1. whether partially or fully, when relaxation occurs do they occur in the whole of the film or not ?? is it possible to happen like part of the films grow fully strained and part of the films get relaxed?
Please give some suggestions on these sub questions. We are working with PLD systems, for growing epitaxial thin films of oxide materials.
It depends. Is this relaxation occurring under ambient conditions, or due to some type of anneal? If it is due to an annealing procedure, then it will depend on the uniformity of temperature across the sample surface. This can vary depending on a gas flow over the surface, of part of the substrate touching a heat sink holder.
If you mean while sitting in your vacuum system following PLD growth, then the strain relaxation should be uniform, unless the film is not covering the entire substrate surface. For example, are you depositing through a mask, growing film over only selected regions of the substrate? In this case, there is a definitely a size effect for relaxation. Smaller area regions will relax more easily than larger film areas. This is due to having a greater circumference to area ratio, i.e. simply more space for the film to expand and/or contract.
Good luck.
Dear Mr. S. Mohan,
I have worked on metal (Au, Ag) thin film growth on reconstructed Si(hkl) substrates in molecular beam epitaxy method. From my understanding, I want to remark that, the strain energy is originated due to lattice mismatch at the thin film-substrate interfaces. And it is gradually increased with increase of thin film thickness. As the magnitude of strain energy is reached to certain critical value, the relaxation takes place with formation of dislocations.
In this paper, we had reported the formation of periodic dislocation at the Ag/Si interface (caused by the lattice mismatch).
Effect of Au thickness on Au-Ag bimetallic growth on reconstructed Si(5 5 12) surface, A. Bhukta, P. Guha, A. Ghosh, P. Maiti, B. Satpati and P. V. Satyam, Applied Physics A 123 (2017) 174.
Hence, relaxation depends on the uniformity of the thin film thickness and substrate temperature. However, I can give a better effort to understand this aspect for your sample, if you can provide some more details about it.
With best regards,
Anjan
Dear Saj Mohan,
The most important parameters that affect on relaxation when using PLD in epitaxial thin films is thickness variation and roughness over the film. Consequentially, it`s essentially to use sample dimension of about 0.5x0.5 cm2 and make the distance between target and substrate not less than 3.5 cm, besides using droplet filter if possible, low deposition rate, good laser beam profile, relatively low power and apply heating on superstate , you will have the best film quality attached with very low thickness variation.
Nevertheless of the material system grown and the method employed the strain depends on the lattice parameter- and thermal mismatch between substrate and epilayer. Full relaxation is possible in the case of homoepitaxy or low mismatch systems at a certain layer thickness as well as in the case of special nucleation templates or formation of defects relaxing the structure.
To you question again
"is it possible to happen like part of the films grow fully and part of the films get relaxed"?
Define the term fully strained please?
It is possible the part of the film (i have no idea how thick is it?) to be strained and a part of it to be relaxed if small cracks or other type of defects are formed - they release the strain.
Make micro-Raman profiling measurements across the sample cleavage and you can monitor the strain relaxation of your samples.
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