Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2020 Jun 4;5(23):13760–13769. doi: 10.1021/acsomega.0c00905

Fundamental Properties of Metal-Adsorbed Silicene: A DFT Study

Ngoc Thanh Thuy Tran †,*, Godfrey Gumbs ‡, Duy Khanh Nguyen §,∥, Ming-Fa Lin †,⊥,#
PMCID: PMC7301544  PMID: 32566841

Abstract

graphic file with name ao0c00905_0010.jpg

Sodium, magnesium, and aluminum adatoms, which possess one, two, and three valence electrons, respectively, in terms of 3s, 3s2, and (3s2, 3p) orbitals, are very suitable for helping us understand adsorption-induced diverse phenomena. In this work, the revealing properties of metal (Na/Mg/Al)-adsorbed graphene systems are investigated by means of the first-principles method. The single- and double-sided chemisorption cases, the various adatom concentrations, the hollow/top/valley/bridge sites, and the buckled structures are taken into account. The hollow and valley adsorptions that correspond to the Na/Mg and Al cases, respectively, create extremely nonuniform environments. This leads to diverse orbital hybridizations in Na/Mg/Al–Si bonds, as indicated by the Na/Mg/Al-dominated bands, as well as the spatial charge density distributions and the orbital-projected density of states (DOS). Out of three types of metal-adatom adsorptions, the Al-adsorption configurations produce the strongest chemical modifications. The ferromagnetic configurations have been shown to survive only in specific Mg and Al adsorptions, but not in the Na cases. The presented theoretical predictions could be verified experimentally, and potential applications are discussed. Additionally, important similarities and differences with graphene-related systems are examined.

Introduction

Ever since graphene, the first two-dimensional (2D) material, was successfully fabricated, the scientific activity related to this substance has continued unabated. Significant effort on exploiting other graphene-related materials reportedly continues for the purpose of extending potential device applications.1,2 Following the early exploration of graphene, another material with a honeycomb lattice of silicon atoms, namely, silicene, was paid considerable attention.3−5 It displays several remarkable properties arising from its hexagonal symmetry and Dirac cone structure, e.g., high charge carrier mobility4 and excellent optical absorption.5 In contrast to the flat geometrical structure of graphene with sp2 hybridization of carbon atoms, silicene possesses low buckling as a consequence of the mixed sp2–sp3 hybridizations of silicon atoms.3 This allows silicene to surpass graphene in some aspects, including greater spin–orbit coupling (SOC) and quantum spin Hall effect,6 more accessible tunability of the band gap,7 stronger valley polarization, and other related properties.8 These impressive characteristics have made silicene a candidate for various areas of applications including field-effect transistors (FET),9,10 Li/Na-batteries,11,12 spintronic and valleytronic devices,13 sensors, etc.14

So far, monolayer silicene has been successfully synthesized by various experimental methods. The principal method has been the bottom-up approach employing epitaxial growth on a substrate, by either deposition onto a supporting template such as Ag(111) and15 Ir(111)16 or by segregation on a buffer layer such as ZrB2.17 To further enhance the applications of silicene, it is highly desirable to grow silicene on a nonmetallic substrate such as MoS218 or SiC.19 The graphene-like honeycomb lattice of silicene on metal substrates has been observed using a scanning tunneling microscope (STM).20 Due to its buckled structure, silicene is a direct-gap semiconductor with a negligible band gap.3 Enhancement of its free-carrier density or opening its band gap is regarded as an important achievement for improving the targeted applications of silicenes. The electronic properties can be significantly modified by doping,21−25 external electric and magnetic fields,26,27 and mechanical strain.28,29 Of these modulation techniques, chemical modification of the silicene surface is the most effective one in creating essential differences between the semiconducting and metallic behaviors (the nonmagnetic and magnetic configurations). The chemical adsorption of metal adatoms is predicted to induce metallic band structures with high densities of conduction electrons.30,31 However, the geometrical relationships between the structures, the electronic properties, and the magnetic configuration for various adatom coverages have not been thoroughly reported. Orbital hybridizations between adatoms and silicene, a key point in understanding the modification of electronic properties, are only briefly mentioned in several studies. Sodium, magnesium, and aluminum, respectively, possess one, two, and three outermost electron orbitals, which are expected to be capable of providing extra carrier density and sufficient metalization for the silicene system. Here, Na-, Mg-, and Al-doped silicene materials will be able to create various orbital hybridizations, diversify the fundamental properties, and provide more information regarding potential applications.

Our first-principles calculations on Na-, Mg-, and Al-adsorbed silicene systems include investigating metalization phenomena, 2D free-carrier densities, π-bonding of the low-lying extended states on a honeycomb lattice, the well-defined/modified/thoroughly suppressed Dirac cone, the rigid shift σ-bands/the undefined ones, and the spin-degenerate or spin-split energy. They are expected to be greatly diversified by the different orbital hybridizations in Na–/Mg– and Al–Si bonds. The number of metal adatom orbitals and silicon host atoms taking part in the significant chemical bondings will be reported in this work. The orbital hybridizations are clearly identified from the atom dominance of the energy band, the orbital-dependent charge distribution, and the orbital-projected DOS. They are responsible for the optimal structure and the unusual electronic properties, and can even diversify their magnetic behaviors. Whether the ferromagnetic spin configuration could survive under the influence of specific adatoms and adsorption configurations is thoroughly examined with the use of total magnetic moments, spin-split energy bands, spin-density distributions, and spin-decomposed DOS. The above-mentioned results can be examined by experimental measurements, such as angle-resolved photoemission spectroscopy (ARPES)32 and scanning tunneling spectroscopy (STS).33 Our reliable and complete results should be very useful in the design and development of promising device applications.

Results and Discussion

Sodium, magnesium, and aluminum adatom adsorption on monolayer silicene surfaces presents diversified geometrical structures, mainly due to the different interlayer chemical bondings. Sodium and magnesium adatoms prefer being adsorbed on the hollow site of silicene, whereas aluminum adatoms are more stable at the valley site illustrated in Figure S1. This could be verified from an STM measurement. Since the valley and top positions possess different chemical environments, they are capable of creating diversified essential properties.

Na Adsorption

Sodium-adsorbed silicene systems are stable under double- and single-sided adsorption, with specific concentrations and distributions, as illustrated in Figure 1. The highest saturation can reach 100% for double-sided adsorption. For pristine silicene, the optimized Si–Si bond length and buckling are 2.28 and 0.48 Å, respectively, which are consistent with previous studies.34,35 At sufficiently low Na concentrations of <12.5%, the degree of buckling is comparable with that of the pristine system, while it might be greatly enhanced at higher concentrations. The fact that the π and σ bondings are nonorthogonal with each other becomes more evident with increased Na concentrations. The Na–Si bond lengths lie in the range of ∼3.10 to 3.26 Å weakly dependent on specific adsorptions, as can be seen in Table 1. The shortest Si–Si bonds are slightly stretched by the observable change from 2.28 to 2.33 Å. This indicates a partial charge transfer across the interlayer chemical bond. Based on the above-mentioned geometrical features, we conclude that the σ-electronic chemical bondings, which arise from the (3s, 3px, 3py) orbitals of silicon atoms, hardly take part in the alkali-adatom chemisorption. Consequently, the allowable orbital hybridization of Na 3s and Si 3pz will dominate the adsorption-induced chemical bonding process and thus the other essential properties.

Figure 1.

Figure 1

Open in a new tab

Optimal geometries of the sodium-adsorbed silicenes with the side and top views for the distinct adsorptions: (a) [3:6], (b) [2:6], (c) [1:6], (d) [1:8], (e) [1:18], and (f) [1:32].

Table 1. Calculated Nearest Passivated Si–Si and Na–Si Bond Lengths, Na Heights, Total Magnetic Moments, Buckling, and Binding Energies of Na-Adsorbed Silicene Systems.

Na/Si passivated Si–Si bond length (Å) Na–Si bond length (Å) Na height (Å) magnetic moment (μB) buckling (Å) Eb (eV)
pristine 2.28 X X 0 0.48 X
6:6 = 100% 2.41 2.94 2.08 0 0.86 –1.74
3:6 = 50% 2.33 3.15 2.28 0 0.62 –3.03
2:6 = 33.3% 2.31 3.10 2.18 0 0.58 –1.48
2:8 = 25% 2.30 3.10 2.12 0 0.57 –2.14
1:6 = 16.7% 2.31 3.12 2.17 0 0.52 –1.44
1:8 = 12.5% 2.30 3.17 2.22 0 0.48 –1.60
1:18 = 5.6% 2.30 3.19 2.26 0 0.48 –1.68
1:32 = 3.1% 2.30 3.26 2.35 0 0.48 –1.86
Open in a new tab

Figure 2a shows that the band structure of pristine silicene exhibits a Dirac cone structure, as indicated by red circles, at the K point with a negligible energy gap estimated as 0.5 meV. This gap could be enlarged to 1.55 meV under the influence of spin–orbit coupling.6 These energy bands are predominantly dominated by 3pz orbitals of the nearest Si atoms as so-called π bands and turn into parabolic dispersion at a saddle M point. The unoccupied and occupied σ parabolic bands are, respectively, initiated around ±1.2 eV. Compared with pristine silicene, the sodium-adsorbed systems exhibit unusual valence and conduction bands, as shown in Figure 2b–h. The main features of the band structures include the highly asymmetric energy spectra near the Fermi energy, EF, the modified Dirac cone structure with/without an energy spacing, a blue shift of EF relative to the Dirac point in accordance with metallic behavior, the roughly rigid σ valence bands, splitting and anticrossing states, Na- or Si-dominated conduction/valence states, and extra critical points in the energy-wave vector space related to band hybridization. The anisotropic and distorted Dirac cone mainly from the 3pz orbitals is initiated from the stable Γ/K valley, as shown in Figure 2i, which is due to zone folding. The initial/bottom valence one is very close to the first σ energy subbands with a concave-downward dispersion relation, where an energy spacing of ≈0.20 eV corresponds to the deeper state. On the other hand, sodium adsorption on a silicene surface is capable of creating free conduction electrons with sufficiently high carrier densities resulting in so-called n-type doping. The Fermi level is significantly adjusted from the middle of the well-behaved Dirac cone structure, as displayed in Figure 2a, to the conduction cone, by which we mean the upper half of the Dirac cone of the modified band structure. This means that only the 3s orbitals in sodium adatoms partially serve as conduction electrons. The Na-induced free electrons correspond to occupied states between EF and the conduction Dirac point. The Na-adatoms only make minor contributions to the deeper valence bands. In general, there exists a separation between the valence and conduction Dirac points, being roughly attributed to the different site energies, i.e., the ionization ones, of Na 3s and Si 3pz orbitals. Specifically, the spin-split electronic structures are absent for various Na-adsorption cases, i.e., there are no spin-dependent ferromagnetic/antiferromagnetic configurations.

Figure 2.

Figure 2

Open in a new tab

Concentration- and configuration-dependent band structures of sodium-adsorbed silicene materials with (a) pristine silicene, (b) Na/Si = [6:6], (c) [3:6], (d) [2:6], (e) [1:6], (f) [1:8], (g) [1:18], and (h) [1:32]. Na and passivated Si dominances are illustrated as the pink and gray circles. The Brillouin zones for different unit cell sizes are shown in (i).

The atomic-, orbital-, and spin-projected van Hove singularities in the density of states (DOS), as clearly illustrated in Figure 3a,h, serve to identify the critical orbital hybridizations of Na-adsorbed silicene and thus the complicated energy spectra as well as the existence of π and σ bonding. The 3s–3pz orbital hybridization in the Na–Si bond is able to create the unusual van Hove singularities in the DOS. This result strongly depends on the Na concentration, and the effect becomes insignificant at sufficiently low concentrations of <3.1%, as depicted in Figure 3h. The Dirac cone-induced structure has a well-defined red shift relative to EF, illustrating the n-type doping behavior. The covered area between the bottom of the conduction dip and the Fermi level determines the Na-created free electron density. Roughly speaking, the valence and conduction band dips are dominated by the Si 3pz orbitals, and we refer to the red curves. However, the Na 3s orbitals also make certain contributions to the latter at very high adatom concentrations of >50%, as shown in Figure 3b,c, mainly due to Na–Na interactions. There exist the splitting π and π* prominent peaks, accompanied by extra minor structures, which are attributed to zone folding, interlayer atomic interactions, and enhanced buckling.

Figure 3.

Figure 3

Open in a new tab

Atom- and orbital-decomposed DOS for the Na-adsorbed silicene systems: (a) pristine silicene, (b) Na/Si = [6:6], (c) [3:6], (d) [2:6], (e) [1:6], (f) [1:8], (g) [1:18], and (h) [1:32].

As for the σ electrons of the silicon host atoms, the 3px and 3py orbitals, the pink and dashed blue curves in Figure 3, display identical/different contributions in the presence of a symmetric/asymmetric environment in the xy-plane projection (Figure 1). The initial σ-electron valence band creates obvious shoulder structures as marked by the green arrow in the range −5.2 eV < E < −4.4 eV, depending on the Na concentrations, being deeper than the pristine case, referring to Figure 3a. The entire bandwidth covers the first shoulder, the symmetric peak, and the second one, which correspond to the parabolic, saddle, and parabolic band edge states at the Γ, M, and K points (Figure 2a–h), respectively. Additionally, few van Hove singularities, which are associated with the four orbitals of Si atoms, occur simultaneously (the red, pink, dashed blue, and green curves), e.g., those at −4.0 eV < E < −3.20 eV related to the anticrossings of π and σ bands. In short, the modified π and σ chemical bondings could be approximately identified from the specific van Hove singularities, and such observations are supported by the band structures and spatial charge densities.

The spatial charge distributions (ρ and their variations Δρ) after sodium adsorption can be used for examining the changes in the π and σ chemical bondings on a silicene surface and the coupling-induced orbital hybridizations, as clearly illustrated in Figure 4. Similar bonding phenomena could be revealed in other alkali-adsorbed silicene systems. Two kinds of orbital bondings in honeycomb lattices could survive simultaneously for any sodium adsorption. The σ electronic orbital hybridizations, with a high charge density between two Si atoms, are scarcely affected by the sodium adsorptions, corresponding to the almost vanishing charge density difference Δρ. This is responsible for the robust red shift of the σ energy bands and the absence of valence bands codominated by Na and Si atoms (Figure 2a–f). On the other hand, the significant modifications on the π bondings are observable through the charge variations between Na and Si atoms (the bright red rectangles), in which a fraction of the number of adatom electrons is transferred to the host atom region (the black arrow). Furthermore, they are relatively easy to observe under high concentration conditions (Figure 4c). These features suggest the existence of only a single 3s–3pz orbital hybridization in the Na–Si bonds, accounting for the (Na, Si) codomination of certain conduction bands. Specifically, the observable charge variation in the yz-plane is revealed between two neighboring Na atoms at sufficiently high concentrations, mainly owing to the creation of Na–Na bonds.

Figure 4.

Figure 4

Open in a new tab

Spatial charge distribution for (a) pristine silicene, (b) [3:6], (d) [1:8], and (f) [1:18]. Their corresponding variations after Na-chemisorptions along the xz- and yz-planes are shown in (c), (e), and (g). The π-bonding variations are indicated by the black arrow, whereas the Na–Na and Na–Si interactions are shown by black and red rectangles, respectively.

Mg Adatoms

Although the structures are similar to those for Na adsorptions (Figure S2), the Mg–Si bond lengths or the adatom heights (≈2.7 and 1.65 Å) are much shorter than the Na–Si ones (≈3.15 Å). The 100% Mg-adsorption could also survive under double-sided adsorption (Table 2), in which there exist sufficiently strong Mg–Mg bonds. Mg-adsorption has the largest buckling of the honeycomb lattice among the three types of metal adatom adsorption at high concentrations of >33%. This enhanced buckling is expected to induce more significant sp3 bondings (nonorthogonality of π and σ bondings) and spin–orbital couplings in silicene. These geometrical features suggest that there are sufficiently strong chemical bondings between Mg adatoms and Si atoms, associated with two 3s valence orbitals of Mg. The π bonding, which is extended on the silicene surface, is strongly modified or even completely disappears due to the critical interlayer atomic interactions.

Table 2. Calculated Nearest Passivated Si–Si and Mg–Si Bond Lengths, Mg Heights, Total Magnetic Moments, Buckling, and Binding Energies of Mg-Adsorbed Silicene Systems.

Mg/Si passivated Si–Si bond length (Å) Mg–Si bond length (Å) Mg height (Å) magnetic moment (μB) buckling (Å) Eb (eV)
6:6 = 100% 2.46 2.86 2.24 0 0.94 –0.77
3:6 = 50% 2.43 2.81 2.08 0 0.86 –1.66
2:6 = 33.3% 2.38 2.81 2.09 0 0.79 –1.33
2:8 = 25% 2.40 2.70 1.95 0 0.73 –1.67
1:6 = 16.7% 2.33 2.76 1.89 0.46 0.61 –0.92
1:8 = 12.5% 2.33 2.81 1.94 0 0.59 –0.98
1:18 = 5.6% 2.31 2.87 2.08 0 0.53 –0.92
1:32 = 3.1% 2.31 2.88 2.12 0.53 0.52 –0.82
Open in a new tab

Mg adsorptions are able to lead to unusual band structures, as clearly indicated in Figure 5a–d. All of them are 2D gapless metals/semimetals, for which the Mg adatoms create the free carriers. Roughly speaking, there exist the drastically modified low-lying energy dispersions, mainly owing to the extremely nonuniform environment in an enlarged unit cell and more important or complicated interlayer orbital hybridizations. The unusual bands are mostly contributed by the significantly distorted π bonding on the silicene surface. Furthermore, the initial σ valence energy subbands come to exist at the Γ valley using the concave-downward dispersions in the range Ev < −1.20 eV. Interestingly, the (Mg, Si)-induced energy bands present partially flat or oscillatory dispersion relations, very close to, or even merging with, the low-lying π/σ-electronic structures. This phenomenon could survive for any Mg adsorption. Since the Mg adatoms possess two 3s orbitals, they can create (Mg, Si)-dominated conduction and valence states. The former phenomena are very obvious at sufficiently high concentrations, such as 50% Mg-doping cases (Figure 5a). However, at low concentrations (Figure 5c,d), the Mg-induced energy bands dominate near the Fermi level.

Figure 5.

Figure 5

Open in a new tab

Concentration- and configuration-dependent band structures of magnesium-adsorbed silicene materials with Mg and Si dominances (the blue and gray circles): (a) [3:6], (b) [1:6], (c) [1:18], and (d) [1:32]. The spin-up and spin-down states in (b) and (d) are denoted as the black and green solid curves, respectively. Their corresponding spin density distributions are clearly shown on the top- and side-views of (e) and (f).

The ferromagnetic configurations, which are clearly characterized by the spin-split valence and conduction energy subbands and the net magnetic moments (see Figure 5 and Table 2), are further examined from the spin density distributions of the specific Mg-adsorption cases. For example, the 16.7 and 3.1% configurations, as clearly displayed in Figure 5b,d, exhibit unusual ferromagnetic phenomena. The Mg adatoms are able to create the dominant spin density associated with two 3s-orbital electrons of Mg adatoms, while the host Si atoms make a minor contribution. They are able to induce the on-site Coulomb interactions in the intrinsic Hamiltonian.36 Consequently, the orbital hybridizations, spin-dependent many-particle interactions, and spin–orbital couplings need to be included in the Hubbard tight-binding model.37

All of the Mg-adsorbed silicene cases, clearly displayed in Figure 6a–d, present either a strong, moderate, or slightly modified dip with an observable/very narrow/negligible energy spacing below the Fermi level. The DOS is finite at the Fermi level for all of the investigated Mg adsorption cases, in which its magnitude is very large for the partially flat bands or oscillatory energy dispersion. The bottom part of the conduction band exhibits a red shift relative to EF. Additionally, the special structures, the red curves (due to the 3pz orbitals) near the Fermi level that mainly arise from the π- and π*-electronic states are merged together. Interestingly, the merged structures are revealed in the Si 3pz and Mg 3s orbitals (the red and cyan curves), where certain energy regions cover the valence and conduction states. Specifically, the Mg 3s orbitals have an obvious valence and conduction band regions of −2.0 eV < E < 2.0 eV under a very high concentration (above 50%), directly reflecting the significant Mg–Mg bonds or the Mg-dominated conduction bands (Figure 6a). The critical orbital hybridizations might be combined with the ferromagnetic configurations, being characterized by the spin-split DOS, in which the spin-up and spin-down determine the net magnetic moment. Most deep valence states cancel each other; furthermore, the main contributions arise from the unbalanced electronic energy spectrum across E0, e.g., those for the 16.7 and 3.1% cases. These results show that the Mg 3s and Si 3pz orbitals dominate the spin-split distribution, especially for the former.

Figure 6.

Figure 6

Open in a new tab

Atom-, orbital-, and spin-projected DOS for the Mg-adsorbed silicene materials under (a) [6:6], (b) [1:6], (c) [1:18], and (d) [1:32] cases. The spatial charge distributions/the variations after Mg adsorptions on the xz- and yz-planes (e)–(h).

The spatial charge distributions and their variations after the Mg-chemisorptions are clearly shown in Figure 6e–h. The π-electronic bondings (Figure 6e–f on the xz-plane) are strongly modified under Mg adsorption, while the opposite is true for the σ-electronic ones. There exist significant and unusual charge density differences between the guest and host atoms. The Mg-induced charge density variation is more obvious compared with the Na adsorption case. The main reason lies in the fact that there are two 3s valence electrons for each Mg atom. The strong orbital hybridizations of 3s–3pz in Mg–Si bonds have led to the strongly modified Dirac cone structures. Specifically, the observed charge density variations, with positive and negative Δρ, are shown between two Mg atoms for the high Mg concentration cases (50%), e.g., that within the black rectangle on the yz-plane. The strong 3s–3s orbital hybridizations in Mg–Mg bonds are responsible for the wide Mg-dominated valence and conduction energy spectra, being consistent with the atom- and orbital-decomposed DOS.

Al Adatoms and Creation of Diversified Phenomena

The optimal aluminum adatom adsorptions on a silicene surface are clearly shown in Figure S3. The highest adatom adsorption can be achieved through the 50% case of single-sided adsorption with greatly enhanced buckling. Different from Na and Mg adsorptions, the 100% saturated adsorption with the double-sided configuration is not stable and thus totally disappears, mainly due to the quite strong repulsive interactions between neighboring Al adatoms. The Al–Si bond lengths, which depend on the adsorption condition, lie in the range of ∼2.58 to 2.89 Å (Table 3). They become longer when the Al concentration is increased. On the other hand, the optimal position of aluminum-adsorbed graphene systems corresponds to the hollow site on a planar honeycomb lattice. The concentration- and configuration-dependent Al–C bond lengths are ∼2.54 to 2.57 Å (for details, see ref (38)), and the highest Al adatom concentration, with a stable geometry, is found to be the 25% case under the double-sided adsorption. The geometrical symmetry is responsible for the critical chemical bondings and thus the electronic and magnetic properties.

Table 3. Calculated Nearest Passivated Si–Si and Al–Si Bond Lengths, Al- Heights, Total Magnetic Moments, Buckling, and Binding Energies of Al-Adsorbed Silicene Systems.

Al/Si passivated Si–Si bond length (Å) Al–Si bond length (Å) Al height (Å) magnetic moment (μB) buckling (Å) Eb (eV)
3:6 = 50% 2.47 2.89 2.14 0 0.74 –3.11
2:6 = 33.3% 2.47 2.71 1.93 0 0.70 –2.69
2:8 = 25% 2.47 2.72 2.05 0.34 0.75 –2.73
1:6 = 16.7% 2.39 2.61 1.90 0 0.75 –3.10
1:8 = 12.5% 2.34 2.60 1.89 0.73 0.64 –3.47
1:18 = 5.6% 2.33 2.57 1.86 0 0.57 –3.54
1:32 = 3.1% 2.32 2.58 1.84 0 0.49 –3.72
Open in a new tab

The valley sites and multiorbital hybridizations in aluminum-adsorbed silicene systems can create rich and unique band structures, as shown in Figure 7, in sharp contrast to the Na and Mg adsorption cases (Figures 2 and 5). The low-lying band structures are very complicated even at low Al concentrations. It is very difficult to accurately identify the π and π* bands or the σ bands at high concentrations in Figure 7a–d, since there exist certain conduction subbands across the Fermi level, the nonmonotonic/oscillatory/partially flat energy dispersions, and the Si- and/or Al-dominated valence and conduction bands. However, the separated Dirac cone structures at the K point will be gradually recovered during the decrease of Al as marked by the red circles. Interestingly, the Al adatoms play a critical role in the low-energy states across the Fermi level, especially for the high concentration cases of >25%, as shown in Figure 7a–c. Also, they make significant contributions to the deeper valence states over the range −5.20 eV < E <−3.0 eV, in which their widths are sensitive to the Al concentration. Therefore, more energy subbands are created after aluminum adsorption because each adatom contributes three orbital electrons. Under certain Al adsorption conditions, the spin-split energy bands come to exist at low energy. These electronic energy spectra clearly illustrate the existence of a ferromagnetic configuration with an observed net magnetic moment (Table 3). That is to say, the spin configuration-induced many-particle Coulomb interactions39 and the orbital hybridizations38,39 compete or cooperate with each other to achieve the lowest ground-state energy.

Figure 7.

Figure 7

Open in a new tab

Concentration- and configuration-enriched energy bands for the Al-adsorbed silicene materials, being combined with the Al and Si contributions (the purple and gray circles): (a) [3:6], (b) [2:6], (c) [1:6], (d) [1:8], (e) [1:18], and (f) [1:32]. The spin-up and spin-down states in (d) and (e) are denoted as the black and green solid curves, respectively.

The significant orbital hybridizations, together with the π and σ bondings, which could survive in Al-adsorbed silicene, are investigated from the behavior of the atom-, orbital-, and spin-projected van Hove singularities, referring to Figure 8a–8f. All of the adsorption cases present a finite DOS at the Fermi level, directly indicating a metallic or semimetallic behavior. The noticeably distorted V-shape structure, corresponding to the modified Dirac cone structures, is controlled by the Si 3pz orbital (the red curve) and lies below EF only at low Al concentrations, e.g., those for 12.5 and 3.1% (Figure 8d,f). This indicates the existence of the mentioned π bonding and n-type doping. In general, the special structures due to the four orbitals of the Si host atoms could appear simultaneously within certain energy ranges of the spectra for the valence and conduction bands. These results suggest the significance of the sp3 bonding in the Si–Si bonds. Most importantly, the Si (3s, 3px, 3py, 3pz) and Al (3s, 3px + 3py) orbitals (the purple, green, dashed blue, red, light blue, and yellow curves) frequently present similar van Hove singularities at the same energies within the whole range except for a very low Al concentration (e.g., the 3.1% case in Figure 8f). Their multiorbital hybridizations play critical roles in the diversified electronic properties. Specifically, at very high Al concentrations, such as 50 and 33.3% configurations, the effective distribution widths of Al 3s/Al (3px + 3py) are more than 5 eV, clearly reflecting the creation of the Al-dominated valence and conduction bands presented in Figure 8a,b.

Figure 8.

Figure 8

Open in a new tab

Atom-, orbital-, and spin-projected DOS for the Al-adsorbed silicenes under the distinct adsorption cases: (a) [3:6], (b) [2:6], (c) [1:6], (d) [1:8], (e) [1:18], and (f) [1:32].

The critical factor in our calculations is the achievement of the strongest chemisorption due to the three valence electrons in each aluminum atom. Sufficiently high carrier density can reach the intermediate region between Al and Si atoms, resulting in the charge redistributions of Al (3s, 3px + 3py) and Si (3s, 3px, 3py, 3pz) orbitals. The prominent Al–Si bonding is also revealed as significant changes in the carrier densities, where large charge transfers, with positive and negative values, simultaneously appear as represented by the heavy red and blue regions in Figure 9, respectively. Additionally, the prominent Al adsorption effects greatly strengthen the sp3 bondings in the Si–Si bonds or destroy the characterizations of the π and σ ones. Specifically, the important Al–Al bonds come to exist only under high Al concentrations, e.g., the 50% configuration with the apparent charge variation between two adatoms (the black rectangle). On the contrary, both Na–Si and Mg–Si atomic interactions are closely related to the host atoms in a different way, comparing Figures 4a–c and 6e,f, where the carrier density is very dilute in the intermediate region close to the Na/Mg adatoms. The important difference with the Al adsorption cases arises from the hollow-site adsorption position and one or two 3s valence electrons in Na or Mg.

Figure 9.

Figure 9

Open in a new tab

Spatial charge distribution/their variations after Al-chemisorptions along the xz- and yz-planes: (a, b) [3:6], (c, d) [1:8], and (e, f) [1:18].

Experimental Measurement and Potential Applications

ARPES measurements have been very successful in identifying the diverse band structures of graphene systems, e.g., the gapless Dirac cone in monolayer graphene,40 two pairs of parabolic energy dispersion relations in AB-stacked bilayer system,40,41 and the coexistent linear and parabolic bands in twisted bilayer graphene.42 Additionally, the Na/Li adatom adsorptions43,44 on graphene surfaces have been verified to present a blue shift of the Fermi level and the linear Dirac cone. For silicene, the linear dispersion with the Fermi velocity vF = 1.3 × 106 m/s comparable to graphene’s has been measured.32,45 Similar ARPES examinations could be carried out for (Na, Mg, Al)-adsorbed silicene to explore the blue shift of the Fermi level, the low-lying energy spectra along with the modified Dirac cones and the adatom-dominated bands, and the splitting middle-energy valence bands near the M point. Consequently, these results could be useful for estimating the partial charge transfer from the guest to host atoms and help us understand the modified π bonding. Also, optical46 and transport47 measurements might be efficient and reliable in determining the (Na, Mg, Al)-created free electron density.

The (Na, Mg, Al) adsorption-enriched van Hove singularities could be directly verified from high-resolution scanning tunneling spectroscopy (STS) measurements, as it was successfully done for carbon-based materials with the well-characterized sp2 bondings. For example, the recent experiments on layered graphene systems have clearly identified an isotropic V-shape structure vanishing at the gapless Dirac point for monolayer graphene,40 the zone folding-created peaks in logarithmic form for twisted bilayer graphene,42 a delta function-like peak near EF for ABC stackings,48 the semimetallic property for graphite,41,44 and its splitting π and π* strong peaks at deeper or higher energies.41 Moreover, STS has successfully confirmed the existence of Dirac fermions in silicene.48 Further STS measurements for (Na, Mg, Al)-adsorbed silicene systems have mainly focused on the modified dip structure below the Fermi level, the split π and π* peaks, and the adatom-generated extended structure. On the other hand, our theoretical predictions for the (Mg, Al) adatom-generated ferromagnetism could be directly examined using a high-resolution spin-polarized STM.

Recently, silicene-related materials have attracted a great deal of attention as being promising for Li/Na ion batteries with high theoretical capacity through electrochemical conversion reactions and low-cost production.11,12,49,50 Further attempts to enhance the application of silicene as anode materials in LIBs have been carried out, such as compositing by doping. It is reported that with Na modification, the performance of silicene could achieve a high theoretical capacity of 954 mAh/g and a low diffusion barrier of 0.23 eV.11 Compared with graphite, Na interactions with silicene lead to a higher electrode potential, which suppresses dendritic Na growth.11,51 Additionally, owing to the strong spin–orbit coupling and easily tunable band gap at the Dirac point, silicene-based materials can be successfully used in spintronic devices13,52,53 and FETs at room temperature.9,10 Silicene materials are expected to be superior to graphene in real applications based on the existing silicon-based industry. Further systematic studies are needed to find the most suitable absorbers on silicene in nanoscale electronic devices.

Concluding Remarks and Summary

In contrast to the behavior of pristine silicene as a tiny-gap semiconductor, all of the metal-adsorbed cases that we have investigated fall into the n-type doping category, thereby implying an enhanced electronic conductivity. On the other hand, Na-, Mg-, and Al-adsorbed silicene differ from each other in their fundamental properties. The important differences cover the optimal adsorption sites, distinct adatom–silicon bond lengths, enhanced buckling degrees, the free-carrier densities, the modified Dirac cone structures, the well-behaved or undefined π and σ valence states (the former and latter in the Na- and Mg/Al-adsorbed silicene), the spin-degenerate or spin-split electronic energy spectra across EF, the adatom-enriched charge density distributions, the ferromagnetic or nonmagnetic spin distributions under certain adsorption configurations, and the adsorption-diversified van Hove singularities. The critical mechanisms are deduced as arising from the distinct orbital hybridizations in adatom–Si, Si–Si, and adatom–adatom bonds. Most importantly, the Na–Si, Mg–Si, and Al–Si bonds, which account for the diverse physical phenomena, have been concluded as possessing 3s–3pz, 3s–3pz, and (3s, 3px + 3py)–(3s, 3px, 3py, 3pz) orbital hybridizations, respectively.

The Al adsorption configurations present the most significant chemical modifications, such as more oscillatory and partially flat energy dispersion relations across the Fermi level, total vanishing of the modified Dirac cone structures at sufficiently high adatom concentrations, and the largest charge density difference in the Al–Si and Al–Al bonds. The ferromagnetic configurations are shown to survive only in specific Mg and Al adsorptions but not in the Na cases. This indicates that the spin-dependent many-particle interactions might play a critical role in reducing the total ground-state energy. The guest or host atom-dominated spin distributions are consistent with the spin-split DOS across the Fermi level. The present work should serve as a first step toward further investigations into other necessary properties of metal-adsorbed silicene for fabrication and potential device applications. Similar metal-adatom adsorption effects could be generalized to Ge, Sn, and Pb-monolayers.

Computational Methods

We note here that our first-principles calculations were performed by the use of the density functional theory (DFT)-based Vienna Ab initio Simulation Package (VASP).54,55 The Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation method56 was employed in evaluating the electron–electron Coulomb interactions, while the electron–ion interactions were treated by the projector augmented wave method.57 The spin configurations were taken into account to meticulously explore the chemical adsorption effects on the magnetic properties. To suppress the van der Waals interactions between two neighboring cells, the vacuum distance along the z-axis was set to be 15 Å. A plane-wave basis set, with a maximum energy cutoff of 500 eV was used in our calculations of Bloch wave functions. All atomic coordinates were relaxed until the change of eigenvalues between two simulation steps was less than 10–5 eV, and the Hellmann–Feynman force convergence on each atom was set to be 0.01 eV/Å. The pristine first Brillouin zone was sampled by 30 × 30 × 1 and 100 × 100 × 1 K-points within the Gamma scheme for structure relaxations and further evaluations of electronic properties, respectively. An equivalent K-point mesh was built for other enlarged cells depending on their sizes. Additionally, the van der Waals force, which utilizes the semiempirical DFT-D2 correction of Grimme,58 played a very useful role in helping us understand the significant atomic interactions between silicene and adatom layers at high doping concentrations.

Acknowledgments

This work was financially supported by the Taiwan Ministry of Science and Technology (MOST) under the project 108-2112-M-006-022-MY3 and also the Hierarchical Green-Energy Materials (Hi-GEM) Research Center, through The Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE) and the Ministry of Science and Technology (MOST 109-2634-F-006-020) in Taiwan.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.0c00905.

  • Supplementary data of binding energy, optimal adsorption positions of Na/Mg/Al on silicene (Figure S1); optimal geometries of the magnesium-adsorbed silicenes (Figure S2) and aluminum-adsorbed silicenes (Figure S3) (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao0c00905_si_001.pdf (2.8MB, pdf)

References

  1. Borenstein A.; Hanna O.; Attias R.; Luski S.; Brousse T.; Aurbach D. Carbon-based composite materials for supercapacitor electrodes: a review. J. Mater. Chem. A 2017, 5, 12653–12672. 10.1039/c7ta00863e. [DOI] [Google Scholar]
  2. Yu X.; Cheng H.; Zhang M.; Zhao Y.; Qu L.; Shi G. Graphene-based smart materials. Nat. Rev. Mater. 2017, 2, 17046 10.1038/natrevmats.2017.46. [DOI] [Google Scholar]
  3. Oughaddou H.; Enriquez H.; Tchalala M. R.; Yildirim H.; Mayne A. J.; Bendounan A.; Dujardin G.; Ali M. A.; Kara A. Silicene, a promising new 2D material. Prog. Surf. Sci. 2015, 90, 46–83. 10.1016/j.progsurf.2014.12.003. [DOI] [Google Scholar]
  4. Shao Z.-G.; Ye X.-S.; Yang L.; Wang C.-L. First-principles calculation of intrinsic carrier mobility of silicene. J. Appl. Phys. 2013, 114, 093712 10.1063/1.4820526. [DOI] [Google Scholar]
  5. Mokkath J. H.; Schwingenschlögl U. Tunable optical absorption in silicene molecules. J. Mater. Chem. C 2016, 4, 7387–7390. 10.1039/C6TC02186G. [DOI] [Google Scholar]
  6. Liu C.-C.; Feng W.; Yao Y. Quantum spin Hall effect in silicene and two-dimensional germanium. Phys. Rev. Lett. 2011, 107, 076802 10.1103/PhysRevLett.107.076802. [DOI] [PubMed] [Google Scholar]
  7. Drummond N. D.; Zolyomi V.; FalKo V. I. Electrically tunable band gap in silicene. Phys. Rev. B 2012, 85, 075423 10.1103/PhysRevB.85.075423. [DOI] [Google Scholar]
  8. Aftab T. Valleytronics and phase transition in silicene. Phys. Lett. A 2017, 381, 935–943. 10.1016/j.physleta.2017.01.020. [DOI] [Google Scholar]
  9. Vali M.; Dideban D.; Moezi N. Silicene field effect transistor with high on/off current ratio and good current saturation. J. Comput. Electron. 2016, 15, 138–143. 10.1007/s10825-015-0758-1. [DOI] [Google Scholar]
  10. Tao L.; Cinquanta E.; Chiappe D.; Grazianetti C.; Fanciulli M.; Dubey M.; Molle A.; Akinwande D. Silicene field-effect transistors operating at room temperature. Nat. Nanotechnol. 2015, 10, 227–231. 10.1038/nnano.2014.325. [DOI] [PubMed] [Google Scholar]
  11. Zhu J.; Schwingenschlogl U. Silicene for Na-ion battery applications. 2D Mater. 2016, 3, 035012 10.1088/2053-1583/3/3/035012. [DOI] [Google Scholar]
  12. Xu S.; Fan X.; Liu J.; Singh D. J.; Jiang Q.; Zheng W. Adsorption of Li on single-layer silicene for anodes of Li-ion batteries. Phys. Chem. Chem. Phys. 2018, 20, 8887–8896. 10.1039/C7CP08036K. [DOI] [PubMed] [Google Scholar]
  13. Ezawa M. Spin valleytronics in silicene: Quantum spin Hall-quantum anomalous Hall insulators and single-valley semimetals. Phys. Rev. B 2013, 87, 155415 10.1103/PhysRevB.87.155415. [DOI] [Google Scholar]
  14. Osborne D. A.; Morishita T.; Tawfik S. A.; Yayama T.; Spencer M. J. Adsorption of toxic gases on silicene/Ag (111). Phys. Chem. Chem. Phys. 2019, 21, 17521–17537. 10.1039/C9CP01901D. [DOI] [PubMed] [Google Scholar]
  15. Vogt P.; De Padova P.; Quaresima C.; Avila J.; Frantzeskakis E.; Asensio M. C.; Resta A.; Ealet B.; Le Lay G. Silicene: compelling experimental evidence for graphenelike two-dimensional silicon. Phys. Rev. Lett. 2012, 108, 155501 10.1103/PhysRevLett.108.155501. [DOI] [PubMed] [Google Scholar]
  16. Meng L.; et al. Buckled silicene formation on Ir (111). Nano Lett. 2013, 13, 685–690. 10.1021/nl304347w. [DOI] [PubMed] [Google Scholar]
  17. Aizawa T.; Suehara S.; Otani S. Phonon dispersion of silicene on ZrB2 (0 0 0 1). J. Phys. Condens. Matter 2015, 27, 305002 10.1088/0953-8984/27/30/305002. [DOI] [PubMed] [Google Scholar]
  18. Zhu J.; Schwingenschlögl U. Silicene on MoS2: role of the van der Waals interaction. 2D Mater. 2015, 2, 045004 10.1088/2053-1583/2/4/045004. [DOI] [Google Scholar]
  19. Liu H.; Gao J.; Zhao J. Silicene on Substrates: A Way to Preserve or Tune its Electronic Properties. J. Phys. Chem. C 2013, 117, 10353–10359. 10.1021/jp311836m. [DOI] [Google Scholar]
  20. Pan Y.; et al. Construction of 2D atomic crystals on transition metal surfaces: graphene, silicene, and hafnene. Small 2014, 10, 2215–2225. 10.1002/smll.201303698. [DOI] [PubMed] [Google Scholar]
  21. Jose D.; Datta A. Structures and chemical properties of silicene: unlike graphene. Acc. Chem. Res. 2013, 47, 593–602. 10.1021/ar400180e. [DOI] [PubMed] [Google Scholar]
  22. Lin S.-Y.; Chang S.-L.; Tran N. T. T.; Yang P.-H.; Lin M.-F. H-Si bonding-induced unusual electronic properties of silicene: a method to identify hydrogen concentration. Phys. Chem. Chem. Phys. 2015, 17, 26443–26450. 10.1039/C5CP04841A. [DOI] [PubMed] [Google Scholar]
  23. Nguyen D. K.; Tran N. T. T.; Chiu Y.-H.; Lin M.-F. Concentration-Diversified Magnetic and Electronic Properties of Halogen-Adsorbed Silicene. Sci. Rep. 2019, 9, 13746 10.1038/s41598-019-50233-w. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Du Y.; et al. Tuning the band gap in silicene by oxidation. ACS Nano 2014, 8, 10019–10025. 10.1021/nn504451t. [DOI] [PubMed] [Google Scholar]
  25. Xu K.; Ben L.; Li H.; Huang X. Silicon-based nanosheets synthesized by a topochemical reaction for use as anodes for lithium ion batteries. Nano Res. 2015, 8, 2654–2662. 10.1007/s12274-015-0772-4. [DOI] [Google Scholar]
  26. Wu C.-H. Integer quantum Hall conductivity and longitudinal conductivity in silicene under the electric field and magnetic field. Eur. Phys. J. B 2019, 92, 25 10.1140/epjb/e2018-90343-x. [DOI] [Google Scholar]
  27. Ni Z.; Liu Q.; Tang K.; Zheng J.; Zhou J.; Qin R.; Gao Z.; Yu D.; Lu J. Tunable bandgap in silicene and germanene. Nano Lett. 2012, 12, 113–118. 10.1021/nl203065e. [DOI] [PubMed] [Google Scholar]
  28. Mirershadi S.; Sattari F. Spin and valley dependent transport in strained silicene superlattice. Phys. E 2020, 115, 113696 10.1016/j.physe.2019.113696. [DOI] [Google Scholar]
  29. Xie H.; Ouyang T.; Germaneau É.; Qin G.; Hu M.; Bao H. Large tunability of lattice thermal conductivity of monolayer silicene via mechanical strain. Phys. Rev. B 2016, 93, 075404 10.1103/PhysRevB.93.075404. [DOI] [Google Scholar]
  30. Sahin H.; Peeters F. M. Adsorption of alkali, alkaline-earth, and 3d transition metal atoms on silicene. Phys. Rev. B 2013, 87, 085423 10.1103/PhysRevB.87.085423. [DOI] [Google Scholar]
  31. Xu Q.; Yang G. M.; Fan X.; Zheng W. T. Adsorption of metal atoms on silicene: stability and quantum capacitance of silicene-based electrode materials. Phys. Chem. Chem. Phys. 2019, 21, 4276–4285. 10.1039/C8CP05982A. [DOI] [PubMed] [Google Scholar]
  32. Avila J.; De Padova P.; Cho S.; Colambo I.; Lorcy S.; Quaresima C.; Vogt P.; Resta A.; Le Lay G.; Asensio M. C. Presence of gapped silicene-derived band in the prototypical (3x3) silicene phase on silver (111) surfaces. J. Phys. Condens. Matter 2013, 25, 262001 10.1088/0953-8984/25/26/262001. [DOI] [PubMed] [Google Scholar]
  33. Siegel D. A.; Regan W.; Fedorov A. V.; Zettl A.; Lanzara A. Charge-carrier screening in single-layer graphene. Phys.Rev. Lett. 2013, 110, 146802 10.1103/PhysRevLett.110.146802. [DOI] [PubMed] [Google Scholar]
  34. Ni Z.; Zhong H.; Jiang X.; Quhe R.; Luo G.; Wang Y.; Ye M.; Yang J.; Shi J.; Lu J. Tunable band gap and doping type in silicene by surface adsorption: towards tunneling transistors. Nanoscale 2014, 6, 7609–7618. 10.1039/C4NR00028E. [DOI] [PubMed] [Google Scholar]
  35. Botari T.; Perim E.; Autreto P. A. S.; van Duin A. C. T.; Paupitz R.; Galvao D. S. Mechanical properties and fracture dynamics of silicene membranes. Phys. Chem. Chem. Phys. 2014, 16, 19417–19423. 10.1039/C4CP02902J. [DOI] [PubMed] [Google Scholar]
  36. Zhang X.-L.; Liu L.-F.; Liu W.-M. Quantum anomalous Hall effect and tunable topological states in 3d transition metals doped silicene. Sci. Rep. 2013, 3, 2908 10.1038/srep02908. [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Jin H.; Jeong H.; Ozaki T.; Yu J. Anisotropic exchange interactions of spin-orbit-integrated states in Sr2IrO4. Phys. Rev. B 2009, 80, 075112 10.1103/PhysRevB.80.075112. [DOI] [Google Scholar]
  38. Lin S.-Y.; Lin Y.-T.; Tran N. T. T.; Su W.-P.; Lin M.-F. Feature-rich electronic properties of aluminum-absorbed graphenes. Carbon 2017, 120, 209–218. 10.1016/j.carbon.2017.04.077. [DOI] [Google Scholar]
  39. Wu Y. P.; Rahm E.; Holze R. Carbon anode materials for lithium ion batteries. J. Power Sources 2003, 114, 228–236. 10.1016/S0378-7753(02)00596-7. [DOI] [Google Scholar]
  40. Ohta T.; Bostwick A.; McChesney J. L.; Seyller T.; Horn K.; Rotenberg E. Interlayer interaction and electronic screening in multilayer graphene investigated with angle-resolved photoemission spectroscopy. Phys. Rev. Lett. 2007, 98, 206802 10.1103/PhysRevLett.98.206802. [DOI] [PubMed] [Google Scholar]
  41. Ohta T.; Bostwick A.; Seyller T.; Horn K.; Rotenberg E. Controlling the electronic structure of bilayer graphene. Science 2006, 313, 951954 10.1126/science.1130681. [DOI] [PubMed] [Google Scholar]
  42. Zhou S. Y.; Siegel D. A.; Fedorov A. V.; Lanzara A. Metal to insulator transition in epitaxial graphene induced by molecular doping. Phys. Rev. Lett. 2008, 101, 086402 10.1103/PhysRevLett.101.086402. [DOI] [PubMed] [Google Scholar]
  43. Papagno M.; Rusponi S.; Sheverdyaeva P. M.; Vlaic S.; Etzkorn M.; Pacile D.; Moras P.; Carbone C.; Brune H. Large band gap opening between graphene Dirac cones induced by Na adsorption onto an Ir superlattice. ACS Nano 2011, 6, 199204 10.1021/nn203841q. [DOI] [PubMed] [Google Scholar]
  44. Sugawara K.; Kanetani K.; Sato T.; Takahashi T. Fabrication of Li-intercalated bilayer graphene. AIP Adv. 2011, 1, 022103 10.1063/1.3582814. [DOI] [Google Scholar]
  45. Vogt P.; De Padova P.; Quaresima C.; Avila J.; Frantzeskakis E.; Asensio M. C.; Resta A.; Ealet B.; Le Lay G. Silicene: compelling experimental evidence for graphenelike two-dimensional silicon. Phys. Rev. Lett. 2012, 108, 155501 10.1103/PhysRevLett.108.155501. [DOI] [PubMed] [Google Scholar]
  46. Borensztein Y.; Prévot G.; Masson L. Large differences in the optical properties of a single layer of Si on Ag (110) compared to silicene. Phys. Rev. B 2014, 89, 245410 10.1103/PhysRevB.89.245410. [DOI] [Google Scholar]
  47. Tao L.; Cinquanta E.; Chiappe D.; Grazianetti C.; Fanciulli M.; Dubey M.; Molle A.; Akinwande D. Silicene field-effect transistors operating at room temperature. Nat. Nanotechnol. 2015, 10, 227–231. 10.1038/nnano.2014.325. [DOI] [PubMed] [Google Scholar]
  48. Chen L.; Liu C.-C.; Feng B.; He X.; Cheng P.; Ding Z.; Meng S.; Yao Y.; Wu K. Evidence for Dirac fermions in a honeycomb lattice based on silicon. Phys. Rev. Lett. 2012, 109, 056804 10.1103/PhysRevLett.109.056804. [DOI] [PubMed] [Google Scholar]
  49. Zhuang J.; Xu X.; Peleckis G.; Hao W.; Dou S. X.; Du Y. Silicene: a promising anode for lithium-ion batteries. Adv. Mater. 2017, 29, 1606716 10.1002/adma.201606716. [DOI] [PubMed] [Google Scholar]
  50. Tritsaris G. A.; Kaxiras E.; Meng S.; Wang E. Adsorption and diffusion of lithium on layered silicon for Li-ion storage. Nano Lett. 2013, 13, 2258–2263. 10.1021/nl400830u. [DOI] [PubMed] [Google Scholar]
  51. Persson K.; Hinuma Y.; Meng Y. S.; Van der Ven A.; Ceder G. Thermodynamic and kinetic properties of the Li-graphite system from first-principles calculations. Phys. Rev. B 2010, 82, 125416 10.1103/PhysRevB.82.125416. [DOI] [Google Scholar]
  52. Wang Y.; Zheng J.; Ni Z.; Fei R.; Liu Q.; Quhe R.; Xu C.; Zhou J.; Gao Z.; Lu J. Half-metallic silicene and germanene nanoribbons: towards high-performance spintronics device. Nano 2012, 7, 1250037 10.1142/S1793292012500373. [DOI] [Google Scholar]
  53. Yang-Yang W.; Ru-Ge Q.; Da-Peng Y.; Jing L. Silicene spintronics-A concise review. Chin. Phys. B 2015, 24, 087201 10.1088/1674-1056/24/8/087201. [DOI] [Google Scholar]
  54. Kresse G.; Furthmüller J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 1996, 54, 11169–11186. 10.1103/PhysRevB.54.11169. [DOI] [PubMed] [Google Scholar]
  55. Kresse G.; Joubert D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 1999, 59, 1758–1775. 10.1103/PhysRevB.59.1758. [DOI] [Google Scholar]
  56. Perdew J. P.; Burke K.; Ernzerhof M. Generalized gradient approximation made simple. Phys. Rev. Lett. 1996, 77, 3865–3868. 10.1103/PhysRevLett.77.3865. [DOI] [PubMed] [Google Scholar]
  57. Blöchl P. E. Projector augmented-wave method. Phys. Rev. B 1994, 50, 17953–17979. 10.1103/PhysRevB.50.17953. [DOI] [PubMed] [Google Scholar]
  58. Grimme S. Semiempirical GGA-type density functional constructed with a long-range dispersion correction. J. Comput. Chem. 2006, 27, 1787–1799. 10.1002/jcc.20495. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao0c00905_si_001.pdf (2.8MB, pdf)

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES