Define energy band gap and how it varies from bulk to nano
Answers
In the bulk matter, the bands are actually formed by the merger of bunch of adjacent energy levels of a LARGE number of atoms and molecules.As the particle size reaches the nano scale, where every particle is made up only a VERY SMALL number of atoms or molecules, the number of overlapping of orbitals or energy level decreases and the WIDTH OF THE BAND GETS NARROWER. This will cause an INCREASE IN ENERGY GAP BETWEEN THE VALENCE BAND AND THE CONDUCTION BAND. This explains the higher energy gap in NP than the corresponding bulk matter. The band gap is the region forbidden for the electrons. THE LARGER THIS FORBIDDEN REGION, THE GREATER WILL BE RESTRICTION ON THE MOVEMENT OF ELECTRONS. Hence theNP exhibit the lower electrical conductivity than the bulk from which they are prepared. So there is a shift of abrorption specrum toward lower wave length or blue region or blue region.