Element-specific hard x-ray diffraction microscopy

An element-specific coherent x-ray imaging technique using anomalous x-ray scattering in the hard x-ray region was first demonstrated. Coherent x-ray diffraction patterns of a sample composed of 500-nm-thick Ni and Cu layers were measured at incident x-ray energies around the $\text{Ni}K$ absorption edge. Non-center-symmetric diffraction patterns due to anomalous scattering phenomenon in the hard x-ray region were observed. Symmetricity of the diffraction pattern was quantitatively analyzed by numerically simulating the x-ray wave field behind the sample position using the Rytov approximation. By calculating the difference between the intensities of reconstructed images of different energies, an image of the Ni layers could be derived although it was not enough to identify precisely. This method is widely applicable to nondestructive analysis of nanometer-scale elemental distribution of materials buried within thick and high-$Z$ samples.

Figure 1

(Color) (a) schematic of the test sample used for element-specific x-ray diffraction microscopy in the hard x-ray region; (b) scanning ion microscope image of the sample.

Figure 2

(Color) (a) Coherent x-ray diffraction pattern of the test sample shown in Fig: 1 at 8.2125 keV. The image is $1201\times 1201$ pixels. The region of the central $35\times 29$ pixels is an immeasurable area due to the direct beam stop. (b) Magnified image of $100\times 100$ pixels around the central speckle of (a). (c) X-ray absorption spectrum of $10\text{−}\mu \text{m}$-thick Ni foil (solid black line). Incident x-ray energy dependence of the intensity ratio of the two speckles at the positions marked by circles in (b) for experiment (solid red line) and numerical simulation (dotted red line).

Figure 3

(Color) (a) Image reconstructed from the diffraction pattern shown in Fig. 2a. The pixel size is 17.4 nm. (b) One-dimensional plots of the reconstructions at 8.2125, 8.3360, and 8.3405 keV along the solid red line indicated in (a). Images are normalized by the sum of each reconstructed intensity at the blue regions in (a). Difference images for (c) 8.3360 and 8.3405 keV and (d) 8.2125 and 8.3360 keV.