Fig. 4. The optical and electrical properties of FTEs. (A) Optical image of transparency change during the FTE fabrication process. (B) The FTEs formed evenly over the 6 inch rounded rectangular substrate (width: 12 cm; height: 10 cm). (B′) SEM image of large-area FTE. (C) 3-D graph of copper nanofiber density distribution of large-area FTE. (D) Numerical analysis graph about (C). (E) Use of the FTE as a flat LED interconnector. (F) Use of the FTE as a bendable light-emitting diode (LED) interconnector.