Macro stress mapping on thin film buckling Page: 3 of 6
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Among the most widely used method for determining the stress level in thin films, X-ray diffraction
(XRD) is phase selective and the unique non destructive technique which allows to determine both
the mechanical and microstructural state of the diffracting phases. Indeed, the distance between
atomic planes is used as an internal strain gage. For polycrystalline samples, the measurement of
the diffraction peak position shift using sinxy method allows to extract the stress tensor and the
stress free lattice parameter [9]. However, x-ray diffraction is difficult to use in low dimensional
systems because the diffracted intensities are weak due to the reduced thicknesses and
nanocrystalline character (grain size) of such materials. These problems may be solved using
intense x-ray sources such as synchrotron radiation (S.R.). In addition to the high flux characteristic
of S.R. facilities, the wide wavelength spectra and the optics (micro beam) which are available on
beam lines (3rd generation SR only) allow to perform specific XRD experiments which are not
possible with classical x-ray sources in laboratories.
100
80 -
60
a 40 -
20
0
0 1 2 3 4
b' (pm)
Figure 3. Variation of the buckle width L as a function its corrected height 6'. The straight line represents the linear fit.
The 7.3.3.1 Microdiffraction beam line [10] at Advanced Light Source of the Lawrence
Berkeley National Laboratory [11] provides a reduced spot size less than 1 pm2 (Kirkpatrick Baez
mirrors) with high flux for white or monochromatic radiation (4-crystals channel cut
monochromator: 6-14 KeV; see figure 4 and 5). These performances are unique and perfectly
adapted to our purpose.
For comparison, the Micro-Fluorescence-Imaging-Diffraction group (ID22) at ESRF has
developed Bragg-Fresnel lens [12] which allow to get reduced spot size greater than 1 x 5 pm2 with
high flux for an higher energy range (up to 30 keV). On the same facility, ID13 beam line achieves
2 pm diameter spot size with the use of capillaries [13]. At the National Synchrotron Light Source
of Brookhaven National Laboratory in New-York (USA), micro beam X-ray diffraction is used to
get a topography of the sample surface in order to determine strains at a scale less than a pm [14].
We can find also specific micro beam lines at the Photon Factory - Japan [15]. The proceeding of
the 7th International Conference on Synchrotron Radiation Instrumentation (Berlin, Germany,
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Goudeau, P.; Villain, P.; Renault, P. O.; Tamura, N.; Celestre, R. S. & Padmore, H.A. Macro stress mapping on thin film buckling, article, November 6, 2002; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc735989/m1/3/: accessed March 29, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.