The density of ultrathin graphite films produced by the heat treatment of spin-coated benzimidazobenzophenanthroline ladder polymer films

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The densities (ρ) of ultrathin graphite films with thicknesses of 41–300 nm were experimentally determined by the sink–float method using acetone and diiodomethane as solvents. The films were prepared using the heat treatment of spin-coated benzimidazobenzophenanthroline ladder polymer films. The measured ρ of the films decreased with decreasing film thickness, with the thinnest film (thickness=41 nm) having the lowest ρ of 1.76±0.01 g/cm³. X-ray absorption near-edge structure measurements of the films in the C K-edge region confirmed their graphitic structure and that the thinner films had a higher degree of orientational disorder. Therefore, for the ultrathin graphitic films prepared from this precursor in the present study, those with thicknesses in the range of several tens to hundreds of nanometers were found to have lower ρ values, which may be attributed to the highly disordered local graphitic structures.