Monolayer SnS Research Articles

Compressive strain-induced enhancement in valley polarization in β-phosphorene like SnS monolayers

Berry curvature (BC), the effective magnetic field in k space, determines the valley Hall effect. Although BC is specific to material, its tunability will provide greater control over this valley polarization. The elasticity in β-phosphorene like 2D SnS monolayer offers ample room for manipulating its electronic properties and BC via mechanical strain. In DFT calculations, SnS monolayer shows a band gap of 2.32 eV, a valley spin splitting (VSS) of 23.8 meV and 140.4 meV, respectively, at K/K’ point on the top (bottom) of the valence (conduction) band. 2.3 % biaxial compressive strain, realizable in experiments, shifts the conduction band minimum (CBM), maximum BC and VSS to the K/K’ point. These features are retained at higher compressive strain. The BC undergoes further enhancement to ∼ 5 Å2 upon continued biaxial compression. The out-of-plane built-in electric field and polarization intrinsically arising from the buckled structure of SnS monolayers is favourably enhanced via in-plane compressive strain, which helps to extend the lifetime of valley polarized excitons. The trend in BC of MX (M = Ge, Sn; X = S, Se, Te) monolayers has been studied. This group of hexagonal buckled monochalcogenide monolayers can pave a new way forward for valleytronics.

Adsorption behavior of transition metal (Pd, Pt, Ag and Au) doped SnS monolayers on SF6 decomposed species and the effects of applied electric field and biaxial strain

The adsorption behavior of SF6 characteristic decomposition products (SO2 and SOF2) on intrinsic and transition metal (TM) atom modified SnS monolayers is investigated based on the first principles. The adsorption structure, adsorption energy, density of states, electron localization function, electron density difference, work function, and desorption properties are discussed to evaluate SnS monolayers as potential candidates as adsorbents for SO2 and SOF2. Our results show that the detection performance of the intrinsic SnS monolayer is poor due to the relatively weak interaction with gas molecules. After introducing TM dopants (TM = Pd, Pt, Ag and Au) on SnS monolayer, Pd and Pt atoms tend to be adsorbed on TH sites, while Ag and Au atoms are more easily captured by TS sites. The results of adsorption energy and electronic properties showed that TM atoms could significantly improve the adsorption properties of SO2 and SOF2 molecules on SnS monolayers. Furthermore, the effects of electric field and biaxial strain on the sensing properties of gas molecules on TM-SnS monolayers are also investigated. Finally, the desorption time of gas molecules from the TM-SnS monolayer is estimated to evaluate its potential application in the detection and removal of faulty gases in SF6 power devices. The research results not only reveal the sensing mechanism of the TM-SnS monolayer for the characteristic decomposition products of SF6, but also provide theoretical guidance for the further development of SnS-based adsorbents or scavengers.

Pd, Ni, Cu and Ag modified SnS: A potential candidate for NH3 and NO2 detection and scavenging

NO2 and NH3 chronically pose serious concerns to the security of industrial production and human health, thus it is essential to accomplish real-time monitoring of harmful gases. In this work, employing density functional theory, four transition metal nano particles, Pd, Ni, Cu, and Ag are adopted to modify the surface of the SnS monolayer further exploring the adsorption mechanism and electrical properties of X-SnS (X = Pd, Ni, Cu, and Ag) for NO2 and NH3 gas molecules. Due to its highest binding energy (−3.793 eV), the results demonstrate that Ni-SnS has the most stable decorated structure. Depending on the degree of orbital hybridization, Pd, Ni, Cu, and Ag modified SnS monolayers have enhanced adsorption energy and electron transfer to varying degrees. Moreover, among four modified structures Ag-SnS exhibits the best adsorption performance. X-SnS (X = Pd, Ni, Cu and Ag) can be applied as a good NO2 adsorbent under both ambient and high temperature. In addition, Ni-SnS, Ag-SnS and Cu-SnS sensing systems have different desorption capacities at different operating temperatures, which will help to achieve differentiated gas sensing and gas selective sensing.

Ferroelectricity-Driven Phonon Berry Curvature and Nonlinear Phonon Hall Transports.

Berry curvature (BC) governs topological phases of matter and generates anomalous transport. When a magnetic field is applied, phonons can acquire BC indirectly through spin-lattice coupling, leading to a linear phonon Hall effect. Here, we show that polar lattice distortion directly couples to a phonon BC dipole, which causes a switchable nonlinear phonon Hall effect. In a SnS monolayer, the in-plane ferroelectricity induces a phonon BC and leads to the phononic version of the nonvolatile BC memory effect. As a new type of ferroelectricity-phonon coupling, the phonon Rashba effect emerges and opens a mass gap in tilted Weyl phonon modes, resulting in a large phonon BC dipole. Furthermore, our ab initio non-equilibrium molecular dynamics simulations reveal that nonlinear phonon Hall transport occurs in a controllable manner via ferroelectric switching. The ferroelectricity-driven phonon BC and corresponding nonlinear phonon transports provide a novel scheme for constructing topological phononic transport/memory devices.

SnS2 monolayer as a promising candidate for NO2 sensor or capturer with high selectivity and sensitivity: A first-principles study

As a common toxic gas, the sensing and capture of NO2 are two important topics closely related to human health and the environment. In this work, the adsorption behavior of a SnS2 monolayer on gas molecules including NO2, CO2, SO2, NH3, acetone, ethanol, methanol and formaldehyde was studied by DFT methods to explore its possibility as a NO2 gas sensor or capturer. Among these gases, only NO2 can be chemisorbed on to the SnS2 monolayer with an adsorption energy of −0.43 eV. Compared with other gases, the significantly altered I–V relationship of the SnS2 monolayer before and after adsorbing NO2 demonstrates that the SnS2 monolayer has superior sensitivity and selectivity for NO2. In particular, the adsorption of NO2 by the SnS2 monolayer strengthens linearly with increasing biaxial strain, while the adsorption of other gases remains weak, thus offering an effective route for the SnS2 monolayer to capture and release NO2 by adjusting the magnitude of an applied biaxial strain. These results demonstrate that the SnS2 monolayer is an excellent candidate material for the effective capture, separation, storage and detection of NO2.

Photocatalytic performance for palm-fiber-like SnS2 nanoflakes with full solar spectrum light response

A palm-fiber-like SnS2 with multilayer structure has been hydrothermally synthesized by anion exchange process from vertically-aligned Sn3O4 nanoflake arrays precursors. Compared to monolayer SnS2, the multilayer SnS2 exhibits obvious photothermal effect and displays excellent photocatalytic activity for RhB degradation and CO2 reduction under full solar spectrum. The multilayer SnS2 is found to have a larger electrochemically active surface area, and increased absorption for full solar spectrum with the merits of micron- and nanometer-scale structure favors to absorb the full spectrum of sunlight. The combined effect for the UV–vis absorption by the nanoscale primary structure and NIR absorption by the secondary micron-structure likely play an important role for its superior absorption capability and photocatalytic activity. This work is expected to provide a foundation to develop photocatalysts, photodetectors, solar cells and other solar energy conversion devices with full solar spectrum light response.

Doping-dependent optoelectronic, and magnetic properties of monolayer SnS

Based on the first-principles calculations, we examine the effects of In/Sb/P doping on the structure, electronics, and magnetic properties of monolayer SnS. We have examined that the In-/Sb-/P-doped SnS is energetically more favorable under the S-rich condition due to high formation energies. The doping of In at Sn site keeps the semiconducting nature of monolayer SnS, and the Sb doping turns it to metallic. Interestingly, the In-doping turns the non-magnetic monolayer SnS to the magnetic one with a magnetic moment of 1.00 μB. Additionally, the ferromagnetic behavior is observed at a larger distance confirming the large range ferromagnetism in the In-doped SnS. Importantly, for the In-doped system, a high MAE of 40.91 meV is calculated. Furthermore, the doping P at the S-site in monolayer SnS trun the semiconductor nature to a metallic one. Additional experimental studies into the efficient utilization of these systems in the fields of photo-electronics and magnetic semiconductor devices are very desirable.

Thermal transport properties of monolayer GeS and SnS: A comparative study based on machine learning and SW interatomic potential models

Phonon transport properties of two-dimensional materials can play a crucial role in the thermal management of low-dimensional electronic devices and thermoelectric applications. In this study, both the empirical Stillinger–Weber (SW) and machine learning interatomic potentials are employed to investigate the lattice thermal conductivity of monolayer GeS and SnS through solving the phonon Boltzmann transport equation. The accuracy of the two types of interatomic potentials and their performance for the evaluation of thermal conductivity are verified by analyzing phonon harmonic and anharmonic properties. Our results indicate that the thermal conductivity can be predicted more accurately with a machine learning approach, while the SW potential gives rise to an overestimated value for both monolayers. In addition, the in-plane anisotropy of thermal transport properties existing in these monolayers can be confirmed by both potential models. Moreover, the origins of the deviation existing in calculated thermal conductivities, including both the effects of interatomic potential models and monolayer compositions, are elucidated through uncovering the underlying phonon transport mechanisms. This study highlights that in contrast to the machine learning approach, more careful verification is required for the simulation of thermal transport properties when empirical interatomic potential models are employed.

Strain engineering and hydrogen effect for two-dimensional ferroelectricity in monolayer group-IV monochalcogenides MX (M = Sn, Ge; X = Se, Te, S)

Two-dimensional (2D) ferroelectric compounds are a special class of materials that meet the need for devices miniaturization, which can lead to a wide range of applications. Here, we investigate ferroelectric properties of monolayer group-IV monochalcogenides MX (M = Sn, Ge; X = Se, Te, S) via strain engineering, and their effects with contaminated hydrogen are also discussed. GeSe, GeTe, and GeS do not go through transition up to the compressive strain of –5%, and consequently have good ferroelectric parameters for device applications that can be further improved by applying strain. According to the calculated ferroelectric properties and the band gaps of these materials, we find that their band gap can be adjusted by strain for excellent photovoltaic applications. In addition, we have determined the most stable hydrogen occupancy location in the monolayer SnS and SnTe. It reveals that H prefers to absorb on SnS and SnTe monolayers as molecules rather than atomic H. As a result, hydrogen molecules have little effect on the polarization and electronic structure of monolayer SnTe and SnS.

Two-Dimensional ZnS/SnS2 Heterojunction as a Direct Z-Scheme Photocatalyst for Overall Water Splitting: A DFT Study.

Direct Z-scheme photocatalysts have attracted extensive attention due to their strong redox ability and efficient separation of photogenerated electron-hole pairs. In this study, we constructed two types of ZnS/SnS2 heterojunctions with different stacking models of ZnS and SnS2 layers, and investigated their structures, stabilities, and electronic and optical properties. Both types of heterojunctions are stable and are direct Z-scheme photocatalysts with band gaps of 1.87 eV and 1.79 eV, respectively. Furthermore, their oxidation and reduction potentials straddle the redox potentials of water, which makes them suitable as photocatalysts for water splitting. The built-in electric field at the heterojunction interface improves the separation of photogenerated electron-hole pairs, thus enhancing their photocatalytic efficiency. In addition, ZnS/SnS2 heterojunctions have higher carrier mobilities and light absorption intensities than ZnS and SnS2 monolayers. Therefore, the ZnS/SnS2 heterojunction has a broad application prospect as a direct Z-scheme visible-light-driven photocatalyst for overall water splitting.

The gas-sensing mechanism of Pt3 cluster doped SnS2 monolayer for SF6 decomposition: A DFT study

In this study, Pt3-cluster-doped SnS2 was first proposed as the adsorption and sensing materials of typical SF6 decomposed gases (SO2, SOF2, SO2F2 and H2S). Based the density functional theory, the possible application of Pt3-SnS2 as gas sensor or absorbents for the SF6 decomposed gas is discussed through the analysis of the density of states, adsorption energy, charge transfer and the frontier molecular orbital. These results illustrate that the doping of Pt metal clusters can greatly improve the response of pure SnS2 monolayer to the characteristic decomposition gas of sulfur hexafluoride (SF6). The excessive high adsorption energy indicates a strong chemical interaction of the Pt3-SnS2 monolayer with SO2 (−2.800 eV) and H2S (−3.346 eV) molecules, which suggests that Pt3-SnS2 is a potential ideal candidate for gas adsorbent. Moreover, the large variation of band gap and appropriate adsorption energy show that Pt3-SnS2 has the promising to be a candidate gas sensor material for the SOF2 (−1.060 eV), and SO2F2 (−0.904 eV). This study also provides guidance for further study of the SnS2 monolayer doped by transition metal clusters.

SnS2 Monolayer-Supported Transition Metal Atoms as Efficient Bifunctional Oxygen Electrocatalysts: A Theoretical Investigation

It is of significance to pursue eminent catalytic activity and nonprecious bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which is beneficial for renewable energy applications. Herein, the electrocatalytic performance of transition metal (TM) atoms supported on a SnS2 monolayer was investigated using first-principles methods based on density functional theory in the present work. Our results reveal that TM atoms supported on the surface of the SnS2 monolayer can effectively improve the catalytic performance of SnS2 for OER and ORR. Interestingly, the OER/ORR overpotentials of Ni/SnS2 and Pt/SnS2 are estimated to be 0.38/0.62 and 0.37/0.58 V, respectively, showing promising catalytic performance. Moreover, the volcano plots also evince that the efficient bifunctional electrocatalysts for OER/ORR are SnS2 monolayer-supported Ni or Pt atoms. This study will pave the way toward the synthesis of high-performance SnS2-based bifunctional oxygen electrocatalysts in future.

Giant Stokes shift for charged vacancies in monolayer SnS

We perform first-principles density-functional theory calculations to determine the equilibrium defect structures, formation energies, charge transition levels, and electronic structures of Sn and S vacancies in monolayer SnS. Both Sn and S vacancies exhibit multiple charge transition levels and in-gap defect states, indicating that they may be stable in different charge states depending on the Fermi level in the system. Depending on the charge state of the vacancy, the easily distorted SnS lattice undergoes different relaxations, and in some cases, symmetry-breaking reconstructions, creating defect states within the gap that electrons can occupy at a lower energetic cost. Due to significant atomic relaxations between the equilibrium defect structures in different charge states, optical charge transitions involving both types of vacancies exhibit significant Stokes shifts of over 1 eV, which may provide opportunities for increased efficiency in light emission diode, solar cell, and solar concentrator applications.

Interfacial Electronic Properties and Photocatalytic CO2 Reduction of a Z-Scheme SnS/(CH3NH3)2AgBiI6 Double Perovskite Heterostructure

The conversion of CO2 into energy fuel is an effective strategy to address energy shortages and environmental problems. To enhance the photocatalytic activity of CO2 reduction, the lead-free halide double perovskite (CH3NH3)2AgBiI6 (010) surface is combined with a SnS monolayer to construct a stable SnS/(CH3NH3)2AgBiI6 photocatalyst. The bandgap of SnS/(CH3NH3)2AgBiI6 is narrow (1.566 eV) compared with the (CH3NH3)2AgBiI6 (010) surface, which enhances the absorption of visible light and leads to the redshift of the absorption edge. The interface interaction between the (CH3NH3)2AgBiI6 (010) surface and the SnS monolayer causes electron flow from the SnS monolayer to the (CH3NH3)2AgBiI6 (010) surface. SnS/(CH3NH3)2AgBiI6 has a good Z-scheme band alignment, which facilitates the separation of electron–hole pairs. The electrons accumulate at the CB of the SnS monolayer and participate in the CO2 reduction reaction. In comparison with the (CH3NH3)2AgBiI6 (010) surface, SnS/(CH3NH3)2AgBiI6 changes the rate-determination step and reduces the Gibbs free energy from 2.17 to 1.72 eV. The results indicate that SnS/(CH3NH3)2AgBiI6 improves the photocatalytic activity of CO2 reduction.

Non-metal atom modified SnS2 sheet for CO2 photoreduction with significant activity and selectivity improvements: A first-principles study

Photocatalytic CO2 reduction suffers from low activity and poor product selectivity, seriously limiting its further application. Here, by means of density functional theory, we investigated the structural and catalytic properties of non-metal atoms X (X = B, C, N, and O) anchored at S vacancy site of SnS2 monolayer denoted as X/Sv-SnS2. The HSE06 result shows that both the band gap and band edge positions of X/Sv-SnS2 substrates are quite suitable for CO2 photoreduction. Interestingly, the adsorption strength of CO2 can be linearly enhanced with the decreasing non-metal atoms X from O to B, and the corresponding value ranges from −0.25 to −1.23 eV. Particularly, the diversity of non-metal atoms X generates completely different preference of CO2 reduction products according to the Gibbs free energy change. Whereas O, C, and B/Sv-SnS2 separately favor to form CO, HCOOH, and CH4 products, with remarkably low energy barrier of 1.07 eV, 0.58 eV, and 1.04 eV, respectively. These peculiar activity and selectivity properties mainly stem from the unique adsorption behavior and frontier orbital interaction between non-metal atoms X and intermediates. Our findings strongly suggest that cooperation of non-metal atoms and intrinsic defect could offer an exciting opportunity to design high activity and selectivity photocatalysis for CO2 reduction.

Ab-initio modelling for gas sensor device: based on Y-doped SnS2 monolayer

In this work, we have investigated the adsorption behavior of small gas molecules like CO, NO, CO 2 , NO 2 and NH 3 on Yttrium(Y) doped SnS 2 monolayer by employing density functional theory simulations. Y-doping effect on the physicochemical properties of the pure SnS 2 monolayer is first studied, then adsorption mechanism was analyzed by adsorption energy, charge transfer, structural properties, magnetic properties , electronic properties such as density of states, charge density and band structure. In addition, the transport properties are evaluated to propound the gas adsorption response of Yttrium (Y) doped -SnS 2 system on the device level. The result shows that all the gas molecules were strongly adsorbed on the Yttrium (Y) site of the Y-doped SnS 2 monolayer through formation of strong covalent bonds and Y- doped SnS 2 monolayers can be employed as a potential candidate for gas sensing applications. Here in, to evaluate the sensing capability, the molecular model of the adsorption systems was constructed, and density functional theory (DFT) was used to calculate the adsorption behavior of these gases. • Yttrium(Y) doped SnS 2 monolayer was investigated as gas sensor. using DFT calculation. • Doping of Y atom modulates the electronic behavior of SnS 2 monolayer from semi-conductor (1.64 eV) to metal. • The gas adsorption energy of all gases are in trend with the interaction distance and charge transfer. • Transport properties are evaluated for device level modeling of Y-doped SnS 2 system.

Adsorption of CO and H2S on pristine and metal (Ni, Pd, Pt, Cu, Ag, and Au)-mediated SnS monolayers: a first-principles study.

A SnS monolayer is a new two-dimensional material with a black phosphorous structure, with high carrier mobility and a large surface-to-volume ratio, and is an ideal candidate material for gas sensors. The adsorption and sensing behaviors between the SnS monolayer and gas molecules are enhanced under the action of TM atoms with high catalytic performance. The adsorption behavior of CO and H2S on intrinsic and transition metal atom modified SnS monolayers is investigated based on the first principles calculations. The adsorption structure, adsorption energy, electron transfer, density of states, electron local density, work function, and desorption properties are discussed to evaluate the potential applications of SnS monolayers as scavengers and gas sensors for CO and H2S molecules. The results show that Ni, Pd, Pt and Cu atoms tend to be adsorbed on TH sites, while Ag and Au atoms are more easily captured by TS sites. Further studies have shown that all TM atoms can significantly enhance the sensing behavior between the SnS monolayer and the gas molecules. The adsorption performance of the CO molecule on the TM-mediated SnS (TM-SnS) monolayer is obviously better than that of the H2S molecule. Furthermore, the effects of electric field and biaxial strain on the sensing properties of gas molecules on Ni-SnS monolayers are also investigated. Finally, the desorption time of gas molecules from the TM-SnS monolayer is estimated. This will provide experimenters with theoretical guidance for the application of SnS-based sensing materials, and our work is of great significance for predicting new monochalcogenide sensing materials.

Transition Metal (Ag, AU, Co) Modified Sns2 Monolayer for the Detection of Representative Gases in Greenhouses Such as Nh3, Cl2, and C2h2

Transition Metal (Ag, AU, Co) Modified Sns2 Monolayer for the Detection of Representative Gases in Greenhouses Such as Nh3, Cl2, and C2h2

First principles study of photogalvanic effect of monolayer SnS

The photogalvanic effect of monolayer SnS was investigated at a small bias voltage under perpendicular irradiation using density functional theory combined with the non-equilibrium Green’s function method. The photocurrent was generated over the entire visible light range, and it was saturated at a small bias voltage for photon energies of 2.4, 2.6, 3.2 and 3.4 eV. The photocurrent shows cosine dependence of the polarization angle, which is attributed to the second-order response to the photoelectric field. These results provide a deeper understanding of the photogalvanic properties of the 2D SnS nanosheet based devices.

Storage of Na in 2D SnS for Na ion batteries: a DFT prediction.

The high demand for renewable and clean energy has driven the exploration of advanced energy storage systems. Sodium-ion batteries (SIBs) are considered to be potential substitutes for Li-ion batteries (LIBs) because they are manufactured from raw materials that are cheap, less toxic, and abundantly available. Recent developments have demonstrated that two-dimensional (2D) materials have gained increasing interest as electrode candidates for efficient SIBs because of their enormous surface area and sufficient accommodating sites for the storage of Na ions. Herein, we explore the binding and diffusion mechanisms of Na on a 2D SnS sheet using density functional theory (DFT). The outcomes reveal that Na has a strong binding strength with SnS as well as charge transfer from Na to SnS, which affirms an excellent electrochemical performance. A transition from semiconducting (1.4 eV band gap) to metallic has been noted in the electronic structure after loading a minor amount of Na. In addition, a low open-circuit voltage (OCV) of 0.87 V and a high storage capacity of 357 mA h g-1 show the suitability of the SnS monolayer for SIBs. In addition, the low activation barrier for Na migration (0.13 eV) is attractive for a fast sodiation/desodiation process. Henceforth, these encouraging outcomes suggest the application of the SnS sheet as an excellent anode for next-generation SIBs.