Monolayer SnS Research Articles

Injection current in ferroelectric group-IV monochalcogenide monolayers

We study the injection current response tensor (also known as circular photogalvanic effect or ballistic current) in ferrolectric monolayer GeS, GeSe, SnS, and SnSe. We find that the injection current is perpendicular to the spontaneous in-plane polarization and could reach peak (bulk) values of the order of ${10}^{10}\phantom{\rule{4pt}{0ex}}\mathrm{A}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ in the visible spectrum. The magnitude of the injection current is the largest reported in the literature to date for a two dimensional material. To rationalize the large injection current, we correlate the injection current spectrum with the joint density of states, electric polarization, strain, etc. We find that various factors such as anisotropy, in-plane polarization and wave function delocalization are important in determining the injection current tensor in these materials. We also find that compression along the polar axis can increase the injection current (or change its sign), and hence strain can be an effective control knob for their nonlinear optical response. Conversely, the injection current can be a sensitive probe of the crystal structure.

Asymmetric Strain‐Introduced Interface Effect on the Electronic and Optical Properties of the CsPbI3/SnS van der Waals Heterostructure

AbstractDifferent 2D materials can be stacked by the weak van der Waals (vdW) force, forming the vdW heterostructures and devices, which opens a new field of engineering regulation of electronic and optical properties at the atomic level. The asymmetric strain‐introduced interface effect is studied on the electronic and optical properties of CsPbI3/SnS vdW heterostructure by employing first‐principles calculations. The biaxial strains deriving from the interface mismatch reduce the work function of the monolayer SnS to a low‐energy level, and lead to monolayer SnS an indirect‐to‐direct bandgap transition. The different charge transfer behaviors in the PbI2‐ (CsI‐) surface indicate that monolayer SnS can act as the promising hole‐ (electron‐) transport material of perovskite solar cells (PSCs). Moreover, the interface effect causes the absorption spectrum of the CsPbI3/SnS heterostructure an obvious redshift and enhances its absorption ability, which is more suitable for photovoltaic devices. This work suggests that the strain‐introduced interface effect plays a significant role in the interface engineering of the vdW heterostructure between perovskite and 2D materials, which provides a new way to fabricate the high performance perovskite/2D materials heterostructure‐based solar cells and optoelectronic devices.

Effect of S-vacancy on the oxidation state of Ce in monolayer SnS2

Outstanding performance in lithium-ion-battery (LIB) of Ce-doped SnS2 nanostructure is attributed to Ce[Formula: see text]. Based on DFT, the stability, electronic and magnetic properties of Ce-doped defective/pristine SnS2 monolayer are calculated. Comparing different doping configurations with/without S-vacancy, the 2Ce atoms locating near S-vacancy (V[Formula: see text]) in SnS2 monolayer is the most stable configuration. The two localized Ce_4[Formula: see text] electrons contribute to the ferromagnetic state of this compound, and confirms the Ce[Formula: see text] not the common Ce[Formula: see text] oxidation state, i.e., 2Ce[Formula: see text]+[Formula: see text]2SnS[Formula: see text][Formula: see text]S(or[Formula: see text]+[Formula: see text]V[Formula: see text])[Formula: see text]=[Formula: see text]Ce[Formula: see text]S3[Formula: see text]+[Formula: see text]2Sn. Larger ionic radius may offer more lattice space for Li[Formula: see text] and coincide with present experimental report. This work clarified the positive effect of intrinsic defect in SnS2 monolayer and will stimulate further experimental and theoretical investigations in this field.

Chemical vapor deposition growth of crystal monolayer SnS2 with NaCl-assistant**Project supported by the National Basic Research Program of China (Grant No. 2016YFA0202302), the National Natural Science Foundation of China (Grant Nos. 61527817, 61875236, 61905010, and 61975007), and the Overseas Expertise Introduction Center for Discipline Innovation, 111 Center, China.

As an important member of the two-dimensional layers of metal dichalcogenides family, the two-dimensional (2D) group IV metal chalcogenides (GIVMCs) have been attracting intensive attention. However, the growth of monolayer tin disulfide (SnS2) remains a great challenge contrasted to transition metal dichalcogenides, which have been studied quite maturely. Till date, there have been scant reports on the growth of large-scale and large-size monolayer SnS2. Here, we successfully synthesized monolayer SnS2 crystal on SiO2/Si substrates via NaCl-assisted CVD and the edge can be as long as 80 μm. Optical microscope, Raman spectroscopy, x-ray diffraction, atomic force microscopy (AFM), and energy-dispersion x-ray (EDX) were performed respectively to investigate the morphology, crystallographic structure, and optical property of the 2D SnS2 nanosheets. In addition, we discussed the growing mechanism of the NaCl-assisted CVD method.

Vacancy‐ and doping‐dependent electronic and magnetic properties of monolayer SnS2

AbstractWe have performed first‐principles calculations to investigate the formation and migration of vacancies and doping with M (M = Ti, V, Co, Mo, W, Re) at the Sn sites and X (X = O, Se, Te) at the S sites in monolayer SnS2. We find that the formation energies for S vacancy under both Sn‐ and S‐rich environments are lower than those for Sn vacancy, indicating that the vacancies at the S sites are likely to be formed during the synthesis. Reducing the possibility of vacancy cluster formation, both the vacancies at the Sn and S sites remain robust due to high migration barrier. Additionally, SnS2 with the vacancies at the Sn sites induces magnetic ground states with a magnetic moment of 4.00 μB. Both the Sn‐ and S‐sites vacancies preserve the semiconducting nature of pristine SnS2 with band gaps of 2.47 eV and 0.30 eV, respectively. Furthermore, we find that the dopants Ti, V, Mo, W, Re can be easily incorporated at the Sn sites in monolayer SnS2 due to the low formation energies under the S‐rich environment. However, Co may not be easily incorporated into SnS2. The doping with M at the Sn sites induces magnetic ground states in non‐magnetic SnS2. Additionally, a long‐range magnetic ordering is observed in SnS2 doped with V, Co, and Mo. In contrast, easy incorporation of O, Se, and Te at the S sites under the Sn‐rich environment has been observed while the semiconducting nature of SnS2 preserves with small band gaps.

Halogenated monolayer SnS: a first-principles studies

The electronic and structural properties of a halogenated monolayer SnS is investigated by using first-principles calculations. The preferred adsorption sites for F, Cl and Br are found to be on top of the Sn atom while I atom prefers to adsorb on top of the SnS ring. All the halogenated monolayers SnS exhibit metallic behavior with charge transfer from the monolayer SnS to the halogen adatom. In the relaxed system, a larger halogen atom is located further away from the monolayer SnS which results in smaller charger transfer and thus weaker binding energy. Compared to the pristine monolayer SnS, the work function of the F, Cl or Br functionalized monolayer SnS is increased by 22 %, while for the case of I adsorption, the work function is further increased by 30%.

Computational insight of monolayer SnS2 as anode material for potassium ion batteries

There is a great challenge to design anode materials for rechargeable batteries with large capacity, excellent cyclic stability and high rate performance. Using first principle calculations, we have calculated electronic properties of monolayer SnS2 which reveal that it is an indirect-gap semiconductor with a band gap of 1.56 eV. The SnS2 becomes metallic after the insertion of small amount of K content, and the electronic conductivity increases by increasing the concentration of K. Also, our predictions show that there is a proper binding energy between K ion and monolayer SnS2 with a low average open circuit voltage (0.84 V) which is in the range of commercial anode materials. The energy surface for the diffusion of K ion on the surface of SnS2 monolayer is analyzed and a very low energy barrier (0.054 eV) is found for the K diffusion. These results indicate that SnS2 is very suitable to be use as a high performance anode material for KIBs.

Adsorption of O3, SO3 and CH2O on two dimensional SnS monolayer: A first principles study

The environment and the health of the masses are being affected by toxic gases such as O3, SO3, CH2O, H2S and HCN. In this study, we investigate the interaction of such toxic gases on SnS monolayer using density functional theory (DFT). The interaction between species and adsorbent is explained on the basis of their adsorption energy, electronic properties and charge transfer. Our results demonstrate that the process of adsorption of O3 and SO3 is chemisorbed in nature whereas CH2O, H2S and HCN is physisorbed. The validity of the adsorption process is further confirmed within the frame of electronic properties and charge transfer. As a result, we find each of the investigated gas molecules is acting as a charge acceptor. Diversity in the adsorption of customary gas molecules on the SnS monolayer gives rise to a possibility to exploit them as chemical gas sensors.

Adsorption behavior of Pd-doped SnS2 monolayer upon H2 and C2H2 for dissolved gas analysis in transformer oil

Dissolved gas analysis (DGA) is an effective technique to evaluate the operation status of the power transformer, and to guarantee the safe operation of the power system. Using density functional theory (DFT), we proposed the application of Pd-doped SnS2 (Pd-SnS2) monolayer as a sensing material to detect H2 and C2H2 in transformer oil. The electronic and geometric structures of Pd-doping behavior on SnS2 were also analyzed to give insight into the physicochemical property of the active surface. The adsorption configuration, density of state (DOS), frontier molecular orbital theory as well as recovery property of the adsorption systems were comprehensively studied to estimate the suitability of our proposed material for sensing application. Our calculations showed that Pd-doping exerts some deformations on the SnS2 monolayer and leads to the narrowed bandgap of such surface. Meanwhile, Pd-SnS2 monolayer has stronger adsorption performance upon C2H2 compared to H2. And the desirable interaction with C2H2 makes it possible for application of a resistance-type sensor given the good electrical response and recovery property. Our calculations are meaningful to suggest novel sensing material for application in the field of electrical engineering.

Shape-Engineered Synthesis of Atomically Thin 1T-SnS2 Catalyzed by Potassium Halides.

Shape engineering plays a crucial role in the application of two-dimensional (2D) layered metal dichalcogenide (LMD) crystalline materials in terms of physical and chemical property modulation. However, controllable growth of 1T phase tin disulfide (SnS2) with multifarious morphologies has rarely been reported and remains challenging. Herein, we report a direct synthesis of large-size, uniform, and atomically thin 1T-SnS2 with multiple morphologies by adding potassium halides via a facile chemical vapor deposition process. A variety of morphologies, i.e., from hexagon, triangle, windmill, and dendritic to coralloid, corresponding to fractal dimensions from 1.01 to 1.81 are accurately controlled by growth conditions. Moreover, the Sn concentration controls the morphology change of SnS2. The edge length of the SnS2 dendritic flake can grow larger than 500 μm in 5 min. Potassium halides can significantly reduce the surface migration barrier of the SnS2 cluster and enhance the SnS2 adhesion force with substrate to facilitate efficient high in-plane growth of monolayer SnS2 compared to sodium halides by density functional theory calculations. More branched SnS2 with higher fractal dimension provides more active sites for enhancing hydrogen evolution reactions. Importantly, we prove that potassium halides are preferable for 1T-phase LMDs structures, while sodium halides are more suitable for 2H-phase materials. The growth mechanism proposed here provides a general approach for controllable-phase synthesis of 2D LMD crystals and related heterostructures. Shape engineering of 2D materials also provides a strategy to tune LMD properties for demanding applications.

Elastic behavior and intrinsic carrier mobility for monolayer SnS and SnSe: First-principles calculations

Abstract Two-dimensional (2D) SnS and SnSe like black phosphorus have recently attracted great attention for their potential applications in next-generation electronics. Here, first-principles calculations are employed to investigate uniaxial strain behaviors and carrier mobilities of these monolayer structures. They are more structurally stable in armchair strain ( y axis strain) than in zigzag strain ( x axis strain), because zigzag deformation of the latter can be spontaneously transformed into former. Band gaps exhibit abnormal behavior with armchair strain changing from e y = −5 % to e y = 15 % , which is elucidated through the orbital hybridization between p states of S or Se atoms and the p states of Sn atoms. Surprisingly, it found that hole mobility is mainly determined by longitudinal acoustic phonon scattering, while electron mobility is mainly dominated by optical phonon scattering. The mobility can be tuned by uniaxial strain. Tensile strain along armchair direction will reduce carrier mobility. At compressive strain of e y = −5 % , the mobility of SnSe is increased to μ x =1.40× 10 3 and μ y =2.35× 10 3 cm 2 V −1 s −1 for electron, and μ x = 1.31 × 10 3 and μ y = 1.46 × 10 3 cm 2 V −1 s −1 for hole. Excellent elastic property, moderate band gap and tunable carrier mobility make SnSe promising for application in nanoelectronics and optoelectronics.

External electric field and strains facilitated nitrogen dioxide gas sensing properties on 2D monolayer and bilayer SnS2 nanosheets

Abstract Two-dimensional (2D) nanostructures materials have attracted an exceptional interest in the structural, electronic and optical characteristics due to their ultrathin and flexible nature. Using first-principle simulations, we studied the electronic structures of Nitrogen dioxide adsorbed monolayer and bilayer SnS2 nanosheets. The results demonstrate that Nitrogen dioxide is physisorbed on monolayer and bilayer SnS2 nanosheets acting as acceptors with obvious charge transfer 0.03 e and 0.05 e from the basal to the adsorbate. Moreover, our results show that electric field and biaxial strains can drastically change the adsorption energy, electronic properties and charge transfer of Nitrogen dioxide adsorbed SnS2 systems. Namely, these external conditions are highly preferred and provide a practicable method for adjustable SnS2 based electrical devices and gas sensors. Especially, the giant Stark effect can easily render the NO2-adsorbed SnS2 system from semiconducting to metallic. These distinctive characters endow the SnS2 nanosheets with high sensitivity as a potential candidate for NO2 gas sensor.

Investigations of the optoelectronic properties of novel polymorphs of single-layered Tin-Sulfide for nanoscale optoelectronic and photovoltaic applications

The low-cost and nontoxic single-layered SnS has been recently predicted as a promising material for cutting-edge nanoscale optoelectronic and photovoltaic applications beyond the graphene and phosphorene. In this article, we assess the optoelectronic properties of five derivatives of single-layered SnS (such as α-, β-, γ-, δ-, and ε-SnS) using first-principles calculations. While the single-layered SnS (α-SnS) itself is an indirect bandgap semiconductor, its derivative δ-SnS demonstrated a direct bandgap and ε-SnS a nearly direct bandgap which makes them promising over phosphorene. This new class of monolayers exhibits structural anisotropy along diagonal components of magnitude 0.098, 0, 0.24, 0.007, and 0.036 for α-SnS, β-SnS, γ-SnS, δ-SnS, and ε-SnS respectively. The large degree of in-plane anisotropy has generated different bands dispersion and effective mass of charge carriers along the 100- and 010- directions that evolve interesting effects on their optoelectronic properties. The optical spectra of the SnS monolayers have been found significantly different along the x- and y-axis. Investigations of the excitonic binding energies indicated that the designed monolayers exhibit thermally stable excitons. The onset optical absorption energies occur over a wide range of the visible part of the electromagnetic spectrum which is appealing applications in optoelectronic and photovoltaic devices. The refractive indices and reflectivity spectra have been found significantly different along x- and y-directions that may find suitable applications in optical polarizers, filters, and shields against UV radiations. The present study is believed to provide useful guidance for the applications of SnS monolayers (δ-, and ε-SnS in particular) in direction-dependent nanoscale optoelectronic and photovoltaic devices beyond phosphorene and graphene.

A theoretical study on tuning band gaps of monolayer and bilayer SnS2 and SnSe2 under external stimuli

Based on density functional theory, we systematically study the mechanical and electronic properties of monolayer and bilayer SnS2 and SnSe2. The electronic properties of these layers can be significantly tuned by applying in-plane strains and electric fields perpendicular to the sheets. The band gaps of monolayer SnS2 and SnSe2 slightly increase with the in-plane tensile strains, and they start to decrease after critical strains (5% for monolayer SnS2 and 7% for monolayer SnSe2). The band gaps of bilayer SnS2 and SnSe2 have a similar tendency to the monolayers with smaller critical strains (1% for bilayer SnS2 and 2% for bilayer SnSe2), which enables a semiconductor-to-metal transition at 10% strain for bilayer SnSe2. We also find that an external electric field perpendicular to bilayer SnS2 and SnSe2 modulates their electronic band gaps. Semiconductor-to-metal transitions are achieved at the electric fields of 0.27 V/Å for bilayer SnS2 and 0.13 V/Å for bilayer SnSe2.

DETECTION OF Na ATOMIC CONCENTRATION BY LAYERED CHALCOGENIDES OF TIN: AB INITIO CALCULATION

The purpose of this work was to study the properties of layered SnS2 , depending on the concentration of Na atoms intercalated in them. Within the methods of electron density functional and ab initio pseudopotential, we have computational experiments on atomic models that reproduce the infinite monolayers SnS2 with intercalated atoms in their interlayer space of Na atoms of different quantities are performed. To reproduce two infinite in a plane monolayers SnS2 , consisting of two atomic layers of sulfur separated by an atomic layer of tin, the atomic basis of the primitive cell consisted of 8 sulfur atoms and 16 tin atoms. In this case, in the interlayer space SnS2 could be from 0 to 16 sodium atoms per cell placed according to their location in a solid body at low temperatures, which corresponded to a two-dimensional concentration of 0 to 100%.We have obtained the spatial distributions of the density of valence electrons and the electron gap energy spectra, the bond of change in the conductivity of the material has been established, depending on the concentration of the intercalated sodium atoms. A monotonous decrease in the band gap width with an increase in the number of sodium atoms in the layer of SnS2 monolayers to a concentration of 40% was recorded. At concentrations of sodium atoms in the layer more than 40% monotony disappears, which reduces the uniqueness of the resistive reaction of monolayers SnS2 on the content of their sodium atoms.

Large magnetoresistance and perfect spin filter effect in Fe doped SnS2 half-metallic monolayers: A first principles study

In this work, the spin-resolved transport properties of the Fe doped SnS2 monolayer devices have been investigated. The results show that the doping systems have the transport properties of negative differential resistance, large magnetoresistance effect and near 100% spin polarization effect when the magnetization directions of two electrodes are in parallel. Moreover, the mechanisms for the properties also have been discussed. The original reason of these results could be due to the half-metallic of the doping system. Our results imply that Fe doped SnS2 monolayer is a promising candidate for the future spintronic devices.

The dual-defective SnS2 monolayers: promising 2D photocatalysts for overall water splitting.

Photocatalytic water splitting is a promising way to produce hydrogen fuel from solar energy. In this regard, the search for new photocatalytic materials that can efficiently split water into hydrogen is essential. Here, using first-principles simulations, we demonstrate that the dual-defective SnS2 (Ni-SnS2-VS), by both single-atom nickel doping and sulfur monovacancies, becomes a promising two-dimensional photocatalyst compared with SnS2. The Ni-SnS2-VS monolayer, in particular, exhibits a suitable band alignment that perfectly overcomes the redox potentials for overall water splitting. The dual-defective monolayer displays remarkable photocatalytic activity, a spatially separated carrier, a broadened optical absorption spectrum, and enhanced adsorption energy of H2O. Therefore, the dual-defective SnS2 monolayer can serve as an efficient photocatalyst for overall water splitting to produce hydrogen fuel. Furthermore, a novel dual-defect method can be an effective strategy to enhance the photocatalytic behavior of 2D materials; it may pave inroads in the development of solar-fuel generation.

Mn-doped SnS2 nanostructure as a potential efficiency CO catalyst: A first-principles study

The SnS2 is a new class of 2D materials with unique properties, which are still largely unexplored in the CO catalyst field. The modulation of electronic structures and chemical activities of the Mn atom substituted for S atom in SnS2 monolayer sheet is studied based on density functional theory. The electrons of doped Mn are introduced to the dangling bond of monovacancy SnS2 system, which can enhance the stability of Mn-Sn bond. The Mn-SnS2 monolayer sheet prefers good catalytic activity for the CO oxidation via the more favorable Langmuir-Hinshelwood mechanism with a two-step route to the Eley-Rideal or the latest report of termolecular Eley-Rideal mechanisms. In summary, we show first-principles evidence toward the realization of SnS2 based catalyst for CO catalytic oxidation which can facilitate the applications of SnS2 in the fields of catalysis and air pollution prevention.

Stacking effect on electronic, photocatalytic and optical properties: A comparison between bilayer and monolayer SnS

In this work, the stacking-dependent optoelectronic performances of a bilayer SnS were explored based on density functional theory (DFT). The results demonstrated that an AB-stacking induces an indirect-to-direct transition, a feature that is capable of vanquishing electron transition impediment from an intrinsic indirect monolayer SnS. An anisotropic and small carrier effective mass exists in all the stacking models, among which the AB-stacking with the lowest value favors high carrier mobility. Calculated band alignments are indicative of acceptable and adjustable photocatalytic activity for all the stacking models, unlike the monolayer SnS. The AB-stacking configuration possesses the strongest redox power, which facilitates it to be a potential candidate for photocatalytic water splitting. Additionally, the AB-stacking does effectively improve optoelectronic properties. The study demonstrated that layer-stacking is an availably adjustable method in the fields of sunlight-driven photocatalysis for nano-optoelectronic devices.

Tunable Schottky barrier width and enormously enhanced photoresponsivity in Sb doped SnS2 monolayer

Doping, which is the intentional introduction of impurities into a material, can improve the metal-semiconductor interface by reducing Schottky barrier width. Here, we present high-quality two-dimensional SnS2 nanosheets with well-controlled Sb doping concentration via direct vapor growth approach and following micromechanical cleavage process. X-ray photoelectron spectroscopy (XPS) measurement demonstrates that Sb contents of the doped samples are approximately 0.22%, 0.34% and 1.21%, respectively, and doping induces the upward shift of the Fermi level with respect to the pristine SnS2. Transmission electron microscopy (TEM) characterization exhibits that Sb-doped SnS2 nanosheets have a high-quality hexagonal symmetry structure and Sb element is uniformly distributed in the nanosheets. The phototransistors based on the Sb-doped SnS2 monolayers show n-type behavior with high mobility which is one order of magnitude higher than that of pristine SnS2 phototransistors. The photoresponsivity and external quantum efficiency (EQE) of Sb-SnS2 monolayers phototransistors are approximately three orders of magnitude higher than that of pristine SnS2 phototransistor. The results suggest that the method of reducing Shottky barrier width to achieve high mobility and photoresponsivity is effective, and Sb-doped SnS2 monolayer has significant potential in future nanoelectronic and optoelectronic applications.