Multifunctional Macroassembled Graphene Nanofilms with High Crystallinity

A “cooling–contraction” method to separate large‐area (up to 4.2 cm in lateral size) graphene oxide (GO)‐assembled films (of nanoscale thickness) from substrates is reported. Heat treatment at 3000 °C of such free‐standing macroscale films yields highly crystalline “macroassembled graphene nanofilms” (nMAGs) with 16–48 nm thickness. These nMAGs present tensile strength of 5.5–11.3 GPa (with ≈3 µm gauge length), electrical conductivity of 1.8–2.1 MS m−1, thermal conductivity of 2027–2820 W m−1 K−1, and carrier relaxation time up to ≈23 ps. As a demonstration application, an nMAG‐based sound‐generator shows a 30 µs response and sound pressure level of 89 dB at 1 W cm−2. A THz metasurface fabricated from nMAG has a light response of 8.2% for 0.159 W mm−2 and can detect down to 0.01 ppm of glucose. The approach provides a straightforward way to form highly crystallized graphene nanofilms from low‐cost GO sheets.