Exploring Doping Characteristics of Various Adatoms on Single-Layer

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Exploring Doping Characteristics of Various Adatoms on Single-layer Stanene Syeda Rabab Naqvi, Tanveer Hussain, Wei Luo, and Rajeev Ahuja J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 23 Mar 2017 Downloaded from http://pubs.acs.org on March 23, 2017

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The Journal of Physical Chemistry

Exploring Doping Characteristics of Various Adatoms on Single-layer Stanene S. R. Naqvi,1 T. Hussain*,3 W. Luo1 and R. Ahuja1,2 1

Condensed Matter Theory Group, Department of Physics and Astronomy,

Box 516, Uppsala University, S-75120 Uppsala, Sweden 2

Applied Materials Physics, Department of Materials and Engineering,

Royal Institute of Technology (KTH), S-100 44 Stockholm, Sweden 3

Centre for Theoretical and Computational Molecular Science,

Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld 4072, Australia [email protected] +61 7 33463976

ABSRACT We have performed first-principles calculations based on density functional theory to investigate the doping characteristics of 31 different adatoms on stanene monolayer, which includes the elements of alkali metals (AM), alkaline earth metals (AEM), transition metals (TMs) and group III-VII. The most stable configurations of all the dopants have been explored by calculating and comparing binding energies of all the possible binding sites. In order to comment on the uniform distribution of adatoms on stanene, the adsorption energies (Eads) of adatoms have been compared with their experimental cohesive energies (Ec) in bulk phase. A further comparison reveals that the binding energies of the most of studied adatoms on stanene are much stronger than other group IV monolayers. Apart from structural and binding characteristics, bond lengths, adatom-adatom distance, charge transfer mechanism, electronic properties and work function has also been explored in pristine and doped monolayers. The strong adsorption of adatoms on stanene, tunable electronic properties and formation of dumbbell structures in the case of AEM and TM shows that doped stanene sheets are worth further exploration.

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INTRODUCTION The discovery of free-standing monolayer of carbon atoms, graphene,1 was followed by a sparkling upsurge of interest in condensed-matter nature of its pristine and functionalized forms for future applications.2 This stable sp2 hybridized -bonded two-dimensional (2D) network exhibited a fascinating electronic behavior. For example, linearly dispersed energies close to the Fermi level ( ) endowed Dirac-type nature of quasiparticles,3 and excellent transportation at room temperature.4, 5 However, zero band gap was a major hindrance for practical implementation of graphene in nanoscale electronics/optoelectronic tools such as transistors and photovoltaic cells.6-8 To tackle this issue, researchers explored the potential of other 2D materials possessing fascinating properties. Presently, 2D honeycomb systems of group IV elements have attracted an extensive interest due to their structural stability and distinctive nature of bonding, examples include, silicene,9-12, 33, 38, 58, 59 germanene13-17, 58, 59 and stanene.18-21, 37, 56-59 Stanene, a 2D honeycomb layer of Sn atoms is structurally analogous to silicene and germanene with a comparatively larger degree of buckling.22 Higher buckling parameter weakens the − orbitals interaction between Sn atoms and enhances an overlay of and orbitals that consequently lead to a higher dynamic stability of Sn monolayer.23 The inclusion of spin-orbit coupling confirmed the existence of Quantum Anomalous Hall (QAH) effect in monolayer stanene at room temperature.24 Additionally, the coexistence of Dirac-type behavior and a small band gap (72 meV)22 suggested a possibility of stanene as a potential candidate for nano-sized optoelectronic devices. Studies revealed that functionalization with foreign adatoms provided several possible routes to tune the electronic and magnetic behavior of pristine 2D monolayers.25-28,30-32,51 Functionalization of graphene with AM and AEM lead to the transfer of electrons from metal species to graphene.25 Pang et al. reported the successful band gap engineering of monolayer germanene via AM adsorption.27 TMs functionalized graphene sheets were capable of serving as a catalyst during particular chemical activities.34,35 Lin et al. investigated the functionalization of silicene with 15 different metal adatoms and found an improved binding energies of elements compared to graphene.39 Recently, Kadioglo et al. reported that electronic and magnetic properties of stanene monolayer were affected by AM) and AEM functionalization.40 Subsequently, Xiong et al. reported the tunable magnetic behavior of TMs embedded stanene monolayers.51 The unique electronic structure of stanene monolayer with


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enhanced sp3-bonding nature and higher dynamic stability distinguished it from the other group IV monolayers. Moreover, the intriguing properties upon AM and AEM metal doping provided an overwhelming urge to explore the bonding and charge transfer characteristics of functionalized stanene monolayers with other metal and non-metal adatoms. In the present work, we have performed a detailed theoretical investigation on the structural, energetics and electronic properties upon the adsorption of 31 different adatoms including AM, AEM and TM atoms, metals and non-metals of group III-VII on stanene monolayer. Most of the studied dopants not only form uniformed distribution over the monolayer but also modified the charge concentration and consequently the electronic properties of stanene monolayer.

METHODOLOGY Electronic structure investigations were accomplished in the framework of spin-polarized density functional theory (DFT) using VASP code.41,42 Exchange and correlation energies of electrons were considered according to Perdew-Burke-Ernzerhof formulation of generalized gradient approximation.43 GGA is expected to underestimate binding energies of adatoms over stanene, thus a semi−empirical van der Waals corrections of Grimme (DFT-D2) were included throughout the calculations. Ion−electron interactions were examined according to projector-augmented wave (PAW)44 approach with an energy cut-off set to 500 eV. Moreover, the calculations performed were not spin-polarized. The reason for not including spin-polarization was that, we did not find considerable difference in total energies while preforming test calculations for pure and doped system. However for obtaining the density of states for specific systems, which resulted into highest binding, we performed spin-polarized calculations. The sampling of Brillouin zone (BZ) was acquired with Monkhorst-pack using a 3× 3× 1 mesh for structural optimization and a denser 7× 7× 1 mesh for the density of states calculations according to tetrahedron method.45 In order to avoid interactions between recurring periodic images of the surface, a vacuum thickness of 15 Å was inserted perpendicular to the plane of the sheet. For structural optimization, total energies were allowed to converge until the difference between energy of two consecutive self-consistency steps was less than 10-5 eV. The component of Hellmann-Feynman force on each individual atom was less than 0.01 eV/Å for ground state configuration. Bader charge analysis46 was


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performed to understand the charge-transfer phenomena and nature of adatom−host binding. The optimized 4× 4× 1 supercell of buckled stanene monolayer is shown in Figure 1.

Figure 1. (a) Top and side views of optimized stanene monolayer (4 × 4). The dotted rhombus indicates the 1 × 1 unit cell. Buckling parameter (δ) is the difference of heights between sub-lattices A and B. Green balls represent Sn atoms.

We considered four symmetry sites for adsorption of adatoms, those include H (hollow of hexagon), T (Top, Sn atom in the upper sub-lattice), V (Valley, Sn atom in the lower sublattice) and B (the bridge between two Sn atoms), as indicated in Figure 2. Adsorption energies at each site were calculated using the following relation, E E − E E

(1)

Here, the first term denotes the total energy of the functionalized sheet and the second term in the parenthesis represents a sum of individual energies of pristine sheet and the adatom. The adsorption of adatoms on stanene can be used as a tool to effectively tune stanene work function. The work function of adatom on stanene monolayer is calculated as ϕ Vϕ − E

(2)

Here ϕ, Vϕ, and E denote work function, electrostatic vacuum potential and Fermi energy of the functionalized stanene sheet, respectively. The surface charge density differences δρ describe the changes in electron density during adatom adsorption to the sheet. Charge densities were acquired using the relation "ρ = ρ (sheet@adatom) – ρ (sheet)- ρ (adatom)

(3)

RESULTS AND DISCUSSIONS We report a detailed investigation on the adsorption geometries, binding energies, chargetransfer mechanism, work-function and electronic structure of stanene monolayer functionalized with AM (Li−K), AEM (Be−Ca), TM (Sc−Zn) and group III−VII atoms such as metals (Al, Ga), metalloids (B, Si, Ge, As) and non-metals (C, N, O, P, S, Se, F, Cl, Br).


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For relaxed 1 × 1 unit-cell, the calculated lattice constants 4.62 Å are in agreement with reported values.40, 47 For adatom adsorption, we optimized a 4× 4 supercell (shown in Figure 1) that was larger enough to avoid the unwanted effects of long-range electrostatic interactions between the recurring images of adatoms.40 The obtained values of lattice parameters, Sn−Sn bond length and buckling parameter for supercell were 18.48 Å, 2.81 Å, and 0.883 Å, respectively. All geometrical parameters showed a reasonable agreement with the previously reported values.40,47-49, 59 Bader charge investigation depicted that each Sn atom in pristine monolayer carries a charge equivalent to +0.01é.

Figure 2. (Left) Possible adsorption sites for adatoms on stanene monolayer are indicated as B (bridge), H (hollow), T (Top, above Sn atom in sub-lattice A) and V (Valley, above Sn atom in sub-lattice B). (Right) Spin-polarized total DOS and the partial DOS (multiplied by a constant) for stanene monolayer.


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Table 1. Energy and structural parameters for the stanene sheet with different adatoms. Most stable adsorption sites are indicated as H (Hollow), B (Bridge), T (Top), and V (Valley) site. The adsorption energy (eV) for the most stable site, adatom-Sn distance (Å), distortion in the monolayer stanene δSn

(Å), Bader charge on adatom (e), and the work function (eV) are listed. For comparison with previously reported data,41 we listed adsorption energy (eV) and dadatom-Sn Å) below.

Atom Site

Eads

Eads/Ecoh dadatom-Sn

(eV)

Li Na K Be Mg Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn B Al Ga N P As O S Se F Cl Br

H H H V H H H H H H H H V V H V V B H V V T B B B T T T

-3.220 -2.643 -2.694 -3.152 -1.756 -3.351 -4.938 -5.277 -4.214 -3.019 -3.075 -3.759 -4.281 -4.839 -3.282 -1.162 -5.41 -3.39 -3.24 -4.12 -3.67 -3.68 -5.70 -4.27 -3.85 -4.88 -3.49 -3.06

(Å

1.98 2.37 2.88 0.94 1.16 1.82 1.27 1.09 0.79 0.73 1.05 0.88 0.97 1.09 0.94 0.86 0.93 1.0 1.15 0.84 1.08 1.24 2.19 1.49 1.56 0.84 2.49 2.51

2.8 3.13 3.5 2.4 2.96 3.12 2.85 2.77 2.76 2.79 2.75 2.68 2.37 2.37 2.71 2.79 2.26 2.76 3.15 2.13 2.59 2.74 2.01 2.44 2.58 2.00 2.44 2.83

Eads41

dadatom-

(eV)

Sn

-2.687 -2.121 -2.303 -3.058 -1.330 -2.769 ---------------------------------------------------------------------------------------------------------------

41

(Å

2.79 3.12 3.45 2.39 2.98 3.14 ---------------------------------------------------------------------------------------------------------------

δSn

Bader

10-1(Å Charge (e)

0.0 0.2 0.4 0.2 0.2 0.2 0.0 0.1 0.1 0.0 0.0 0.2 0.2 0.2 0.0 0.1 0.3 0.1 0.3 0.3 0.0 0.3 0.0 0.2 0.2 0.0 0.1 0.3

+0.851 +0.801 +0.808 +1.065 +0.902 +1.314 +1.298 +0.976 +0.666 +0.835 +0.435 +0.122 -0.508 -0.555 -0.011 +0.070 -0.781 +0.684 +0.224 -1.380 -0.664 -0.508 -1.164 -0.803 -0.659 -0.725 -0.549 -0.524

Work Function (eV)

4.21 4.14 3.89 4.42 4.35 4.00 4.08 4.22 4.21 5.14 4.10 4.14 4.39 4.40 4.37 4.44 4.36 4.36 4.28 4.19 4.39 4.34 4.47 4.46 4.45 4.60 4.59 4.48

AM, AEM and TM metal adatoms. For convenience we have divided the dopants into two sections, one that consists of AM, AEM, TMs and other section with the remaining dopants. In this section, we discuss the


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adsorption of AM, AEM and TM metals on pure stanene sheet. Adsorption energies were calculated for each adatom for all the four adsorptions sites and the most preferential adsorption sites were the ones corresponding to the highest binding energy of the dopants in functionalized systems. The differences of adsorption energies among the adsorption sites, in turn, yield the diffusion energies of adatoms. For example, the energy barrier for migration of Li adatom between H and T sites is obtained as Eads(Li@H)-Eads(Li@T). Similar to the work,40 AM adatoms (Li−K) show a stronger tendency to bind to H sites, which is in accordance with adsorption of such atoms on graphene, silicene, and germanene.25,28,39 Similarly, B site is a transition configuration and AM adatom placed at B site migrates to a nearby V site. The similar behavior of AM adatoms was previously reported for silicene sheet.26 Adsorption energies of AM adatoms on V sites are lower as compared to H site but higher than T site. All the three AM adatoms follow a similar kind of adsorption trend, however, this is not true for the adsorption behavior of AEM adatoms (Be−Ca), where V site is the most preferential substitutional binding site for Be. Due to the electrostatic repulsion, Be exerts an outward thrust on the Sn atom, which is initially located at V site and finally Be dopant substitutes it. Similarly, Be atom placed at B site migrates towards V site and substitutes the Sn atom while propelling it outwards, indicating that B site is a transition site for Be atom. The similar adsorption behavior of Be on silicene was previously reported26. In the most stable configuration, Mg atom prefers to adsorb on H site. V site is the next stable site, where Mg slightly propels Sn out of the sheet and forms a dumbbell structure. These kinds of structures were formed when group IV elements were doped on silicene and germanene.40,50 It is observed that B site does not prove to be a stable adsorption configuration for Mg and Ca atoms. Adsorption energy of Ca is highest at H site compared to other adsorption sites, however Ca placed on B and V sites forms a dumbbell structure at V site similar to other AEM atoms. We have tabulated the distances between adatoms and the closest Sn atom in the sheet. For comparison, adsorption energies and adsorption distances for AM, AEM, TM and group III-VII adatoms are presented in Table 1 along with the results of Kadioglu et al.40 Distortion δSn in doped single-layer stanene is quantified as a deviation of zcoordinate of Sn atoms in doped stanene compared to their average position in pure stanene. Distortion in doped stanene for all the elements (see Table. 1) remains less than 0.05 Å.


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Figure 3. Adsorption energies of (a) AM, (b) AEM, (c) and (d) TM adatoms for the corresponding adsorption sites on 4× 4× 1 stanene monolayers.

Adsorption energies of TM adatoms on all the four adsorption sites on stanene as plotted in Figure 3c are higher than those of graphene, silicene and germanene.25, 28, 39, 52-53 Like AM adatoms, TMs prefer H site for adsorption in all cases except for Co, Ni, and V dopants who preferred to sit on V site. For all TM adatoms except Zn, B is a transition site and the adatom placed at B site migrates towards V site, which is the minimum energy configuration for Co, Ni, and Zn, while the second preferred site for the other TM adatoms. Each TM adatom on the V site comes closer to the sheet and propels Sn atom out of the plane of sheet to a small distance, whilst forming a dumbbell structure. The adsorption energies (Eads) of Sc, Ti, Mn, and Ni are higher than their respective cohesive energies (Ec) in bulk phase, which depicts that these atoms are capable of forming two-dimensional layers on the surface of stanene. The binding of Ti to stanene is the strongest amongst all other investigated TM adatoms, which is consistent to its binding on graphene.25 The binding enthalpy is highly site-dependent and there is a large diffusion barrier between H and other adsorption sites (> 0.57 eV). The T site preserves the weakest binding affinity for all TM atoms. V atom, which was initially introduced at T site showed a different behavior from other TMs and substituted the Sn atom propelling it out of the plane of stanene sheet to a small distance. The binding energy of Co


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adatom on stanene is higher than graphene but lower than its value on silicene where the ratio Eads/Ec was greater than unity.39,

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Adsorption energies of AM, AEM and TM adatoms

corresponding to different adsorption sites and adsorption pathways are plotted in Figure 3. Bonding nature of the stanene monolayer upon the introduction of various dopants has been investigated by means of Bader charge analysis. Due to the difference of electronegativities of Sn and the dopants considered here, there is a transfer of charge from the Sn-sheet to the dopants and vice versa. In case of AMs and AEMs, comparatively lower electronegativities cause these dopants to lose a portion of their electronic charge to the stanene sheet and acquire a partial positive state. TM with higher electron affinities compared to Sn, such as Ni, Co, and Cu gain electronic charge from the Sn-sheet. Isosurface charge densities in Figure 4(a-d) clearly show the depletion and accumulation of charge on selected dopants Li, Ca, Sc and Ti. Similarly, the elements of group III-VII would lose (electronegativities < Sn) or gain (electronegativities > Sn) electronic charge when doped to stanene sheet. Complete results of the amount of charge transfer between Sn sheet and the dopants are given in Table 1. Similarly, isosurface charge densities in Figure 6(a-d) display an accumulation of charge on selected dopants of B, N, O and F, which correspond to the highest binding energies among the dopants of group III, V, VI and VII respectively. The variation of charge concentration in the functionalized stanene monolayers is coupled with the change in their electronic properties, which has been studied by plotting total (TDOS) and the partial density of states (PDOS). For convenience, we have reported DOS plots for only those dopants, which corresponds to the highest binding energies among their respective groups. For comparison to the doped systems, the TDOS and PDOS of pristine stanene monolayer has been given in Figure 4(a-d), which shows its semi-metallic nature with the valence and conduction band dominated by Sn (p) orbitals. The Sn (p) orbitals, which in the case of pristine sheet (Figure 2) touch at the Fermi level combining the valence and conduction bands, moved towards the left of Fermi in the case of both Li and Ca doping and touch each other at -0.3 eV as shown in Figure 4(a,b). The main contribution is still from Sn (p) on either side of the Fermi with a small contribution of Li (s) at -1.6 eV on the left and 1.5 eV on right. However in the case of Ca doping, more pronounced Ca (s) contributions occurred at 0.3 eV and 1.3 eV on right of the Fermi. For TMs doping, we have reported the cases of Sc and Ti as shown in Figure 4(c,d). It is evident from DOS that in contrast to AM and AEM, TMs dopants have significant contribution with Sc (d) and Ti (d) not only overlapping with Sn (p) at the Fermi but also at -1.60 eV on the its left. Major peaks can also be seen in Figure 4(c, d) at 1.1 eV and 1.5 eV on right of the Fermi level


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for Sc (d) and Ti (d) respectively. From above discussion, it can be concluded that upon functionalization all the metal dopants (AM, AEM, TMs) transform semi-metallic stanene to a pure metallic one.


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Figure 4. (Left) Total (TDOS) and the partial density of states (PDOS) are plotted for (a) Li, (b) Ca, (c) Sc, and (d) Ti. (Right) Isosurface charge density plots of the similar systems. The elements Li, Ca, Sc, and Ti are chosen as representative elements of the corresponding group due to the strongest adsorption energies on stanene.

Adsorption of Group III−VII atoms on Stanene. In this section, we report the adsorption characteristics of group III−VII atoms on stanene. The structural properties, adsorption energies, charge transfer, and work function are listed in Table 1. For B and Al atoms, B site is a transition site as adatoms introduced at B site migrate towards V site and substitutes the Sn atom by pushing it out of the stanene’s plane to a small distance. The V site is the most preferred for both of these dopants followed by the H site being second most preferred one. However, the diffusion barrier for B atom (-1.98 eV) is quite large as compared to Al (0.08 eV). Unlike B and Al, Ga atom favors the H site, where V and B sites come after that in adsorption preference. The Eads for Al and Ga on stanene is much higher than their values reported for graphene and silicene.29,39 Moreover, the ratio Eads/Ec ensures a potential for cluster-free adsorption of these dopants on stanene, which was previously not achievable. Previously, Ozcelik et al. reported that the adsorption of group IV adatoms C, Si, Ge, and Sn on silicene and germanene forms the dumbbell structures, however, stanene sheets become unstable upon adsorption of these adatoms.50 We performed MD calculations using Nose-Thermostat algorithm to test the stability of stanene monolayers with C, Si and Ge adatoms. Our results indicate that C, Si and Ge-doped stanene monolayers become highly distorted at temperature higher than 150 K, which is in agreement with the reference.50 Adsorption energies of group VA elements in the most stable configurations are strong enough to avoid formation of three-dimensional clusters over the stanene. Particularly for P and As, the ratio of Eads to Ec is higher than 1. For the lowest energy configurations, N and P


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atoms prefer to bind at V site whereas N atom initially placed at the V site propels the Sn atom out of the stanene’s plane and substitutes it. The P atom fails to completely substitute Sn and forms a dumbbell structure at V site. However, both P and As initially placed at B site migrate towards V site. The lowest Eads of N and P adatoms is observed at T site. Unlike N and P, As prefers to adsorb at T site and forms a dumbbell. V is the second and H is the third favored site for As. Group VIA elements O, S, and Se prefer B site in their most stable configurations with V, H and T are the second, third and least favored adsorption sites respectively. The O dopant propels the Sn atom at V site and substitutes it. S atom slightly pushes the Sn atom out of the plane of stanene but fails to substitute it and ends up forming a dumbbell structure. The Eads for each of these atoms is higher than Ec, which is desirable to avoid the clustering and facilitating uniform dispersion of dopants over the monolayer. Halogens F, Cl, and Br prefer to adsorb at T site, while V, B and H are next favored sites for adsorption of each of them. The adsorption energies for F are weaker compared to Ec. However, Cl and Br adsorb with a sufficiently large Eads.


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Figure 5. Adsorption energies of (a) Group III (b) Group V (c) Group VI, and (d) Group VII (Halogens) adatoms for the corresponding adsorption sites on 4× 4× 1 stanene monolayers.

Charge analysis reveals that each atom in the group IIIA−VIIA gets a bulk of electronic charge from the stanene monolayer except Al and Ga. The difference of electron affinities explains the amount of charge transfer and donor/acceptor elements. Sn being more electronegative compared to Al and Ga gets electronic charge from the adatoms. Other adatoms are more electronegative than Sn, thus the adsorbed elements are in the partial negative state. To study the electronic properties of group III-VII, we have selected the cases of B, N, O and F as these dopants yielded the highest binding energies among the elements of their respective groups. Similar to the case of metals (AM, AEM, TMs) doping, even here we have plotted TDOS and PDOS for pure and doped monolayers to have a better understanding of the effect of foreign adatoms in the electronic properties of stanene in Figure 6(a-d). In the case of Bdoped stanene, there is a strong hybridization between Sn (p) and B (p) at -1.85 eV on the left of Fermi as shown in Figure 6a. A small overlap between the p orbitals of both Sn and B can also be seen right at Fermi. This overlap also occurred at 1.40 eV and 2.0 eV on the right of the Fermi level. For N-doped stanene, there is mainly Sn (p) contribution at and on the left of the Fermi with N (p) states appearing relatively deep in the valence band between -3.5 eV to -3.0 eV. However, Sn (p) and N (p) do overlap at 1.0 eV on the right of the Fermi. When it comes to O doping, several states from O (p) appear on the left of the Fermi and few of them overlap with Sn (p) between -3.0 eV and -0.90 eV as shown in Figure 6c. Nevertheless, the conduction band is mainly dominated by Sn (p) with a small contribution of O (p) at 1.1 eV. Finally, we describe the case of F-doped stanene, which also constitutes a metallic system. Similar to N and O dopants mentioned above, even here bulk of the F (p) states appear quite deep in the valence band between -3.55 eV to -2.90 eV and then two overlapping F (p) and Sn (p) states at -1.20 eV and -0.75 eV close to the Fermi.


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Figure 6. (Left) Total (TDOS) and the partial density of states (PDOS) are plotted for (a) B, (b) N, (c) O, and (d) F. (Right) Isosurface charge density plots of the similar systems. The elements B, N, O, and F are chosen as representative metals of the corresponding group due to the strongest adsorption energies on stanene.

Adsorption of adatoms on stanene leads to the variation of charge concentration as well as surface potential, which could be depicted in terms of the variation of work function (Φ) of pure and functionalized systems.54,

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Work function of pure stanene sheet is calculated as

4.466 eV whereas Cr and K are the dopants that resulted into the highest and the lowest values of 5.14 eV and 3.89 eV respectively. The complete results of Φ for all the functionalized systems are presented in Table 1. Adsorption energies of adatoms on the host materials typically become weaker at higher doping concentrations. We have plotted the adsorption energies of adatoms on stanene at two different coverages Θ =1:32 and 1:18 in Figure 7. Adatoms having the strongest binding on stanene sheet were chosen as representative elements of the corresponding group for the investigation of adsorption behavior at different coverages. For Θ =1:18, the adsorption energies of all the adatoms except B and N still remain higher than experimental cohesive energies.


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Figure 7. Adsorption energies (eV) of adatoms on the stanene sheet for two different coverages (Θ 1: 32 and 1: 18 are plotted. Adsorption energies at higher coverage are obtained only for the representative elements of corresponding group having the strongest binding on stanene.

CONCLUSION: In summary, we have studied the electronic structure, adsorption energies, charge transfer mechanism and work function variations of 31 different adatoms on stanene sheet by means density functional theory. We have also established the possibilities to form a uniform distribution of the dopants over the monolayer and the probability of cluster formation by drawing a comparison between binding and cohesive energies of the studied dopants. Our findings have yielded that stanene monolayer exhibits strong adsorption energies for most of the adatoms, which ensured that the formation of two-dimensional layers of these adatoms on the surface of stanene is possible. It is observed that elements of AM, AEM, and TMs being less electronegativities transfer a portion of their electronic charge to the stanene sheet whereas majority of the remaining dopants being more electronegative behave opposite to the formers. The accumulation or depletion of charges modified the charge concentrations in the doped systems and hence electronic properties, which were studied by plotting the TDOS and PDOS. Interestingly the group IV elements led to a large amount of distortion in the stanene sheet, indicating the instability of these doped systems, which was consistent with the


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literature. Upon structural optimization AEM, TMs and some other group III-VII elements form dumbbell structures on stanene.

Thus, the captivating properties explored by

introducing various foreign adatoms on stanene sheets opened up the doors for several practical explorations.

ACKNOWLEDGEMENT: The Swedish Research Council (VR), StandUp, Carl Tryggers Stiftelse För Vetenskaplig Forskning are acknowledged for financial support. Authors are grateful to SNIC and UPPMAX for provided computing time. T. Hussain is indebted to UQ for financial support under UQ postdoctoral fellowship scheme and the resources at NCI National Facility systems at the Australian National University through National Computational Merit Allocation Scheme supported by the Australian Government and the University of Queensland Research Computing Centre.

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Li Mg Sc Ga Mn S As Ni Cl



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Exploring Doping Characteristics of Various Adatoms on Single-Layer

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