Dear colleague Rahul S. Ingole ,

Have a nice time and good day.

This can be partially explained using the density of states model in amorphous solids

proposed by Mott and Davis [N.F. Mott, E.A. Davis, Electronic Processes in Non-

Crystalline Materials, Clarendon Press, Oxford, 1979,p. 210, and M. Dongol, M. Abou Zied,

G.A. Gamal, A. EI-Denglawey, Physica B 353 (2004) 169–175].

According to this model, the width of the localized states nearthe mobility edge depends on the degree of disorder and on the defects present in the amorphous structure. In particular, it is known that unsaturated bonds are responsible for the formation of some defects in amorphous solids. Such defects produce localized states in the band structure.

The presence of a high concentration of localized states is responsible for relatively

low values of the optical gap in the case of as-deposited amorphous films. According to the

thermal literature and the bond strength, the process of heat treatment

may increase or decrease the unsaturated defects or localized states;

1-       The unsaturated defects or localized states may gradually annealed out (decreases), producing a large number of structure bonds. The reduction of the number of unsaturated defects reduces the density of localized states and shifts the amorphous to crystalline state

and in the band structure and consequently increases the optical gap.

2-      The process of heat treatment [which represents your case] may affect the bond strength and break the atomic bonds and produces dangling or unsaturated bonds or localized states. The resultant is reducing the ordering of the material and increasing the density of disorder. So the localized states and the amorphous state are increasing and the shift of crystalline to amorphous state is dominant. Such this effect can be easily detected by X-ray diffraction (XRD), Scanning electron microscope(SEM) and   Transmission electron microscope (TEM). You can distinguish between the amorphous, poly crystalline and the crystalline materials through the aforementioned three techniques:1- XRD the produced curve of  amorphous materials has a broad hump and no any sharp diffraction peaks, the presence of sharp diffraction peaks is an indication of crystalline material. 2-  SEM of of amorphous material don't release any features and no particles can be distinguished  otherwise crystalline material. 3- TEM of  amorphous material contains a hallow (white) and no diffraction rings otherwise crystalline material. 4- The presence of spotlight is an indication of single crystals. I wish this issue is useful. Check the attached files.

I wish this issue is useful.

yours

A. El-Denglawey