ACS Publications. Most Trusted. Most Cited. Most Read
My Activity
CONTENT TYPES

Figure 1Loading Img
RETURN TO ISSUEPREVC: Physical Properti...C: Physical Properties of Materials and InterfacesNEXT

Novel Metalless Chalcogen-Based Janus Layers: A Density Functional Theory Study

  • M. Vallinayagam*
    M. Vallinayagam
    TU Bergakademie Freiberg, Leipziger Straße 23, D-09596 Freiberg, Germany
    *Email: [email protected]
  • A. E. Sudheer
    A. E. Sudheer
    Indian Institute of Information Technology Design and Manufacturing, 518008 Kurnool, India
  • S. Assa Aravindh
    S. Assa Aravindh
    Nano and Molecular Systems Research Unit, Pentti Kaiteran katu 1, 90570 Oulu, Finland
  • D. Murali
    D. Murali
    Indian Institute of Information Technology Design and Manufacturing, 518008 Kurnool, India
    More by D. Murali
  • N. Raja
    N. Raja
    The Institute of Mathematical Sciences, C.I.T. Campus, Taramani, 600113 Chennai, India
    More by N. Raja
  • R. Katta
    R. Katta
    Indian Institute of Information Technology Design and Manufacturing, 518008 Kurnool, India
    More by R. Katta
  • M. Posselt
    M. Posselt
    Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Bautzner Landstraße 400, 01328 Dresden, Germany
    More by M. Posselt
  • , and 
  • M. Zschornak
    M. Zschornak
    TU Bergakademie Freiberg, Leipziger Straße 23, D-09596 Freiberg, Germany
    More by M. Zschornak
Cite this: J. Phys. Chem. C 2023, 127, 34, 17029–17038
Publication Date (Web):August 21, 2023
https://doi.org/10.1021/acs.jpcc.3c02248

Copyright © 2023 The Authors. Published by American Chemical Society. This publication is licensed under

CC-BY 4.0.
  • Open Access

Article Views

798

Altmetric

-

Citations

LEARN ABOUT THESE METRICS
PDF (4 MB)

Abstract

The electronic, thermodynamic, and optical properties of a new type of two-dimensional Janus layer (JL) consisting exclusively of chalcogens are investigated using first-principles calculations. The permutations on atomic sites provide increased stability due to the multi-valency of chalcogens, and a heavier central atom further stabilizes the layer due to the increased coordination number. The investigated JLs are indirect bandgap materials with a bandgap larger than 1.23 eV, making them suitable for photocatalytic activity. Different feasible chemical potentials are analyzed, and chalcogens’ poor limits are proposed to fabricate the JLs. Based on the comparison of the formation energy, the energetic profile of the JLs is identified as EfTeSeS < E fSSeTe < EfSeSTe, irrespective of the chemical potentials of chalcogen. Hence, TeSeS is more stable than the JL arrangements SSeTe and SeSTe. The flat bands around the Fermi energy level and the reduction in path length between the maximum of conduction and minimum of valence bands explain the magnitude of multiple peaks observed in the optical spectra of the JLs. These absorptions turn the studied JLs into potential candidates for water splitting. The optimized bandgap reveals that the band edges efficiently straddle the water redox potentials at different pH levels. In addition, the positive vibrational frequencies depict the stability of these layers. Because of the minimal formation energy requirement, higher density of states around the Fermi level, as well as enhanced optical absorption compared to other JL, TeSeS JLs may lead to enhanced performance in photovoltaic and photocatalytic applications. These results add new members to the JL family of pure chalcogens and pave the way toward novel materials for respective applications.

This publication is licensed under

CC-BY 4.0.
  • cc licence
  • by licence

Introduction

ARTICLE SECTIONS
Jump To

In recent years, the research topic “beyond graphene” has attained a boom of interest in the family of two-dimensional (2D) materials due to the requirement for superior properties such as tunable electronic behavior, high carrier density, and carrier mobility, photoconductivity, as well as thermal conductivity, providing a tremendous application perspective. (1−9) In order to overcome the limiting semi-metallic nature of graphene, many 2D materials are theoretically and experimentally studied, and in general, they can be sorted into two major groups: multi-element 2D layers (called MXenes, for example, transition metal dichalcogenides like MoS2) (10,11) and single-element 2D layers (called Xenes, for example, silicene, and germanene). (12−19) The Xenes materials offer great merits over MXenes due to metalless structures, similar atomic thickness, and characteristics as of graphene. (20−22) Also, the electronic, optical, and thermal properties of Xenes 2D layers are strongly correlated with their multi-valency and allotropes. (21,23−26) To date, dozens of Xenes from Group III–VI elements are theoretically and experimentally studied. For example, borophene (Group-III), silicene (Group-IV), arsenene (Group-V), and selenene (Group-VI) are the 2D counterparts of B, Si, As, and Se bulk materials, respectively. Each Xene has a wide spectrum of optical, electronic, and chemical properties, and those can be fitted into various applications, such as agent for imaging in biology, excellent photodetector, optimal materials for optoelectronic devices, and candidates for catalysis and energy storage. (13,14,27)
Interestingly in bulk state, Se or Te contains special helical atomic chains along c direction, which is coupled via van der Waals (vdW)-type interactions. (28) Their respective 2D counterparts, called selenene for Se and tellurene for Te, are fabricated via different techniques such as the liquid-phase exfoliation, (29) vdW epitaxy, (28) and solution synthesis. (30) More comprehensive experimental methods are discussed by Shi et al., including molecular beam epitaxy, physical vapor deposition, and chemical vapor deposition (CVD). (31) Due to the excellent properties of tellurene, it has been given special focus recently. Wang et al. fabricated field-effect transistors using free-standing tellurene layers. (32) As a replacement for Si, the helical nature is utilized to model Te-nanowire, and it is shown that Te nanowires have a bandgap of 1 eV. (33) Similar to Te, 2D Se nanoflakes are prepared using liquid-phase exfoliation. (29) Also, a theoretical investigation on Se 2D allotropes depicts the presence of ferroelectric and ferrielectric polarization in Se 2D layers. (25) Hence, the experimental observations of 2D layers of Te and Se further motivate to investigate the mixing of Group-VI elements. In particular, the CVD technique may provide a suitable method to mix the element and the mixing can be coated on a suitable substrate to fabricate allotropes of XYZ (X/Y/Z = S, Se, Te). Under this XYZ formulation, many 2D layers can be visualized such as SeTe2, Se2Te, and SeS2 or even all elements can be distinct. However, only a few publications on mixing Group-VI elements are found. Liu et al. studied the 1T allotropy of SeTe2 and Se2Te layers, whereas in the literature, they are called α-SeTe2 and α-Se2Te phases. (34) The α-SeTe2 and α-Se2Te layers possess direct and indirect bandgaps of 0.38 and 0.33 eV, respectively, calculated within generalized gradient approximation (GGA). Also, the imaginary frequency-free vibrations prove the stability of these layers. The broken symmetry due to the atomic layers arrangement, such as in Te2Se, induces large piezoelectricity with the 2D layers. (35) The addition of transition metal atoms magnifies the piezoelectricity further. (36) Moreover, these new 2D layers possess very low lattice thermal conductivity and hence have a high thermoelectric figure of merit. (37) From the vibrational spectrum, it is proven that the soft acoustic modes, low-energy levels for optical modes, and higher value of the Grüneisen parameter together reduce the thermal conductivity κl to 1.89 Wm–1 K–1 and 0.25 Wm–1 K–1 for α-SeTe2 and α-Se2Te at 300 K. These low κl ultimately make these layers better candidate materials for thermoelectric devices.
The outlined observations suggest further modeling to include S in the layer construction. In particular, to increase both structural and chemical flexibility, instead of binary compounds, we opt for layers with XYZ chemical formula where X/Y/Z = S, Se, Te, and X ≠ Y ≠ Z. In this work, we study the formation, as well as electronic, vibrational, and optical properties of SeSTe, SSeTe, and TeSeS Janus layers (JLs). Similar to the allotropes of Se, initially, we have considered three different phases, namely 1T, square, and rectangular, for SeSTe, SSeTe, and TeSeS JLs. We found that the 1T and square phases are not stable, and hence, here we report and discuss only the rectangular phase. In our study, we discuss first the simulation settings, structures of optimized JLs, and chemical bondings. Then we analyze the feasible fabrication chemical conditions which can be utilized in preparation techniques such as CVD. Following this, we report the electronic and vibrational properties, and finally, we discuss the absorption spectrum of the JLs.

Computational Details

ARTICLE SECTIONS
Jump To

Spin-polarized ab-initio calculations are carried out using the VASP code. (38,39) The exchange-correlation interaction effects of electrons are treated with Perdew–Burke–Ernzerhof (PBE) functional type GGA. (40) The projector augmented wave (PAW) type pseudopotential (41,42) is used to approximate electron–ion interaction. The plane-wave basis sets are created with a cutoff energy of 500 eV. The atomic positions in the unit cell are optimized until the Hellmann–Feynman forces on each atom become lower than 10–4 eV/Å, and total energies are converged up to 10–6 eV. Since the lattice parameters of 2D layers are not known clearly, the layers must be optimized by allowing the in-plane lattice parameters (a and b) to relax while fixing the third dimension.
The Brillouin zone integration is carried out with sampling by a grid of 16× 16 ×1 k-points within the Monkhorst–Pack scheme. (43) The phonon vibration frequencies of JLs are investigated using the supercell approach of size 5 × 5 × 1. For phonon calculations, the criteria on energy and force are further set to higher values 10–8 eV and 10–6 eV/Å, respectively, to avoid any sort of artifacts. The same precision level is used to calculate the frequency-dependant dielectric function ϵ(ω). (44) Also, in relaxation and phonon calculations, the inter-layer vdW interaction is accounted for with a dispersion energy correction developed within the DFT-D3 method. (45) In addition, the single layer is isolated from periodic repetitions of layers along the c-direction with a vacuum region of 15 Å. With these settings, the JLs relaxed well and the final structure of all proposed JLs are shown in Figure 1 as generated using the visualization tool VESTA. (46) The VASP outputs are post-processed with the post-processing code VASPKIT. (47) The calculated lattice parameters and bond lengths between different atomic species are given in Table 1 and compared with the available literature. Furthermore, the bonding between the layer constituents is analyzed using differential charge density (DCD), shown in Figure 2. The DCD is calculated using δ ρ = ρJL – ∑ ρA, where ρJL is the charge density of considered JL and ρA is the charge density of individual chalcogens, i.e., A = S, Se, and Te. Hereafter, all chalcogens (S, Se, and Te) are collectively represented as A.

Figure 1

Figure 1. Optimized structures of (a) SeSTe, (b) SSeTe, and (c) TeSeS JLs. The top row is the perpendicular view, and the bottom row shows the cross-sectional view. The black line defines the unit cell.

Figure 2

Figure 2. Differential charge density of (a) SeSTe, (b) SSeTe, and (c) TeSeS JLs. The isosurface of value 0.005 e3 is selected to illustrate the bonding between S, Se, and Te. The blue and yellow surfaces indicate charge depletion and accumulation, respectively. The BC analysis shows that the Se originates covalent nature bonding in SeSTe and SSeTe while S and Te are leading to ionic nature in the JLs.

Table 1. Optimized Lattice Parameter a and b/a, Bond Length dAA, and Differential Bader Charge Δ Q of the 2D Janus Layersa
layerlattice parameter (Å)bond length (Å)Δ Q (e)
 ab/adS-TedSe-TedS-SeSSeTe
Se4.9850.815      
 4.990 (52)0.827 (52)      
Te5.6080.753      
 5.490 (53)0.759 (53)      
SeSTe5.0520.8132.4122.593 (3.253)2.291 (3.230)1.1060.030–1.136
SSeTe5.0480.8532.432 (3.471)2.5452.255 (3.477)1.0430.082–1.125
TeSeS5.0570.7962.522 (3.052)2.648 (3.102)2.2480.4750.106–0.581
a

The Δ Q of atom A in JL is defined as Δ Q = ZV ALq, where ZV AL is the valency of atom A and q is the charge on atom A from Bader analysis. Δ Q is calculated in the unit of e, where e is the electron charge. The bond lengths within () are second NN distances.

Formation Energy of Janus Layers

The JL formation is studied using respective formation energy calculated according to
Ef=EJLμA×NA
(1)
where EJL is the ground-state energy of either the SeSTe or SSeTe or TeSeS JL. The term μA represents the chemical potential of chalcogens A, and NA is the number of atoms of species A in the JL unit cell. In order to investigate the feasible combination of μA to fabricate considered JL, we set μA using A-dimer and A-bulk. The A deficit condition, called A-poor, is defined by μA calculated from the ground-state energies of A-dimer, and the A surplus condition, called A-rich, is defined by μA calculated from the ground-state energies of A-bulk. Suitable A-bulk systems, which have zero energy above the hull, are selected from the Materials Project repository. (48−51) With this constrain, the monoclinic-S (P2/c─space group), (49) monoclinic-Se (P21/c─space group), (50) and trigonal-Te (P3121─space group) (51) are selected to set the A-rich limit. Hence, for the A-rich limit, μA is set as μA = Ebulk/NA, where Ebulk is the ground-state energy of A-bulk and NA is the number of atoms in the A-bulk cell. Similarly for the A-poor limit, the μA is set to μA = Edimer/2, where Edimer is the ground-state energy of A-dimer. The variation in μA can account for the removal or addition of A chalcogen from or to the reaction chamber, indicating the particle exchange with the reservoir within the reaction chamber.

Results and Discussion

ARTICLE SECTIONS
Jump To

Structural Properties

The relaxed ground state of JLs is compared with the elemental Se monolayer. The JL monolayers have a similar spatial arrangement as the theoretically observed Se elemental monolayer (52) except for the layer composition. The JL unit cell has one atom from each chalcogen and hence three atoms in total. The atomic arrangement within each JL can be seen as a central chalcogen (Se in SeSTe, S in SSeTe, and Te in TeSeS) binding in a tilted plane the remaining two chalcogens, cf. the cross-sectional view in Figure 1. In the orthogonal cross-section, the chalcogens form a helical chain within the monolayer and the chains are connected by the next central chalcogen to complete the two-dimensional periodicity. Such spatial arrangements are seen in theoretically studied helical Se-chains (52) and Te bulk systems. (28,53) Also experimentally studied hexagonal Te bulk crystals expose Te helical chains along [001] direction with weak vdW interactions in-between the chains. (26,28) In each JL, there are two different bonds, at first and second nearest neighbor (NN) distances, between the central and remaining chalcogens and there is only the first-NN bond between the chalcogens in the tilted plane. All bond lengths are measured (dS–Se, dS–Te, and dTe–Se) and listed in Table 1. All first-NN bonds interlink chalcogens within the chain, and the second-NN bonds bind nearby chains. Thus the position of chalcogens redefines the interactions between them and affects the lattice parameters. The lattice parameter in a-direction is nearly independent of the type of the central atom. However, the lattice parameter in the b-direction is considerably reduced by 1.7 and 5.7% in SSeTe and TeSeS JLs, respectively, compared to that of the SeSTe JL. Hence, it is expected to observe different chemistry between the helical chains in each JL.
Figure 2 shows the DCD of SeSTe, SSeTe, and TeSeS JLs. It is evident that the SeSTe JL (Figure 2a) has both ionic and covalent bindings. Through the short dS–Se bond, S–Se interacts covalently. In the longer dS–Se bond, positive and negative charges accumulate on S and Se, respectively, and form ionic bonds. Similar ionic behavior between Se–Te and S–Te is observed. Unlike the S–Se first-NN interaction, Se binds with Te and S binds with Se via a strong ionic bond. Also, the ionic bonding mediates strong interaction between the helical chains. In SSeTe, all bonds are ionic in nature, and rearranging S and Se atomic positions elongates the second-NN distance, in comparison with that in the SeSTe layer. However, in the first NN, the ionic bonding is even stronger than that in the SeSTe JL. The ionic character in the helical chain is further improved in the TeSeS JL. The interaction between S–Te and Se–Te is stronger in the first NN. We observe higher charge accumulation and depletion within the helical chain, and the bond between the helical chains is weaker than that in the other JLs. The charge distribution on each atom is calculated using Bader charge (BC) analysis (54−57) and given in Table 1. The BC on Se in SeSTe and SSeTe clearly shows that Se drives the covalent bonding while S and Te take anionic and cationic states, respectively, and lead to ionic character. The change in b/a lattice parameter in the TeSeS layer induces in-plane strain and is accompanied by about half the effective charge transfer from Te to S as observed for the other JL. Such changes in covalent and ionic bindings are expected to affect the formation of these JLs in the fabrication process. Hence, the ground-states energies of JLs are used to investigate the feasible chemical potential conditions for the preparation of JLs. Furthermore, specifically, the SeSTe layer is expected to bear a significant electric polarization as the charge centers on S and Te are prominently developed and well displaced, whereas TeSeS will have the lowest polarization due to reduced charge transfer as well as about half the displacement.

Chemical Conditions for Janus Layer Formation

2D materials are most commonly exfoliated from respective bulk materials which have layered structural arrangements. Graphene and MoS2 monolayer are the best examples of this scenario. In case of the absence of layered bulk materials, the epitaxial method offers a vital route to fabricate the 2D materials. (24,58−61) Recently, a more relevant mechanism, inducing structural phase transition on increasing layer thickness, is proposed for β-Te elemental layers. (53) Though successful fabrication of β-Te layers, Feng et al. (53) still suggest the use of the hexagonal layered bulk Te. For our proposed JLs, to the best of our knowledge, there is no theoretical or experimental report available. Hence, here we suggest the feasible route based on the CVD technique which has been utilized to fabricate SMoSe JL (62,63) since the growth of our JLs can be controlled by the concentration of chalcogens. In the following, we discuss the required conditions for chalcogen potentials to grow as free-standing layers.
The formation energy of JLs as a function of the chemical potential of chalcogens is calculated by eq 1 and using the common procedures, (64) where smaller values specify increased stability and are shown in Figure 3. We have assumed two different settings of varying μA in order to reflect certain chemical conditions to calculate Ef. In the first setting, the extreme conditions are defined by all μA, μArich being set to the A-bulk system and μApoor to the A-dimer, respectively, refer to Figure 3a. Under this framework, we propose that the theoretically studied JLs can be fabricated in the laboratory by selecting proper chemical conditions for the chalcogens. By controlling the A chalcogens in separate crucibles, all chalcogens can be introduced simultaneously into the reaction chamber and the respective JL can be coated onto a suitable substrate. Hence, A-gases are introduced into the reaction chamber either from A-bulk or A-dimer, and the concentrations of gases are controlled to reach the desired chemical potential. From Figure 3, it is clear that at the A-poor limit, the considered three JLs are identified as stable. Nevertheless, in the entire range of μS, the order of Ef of JLs can be arranged as EfTeSeS < EfSSeTe < EfSeSTe, i.e., TeSeS is more stable than other layers. Compared with the DCD in the JLs, the mixed covalent-ionic bonding among A destabilizes the SeSTe JL, i.e., the ionic interaction between the helical chains causes the increased formation energy. The strong ionic bonding within the helical chain in the TeSeS JL drives the higher stability and eases the formation. However, other combinations between μA’s are also considered to probe for the effect of the fractional concentrations of A.

Figure 3

Figure 3. Formation energy of SeSTe, SSeTe, and TeSeS JLs under different μA. In (a), all μA is linearly set between A-bulk and A-dimer, and in (b), μA is varied as described in the text. The μS scale is given, whereas Se-rich and Te-rich limits are indicated by an arrow mark in (a). In (b), the continuous, dashed, dash-dot, and dotted lines represent, respectively, Sepoor–Tepoor, Serich–Tepoor, Sepoor–Terich, and Serich–Terich limits for Se and Te. The μS scale is calibrated in order to shift the S-poor limit to 0 eV.

In the second (intermediate) setting, the chemical potential of S is changed from S-bulk to S-dimer by fixing that of Se and Te to a particular limit. Hence, we selected the combinations Sepoor–Tepoor, Serich–Tepoor, Sepoor–Terich, and Serich–Terich. As an example, with Sepoor–Terich condition, the μSe is calculated using Se-dimer and μTe is calculated using Te-bulk system. These considerations for μA help to understand the interaction between the chalcogens and to find the best possible μA to fix the concentration of A to fabricate the intended layer. Varying the Se–Te chemical conditions favors again the TeSeS JL more than other JLs. The energetic profile observed in the first setting is replicated in the second along with the reduction in formation energy. Among the possible combinations of μA, the best suitable μA combination is Sepoor–Tepoor. For this limit, the Ef is reduced down to values between −1.6 eV (for μSrich) and −2.1 eV (for μmathrmSpoor) for the TeSeS JL irrespective of Se–Te limits and the order of Ef once again has the profile EfTeSeS < EfSSeTe < EfSeSTe equivalent to the profile from the first setting. Hence, keeping the μA at the poor limit for all chalcogen, the formation of TeSeS JL is assured from Figure 3. Interestingly, the stability (Ef = -0.122 eV (52)) of the Se-elemental non-centrosymmetric helical-chain monolayer is significantly lower than that of the TeSeS JLs. The considered chemical conditions clearly project proper conditions to be set in the fabrication process such as the CVD technique.

Electronic Properties

After investigating the feasible formation under certain conditions, we studied the electronic properties of the JLs. Figure 4 shows the band structure of equilibrium JL structures, along with the spin-polarized density of states (DOS) simulated within the PBE framework. The bands are projected along the high-symmetric points Γ(0,0,0)–X(0.5,0,0)–S(0.5,0.5,0)–Y(0,0.5,0)−Γ(0,0,0). When the central atomic layer changes from Se to S to Te, cf. Figure 1, the band gap Eg increases from 1.49 to 1.74 eV. Interestingly, the Eg of TeSeS JL is comparable to that of a single elemental Se monolayer (Eg = 1.74 eV, calculated with the same PBE framework). (52) Though all JLs are indirect band gap materials, the path length of the indirect gap is decreased from SeSTe to TeSeS due to the development of more states at the Fermi level, which ultimately induces nearly flat bands at valence band maximum (VBM). The bandgap is recalculated using the HSE06 functional. The standard default settings for HSE06 available in VASP are applied due to the absence of any experimental descriptor to optimize HSE06 parameters. The estimated bandgaps of SeSTe, SSeTe, and TeSeS are 2.28, 2.44, and 2.46 eV, respectively. The bandgaps are significantly increased in comparison to GGA bandgaps, which indicates the shifting of the band edges. In addition, it is shown that the larger values alter the photocatalytic behavior of the JLs, cf. the Band Edge Alignment Section. The curvature of the valence band decreases considerably, which may assist in the significant enhancement of optical absorbance. Such reduction in the path length of the indirect band gap reduces, next to the required impulse, also the energy for the transition from the valence band to the conduction band. The DOS shows that the JLs have no magnetism as the up and down spin densities cancel each other. The states are mostly contributed from Te and Se rather than from S. In comparison, the Te atomic layer induces finite DOS values closer to the Fermi level than in the other two cases.

Figure 4

Figure 4. Band structure of optimized JLs, (a) for SeSTe, (b) for SSeTe, and (c) for TeSeS along with DOS (in states/eV unit) and partial DOS. The blue and black arrows respectively indicate the bandgap and observed peaks in the absorption spectrum shown in Figure 6. The horizontal dashed line represents the Fermi level, which is set to 0 eV. The computed partial DOS depicts that the VBM is intensely contributed by Te(p) orbital in SeSTe and SSeTe, and by S(p), Se(p), and Te(p) orbitals in TeSeS JL. The equivalent up and down spin states indicate the absence of magnetic characters in optimized JLs.

Vibrational Properties and Thermodynamic Stability

The energetic profile is in favor of considered JLs, and the dynamic stability is a further crucial constraint to be satisfied by a postulated structure model, which is determined by the phonon vibrations in the structure. (65) As mentioned in the Computational Details Section, a tight cutoff is set to compute the force on each atom in the JL. The PHONOPY code (66) is used to calculate the dynamical matrix in order to get phonon frequencies. The calculated phonon dispersion is shown in Figure 5 along with the phonon-DOS. At the Brillouin zone center (at Γ high-symmetric point), all JLs have positive phonon frequencies, i.e., 3N modes of the layers are positive where N is the number of atoms in the unit cell. These positive frequencies indicate the dynamical stability of considered JLs. Only for the SSeTe JL, a negative frequency of 4 cm–1 is exhibited at Γ. The SSeTe JL may require even higher precision or a larger supercell for the force calculation than the criteria presently used in this study, which is computationally resource-demanding. However, the numerical error in phonon frequencies calculation using VASP is about 0.1 THz (or ≈4 cm–1) due to uncertainty in preserving the translation symmetry. (52,67) Hence, our predicted frequencies validate the stability of the JLs.

Figure 5

Figure 5. Phonon dispersion bands of optimized JLs, (a) for SeSTe, (b) for SSeTe, and (c) for TeSeS along with frequency resolved phonon DOS (in states/cm–1 unit). In all JL, low-frequency regimes originate from Se and Te and the major contribution to the high-frequency regime is from S vibrations. Due to the denser phonon modes, the phonon DOS strongly disperses for the TeSeS JL. The abrupt rise in S modes around 150 cm–1 in SSeTe and 350 cm–1 in TeSeS JLs indicates that S vibrational mode is almost directional independent. The positive vibrational frequencies along the entire high symmetric locations in the Brillouin zone depict the stability of the JLs.

Though all layers have similar compositions and the same number of atoms in the unit cell, the permutation of atomic positions entails different phonon spectra in terms of phonon density. For the TeSeS JL, a denser distribution with stronger dispersion is observed within the low and medium frequency region in comparison to the density distribution of the other JLs. This can be understood using the number and type of nearest bonds of the central chalcogen in each layer. As mentioned before, the central atom Te in TeSeS (cf. Figure 1) attains two first-NN and two second-NN ionic bonds with S and Se, cf. Figure 2. The Te in SeSTe and SSeTe layers are structurally connected to only three nearby atoms instead of four. As discussed in the Chemical Conditions for Janus Layer Formation Section, the layer with more Te-bonding is more stable and has lower formation energy, which in comparison can now further be correlated with the stronger Te partial phonon DOS dispersion, next to the reduced electric polarization. The phonon band gap in JLs varies along the predefined high symmetry trajectory within the Brillouin zone similar to the Se elemental layer. The phonon bandgap is defined as the frequency difference between the uppermost acoustic and lowermost optic phonon modes. At the Brillouin zone center, the gap is 75, 60, and 90 cm–1 in SeSTe, SSeTe, and TeSeS JLs, respectively. These gaps reduce to a value close to zero as moving away from the zone center to other symmetric points. Hence, a wide window of lower frequencies is forbidden before the first photon absorption sets in.
In order to analyze the contribution of individual chalcogens, the partial phonon-DOS (pDOS) has been calculated. From the data, ref. Figure 5, it is clear that the acoustic and most lower optical modes are governed by Se and Te and higher optical modes are contributed mostly by S owing to their atomic mass differences. Te and Se chalcogens are heavier than S, and hence, the latter vibrates at high frequencies. These characteristics of chalcogens can be mapped to their contributions to the dielectric behavior of the material. In general, the dielectric function at high frequencies is responsible for the optical behavior of the material. (68,69) Hence, the dynamics of Se and Te control the optical response of the JLs. On the other hand, the response to lower frequencies of incoming electromagnetic radiation yields a static dielectric constant, to which the S atom dominantly contributes.

Optical Absorption Spectra

The frequency-dependent dielectric function ϵ(ω) describes the optical properties of materials. ϵ(ω) is a complex function expressed as ϵ(ω) = ϵ1(ω) + i ϵ2(ω) where ϵ1(ω) and ϵ2(ω) are real and imaginary parts. The imaginary part is calculated by a summation over empty bands as (44,70)
ϵ2(ω)=2πe2Ωϵ0k,v,cδ(EkcEkvω)|ψkc|u.r|ψkv|2
(2)
where Ω and ϵ0 are volume of the simulation cell and vacuum dielectric constant, respectively, ω and u.r are the energy of incoming radiation and momentum operator, respectively, and v and c symbolize valence and conduction bands, respectively. The momentum operator runs over valence and conduction bands. It is important to consider enough empty bands (44) which renders accurate optical properties. The imaginary and real parts of the dielectric constant can be related using the Kramers–Kronig relation as
ϵ1(ω)=1+2πP0ωϵ2(ω)ω2ω2+iηdω
(3)
where P is the principle value. Once eqs 2 and 3 are solved, other optical properties such as reflectance, absorption, and energy loss spectrum can be derived. The computed ϵ2(ω) for the considered JLs are shown in Figure 6 and compared to that of the parent Se monolayer. The in-plane (xx and yy) and out-of-plane (zz) ϵ(ω) are also projected. In all JLs and Se-monolayer, the out-of-plane vibration contributes to the higher frequency window.

Figure 6

Figure 6. Imaginary part of the dielectric function (a) for SeSTe, (b) for SSeTe, and (c) for TeSeS JLs. The red and blue lines indicate parallel (ϵ, xx, yy) components, and the yellow line indicates the perpendicular (ϵ, zz) component. The visible frequency window is denoted by vertical dashed red and violet lines. In comparison, TeSeS has three peaks with high ϵ2 within the visible frequency window and, hence, has enhanced absorbance than other JLs.

The pristine-Se has two peaks, and only one of them falls into the visible frequency window, clearly demonstrating that the Se-monolayer has less efficiency for visible light absorption. Solely the vibration along the x direction shows a distinct resonance, whereas the yy contribution is broadly distributed. In addition, the transition starts right from the low-frequency region. However, this property is altered upon introducing other chalcogens. There are three distinct peaks observed for the SeSTe JL. The excitations occur at 1.92, 2.26, and 2.82 eV, respectively, represented as a1, b1, and c1 in Figure 6. The vibration along the y direction contributes now stronger to the low-frequency response, and the x direction controls the high-frequency response within the visible window. The distinct peak a1 arises from the transition between the Te(p) orbital and the hybridized Te(p)–Se(p) orbitals in the conduction band, cf. DOS in Figure 4a. Similarly for b1 and c1, the Se(p) orbital contributes rather than Te or S. Also the peak magnitude reduces as the wavelength of radiation increases from 400 to 700 nm. Hence, in SeSTe, specific excitation can be induced by suitably polarizing the incoming radiation along xx or yy. In the SSeTe JL, the central atom S changes the dynamics. The magnitude of peaks a2, b2, and c2 reduces drastically compared to SeSTe. However, the peaks b2 and c2 broaden and overlap with each other. Both these transitions occur between the Te(p) orbital in VBM and the Se(p)–Te(p) hybrid orbital in CBM. The hybrid orbital in CBM is readily available for multiple transitions, and hence, the peak broadening is observed. The a2 is contributed by the Te(p) orbital which defines the VBM, cf. Figure 4b. The resonances are excited only by vibration along the x directions, whereas yy contributions are weak. Hence, there is an overall reduction in magnitude.
The absorption character of the layer is redefined when the curvature of the valence band varies. The valence and conduction bands of the TeSeS JL are modified to attain less curvature. Due to these facts, we observe multiple locations for resonance b3 (however, only one is shown, cf. Figure 4c), which excites around the high-symmetric point S, located at (1/2, 1/2, 0) in reciprocal space. Since S, Se, and Te states together contribute to enriching the valence band, unlike for the other JLs, peaks with nearly similar high magnitudes are observed. This fact leads to enhanced absorbance in the TeSeS JL. Thus compared with SeSTe and SSeTe JLs, TeSeS is recommended for applications such as photovoltaic cells and photocatalytic materials.
Owing to the interaction between layer constituents, as discussed in the Structural Properties Section, the chalcogen is interacting strongly in the ab plane rather than along the c direction. These interactions are visualized using DCD as shown in Figure 2. More details can be deduced from the angular-momentum resolved PDOS. Specifically, due to the low density of pz states in the vicinity of the fermi energy, the absorption at lower frequencies is vanishing in the perpendicular zz direction, which is reflected in ϵ displaying contributions only above about 5 eV.

Band Edge Alignment

The optical properties of JL discussed above indicate that the CB and VB band edges fulfill the basic criteria for water splitting given by a minimum bandgap value of 1.23 eV. (71) In order to check this issue in more detail, the band structure was also calculated using the HSE06 exchange and correlation functional, which yields more precise band gap values than the GGA functional. Hence, there is a large predicted flexibility with respect to possibly occurring overpotential effects, such as reactant diffusion, side reactions, solvate shell stripping, and electron transfer. The aligned band edges are compared and shown in Figure 7 along with the redox potential of water. The chemical biasing due to the pH electrolyte controls the reduction and oxidation potentials of water as EH+/H2 = −4.44 + pH · 0.059 for H reduction and EO2/H2O = −5.67 + pH · 0.059 for oxidation. (71−75) Our results show that the band edges obtained from GGA support only the H reduction irrespective of pH condition and fail to perform the oxidation evolution reaction. However, the improved band edges from HSE06 support the water splitting under irradiation. Interestingly, the JLs perform the splitting reaction even under acidic conditions pH = 14. The results are in favor of photocatalytic device fabrication using the proposed JLs.

Figure 7

Figure 7. Estimated band edge positions of the JLs using HSE06 and GGA potentials on vacuum scale. For comparison, the redox potentials of water-splitting reactions at different pH levels are shown by continuous, dashed, and dotted lines. The green and blue bars represent VBM and CBM positions, respectively. The vacuum level is set at 0 eV.

Conclusions

ARTICLE SECTIONS
Jump To

Spin-polarized first-principles calculations have been carried out to explore new types of metal element-free JLs exclusively from chalcogens. Three different layers are created using the permutation of atomic positions of S, Se, and Te. The electronic, thermodynamic, and optical properties of this new type of two-dimensional JL have been derived. From the charge distribution on each chalcogen, it is shown that the layer with less effective charge transfer and electric polarization attains enhanced stability. Such an ionic bonding is derived from the heavier central chalcogen atom, and hence, TeSeS depicts more stability than SeSTe and SSeTe JLs. The electronic structure calculations show that the investigated JLs are indirect bandgap materials with a bandgap larger than 1.23 eV, making these JLs a suitable material for photocatalytic applications. The flat bands around the Fermi energy level and the reduction in path length between the maximum of conduction and minimum of valence bands explain the magnitude of multiple peaks observed in the optical spectra of the JLs. Moreover, different feasible chemical potentials are analyzed to shed light on required chemical conditions. It is shown that chalcogen-poor limits are most suitable to fabricate the JLs. The formation energy profiles of the JL vary according to EfTeSeS < E fSSeTe < E fSeSTe, irrespective of the chemical potentials, and thus, the TeSeS dominates other JLs. In addition, the vibrational frequencies without any imaginary tails depict the stability of the layers. The detailed analysis of band edges employing the HSE06 functional reveals the potential of the JLs for the water-splitting process. The superiority in Ef and enhanced optical absorption prove that the TeSeS JL could be a suitable material for photovoltaic and photocatalytic applications. Our results add new metal atom-free members to the family of JLs and novel materials for relevant applications such as photovoltaic.

Author Information

ARTICLE SECTIONS
Jump To

  • Corresponding Author
  • Authors
    • A. E. Sudheer - Indian Institute of Information Technology Design and Manufacturing, 518008 Kurnool, India
    • S. Assa Aravindh - Nano and Molecular Systems Research Unit, Pentti Kaiteran katu 1, 90570 Oulu, Finland
    • D. Murali - Indian Institute of Information Technology Design and Manufacturing, 518008 Kurnool, India
    • N. Raja - The Institute of Mathematical Sciences, C.I.T. Campus, Taramani, 600113 Chennai, India
    • R. Katta - Indian Institute of Information Technology Design and Manufacturing, 518008 Kurnool, India
    • M. Posselt - Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Bautzner Landstraße 400, 01328 Dresden, Germany
    • M. Zschornak - TU Bergakademie Freiberg, Leipziger Straße 23, D-09596 Freiberg, Germany
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

ARTICLE SECTIONS
Jump To

M.V. and M.Z. acknowledge funding by the DFG within the project DFG 442646446, ZS 120/5-1. N.R. would like to thank Rajesh Ravindran and the Institute of Mathematical Sciences, Chennai, India, for the visiting researcher position. M.V. and M.Z. thank Prof. Dirk C. Meyer for providing ideal research conditions at the Center for Efficient High-Temperature Processes and Materials Conversion ZeHS Freiberg. M.V. thanks both the Department of Information Service and Computing at Helmholtz-Zentrum Dresden-Rossendorf and the Center for Information Services and High-Performance Computing (ZIH), Technische Universität Dresden, for providing extensive computing facilities.

References

ARTICLE SECTIONS
Jump To

This article references 75 other publications.

  1. 1
    Chen, W.; Hou, X.; Shi, X.; Pan, H. Two-Dimensional Janus Transition Metal Oxides and Chalcogenides: Multifunctional Properties for Photocatalysts, Electronics, and Energy Conversion. ACS Appl. Mater. Interfaces 2018, 10, 3528935295,  DOI: 10.1021/acsami.8b13248
  2. 2
    da Silva, R.; Barbosa, R.; Mançano, R. R.; Durães, N.; Pontes, R. B.; Miwa, R. H.; Fazzio, A.; Padilha, J. E. Metal Chalcogenides Janus Monolayers for Efficient Hydrogen Generation by Photocatalytic Water Splitting. ACS Appl. Nano Mater. 2019, 2, 890897,  DOI: 10.1021/acsanm.8b02135
  3. 3
    Kirubasankar, B.; Won, Y. S.; Adofo, L. A.; Choi, S. H.; Kim, S. M.; Kim, K. K. Atomic and structural modifications of two-dimensional transition metal dichalcogenides for various advanced applications. Chem. Sci. 2022, 13, 77077738,  DOI: 10.1039/D2SC01398C
  4. 4
    Jiang, X.; Xie, W.; Xu, X.; Gao, Q.; Li, D.; Cui, B.; Liu, D.; Qu, F. A bifunctional GeC/SnSSe heterostructure for highly efficient photocatalysts and photovoltaic devices. Nanoscale 2022, 14, 72927302,  DOI: 10.1039/D2NR01387H
  5. 5
    Yagmurcukardes, M.; Sozen, Y.; Baskurt, M.; Peeters, F. M.; Sahin, H. Interface-dependent phononic and optical properties of GeO/MoSO heterostructures. Nanoscale 2022, 14, 865874,  DOI: 10.1039/D1NR06534C
  6. 6
    Jin, H.; Wang, T.; Gong, Z.-R.; Long, C.; Dai, Y. Prediction of an extremely long exciton lifetime in a Janus-MoSTe monolayer. Nanoscale 2018, 10, 1931019315,  DOI: 10.1039/C8NR04568B
  7. 7
    Guan, Z.; Ni, S. Predicted 2D ferromagnetic Janus VSeTe monolayer with high Curie temperature, large valley polarization and magnetic crystal anisotropy. Nanoscale 2020, 12, 2273522742,  DOI: 10.1039/D0NR04837B
  8. 8
    Tao, W.-L.; Lan, J.-Q.; Hu, C.-E.; Cheng, Y.; Zhu, J.; Geng, H.-Y. Thermoelectric properties of Janus MXY (M=Pd, Pt; X, Y=S, Se, Te) transition-metal dichalcogenide monolayers from first principles. J. Appl. Phys. 2020, 127, 035101  DOI: 10.1063/1.5130741
  9. 9
    Varjovi, M. J.; Yagmurcukardes, M.; Peeters, F. M.; Durgun, E. Janus two-dimensional transition metal dichalcogenide oxides: First-principles investigation of WXO monolayers with X = S, Se, and Te. Phys. Rev. B 2021, 103, 195438  DOI: 10.1103/PhysRevB.103.195438
  10. 10
    Ren, K.; Wang, S.; Luo, Y.; Chou, J.-P.; Yu, J.; Tang, W.; Sun, M. High-efficiency photocatalyst for water splitting: a Janus MoSSe/XN (X=Ga, Al) van der waals heterostructure. J. Phys. D: Appl. Phys. 2020, 53, 185504  DOI: 10.1088/1361-6463/ab71ad
  11. 11
    Choi, W.; Choudhary, N.; Han, G. H.; Park, J.; Akinwande, D.; Lee, Y. H. Recent development of two-dimensional transition metal dichalcogenides and their applications. Mater. Today 2017, 20, 116130,  DOI: 10.1016/j.mattod.2016.10.002
  12. 12
    Qin, J.; Qiu, G.; Jian, J.; Zhou, H.; Yang, L.; Charnas, A.; Zemlyanov, D. Y.; Xu, C.-Y.; Xu, X.; Wu, W. Controlled Growth of a Large-Size 2D Selenium Nanosheet and Its Electronic and Optoelectronic Applications. ACS Nano 2017, 11, 1022210229,  DOI: 10.1021/acsnano.7b04786
  13. 13
    Chen, W.; Pan, W.; Wang, J.; Cheng, L.; Wang, J.; Song, L.; Hu, Y.; Ma, X. Emerging two-dimensional monoelemental materials (Xenes): Fabrication, modification, and applications thereof in the field of bioimaging as nanocarriers. Wiley Interdiscip. Rev.: Nanomed. Nanobiotechnol. 2022, 14, e1750  DOI: 10.1002/wnan.1750
  14. 14
    Balendhran, S.; Walia, S.; Nili, H.; Sriram, S.; Bhaskaran, M. Elemental Analogues of Graphene: Silicene, Germanene, Stanene, and Phosphorene. Small 2015, 11, 640652,  DOI: 10.1002/smll.201402041
  15. 15
    Zhu, Z.; Cai, X.; Yi, S.; Chen, J.; Dai, Y.; Niu, C.; Guo, Z.; Xie, M.; Liu, F.; Cho, J.-H. Multivalency-Driven Formation of Te-Based Monolayer Materials: A Combined First-Principles and Experimental study. Phys. Rev. Lett. 2017, 119, 106101  DOI: 10.1103/PhysRevLett.119.106101
  16. 16
    Song, J.-M.; Lin, Y.-Z.; Zhan, Y.-J.; Tian, Y.-C.; Liu, G.; Yu, S.-H. Superlong High-Quality Tellurium Nanotubes: Synthesis, Characterization, and Optical Property. Cryst. Growth Des. 2008, 8, 19021908,  DOI: 10.1021/cg701125k
  17. 17
    Yan, Z.; Yang, H.; Yang, Z.; Ji, C.; Zhang, G.; Tu, Y.; Du, G.; Cai, S.; Lin, S. Emerging Two-Dimensional Tellurene and Tellurides for Broadband Photodetectors. Small 2022, 18, 2200016  DOI: 10.1002/smll.202200016
  18. 18
    Tang, Q.; Zhou, Z. Graphene-analogous low-dimensional materials. Prog. Mater. Sci. 2013, 58, 12441315,  DOI: 10.1016/j.pmatsci.2013.04.003
  19. 19
    Zhang, Y.; Rubio, A.; Lay, G. L. Emergent elemental two-dimensional materials beyond graphene. J. Phys. D: Appl. Phys. 2017, 50, 053004  DOI: 10.1088/1361-6463/aa4e8b
  20. 20
    Mannix, A. J.; Kiraly, B.; Hersam, M. C.; Guisinger, N. P. Synthesis and chemistry of elemental 2D materials. Nat. Rev. Chem. 2017, 1, 0014  DOI: 10.1038/s41570-016-0014
  21. 21
    Glavin, N. R.; Rao, R.; Varshney, V.; Bianco, E.; Apte, A.; Roy, A.; Ringe, E.; Ajayan, P. M. Emerging Applications of Elemental 2D Materials. Adv. Mater. 2020, 32, 1904302  DOI: 10.1002/adma.201904302
  22. 22
    Kaloni, T. P.; Schreckenbach, G.; Freund, M. S.; Schwingenschlögl, U. Current developments in silicene and germanene. Phys. Status Solidi RRL 2016, 10, 133142,  DOI: 10.1002/pssr.201510338
  23. 23
    Bhimanapati, G. R.; Lin, Z.; Meunier, V.; Jung, Y.; Cha, J.; Das, S.; Xiao, D.; Son, Y.; Strano, M. S.; Cooper, V. R. Recent Advances in Two-Dimensional Materials beyond Graphene. ACS Nano 2015, 9, 1150911539,  DOI: 10.1021/acsnano.5b05556
  24. 24
    Cai, X.; Han, X.; Zhao, C.; Niu, C.; Jia, Y. Tellurene: An elemental 2D monolayer material beyond its bulk phases without van der Waals layered structures. J. Semicond. 2020, 41, 081002  DOI: 10.1088/1674-4926/41/8/081002
  25. 25
    Liu, D.; Han, L.; Wei, R.; Song, S.; Guan, J.; Dong, S.; Tománek, D. Unusual electric polarization behavior in elemental quasi-two-dimensional allotropes of selenium. Phys. Rev. Mater. 2022, 6, 103403  DOI: 10.1103/PhysRevMaterials.6.103403
  26. 26
    Yi, S.; Zhu, Z.; Cai, X.; Jia, Y.; Cho, J.-H. The Nature of Bonding in Bulk Tellurium Composed of One-Dimensional Helical Chains. Inorg. Chem. 2018, 57, 50835088,  DOI: 10.1021/acs.inorgchem.7b03244
  27. 27
    Xie, Z.; Zhang, B.; Ge, Y.; Zhu, Y.; Nie, G.; Song, Y.; Lim, C.-K.; Zhang, H.; Prasad, P. N. Chemistry, Functionalization, and Applications of Recent Monoelemental Two-Dimensional Materials and Their Heterostructures. Chem. Rev. 2022, 122, 11271207,  DOI: 10.1021/acs.chemrev.1c00165
  28. 28
    Wang, Q.; Safdar, M.; Xu, K.; Mirza, M.; Wang, Z.; He, J. Van der Waals Epitaxy and Photoresponse of Hexagonal Tellurium Nanoplates on Flexible Mica Sheets. ACS Nano 2014, 8, 74977505,  DOI: 10.1021/nn5028104
  29. 29
    Fan, T.; Xie, Z.; Huang, W.; Li, Z.; Zhang, H. Two-dimensional non-layered selenium nanoflakes: facile fabrications and applications for self-powered photo-detector. Nanotechnology 2019, 30, 114002,  DOI: 10.1088/1361-6528/aafc0f
  30. 30
    Amani, M.; Tan, C.; Zhang, G.; Zhao, C.; Bullock, J.; Song, X.; Kim, H.; Shrestha, V. R.; Gao, Y.; Crozier, K. B. Solution-Synthesized High-Mobility Tellurium Nanoflakes for Short-Wave Infrared Photodetectors. ACS Nano 2018, 12, 72537263,  DOI: 10.1021/acsnano.8b03424
  31. 31
    Shi, Z.; Cao, R.; Khan, K.; Tareen, A. K.; Liu, X.; Liang, W.; Zhang, Y.; Ma, C.; Guo, Z.; Luo, X. Two-Dimensional Tellurium: Progress, Challenges, and Prospects. Nano-Micro Lett. 2020, 12, 99,  DOI: 10.1007/s40820-020-00427-z
  32. 32
    Wang, Y.; Qiu, G.; Wang, R.; Huang, S.; Wang, Q. x.; Liu, Y.; Du, Y.; Goddard, W. A.; Kim, M. J.; Xu, X. Field-effect transistors made from solution-grown two-dimensional tellurene. Nat. Electron. 2018, 1, 228236,  DOI: 10.1038/s41928-018-0058-4
  33. 33
    Kramer, A.; Van de Put, M. L.; Hinkle, C. L.; Vandenberghe, W. G. Tellurium as a successor of silicon for extremely scaled nanowires: a first-principles study. npj 2D Mater. Appl. 2020, 4, 18
  34. 34
    Liu, G.; Wang, H.; Li, G.-L. Structures, mobilities, electronic and optical properties of two-dimensional α-phase group-VI binary compounds: α-Se2Te and α-SeTe2. Phys. Lett. A 2020, 384, 126431  DOI: 10.1016/j.physleta.2020.126431
  35. 35
    Chen, Y.; Liu, J.; Yu, J.; Guo, Y.; Sun, Q. Symmetry-breaking induced large piezoelectricity in Janus tellurene materials. Phys. Chem. Chem. Phys. 2019, 21, 12071216,  DOI: 10.1039/C8CP04669G
  36. 36
    Ahammed, R.; Jena, N.; Rawat, A.; Mohanta, M. K.; Dimple; De Sarkar, A. Ultrahigh Out-of-Plane Piezoelectricity Meets Giant Rashba Effect in 2D Janus Monolayers and Bilayers of Group IV Transition-Metal Trichalcogenides. J. Phys. Chem. C 2020, 124, 2125021260,  DOI: 10.1021/acs.jpcc.0c05134
  37. 37
    Chen, S.; Tao, W.-L.; Zhou, Y.; Zeng, Z.-Y.; Chen, X.-R.; Geng, H.-Y. Novel thermoelectric performance of 2D 1T- Se2Te and SeTe2 with ultralow lattice thermal conductivity but high carrier mobility. Nanotechnology 2021, 32, 455401,  DOI: 10.1088/1361-6528/ac1a91
  38. 38
    Kresse, G.; Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 1996, 6, 1550,  DOI: 10.1016/0927-0256(96)00008-0
  39. 39
    Kresse, G.; Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 1996, 54, 1116911186,  DOI: 10.1103/PhysRevB.54.11169
  40. 40
    Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 38653868,  DOI: 10.1103/PhysRevLett.77.3865
  41. 41
    Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 1994, 50, 1795317979,  DOI: 10.1103/PhysRevB.50.17953
  42. 42
    Kresse, G.; Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 1999, 59, 17581775,  DOI: 10.1103/PhysRevB.59.1758
  43. 43
    Monkhorst, H. J.; Pack, J. D. Special points for Brillouin-zone integrations. Phys. Rev. B 1976, 13, 51885192,  DOI: 10.1103/PhysRevB.13.5188
  44. 44
    Gajdoš, M.; Hummer, K.; Kresse, G.; Furthmüller, J.; Bechstedt, F. Linear optical properties in the projector-augmented wave methodology. Phys. Rev. B 2006, 73, 045112  DOI: 10.1103/PhysRevB.73.045112
  45. 45
    Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010, 132, 154104,  DOI: 10.1063/1.3382344
  46. 46
    Momma, K.; Izumi, F. VESTA3 for three-dimensional visualization of crystal, volumetric and morphology data. J. Appl. Crystallogr. 2011, 44, 12721276,  DOI: 10.1107/S0021889811038970
  47. 47
    Wang, V.; Xu, N.; Liu, J.-C.; Tang, G.; Geng, W.-T. VASPKIT: A user-friendly interface facilitating high-throughput computing and analysis using VASP code. Comput. Phys. Commun. 2021, 267, 108033  DOI: 10.1016/j.cpc.2021.108033
  48. 48
    Jain, A.; Ong, S. P.; Hautier, G.; Chen, W.; Richards, W. D.; Dacek, S.; Cholia, S.; Gunter, D.; Skinner, D.; Ceder, G. Commentary: The Materials Project: A materials genome approach to accelerating materials innovation. APL Mater. 2013, 1, 011002  DOI: 10.1063/1.4812323
  49. 49
    Materials Explorer App by Materials Project.  DOI: 10.17188/1313363 , (accessed on 01.02.2023).
  50. 50
    Materials Explorer App by Materials Project.  DOI: 10.17188/1275729 , (accessed on 01.02.2023).
  51. 51
    Materials Explorer App by Materials Project.  DOI: 10.17188/1193780 , (accessed on 01.02.2023).
  52. 52
    Liu, C.; Hu, T.; Wu, Y.; Gao, H.; Yang, Y.; Ren, W. 2D selenium allotropes from first principles and swarm intelligence. J. Phys.: Condens. Matter 2019, 31, 235702,  DOI: 10.1088/1361-648X/ab059d
  53. 53
    Zhu, Z.; Cai, X.; Yi, S.; Chen, J.; Dai, Y.; Niu, C.; Guo, Z.; Xie, M.; Liu, F.; Cho, J.-H. Multivalency-Driven Formation of Te-Based Monolayer Materials: A Combined First-Principles and Experimental study. Phys. Rev. Lett. 2017, 119, 106101  DOI: 10.1103/PhysRevLett.119.106101
  54. 54
    Sanville, E.; Kenny, S. D.; Smith, R.; Henkelman, G. Improved grid-based algorithm for Bader charge allocation. J. Comput. Chem. 2007, 28, 899908,  DOI: 10.1002/jcc.20575
  55. 55
    Bader, R. F. Atoms in molecules. Acc. Chem. Res. 1985, 18, 915,  DOI: 10.1021/ar00109a003
  56. 56
    Henkelman, G.; Arnaldsson, A.; Jónsson, H. A fast and robust algorithm for Bader decomposition of charge density. Comput. Mater. Sci. 2006, 36, 354360,  DOI: 10.1016/j.commatsci.2005.04.010
  57. 57
    Tang, W.; Sanville, E.; Henkelman, G. A grid-based Bader analysis algorithm without lattice bias. J. Phys.: Condens. Matter 2009, 21, 084204  DOI: 10.1088/0953-8984/21/8/084204
  58. 58
    Heilmann, M.; Deinhart, V.; Tahraoui, A.; Höflich, K.; Lopes, J. M. J. Spatially controlled epitaxial growth of 2D heterostructures via defect engineering using a focused He ion beam. npj 2D Mater. Appl. 2021, 5, 70,  DOI: 10.1038/s41699-021-00250-z
  59. 59
    Zhang, Z.; Yang, X.; Liu, K.; Wang, R. Epitaxy of 2D Materials toward Single Crystals. Adv. Sci. 2022, 9, 2105201  DOI: 10.1002/advs.202105201
  60. 60
    Sarma, P. V.; Nadarajan, R.; Kumar, R.; Patinharayil, R. M.; Biju, N.; Narayanan, S.; Gao, G.; Tiwary, C. S.; Thalakulam, M.; Kini, R. N. Growth of highly crystalline ultrathin two-dimensional selenene. 2D Mater. 2022, 9, 045004  DOI: 10.1088/2053-1583/ac787f
  61. 61
    Yu, W.; Gong, K.; Li, Y.; Ding, B.; Li, L.; Xu, Y.; Wang, R.; Li, L.; Zhang, G.; Lin, S. Flexible 2D Materials beyond Graphene: Synthesis, Properties, and Applications. Small 2022, 18, 2105383  DOI: 10.1002/smll.202105383
  62. 62
    Zhang, J.; Jia, S.; Kholmanov, I.; Dong, L.; Er, D.; Chen, W.; Guo, H.; Jin, Z.; Shenoy, V. B.; Shi, L. Janus Monolayer Transition-Metal Dichalcogenides. ACS Nano 2017, 11, 81928198,  DOI: 10.1021/acsnano.7b03186
  63. 63
    Gan, Z.; Paradisanos, I.; Estrada-Real, A.; Picker, J.; Najafidehaghani, E.; Davies, F.; Neumann, C.; Robert, C.; Wiecha, P.; Watanabe, K. Chemical Vapor Deposition of High-Optical-Quality Large-Area Monolayer Janus Transition Metal Dichalcogenides. Adv. Mater. 2022, 34, 2205226  DOI: 10.1002/adma.202205226
  64. 64
    Zschornak, M.; Gemming, S.; Gutmann, E.; Weißbach, T.; Stöcker, H.; Leisegang, T.; Riedl, T.; Tränkner, M.; Gemming, T.; Meyer, D. Surface modeling and chemical solution deposition of SrO(SrTiO3)n Ruddlesden–Popper phases. Acta Mater. 2010, 58, 46504659,  DOI: 10.1016/j.actamat.2010.04.035
  65. 65
    Malyi, O. I.; Sopiha, K. V.; Persson, C. Energy, Phonon, and Dynamic Stability Criteria of Two-Dimensional Materials. ACS Appl. Mater. Interfaces 2019, 11, 2487624884,  DOI: 10.1021/acsami.9b01261
  66. 66
    Togo, A.; Tanaka, I. First principles phonon calculations in materials science. Scr. Mater. 2015, 108, 15,  DOI: 10.1016/j.scriptamat.2015.07.021
  67. 67
    Voss, J.; Hummelshøj, J. S.; Łodziana, Z.; Vegge, T. Structural stability and decomposition of Mg(BH4)2 isomorphs─an ab initio free energy study. J. Phys.: Condens. Matter 2009, 21, 012203  DOI: 10.1088/0953-8984/21/1/012203
  68. 68
    Osanloo, M. R.; Van de Put, M. L.; Saadat, A.; Vandenberghe, W. G. Identification of two-dimensional layered dielectrics from first principles. Nat. Commun. 2021, 12, 5051,  DOI: 10.1038/s41467-021-25310-2
  69. 69
    Laturia, A.; van de Put, M. L.; Vandenberghe, W. G. Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk. npj 2D Mater. Appl. 2018, 2, 6,  DOI: 10.1038/s41699-018-0050-x
  70. 70
    Dresselhaus, M.; Dresselhaus, G.; Cronin, S.; Filho, A. Solid State Properties: From Bulk to Nano; Graduate Texts in Physics; Springer: Berlin Heidelberg, 2018.
  71. 71
    Singh, A. K.; Mathew, K.; Zhuang, H. L.; Hennig, R. G. Computational Screening of 2D Materials for Photocatalysis. J. Phys. Chem. Lett. 2015, 6, 10871098,  DOI: 10.1021/jz502646d
  72. 72
    Chakrapani, V.; Angus, J. C.; Anderson, A. B.; Wolter, S. D.; Stoner, B. R.; Sumanasekera, G. U. Charge Transfer Equilibria Between Diamond and an Aqueous Oxygen Electrochemical Redox Couple. Science 2007, 318, 14241430,  DOI: 10.1126/science.1148841
  73. 73
    Din, H. U.; Idrees, M.; Albar, A.; Shafiq, M.; Ahmad, I.; Nguyen, C. V.; Amin, B. Rashba spin splitting and photocatalytic properties of GeC – MSSe (M =Mo, W) van der Waals heterostructures. Phys. Rev. B 2019, 100, 165425  DOI: 10.1103/PhysRevB.100.165425
  74. 74
    Ju, L.; Bie, M.; Tang, X.; Shang, J.; Kou, L. Janus WSSe Monolayer: An Excellent Photocatalyst for Overall Water Splitting. ACS Appl. Mater. Interfaces 2020, 12, 2933529343,  DOI: 10.1021/acsami.0c06149
  75. 75
    Vu, T. V.; Vi, V. T. T.; Phuc, H. V.; Nguyen, C. V.; Poklonski, N. A.; Duque, C. A.; Rai, D. P.; Hoi, B. D.; Hieu, N. N. Electronic, optical, and thermoelectric properties of Janus In-based monochalcogenides. J. Phys.: Condens. Matter 2021, 33, 225503,  DOI: 10.1088/1361-648X/abf381

Cited By

ARTICLE SECTIONS
Jump To

This article is cited by 1 publications.

  1. Kati Asikainen, Matti Alatalo, Marko Huttula, Assa Aravindh Sasikala Devi. Tuning the Electronic Properties of Two-Dimensional Lepidocrocite Titanium Dioxide-Based Heterojunctions. ACS Omega 2023, 8 (47) , 45056-45064. https://doi.org/10.1021/acsomega.3c06786
  • Abstract

    Figure 1

    Figure 1. Optimized structures of (a) SeSTe, (b) SSeTe, and (c) TeSeS JLs. The top row is the perpendicular view, and the bottom row shows the cross-sectional view. The black line defines the unit cell.

    Figure 2

    Figure 2. Differential charge density of (a) SeSTe, (b) SSeTe, and (c) TeSeS JLs. The isosurface of value 0.005 e3 is selected to illustrate the bonding between S, Se, and Te. The blue and yellow surfaces indicate charge depletion and accumulation, respectively. The BC analysis shows that the Se originates covalent nature bonding in SeSTe and SSeTe while S and Te are leading to ionic nature in the JLs.

    Figure 3

    Figure 3. Formation energy of SeSTe, SSeTe, and TeSeS JLs under different μA. In (a), all μA is linearly set between A-bulk and A-dimer, and in (b), μA is varied as described in the text. The μS scale is given, whereas Se-rich and Te-rich limits are indicated by an arrow mark in (a). In (b), the continuous, dashed, dash-dot, and dotted lines represent, respectively, Sepoor–Tepoor, Serich–Tepoor, Sepoor–Terich, and Serich–Terich limits for Se and Te. The μS scale is calibrated in order to shift the S-poor limit to 0 eV.

    Figure 4

    Figure 4. Band structure of optimized JLs, (a) for SeSTe, (b) for SSeTe, and (c) for TeSeS along with DOS (in states/eV unit) and partial DOS. The blue and black arrows respectively indicate the bandgap and observed peaks in the absorption spectrum shown in Figure 6. The horizontal dashed line represents the Fermi level, which is set to 0 eV. The computed partial DOS depicts that the VBM is intensely contributed by Te(p) orbital in SeSTe and SSeTe, and by S(p), Se(p), and Te(p) orbitals in TeSeS JL. The equivalent up and down spin states indicate the absence of magnetic characters in optimized JLs.

    Figure 5

    Figure 5. Phonon dispersion bands of optimized JLs, (a) for SeSTe, (b) for SSeTe, and (c) for TeSeS along with frequency resolved phonon DOS (in states/cm–1 unit). In all JL, low-frequency regimes originate from Se and Te and the major contribution to the high-frequency regime is from S vibrations. Due to the denser phonon modes, the phonon DOS strongly disperses for the TeSeS JL. The abrupt rise in S modes around 150 cm–1 in SSeTe and 350 cm–1 in TeSeS JLs indicates that S vibrational mode is almost directional independent. The positive vibrational frequencies along the entire high symmetric locations in the Brillouin zone depict the stability of the JLs.

    Figure 6

    Figure 6. Imaginary part of the dielectric function (a) for SeSTe, (b) for SSeTe, and (c) for TeSeS JLs. The red and blue lines indicate parallel (ϵ, xx, yy) components, and the yellow line indicates the perpendicular (ϵ, zz) component. The visible frequency window is denoted by vertical dashed red and violet lines. In comparison, TeSeS has three peaks with high ϵ2 within the visible frequency window and, hence, has enhanced absorbance than other JLs.

    Figure 7

    Figure 7. Estimated band edge positions of the JLs using HSE06 and GGA potentials on vacuum scale. For comparison, the redox potentials of water-splitting reactions at different pH levels are shown by continuous, dashed, and dotted lines. The green and blue bars represent VBM and CBM positions, respectively. The vacuum level is set at 0 eV.

  • References

    ARTICLE SECTIONS
    Jump To

    This article references 75 other publications.

    1. 1
      Chen, W.; Hou, X.; Shi, X.; Pan, H. Two-Dimensional Janus Transition Metal Oxides and Chalcogenides: Multifunctional Properties for Photocatalysts, Electronics, and Energy Conversion. ACS Appl. Mater. Interfaces 2018, 10, 3528935295,  DOI: 10.1021/acsami.8b13248
    2. 2
      da Silva, R.; Barbosa, R.; Mançano, R. R.; Durães, N.; Pontes, R. B.; Miwa, R. H.; Fazzio, A.; Padilha, J. E. Metal Chalcogenides Janus Monolayers for Efficient Hydrogen Generation by Photocatalytic Water Splitting. ACS Appl. Nano Mater. 2019, 2, 890897,  DOI: 10.1021/acsanm.8b02135
    3. 3
      Kirubasankar, B.; Won, Y. S.; Adofo, L. A.; Choi, S. H.; Kim, S. M.; Kim, K. K. Atomic and structural modifications of two-dimensional transition metal dichalcogenides for various advanced applications. Chem. Sci. 2022, 13, 77077738,  DOI: 10.1039/D2SC01398C
    4. 4
      Jiang, X.; Xie, W.; Xu, X.; Gao, Q.; Li, D.; Cui, B.; Liu, D.; Qu, F. A bifunctional GeC/SnSSe heterostructure for highly efficient photocatalysts and photovoltaic devices. Nanoscale 2022, 14, 72927302,  DOI: 10.1039/D2NR01387H
    5. 5
      Yagmurcukardes, M.; Sozen, Y.; Baskurt, M.; Peeters, F. M.; Sahin, H. Interface-dependent phononic and optical properties of GeO/MoSO heterostructures. Nanoscale 2022, 14, 865874,  DOI: 10.1039/D1NR06534C
    6. 6
      Jin, H.; Wang, T.; Gong, Z.-R.; Long, C.; Dai, Y. Prediction of an extremely long exciton lifetime in a Janus-MoSTe monolayer. Nanoscale 2018, 10, 1931019315,  DOI: 10.1039/C8NR04568B
    7. 7
      Guan, Z.; Ni, S. Predicted 2D ferromagnetic Janus VSeTe monolayer with high Curie temperature, large valley polarization and magnetic crystal anisotropy. Nanoscale 2020, 12, 2273522742,  DOI: 10.1039/D0NR04837B
    8. 8
      Tao, W.-L.; Lan, J.-Q.; Hu, C.-E.; Cheng, Y.; Zhu, J.; Geng, H.-Y. Thermoelectric properties of Janus MXY (M=Pd, Pt; X, Y=S, Se, Te) transition-metal dichalcogenide monolayers from first principles. J. Appl. Phys. 2020, 127, 035101  DOI: 10.1063/1.5130741
    9. 9
      Varjovi, M. J.; Yagmurcukardes, M.; Peeters, F. M.; Durgun, E. Janus two-dimensional transition metal dichalcogenide oxides: First-principles investigation of WXO monolayers with X = S, Se, and Te. Phys. Rev. B 2021, 103, 195438  DOI: 10.1103/PhysRevB.103.195438
    10. 10
      Ren, K.; Wang, S.; Luo, Y.; Chou, J.-P.; Yu, J.; Tang, W.; Sun, M. High-efficiency photocatalyst for water splitting: a Janus MoSSe/XN (X=Ga, Al) van der waals heterostructure. J. Phys. D: Appl. Phys. 2020, 53, 185504  DOI: 10.1088/1361-6463/ab71ad
    11. 11
      Choi, W.; Choudhary, N.; Han, G. H.; Park, J.; Akinwande, D.; Lee, Y. H. Recent development of two-dimensional transition metal dichalcogenides and their applications. Mater. Today 2017, 20, 116130,  DOI: 10.1016/j.mattod.2016.10.002
    12. 12
      Qin, J.; Qiu, G.; Jian, J.; Zhou, H.; Yang, L.; Charnas, A.; Zemlyanov, D. Y.; Xu, C.-Y.; Xu, X.; Wu, W. Controlled Growth of a Large-Size 2D Selenium Nanosheet and Its Electronic and Optoelectronic Applications. ACS Nano 2017, 11, 1022210229,  DOI: 10.1021/acsnano.7b04786
    13. 13
      Chen, W.; Pan, W.; Wang, J.; Cheng, L.; Wang, J.; Song, L.; Hu, Y.; Ma, X. Emerging two-dimensional monoelemental materials (Xenes): Fabrication, modification, and applications thereof in the field of bioimaging as nanocarriers. Wiley Interdiscip. Rev.: Nanomed. Nanobiotechnol. 2022, 14, e1750  DOI: 10.1002/wnan.1750
    14. 14
      Balendhran, S.; Walia, S.; Nili, H.; Sriram, S.; Bhaskaran, M. Elemental Analogues of Graphene: Silicene, Germanene, Stanene, and Phosphorene. Small 2015, 11, 640652,  DOI: 10.1002/smll.201402041
    15. 15
      Zhu, Z.; Cai, X.; Yi, S.; Chen, J.; Dai, Y.; Niu, C.; Guo, Z.; Xie, M.; Liu, F.; Cho, J.-H. Multivalency-Driven Formation of Te-Based Monolayer Materials: A Combined First-Principles and Experimental study. Phys. Rev. Lett. 2017, 119, 106101  DOI: 10.1103/PhysRevLett.119.106101
    16. 16
      Song, J.-M.; Lin, Y.-Z.; Zhan, Y.-J.; Tian, Y.-C.; Liu, G.; Yu, S.-H. Superlong High-Quality Tellurium Nanotubes: Synthesis, Characterization, and Optical Property. Cryst. Growth Des. 2008, 8, 19021908,  DOI: 10.1021/cg701125k
    17. 17
      Yan, Z.; Yang, H.; Yang, Z.; Ji, C.; Zhang, G.; Tu, Y.; Du, G.; Cai, S.; Lin, S. Emerging Two-Dimensional Tellurene and Tellurides for Broadband Photodetectors. Small 2022, 18, 2200016  DOI: 10.1002/smll.202200016
    18. 18
      Tang, Q.; Zhou, Z. Graphene-analogous low-dimensional materials. Prog. Mater. Sci. 2013, 58, 12441315,  DOI: 10.1016/j.pmatsci.2013.04.003
    19. 19
      Zhang, Y.; Rubio, A.; Lay, G. L. Emergent elemental two-dimensional materials beyond graphene. J. Phys. D: Appl. Phys. 2017, 50, 053004  DOI: 10.1088/1361-6463/aa4e8b
    20. 20
      Mannix, A. J.; Kiraly, B.; Hersam, M. C.; Guisinger, N. P. Synthesis and chemistry of elemental 2D materials. Nat. Rev. Chem. 2017, 1, 0014  DOI: 10.1038/s41570-016-0014
    21. 21
      Glavin, N. R.; Rao, R.; Varshney, V.; Bianco, E.; Apte, A.; Roy, A.; Ringe, E.; Ajayan, P. M. Emerging Applications of Elemental 2D Materials. Adv. Mater. 2020, 32, 1904302  DOI: 10.1002/adma.201904302
    22. 22
      Kaloni, T. P.; Schreckenbach, G.; Freund, M. S.; Schwingenschlögl, U. Current developments in silicene and germanene. Phys. Status Solidi RRL 2016, 10, 133142,  DOI: 10.1002/pssr.201510338
    23. 23
      Bhimanapati, G. R.; Lin, Z.; Meunier, V.; Jung, Y.; Cha, J.; Das, S.; Xiao, D.; Son, Y.; Strano, M. S.; Cooper, V. R. Recent Advances in Two-Dimensional Materials beyond Graphene. ACS Nano 2015, 9, 1150911539,  DOI: 10.1021/acsnano.5b05556
    24. 24
      Cai, X.; Han, X.; Zhao, C.; Niu, C.; Jia, Y. Tellurene: An elemental 2D monolayer material beyond its bulk phases without van der Waals layered structures. J. Semicond. 2020, 41, 081002  DOI: 10.1088/1674-4926/41/8/081002
    25. 25
      Liu, D.; Han, L.; Wei, R.; Song, S.; Guan, J.; Dong, S.; Tománek, D. Unusual electric polarization behavior in elemental quasi-two-dimensional allotropes of selenium. Phys. Rev. Mater. 2022, 6, 103403  DOI: 10.1103/PhysRevMaterials.6.103403
    26. 26
      Yi, S.; Zhu, Z.; Cai, X.; Jia, Y.; Cho, J.-H. The Nature of Bonding in Bulk Tellurium Composed of One-Dimensional Helical Chains. Inorg. Chem. 2018, 57, 50835088,  DOI: 10.1021/acs.inorgchem.7b03244
    27. 27
      Xie, Z.; Zhang, B.; Ge, Y.; Zhu, Y.; Nie, G.; Song, Y.; Lim, C.-K.; Zhang, H.; Prasad, P. N. Chemistry, Functionalization, and Applications of Recent Monoelemental Two-Dimensional Materials and Their Heterostructures. Chem. Rev. 2022, 122, 11271207,  DOI: 10.1021/acs.chemrev.1c00165
    28. 28
      Wang, Q.; Safdar, M.; Xu, K.; Mirza, M.; Wang, Z.; He, J. Van der Waals Epitaxy and Photoresponse of Hexagonal Tellurium Nanoplates on Flexible Mica Sheets. ACS Nano 2014, 8, 74977505,  DOI: 10.1021/nn5028104
    29. 29
      Fan, T.; Xie, Z.; Huang, W.; Li, Z.; Zhang, H. Two-dimensional non-layered selenium nanoflakes: facile fabrications and applications for self-powered photo-detector. Nanotechnology 2019, 30, 114002,  DOI: 10.1088/1361-6528/aafc0f
    30. 30
      Amani, M.; Tan, C.; Zhang, G.; Zhao, C.; Bullock, J.; Song, X.; Kim, H.; Shrestha, V. R.; Gao, Y.; Crozier, K. B. Solution-Synthesized High-Mobility Tellurium Nanoflakes for Short-Wave Infrared Photodetectors. ACS Nano 2018, 12, 72537263,  DOI: 10.1021/acsnano.8b03424
    31. 31
      Shi, Z.; Cao, R.; Khan, K.; Tareen, A. K.; Liu, X.; Liang, W.; Zhang, Y.; Ma, C.; Guo, Z.; Luo, X. Two-Dimensional Tellurium: Progress, Challenges, and Prospects. Nano-Micro Lett. 2020, 12, 99,  DOI: 10.1007/s40820-020-00427-z
    32. 32
      Wang, Y.; Qiu, G.; Wang, R.; Huang, S.; Wang, Q. x.; Liu, Y.; Du, Y.; Goddard, W. A.; Kim, M. J.; Xu, X. Field-effect transistors made from solution-grown two-dimensional tellurene. Nat. Electron. 2018, 1, 228236,  DOI: 10.1038/s41928-018-0058-4
    33. 33
      Kramer, A.; Van de Put, M. L.; Hinkle, C. L.; Vandenberghe, W. G. Tellurium as a successor of silicon for extremely scaled nanowires: a first-principles study. npj 2D Mater. Appl. 2020, 4, 18
    34. 34
      Liu, G.; Wang, H.; Li, G.-L. Structures, mobilities, electronic and optical properties of two-dimensional α-phase group-VI binary compounds: α-Se2Te and α-SeTe2. Phys. Lett. A 2020, 384, 126431  DOI: 10.1016/j.physleta.2020.126431
    35. 35
      Chen, Y.; Liu, J.; Yu, J.; Guo, Y.; Sun, Q. Symmetry-breaking induced large piezoelectricity in Janus tellurene materials. Phys. Chem. Chem. Phys. 2019, 21, 12071216,  DOI: 10.1039/C8CP04669G
    36. 36
      Ahammed, R.; Jena, N.; Rawat, A.; Mohanta, M. K.; Dimple; De Sarkar, A. Ultrahigh Out-of-Plane Piezoelectricity Meets Giant Rashba Effect in 2D Janus Monolayers and Bilayers of Group IV Transition-Metal Trichalcogenides. J. Phys. Chem. C 2020, 124, 2125021260,  DOI: 10.1021/acs.jpcc.0c05134
    37. 37
      Chen, S.; Tao, W.-L.; Zhou, Y.; Zeng, Z.-Y.; Chen, X.-R.; Geng, H.-Y. Novel thermoelectric performance of 2D 1T- Se2Te and SeTe2 with ultralow lattice thermal conductivity but high carrier mobility. Nanotechnology 2021, 32, 455401,  DOI: 10.1088/1361-6528/ac1a91
    38. 38
      Kresse, G.; Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 1996, 6, 1550,  DOI: 10.1016/0927-0256(96)00008-0
    39. 39
      Kresse, G.; Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 1996, 54, 1116911186,  DOI: 10.1103/PhysRevB.54.11169
    40. 40
      Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 38653868,  DOI: 10.1103/PhysRevLett.77.3865
    41. 41
      Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 1994, 50, 1795317979,  DOI: 10.1103/PhysRevB.50.17953
    42. 42
      Kresse, G.; Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 1999, 59, 17581775,  DOI: 10.1103/PhysRevB.59.1758
    43. 43
      Monkhorst, H. J.; Pack, J. D. Special points for Brillouin-zone integrations. Phys. Rev. B 1976, 13, 51885192,  DOI: 10.1103/PhysRevB.13.5188
    44. 44
      Gajdoš, M.; Hummer, K.; Kresse, G.; Furthmüller, J.; Bechstedt, F. Linear optical properties in the projector-augmented wave methodology. Phys. Rev. B 2006, 73, 045112  DOI: 10.1103/PhysRevB.73.045112
    45. 45
      Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010, 132, 154104,  DOI: 10.1063/1.3382344
    46. 46
      Momma, K.; Izumi, F. VESTA3 for three-dimensional visualization of crystal, volumetric and morphology data. J. Appl. Crystallogr. 2011, 44, 12721276,  DOI: 10.1107/S0021889811038970
    47. 47
      Wang, V.; Xu, N.; Liu, J.-C.; Tang, G.; Geng, W.-T. VASPKIT: A user-friendly interface facilitating high-throughput computing and analysis using VASP code. Comput. Phys. Commun. 2021, 267, 108033  DOI: 10.1016/j.cpc.2021.108033
    48. 48
      Jain, A.; Ong, S. P.; Hautier, G.; Chen, W.; Richards, W. D.; Dacek, S.; Cholia, S.; Gunter, D.; Skinner, D.; Ceder, G. Commentary: The Materials Project: A materials genome approach to accelerating materials innovation. APL Mater. 2013, 1, 011002  DOI: 10.1063/1.4812323
    49. 49
      Materials Explorer App by Materials Project.  DOI: 10.17188/1313363 , (accessed on 01.02.2023).
    50. 50
      Materials Explorer App by Materials Project.  DOI: 10.17188/1275729 , (accessed on 01.02.2023).
    51. 51
      Materials Explorer App by Materials Project.  DOI: 10.17188/1193780 , (accessed on 01.02.2023).
    52. 52
      Liu, C.; Hu, T.; Wu, Y.; Gao, H.; Yang, Y.; Ren, W. 2D selenium allotropes from first principles and swarm intelligence. J. Phys.: Condens. Matter 2019, 31, 235702,  DOI: 10.1088/1361-648X/ab059d
    53. 53
      Zhu, Z.; Cai, X.; Yi, S.; Chen, J.; Dai, Y.; Niu, C.; Guo, Z.; Xie, M.; Liu, F.; Cho, J.-H. Multivalency-Driven Formation of Te-Based Monolayer Materials: A Combined First-Principles and Experimental study. Phys. Rev. Lett. 2017, 119, 106101  DOI: 10.1103/PhysRevLett.119.106101
    54. 54
      Sanville, E.; Kenny, S. D.; Smith, R.; Henkelman, G. Improved grid-based algorithm for Bader charge allocation. J. Comput. Chem. 2007, 28, 899908,  DOI: 10.1002/jcc.20575
    55. 55
      Bader, R. F. Atoms in molecules. Acc. Chem. Res. 1985, 18, 915,  DOI: 10.1021/ar00109a003
    56. 56
      Henkelman, G.; Arnaldsson, A.; Jónsson, H. A fast and robust algorithm for Bader decomposition of charge density. Comput. Mater. Sci. 2006, 36, 354360,  DOI: 10.1016/j.commatsci.2005.04.010
    57. 57
      Tang, W.; Sanville, E.; Henkelman, G. A grid-based Bader analysis algorithm without lattice bias. J. Phys.: Condens. Matter 2009, 21, 084204  DOI: 10.1088/0953-8984/21/8/084204
    58. 58
      Heilmann, M.; Deinhart, V.; Tahraoui, A.; Höflich, K.; Lopes, J. M. J. Spatially controlled epitaxial growth of 2D heterostructures via defect engineering using a focused He ion beam. npj 2D Mater. Appl. 2021, 5, 70,  DOI: 10.1038/s41699-021-00250-z
    59. 59
      Zhang, Z.; Yang, X.; Liu, K.; Wang, R. Epitaxy of 2D Materials toward Single Crystals. Adv. Sci. 2022, 9, 2105201  DOI: 10.1002/advs.202105201
    60. 60
      Sarma, P. V.; Nadarajan, R.; Kumar, R.; Patinharayil, R. M.; Biju, N.; Narayanan, S.; Gao, G.; Tiwary, C. S.; Thalakulam, M.; Kini, R. N. Growth of highly crystalline ultrathin two-dimensional selenene. 2D Mater. 2022, 9, 045004  DOI: 10.1088/2053-1583/ac787f
    61. 61
      Yu, W.; Gong, K.; Li, Y.; Ding, B.; Li, L.; Xu, Y.; Wang, R.; Li, L.; Zhang, G.; Lin, S. Flexible 2D Materials beyond Graphene: Synthesis, Properties, and Applications. Small 2022, 18, 2105383  DOI: 10.1002/smll.202105383
    62. 62
      Zhang, J.; Jia, S.; Kholmanov, I.; Dong, L.; Er, D.; Chen, W.; Guo, H.; Jin, Z.; Shenoy, V. B.; Shi, L. Janus Monolayer Transition-Metal Dichalcogenides. ACS Nano 2017, 11, 81928198,  DOI: 10.1021/acsnano.7b03186
    63. 63
      Gan, Z.; Paradisanos, I.; Estrada-Real, A.; Picker, J.; Najafidehaghani, E.; Davies, F.; Neumann, C.; Robert, C.; Wiecha, P.; Watanabe, K. Chemical Vapor Deposition of High-Optical-Quality Large-Area Monolayer Janus Transition Metal Dichalcogenides. Adv. Mater. 2022, 34, 2205226  DOI: 10.1002/adma.202205226
    64. 64
      Zschornak, M.; Gemming, S.; Gutmann, E.; Weißbach, T.; Stöcker, H.; Leisegang, T.; Riedl, T.; Tränkner, M.; Gemming, T.; Meyer, D. Surface modeling and chemical solution deposition of SrO(SrTiO3)n Ruddlesden–Popper phases. Acta Mater. 2010, 58, 46504659,  DOI: 10.1016/j.actamat.2010.04.035
    65. 65
      Malyi, O. I.; Sopiha, K. V.; Persson, C. Energy, Phonon, and Dynamic Stability Criteria of Two-Dimensional Materials. ACS Appl. Mater. Interfaces 2019, 11, 2487624884,  DOI: 10.1021/acsami.9b01261
    66. 66
      Togo, A.; Tanaka, I. First principles phonon calculations in materials science. Scr. Mater. 2015, 108, 15,  DOI: 10.1016/j.scriptamat.2015.07.021
    67. 67
      Voss, J.; Hummelshøj, J. S.; Łodziana, Z.; Vegge, T. Structural stability and decomposition of Mg(BH4)2 isomorphs─an ab initio free energy study. J. Phys.: Condens. Matter 2009, 21, 012203  DOI: 10.1088/0953-8984/21/1/012203
    68. 68
      Osanloo, M. R.; Van de Put, M. L.; Saadat, A.; Vandenberghe, W. G. Identification of two-dimensional layered dielectrics from first principles. Nat. Commun. 2021, 12, 5051,  DOI: 10.1038/s41467-021-25310-2
    69. 69
      Laturia, A.; van de Put, M. L.; Vandenberghe, W. G. Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk. npj 2D Mater. Appl. 2018, 2, 6,  DOI: 10.1038/s41699-018-0050-x
    70. 70
      Dresselhaus, M.; Dresselhaus, G.; Cronin, S.; Filho, A. Solid State Properties: From Bulk to Nano; Graduate Texts in Physics; Springer: Berlin Heidelberg, 2018.
    71. 71
      Singh, A. K.; Mathew, K.; Zhuang, H. L.; Hennig, R. G. Computational Screening of 2D Materials for Photocatalysis. J. Phys. Chem. Lett. 2015, 6, 10871098,  DOI: 10.1021/jz502646d
    72. 72
      Chakrapani, V.; Angus, J. C.; Anderson, A. B.; Wolter, S. D.; Stoner, B. R.; Sumanasekera, G. U. Charge Transfer Equilibria Between Diamond and an Aqueous Oxygen Electrochemical Redox Couple. Science 2007, 318, 14241430,  DOI: 10.1126/science.1148841
    73. 73
      Din, H. U.; Idrees, M.; Albar, A.; Shafiq, M.; Ahmad, I.; Nguyen, C. V.; Amin, B. Rashba spin splitting and photocatalytic properties of GeC – MSSe (M =Mo, W) van der Waals heterostructures. Phys. Rev. B 2019, 100, 165425  DOI: 10.1103/PhysRevB.100.165425
    74. 74
      Ju, L.; Bie, M.; Tang, X.; Shang, J.; Kou, L. Janus WSSe Monolayer: An Excellent Photocatalyst for Overall Water Splitting. ACS Appl. Mater. Interfaces 2020, 12, 2933529343,  DOI: 10.1021/acsami.0c06149
    75. 75
      Vu, T. V.; Vi, V. T. T.; Phuc, H. V.; Nguyen, C. V.; Poklonski, N. A.; Duque, C. A.; Rai, D. P.; Hoi, B. D.; Hieu, N. N. Electronic, optical, and thermoelectric properties of Janus In-based monochalcogenides. J. Phys.: Condens. Matter 2021, 33, 225503,  DOI: 10.1088/1361-648X/abf381

Pair your accounts.

Export articles to Mendeley

Get article recommendations from ACS based on references in your Mendeley library.

Pair your accounts.

Export articles to Mendeley

Get article recommendations from ACS based on references in your Mendeley library.

You’ve supercharged your research process with ACS and Mendeley!

STEP 1:
Click to create an ACS ID

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

MENDELEY PAIRING EXPIRED
Your Mendeley pairing has expired. Please reconnect