Textured Asymmetric Membrane Electrode Assemblies of Piezoelectric Phosphorene and Ti_(3)C_(2)T_(x)MXene Heterostructures for Enhanced Electrochemical Stability and Kinetics in LIBs

Black phosphorus with a superior theoretical capacity(2596 mAh g^(-1))and high conductivity is regarded as one of the powerful candidates for lithium-ion battery(LIB)anode materials,whereas the severe volume expansion and sluggish kinetics still impede its applications in LIBs.By contrast,the exfoliated two-dimensional phosphorene owns negligible volume variation,and its intrinsic piezoelectricity is considered to be beneficial to the Li-ion transfer kinetics,while its positive influence has not been discussed yet.Herein,a phosphorene/MXene heterostructure-textured nanopiezocomposite is proposed with even phosphorene distribution and enhanced piezo-electrochemical coupling as an applicable free-standing asymmetric membrane electrode beyond the skin effect for enhanced Li-ion storage.The experimental and simulation analysis reveals that the embedded phosphorene nanosheets not only provide abundant active sites for Li-ions,but also endow the nanocomposite with favorable piezoelectricity,thus promoting the Li-ion transfer kinetics by generating the piezoelectric field serving as an extra accelerator.By waltzing with the MXene framework,the optimized electrode exhibits enhanced kinetics and stability,achieving stable cycling performances for 1,000 cycles at 2 A g^(-1),and delivering a high reversible capacity of 524 m Ah g^(-1)at-20℃,indicating the positive influence of the structural merits of self-assembled nanopiezocomposites on promoting stability and kinetics.

Electrically controllable spin filtering in zigzag phosphorene nanoribbon based normal–antiferromagnet–normal junctions

We investigated the electric controllable spin-filtering effect in a zigzag phosphorene nanoribbon(ZPNR) based normal–antiferromagnet–normal junction. Two ferromagnets are closely coupled to the edges of the nanoribbon and form the edge-to-edge antiferromagnetism. Under an in-plane electric field, the two degenerate edge bands of the edge-to-edge antiferromagnet split into four spin-polarized sub-bands and a 100% spin-polarized current can be easily induced with the maximal conductance 2e~2/h. The spin polarization changes with the strength of the electric field and the exchange field,and changes sign at opposite electric fields. The spin-polarized current switches from one edge to the other by reversing the direction of the electric field. The edge current can also be controlled spatially by changing the electric potential of the scattering region. The manipulation of edge current is useful in spin-transfer-torque magnetic random-access memory and provides a practical way to develop controllable spintronic devices.

Phosphorene-Based Heterostructured Photocatalysts

Semiconductor photocatalysis is a potential pathway to solve the problems of global energy shortage and environmental pollution.Black phosphorus(BP)has been widely used in the field of photocatalysis owing to its features of high hole mobility,adjustable bandgap,and wide optical absorption range.Nevertheless,pristine BP still exhibits unsatisfactory photocatalytic activity due to the low separation efficiency of photoinduced charge carriers.In recent years,the construction of heterostructured photocatalysts based on BP has become a research hotspot in photocatalysis with the remarkable improvement of photoexcited charge-separation efficiency.Herein,progress on the design,synthesis,properties,and applications of BP and its corresponding heterostructured photocatalysts is summarized.Furthermore,the photocatalytic applications of BP-based heterostructured photocatalysts in water splitting,pollutant degradation,carbon dioxide reduction,nitrogen fixation,bacterial disinfection,and organic synthesis are reviewed.Opportunities and challenges for the exploration of advanced BP-based heterostructured photocatalysts are presented.This review will promote the development and applications of BP-based heterostructured photocatalysts in energy conversion and environmental remediation.

Defect engineering on the electronic and transport properties of one-dimensional armchair phosphorene nanoribbons

We investigate the electronic and transport properties of one-dimensional armchair phosphorene nanoribbons(APNRs) containing atomic vacancies with different distributions and concentrations using ab initio density functional calculations. It is found that the atomic vacancies are easier to form and detain at the edge region rather than a random distribution through analyzing formation energy and diffusion barrier. The highly local defect states are generated at the vicinity of the Fermi level, and emerge a deep-to-shallow transformation as the width increases after introducing vacancies in APNRs.Moreover, the electrical transport of APNRs with vacancies is enhanced compared to that of the perfect counterparts. Our results provide a theoretical guidance for the further research and applications of PNRs through defect engineering.

Superconductivity of bilayer phosphorene under interlayer compression

According to first-principles calculations, it is our prediction that bilayer phosphorene（BLP） will become a quasitwo-dimensional superconductor under a certain degree of interlayer compression. A decreasing interlayer distance may realize the transition in the BLP from a semiconducting phase to a metallic phase. On the other hand, a severe vertical compression may make the BLP lattice become dynamically unstable. It is found that in the stable metallic phase of the BLP, interlayer phonon modes dominate the electron-phonon coupling λ. The obtained λ can be greater than 1 and the superconducting temperature T_c can be higher than 10 K.

Double band-inversions of bilayer phosphorene under strain and their effects on optical absorption

Strain is a powerful tool to engineer the band structure of bilayer phosphorene.The band gap can be decreased by vertical tensile strain or in-plane compressive strain.At a critical strain,the gap is closed and the bilayer phosphorene is turn to be a semi-Dirac semimetal material.If the strain is stronger than the criterion,a band-inversion occurs and it re-happens when the strain is larger than another certain value.For the zigzag bilayer phosphorene ribbon,there are two edge band dispersions and each dispersion curve represents two degenerate edge bands.When the first band-inversion happens,one of the edge band dispersion disappears between the band-cross points while the other survives,and the latter will be eliminated between another pair of band-cross points of the second band-inversion.The optical absorption of bilayer phosphorene is highly polarized along armchair direction.When the strain is turn on,the optical absorption edge changes.The absorption rate for armchair polarized light is decreased by gap shrinking,while that for zigzag polarized light increases.The bandtouch and band-inversion respectively result in the sublinear and linear of absorption curve versus light frequency in low frequency limit.

Phosphorene-Based van der Waals Heterojunction for Solar Water Splitting

As a clean and renewable future energy source, hydrogen fuel can be produced via solar water splitting. Two-dimensional (2D) black phosphorene (black-P) can harvest visible light due to the desirable band gap, which promises it as a metal-free photocatalyst. However, black-P can be only used to produce hydrogen since the oxidation potential of water locates lower than the position of the valence band maximum. To improve the photocatalytic performance of black-P, here, using black-P and blue phosphorene (blue-P) monolayers, we propose a 2D van der Waals (vdW) heterojunction. Theoretical results, including the band structures, density of states, Bader charge population, charge density di erence, and optical absorption spectra, clearly reveal that the visible light absorption ability is obviously improved, and the band edge alignment of the proposed vdW heterojunction displays a typical type-II feature to effectively separate the photogenerated carriers. At the same time, the built-in interfacial electric field prevents the electron-hole recombination. These predictions suggest that the examined phosphorene-based vdW heterojunction is an efficient photocatalyst for solar water splitting.

Enhanced Catalytic Hydrogen Evolution Reaction in Phosphorene Nanosheet via Cobalt Intercalation

Searching alternatives to Pt-based catalyst for producing hydrogen via water splitting has gathered enormous attention to develop renewable energy. Phosphorene has been investigated widely for its large surface area, low cost, and high carrier mobility, however, the poor activity in hydrogen evolution reaction (HER) and low conductivity limit its practical application. Herein, on the basis of first-principles calculations, we demonstrate that the catalytic HER in phosphorene can be enhanced significantly with cobalt intercalations. The Co-intercalated phosphorene is metallic with charge transfer from Co atoms to phosphorene, which could enhance the catalytic activity of phosphorene. In addition, the calculated Gibbs free energy of hydrogen adsorption on Co-intercalated phosphorene bilayer is comparable to that on Pt(111) surface, independent of the degree of hydrogen coverage. Our study implies that the Co intercalation provides an effective approach to enhance the catalytic HER in phosphorene.

Optical properties of phosphorene

Phosphorene is a two-dimensional semiconductor with layers-dependent bandgap in the near-infrared range and it has attracted a great deal of attention due to its high anisotropy and cartier mobility. The highly anisotropic nature of phos- phorene has been demonstrated through Raman and polarization photoluminescence measurements. Photoluminescence spectroscopy has also revealed the layers-dependent bandgap of phosphorene. Furthermore, due to the reduced dimension- ality and screening in phosphorene, excitons and trions can stably exist at elevated temperatures and have large binding energies. The exciton and trion dynamics are thus detected by applying electrical bias or optical injection to the phospho- rene system. Finally, various optical and optoelectronic applications based on phosphorene have been demonstrated and discussed.

Van der Waals heterostructure of phosphorene and hexagonal boron nitride: First-principles modeling

We have studied the structural and electronic properties of a hybrid hexagonal boron nitride with phosphorene nanocomposite using ab initio density functional calculations. It is found that the interaction between the hexagonal boron nitride and phosphorene is dominated by the weak van der Waals interaction, with their own intrinsic electronic properties preserved. Furthermore, the band gap of the nanocomposite is dependent on the interfacial distance. Our results could shed light on the design of new devices based on van der Waals heterostructure.

Anisotropic Transport on Monolayer and Multilayer Phosphorene in the Presence of an Electric Field

We demonstrate theoretically the anisotropic quantum transport of electrons through an electric field on monolayer and multilayer phosphorene. Using the long-wavelength Hamiltonian with continuum approximation, we find that the transmission probability for transport through an electric field is an oscillating function of incident angle, electric field intensity, as well as the incident energy of electrons. By tuning the electric field intensity and incident angle, the channels can be transited from opaque to transparent. The conductance through the quantum waveguides depends sensitively on the transport direction because of the anisotropic effective mass, and the anisotropy of the conductance can be tuned by the electric field intensity and the number of layers. These behaviors provide us an efficient way to control the transport of phosphorene-based microstructures.

Ab initio Study of Tunable Band Gap of Monolayer and Bilayer Phosphorene by the Vertical Electronic Field

Using the ab initio plane-wave ultrasoft pseudopotential method based on generalized gradient approximation（GGA）,we investigated the band-gap tuning in monolayer phosphorene（MLP） and bilayer phosphorene（BLP） by external electric fields applied perpendicular to the layers.The band continuously decreases with increasing applied electric fields,eventually rendering them metallic.For MLP,the phenomenon is explained in the light of the giant Stark effect,which is essentially characterized by the interlayer spacing,for the rate of change of bandgap with applied external field.The atomic distance and charges also contribute to the semiconductor-metal transition.The BLP is more sensitive to electric fields than MLP,since their charges are rearranged among bilayers and the bandgap can dramatically drop in terms of electronic field.The results show the bandgap will change for the fabrication of novel electronic and photonic devices.

Theoretical Investigation on Self-passivation in Bare Zigzag Phosphorene Nanoribbons

Several bare zigzag phosphorene nanoribbons with odd number of atoms in the direction perpendicular to the extended line are investigated by using HSE06 density functional theory.These nanoribbons are as stable as those with even number of atoms.Primitive cells of the nanoribbons are metals,while edge self-passivation and distortion in the supercell structures cause metal-semiconductor transition.The band gaps of semiconducting nanoribbons are around 0.4 eV,which is enough for high on/off ratio in device operation.Compared to the conduction bands,the valence bands have smaller deformation potential constants and larger band width.Thus,the hole mobilities of the nanoribbons（10 cm^2·V^（-1）·s^（-1）） are one order higher than the electron mobilities.Bare zigzag phosphorene nanoribbons with odd number of atoms can also be candidates for small-size high-speed electronic devices.

Anisotropic Ballistic Transport through a Potential Barrier on Monolayer Phosphorene

We demonstrate theoretically the anisotropic quantum transport of electrons through a single barrier on monolayer phosphorene. Using an effective k .p Hamiltonian, we find that the transmission probability for transport through n-n-n （or n p-n） junction is an oscillating function of the incident angle, the barrier height, as well as the incident energy of electrons. The conductance in such systems depends sensitively on the transport direction due to the anisotropic effective mass. By tuning the Fermi energy and gate voltage, the channels can be transited from opaque to transparent, which provides us with an efficient way to control the transport of monolayer phosphorene-based microstructures.

A first-principles study on zigzag phosphorene nanoribbons terminated by transition metal atoms

We have investigated the electronic and magnetic properties of zigzag phosphorene nanoribbons(ZPNRs)with transition metal(TM)passivated atoms,it can be found that the ZPNRs with TM passivated atoms exhibit different magnetisms except for the Ni-passivated system.Meanwhile,the results show that the magnetic moments of ZPNRs with TM passivated atoms are larger than that of ZPNRs with other passivated non-metals/groups.Interestingly,it can be found that Fe-passivated ZPNR exhibits magnetic semiconducting character,which provides the possbility for the application of phosphorene in information storage.For Mn-passivated ZPNRs,it exhibits the half-metallicity.These results may be useful for potential applications of phosphorene in electronic and high-performance spintronic devices.

Topological Transition in Monolayer Blue Phosphorene with Transition-Metal Adatom under Strain

We carried out first-principles calculations to investigate the electronic properties of the monolayer blue phosphorene(BlueP)decorated by the group-IVB transition-metal adatoms(Cr,Mo and W),and found that the Cr-decorated BlueP is a magnetic half metal,while the Mo-and W-decorated BlueP are semiconductors with band gaps smaller than 0.2 eV.Compressive biaxial strains make the band gaps close and reopen,and band inversions occur during this process,which induces topological transitions in the Mo-decorated BlueP(with strain of-5.75%)and W-decorated BlueP(with strain of-4.25%)from normal insulators to topological insulators(TIs).The TI gap is 94 meV for the Mo-decorated BlueP and218 me V for the W-decorated BlueP.Such large TI gaps demonstrate the possibility to engineer topological phases in the monolayer BlueP with transition-metal adatoms at high temperature.

Ballistic Transport through a Strained Region on Monolayer Phosphorene

We investigate quanturn transport of carriers through a strained region on monolayer phosphorene theoretically. The electron tunneling is forbidden when the incident angle exceeds a critical value. The critical angles for electrons tunneling through a strain region for different strengths and directions of the strains are different. Owing to the anisotropic effective masses, the conductance shows a strong anisotropic behavior. By tuning the Fermi energy and strain, the channels can be transited from opaque to transparent, which provides us with an efiqcient way to control the transport of monolayer phosphorene-based microstruetures.

The Effects of Boron-Doping on the Electronic Properties of Blue Phosphorene

In this paper, the effects of different boron (nitrogen)-doping on the electronic properties of blue phosphorene have been investigated by the first- principles calculations. We have taken eight doping configurations into account, the calculated results show that the bond length of P-B is decreasing with the doping concentration increasing. For the four boron atoms doping configuration, the geometric structure appears the distinct distortion. The band gap is decreasing with the doping concentration increasing, and it appears the transition from indirect band gap to direct band gap for boron doping configurations. It is hoped that the calculated results may be useful for designing electronic devices based on blue phosphorene.

Hydrogen bond-bridged phosphorene flexible film for photodynamic inhibiting Staphylococcus aureus

Antibiotics are a widely used and effective treatment for bacterial infections.However,bacteria can gradually evolve during infection,leading to developing resistance to antibiotics,which renders previously effective treatments ineffective.Finding a useful and convenient manner to treat bacterial infections is a great challenge.Here,we report a flexible hydrogen-bond-bridged phosphorene film with photodynamic antibacterial properties and excellent mechanical properties,fabricated from electrochemical exfoliation of black phosphorus(BP).When illuminated under 700 nm light,the hydrogen bond-bridged phosphorene flexible film is capable of converting ground-state triplet oxygen(O_(2))into excited-state singlet oxygen(^(1)O_(2)),destroying the structure of the membrane of Staphylococcus aureus,and eventually leading to bacterial death,via breaking the C=C of unsaturated fatty acids within the bacterial cell membrane after the reaction between^(1)O_(2)and unsaturated fatty acids,thus realizing a highly efficient antibacterial approach,which is supported by gas chromatography-mass spectrometry(GC-MS)technique.This work establishes an effective phototherapy platform for treating bacterial traumatic infections.

Excitation-assisted pseudo-ferroelectric effect in ultrathin graphene/phosphorene heterostructure

Pseudo-ferroelectric transistors have attracted particular interest owing to their applications in the non-volatile memories and neuromorphic circuits;however,it remains to be explored in the limit of few-layer devices.Here we reveal a pseudo-ferroelectric phenomenon in the ultrathin graphene/black phosphorene(G/BP)heterostructure by first-principles calculations.Putting forward an excitation-assisted mechanism,the ferroelectric-like hysteresis loop can be explained by a combined effect of the external electric fields dependent bipolarity and anisotropy in the G/BP heterostructure.Considering the build-in electric field,the bipolar behavior results in the multistate effect of the G/BP heterostructure when modulating the applied electric field.The anisotropic hybridization caused by the susceptible Dirac electrons in graphene and the large in-plane anisotropy in BP provides the interfacial states,which trap excitations and stabilize the multistate.The pseudo-ferroelectric behavior should be useful for interpreting transport experiments in gated G/BP devices and exploring its applications in memories or synaptic devices.