The shift in 2teta angle of XRD peaks is related to stress in the film. But for peak broadening how is it related to stress ?
Thanks
Zaidi, Umi Zalilah Mohamad, Abdul Razak Bushroa, Reza Rahbari Ghahnavyeh, and Reza Mahmoodian. "Crystallite size and microstrain: XRD line broadening analysis of AgSiN thin films." Pigment & Resin Technology (2019).
Broadening of XRD peaks comes from the crystallite size and residual stress of the films. Generally, XRD peak broadening suggesting the increase in intrinsic stress.
Residual stress DOES NOT CAUSE PEAK BROADENING.
Residual stress refers to a macroscopic hydrostatic, shear, biaxial, uniaxial, or the like stress. These shift the peaks, but do not broaden the peaks.
Microscopic strains, such a dislocations, interstials, etc., do broaden peaks, but these are not residual stress. Residual stress measurements are often acquired on work hardened or surface treated materials that have a high dislocation density, which results in large peak widths.
During residual stress measurements, tilts are often used with divergent beam systems that cause the measurement geometry to vary from Bragg-Brentano theta/2theta parafocusing geometry - that broadens peaks.
regarding "Broadening of XRD peaks comes from the crystallite size"
True
regarding "... and residual stress of the films. Generally, XRD peak broadening suggesting the increase in intrinsic stress."
False
Thank you, Liviu Popa-Simil. I think you may be envisioning a different scenario giving rise to the residual stress, such as epitaxial mismatch, perhaps?
I believe you are describing lattice defects which give rise to stress fields that extend accross only a few (or even many) atoms "... which gives a peak near the main peak and by summation makes the main diffraction peak look larger." You are describing microstrains, which do broaden peaks, as you say. But that is not residual stress - it is microstrain - strains in the lattice over only microscopic distances; these microstrains do indeed broaden peaks.
But residual stress refers to macroscopic stress such as arises from depositing a metal film on a substrate which is at elevated temperature; then when the film plus substrate is cooled to room temperature, if there is a difference between the coefficient of thermal expansion (CTE) between the film and substrate, the one with the larger CTE will be in tension and the one with smaller CTE will be in compression. Another example: conder a weld; when the molten material solidifies, its dimensions become constrained by the surrounding material. As the previously-molten material cools, it tries to shrink, but it is attached to surrounding material, so it cannot shrink, which puts it in a state of tension when it reaches room temperature. It both of these scenarious, there is not necessarily any plastic deformation, not necessarily any crystal defects.
Other mechanisms of producing residual stress do involve plastic deformation and thus crystal defects. In those cases you will get peak broadening, but it is caused by the microstrain, not the residual stress.
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