Quantum confinement and effective masses dependence in black phosphorus quantum dots and phosphorene

In the present study, quantum confinement effect in phosphorene and black phosphorus quantum dots is extensively studied from experimental and theoretical viewpoints. These quantum structures were prepared with the help of Benzonitrile solvent using Liquid Phase Exfoliation and solvothermal-assisted Liquid Phase Exfoliation, respectively. On one hand, Fourier-transform infrared spectroscopy shows no sign of phosphorus oxidation in both phosphorene and black phosphorus quantum dots solutions. Furthermore, Raman spectroscopy showed a shift in B2gandAg2 phonon modes for phosphorene and black phosphorus quantum dots as compared to bulk black phosphorus. On the other hand, structural characterization via high-resolution transmission electron microscopy imaging and electron diffraction patterns showed a high degree of crystallinity in both quantum structures with no sign of aggregations. Optical properties characterization showed the expected increase in the bandgap value for both quantum structures, which were supported by theoretical calculations using density functional theory and effective mass approximation. Interestingly, we demonstrate that the quantum confinement observed in phosphorene is weakened to the expected extent, relative to that in BPQDs, by the loss of two confinement dimensions. Appropriate models, describing the bandgap and effective mass dependence as a function of the confinement regime, are presented.