High-pressure response of vibrational properties of b-As x P 1-x : in-situ Raman studies.

The structural evolution of black arsenic-phosphorous (b-As x P 1-x ) alloys with varying arsenic concentrations was investigated under hydrostatic pressure using in-situ Raman spectroscopy. High-pressure experiments were conducted using a Diamond Anvil Cell (DAC), which revealed pressure-induced shifts in vibrational modes associated with P-P bonds (A 1 g , A 2 g , B 2g ), As-As bonds (A 1 g , A 2 g , B 2g ), and As-P bonds in b-As x P 1-x alloys. Two distinct pressure regimes were observed. In the first regime (Region I), all vibrational modes exhibited a monotonic upshift, indicating phonon hardening due to hydrostatic pressure. In the second regime (Region II), As 0.4 P 0.6 and As 0.6 P 0.4 alloys displayed a linear blueshift (or negligible change in some modes) at a reduced rate, suggesting local structural reorganization with less compression on the bonds. Notably, the alloy with the highest As concentration, As 0.8 P 0.2 , exhibited anomalous behavior in the second pressure regime, with a downward shift observed in all As-As and As-P Raman modes (and some P-P modes). Interestingly, the emergence of new peaks corresponding to the E g mode and A 1g mode of the gray-As phase was observed in this pressure range, indicating compressive strain-induced structural changes. The anomalous change in Region II confirms the formation of a new local structure, characterized by elongation of the P-P, As-As, and As-P bonds along the zigzag direction within the b-As x P 1-x phase, possibly near the grain boundary. Additionally, a gray-As phase undergoes compressive structural changes. This study underscores the significance of pressure in inducing structural transformations and exploring novel phases in two-dimensional (2D) materials, including b-As x P 1-x alloys.&#xD.