I rolled the Cu foil to different thickness reductions. XRD peaks were shifted to lower angle with the increase in thickness reduction. What Can be the reason?
I agree in particular with (2) of the previous contributor. However, be aware of about which type of diffractometer you use to observe the peak shift. Use of focussing Bragg-Brentano diffractomers can lead to height errors and associated peak shifts, which are unrelated with change of lattice spacings. You can figure that out upon comparing the peak shifts pertaining to different (best higher-order) reflections. However, also consider the fact that at different 2theta you have different information depths for your diffracted radiation.
The peaks in the XRD shift only when there is a change in the lattice parameter (or d spacing), and the reasons for this lattice parameter change are
(1) alloying-which is definitely not the case in your samples (but sometime some high temp. treatment in uncontrolled atmosphere can also change the surface chemistry). Shifting of peaks toward lower side indicates the expansion of lattice.
(2) Residual stresses- This can be the case in your samples, as stresses can easily be generated by rolling treatment (also depends upon the extent of rolling). Shifting of peaks toward lower side indicates the expansion of lattice or the compressive stresses at the surface. You can also calculate the values of these stresses by XRD measurements.
I agree in particular with (2) of the previous contributor. However, be aware of about which type of diffractometer you use to observe the peak shift. Use of focussing Bragg-Brentano diffractomers can lead to height errors and associated peak shifts, which are unrelated with change of lattice spacings. You can figure that out upon comparing the peak shifts pertaining to different (best higher-order) reflections. However, also consider the fact that at different 2theta you have different information depths for your diffracted radiation.
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