gap, good for THz detection.
• it has indirect band gap.

Transparent conductors is a potential application of graphene,

• since it allows a highly transparent, stretchable, flexible layer.
• however it is less transparent than existing ITO layers.
• however its sheet resistance is larger than for ITO.
• however its toxicity is a problem.

Graphene band structure is special

• since it has inverted gap.
• since it has a linear spectrum with zero band gap.
• since it has 2D Brillouin zone.
• since it has large mobility.

In Van der Waals heterostrucutres

• single layer 2D crystals are grown on top of each other by MBE.
• the angle of the different layers matters in electron structure.
• dust between layers does no allow clean interfaces.
• van der Waals interaction electron hopping from layer to layer.