I am depositing ZnO thin films on glass substrate by spin coating technique. Literature suggested me that, biaxial strain model has to be used to calculate the stress induced during deposition. But i am unable to understand about this model.
"Biaxial strain" in general means that in two of the three independent spatial directions (Cartesian system) there are mechanical clamping mechanisms present so that an elastic relaxation can only occur in the third direction. In your case, the glass substrate surface mechanically clamps the ZnO film (i.e., it induces strain), which can relax perpendicular to the surface only.
In the case of ZnO films exhibiting a preferred orientation along the (002) direction are the c-axis oriented films, and for such films the c-axis is normal to the substrate surface. In case of polycrystalline films you will find the appearance of all the other Bragg reflections when you exmaine them with X-ray diffraction. Mostly sputtered films have exhibited the preferred orientation, and in some case the sol gel deposited films as well.
The previous response to your question by Dr. Jan Martin very nicely explains the reason for the biaxial strain, and is normally see in ZnO films which have the preferred orientation, and the induced strain is found to depend greatly on the thin film deposition conditions, and the nature of the substrate surface.
K. Sreenivas
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