Fig. 3
SEM micrographs of the NbBL and the \(\textrm{Nb}{}_{3}\textrm{Sn}\) samples. Upper table: the first row shows the surface morphology of NbBLs of varying thickness (left to right: 1 \(\upmu\)m, 10 \(\upmu\)m, 30 \(\upmu\)m) and of a bulk Nb substrate; the middle row shows the surface morphology of \(\textrm{Nb}{}_{3}\textrm{Sn}\) film samples deposited on the respective substrate indicated by the corresponding column, at \({600}~^{\circ }\textrm{C}\) deposition temperature; the samples shown in the third row are deposited at \({650}~^{\circ }\textrm{C}\). The green and blue dots on the SEM micrograph of the film on bulk Nb substrate in this last row represent, respectively, examples of the “\(\textrm{Nb}{}_{3}\textrm{Sn}\) film base surface” and the “island formations” EDS analysis points mentioned in Fig. 4. Lower table: (a) ion-milled cross section of a \(\textrm{Nb}{}_{3}\textrm{Sn}\) film sample deposited on a NbBL-30; (b) ion-milled cross section of a sample deposited on bulk Nb, whit the inset at the top-left showing a close-up on the \(\textrm{Nb}{}_{3}\textrm{Sn}\) film surface exhibiting island formations; (c) cross section obtained by cracking a sample deposited on sapphire, highlighting (dotted yellow line) the in-depth structure of the island formations. The inset at the top-right shows a close-up of the sample surface. All samples shown in the lower table are deposited at \({650}~^{\circ }\textrm{C}\).
