Four-phonon scattering of so-As and improvement of the thermoelectric properties by increasing the buckling height

In recent years, more and more thermoelectric (TE) materials have been discovered as the research boom of TE materials advances. However, due to the low conversion efficiency, most of the current TE materials cannot meet the commercial demand. The low-dimensional nanomaterials are promising to break the current status quo of low conversion efficiency of TE materials. Here, we predicted a stable two-dimensional TE material, namely so-As, based on density functional theory. The so-As has an ultra-low lattice thermal conductivity,κl= 1.829 W m-1K-1at 300 K, and when the temperature rises to 700 K theκlis only 0.788 W m-1K-1. This might be caused by the strong anharmonic interaction among the so-As phonon and the out-of-plane vibration of the low-frequency acoustic modes. Moreover, the maximumZTvalue of thep-type so-As is 0.18 at room temperature (0.45 at 700 K), while that of then-type can even reach 0.75 at 700 K. In addition, we have also studied the difference between the four- and three-phonon scattering rates. The increase of scattering channels leads to the ultra-lowκl, which is only 3.33 × 10-4W m-1K-1at room temperature, showing an almost adiabatic property. Finally, we adjust the TE properties of so-As by changing the buckling height. With the buckling height is increased by 2%, the scattering rate of so-As is extremely high. WhenTis 700 K, the maximumZTof then-type is 0.94 (p-type can also reach 0.7), which is 25% higher than the pristine one. Our work reveals the impact of buckling height on the TE figure of merit, which provides a direction for future search and regulation of the highZTTE materials.

Elucidation of the synergistic effects of 3d metal (M = Cu, Co, and Ni) dopants and terminations (T = -O- and -OH) of Ti3C2Tx MXenes for urea adsorption ability via DFT calculations and experiments

Dialysis is an artificial process to remove excess urea toxins from the body through adsorption or conversion. Urea adsorption by emergent 2D materials such as MXenes is one probable approach. Based on density functional theory (DFT) studies, the surface of Ti3C2Tx (T = -O- and -OH) MXenes is not optimum for urea adsorption. Therefore, functionalization with 3d metal dopants (Cu, Co, and Ni) is proposed to improve their urea adsorption ability. DFT calculations indicate that oxygen-terminated Ti3C2O2 has a much better urea adsorption ability when doped with Cu, Co, and Ni, with adsorption energy (Eads) values of -2.11 eV, -1.90 eV and -1.72 eV, respectively. These adsorption energies are much more favourable than that of the undoped one (Eads = -0.52 eV). To verify the calculation results, MILD Ti3C2Tx, or MXenes synthesized via the safer and easier minimally intensive layer delamination (MILD) method, were utilized to simulate Ti3C2O2 since they have -O- termination as the dominant species. Experimentally, the adsorption studies found that low concentration of Cu, Co, and Ni on MILD Ti3C2Tx showed a urea removal efficiency of 21.9%, 6.0% and 0.2%, respectively, much better than 0% removal efficiency of unfunctionalized Ti3C2Tx. Therefore, both DFT calculations and experiments showed that various metal functionalized MXenes have a similar trend for urea adsorption, highlighting the feasibility of using the computational approach to predict urea adsorption and further opening a new promising direction for the urea adsorption. Finally, this study is also the first to examine synergistic effects of metal dopants and surface terminations on MXenes for urea adsorption.

Comprehensive Insights into the Family of Atomically Thin 2D-Materials for Diverse Photocatalytic Applications

2D materials with their fascinating physiochemical, structural, and electronic properties have attracted researchers and have been used for a variety of applications such as electrocatalysis, photocatalysis, energy storage, magnetoresistance, and sensing. In recent times, 2D materials have gained great momentum in the spectrum of photocatalytic applications such as pollutant degradation, water splitting, CO2 reduction, NH3 production, microbial disinfection, and heavy metal reduction, thanks to their superior properties including visible light responsive band gap, improved charge separation and electron mobility, suppressed charge recombination and high surface reactive sites, and thus enhance the photocatalytic properties rationally as compared to 3D and other low-dimensional materials. In this context, this review spot-lights the family of various 2D materials, their properties and their 2D structure-induced photocatalytic mechanisms while giving an overview on their synthesis methods along with a detailed discussion on their diverse photocatalytic applications. Furthermore, the challenges and the future opportunities are also presented related to the future developments and advancements of 2D materials for the large-scale real-time photocatalytic applications.

A new type of stable borophene with flat-band-induced magnetism

Based on first-principles calculations, we propose a new type of thermally and dynamically stable magnetic borophene (B11) with a tetragonal lattice. The magnetism is found coming from spin polarization of one bonding flat band located at the Fermi level. Despite of the 'anti-molecular' behavior in the monolayer, the interactions between thepzorbitals of the B atoms in the double-octahedron structural unit lead to the formation of the flat bands with localization behaviors. One tight binding model is built to comprehend the magnetic mechanism, which can guide us to tune other nonmagnetic borophene becoming magnetic. Biaxial tensile strain (>2.1%) is found triggering a phase transition from a semimetal to a semiconductor in the B11monolayer. The mechanism is analyzed based on the orbital-resolved crystal field effect. Our work provides a new route for designing and achieving two-dimensional magnetic materials with light elements.

Semiconductor and topological phases in lateral heterostructures constructed from germanene and AsSb monolayers

Two-dimensional (2D) heterostructures have attracted a lot of attention due to their novel properties induced by the synergistic effects of the constituent building blocks. In this work, new lateral heterostructures (LHSs) formed by stitching germanene and AsSb monolayers are investigated. First-principles calculations assert the semimetal and semiconductor characters of 2D germanene and AsSb, respectively. The non-magnetic nature is preserved by forming LHSs along the armchair direction, where the band gap of the germanene monolayer can be increased to 0.87 eV. Meanwhile, magnetism may emerge in the zigzag-interline LHSs depending on the chemical composition. Such that, total magnetic moments up to 0.49 μ_B can be obtained, being produced mainly at the interfaces. The calculated band structures show either topological gap or gapless protected interface states, with quantum spin-valley Hall effects and Weyl semimetal characters. The results introduce new lateral heterostructures with novel electronic and magnetic properties, which can be controlled by the interline formation.

Novel germanene-arsenene and germanene-antimonene lateral heterostructures: interline-dependent electronic and magnetic properties

Seamlessly stitching two-dimensional (2D) materials may lead to the emergence of novel properties triggered by the interactions at the interface. In this work, a series of 2D lateral heterostructures (LHSs), namely germanene-arsenene (Ge_m-As_8-m) and germanene-antimonene (Ge_m-Sb_8-m), are investigated using first-principles calculations. The results demonstrate a strong interline-dependence of the electronic and magnetic properties. Specifically, the LHS formation along an armchair line preserves the non-magnetic nature of the original materials. However, this is an efficient approach to open the electronic band gap of the germanene monolayer, where band gaps as large as 0.74 and 0.76 eV are induced for Ge₂-As₆ and Ge₂-Sb₆ LHSs, respectively. Meanwhile, magnetism may appear in the zigzag-LHSs depending on the chemical composition (m = 3, 4, 5, and 6 for germanene-arsenene and m = 2, 3, 4, 5, and 6 for germanene-antimonene), where total magnetic moments between 0.13 and 0.50 μ_B are obtained. Herein, magnetic properties are produced mainly by the spin-up state of Ge atoms at the interface, where a small contribution comes from As(Sb) atoms. Spin-resolved band structures show a multivalley profile in both the valence band and the conduction band with a topological insulator-like behavior, where the interface states are derived mainly from the interface Ge-p_z state. The results introduce new 2D lateral heterostructures with novel electronic and magnetic properties to allow new functionalities, which could be further explored for optoelectronic and spintronic applications.

Structural, electronic and optical properties of monolayer InGeX3(X = S, Se, Te) by first-principles calculations

Recently, two-dimensional materials have attracted enormous attentions for electronic and optoelectronic applications owing to their unique surface structures and excellent physicochemical properties. Herein, the structural, electronic and optical properties of a series of novel monolayer InGeX₃(X = S, Se, Te) materials are investigated systematically by means of comprehensive first-principles calculations. All these three materials exhibit hexagonal symmetries and dynamical stabilities with no imaginary phonon mode. For monolayer InGeX₃(X = S, Se, Te), there exist obvious In-X ionic bonds and the partially covalent interactions of Ge-Ge and Ge-X. By using the HSE06 method, the band gaps of monolayer InGeX₃are predicted to 2.61, 2.24 and 1.80 eV, respectively. Meanwhile, thep-sorbital hybridizations are happened between X and In atoms in the conduction band regions and their interactions become smaller with the increase of X atomic number. In addition, the dielectric function, absorption coefficient and reflectivity spectra of monolayer InGeS₃, InGeSe₃and InGeTe₃show the strong optical peaks along the in-plane direction in the UV light region. The definite bandgaps and optical properties make monolayer InGeX₃(X = S, Se, Te) materials viable candidates for future electronic and optoelectronic applications.

2D Layers of Group VA Semiconductors: Fundamental Properties and Potential Applications

Members of the 2D group VA semiconductors (phosphorene, arsenene, antimonene, and bismuthine) present a new class of 2D materials, which are recently gaining a lot of research interest. These materials possess layered morphology, tunable direct bandgap, high charge carrier mobility, high stability, unique in-plane anisotropy, and negative Poisson's ratio. They prepare the ground for novel and multifunctional applications in electronics, optoelectronics, and batteries. The most recent analytical and empirical developments in the fundamental characteristics, fabrication techniques, and potential implementation of 2D group VA materials in this review, along with presenting insights and concerns for the field's future are analyzed.

Photocatalytic properties of anisotropic β-PtX2 (X = S, Se) and Janus β-PtSSe monolayers

The highly efficient photocatalytic water splitting process to produce clean energy requires novel semiconductor materials to achieve a high solar-to-hydrogen energy conversion efficiency. Herein, the photocatalytic properties of anisotropic β-PtX₂ (X = S, Se) and Janus β-PtSSe monolayers were investigated based on the density functional theory. The small cleavage energy for β-PtS₂ (0.44 J m^-2) and β-PtSe₂ (0.40 J m^-2) endorses the possibility of mechanical exfoliation from their respective layered bulk materials. The calculated results revealed that the β-PtX₂ monolayers have an appropriate bandgap (∼1.8-2.6 eV) enclosing the water redox potential, light absorption coefficient (∼10⁴ cm^-1), and exciton binding energy (∼0.5-0.7 eV), which facilitates excellent visible-light-driven photocatalytic performance. Remarkably, the inherent structural anisotropy leads to an anisotropic high carrier mobility (up to ∼5 × 10³ cm² V^-1 S^-1), leading to a fast transport of photogenerated carriers. Notably, the required small external potential to realize hydrogen evolution reaction and oxygen evolution reaction processes with an excellent solar-to-hydrogen energy conversion efficiency for β-PtSe₂ (∼16%) and β-PtSSe (∼18%) makes them promising candidates for solar water splitting applications.

The Pnictogen Bond: The Covalently Bound Arsenic Atom in Molecular Entities in Crystals as a Pnictogen Bond Donor

In chemical systems, the arsenic-centered pnictogen bond, or simply the arsenic bond, occurs when there is evidence of a net attractive interaction between the electrophilic region associated with a covalently or coordinately bound arsenic atom in a molecular entity and a nucleophile in another or the same molecular entity. It is the third member of the family of pnictogen bonds formed by the third atom of the pnictogen family, Group 15 of the periodic table, and is an inter- or intramolecular noncovalent interaction. In this overview, we present several illustrative crystal structures deposited into the Cambridge Structure Database (CSD) and the Inorganic Chemistry Structural Database (ICSD) during the last and current centuries to demonstrate that the arsenic atom in molecular entities has a significant ability to act as an electrophilic agent to make an attractive engagement with nucleophiles when in close vicinity, thereby forming σ-hole or π-hole interactions, and hence driving (in part, at least) the overall stability of the system’s crystalline phase. This overview does not include results from theoretical simulations reported by others as none of them address the signatory details of As-centered pnictogen bonds. Rather, we aimed at highlighting the interaction modes of arsenic-centered σ- and π-holes in the rationale design of crystal lattices to demonstrate that such interactions are abundant in crystalline materials, but care has to be taken to identify them as is usually done with the much more widely known noncovalent interactions in chemical systems, halogen bonding and hydrogen bonding. We also demonstrate that As-centered pnictogen bonds are usually accompanied by other primary and secondary interactions, which reinforce their occurrence and strength in most of the crystal structures illustrated. A statistical analysis of structures deposited into the CSD was performed for each interaction type As···D (D = N, O, S, Se, Te, F, Cl, Br, I, arene’s π system), thus providing insight into the typical nature of As···D interaction distances and ∠R–As···D bond angles of these interactions in crystals, where R is the remainder of the molecular entity.

Effect of UV Radiation on Structural Damage and Tribological Properties of Mo/MoS2-Pb-PbS Composite Films

To investigate ultraviolet (UV) radiation effects on tribological properties of Mo/MoS2-Pb-PbS film, ultraviolet (UV) radiation exposure tests were carried out for 20 h, 40 h, 60 h and 80 h by space UV radiation simulation device developed by our team, which can reach 3 UV radiation intensity. The exposure time in test was equivalent to the radiation of 100 h, 200 h, 300 h and 400 h in the space. Then, the vacuum friction test of Mo/MoS2-Pb-PbS thin film was performed under the 6 N load and 100 r/min, and friction test time of each sample was 20 min. By SEM, TEM, XPS the composition and morphology of Mo/MoS2-Pb-PbS film surface after UV radiation were analyzed. UV radiation could change the microstructure significantly and relative content of S element and MoS2 on the surface of the films decreased, and light mass loss of the films occurred. The tribological properties will also recover with the increase of sliding time, although the friction coefficient fluctuation of the film increased at the starting stage of the friction test. The damage of Mo/MoS2-Pb-PbS under UV irradiation was mainly caused by the volatilization of the enriched S element in the surface layer due to the high temperature heating of UV irradiation.

Quasiparticle energies and significant exciton effects of monolayered blue arsenic phosphorus conformers

Low-dimensional systems have strong multi-body interactions and fewer geometric constraints due to the screening effect of the Coulomb interaction. We use the single-shot GW-Bethe Salpeter equation (G₀W₀-BSE) to calculate the electronic and optical properties of six-blue arsenic phosphorus (β-AsP) conformers. The results show significant anisotropic exciton effects of covering visible regions, which apparently changed the light absorption. The maximum exciton binding energy is up to 0.99 eV, which is more extensive than the black phosphorus monolayer (0.9 eV). We predict that the different orbital contributions to valence bands may cause the anisotropic exciton effect difference. Our results indicate that β-AsP monolayers with the large binding energies of exciton hold a great promise for applications in optoelectronic devices.

Two-Dimensional TeB Structures with Anisotropic Carrier Mobility and Tunable Bandgap

Two-dimensional (2D) semiconductors with desirable bandgaps and high carrier mobility have great potential in electronic and optoelectronic applications. In this work, we proposed α-TeB and β-TeB monolayers using density functional theory (DFT) combined with the particle swarm-intelligent global structure search method. The high dynamical and thermal stabilities of two TeB structures indicate high feasibility for experimental synthesis. The electronic structure calculations show that the two structures are indirect bandgap semiconductors with bandgaps of 2.3 and 2.1 eV, respectively. The hole mobility of the β-TeB sheet is up to 6.90 × 10² cm² V^-1 s^-1. By reconstructing the two structures, we identified two new horizontal and lateral heterostructures, and the lateral heterostructure presents a direct band gap, indicating more probable applications could be further explored for TeB sheets.

First principles study of Janus WSeTe monolayer and its application in photocatalytic water splitting

By employing the state-of-the-art density functional theory method, we demonstrate that Janus WSeTe monolayer exhibits promising photocatalytic properties for solar water splitting. The results show that the monolayer possesses thermodynamic stability, suitable bandgap (∼1.89 eV), low excitons binding energy (∼0.19 eV) together with high hole mobility (∼10³cm²V^-1s^-1). Notably, the results suggest that the oxygen evolution reaction can undergo spontaneously without any sacrificial reagents. In contrast, the overpotential of hydrogen evolution reaction can partially be overcome by the external potential under solar light irradiation. Furthermore, the intrinsic electric field induced by the symmetry breaking along the perpendicular direction of Janus WSeTe monolayer not only suppresses the electron-hole recombination but also contributes to the solar-to-hydrogen efficiency, which is calculated to be ∼19%. These characteristics make the Janus WSeTe monolayer to be a promising candidate for solar water splitting.

Twisted bilayer arsenene sheets as a chemical sensor for toluene and M-xylene vapours - A DFT investigation

2D (two-dimensional) materials are emerging in today's world. Among the 2D materials, arsenene sheets are prominently used as chemical and biosensors. In the present work, the twisted bilayer arsenene sheets (TB-AsNS) are used to adsorb toluene and M-xylene vapours. Moreover, the band gap of pristine TB-AsNS is calculated to be 0.437 eV. Besides, the surface adsorption of toluene and M-xylene vapours modify the electronic properties of TB-AsNS noticed from the band structure, density of states, and electron density difference diagrams. The surface assimilation of target toluene and M-xylene on TB-AsNS falls in the physisorption regime facilitating the adsorption and desorption of molecules. Also, the charge transfer analysis infers that TB-AsNS acts as acceptor and target molecules play as donors. The findings support that TB-AsNS can be used as a sensing medium towards M-xylene and toluene.

Effect of Si, Be, Al, N and S dual doping on arsenene: first-principles insights

First-principles calculations based on density functional theory (DFT) have been performed to investigate the effect of Si/Be, Si/Al, Si/N and Si/S co-doping on the geometries, electronic structure, magnetism and particularly the adsorption of CO in arsenene. The results show that the incorporation of foreign atoms slightly distorts the host lattice. All doped structures are found to be thermodynamically stable. The replacement of host As atoms with foreign atoms results in some interesting changes in the electronic and magnetic properties of arsenene. The doped arsenene systems exhibit a semiconducting character with band gaps smaller than the original value of 1.59 eV due to the emergence of defect states within the actual band gap. Besides, arsenene remains nonmagnetic (NM) upon Si/Be or Si/S dual doping, whereas both Si/Al and Si/N dopings induce magnetism with a total magnetic moment of 1 μ_B. Finally, the adsorption of CO molecules over pristine arsenene (p-As) and dual doped arsenene systems is investigated in terms of adsorption energy, adsorption height, charge transfer, charge density difference (CDD), work function, electronic band structures and density of states. It is observed that CO molecule has physisorption over p-As, SiAl-As, SiN-As and SiS-As systems, whereas chemisorption is reported for the SiBe-As system. Our study suggests that chemically modifying arsenene with suitable dopants might extend its applications in spintronic and gas sensing applications.

Small Polarons in Two-Dimensional Pnictogens: A First-Principles Study

We report the first-principles study of small polarons in the most stable two-dimensional pnictogen allotropes: blue and black phosphorene and arsenene. While both cations and anions of small hydrogen-passivated clusters show charge localization and local lattice distortions, only the hole polaron in the blue allotrope is stable in the infinite size cluster limit. The adiabatic polaron relaxation energy is found to be 0.1 eV for phosphorene and 0.15 eV for arsenene. The polaron is localized on lone-pair orbitals with half of the extra charge distributed among 13 atoms. In the blue phosphorene, these orbitals form the valence band's top with a relatively flat band dispersion. However, in the black phosphorene, lone-pair orbitals hybridize with bonding orbitals, which explains the difference in hole localization strength between the two topologically equivalent allotropes. The polaron's adiabatic barriers for motion are small compared to the most strongly coupled phonon frequency, implying the polaron barrierless motion.

Schottky barrier heights in two-dimensional field-effect transistors: from theory to experiment

Over the past decade, two-dimensional semiconductors (2DSCs) have aroused wide interest due to their extraordinary electronic, magnetic, optical, mechanical, and thermal properties, which hold potential in electronic, optoelectronic, thermoelectric applications, and so forth. The field-effect transistor (FET), a semiconductor gated with at least three terminals, is pervasively exploited as the device geometry for these applications. For lack of effective and stable substitutional doping techniques, direct metal contact is often used in 2DSC FETs to inject carriers. A Schottky barrier (SB) generally exists in the metal-2DSC junction, which significantly affects and even dominates the performance of most 2DSC FETs. Therefore, low SB or Ohmic contact is highly preferred for approaching the intrinsic characteristics of the 2DSC channel. In this review, we systematically introduce the recent progress made in theoretical prediction of the SB height (SBH) in the 2DSC FETs and the efforts made both in theory and experiments to achieve low SB contacts. From the comparison between the theoretical and experimentally observed SBHs, the emerging first-principles quantum transport simulation turns out to be the most powerful theoretical tool to calculate the SBH of a 2DSC FET. Finally, we conclude this review from the viewpoints of state-of-the-art electrode designs for 2DSC FETs.

Blue-AsP monolayer as a promising anode material for lithium- and sodium-ion batteries: a DFT study

Based on first-principle calculations, we proposed a one two-dimensional (2D) blue AsP (b-AsP) monolayer as an ideal anode material for lithium/sodium-ion (Li/Na-ion) batteries for the first time. The b-AsP monolayer possesses thermal and dynamic stabilities. The system undergoes the transition from semiconductor to metal after Li/Na atoms are embedded, which ensures good electric transportation. Most remarkably, our results indicate that the b-AsP monolayer exhibits high theoretical capacities of 1011.2 mA h g^-1 (for Li) and 1769.6 mA h g^-1 (for Na), low average open circuit voltages of 0.17 eV for Li₄AsP and 0.14 eV for Na₇AsP systems and ultrafast diffusivity with the low energy barriers of 0.17/0.15 eV and 0.08/0.07 eV of the P/As sides for Li and Na, respectively. Given these exceptional properties, the synthesis of a buckled b-AsP monolayer is desired to achieve a promising electrode material for Li- and Na-ion batteries.

Adsorption studies of nucleobases on ε-arsenene nanosheet based on first-principles research

The electronic attributes and energetics of ε-arsenene nanosheet (ε-As) are explored with regard to the density functional theory basis. Initially, based on formation energy (-3.715 eV/atom), we ensured the structural firmness of ε-As. The ε-As is used as a base substrate to adsorb nucleobases viz., adenine (A), guanine (G), thymine (T), cytosine (C) & uracil (U). The surface adsorption of nucleobases on ε-As is analysed based on band structure, the density of states, adsorption energy, energy gap variation & charge transfer. Besides, we observed the exothermic nature of binding energy (ranging from -0.453 eV to -0.819 eV) upon nucleobase adsorption on ε-As. Also, the energy gap variation & charge transfer takes place owing to adsorption of nucleobases on the ε-As sheet. The present report reveals the adsorption of nucleobases on ε-arsenene nanosheet.

Two-Dimensional As/BlueP van der Waals Hetero-Structure as a Promising Photocatalyst for Water Splitting: A DFT Study

Constructing van der Waals (vdW) hetero-structure by stacking different two-dimensional (2D) materials has become an effective method for designing new-type and high-quality electronic and optoelectronic nano-devices. In this work, we designed a 2D As/BlueP vdW hetero-structure by stacking monolayer arsenene (As) and monolayer blue phosphorous (BlueP) vertically, which were recently implemented in experiments, and investigated its structural, electronic, and photocatalytic water splitting properties by using the standard first principles calculation method with HSE06 hybrid exchange-correlation functional. Numerical results show that the As/BlueP vdW hetero-structure is structural robust, even at room temperature. It presents semi-conducting behavior, and the conduction band minimum (CBM) and the valence band maximum (VBM) are dominated by BlueP and As, respectively. The typical type-II band alignment predicts the potential application of the hetero-structure in highly efficient optoelectronics and solar energy conversion. Moreover, the CBM and the VBM straddle the redox potentials of water in acid environment, predicting the possibility of the As/BlueP hetero-structure as a 2D photocatalyst for water splitting. When an in-plane strain is applied, the band edges and, further, the optoelectronic properties of the hetero-structure can be effectively tuned. Especially, when tensile strain is equal to 4.5%, the optical absorption spectrum is effectively broadened in a visible light region, which will largely improve its photocatalytic efficiency, although the pH value of the solution range reduction. This work provides theoretical evidence that the As/BlueP hetero-structure has potential application as a 2D photocatalyst in water splitting.

Investigation on adsorption features of nitroglycerin on novel red tricycle arsenene nanosheet - A first-principles study

The chemo sensing features of red tricycle arsenene nanosheet (RTANS), a monolayer obtained from allotropes of arsenic is employed in sensing the hazardous vapor nitroglycerin (NG) based on the first-principles investigation. The computations are carried out with the ATK-VNL package. The stability of the RTANS is validated by its formation energy, which is calculated as -4.171 eV/atom. The adsorption energy, Bader charge transfer, energy gap, and its variation after adsorption are the essential parameters that hold up the discussion on RTANS base material as an efficient chemical sensor. Moreover, the target vapor NG is physisorbed on RTANS. Besides, all the essential parameters have been investigated for the interaction of NG on RTANS. The comprehensive study reveals that RTANS can be used as a chemical sensor for the detection of nitroglycerin vapors.

Novel phosphorus-based 2D allotropes with ultra-high mobility

Electronic structure calculations based on density functional theory were performed to investigate structural, mechanical, and electronic properties of phosphorene-based large honeycomb dumbbell (LHD) hybrid structures and a new phosphorene allotrope, referred to as ψ″-P. The LHD hybrids (i.e., X₆P₄; X being C or Si or Ge or Sn) and ψ″-P have significantly higher bandgaps than the corresponding pristine LHD structures, except the case of C₆P₄, which is metallic. ψ″-P is found to be a highly flexible p-type material which shows strain-engineered photocatalytic activity in a highly alkaline medium. The carrier mobility of the considered systems is as high as 10⁵ cm² V^-1 s^-1 (specifically the electron mobility of LHD structures). The calculated STM images display the surface morphologies of the LHD hybrids and ψ″-P. The predicted phosphorus-based 2D structures with novel electronic properties may be candidate materials for nanoscale devices.

Stability, electronic and mechanical properties of chalcogen (Se and Te) monolayers

The successful experimental fabrication of 2D tellurium (Te) has resulted in growing interest in the monolayers of group VI elements. By employing density functional theory, we have explored the stability and electronic and mechanical properties of 1T-MoS₂-like chalcogen (α-Se and α-Te) monolayers. Phonon spectra are free from imaginary modes suggesting these monolayers to be dynamically stable. The stability of these monolayers is further confirmed by room temperature AIMD simulations. Both α-Se and α-Te are indirect gap semiconductors with a band gap (calculated using the hybrid HSE06 functional) of 1.16 eV and 1.11 eV, respectively, and these gaps are further tunable with mechanical strains. Both monolayers possess strong absorption spectra in the visible region. The ideal strengths of these monolayers are comparable with those of many existing 2D materials. Significantly, these monolayers possess ultrahigh carrier mobilities of the order of 10³ cm² V^-1 s^-1. Combining the semiconducting nature, visible light absorption and superior carrier mobilities, these monolayers can be promising candidates for the superior performance of next-generation nanoscale devices.

Band engineering and hybridization of competing arsenene allotropes: a computational study

Arsenene is an emerging two-dimensional material similar to its group-V isologue phosphorene. Based on first-principles calculations and finite-temperature ab initio molecular dynamics (AIMD), we investigated the dynamical stability and electronic properties of three competing phases of two-dimensional (2D) arsenic, namely γ-As, the newly discovered δ'-As, and s/o-As. Phonon calculations and AIMD results confirm their dynamical stabilities. It is also found that the band structures of these allotropes can be effectively engineered by changing the number of layers or in-layer strain, realizing direct-indirect bandgap and metal-insulator transitions. The highly tunable electronic structures and the broad range bandgaps evidence potential applications in nanoelectronics and optoelectronics. Moreover, δ'-As is predicted to transform to a higher symmetry δ-As phase when the number of layers is sufficiently large. An intriguing phenomenon unveiled is the potential hybridization of different allotropes at an energy cost lower than 0.02 eV Å^-1. This becomes particularly valuable for assembling heterostructures with different well-defined regions in one contiguous arsenene layer.

The sp2 character of new two-dimensional AsB with tunable electronic properties predicted by theoretical studies

As a competitive candidate for replacing graphene that possesses an appropriate fundamental bandgap, structural stability and tunable electronic properties, the recently synthesized honeycomb arsenene has rekindled much enthusiasm in the area of two-dimensional materials. By using first-principles calculations and acoustic phonon limited deformation potential theory, we identify a compelling two-dimensional electronic material, single-layer AsB, which is a direct-gap semiconductor with a bandgap (E_g) of 1.18 eV, almost the same as that of bulk silicon. The orbital projected band structure and electron density as well as partial density of states demonstrate that the frontier state of the planar atomic structural AsB is sp² orbital hybridization, which is distinct from that of buckled arsenene monolayers. Layer thickness, stacking order and strain are effective ways to tune the frontier states, and thus the band structure and bandgap of AsB. Moreover, thicker AsB exhibits one-layer localized states in the AB-stacking structure, which is in sharp contrast to other layered materials such as MoS₂ and phosphorene. Benefiting from the non-localized p_z orbital and larger elastic modulus, the carrier mobility of AsB is in the range of 10³-10⁴ cm² V^-1 s^-1, which is much higher than that of pristine arsenene and some other analogues. Our work provides an effective way to tailor the electronic properties of 2D arsenene, which may open up new avenues for applying it in future nano-optoelectronics and electronics.

Two-dimensional Blue-AsP monolayers with tunable direct band gap and ultrahigh carrier mobility show promising high-performance photovoltaic properties

The successful fabrication of black phosphorene (Black-P) in 2014 and subsequent synthesis of layered black As1-xPx alloys have inspired research into two-dimensional (2D) binary As-P compounds. The very recent success in growing blue phosphorene (Blue-P) further motivated exploration of 2D Blue-AsP materials. Here, using ab initio swarm-intelligence global minimum structure-searching methods, we have obtained a series of novel and energetically favored 2D Blue-AsP (denoted x-AsP, x = I, II, III, IV, V) compounds with As : P = 1 : 1 stoichiometry. They display similar honeycomb structures to Blue-P. Remarkably, the lowest-energy AsP monolayer, namely I-AsP, not only possesses a quasi-direct band gap (2.41 eV), which can be tuned to a direct and optimal gap for photovoltaic applications by in-plane strain, but also has an ultrahigh electronic mobility up to ∼7.4 × 104 cm2 V-1 s-1, far surpassing that of Blue-P, and also exhibits high absorption coefficients (×105 cm-1). Our simulations also show that 30 nm-thick I-AsP sheet-based cells have photovoltaic efficiency as high as ∼12%, and the I-AsP/CdSe heterostructure solar cells possess a power conversion efficiency as high as ∼13%. All these outstanding characteristics suggest the I-AsP sheet as a promising material for high-efficiency solar cells.