Ternary Monolayers Research Articles

Recent Advances in the Growth and Compositional Modelling of III-V Nanowire Heterostructures.

Nanowire heterostructures offer almost unlimited possibilities for the bandgap engineering and monolithic integration of III-V photonics with Si electronics. The growth and compositional modelling of III-V nanowire heterostructures provides new insight into the formation mechanisms and assists in the suppression of interfacial broadening and optimization of optical properties. Different models have been proposed in the past decade to calculate the interfacial profiles in axial nanowire heterostructures mainly grown by molecular beam epitaxy and metal-organic vapour phase epitaxy. Based on various assumptions, existing models have different sets of parameters and can yield varying results and conclusions. By focusing on deterministic models based on classical nucleation theory and kinetic growth theory of III-V ternary monolayers in nanowires, we summarize recent advancements in the modelling of axial heterostructures in III-V nanowires, describe and classify the existing models, and determine their applicability to predictive modelling and to the fitting of the available experimental data. In particular, we consider the coordinate-dependent generalizations of the equilibrium, nucleation-limited, kinetic, and regular growth models to make interfacial profiles across axial heterostructures in different III-V nanowires. We examine the factors influencing the interfacial abruptness, discuss the governing parameters, limitations, and modelling of particular material systems, and highlight the areas that require further research.

Computational screening of 2D ternary penta-materials with auxetic properties and efficient photocatalytic CO2 reduction

Due to unique structural and electronic properties, pentagon-based two-dimensional (2D) materials have captured significant interest in recent years. However, previous studies on these materials have primarily focused on unary and binary systems, with less exploration of ternary pentagonal structures. Herein, we conducted first-principles calculations to evaluate the stability of 122 ternary pentagonal monolayers composed of metals, nitrogen, and chalcogen. We identify six highly stable candidates, including AuNS, CuNTe, GaNS, InNS, SbNS, and SbNSe that meet the criteria for thermodynamic, mechanical, and dynamic stability. Mechanical property analysis reveals that five of these monolayers demonstrate auxetic behavior. Electronic structure calculations show that all candidates are semiconductors with band gaps ranging from 0.12 to 3.42 eV. Specifically, the SbNS and SbNSe monolayers are indirect semiconductors with band gaps of 2.25 and 2.27 eV, respectively. These materials exhibit strong visible light absorption, and potentially serve as exceptional photocatalysts for the reduction of CO2 to CH4 due to the optimal band alignment. The free energy change in the rate-limiting step is even lower than those found in g-C3N4 and MoS2-based systems. Our findings highlight new pentagon-based 2D materials with remarkable electronic, mechanical, and optical properties, making them promising candidates for applications in mechanics and energy conversion.

First-principles prediction of high carrier mobility for β-phase MX2N4 (M = Mo, W; X = Si, Ge) monolayers

The recently synthesized monolayer MoSi2N4 (Science 2020, 369, 367) exhibits exceptional environmental stability, a moderate band gap, and excellent mechanical properties, presenting exciting opportunities for the exploration of two-dimensional (2D) MX2Z4 materials. However, the low carrier mobility of α-phase MoSi2N4 significantly limits its potential applications in field-effect transistor (FET) devices. In this study, we systematically investigate the structural stability, elastic properties, and carrier mobility of a novel family of β-phase MX2N4 (M = Mo, W; X = Si, Ge) monolayers through first-principles calculations. Our findings reveal that these β-phase MX2N4 monolayers demonstrate remarkable dynamic, thermal, and mechanical stability. Specifically, we identify the MoSi2N4, MoGe2N4, WSi2N4, and WGe2N4 monolayers as semiconductors with band gaps of 2.70 eV, 1.57 eV, 3.12 eV, and 1.93 eV, respectively, as calculated using the HSE06 functional. Moreover, the MX2N4 monolayers exhibit significant elastic anisotropy, characterized by high ideal tensile strengths and a critical tensile strain exceeding 25%. Notably, the WGe2N4 monolayer displays exceptional anisotropic in-plane charge transport, achieving mobility levels of up to 104 cm2V− 1S− 1, surpassing those of the α-phase MX2N4 monolayers. These novel ternary monolayer structures have the potential to broaden the 2D MX2Z4 material family and emerge as promising candidates for applications in field-effect transistors.

Stability, electronic and magnetic properties of boronphosphide (BP) graphenylene induced by interstitial atomic doping

In the context of low-dimensional materials, incorporating foreign atoms through doping processes has the potential to modulate the properties of host materials, which is favorable for diverse functional applications. In this study, we introduce a series of six distinct B6P6X ternary graphenylene monolayers. The B6P6X is designed through interstitial X = Cl, Br, I, O, S, and Te atomic doping of pure BP graphenylene. Through spin-polarized density functional theory (DFT), we comprehensively investigate the stability, electronic, and magnetic properties of B6P6X monolayers. We demonstrate that B6P6X monolayers are mechanically, dynamically and thermally stable with ferromagnetic ground state properties. We show that the metallic features of B6P6X (X = Cl, Br, I, O, S) and half-metallic property of B6P6Te monolayers at the PBE level can be further modulated when subjected to the HSE06 level. It is revealed that the B6P6X (X = O, S) monolayers exhibit a sizeable magnetic moment and a large magnetic anisotropy energy (MAE) value with an easy out-of-plane magnetization axis. We also found an out-of-plane MAE magnetization axis for B6P6X (X = Br, I) monolayers and an in-plane easy magnetization axis for B6P6X (X = Cl, Te) monolayers. Further investigation show that the B6P6S monolayer exhibit above room-temperature TC up to 565 K. The estimated Berezinskii–Kosterlitz–Thouless transition (BKT) temperature value of B6P6Te monolayer is 254 K. Our findings show that the B6P6X monolayers, particularly doped with chalcogens are potential candidates for nanoscale electronics and spintronics applications.

Theoretical Study of the Ternary Compound Monolayer CuP2Se for Photocatalytic Water Splitting with Efficient Optical Absorption.

Utilizing photocatalytic method to produce hydrogen by splitting water is an efficient strategy to solve the hotspot issues of energy crisis and environmental pollution. Herein, we systematically investigate the corresponding properties of the reported Cu-bearing ternary compound monolayer CuP2Se by using the first-principle calculations. The monolayer CuP2Se has quite small cleavage energy of 0.51 J/m2, indicating it can be easily produced by the mechanical exfoliation method experimentally. In addition, it is an indirect bandgap semiconductor material which has a moderate value of 1.91 eV. The conduction band minimum (CBM) and valence band maximum (VBM) can perfectly straddle the redox potentials of water when a biaxial strain of -4% to 4% is applied, unveiling the high photocatalytic thermodynamic stability of monolayer CuP2Se in response to the effect of solvent tension. Remarkably, the monolayer CuP2Se also demonstrates significant sunlight capturing ability in the visible region. The outstanding electronic and optical properties suggest that the monolayer CuP2Se is undoubtedly a viable material for photocatalytic water splitting.

New 2D penta-SiPN: A wide and indirect bandgap semiconductor

In recent years, two-dimensional (2D) pentagonal ternary monolayers have attracted much attention and emerged as a new class of materials because of their new feature and extensive applicability. Using first-principles density functional theory (DFT) calculations, we predict a new 2D pentagonal-SiPN or p-SiPN monolayer material. The new monolayer has shown to be structurally, thermodynamically, and dynamically stable. Our findings imply that p-SiPN is a wide and indirect bandgap semiconductor, with a highly tunable bandgap with applied equ-biaxial strain. This makes p-SiPN a promising candidate for futuristic optoelectronics and nanomechanics device applications.

Dioxides transition metal monolayers: A first-principles calculations

We carried out first-principles computational calculations within the framework of density functional theory using the generalized gradient approximation along with the pseudo-potential method, in order to investigate the structural and electronic properties and the energy stability of ternary bidimensional alloys based on TMxV1-xO2 (TM = Cr, Mo, and W) for x = 0.0, 0.25, 0.50, 0.75, and 1.0 transition metal dioxides in the 1H structure (group #187). We found that the values of the lattice constants of the VO2, CrO2, MoO2 and WO2 monolayers are in good agreement with reported results and that the lattice constants of ternary alloys obey Vegard's law, with a maximum deviation of 0.362% (less than 1%) for the alloy W0.25V0.75O2. We found that the values calculated for formation energies are negatives, therefore the ternary monolayers are thermodynamically stable. In addition, we found that the Cr0.25V0.75O2 monolayer has a half-metallic character with a magnetic moment of 1.0 μB/cell, while the Mo0.25V0.75O2 and W0.25V0.75O2 monolayers exhibit a metallic behavior, with magnetic moments of 0.40 μB/cell and 1.16 μB/cell, respectively. These magnetic properties come from the hybridization between the V-d, Cr-d, and O-p orbitals. The TMxV1-xO2 (TM = Cr, Mo, and W, with x = 0.50 and 0.75) alloys exhibit a metallic behavior and do not exhibit magnetic properties. In particular, we carried out a study of the mechanical and dynamic stability of the Cr0.25V0.75O2 monolayer, in view of the fact that it is the system of greatest interest for applications in spintronics, through calculations of the elastic constants (a criterion for mechanical stability) and calculations of the vibrational properties of the lattice (phonons).

Atomic insights into the interaction of N2, CO2, NH3, NO, and NO2 gas molecules with Zn2(V, Nb, Ta)N3 ternary nitride monolayers.

The search for promising carrier blocking layer materials with high stability, including resistance to surface inhibition by environmental molecules that cause a drop in carrier mobility, is critical for the production of tandem solar cells. Based on density functional theory calculations, the reaction of atmospheric gases, including N2, CO2, NH3, NO, and NO2, with three promising Zn2(V, Nb, Ta)N3 monolayers is discovered. The results suggest the chemical adsorption of NH3 and physical adsorption of NO and NO2. In addition, the Zn2(V, Nb, Ta)N3 monolayers are characterized by a weak bonding with N2 and CO2. Charge redistribution is found at the interface between the monolayers and NH3, NO and NO2 molecules, leading to the formation of a local surface dipole that affects the functionality of the Zn2(V, Nb, Ta)N3 monolayers. The Zn2VN3 monolayer is less reactive with atmospheric gases and thus is the most promising for application in tandem solar cells. Notably, the revealed nontrivial behavior of the Zn2(V, Nb, Ta)N3 monolayers towards N-containing gases makes them promising for application in gas sensing. Specifically, the Zn2TaN3 monolayer is the most promising for application in molecular sensing due to its high reversibility and distinguished interaction with NH3, NO, and NO2 gases.

Two-dimensional ternary pentagonal BCX (X = P, As, and Sb): promising photocatalyst semiconductors for water splitting with strong piezoelectricity.

Seeking high-performance energy conversion materials is one of the most important issues in designing 2D materials. In the framework of density functional theory, we propose a series of ternary monolayers, penta-BCX (X = P, As, and Sb), and systematically investigate their structural stability, mechanical, piezoelectric, and photocatalytic properties. All three materials are semiconductors with a bandgap ranging from 2.56 eV to 3.24 eV, so they could be promising catalysts for the photolysis of water. Penta-BCX exhibits significant piezoelectric properties attributed to their non-centrosymmetric structure and low in-plane Young's modulus, which are expected to efficiently drive photocatalytic water decomposition. Moreover, the bandgap, band edge position, and light absorption of penta-BCX can be modulated by tensile or compressive strain to enhance their photocatalytic performance in the visible light and ultraviolet regions.

Unpinned Dirac-Fermions in Carbon–Phosphorus–Arsenic-Based Ternary Monolayers

Unpinned Dirac-Fermions in Carbon–Phosphorus–Arsenic-Based Ternary Monolayers

High external quantum efficiency monolayer MoS2(1−x)Se2x phototransistor with alloying-induced near-infrared absorption

Due to intriguing electrical and optical properties, two-dimensional MoS2 has gained significant attention and emerged as a promising material in photonic and optoelectronic fields. Nevertheless, the intrinsic optical absorption of monolayer MoS2 is limited in the visible region only, restricting applications toward near-infrared (NIR) photodetection. Herein, we engineered the optical properties of MoS2 via alloying with Se to extend its optical absorption to the NIR region, and the phototransistor was fabricated based on monolayer MoS2(1−x)Se2x (x = ∼0.1). When under 780 nm (∼1.59 eV) illumination, the device delivered a photoresponsivity of 75.38 A/W, a specific detectivity of ∼1012 Jones, and an external quantum efficiency up to 11 230%. Additionally, it was revealed by density functional theory calculations that NIR absorption originated from the transition of valence states of sulfur vacancy (Vs) interband energy states between +1 and 0, providing an interband energy level of 1.58 eV away from the conduction band minima. Moreover, alloying of Se can suppress deep-level defects formed via Vs, further boosting device performance. This work has demonstrated high-performance NIR phototransistors based on ternary monolayer MoS2(1−x)Se2x, providing both a viable solution and fundamental mechanisms for NIR-blind MoS2 with extended optical absorption.

Two-dimensional type-II MSi2N4/InS (M = Mo, W) heterostructures for photocatalysis

Recently, two-dimensional (2D) ternary monolayer MSi2N4 (M = Mo, W) was synthesized by chemical vapor deposition. However, monolayer MSi2N4 (M = Mo, W) has an indirect bandgap, which seriously hinders its application in optoelectronic devices. Herein, we propose two MSi2N4/InS (M = Mo, W) van der Waals heterojunctions (vdWHs) possessing type-II band alignments by first-principles. Our results indicate that these vdWHs achieve an indirect-to-direct bandgap transition and exhibit fascinating optical absorption spectra in the range of visible light. Moreover, the light absorption efficiencies of both vdWHs are significantly strengthened, and the intrinsic electric field of vdWHs can effectively promote the separation of photogenerated electron–hole pairs. In particular, the most significant electron mobility of MSi2N4/InS (M = Mo, W) vdWHs is up to 6.6 × 103 cm2 V−1 s−1, demonstrating their considerable potential for optoelectronic device applications. Notably, MSi2N4/InS (M = Mo, W) vdWHs can facilitate water splitting due to their suitable band edges. Therefore, our findings demonstrate two 2D MSi2N4/InS (M = Mo, W) type-II vdWHs with fascinating potentials for photocatalysis.

A computational study of 2D group-III ternary chalcogenide monolayer compounds MNTe2 (M, N = In, Ga, Al)

First principle calculations of novel two-dimensional (2D) group-III ternary chalcogenide monolayer (G3TCM) compounds have been carried out using density functional theory. The 2D hexagonal structure has a honeycomb-like appearance from both the top and bottom views. Both pristine and G3TCM compounds are energetically favourable and have been found to be dynamically stable via phonon calculations. The ab-initio molecular dynamics calculations show the thermodynamical stability of the G3TCM compounds. The G3TCM compounds exhibit semiconductor behaviour with a decreased indirect bandgap compared to the pristine monolayers. Chalcogen atoms contribute mainly to the valence bands, while group-III atoms have a major contribution to the conduction band. A red shift has been observed in the absorption of light, mainly in the visible and ultraviolet regions, and the refractive index is increased compared to the pristine material. Both pristine and G3TCM compounds have been found to be more active in the ultraviolet region, and low reflection has been observed. In the 6–8 eV range of the ultraviolet region, zero reflection and the highest absorption are observed. The monolayer has shown potential applications in optoelectronics devices as an ultraviolet and visible light detector, absorber, coating material, and more. The band alignment of the 2D G3TCM monolayer is calculated to observe its photo-catalyst behaviour.

Controllable phase modulation and electronic structures of monolayer MoSe2xTe2(1−x) alloys grown via molecular beam epitaxy

Controllable phase modulation and electronic structure are essential factors in the study of two-dimensional transition metal dichalcogenides due to their impact on intriguing physical properties and versatile optoelectronic applications. Here, we report the phase-controlled growth of ternary monolayer MoSe2xTe2(1−x) (0 ≤ x ≤ 1) alloys induced through in situ doping and composition tuning via molecular beam epitaxy. Our approach leverages the substitution of selenium for tellurium to lower the energy barrier of the semi-conducting 2H and semi-metallic 1T′ phase transition. The alloys’ lattice constants, Mo-3d binding energy and electronic bandgap were demonstrated to be tunable by varying the selenium composition (x), respectively. First-principles calculations agree well with our experimental results, revealing that the valence band bowing effect of the monolayer alloys is attributed to the difference in coupling between anions and cations. This work provides a new pathway for phase modulation growth and controllable electronic structure of ternary monolayer transition metal dichalcogenide alloys, which is of great significance for ohmic contact and band engineering in developing transistor device applications using two-dimensional semiconductors.

Two-Dimensional Planar Penta-NiPN with Ultrahigh Carrier Mobility and Its Potential Application in NO and NO2 Gas Sensing.

Two-dimensional (2D) materials with novel structures and electronic properties are promising candidates for the next generation of micro- and nano-electronic devices. Herein, inspired by the recent experimental synthesis of penta-NiN2 (ACS Nano, 2021, 15, 13539-13546), we propose for the first time a novel ternary penta-NiPN monolayer with high stability by partial element substitution. Our predicted penta-NiPN monolayer is a quasi-direct bandgap (1.237 eV) semiconductor with ultrahigh carrier mobilities (103-105 cm2V-1s-1). Furthermore, we systematically studied the adsorption properties of common gas molecules (CO, CO2, CH4, H2, H2O, H2S, N2, NO, NO2, NH3, and SO2) on the penta-NiPN monolayer and its effects on electronic properties. According to the energetic, geometric, and electronic analyses, the penta-NiPN monolayer is predicted to be a promising candidate for NO and NO2 molecules. The excellent electronic properties of and the unique selectivity of the penta-NiPN monolayer for NO and NO2 adsorption suggest that it has high potential in advanced electronics and gas sensing applications.

Rational Modulation of Single Atom Coordination Microenvironments in a BCN Monolayer for Multifunctional Electrocatalysis.

Single-atom (SA) catalysts (SACs) have demonstrated outstanding catalytic performances toward plenty of relevant electrochemical reactions. Nevertheless, controlling the coordination microenvironment of catalytically active SAs to further enhance their catalytic oerformences has remained elusive up to now. Herein, a systematic investigation of 20 transition metal atoms that are coordinated with 20 different microenvironments in a boroncarbon-nitride monolayer (BCN) is conducted using high-throughput density functional theory calculations. The experimentally synthesized ternary BCN monolayer contains carbon, nitrogen, and boron atoms in its 2D network, thus providing a lot of new coordination environments than those of the current Cx Ny nanoplatforms. By exploring the structural/electrochemical stability, catalytic activity, selectivity, and electronic properties of 400 (20 × 20) TM-BCN moieties, it is discovered that specific SA coordination environments can achieve superior stability and selectivity for different electrocatalytic reactions. Moreover, a universal descriptor to accelerate the experimental process toward the synthesis of BCN-SACs is reported. These findings not only provide useful guidance for the synthesis of efficient multifunctional BCN-SACs but also will immediately benefit researchers by levering up their understanding of the mechanistic effects of SA coordination microenvironments on electrocatalytic reactions.

A type-II MnPSe3/GeC heterostructure with tunable spin and valley splitting

The ternary chalcogenide MnPSe3 monolayer recently gets a lot of attention because of its two nonequivalent energy valleys. The existence of spin–orbit coupling (SOC) effect can cause the valley splitting of around 24 meV. However, the spin degeneracy is still kept in MnPSe3 monolayer owing to the antiferromagnetic coupling between Mn2+ ions. The interlayer coupling effect in the van der Waals (vdW) heterostructures can break the symmetry of MnPSe3 and induce the spin splitting. Here, we simulate the MnPSe3/GeC vdW heterostructure and investigate the effects of the stacking and interlayer coupling effect on both spin and valley splitting. The excitation mode of valley excitons is greatly related to the stacking of heterostructures. The interlayer excitons can only be formed in one of the configurations with C3 symmetry according to optical selection transition rule. The interlayer coupling effect is modulated by changing interlayer distance. With vertical compressive strain (−20%), the spin and valley splitting higher than 50 meV and 30 meV can be obtained in MnPSe3/GeC vdW heterostructures, respectively. This study suggests that the stacking and vertical strain are both efficient approaches to modulate the spin and valley splitting through the interlayer coupling effect in the vdW heterostructures.

Revealing the structure and mechanisms of action of a synthetic opioid with model biological membranes at the air-water interface

Synthetic opioids such as piperazine derivative called MT-45 interact with opioid receptors in a manner similar to morphine leading to euphoria, a sense of relaxation and pain relief and are commonly used as substituents of natural opioids. In this study we show the changes in the surface properties of nasal mucosa and intestinal epithelial model cell membranes formed at the air – water interface using Langmuir technique upon the exposure to MT-45. Both membranes constitute the first barrier to absorb this substance into the human body. The presence of the piperazine derivative affects the organization of both DPPC and ternary DMPC:DMPE:DMPS monolayers treated as simple models of nasal mucosa and intestinal cell membranes, respectively. This novel psychoactive substance (NPS) leads to the fluidization of the model layers, which may indicate their increased permeability. MT-45 has a greater influence on the ternary monolayers characteristic of the intestinal epithelial cells than nasal mucosa. It might be attributed to the increased attractive interactions between the components of the ternary layer, which in turn increase the interactions with a synthetic opioid. Additionally, the crystal structures of MT-45 determined by single-crystal and powder X-ray diffraction methods allowed us to both provide useful data for facilitating the identification of synthetic opioids as well as to attribute the effect of MT-45 to the ionic interactions between protonated nitrogen atoms and negatively charged parts of the polar heads of the lipids.

Pentagonal CmXnY6-m-n (m = 2, 3; n = 1, 2; X, Y = B, N, Al, Si, P) Monolayers: Janus Ternaries Combine Omnidirectional Negative Poisson Ratios with Giant Piezoelectric Effects.

Two-dimensional (2D) materials composed of pentagon and Janus motifs usually exhibit unique mechanical and electronic properties. In this work, a class of ternary carbon-based 2D materials, CmXnY6-m-n (m = 2, 3; n = 1, 2; X, Y = B, N, Al, Si, P), are systematically studied by first-principles calculations. Six of 21 Janus penta-CmXnY6-m-n monolayers are dynamically and thermally stable. The Janus penta-C2B2Al2 and Janus penta-Si2C2N2 exhibit auxeticity. More strikingly, Janus penta-Si2C2N2 exhibits an omnidirectional negative Poisson ratio (NPR) with values ranging from -0.13 to -0.15; in other words, it is auxetic under stretch in any direction. The calculations of piezoelectricity reveal that the out-of-plane piezoelectric strain coefficient (d32) of Janus panta-C2B2Al2 is up to 0.63 pm/V and increases to 1 pm/V after a strain engineering. These omnidirectional NPR, giant piezoelectric coefficients endow the Janus pentagonal ternary carbon-based monolayers as potential candidates in the future nanoelectronics, especially in the electromechanical devices.

2D Mg2M2X5 (M = B, Al, Ga, In, Tl; X = S, Se, Te) monolayers: Novel stable semiconductors for water splitting photocatalysts

Two-dimensional (2D) semiconductors with appropriate band gaps can be promising candidates for being efficient water splitting photocatalysts and are also applicable in optical devices. Herein, a new series of ternary 2D monolayer materials Mg2M2X5 (M = B Al, Ga, In, Tl and X = S, Se, Te) is designed based on density functional theory. Structural, thermal, dynamical, and optoelectronic properties of 15 distinct Mg2M2X5 monolayer nanomaterials are discussed. We show that all designed monolayer structures are thermally, dynamically, and thermodynamically stable. All of the 2D Mg2M2X5 monolayers are semiconductors, except for monolayer Mg2B2Te5 which has metallic properties. The 2D Mg2Al2Se5, Mg2B2S5, Mg2B2Se5, Mg2Ga2S5, Mg2Ga2Se5, Mg2Ga2Te5, Mg2In2S5, and Mg2Tl2S5 monolayers have direct band gaps (0.80–2.50 eV), whereas the rest of the investigated 2D Mg2M2X5 monolayers are semiconductors with indirect gaps (0.40–3.05 eV). Based on our calculations, Mg2Ga2S5, Mg2Al2Se5, and Mg2B2S5 monolayers possess extremely high anisotropies with high electron mobilities of 1208.28, 629.94 and 6144.28 cm2V-1s−1 along the Y direction, respectively. Remarkably, these new 2D monolayers have pronounced strong optical absorption (>105 cm−1) over a broad range of the visible light spectrum. The Mg2Ga2S5, Mg2B2S5, and Mg2Al2Se5 monolayers exhibit excellent potential for application in solar water splitting due to the moderate band gaps, high electron mobilities and ideal band alignments for photon excitation for both hydrogen and oxygen evolution reactions.