Quantitative Tracking of the Oxidation of Black Phosphorus in the Few-Layer Regime

Previous theoretical reports have described the oxidation of few-layer black phosphorus and its effects on the electronic properties. Theoretically, native oxide layers bring opportunities for band gap engineering, but the detection of the different types of oxides is still a challenge at the experimental level. In this work, we uncover a correlation between thermal processes and Raman shift for the A_g ¹, B_2g, and A_g ² vibrational modes. The thermal expansion coefficients (temperature range, 290-485 K) for the A_g ¹, B_2g, and A_g ² were -0.015, -0.027, and -0.028 cm^-1 K^-1, respectively. Differential scanning calorimetry analysis shows an endothermic process centered at 528 K, and it was related with a mass increase according to thermogravimetric analysis. Raman shift temperature dependence was correlated to theoretical lattice thermal expansion, and a significant deviation was detected in the stacking direction at 500 K.