Unraveling Structural Details in Ga-Pd SCALMS Systems Using Correlative Nano-CT, 360° Electron Tomography and Analytical TEM

Figure 4. Direct comparison of HRES-PC Nano-CT and 360°-ET reconstructions (sample routine 2 in Table 1). (A) Virtual slice through the HRES Nano-CT reconstruction of a pillar with a diameter of 12 µm revealing the structure of the porous support network and of the distributed Ga-Pd droplets. (B) Virtual slice through the HRES Nano-CT reconstruction of a smaller pillar with a diameter of 2 µm, site-specifically prepared from the region indicated with a red rectangle in (A). The data is in excellent agreement with the corresponding virtual slice of (C) the 360°-ET reconstruction of the same pillar volume, but also with the corresponding location in the larger pillar volume in (A). Due to the pronounced Z-contrast and higher resolution, 360°-ET provides a more detailed reconstruction of the embedded Ga-Pd droplets (red arrow) than the corresponding HRES Nano-CT data. (D) FSC calculation determines a resolution of 53.09 nm/48.27 nm at one-bit/half-bit criterion for the Nano-CT dataset in (B). (E) FSC calculation determines a resolution of 11.88 nm/8.10 nm at one-bit/half-bit criterion for the 360°-ET reconstruction in (C).

2.3.2. Direct Correlation of HRES-PC Nano-CT and 360°-ET

Since the reconstructed volume of the 360°-ET pillar of the first sample (sample routine 1) in Figure 3C was included in the LFOV nano-CT reconstruction (Figure 3A), but not in the stitched-HRES volume (Figure 3B), we investigated a second sample (sample routine 2) of the same SCALMS system for a direct correlation of HRES-PC nano-CT and 360°-ET. Whereas for the first sample, we compared LFOV and stitched-HRES nano-CT of the same sample volume (pillar with 28 µm diameter), we were now able to directly correlate data from a specific site in a larger volume with data from that same location included in a significantly smaller volume reconstructed from both HRES nano-CT and 360°-ET datasets. Figure 4A shows a slice through the HRES-PC nano-CT reconstruction of this second larger pillar (d = 12 µm) resolving the Ga-Pd droplets in the porous support network.
Similar to the first sample, we prepared a smaller pillar with a diameter of ~2 µm by FIB milling from the larger pillar, as indicated by a red rectangle in Figure 4A. Figure 4B,C show slices through the HRES-PC nano-CT and 360°-ET reconstructions of the smaller pillar, respectively. The morphology of the porous network and the Ga-Pd droplets are clearly visible in both reconstructed volumes. The FSC analysis determines a resolution at a half-bit/one-bit criterion of 11.88 nm/8.10 nm for the 360°-ET dataset and 53.09 nm/48.27 nm for the HRES nano-CT dataset (Table 1). As for the first sample in Figure 3C,F, the 360°-ET volume exhibits a significantly higher resolution, less artifacts and a higher fidelity of the local reconstructed density due to the pronounced mass-thickness contrast of HAADF STEM imaging. On the contrary, the nano-CT dataset shows a much smaller contrast difference between droplets and the glass network and furthermore exhibits Zernike PC artifacts (see red arrow in Figure 4B,C and Figure S3). We address these PC artifacts in the HRES nano-CT reconstructions (Figure 4A,C) by comparing corresponding slices through the 360°-ET (Figure 4C) and HRES-PC nano-CT (Figure 4B) volumes and directly utilize the higher reconstruction fidelity of 360°-ET to inform the segmentation of the pore space and the Ga-Pd droplets in the nano-CT volumes (Figure S3).

Leave a Comment