Based on first-principles density functional theory calculations, we systemically study the properties of two-dimensional buckled single-layer bismuth (b-bismuthene).

We study the equilibrium geometry and electronic structure of alloyed and doped arsenene sheets based on the density functional theory calculations. AsN, AsP and SbAs alloys possess indirect band gap and BiAs is direct band gap. Although AsP, SbAs and BiAs alloyed arsenene sheets maintain the semiconducting character of pure arsenene, they have indirect-direct and semiconducting-metallic transitions by applying biaxial strain. We find that B- and N-doped arsenene render p-type semiconducting character, while C- and O-doped arsenene are metallic character. Especially, the C-doped arsenene is spin-polarization asymmetric and can be tuned into the bipolar spin-gapless semiconductor by the external electric field. Moreover, the doping concentration can effectively affect the magnetism of the C-doped system. Finally, we briefly study the chemical molecule adsorbed arsenene. Our results may be valuable for alloyed and doped arsenene sheets applications in mechanical sensors and spintronic devices in the future.

A new type of chitosan-modified hyperbranched polymer (named HPDACS) was synthesized through the free-radical polymerization of surface-modified chitosan with acrylic acid (AA) and acrylamide (AM) to achieve an enhanced oil recovery. The optimal polymerization conditions of HPDACS were explored and its structure was characterized by Fourier-transform infrared spectroscopy, hydrogen nuclear magnetic resonance, and environmental scanning electron microscopy. The solution properties of HPDACS in ultrapure water and simulated brine were deeply studied and then compared with those of partially hydrolyzed polyacrylamide (HPAM) and a dendritic polymer named HPDA. The experimental results showed that HPDACS has a good thickening ability, temperature resistance, and salt resistance. Its viscosity retention rate exceeded 79.49% after 90 days of aging, thus meeting the performance requirements of polymer flooding. After mechanical shearing, the viscosity retention rates of HPDACS in ultrapure water and simulated brine were higher than those of HPAM and HPDA, indicating its excellent shear resistance and good viscoelasticity. Following a 95% water cut after preliminary water flooding, 0.3 pore volume (PV) and 1500 mg/L HPDACS solution flooding and extended water flooding could further increase the oil recovery by 19.20%, which was higher than that by HPAM at 10.65% and HPDA at 13.72%. This finding indicates that HPDACS has great potential for oil displacement.

As the isoelectronic counterpart of phosphorene, monolayer group IV-VI binary MX (M = Ge, Sn; X = Se, S) compounds have drawn considerable attention in recent years. In this paper, we construct four high-symmetry stacking models for bilayer MX to tune their electronic properties. We systematically explore the dynamical and thermal stabilities of all bilayer MX. It is found that five of them are possible at room temperature. Then, we perform first-principles calculations to study how the bilayer structure affects their electronic properties. The results demonstrate that the electronic properties of MX materials can be modulated by forming bilayer structures. Their bandgap can be tuned over a wide range from 0.789 to 1.617 eV, and an indirect-to-direct transition occurs in three cases. Considering the flexibility of bilayer MX, we utilize in-plane uniaxial tensile strain to adjust their band structures and achieve much more indirect-to-direct bandgap transitions. The realization of direct bandgaps will be helpful for their application in next-generation high-efficiency modern nano-optoelectronic and photovoltaic devices. We also study the responses of different bilayer MX to an external vertical electric field. It is found that their bandgaps decrease rapidly with the increase of the electric field.