Monolayer Stanene Research Articles

Electric-field-tuned Binding Energies of Trions in Silicene, Germanene, and Stanene Monolayers

Electric-field-tuned Binding Energies of Trions in Silicene, Germanene, and Stanene Monolayers

Atomic-scale magnetic doping of monolayer stanene by revealing Kondo effect from self-assembled Fe spin entities

Atomic-scale spin entity in a two-dimensional topological insulator lays the foundation to manufacture magnetic topological materials with single atomic thickness. Here, we have successfully fabricated Fe monomer, dimer and trimer doped in the monolayer stanene/Cu(111) through a low-temperature growth and systematically investigated Kondo effect by combining scanning tunneling microscopy/spectroscopy (STM/STS) with density functional theory (DFT) and numerical renormalization group (NRG) method. Given high spatial and energy resolution, tunneling conductance (dI/dU) spectra have resolved zero-bias Kondo resonance and resultant magnetic-field-dependent Zeeman splitting, yielding an effective spin Seff = 3/2 with an easy-plane magnetic anisotropy on the self-assembled Fe atomic dopants. Reduced Kondo temperature along with attenuated Kondo intensity from Fe monomer to trimer have been further identified as a manifestation of Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between Sn-separated Fe atoms. Such magnetic Fe atom assembly in turn constitutes important cornerstones for tailoring topological band structures and developing magnetic phase transition in the single-atom-layer stanene.

Single-Atomic-Layer Stanene on Ferromagnetic Co Nanoislands with Topological Band Structures.

Introducing magnetism to two-dimensional topological insulators is a central issue in the pursuit of magnetic topological materials in low dimensionality. By means of low-temperature growth at 80 K, we succeeded in fabricating a monolayer stanene on Co/Cu(111) and resolving ferromagnetic spin contrast by field-dependent spin-polarized scanning tunneling microscopy (SP-STM). Increases of both remanence to saturation magnetization ratio (Mr/Ms) and coercive field (Hc) due to an enhanced perpendicular magnetic anisotropy (PMA) are further identified by out-of-plane magneto-optical Kerr effect (MOKE). In addition to ultraflat stanene fully relaxed on bilayer Co/Cu(111) from density functional theory (DFT), characteristic topological properties including an in-plane s-p band inversion and a spin-orbit coupling (SOC) induced gap about 0.25 eV at the Γ̅ point have also been verified in the Sn-projected band structure. Interfacial coupling of single-atomic-layer stanene with ferromagnetic Co biatomic layers allows topological band features to coexist with ferromagnetism, facilitating a conceptual design of atomically thin magnetic topological heterostructures.

Geometrical Stability and Nonlinear Optical Properties of Crystallogen and Pnictogen Fullerene Analogues

The linear and nonlinear optical (NLO) properties of fullerene and fullerene-like structures, including crystallogen and pnictogen elements, are computed quantum mechanically. The tensors of optical polarizability, α, and second hyperpolarizability, γ, for a series of buckyball fullerene analogues, namely, Si60, Ge60, Sn60, Pb60, P60, As60, Sb60, and Bi60, are reported and analyzed. The eight considered nanocages are here classified into four categories: nanocages stabilized in the X60 form, including C60, As60, Sb60, and Bi60; nanocages that are not stabilized in the X60 form but are found to be stable in a distorted buckled b-X60 form, with X = Si and Ge; nanocages stabilized only in an exohedral decorated X60-Y60 form, X = Sn, Y = H or F; and finally nanocages that are not stable in either distorted or decorated form; however, their corresponding tabular nanotubes are found to be stable; such group includes P and Pb elements. A suggested nomenclature for the above-mentioned fullerenes is given for the first time, where many geometrical, energetic, and optical parameters are discussed extensively. These systems are energetically stable. The cohesive energies of Bi60 and Sn60-F60 range from -1.2 to -4.8 eV/atom and can be compared to -2.4 and -3.3 eV/atom from the corresponding 2D bismuthene and stanene monolayers, respectively. While bismuthellene, Bi60, shows vigorous optical responses compared to standard fullerene, the (9, 0) phosphorus nanotube gives not only enhanced polarizability and second hyperpolarizability but also an inducing first hyperpolarizability, β, which was null by symmetry in the case of spherical fullerenes. The proposed models are expected to be promising materials for optoelectronic and NLO applications.

Adsorption and sensing behaviors of SF6 decomposed species on pristine and Ru/Ti-modified stanene monolayer: A first-principles study

In this article, the effects of TM(TM = Ru, Ti) doping on the geometric and electronic structures of pristine stanene monolayer are investigated by using first-principles. Our calculated results show that TM atom can stably adsorb on the stanene monolayer surface. In particular, the Ti atom modification dramatically enhanced the adsorption energy. For instance, for the case of gas-stanene adsorption, adsorption properties are SF6 (3.24eV) > SO2F2 (2.7eV) > SOF2 (2.25eV) > H2S (0.36eV). Upon Ru-stanene adsorption, adsorption properties are SF6 (3.87eV) > SO2F2 (2.44eV) > SOF2 (1.51eV) > H2S (1.04eV). In the Ti-stanene adsorbing system, adsorption properties are SO2F2 (7.85eV) > SOF2 (7.47eV) > SF6 (6.56eV) > H2S (1.04eV). Besides, the density of states (DOS) and band structure demonstrate that these systems are direct semiconductor. And charge density analysis reveals a significant charge transfer from TM-stanene to adsorbed gases, especially for the Ti-stanene adsorption system, it appears larger charge transfer than that of the pristine stanene and Ru-stanene adsorption system. In addition, the resolution time of SF6 and its related decomposition gases show that Ru-stanene monolayer has a better sensing performance for H2S gas. Therefore, these results indicate that TM-stanene shows great sensing potential for a new type gas adsorbent.

Epitaxial binding and strain effects of monolayer stanene on the Al2O3(0001) surface

Stanene, the two-dimensional (2D) monolayer form of tin, has been predicted to be a 2D topological insulator due to its large spin-orbit interaction. However, a clear experimental demonstration of stanene's topologically nontrivial properties has eluded observation, in part because of the difficulty of choosing a substrate on which stanene will remain topologically nontrivial. In this paper, we present first-principles density functional theory calculations of epitaxial monolayer stanene grown on the (0001) surface of alumina, ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$, as well as freestanding decorated stanene under strain. By describing the energetics and nature of how monolayer stanene binds to alumina, we show a strong energetic drive for the monolayer to be coherently strained and epitaxial to the substrate. By analyzing the electronic structure of strained stanene, we find it to be a quantum spin Hall insulator on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$. We also describe the effect of in situ fluorine decoration on the bound stanene monolayer, including on its potential for mechanical exfoliation.

Ab-Initio investigations of electronic and optical properties of Sn-hBN hetero-structure

In this manuscript, we have investigated the electronic and optical properties of Stanene and hexagonal Boron Nitride (Sn/h-BN) heterostructure using the Projected Augmented Wave (PAW) method within the framework of density functional theory (DFT). van der Waals forces are also considered to counter the inter-layer interactions between Sn and h-BN. The significant band gap opening has been observed in Sn/h-BN heterostructure compared to pristine Stanene (Sn). However, the band gap is much lesser than the Boron Nitride (h-BN). In order to use the proposed structure in futuristic opto-electronic devices, we have investigated the various optical parameters such as absorption coefficient, refractive index, extinction coefficient, reflectivity and dielectric constant of Sn/h-BN heterostructure along with monolayer Stanene and hexagonal Boron Nitride. As a significant finding of the results, a strong redshift has been observed in the absorption coefficient, extinction coefficient and reflectivity, also a strong absorption peak appears in ultra-violet region. The excellent optical properties of heterostructure make it viable for potential optical applications.

The potential of stanene with transition metal adsorbed as a promising gas sensor: A first-principles study

In this paper, the structural, electronic and magnetic properties of TM (TM = Zr, Mo, Nb) absorbed stanene with the adsorption of toxic gas molecules (CO, CO2, NO, NO2, SO2, and NH3) have been investigated using the first-principles calculations. The calculated results show that the adsorption of TM induces the magnetic properties of stanene, and the adsorption of gas molecule on TM-stanene can tune the magnetic moment. For the adsorption of CO, CO2 and NH3 on Nb-stanene, it can be clearly seen that the whole system represent half-metallic character. When six gas molecules are adsorbed on the Mo-stanene system, it is found that they all exhibit semiconducting properties. However, for the adsorption of NO and NO2 on the Zr-stanene system, it is shown that the whole system appears the transition from half-metallic character to metallic character. At the same time, it can be seen that the adsorption energy of TM-stanene with gas molecules adsorbed have increased by 3 ~ 5 times compared with that of pristine stanene monolayer, and the charge transfer have also significantly increased by 10 times. It indicates that TM-stanene with gas molecules adsorbed exhibit strong interactions, especially in the Zr-stanene system. Therefore, the TM-stanene is more suitable for gas molecules detection compared with the pristine stanene, and the calculated results suggest Zr-stanene is potential for gas sensing. This paper is expected to provide theoretical guidance for the design of toxic gas sensors.

Bayesian force fields from active learning for simulation of inter-dimensional transformation of stanene

We present a way to dramatically accelerate Gaussian process models for interatomic force fields based on many-body kernels by mapping both forces and uncertainties onto functions of low-dimensional features. This allows for automated active learning of models combining near-quantum accuracy, built-in uncertainty, and constant cost of evaluation that is comparable to classical analytical models, capable of simulating millions of atoms. Using this approach, we perform large-scale molecular dynamics simulations of the stability of the stanene monolayer. We discover an unusual phase transformation mechanism of 2D stanene, where ripples lead to nucleation of bilayer defects, densification into a disordered multilayer structure, followed by formation of bulk liquid at high temperature or nucleation and growth of the 3D bcc crystal at low temperature. The presented method opens possibilities for rapid development of fast accurate uncertainty-aware models for simulating long-time large-scale dynamics of complex materials.

Band gap opening in tetragonal stanene monolayer by hydrogenation engineering

Based on first-principles calculations, we systematically investigate the stability, structural and electronic properties of two-dimensional (2D) hydrogenated tetragonal stanene (tetra-SnH). The calculated binding and formation energies, AIMD simulations and phonon dispersion show 2D tetra-SnH is stable. The hydrogenation also affects the electronic structure of tetragonal stanene monolayer, which is transformed from semimetal to semiconductor with a direct band gap. The optical response of 2D tetra-SnH is isotropic along the in-plane directions. Our results demonstrate that hydrogenation is an efficient way to modulate the electronic properties of tetragonal stanene, and provides a new prospect for the potential application in nanoelectronics.

A first-principles study on strain engineering of monolayer stanene for enhanced catalysis of CO2 reduction

Using first-principles calculations, we investigated the changes in the lattice structure, electronic structures and catalytic performance for CO2 reduction reaction (CO2RR) of stanene under applied strain. Our calculations showed that the initial buckled honeycomb structure of free-standing stanene becomes increasingly flat upon the increase of tensile strain. Stanene remains its gapless semiconductor characteristic within the strain range of −2% and 2%, beyond which a semiconductor-to-metal transition occurs. Under strain, the adsorption of CO is weakened, which can facilitate the desorption of product CO, enabling a strained stanene to be a better catalyst for CO2RR to CO than strain-free stanene. In particular, the stanene with 4% strain may give rise to the best performance because of the weakest CO adsorption (Eadsorp= −0.15 eV). The adsorption of intermediate product COOH on stanene is tunable with strain. We also evaluated the overall catalytic performance of the strained stanene based on the adsorption of CO and COOH and the selectivity against HER. If the reduction of COOH is governed by adsorption of the intermediate, a 10% strain may give a stronger COOH adsorption, weaker CO adsorption and better selectivity against HER, leading to an enhanced catalytic performance for CO2RR to CO. On the other hand, if the reduction of COOH is governed by desorption, a tensile strain higher than 4% may result in an enhanced catalytic performance. Our study here suggests that strain-tuned stanene might serve as an optimal electrocatalyst for CO2RR to CO with a high activity and selectivity.

WITHDRAWN: Hydrogen molecule detection based on Ti-embedded single vacancy defective stanene monolayer as an appropriate sensing material: A DFT study

Abstract Density functional theory calculations were carried out to investigate the interaction between hydrogen molecule and pristine/Ti-embedded defective stanene nanosheets. Ti embedding in stanene provides a satisfied surface for hydrogen molecule adsorption and sensing as can be evidenced by the enhanced adsorption energy on the Ti-embedded stanene system. The van der Waals (vdW) interactions were included to obtain the stable geometrical structures of stanene monolayers with adsorbed hydrogen molecules. Both pure and Ti-embedded stanene nanosensors exhibited semiconducting behavior as confirmed by the electronic band structure diagrams. Besides, the Ti doping provides a band gap opening for stanene at the Fermi level. The charge density difference and total electron density plots also revealed the accumulation of electron density on the adsorbed hydrogen molecule. Furthermore, there are electron depletion between the hydrogen molecule and stanene nanosheet, indicating the weak physical interaction between them. The work function was slightly reduced after doping of Ti atom, as well as the binding of hydrogen molecules on the Ti-embedded stanene sensors. The calculated recovery time values showed the unique reusability of the stanene based hydrogen molecule sensors. These insights would be quite relevant to the rational design of novel Ti-embedded stanene based sensors for hydrogen molecule detection.

Electronic and optical properties of W–Sn-Z and W′-Sn-W′ monolayers using density functional theory

Similar to graphene, the subject of stanene has stolen significant recognition both in experimental and theoretical areas. Nevertheless, stanene is poor when put into practice because it has zero band-gap energy, therefore it is necessary to use a universal strategy to achieve a material with a large band-gap. Employing density functional theory, we study the structural, electronic, and optical properties such as dielectric function and absorption coefficient of stanene monolayer functionalized with chemical groups, i.e., W–Sn-Z, Cl–Sn–Br, and W′-Sn-W′ (where W = Cl, F, or OH; Z = CN; and W′ = CN, CH, or NH). Our calculations reveal that the band-gap energy at the high symmetry points tuned in a range of 1.019–1.751 eV, which is significantly higher than the stanene monolayer with hydrogenation (0.3 eV). Furthermore, we found that under an external electric field the electronic band structures of various compounds are changed down in energy producing in a semiconductor to metal transition. Furthermore, we have computed other properties like the absorption coefficient, the refractive index, and the conductivity of our systems.

The effects of transition metal adatoms on the electronic properties of stanene

Abstract The electronic characteristics of transition metal adatoms (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt and Au) adsorbed on monolayer stanene have been investigated by using the first-principles calculations. The results show that the transition metal atoms are energetically favorable at the hollow and top sites of the stanene. Stanene has good adsorption capacity to foreign adsorbed atoms, and the adsorption energy is up to 6.241 eV, which is stronger than that of phosphorene and graphene. For Ni-, Ru- and Pd-adatoms, a narrow bandgap is opened in the monolayer stanene with the bandgap of 109.4 meV, 69.6 meV and 32.4 meV, respectively. The adsorption of Fe, Co, Cu, Ag, and Au adatoms upshifts the Fermi level to the conduction band and causing n-type doping. For the Fe-, Co-, Ru-, Rh- and Os-adsorbed stanene, it can be found that the magnetic moments are 3.144 μ B , 2.024 μ B , 2.028 μ B , 1.007 μ B and 1.995 μ B , respectively. Interestingly, for Os-adsorbed stanene, the spin upward is a metal, and the spin down is a semiconductor with 215.5 meV, namely, it shows the half-metallicity. The remaining (Fe-, Co-, Cu-, Ag-, Pt-) adsorbed stanene all exhibit metallic character. Our results indicate that the transition metal adsorption may be pave the way for the study of nanoelectronics and spintronics of stanene.

Tuning the electronic properties and band gap engineering in stanene monolayers via codoping of Mn and Al/P/Ga/As atoms: A DFT study

Using density functional theory computations, we investigated the doping characteristics of the transition metals (Mn) and group III/V elements in the stanene monolayers. The substitutional doping of atoms is described based on the electronic band structures and electron density difference plots. The codoping of Mn/Al, Mn/P, Mn/Ga and Mn/As pairs into the structure of stanene nanosheets were explored. Our results suggested that all the codoped structures are energetically stable. The single Mn-doped stanene nanosheet represents metallic character, while the pair Mn/P and Mn/As doped systems exhibit semiconductor property. In contrast, the Mn/Al and Mn/Ga codoped structures appear to be of metallic nature because of the shift of Fermi level to the valence band edge. The electron density difference diagrams showed the substantial charge accumulation around the doped adatoms. The results obtained in this work would be useful for the design of future nanoelectronic devices.

DFT insights into the adsorption properties of toxic gas molecules on pure and transition metal embedded stanene monolayers: Towards gas sensor devices

The first principles calculations were conducted to gain insights into how the interactions of gas molecules can be strengthened over the stanene monolayers upon modifying the surface of stanene by transition metal incorporation. At the first stage, the structures of the transition metal adsorbed stanene monolayers were optimized to obtain the energy favorable frameworks for gas adsorption and sensing. Focused on the band structure results, we found that the Ni-adsorbed stanene monolayers represent semiconductor feature, while the Cu and Au-adsorbed ones exhibit metallic property. Various adsorption sites and directions were examined for the binding of gas molecules to the Au-adsorbed stanene systems. The Au adsorption enhances the adsorption of gas molecules on the stanene system. The difference in the electron densities indicated that the bond in the Au-embedded stanene with adsorbed gas molecules is of covalent nature for the reason that the favored electron accumulation sites are largely located at the middle of the Au-gas molecule bond. Thus, our theoretical findings suggest great potential for Au-adsorbed stanene systems as superior candidates for gas sensing.

RETRACTED: Efficient band gap opening in single-layer stanene via patterned Ga-As codoping: Towards semiconducting nanoelectronic devices

Abstract Stanene is considered as an auspicious candidate for the design and exploitation of future prosperous electronic devices. The equilibrium structures and electronic behaviors of the Ga, As and Ga-As codoped stanene nanosheets were scrutinized to fully expedite the advances in the field of semiconducting materials technology. The formation energy calculations indicated that Ga/As doped/codoped stanene monolayers are thermodynamically stable. The variability of the band gap of the intrinsic stanene through codoping of Ga and As atoms was probed in detail. The emergence of band gap around the Fermi level of stanene was also accomplished by patterned Ga and As codoping. Thus, Ga-As codoped stanene behaves as a productive semiconductor material. Both Ga-doped and As-doped stanene nanosheets display metallicity because of the remarkable shifts in the position of Fermi level to the valence and conductance bands. The total charge density schemes indicate the formation of covalent bond between the Ga and As, as well as Ga/As and adjacent Sn atoms. As a result, Ga-As codoped stanene exhibits superior semiconducting behavior compared to the perfect system, and can be applied as a promising material for nanosensors and nanoelectronic devices.

Tuning the structural and electronic properties of single-layer stanene through doping 4d transition metals (Mo, Nb, Rh and Ru): A DFT study

Density functional theory computations were carried out to examine the effects of doping 4d transition metals (Mo, Nb, Rh and Ru) on the structural and electronic properties of stanene monolayers. Our results suggested that Mo-doped stanene nanosheet exhibited metallic behavior, while the Nb, Rh and Ru-doped ones revealed semiconducting character. The metallic behavior of the Mo-doped stanene is mainly attributed to the emergence of electronic band across the Fermi level. Our formation energy calculations also showed that all considered 4d transition metal doped stanene nanosheets are energetically stable. The lowest formation energy and highest stability belongs to Ru-doped stanene system. The electron density difference graphs of the transition metal doped systems also showed the accumulation of charge density over the interaction sites between metal adatoms and neighboring tin atoms. Thus, all the studied transition metals strongly coordinated to the tin atoms, as confirmed by the projected density of states graphs. Our results could help to understand the influence of 4d transition metals in 2D buckled stanene nanosheets.

A DFT study on the possibility of embedding a single Ti atom into the perfect stanene monolayer as a highly efficient gas sensor

In this work, we have surveyed, the interaction of various molecules (CO, NO, CO2, NO2, NH3 and SO2) with the pristine and Ti-embedded stanene monolayers employing the first-principles calculations. Firstly, the electronic properties of the pristine and Ti-embedded stanene were investigated. We found that after the adsorption of transition metal on stanene, the charge densities were remarkably accumulated on the embedded metal site. The most stable adsorption geometry, adsorption energies, charge density differences, charge transfer and electronic properties were thoroughly discussed. The results suggest that the Ti-embedded stanene can react with gas molecules more effectively as compared to the pristine one. All the studied gas molecules were strongly chemisorbed on the Ti-embedded stanene monolayer, whereas, on the pristine monolayer, these gas molecules show a weak physisorption. The considerable overlaps between the PDOS profiles of the Ti atom and different atoms of gas molecules indicate the formation of covalent bond between them. Our adsorption energy calculations indicate that the gas molecule interaction with Ti-embedded system gives rise to the most stable configuration as compared with that on the pristine stanene. Besides, the analysis of the charge difference plots represents the accumulation of charge densities on the adsorbed gas molecules. Our results thus suggest superior electronic properties for Ti-embedded stanene monolayers.

RETRACTED: Adsorption of gas molecules on the defective stanene nanosheets with single vacancy: A DFT study

Abstract Using the first-principles calculations, we have systematically examined the adsorption of gas molecules on the pristine and vacancy defective stanene monolayers. The adsorption of gas molecules on the defective monolayers is much stronger than that on the perfect ones, indicating the suitability of defective stanene nanosheets for adsorption processes. The large adsorption energies for SO2 and SO3 adsorbed complexes indicate the strong reactivity of stanene systems with adsorbed gas molecules, leading to the formation of multiple contacting points at the interface. The formation energies for the defective stanene systems were calculated. Our results indicated that the single vacancy defective stanene monolayers are thermodynamically stable, and can be used as effective gas sensors. The charge density difference calculations indicate that the electronic densities were largely accumulated between the atoms interacting with each other. This strong chemical interaction was also evidenced by the large overlaps of the density of states between the interacting atoms. The band structure calculations reveal the semiconductor features for defective stanene monolayers with adsorbed gas molecules. Our obtained results would be useful to search for promising gas sensor devices based on vacancy defective stanene monolayers.