Tunable Electronic Structures of Hydrogenated Zigzag and Armchair

Article pubs.acs.org/JPCC

Cite This: J. Phys. Chem. C XXXX, XXX, XXX−XXX

Tunable Electronic Structures of Hydrogenated Zigzag and Armchair Dumbbell Silicene Nanosheets: A Computational Study Yi Ding*,† and Yanli Wang*,‡ †

Department of Physics, Hangzhou Normal University, Hangzhou, Zhejiang 311121, People’s Republic of China Department of Physics, Zhejiang Sci-Tech University, Hangzhou, Zhejiang 310018, People’s Republic of China

‡

J. Phys. Chem. C Downloaded from pubs.acs.org by KAOHSIUNG MEDICAL UNIV on 10/04/18. For personal use only.

S Supporting Information *

ABSTRACT: Very recently, zigzag and armchair dumbbell silicene (zd-Si and ad-Si) nanosheets have been identified as the most stable structures of two-dimensional silicon systems. Here, utilizing the first-principle calculations, we have investigated the fully hydrogenated forms of these dumbbell silicene (H-zd-Si and H-ad-Si). It is found that the hydrogenation is an energetically favorable process on the dumbbell silicene, for which the formed structures possess robust mechanical, dynamical, and thermal stabilities. Semiconducting behaviors are well preserved in these H-zd-Si and H-ad-Si nanosheets, which are indirect- and direct-gap semiconductors with larger band gaps than the pristine cases. The gap sizes and band features can be significantly modulated by uniaxial strains, and an indirect-to-direct (direct-to-indirect) band gap transition occurs in the H-zd-Si (H-ad-Si) nanosheet under a small y-axial tensile strain. More interestingly, a ultra high electron mobility is present in the H-ad-Si nanosheet, which reaches up to 3.6/1.5 × 104 cm2/(V s) in the x/y direction. Besides that, the carrier mobility ratio in the H-ad-Si nanosheet is as large as 9.93/15.34 in the x/y direction, which benefits the hole and electron separation. For these dumbbell silicene, a type-II band alignment can be formed between the hydrogenated and pristine nanosheets. In particular, the combined H-ad-Si/ad-Si system will be a promising excitonic solar cell material, whose power conversion efficiency is up to 13−20%. Owing to these peculiar electronic properties, the hydrogenated dumbbell silicene nanosheets are promising nanomaterials for the potential nanoelectric and green-energy applications.

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silicene nanosheet.19 Very recently, based on the minimahopping method, Borlido et al. have used a constrained structure prediction approach to investigating the ground state structures of 2D silicon systems.20,21 They have found the zigzag and armchair dumbbell silicene nanosheets are the most stable structures, which are both indirect-gap semiconductors.21 We notice that the outside Si atoms are high-buckled in these dumbbell silicenes, which will possess enough chemical activity to foreign atoms. Since the hydrogen functionalization is a common way to tailor the electronic properties of 2D silicene-related nanomaterials,6 it will be promising to explore the hydrogenation effects on these newly discovered dumbbell silicene nanosheets. Are the hydrogenated geometries structurally stable? Do they possess peculiar electronic properties? How can they be tuned for potential applications? To address these issues, we perform a computational study on the hydrogenated zigzag and armchair dumbbell silicene nanosheets.

INTRODUCTION As the cousin of graphene, two-dimensional (2D) silicene nanosheet has attracted sufficient scientific attention due to the extraordinary electronic properties and practical applications.1−4 Because of the pseudo-Jahn−Teller effect, the basal plane of silicene is buckled,5 which facilitates the chemical decoration on the Si honeycomb.6 In fact, several silicenebased derivatives, such as silicane (fully hydrogenated silicene),7,8 half-silicane (one-side hydrogenated silicene),9,10 and Siloxene (hydrogenated silicene with embedded oxygen bridges),11,12 have been observed in the experiments. Besides that, when an additional Si atom is adsorbed on the surface, a local reconstruction will occur in silicene, forming a pair of Si atoms like the dumbbell.13,14 Depending on the ordered distributions of Si dumbbells, several dumbbell silicene nanostructures have been proposed, which are all energetically more favorable than the pristine silicene system.15−17 Different from pristine silicene, the dumbbell silicene nanosheet becomes a semiconductor with a small direct band gap when the Si dumbbells are arranged in a homogeneous 2 × 2 pattern.18 The gap size can be effectively modulated by the strain and the system could even be transformed to a topological insulator.18 In addition, a low lattice thermal conductivity is also present in this dumbbell © XXXX American Chemical Society

Received: August 24, 2018 Revised: September 24, 2018 Published: September 25, 2018 A

DOI: 10.1021/acs.jpcc.8b08268 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

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METHOD The first-principles calculations are performed by the VASP code,22,23 which adopts the Perdew−Burke−Ernzerhof (PBE) projector augmented wave pseudopotentials and plane-wave basis sets with a cutoff energy of 500 eV. A vacuum layer of more than 20 Å is used in the calculations, and the Brillouine zone is sampled by the Wisesa−McGill−Mueller k-grid with a minimum period distance of 25 and 36 Å in the relaxation and static calculations, respectively.24 All the geometrical structures are fully optimized until the residual force is less than 0.01 eV/ Å. The dynamical and thermal stabilities of systems are verified by the phonon calculations and density functional based tight binding molecular dynamics (DFTB-MD) simulations, which are performed by the Phonopy and DFTB+ codes.25,26 The hybrid Heyd−Scuseria−Ernzerhof (HSE) calculations are further performed to check the obtained band structures by the FHI-aims code,27 which utilizes the HSE06 form with a screening parameter of 0.25 bohr−1 and a mixing parameter of 0.5 for the short-range exchange.28 The atom structures in the pictures are depicted by the Vesta software.29

total energies of hydrogenated and pristine dumbbell silicene, nH is the number of H atoms, and EH2 is the energy of an isolated H2 molecule. The Eform of H-zd-Si and H-ad-Si nanosheets are obtained as −0.373 and −0.396 meV/H atom, indicating the hydrogenation is an energetically favorable process on the dumbbell silicene nanosheets under the H2 surrounding. The mechanical, dynamical, and thermal stabilities are examined on these H-zd-Si and H-ad-Si nanosheets. Utilizing the energy-vs-strain method,32 the elastic constants of H-zd-Si/ H-ad-Si nanosheet are obtained as C11 = 76/66 N/m, C22 = 80/92 N/m, C12 = 23/16 N/m, and C44 = 30/27 N/m, respectively. These constants satisfy the Born−Huang criteria of tetragonal nanosheet (C11C22 − C212 > 0 and C44 > 0),33 which verifies the mechanical stabilities of these hydrogenated systems. On the basis of the elastic constants, the orientationdependent Young’s moduli (Y) and Possion ratio (ν) are calculated as illustrated in Figure 2(a) and (b). The Y values are 70/64 and 73/88 N/m in the x/y direction of H-zd-Si and H-ad-Si nanosheet, which are a little stiffer than the silicene and silicane ones (64 and 56 N/m).3,34 Their ν are in the range of [0.17, 0.27] and [0.24, 0.30], which are comparable to the silicene and silicane cases (0.33 and 0.24).34 The phonon dispersions of H-zd-Si and H-ad-Si nanosheets are displayed in Figure 2(c) and (d), which show all the vibrational frequencies are positive. It demonstrates that the H-zd-Si and H-ad-Si nanosheets exhibit good dynamic stability at the free-standing state. The DFTB-MD simulations are performed on a supercell with 3 × 3 units for H-zd-Si and H-ad-Si nanosheets, which adopt a Nose thermostat at 800 K and a step time of 1 fs. The final structures after 104 steps are depicted in Figure 2(e) and (f). It can be seen that although there are some distortions in H-zd-Si and H-ad-Si nanosheets, the whole structures are still kept integrated. Therefore, through the mechanical, dynamical, and thermal analysis, these H-zd-Si and H-ad-Si nanosheets are confirmed to possess robust structural stabilities, which are essential for their practical applications. Then, we focus on the electronic properties of these H-zd-Si and H-ad-Si nanosheets. For comparison, the band structures of pristine zd-Si and ad-Si systems are also calculated. Consistent with previous results,21 we also obtain that they are both indirect-gap semiconductors, whose band gaps are 0.624 and 1.012 eV by the PBE calculations. After the hydrogenation, the gap sizes are raised to 1.382 and 1.235 eV in the H-zd-Si and H-ad-Si nanosheets, respectively. As shown in Figure 3(a) and (b), the H-zd-Si nanosheet is still an indirect-gap semiconductor, whose valence band maximum (VBM) is at the Γ point and the conduction band minimum (CBM) is at the X point. While in the H-ad-Si nanosheet, a direct band gap is formed at the X point. The HSE calculations obtain similar band structures to the PBE ones, which predict larger band gaps of 2.068 and 1.775 eV for the H-zd-Si and Had-Si nanosheets, respectively. The corresponding partial charge densities of band edges are illustrated in Figure 3(c) and (d). In the H-zd-Si nanosheet, the VBM and CBM are mainly composed of the bonding and antibonding states of inplane Si−Si bonds that link the Si zigzag lines. While in the Had-Si nanosheet, the VBM and CBM are originated from the bonding and antibonding states of titled Si−Si bonds that connect the outside dumbbell Si atoms. We have further investigated the halogenated dumbbell silicene. The band structures and gap sizes of these X-zd-Si and X-ad-Si (X = F, Cl, Br, I) nanosheets from the PBE calculations

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RESULTS AND DISCUSSION The schematic diagrams of zigzag and armchair dumbbell silicene geometries are depicted in Figure 1, where the

Figure 1. Top and lateral views of [(a), (c)] H-zd-Si and [(b), (d)] H-ad-Si nanosheets. The schematic diagrams of (e) zigzag and (f) armchair dumbbell geometries. (g) The Brillouine zone and the highsymmetrical points for the investigated dumbbell systems.

dumbbell atoms are arranged in zigzag and armchair patterns on the Si honeycomb sheet, respectively. For the zd-Si/ad-Si nanosheets, the lattice constants are Lx = 6.40/7.24 and Ly = 7.42/6.49 Å. Compared to pristine silicene, these zd-Si and adSi systems are energetically more favorable by 219 and 218 meV/atom, which agree well with previous results.21 For these dumbbell silicene, the fully hydrogenated structures are constructed by hydrogenating the outside dumbbell Si atoms since these high-buckled Si atoms are more activated than the others.30,31 Figure 1(a) and (b) displays the optimized structures of hydrogenated zigzag and armchair dumbbell silicene (H-zd-Si and H-ad-Si) nanosheets. Compared to the pristine counterparts, the lattice constants of H-zd-Si/H-ad-Si are slightly shrunk to Lx = 6.35/7.06 and Ly = 7.37/6.42 Å. The formation energies of hydrogenated structures are calculated as Eform = (Ehd − Epd − nHEH2/2)/nH, where Ehd and Epd are the B


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Figure 2. [(a) and (b)] The polar diagrams for the Y(θ) and ν(θ) of H-zd-Si and (d) H-ad-Si nanosheets. [(c), (d)] Their phonon bands, and [(e), (f)] the final structures after the DFTB-MD simulations.

potential constants of VBM and CBM (−9.62 and −11.94 eV) are about 1 order of magnitude larger than the ones in the y direction (−1.53 and −1.22 eV). For the anisotropic systems, the carrier mobilities are calculated by the recently proposed formula,37 which is expressed as follows:

are supplied in the Supporting Information (SI). It can be seen that for the X-zd-Si nanosheets, their band structures are a little different from the H-zd-Si ones. The VBM moves into the X−S line, and in the Br-zd-Si and I-zd-Si systems, the CBM is shifted to the Γ point. However, in the X-ad-Si nanosheets, their VBM and CBM are still located at X point as in the case of H-ad-Si system. The gap sizes of X-zd-Si nanosheets are varied in the range of [1.149, 1.378] eV, just comparable to the H-zd-Si one. Whereas for the X-ad-Si ones, their gap sizes are about 30% smaller than the H-ad-Si case, which are only in the range of [0.715, 0.817] eV. This phenomenon is similar to the case of halogenated silicene, whose band gaps are also noticeably declined by the halogen functionalization.35,36 According to the compositions of band edges, different performances of carrier mobilities will be expected in H-zd-Si and H-ad-Si nanosheets. As shown in Table 1, anisotropic characteristics are observed in the effective masses and deformation potential constants of H-zd-Si nanosheet. For the hole and electron carriers, their masses are as small as about 0.12 m0 in the x direction, while they become more than four times larger in the y direction, which are 0.53 and 0.51 m0 for the holes and electrons, respectively. However, due to the localization of band edges in the x direction, the deformation

(

eℏ3

μα =

5Cα + 3Cβ

ij kBTmα3/2m1/2 β j j k

8 9Eα2

)

+ 7EαEβ + 4Eβ2 y 20

zz z {

, (α , β = x , y )

This formula will be equivalent to the previously used one in isotropic systems,38,39 and give more close data to the experimental results for anisotropic systems.37,40 It is found that the carrier mobilities of H-zd-Si nanosheet are small in both x and y directions. For the holes and electrons, the mobilities are 1.15 and 0.85 × 103 cm2/(V s) in the x direction, and smaller values of 0.50 and 0.39 × 103 cm2/(V s) are obtained in the y direction, respectively. Whereas for the H-adSi nanosheet, as shown in Table 1, its carrier masses are almost isotropic, which are 0.38/0.42 m0 for holes and 0.45/0.46 m0 for electrons in the x/y direction. Because the VBM and CBM are distributed on the tilted Si−Si bonds, the effects of in-plane C


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Figure 3. Band structures of (a) H-zd-Si and (b) H-ad-Si nanosheets, and [(c), (d)] the partial charge densities of their VBM and CBM.

Table 1. Effective Masses, Deformation Potential Constants, Carrier Mobilities, As Well As the Ratio between Hole and Electron Mobilities for the H-zd-Si and H-ad-Si Nanosheets H-zd-Si H-ad-Si

x: y: x: y:

mh m0

me m0

EVBM (eV)

ECBM (eV)

μh (103 cm2/(V s))

μe (103 cm2/(V s))

Rμ

0.12 0.53 0.38 0.42

0.12 0.51 0.45 0.46

−9.62 −1.53 −3.30 −1.33

−11.94 −1.22 −1.31 0.63

1.15 0.50 1.56 2.34

0.85 0.39 13.93 35.90

1.35 1.28 9.93 15.34

Figure 4. Strain−stress curves for the (a) H-zd-Si and (b) H-ad-Si nanosheets. The variations of band gaps versus strains on (c) H-zd-Si and (d) H-ad-Si nanosheets.

D


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Figure 5. Band structures of [(a), (b)] H-zd-Si and [(c), (d)] H-ad-Si nanosheet under the ϵx = 0.06 and ϵy = 0.06 cases.

Figure 6. (a) The strain−stress curves for the H-zd-Si and H-ad-Si nanosheets under the biaxial strains. (b) Their variations of band gaps versus biaxial strains and [(c), (d)] the band structures of H-zd-Si and H-ad-Si nanosheets under the ϵb = 0.10 case.

in H-ad-Si nanosheet is the highest value (35.90 × 103 cm2/(V s)) in the anisotropic monolayers so far. Compared to the reported high mobilities in the literature, the electron mobility of H-ad-Si nanosheet is even larger than those of of Sc2CF2 (5.62 × 103 cm2/(V s)), TiS3 (10.6 × 103 cm2/(V s)), and BC2N (22.3 × 103 cm2/(V s)) ones.37 Such high electron mobilities facilitate the charge separation and hence transfer in

strains will be marginal. As a result, the deformation potential constants of VBM and CBM are small in the H-ad-Si nanosheet, which leads to large carrier mobilities. For the holes and electrons, the mobilities reach up to 1.56 and 13.93 × 103 cm2/(V s) in the x direction, and they further rise to 2.34 and 35.90 × 103 cm2/(V s) in the y direction, respectively. It would be noted that the maximum value of electron mobility E


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Figure 7. (a) The band offsets for the hydrogenated and pristine zigzag and armchair dumbbell silicene systems from the PBE and HSE calculations. (b) The HSE band structures of H-ad-Si nanosheet at the strain-free and ϵx = 0.06 cases. (c) Calculated power-conversion efficiency as a function of the donor bandgap and conduction band offset, in which the cases of strained H-ad-Si/ad-Si heterostructures are marked as stars and their data are displayed in (d).

typical band structures under the ϵx/ϵy = 0.06 are displayed in Figure 5. As shown in Figure 4(c) and (d), for the H-zd-Si nanosheet, the band gap is monotonously reduced by the x-/yaxial strain. The system becomes a direct-gap semiconductor under the y-axial strain in the range of [0.01, 0.08], while it is converted to a metal under a large x-axial strain of ϵx = 0.14. However, the band gap of H-ad-Si nanosheet is first raised and reaches the maximum value of 1.285/1.246 eV at ϵx = 0.03/ϵy = 0.01. Then the gap size is declined fast under the x-/y-axial strains. A direct-to-indirect-band gap transition is induced by the y-axial strain, which shifts the CBM away from the high symmetrical point. While under the x-axial strain, the directband gap feature is preserved although the VBM and CBM are moved to Γ point when ϵx > 0.03. Hence, in addition to the modulation of gap magnitude, the band feature of H-zd-Si and H-ad-Si nanosheets can also be altered by the strain, which can induce an indirect−direct or direct−indirect band gap transition by a small y-axial strain. Besides that, we have also investigated the biaxial strain (ϵb) on these systems. As shown in Figure 6, the H-zd-Si and H-ad-Si nanosheets can endure the biaxial strains up to the values of 0.13 and 0.15, respectively. There are no phonon instabilities before the elastic limits. Akin to the uniaxial strained cases, the gap sizes are also prominently reduced under biaxial strains. The H-zd-Si nanosheet undergoes an indirect-to-direct-band gap transition at the strain of ϵb = 0.10, which is larger than the y-axial strain case. While for the H-ad-Si nanosheet, it away possesses an indirect band gap under the biaxial strain that is similar to the y-axial strained one.

the H-ad-Si nanosheet. To this end, the carrier mobility ratio of hole and electron (Rμ), which is defined as Rμ = max(μh, μe)/min(μh, μe),41 is calculated. In the H-ad-Si nanosheet, as shown in Table 1, the Rμ reach up to 9.93 and 15.34 in the x and y directions, respectively, which are much bigger than the values of H-zd-Si nanosheet (1.35 and 1.28) and common transition metal dichalcogenides (Rμ = 2−3).42 Such large Rμ values in the H-ad-Si nanosheet suggest that there will be a pronounced difference between the hole and electron transport, which can lower the possibility of carrier recombination and benefit the hole and electron separation in it. It is well-known that the strain engineering is a valid away to tailor the electronic properties of nanomaterials.43 Figure 4(a) and (b) depict the stress−strain curves of H-zd-Si and H-ad-Si nanosheets. It is found that the H-zd-Si can endure a large xaxial strain (ϵx) up to the elastic limit of 0.15, whose ideal strength corresponds to 7.1 N/m. While under the y-axial strain (ϵy), a phonon instability occurs at ϵy = 0.10, which results in a smaller critical strain of 0.09 and a smaller ideal strength of 5.6 N/m in the H-zd-Si nanosheet. Similar phonon instability is also present in the x-axial strained H-ad-Si nanosheet, whose critical strain and ideal strength are 0.14 and 7.2 N/m, respectively. Moreover, the H-ad-Si nanosheet can endure a large y-axial strain up to the elastic limit of 0.19 and the corresponding ideal strength is as large as 9.6 N/m. This value reaches the Griffith strength limit of material, i.e., the one-ninth of its Young’s modulus (Y/9).44 It indicates that the H-ad-Si nanosheet can exhibit a superior flexibility in the y direction. Under the strains, the band gaps of H-zd-Si and Had-Si nanosheets can be effectively modulated, for which the F


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H-ad-Si nanosheets possess robust structural stabilities from the mechanical, dynamical and thermal points of view. (2) Akin to the pristine counterparts, both the H-zd-Si and the Had-Si nanosheets are semiconductors with larger band gaps. Their gap values and band features are sensitive to strains, and a small y-axial tensile strain will cause an indirect-to-direct (direct-to-indirect) band gap transition in the H-zd-Si (H-adSi) nanosheet. (3) A ultra high electron mobility is present in the H-ad-Si nanosheet, which reaches up to 35.90 × 103 cm2/ (V s) in the y direction. This value is the highest among the reported electron mobilities in the anisotropic monolayer systems so far. (4) The hydrogenation up-shifts the energies of band edges, which results in a type-II band alignment between the hydrogenated and pristine dumbbell silicene. In particular, the combined H-ad-Si/ad-Si system will be a promising solar cell material, which possesses a high power conversion efficiency of up to 13−20%. Our study demonstrates that the hydrogenated dumbbell silicene nanosheets possess robust structural stabilities and tunable electronic properties, which endow them many promising applications in nanoelectrics and nanoenergy fields.

Finally, the absolute energies of CBM and VBM in the hydrogenated and pristine zd-Si/ad-Si nanosheets are provided in Figure 7(a), where the vacuum level is referenced as the zero point. It can be seen that the hydrogenation raises the band edges in the H-zd-Si and H-ad-Si nanosheets. Taking the H-adSi and ad-Si nanosheets as an example, the CBM of H-ad-Si nanosheet is located at −3.435/-3.208 eV by the PBE/HSE calculation, which is above that of ad-Si (PBE/HSE: −3.859/− 3.694 eV). The VBM of H-ad-Si nanosheet (PBE/HSE: −4.670/−4.981 eV) is also larger the VBM of ad-Si nanosheet (PBE/HSE: −4.871/−5.250 eV). As a result, a type-II band alignment can be formed between H-ad-Si and ad-Si nanosheets. Similar band offset is also present between the H-zd-Si and zd-Si systems. It means when the hydrogenated nanosheet is superimposed onto the pristine one, the H-ad-Si (H-zd-Si) will act as a donor while the pristine ad-Si (zd-Si) one serves as an acceptor. Interestingly, the HSE calculation shows the conduction band offset (CBO) between the H-ad-Si and ad-Si nanosheets is only 0.486 eV. Along with the appropriate direct band gap of H-ad-Si one, the combined heretostructure will be a promising excitonic solar cell material, whose power conversion efficiency (PCE) can be estimated as follows: ηPCE =

Jsc VocβFF Psolar

0.65(Edg − ECBO − 0.3) ∫ =

∞

Edg

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ASSOCIATED CONTENT

S Supporting Information *

[P(ℏω)/ℏω]d(ℏω)

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.8b08268. The band structures and gap sizes of halogenated zigzag and armchair dumbbell silicene nanosheets (PDF)

∞

∫0 P(ℏω)d(ℏω)

where Jsc, Voc, βFF, and Psolar are the short circuit current, the open-circuit voltage, the band-fill factor, and the incident solar radiation, respectively.45,46 Here, the βFF value is set to 0.65, Voc is adopted to Edg − ECBO − 0.3, where Edg is the band gap of donor part, ECBO is the conduction band offset between the acceptor and donor materials, and 0.3 is an empirical factor for energy conversion kinetics. The Jsc is calculated by the integral in the numerator in the limit external quantum efficiency of 100%, and the Psolar in the denominator is the integrated AM 1.5 solar energy flux, which amounts to 1000 W/m2.47,48 Utilizing this formula, the ηPCE is estimated to be 13.1% for the H-ad-Si/ad-Si heterostructure. This value is comparable to the previously predicted phosphorene/ZrS2 (12%), AlC/ZnO (12.6%), Al2C/MoTe2 (13%), and SiC2/GaN (14.2%)49−51 systems, but is still lower than AsI3/SbI3 (18.4%),52 AsP/GaN (22.1%)53 ones. We note that the direct band gap of H-ad-Si nanosheet can be effectively reduced under sufficient x-axial strain, which also lowers the absolute energy of CBM as shown in Figure 7(b). The CBO and Edg for the strained H-ad-Si nanosheet comparing to the ad-Si one are marked in Figure 7(c). It can be seen that when the ϵx ≤ 0.03, the ηPCE of investigated heterostructures are still about 13.1−13.2%. However, if ϵx > 0.03, both the Edg and CBO are close to the perfect ηPCE region. Thus, the ηPCE is prominently increased to 13.9%, 16.7%, and 20.1% under the ϵx = 0.04, 0.05, 0.06 cases as shown in Figure 7(d). These high ηPCE data suggest that the H-ad-Si/ad-Si heterostructure would be fascinating materials for the green and sustainable energy applications.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Y.D.). *E-mail: [email protected] (Y.W.). ORCID

Yi Ding: 0000-0001-7461-0213 Yanli Wang: 0000-0002-1255-0937 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the supports from National Natural Science Foundation of China (11474081 and 11774312), and Zhejiang Provincial Natural Science Foundation of China (LY15A040008). Parts of the calculations were performed in the Tianhe-2 at National Supercomputer Center in Guangzhou (NSCC-GZ), China.

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REFERENCES

(1) Balendhran, S.; Walia, S.; Nili, H.; Sriram, S.; Bhaskaran, M. Elemental Analogues of Graphene: Silicene, Germanene, Stanene, and Phosphorene. Small 2015, 11, 640−652. (2) 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. (3) Zhao, J.; Liu, H.; Yu, Z.; Quhe, R.; Zhou, S.; Wang, Y.; Liu, C. C.; Zhong, H.; Han, N.; Lu, J.; et al. Rise of Silicene: A Competitive 2D Material. Prog. Mater. Sci. 2016, 83, 24−151. (4) Grazianetti, C.; Cinquanta, E.; Molle, A. Two-dimensional Silicon: The Advent of Silicene. 2D Mater. 2016, 3, 012001. (5) Jose, D.; Datta, A. Structures and Chemical Properties of Silicene: Unlike Graphene. Acc. Chem. Res. 2014, 47, 593−602.

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CONCLUSIONS In summary, we have investigated the hydrogenation on the recently proposed ground state structures of 2D silicon nanosheets, i.e., the zigzag and armchair dumbbell silicene. We find that (1) The hydrogenation on these dumbbell silicene is energetically favorable and the formed H-zd-Si and G


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Tunable Electronic Structures of Hydrogenated Zigzag and Armchair

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