Hierarchical self‐assembly of black phosphorus quantum dots with quantum confinement effects to a centimeter‐scale membrane

The self-assembly of simple building blocks to complex superstructures is significant for engineering materials with enhanced and synergistic properties. In this work, black phosphorus quantum dots (BPQDs) showing quantum confinement effects were prepared. The BPQDs are hierarchically self-assembled to paper-like membranes as large as in the centimeter range in two main stages: aggregation driven by Brownian motions due to minimization of the surface free energy and an interfacial self-concentrating process by capillary interactions. Moreover, from the absorption band edges, the band gap of BPQDs is estimated to be about 1.3eV, which is evidently larger than the 0.8eV of bulk black phosphorus. The remarkable extension of the band gap indicates the quantum confinement effects of the electrons. The Raman spectrum of BPQDs shows that all the phonon modes shift to lower frequencies and broaden dramatically compared with that of the bulk BP, which suggests phonon confinement effects.