Fig. 5 Alignment of nanomaterials in BBFs. (a) Illustration of the
bubble solution passing over the edge of the die at a speed of Ufluid during
the expansion process. (b) Illustration of the migration of nanomaterials
in the bubble film toward the outer wall of the bubble. (c) Cross-sectional
SEM image of a SiNW-BBF showing three aligned NWs sitting close to
the bottom of the film. Scale bar: 500 nm. (d) Cross-sectional TEM image
showing that most of the NWs are located at the bottom of the film, thus
near the substrate. Scale bar: 100 nm.