Search

The performance of lithium–sulfur (Li–S) battery is strongly dependent on the sulfur electrodes materials. Due to the chemical interaction between electrodes and intermediates produced in charging and discharging process, the Janus‐polar two dimensional (2D) electrode materials can enhance the electrochemical performance of Li–S battery by overcoming shuttle effect and increasing diffusion rates. Here, it is explored the structural, electronic, and dynamic characteristics of Li ion, S8 cluster, and lithium polysulfides adsorbed over Janus Phosphorus Nitride monolayer with blue phosphorene phase (b‐PN) by using first‐principles calculations. The reported findings highlight potential of the b‐PN monolayer as a good host material, given that the large absorption energies of different clusters vary from −0.47 to −3.78 eV, which can suppress shuttle effect effectively. These strong adsorptions are origin from the chemical interaction between nitrogen atoms of the b‐PN and Li atoms in lithium polysulfides in present work. Particularly, it is predicted that b‐PN monolayer has extremely small diffusion barriers for Li ion and Li2S8 clusters of 0.10 and 0.03 eV, which leading to a higher battery charge and discharge rate than reported graphene and MoS2. It is hoped that this efficient strategy for promising host materials of sulfur‐electrode guides the development of next‐generation lithium–sulfur batteries. [ABSTRACT FROM AUTHOR]

The recent synthesis of "borophane" polymorphs through hydrogenation has promoted the development of boron-based two-dimensional (2D) materials. In this work, the electronic structures and transport properties of hydrogenated borophene are investigated using first-principles calculations. The results show that the metallic character is preserved after hydrogenation, whereas electronic structures are greatly modulated by the position and number of introduced hydrogen atoms. More importantly, the presence of three-center-two-electron (3c-2e) bonds results in the formation of distorted Dirac points below the Fermi level in rect-1Hbridge and rect-2H borophane structures. The transport properties and the current–voltage (I–V) curve characters in those borophane structures can be efficiently modulated by the type of hydrogenations. Different hydrogenation patterns dominate diverse electronic transport behaviors. Such hydrogen atom-participant transport states endow borophane structures with potential applications in boron-based 2D electronics devices. [ABSTRACT FROM AUTHOR]

Optical nonlinearity of two-dimensional (2D) materials with a permanent dipole is a subject of intense research in the fields ranging from all-optical signal processing to laser nanotechnology due to the potential outstanding performance of 2D materials in nonlinear optical processes, and the feasibility for extensive integration into optoelectronic devices. In the present work, the group-VA binary monolayers are predicted to have giant and broadband second harmonic generation (SHG) properties superior to some of the most popular NLO materials by first-principles calculations. The SHG susceptibility of the α-PAs reaches up to 8.0 × 106 pm2 V−1, which is nearly 1–2 orders of magnitude higher than that of honeycomb monolayer MoS2 and h-BN, and twice larger than the record-high SHG susceptibility of a 2D ferroelectric GeSe monolayer. This intriguing peak is formed by intraband two photon transition ascribed to the relatively small bandgap and large transition matrix elements between valence and conduction band edges. A high-performance nonlinear optical device can be developed using those 2D group-VA monolayer materials with puckled structure and in-plane polarizabilities for multifunctional and integrated optoelectronic applications. [ABSTRACT FROM AUTHOR]

Using the density functional theory (DFT) calculations, we find that  Janus group-III chalcogenide monolayers can serve as a suitable substrate for silicene, and the Dirac electron band properties of silicene are also fully preserved. The maximum opened band gap can reach 179 meV at the Dirac point due to the interaction of silicene and the polar two-dimensional (2D) substrate. In addition, the electronic band structure of the heterostructure can be modulated by applying an electric field where its predicted band gap increases or decreases according to the direction of the applied external electric field. Furthermore, an insight into the electron structures can be understood by analyzing the electron energy-loss (EEL) spectra. From these results, we also predict that heterostructures with polar 2D substrates have broad application prospects in multi-functional devices. Besides, Janus group-III chalcogenide monolayers can be used as good substrates for growing silicene and the modulation of the electronic structure can also be applied to nanodevices and optoelectronic devices. [ABSTRACT FROM AUTHOR]

By first-principles calculations, we investigate the geometric stability, electronic and optical properties of the type-II PN-WSe2 and type-I PAs-WSe2 van der Waals heterostructures(vdWH). They are p-type semiconductors with indirect band gaps of 1.09 eV and 1.08 eV based on PBE functional respectively. By applying the external gate field, the PAs-WSe2 heterostructure would transform to the type-II band alignment from the type-I. With the increasing of magnitude of the electric field, two heterostructures turn into the n-type semiconductors and eventually into metal. Especially, PN/PAs-WSe2 vdWH are both high refractive index materials at low frequencies and show negative refractive index at high frequencies. Because of the steady absorption in ultraviolet region, the PAs-WSe2 heterostructure is a highly sensitive UV detector material with wide spectrum. The type-II PN-WSe2 heterostructure possesses giant and broadband absorption in the near-infrared and visible regions, and its solar power conversion efficiency of 13.8% is higher than the reported GaTe–InSe (9.1%), MoS2/p-Si (5.23%) and organic solar cells (11.7%). It does project PN-WSe2 heterostructure a potential for application in excitons-based solar cells. [ABSTRACT FROM AUTHOR]

The breaking of the out-of-plane symmetry makes a two-dimensional (2D) Janus monolayer a new platform to explore the coupling between ferroelectricity and ferromagnetism. Using density functional theory in combination with Monte Carlo simulations, we report a novel phase-switchable 2D multiferroic material VInSe 3 with large intrinsic out-of-plane spontaneous electric polarization and a high Curie temperature ( T c ). The structural transition energy barrier between the two phases is determined to be 0.4 eV, indicating the switchability of the electric polarizations and the potential ferroelectricity. Carrier doping can boost the Curie temperature above room temperature, attributing to the enhanced magnetic exchange interaction. A transition from the ferromagnetic (FM) state to the antiferromagnetic (AFM) state can be induced by carrier doping in octahedra-VInSe 3 , while FM coupling is well-preserved in tetrahedron-VInSe 3 , which can be regulated to be either an XY or Ising magnet at an appropriate carrier concentration. These findings not only enrich the family of high -T c low-dimensional monolayers but also offer a new direction for the design and multifunctional application of multiferroic materials.

Group IV monochalcogenides exhibit spontaneous polarization and ferroelectricity, which are important in photovoltaic materials. Since strain engineering plays an important role in ferroelectricity, in the present work, the effect of equibiaxial strain on the band structure and shift currents in monolayer two-dimensional (2D) GeS and SnS has systematically been investigated using the first-principles calculations. The conduction bands of those materials are more responsive to strain than the valence bands. Increased equibiaxial compressive strain leads to a drastic reduction in the band gap and finally the occurrence of phase transition from semiconductor to metal at strains of -15 and -14% for GeS and SnS, respectively. On the other hand, tensile equibiaxial strain increases the band gap slightly. Similarly, increased equibiaxial compressive strain leads to a steady almost four times increase in the shift currents at a strain of -12% with direction change occurring at -8% strain. However, at phase transition from semiconductor to metal, the shift currents of the two materials completely vanish. Equibiaxial tensile strain also leads to increased shift currents. For SnS, shift currents do not change direction, just as the case of GeS at low strain; however, at a strain of +8% and beyond, direction reversal of shift currents beyond the band gap in GeS occur., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)