Dear Hasan,

the transparency of a material is due to 2 essential properties of a solid:

Energy gap and thickness.

The energy gap of ITO is about 4 eV. That means, visible radiation cannot be absorbed - provided that no optical active impurities are present. The energy gap is determined by the electronic structure of a solid. Another example is diamond - a clear material - but if it is impure, absorption can be occur and you have a coloured material.

If the thickness is smaller than the reciprocal absorbtion coefficient, than light can penetrate a material - this may be the main effect in graphen because the thickness is only some atomic layers.

The conductivity is determined by the product of carrier concentration n and the mobility. In ITO the concentration n is high, because the Fermi level lies in the band of conductivity - one says the semiconductor is degenerated. The mobility depends on the scattering time and the inverse effective electron masses. In pure materials with precise periodicity of lattice the life time is high. In graphen, additionally we have a very small electron mass. This makes the mobility very high.

So we can say (very rough): In ITO dominates the high carrier concentration and in Graphen the conductivity is dominated by a very high mobility.

With Regard

R. Mitdank

Dear Hasan,

the transparency of a material is due to 2 essential properties of a solid:

Energy gap and thickness.

The energy gap of ITO is about 4 eV. That means, visible radiation cannot be absorbed - provided that no optical active impurities are present. The energy gap is determined by the electronic structure of a solid. Another example is diamond - a clear material - but if it is impure, absorption can be occur and you have a coloured material.

If the thickness is smaller than the reciprocal absorbtion coefficient, than light can penetrate a material - this may be the main effect in graphen because the thickness is only some atomic layers.

The conductivity is determined by the product of carrier concentration n and the mobility. In ITO the concentration n is high, because the Fermi level lies in the band of conductivity - one says the semiconductor is degenerated. The mobility depends on the scattering time and the inverse effective electron masses. In pure materials with precise periodicity of lattice the life time is high. In graphen, additionally we have a very small electron mass. This makes the mobility very high.

So we can say (very rough): In ITO dominates the high carrier concentration and in Graphen the conductivity is dominated by a very high mobility.

With Regard

R. Mitdank

Dear Hasan,

The optical and electrical properties of materials are determined by their electronic band structures. Indium tin oxide (ITO) is typically made of 80%indium oxide and 20% tin oxide. Indium oxide is a semiconductor and has bandgap between 3.5 to 3.7 eV. Therefore the large band gap leads to visible light transparent window. The conductivity is from the presence of tin that provides charge carrying electrons into conduction band like doping into the semiconductor. This leads to ITO conducting.

The graphene is a single atomic layer of graphite, which has zero energy bandgap. That is why it is conducting. The thin atomic layer of graphene leads to transparency in the visible light.

Hope it answers your questions.

Best wishes

Xuhua

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One point is not covered yet, which concerns graphine. Graphine can be considered a material with high conductivity like metal. One conducting layer is not sufficient to totally reflect the electromagnetic waves of the light. It is so that the light penetrates a depth called the penetration depth. If the thickness of the metal is smaller than the penetration depth a part of the radiation can pass through this extremely small thickness. It is so that one can express the light intensity across the path by the relation

I= I0 exp - x/delta, where I0 is the intensity of light at the surface and delta is the penetration depth.

Best wishes