RESUMO
The structural evolution of black arsenic-phosphorous (b-AsxP1-x) alloys with varying arsenic concentrations was investigated under hydrostatic pressure usingin situRaman spectroscopy. High-pressure experiments were conducted using a diamond anvil cell, which revealed pressure-induced shifts in vibrational modes associated with P-P bonds (A1g,A2g,B2g), As-As bonds (A1g,A2g,B2g), and As-P bonds in b-AsxP1-xalloys. 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), As0.4P0.6and As0.6P0.4alloys 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, As0.8P0.2, 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 theEgmode andA1gmode 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-AsxP1-xphase, 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 materials, including b-AsxP1-xalloys.
RESUMO
Two-dimensional (2D) polar materials experience an in-plane charge transfer between different elements due to their electron negativities. When they form vertical heterostructures, the electrostatic force triggered by such charge transfer plays an important role in the interlayer bonding beyond van der Waals (vdW) interaction. Our comprehensive first principle study on the structural stability of the 2D SiC/GeC hybrid bilayer heterostructure has found that the electrostatic interlayer interaction can induce theπ-πorbital hybridization between adjacent layers under different stacking and out-of-plane species ordering, with strong hybridization in the cases of Si-C and C-Ge species orderings but weak hybridization in the case of the C-C ordering. In particular, the attractive electrostatic interlayer interaction in the cases of Si-C and C-Ge species orderings mainly controls the equilibrium interlayer distance and the vdW interaction makes the system attain a lower binding energy. On the contrary, the vdW interaction mostly controls the equilibrium interlayer distance in the case of the C-C species ordering and the repulsive electrostatic interlayer force has less effect. Interesting finding is that the band structure of the SiC/GeC hybrid bilayer is sensitive to the layer-layer stacking and the out-of-plane species ordering. An indirect band gap of 2.76 eV (or 2.48 eV) was found under the AA stacking with Si-C ordering (or under the AB stacking with C-C ordering). While a direct band gap of 2.00-2.88 eV was found under other stacking and species orderings, demonstrating its band gap tunable feature. Furthermore, there is a charge redistribution in the interfacial region leading to a built-in electric field. Such field will separate the photo-generated charge carriers in different layers and is expected to reduce the probability of carrier recombination, and eventually give rise to the electron tunneling between layers.