The resulting q2D-PANI thin film can fully float on water surface with more than 28 cm
2 (
Fig. 1b), or suspend over large holes of ~20 µm on a copper grid (
Fig. 1c), suggesting high mechanical strength of the q2D-PANI. The resultant film was fished using a 300 nm SiO
2/Si wafer and visualized under optical microscopy (
Fig. 1d), which shows a large-area continuous morphology with excellent uniformity. After cleaning with chloroform, atomic force microscopy (AFM) measurements at edges by random sampling revealed a thickness of
ca. 10 nm (
Figs. 2a and
b). In order to prove the existence of long-range order within q2D-PANI, the film was suspended over copper grid and characterized by selected-area electron diffraction (SAED) that gives a clear and very reproducible diffraction spots of single crystal structure (
Fig. 2c). The nearest reflections revealed a rectangle unit cell with lattice parameters of
a = 6.8 Å and
b = 7.4 Å [
11]. Further characterization by aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM) shows that the linear polymer chains align parallel to each other (
Figs. 2d and
e), packing into a q2D molecular sheet. Unlike polymers obtained by solution synthesis [
33,
34], the PANI chains in the molecular sheet exhibit long-range order, showing no chain folding or any entanglement. X-ray photoelectron spectroscopy (XPS) reveals that the q2D-PANI film contains carbon, nitrogen, chlorine, sulfur, and oxygen in a ratio of 63.4%, 7.0%, 1.2%, 0.2% and 28.1% (Fig. S1 and Table S1 in Supporting information), respectively. The two prominent peaks of N1s signal at 401.9 eV and 399.8 eV can be attributed to two types of nitrogen (-NH- and =NH-) in q2D-PANI (
Fig. 2f). The four peaks of C 1s signal can be assigned to C 1s of C=C at 284.5 eV, C-C at 285.0 eV, C-N at 285.9 eV, and C-O at 288.2 eV (Fig. S2 in Supporting information), respectively. The peak at 197.7 eV belongs to the Cl
− counterions of acid dopant (
Fig. 2e). The infrared spectroscopic data of the q2D-PANI film showed that the characteristic bands at 1563 and 1488 cm
−1, attributable to the C=C a stretching deformation mode of the quinoid and benzenoid rings (Fig. S3 in Supporting information). Band at 1287 cm
−1 arises from the C–N stretching of the secondary aromatic amine and C–N stretching vibration in the polaron structures, respectively.