Correlation of optical energy gap with the nearest neighbour short range order in amorphous V2O5 films

The optical and structural properties of well characterized vacuum-evaporated amorphous V2O5 films were studied in the thickness range 5-500 nm. The structural analyses show that V-O, O-O and V-V nearest neighbour distances defining the short range order vary nonlinearly with film thickness. The optical absorption shows thickness-dependent energy gap (Eg) and the nonlinear behaviour of thickness-dependent Eg is similar to that of nearest neighbour distance with film thickness. The Eg correlates linearly very well with all the three nearest neighbour distances. The variation of Eg with film thickness is attributed to the residual stress in the film which causes the changes in short range order. The change in Eg corresponding to the change in V-O distance was found to be 35 eV nm-1. This change is almost three times of that with V-V distance.