Depth Resolved Structural Studies in Multilayers Using X-ray Standing Waves

Abstract

X-ray based characterization techniques are powerful tools for the study of atomic scale structure of materials. However, high penetrating power of X-rays make them less suitable for depth selective studies, as required in the characterization of multilayer structures. In the present work, it is shown that depth selectivity of the techniques like, X-ray fluorescence, X-ray absorption spectroscopy and nuclear resonance fluorescence can be greatly enhanced by generating X-ray standing waves inside the multilayer structure. The concentration profiles of various elements can be obtained with a depth resolution of the order of 0.1 nm. Depth dependent information about the local structure around a given atom can be obtained from XAFS under standing wave conditions. It is demonstrated that detection of nuclear resonance fluorescence by tuning the energy of the incident X-rays to a Mössbauer transition can yield depth profile of a particular isotope, and can be used for self-diffusion studies. The techniques of X-ray reflectivity and conversion electron Mössbauer spectroscopy are used to provide useful complementary information.

Interface-resolved study of magnetism in MgO/FeCoB/MgO trilayers using x-ray standing wave techniques

“…An avalanche photodiode detector was used for GINRS measurement, having a time resolution of ∼1 ns. The nuclear (NRR) and electronic (XRR) parts of the signal were separated by making use of the fact that nuclear transitions are delayed in time due to the finite lifetime of the Mössbauer excited state (140 ns in the case of 57 Fe isotope) [47,48]. Thus, photons detected within a few nanoseconds of the incident x-ray pulse constitute the XRR signal due to electronic scattering, while those detected in an interval of 10-160 ns after the incident x-ray pulse are used to get NRR and GINRS patterns.…”

Formation Mechanism of Ti–Si Multi-Layer Coatings on the Surface of Ti–6Al–4V Alloy

“…This is attributed to the limited penetration depth of X-rays and the gradual increase in coating thickness with the extension of the holding time. X-rays are unable to penetrate the single-phase TiSi 2 region in the outermost layer of the coating [31,32]. Hence, after a holding time of more than 1 h, only the TiSi 2 can be detected on the coating surface by XRD.…”

Atomic spectrometry update—X-ray fluorescence spectrometry

“…The example studied was the effects of swift heavy ion irradiation on a Si/M/Si trilayer (M = Fe, W) forming the cavity of the waveguide structure in which Fe was found to be much more sensitive that W, even in thin film form. In a second contribution, Gupta 63 further considered the issue of depth resolve structures in multilayers emphasising the benefit of generating X-ray standing waves inside the multilayer structure when using techniques such as XRF, X-ray absorption spectroscopy and nuclear resonance fluorescence.…”