Band Gap on Nano Materials

BAND GAP ON NANO MATERIALS

Very few atoms in a material not only causes the energy states to spread out but also widens the band gap for semiconductors and insulators as shown in Fig. 5.17.

Fig. 5.17 The band gap gets bigger as the material gets smaller. Once the volume is reduced from that of a solid, which has bands for sublevels, to that of a nanomaterial, which has distinct splits in each sub level, the band gap will widen even if only a few atoms are removed. This allows us to tune the electronic and optical characteristics of a nanomaterial.

When the energy states are discrete, the addition or removal of just a few atoms adjusts the boundaries of the band gap. This is because once two atoms are next to each other, the sublevels split and then begin to broaden into bands.

The broader the bands get, the smaller the band gaps between them get. Finally, the bands reach a point where they will not get any wider no matter how many atoms are in the solid.

In the case of quantum dots, the smaller the particle, the bigger the band gap.

The band gap gets bigger as the material gets smaller.

Once volume is reduced from that of a solid, which has bands for sublevels, to that of a nanomaterial, which has distinct splits in each sublevel, the band gap will widen if only a few atoms are removed.

This allows us to 'tune' the electronic and optical characteristics of the nanomaterial.

When an electron is excited across the band gap into the conduction band, it rarely stays there very long. It releases its energy in the form of a photon as it falls back to the valence band.

The energy of this photon is equal to the energy the electron loses in its transition: it is same as the band gap energy.

Thus, if we change a material's band gap energy, we change the electromagnetic radiation it emits. This phenomena is especially used in optical applications.