A total of four disks for each material underwent SEM/EDS analyses using a tabletop scanning electron microscope (TM4000Plus, Hitachi, Schaumburg, IL, USA) equipped with an EDS probe (Quantax 75 with XFlash 630H Detector, Bruker Nano GmbH, Berlin, Germany). Dry specimens were mounted on stubs using conductive tape and analyzed without sputter-coating, using the secondary electron (SE) and backscattered electron (BE) detector at an accelerating voltage of 15 kV in a surface-charge reduction mode. The surface morphology of the tested materials were thus analyzed, with greater attention on filler particle distribution, shape, and dimensions. In particular, the BE mode that was sensitive to an element’s atomic number enabled differentiation between fillers of different compositions, making elements with higher atomic numbers appear whiter. Three randomly selected micrographs were obtained for each disk (500×, 2000×, and 5000×) for morphological observation of the surface and with the EDS probe (300 × 300 μm fields) in full-frame mode at 150 s acquisition time. The data acquired by EDS were averaged for each specimen and element, representing the wt.% distribution in a ≈1 μm superficial layer (See Ionescu et al., 2022, Figure 6 [27 (link)]). Elemental distribution at the surface level was visually displayed using the map mode (5000×), with an acquisition time of 600 s.
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