Figure 3: Composition and structure of SiGe-core fibres.

(a–c) 25 at% Ge fibre (a) XCT image of dendritic structures, showing a large grain, and red arrows indicating grain boundaries. (b) Cross-sectional BSE image (grey), EDX compositional maps for Ge (green) and Si(red), and (c) X-ray diffraction patterns of a polycrystalline region as a function of axial position (numbers shown are relative position in μm). Note that there are numerous peaks, the placement and number of which varies from frame to frame. (d–f) 6 at% Ge fibre (d) XCT image showing Ge segregation without dendrite formation (e) Cross sectional BSE image (grey), EDX compositional maps for Ge (green) and Si(red); and (f) truncated X-ray diffraction patterns of a fibre as a function of axial position (numbers are relative position in micrometre). Fewer peaks are seen, and the positions are constant over larger distances. The fibre has a grain boundary between 2,000 and 3,000 μm, as revealed by the sudden change in the pattern. Scale bar, 200 μm (a,d), 20 μm (b), 40 μm (e) and 1 Å⁻¹ (c,f). X-ray diffraction patterns in c,f are rotated 90° counter-clockwise to match the shown fibre orientation.