Silicene on Substrates - American Chemical Society

Subscriber access provided by University of Glasgow Library

Article

Silicene on Substrates: A Way to Preserve or Tune its Electronic Properties Hongsheng Liu, Junfeng Gao, and Jijun Zhao J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp311836m • Publication Date (Web): 30 Apr 2013 Downloaded from http://pubs.acs.org on May 2, 2013

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Silicene on Substrates: A Way to Preserve or Tune its Electronic Properties Hongsheng Liu, Junfeng Gao, Jijun Zhao* Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Ministry of Education, Dalian 116024, China KEYWORDS: silicene, substrate, electronic properties ABSTRACT: Silicene, a two-dimensional hexagonal lattice of silicon, has been synthesized recently and exhibits fascinating electronic properties that resemble graphene. The substrate effect on the electronic properties of silicene is important for the practical applications of silicene. First-principles calculations were performed for silicene on two kinds of representative inert substrates, i.e., hexagonal boron nitride (h-BN) monolayer and SiC(0001) surface. The silicene-substrate interaction energies range in 0.067~0.089 eV per Si atom, belonging to typical van der Waals interaction. The characteristic Dirac cone is preserved for silicene on h-BN monolayer or hydrogenated Si-terminated SiC(0001) surface. On the other hand, the silicene becomes metallic when it is placed on a hydrogenated C-terminated SiC(0001) surface. This effect was explained by the work functions for silicene and the substrates. The present results provide some guidelines for selecting proper substrates for silicene in future microelectronic devices.

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 25

I. Introduction Silicene, a monolayer of silicon atoms, resembling the honeycomb lattice and relativistic Dirac fermions of graphene, has been synthesized recently.1-8 Different from the planar graphene sheet, phonon calculations by Ciraci’s and Ni’s groups proposed that planar silicene is unstable with imaginary frequencies; instead, it prefers to form a low-buckled structure with height difference of about 0.44 Å.9-10 It is exciting that silicene possesses most of the astonishing electronic properties of graphene sheets.9, 11-16 For example, the charge carriers in the silicene material were predicted to be massless Dirac Fermions due to the linear dispersion around Fermi level at symmetric point K in the reciprocal lattice. The velocity of charge carriers near Fermi level in silicene was estimated to be 105~106 m/s2, 9, 13, 17, comparable to that in graphene16, 18-19. The spin-orbit coupling is even stronger in silicene with regard to graphene, resulting in a more significant quantum spin Hall effect.20 Moreover, first-principles calculations predicted that a tunable gap can be opened up in silicene at the Fermi level via hydrogenation21-23, fluorination24 or applying electric field25. Most attractively, the easier integration into the current Si-based technology makes silicene a potential candidate for microelectronic devices. Before the fabrication of large-scale silicene, graphene-like silicene nanoribbons were successfully synthesized on Ag(001)26 and Ag(110)27-29 surfaces, respectively. In 2010, Lalmi et al. reported epitaxial growth of silicene on Ag(111) substrate and observed a (2 3 ×2 3 )R30° superstructure.1 However, the reported Si-Si bond length was only 0.19±0.01 nm, substantially shorter than the Si-Si bond lengths (0.22～0.24 nm) from previous theoretical prediction10 and experimental observation in silicon nanoribbons26-27. Recently, several experimental groups repeated the epitaxial growth of silicene on Ag(111) surface with reasonable average Si-Si distances of 0.22±0.01 nm.2-5, 7 Various superstructure, such as (4×4), ( 13 × 13 )R13.9°, ( 7


2

Page 3 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


× 7 )R19.1°, (2 3 ×2 3 )R30° with respect to Ag(111) were observed. Our first-principles study shows excellent stability of silicene on Ag(111) surface due to the passivation effect by Ag and low local energy difference of silicon adatoms on different sites of Ag(111) surface.30 Meanwhile, Yamada-Takamura et al. successfully synthesized silicene on zirconium diboride thin films grown on Si wafers via epitaxial growth.6 Very recently, silicene has been successfully fabricated on Ir(111) surface by directly depositing silicon on the Ir(111) surface and annealing the sample at 670 K.8 The successful synthesis of silicene ribbons and sheets implies promising applications in nanoscale materials and devices. In the graphene-based field effect transistors (FETs), the graphene sheets are placed on insulator substrates (such as SiO2, SiC, h-BN)31-39, providing a mechanical support and the precondition for applying gate voltage. However, both the electronic structures and the carrier mobility of graphene are greatly influenced by h-BN, SiC and SiO2 substrates.38-49 For example, a small gap of 53 meV was induced in graphene when it was put on a h-BN substrate due to break of equivalence of two sublattices in graphene.40 The linear dispersing π bands of pristine graphene were destroyed by SiC substrate.46-47, 49 However, after hydrogen treatment of the SiC substrates, the graphene-type electronic features were recovered.49 Similar to graphene, the effect of inert substrates on the electronic and conductive properties of silicene is also an important issue for the practical applications of silicene in microelectronic devices. Recently, Houssa et al. proposed that a silicene flake could preserve the semimetallic behavior when it is embedded into ultrathin AlN layers.50 However, as far as we know, there was no report for silicene on insulating inert substrates yet. In this paper, we have systematically explored the electronic structure of silicene on the top of different insulating substrates using ab initio calculations, assuming that the pre-prepared silicene sheet (synthesized on other substrate like Ag(111) and zirconium diboride) can be transferred to the insulating substrates. We found


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 25

that the Dirac cone of silicene is nearly preserved on the h-BN monolayer and hydrogenated Siterminated SiC(0001) surface (Si-SiC). However, the silicene on the hydrogenated C-terminated SiC(0001) surface (C-SiC) becomes metallic, providing an efficient way of tuning the electronic properties of silicene.

II. Computational methods All calculations were carried out using the Vienna Ab initio Simulation Package (VASP) based on density functional theory (DFT).51 The electron-ion interactions were represented by the projector augmented wave (PAW) potentials.52 To treat exchange-correlation interaction of electrons, we chose the Perdew-Burke-Ernzerhof (PBE) functional within the generalizedgradient approximation (GGA).53 In order to properly take into account the long-range van der Waals (vdW) interactions in the layered structures, the DFT-D2 method54-55 was used throughout all the calculations. A kinetic energy cutoff of 400 eV for the planewave basis and a convergence criterion of 10-5 eV for the total energies were carefully tested and adopted in all calculations. Here we considered two substrates, i.e., h-BN monolayer and hydrogenated

SiC(0001)

surface, both of which have been frequently used to study the substrate effect for graphene.40, 46-49 These substrates were chosen also because that they are insulators.56-57 There are two types of configurations for H-terminated SiC(0001) surface, namely, Si-SiC (Figure 1b) and C-SiC (Figure 1c), depending on the upper surface contacting the silicene sheet. First, we carefully optimized the two-dimensional (2D) primitive cells of silicene and h-BN monolayer as well as bulk SiC solid. Our DFT calculations yield a lattice parameter of 3.848 Å for silicene and a Si−Si bond length of 2.27 Å, consistent with previous theoretical results (lattice parameter is 3.83 Å9, 3.93 Å50 or 3.901 Å58, Si-Si bond length is 2.25 Å9 or 2.26 Å50). The (0001) surface of SiC was modeled by three-layer slab with the bottom layer fixed to mimic


4

Page 5 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


semi-infinite solid, and both sides of the SiC(0001) slab model are hydrogenated. Without hydrogen passivation, the silicene may form direct covalent bonds with the bare SiC(0001) surface, which may destroy the π bands of silicene, similar to that in graphene/SiC system.46-49

Table I. Detailed structural information for various silicene on substrate systems (Figure 1): periodicity, number of atoms, and lattice constants of silicone and substrate supercells (aSi and asub), mismatch ∆, range of Si-Si bond lengths for silicene on substrates (lSi-Si). configuration

Silicene

aSi (Å)

(4 × 4), Silicene/BN

substrate

15.392

lSi-Si (Å)

15.078

2.04

2.272~2.279

15.380

0.08

2.272~2.275

15.380

0.08

2.271~2.278

72 atoms

(4 × 4),

(5 × 5), 15.392

32 atoms

200 atoms

(4 × 4), Silicene/C-SiC

∆ (%)

(6 × 6),

32 atoms

Silicene/Si-SiC

asub (Å)

(5 × 5), 15.392

32 atoms

200 atoms

A (4×4) supercell for silicene, a (6×6) supercell for h-BN monolayer, and a (5×5) supercell for SiC(0001) slab were used to build coperiodic lattices30. Here we slightly expanded the substrate lattice to fit the silicene lattice. The small lattice mismatches (∆) between silicene and substrates (i.e., 2.08% for h-BN and 0.08% for SiC(0001) is defined as: ∆=

1

a

a −a Si

sub

,

(1)

Si

where aSi and asub are the lattice parameters of the silicene supercell and substrate supercell, respectively. Note that the current supercell models of co-periodic lattices were built by


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 25

considering the computational cost and lattice mismatch. In reality, there should be no mismatch if the supercell is big enough. Detailed structural information for various silicene on substrate systems are shown in Table I. The atomic coordinates for all supercell structures with inclusion of vacuum space of more than 15 Å were fully relaxed. The k points generated by the Monkhorst-Pack scheme are chosen to be 3×3×1 in all geometry optimization and 6×6×1 for computations of electronic properties, such as electron density of states (DOS) and work function, based on the equilibrium geometries. To estimate the charge transfer from C-SiC to silicene, Bader analysis59-61 was preformed by setting LEACHG=.TRUE. in the INCAR file. A fine FFT-grids (NGXF=200, NGYF=200, NGZF=420) was used to accurately produce the total core charge, which was carefully tested to be converged to that with more precise grids.

Figure 1. Side (upper) and top (lower) views of the atomic configurations of (a) silicene/BN; (b) silicene/Si-SiC; (c) silicene/C-SiC hybrid systems.


6

Page 7 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. Cohesive energy versus the height of silicene from the substrate surface.

III. Results and discussions A. Atomic structures and interaction energies. The atomic structures for various silicene/substrate hybrid systems are illustrated in Figure 1. After relaxation, the silicene sheets stay stably on the substrates and the equilibrium silicene-substrate distances (Figure 1) are 3.32 Å, 2.73 Å and 2.71 Å for h-BN, Si-SiC and C-SiC, respectively, which are comparable to that for graphene/BN system (3.22 Å).40 The buckled height of supported silicene slightly changes with regard to the free standing silicene and depends on the relative position between silicene and the substrates (i.e. 0.47 Å for free standing silicene, 0.43~0.51 Å for silicene/BN, 0.48~0.50 Å for silicene/Si-SiC, and 0.48~0.50 Å for silicene/C-SiC, respectively). Hence, these substrates can provide effective mechanical supports for silicene without disturbing the geometry of silicene. The interaction strength between silicene and a substrate can be characterized by the cohesive energy Ec, defined as:


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Ec =

1 ( E sub + E Si − E t ) N

Page 8 of 25

(2),

where Esub is the energy of substrate, ESi is the energy of silicene, Et is the total energy of silicene/substrate system, N is the number of Si atoms in silicene supercell. The cohesive energies are 0.089 eV, 0.067 eV and 0.084 eV per Si atom for the configuration a (h-BN), b (SiSiC), and c (C-SiC) in Figure 1, respectively. Hence the interactions between silicene and those substrates are relatively weak and can be considered as van der Waals type. The cohesive energies of the three configurations are shown as functions of the distance between silicene and the substrates in Figure 2. For all the three configurations, the energy landscape seems to be very flat around the energy minimum.

B. Electron densities of states. As shown in Figure 3a, silicene is a zero-gap semimetal that is consistent with previous results.9, 11-13 BN monolayer is an insulator with a theoretical band gap of 4.44 eV (Figure 3d), which is underestimated by 26.8% with respect to the experimental value (6.07 eV).56 For the three-layered slab models of Si-SiC and C-SiC, the theoretical band gaps are 2.42 eV (Figure 3e) and 2.51 eV (Figure 3e), respectively, compared to the experimental band gap of bulk SiC of 3.023 eV.57 Thus, all these three substrates are insulators with sufficiently wide band gaps for practical applications in microelectronic devices.


8

Page 9 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. DOS of (a)~(c) silicene; (d) BN sheet; (e) Si-SiC substrate; (f) C-SiC substrate; (g) silicene/BN; (h) silicene/Si-SiC; (i) silicene/C-SiC.

As shown in Figure 3, the characteristic of DOS near Fermi level for silicene/BN and silicene/Si-SiC hybrid systems are identical to that of free-standing silicene (see Figure 3a,b,g,h), implying the h-BN and Si-SiC substrates have no influence on the electronic properties of silicene. Suprisingly, the silicene becomes metallic when it is placed on C-SiC substrate, which is clearly shown in Figure 3i. To further understand the DOS of silicene/substrate systems, some characteristic peaks are marked in Figure 3. The p1 and p2 peaks in Figure 3g and 3h correspond to the p1 and p2 peaks in Figure 3a and 3b, while the p2 and p3 peaks in Figure 3i correspond to the p2 and p3 peaks in Figure 3c and 3f, respectively. Therefore, the DOS of silicene/substrate


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 25

hybrid systems are simply the superimposition of that of silicene and the substrates with a small energy shift for the silicene/BN (~0.45 eV) and silicene/Si-SiC (~0.29 eV) systems, but a large energy shift for the silicene/C-SiC system (~1.29 eV). We attribute the superimposition of DOS to the weak vdW interactions between silicene and the substrates, similar to the previous results for nanocable formed by conducting copper nanowire encapsulated in insulating BN nanotube.62 The large energy shift of electronic states in silicene/C-SiC hybrid system will be explained latter.

Figure 4. Electron band structures of (a) silicene, (b) silicene/BN, (c) silicene/Si-SiC, (d) silicene/C-SiC. The red lines highlight the π-bands of silicene in different configurations.

C. Band structures, partial charge densities and work functions. The electron band structures shown in Figure 4b and 4c confirm the preservation of the Dirac cone of pristine silicene when a silicene sheet is supported on BN and Si-SiC substrates. Careful examination of


10

Page 11 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the detailed band structure at the K-point of Brillioun zone of silicene on substrates revealed that a tiny gap of the magnitude of meV is opened, i.e., 4 meV on BN and 3 meV on Si-SiC. From the dispersion of characteristic π-bands near Fermi level (highlighted by red lines in Figure 4), the Fermi velocity of carriers is estimated to be vF~106 m/s for both free-standing and BN or Si-SiC supported silicene using the following linear fitting relationship:

vF ≈

1 dE ⋅ h dk

(3).

The estimated Fermi velocity of suspended silicene agrees well with previous data.10 The invariability of Fermi velocity further illustrates that the h-BN and Si-SiC substrates have no influence on the electronic and transport properties of silicene. Our present results are in contrast to previous finding for graphene on h-BN, in which a gap of 53 meV is induced.40 For silicene/BN and silicene/Si-SiC systems, the characteristic electronic properties of silicene which result from the linear dispersion at Fermi level (as evidence by the presence of Dirac cone) are almost preserved. Thus, BN monolayer and Si-SiC can serve as effective mechanical supports for the silicene without disturbing its electronic properties, which is essential for potential applications of silicene in microelectronic devices. On the contrary, for the silicene/C-SiC system, the silicene becomes metallic, which is clearly shown in Figure 4d, where the π-bands of silicene are depicted in red lines. The upper segment of the Dirac cone is well preserved, while the lower one is mixed up with the valence bands of the substrate. Nevertheless, the destruction of the pristine Dirac cone is obvious, implying the metallic identity of silicene, similar to the previous findings for bilayer graphene/Si-SiC system.46-47 In previous theoretically studies,9-10 it was found that the electronic properties of silicene nanoribbons rely on the width and geometry. For example, silicene armchair nanoribbon is


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 25

nonmagnetic semiconductor with band gap that increases with decreasing width; out-of-plane (2×1) reconstruction geometry for zigzag nanoribbon has a nonmagnetic, metallic ground state.9 Since the silicene-substrate interaction is rather weak, the electronic properties of substratesupported silicene nanoribbons are expected to resemble those of free-standing ones, providing more opputunity of band engineering.

Figure 5. Partial charge densities for the π-bands near Fermi level: (a) and (d) for silicene/BN, (b) and (e) for silicene/Si-SiC, (c) and (f) for silicene/C-SiC. (a)~(c) denote partial charge densities in the energy range of EF~EF+0.2 eV. (d)~(f) represent the partial charge densities in the energy range of EF~EF−0.2 eV.


12

Page 13 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


As displayed in Figure 5, the partial charge density for π bands in the energy ranges of EF~EF+0.2 eV and EF~EF−0.2 eV for silicene/BN and silicene/Si-SiC systems concentrates on the silicene sheet (Figure 5a,b,d,e), further indicating that the substrates have no noticeable influence on the pristine π bands. However, as for the silicene/C-SiC system, the partial charge density in the energy range of EF~EF+0.2 eV concentrates on the silicene sheet (see Figure 5e); but the πbands in the energy range of EF~EF−0.2 eV widely distribute in silicene and C-SiC substrate (Figure 5f), suggesting that the Fermi level has already entered the vicinity of the valence band maximum (VBM) of the C-SiC slab. Clearly, the analysis of partial charge densities agrees with the pictures of DOS and band structures described above. To explain the effects of different substrates on the electronic properties of silicene, we calculated the work functions (WFs) of silicene and the three substrates. The computed WFs are 4.59 eV, 5.86 eV, 5.54 eV and 4.49 eV for individual silicene, BN, Si-SiC, and C-SiC systems, respectively. By setting the vacuum energy as zero, the position of VBM can be located as the negative value of WF. The VBM and conduction band minima (CBM) of silicene, h-BN, Si-SiC, and C-SiC substrates with respect to the vacuum level are depicted in Figure 6. Since the pristine silicene is a semimetal, its CBM and VBM overlap exactly. The CBM (or VBM) of silicene is lower than the VBM of C-SiC substrate by 0.1 eV (Figrue 6). Due to the interaction between silicene and the C-SiC substrate, some new electron strates in energy range between the VBM of C-SiC and silicene arise, lowering the total energy of the hybrid system. After the combination of silicene and C-SiC substrate, the Fermi energy of the hybrid system will stay between the VBM of C-SiC and the VBM of silicene (Figure 7b). Hence, the Dirac cone of the pristine silicene is submerged under the Fermi level (Figure 7c). Consequently, the silicene in the hybrid system shows metallic behavior. The decline of the conical point of the Dirac cone with respect to the Fermi level gives the reason for the large energy shift shown in Figure 3i.


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 25

According to the Bader analysis, there is no noticeable charge transfer from C-SiC to silicene. But the C-SiC substrate can significantly affect the electron structure of silicene, as if there is an ‘electron state transfer’ from C-SiC substrate to silicene (see Figure 7a,b). In sharp contrast, for the silicene/BN and silicene/Si-SiC systems, the CBM of silicene locates in the gap region of BN and Si-SiC. The CBM of silicene is higher than the VBM of the BN and Si-SiC by 1.3 eV and 0.9 eV, respectively, and lower than the CBM of the BN and Si-SiC by 3.2 eV and 1.5 eV, respectively. The electrons states ranging between the VBM of Si-SiC (or BN) and the CBM of silicene are forbidden. Consequently, the conical point of the Dirac cone in silicene is basically retained at the Fermi level (with openning of tiny band gaps of 4meV on BN and 3 meV on SiSiC).

Figure 6. CBM and VBM of BN monolayer, Si-SiC substrate, silicene, and C-SiC substrate with respect to the vacuum level (set as zero energy). The values of CBM and VBM of silicene are exactly identical.


14

Page 15 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. Schematic for the formation of metallic property for silicene/C-SiC hybrid system. Blue areas present the energy states occupied by electron. (a) the states occupied by electron in isolated C-SiC and silicene respectively; (b) the states occupied by electron in the silicene/C-SiC hybrid system; (c) the states occupied by electron of silicene in the silicene/C-SiC hybrid system.

IV. Conclusions In summary, our first-principles calculations show that the insulating substrates, including hBN monolayer, Si-SiC and C-SiC, can afford effective mechanical support for silicene with vdW interaction and equilibrium silicene-substrate distances of about 3 Å. The Dirac cone of silicene is nearly retained on BN monolayer and Si-SiC surface, which provides a way to practically utilize the outstanding electronic properties of silicene based on the linear dispersing π bands. Meanwhile, the silicene becomes metallic when it is placed on C-SiC, due to the decline of the Fermi level. Silicene shows distinct electronic properties on various substrates, allowing engineering of the electronic band structure via substrate. Furthermore, we demonstrate that the work function of the substrate determines the coupling of electronic states between silicene and


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 25

substrate. These theoretical results are doubtless helpful to understand the substrate effect on silicene and for the practical design of silicene-based devices in future microelectronic

AUTHOR INFORMATION Corresponding Author *

Email: [email protected]

ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (11134005), the Fundamental Research Funds for the Central Universities of China (No. DUT12YQ05), and the Program for SCI@guoshi of CETV.

REFERENCES (1) Lalmi, B.; Oughaddou, H.; Enriquez, H.; Kara, A.; Vizzini, S.; Ealet, B.; Aufray, B. Epitaxial Growth of A Silicene Sheet. Appl. Phys. Lett. 2010, 97 (22), 223109. (2) 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 TwoDimensional Silicon. Phys. Rev. Lett. 2012, 108 (15), 155501. (3) Feng, B.; Ding, Z.; Meng, S.; Yao, Y.; He, X.; Cheng, P.; Chen, L.; Wu, K. Evidence of Silicene in Honeycomb Structures of Silicon on Ag(111). Nano Lett. 2012, 12 (7), 3507-3511. (4) Lin, C. -L.; Arafune, R.; Kawahara, K.; Tsukahara, N.; Minamitani, E.; Kim, Y.; Takagi, N.; Kawai, M. Structure of Silicene Grown on Ag(111). Appl. Phys. Express 2012, 5 (4), 045802.


16

Page 17 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(5) Jamgotchian, H.; Colignon, Y.; Hamzaoui, N.; Ealet, B.; Hoarau, J. Y.; Aufray, B.; Biberian, J. P. Growth of Silicene Layers on Ag(111): Unexpected Effect of The Substrate Temperature. J. Phys.: Condens. Matter 2012, 24 (17), 172001. (6) Fleurence, A.; Friedlein, R.; Ozaki, T.; Kawai, H.; Wang, Y.; Yamada-Takamura, Y. Experimental Evidence for Epitaxial Silicene on Diboride Thin Films. Phys. Rev. Lett. 2012, 108 (24), 245501. (7) Chiappe, D.; Grazianetti, C.; Tallarida, G.; Fanciulli, M.; Molle, A. Local Electronic Properties of Corrugated Silicene Phases. Adv. Mater. 2012, 24 (37), 5088-5093. (8) Meng, L.; Wang, Y.; Zhang, L.; Du, S.; Wu, R.; Li, L.; Zhang, Y.; Li, G.; Zhou, H.; Hofer, W. A. et al. Buckled Silicene Formation on Ir(111). Nano Lett. 2013, 13, 685−690. (9) Cahangirov, S.; Topsakal, M.; Aktürk, E.; Şahin, H.; Ciraci, S. Two- and One-Dimensional Honeycomb Structures of Silicon and Germanium. Phys. Rev. Lett. 2009, 102 (23), 236804. (10) Ding, Y.; Ni, J. Electronic Structures of Silicon Nanoribbons. Appl. Phys. Lett. 2009, 95 (8), 083115. (11) Pan, L.; Liu, H. J.; Wen, Y. W.; Tan, X. J.; Lv, H. Y.; Shi, J.; Tang, X. F. First-Principles Study of Monolayer and Bilayer Honeycomb Structures of Group-IV Elements and Their Binary Compounds. Phys. Lett. A 2011, 375 (3), 614-619. (12) Şahin, H.; Cahangirov, S.; Topsakal, M.; Bekaroglu, E.; Akturk, E.; Senger, R. T.; Ciraci, S. Monolayer Honeycomb Structures of Group-IV Elements and III-V Binary Compounds: FirstPrinciples Calculations. Phys. Rev. B 2009, 80 (15), 155453.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 25

(13) 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 (5), 056804. (14) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306 (5696), 666-669. (15) Berger, C.; Song, Z.; Li, X.; Wu, X.; Brown, N.; Naud, C.; Mayou, D.; Li, T.; Hass, J.; Marchenkov, A. N.; Conrad, E. H.; First, P. N.; de Heer, W. A. Electronic Confinement and Coherence in Patterned Epitaxial Graphene. Science 2006, 312 (5777), 1191-1196. (16) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Katsnelson, M. I.; Grigorieva, I. V.; Dubonos, S. V.; Firsov, A. A. Two-dimensional Gas of Massless Dirac Fermions in Graphene. Nature 2005, 438 (7065), 197-200. (17) Liu, C. -C.; Jiang, H.; Yao, Y. Low-Energy Effective Hamiltonian Involving Spin-orbit Coupling in Silicene and Two-Dimensional Germanium and Tin. Phys. Rev. B 2011, 84 (19), 195430. (18) Knox, K. R.; Wang, S.; Morgante, A.; Cvetko, D.; Locatelli, A.; Mentes, T. O.; Niño, M. A.; Kim, P.; Osgood, R. M., Jr. Spectromicroscopy of Single and Multilayer Graphene Supported by A Weakly Interacting Substrate. Phys. Rev. B 2008, 78 (20), 201408. (19) Castro Neto, A. H.; Guinea, F.; Peres, N. M. R.; Novoselov, K. S.; Geim, A. K. The Electronic Properties of Graphene. Rev. Mod. Phys. 2009, 81 (1), 109-162.


18

Page 19 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(20) Liu, C. -C.; Feng, W.; Yao, Y. Quantum Spin Hall Effect in Silicene and Two-Dimensional Germanium. Phys. Rev. Lett. 2011, 107 (7), 076802. (21) Osborn, T. H.; Farajian, A. A.; Pupysheva, O. V.; Aga, R. S.; Lew Yan Voon, L. C. Ab Initio Simulations of Silicene Hydrogenation. Chem. Phys. Lett. 2011, 511 (1–3), 101-105. (22) Houssa, M.; Scalise, E.; Sankaran, K.; Pourtois, G.; Afanas'ev, V. V.; Stesmans, A. Electronic Properties of Hydrogenated Silicene and Germanene. Appl. Phys. Lett. 2011, 98 (22), 223107. (23) Lew Yan Voon, L. C.; Sandberg, E.; Aga, R. S.; Farajian, A. A. Hydrogen Compounds of Group-IV Nanosheets. Appl. Phys. Lett. 2010, 97 (16), 163114. (24) Ding, Y.; Wang, Y. Electronic Structures of Silicene Fluoride and Hydride. Appl. Phys. Lett. 2012, 100 (8), 083102. (25) Drummond, N.; Zólyomi, V.; Fal’ko, V. Electrically Tunable Band Gap in Silicene. Phys. Rev. B 2012, 85 (7), 075423. (26) Léandri, C.; Oughaddou, H.; Aufray, B.; Gay, J. M.; Le Lay, G.; Ranguis, A.; Garreau, Y. Growth of Si Nanostructures on Ag(001). Surf. Sci. 2007, 601 (1), 262-267. (27) Aufray, B.; Kara, A.; Vizzini, S. b.; Oughaddou, H.; Léandri, C.; Ealet, B.; Le Lay, G. Graphene-like Silicon Nanoribbons on Ag(110): A Possible Formation of Silicene. Appl. Phys. Lett. 2010, 96 (18), 183102.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 25

(28) De Padova, P.; Quaresima, C.; Ottaviani, C.; Sheverdyaeva, P. M.; Moras, P.; Carbone, C.; Topwal, D.; Olivieri, B.; Kara, A.; Oughaddou, H. et al. Evidence of Graphene-like Electronic Signature in Silicene Nanoribbons. Appl. Phys. Lett. 2010, 96 (26), 261905. (29) De Padova, P.; Quaresima, C.; Olivieri, B.; Perfetti, P.; Le Lay, G. Strong Resistance of Silicene Nanoribbons Towards Oxidation. J. Phys. D: Appl. Phys. 2011, 44 (31), 312001. (30) Gao, J.; Zhao, J. Initial Geometries, Interaction Mechanism and High Stability of Silicene on Ag(111) Surface. Sci. Rep. 2012, 2, 861. (31) Lin, Y.-M.; Chiu, H. -Y.; Jenkins, K. A.; Farmer, D. B.; Avouris, P.; Valdes-Garcia, A. Dual-Gate Graphene FETs With fT of 50 GHz. IEEE Electr. Device L. 2010, 31 (1), 68-70. (32) Lemme, M. C.; Echtermeyer, T. J.; Baus, M.; Kurz, H. A Graphene Field-Effect Device. IEEE Electr. Device L. 2007, 28 (4), 282-284. (33) Lin, Y.-M.; Jenkins, K. A.; Valdes-Garcia, A.; Small, J. P.; Farmer, D. B.; Avouris, P. Operation of Graphene Transistors at Gigahertz Frequencies. Nano Lett. 2008, 9 (1), 422-426. (34) Farmer, D. B.; Chiu, H.-Y.; Lin, Y.-M.; Jenkins, K. A.; Xia, F.; Avouris, P. Utilization of A Buffered Dielectric to Achieve High Field-Effect Carrier Mobility in Graphene Transistors. Nano Lett. 2009, 9 (12), 4474-4478. (35) Lin, Y.-M.; Dimitrakopoulos, C.; Jenkins, K. A.; Farmer, D. B.; Chiu, H.-Y.; Grill, A.; Avouris, P. 100-GHz Transistors from Wafer-Scale Epitaxial Graphene. Science 2010, 327 (5966), 662.


20

Page 21 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(36) Moon, J. S.; Curtis, D.; Hu, M.; Wong, D.; McGuire, C.; Campbell, P. M.; Jernigan, G.; Tedesco, J. L.; VanMil, B.; Myers-Ward, R. et al. Epitaxial-Graphene RF Field-Effect Transistors on Si-Face 6H-SiC Substrates. IEEE Electr. Device L. 2009, 30 (6), 650-652. (37) Kedzierski, J.; Pei-Lan, H.; Healey, P.; Wyatt, P. W.; Keast, C. L.; Sprinkle, M.; Berger, C.; de Heer, W. A. Epitaxial Graphene Transistors on SiC Substrates. IEEE T. Electron Dev. 2008, 55 (8), 2078-2085. (38) Gannett, W.; Regan, W.; Watanabe, K.; Taniguchi, T.; Crommie, M. F.; Zettl, A. Boron Nitride Substrates for High Mobility Chemical Vapor Deposited Graphene. Appl. Phys. Lett. 2011, 98 (24), 242105. (39) Dean, C. R.; Young, A. F.; MericI; LeeC; WangL; SorgenfreiS; WatanabeK; TaniguchiT; KimP; Shepard, K. L. et al. Boron Nitride Substrates for High-Quality Graphene Electronics. Nat. Nanotechnol. 2010, 5 (10), 722-726. (40) Giovannetti, G.; Khomyakov, P.; Brocks, G.; Kelly, P.; van den Brink, J. Substrate-Induced Band Gap in Graphene on Hexagonal Boron Nitride: Ab Initio Density Functional Calculations. Phys. Rev. B 2007, 76 (7), 073103. (41) Yelgel, C.; Srivastava, G. P. Ab Initio Studies of Electronic and Optical Properties of Graphene and Graphene–BN Interface. Appl. Surf. Sci. 2012, 258 (21), 8338-8342. (42) Sławińska, J.; Zasada, I.; Klusek, Z. Energy Gap Tuning in Graphene on Hexagonal Boron Nitride Bilayer System. Phys. Rev. B 2010, 81 (15), 155433.


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 25

(43) Zhong, X.; Yap, Y.; Pandey, R.; Karna, S. First-Principles Study of Strain-Induced Modulation of Energy Gaps of Graphene/BN and BN Bilayers. Phys. Rev. B 2011, 83 (19), 193403. (44) Chen, J. H.; Jang, C.; Xiao, S.; Ishigami, M.; Fuhrer, M. S. Intrinsic and Extrinsic Performance Limits of Graphene Devices on SiO2. Nat. Nanotechnol. 2008, 3 (4), 206-209. (45) Hwang, C.; Siegel, D. A.; Mo, S.-K.; Regan, W.; Ismach, A.; Zhang, Y.; Zettl, A.; Lanzara, A. Fermi Velocity Engineering in Graphene by Substrate Modification. Sci. Rep. 2012, 2, 590. (46) Mattausch, A.; Pankratov, O. Ab Initio Study of Graphene on SiC. Phys. Rev. Lett. 2007, 99 (7), 076802. (47) Varchon, F.; Feng, R.; Hass, J.; Li, X.; Nguyen, B.; Naud, C.; Mallet, P.; Veuillen, J. Y.; Berger, C.; Conrad, E. et al. Electronic Structure of Epitaxial Graphene Layers on SiC: Effect of the Substrate. Phys. Rev. Lett. 2007, 99 (12), 126805. (48) Magaud, L.; Hiebel, F.; Varchon, F.; Mallet, P.; Veuillen, J. Y. Graphene on The C_

Terminated SiC (0001) Surface: An Ab Initio Study. Phys. Rev. B 2009, 79 (16), 161405.

(49) Riedl, C.; Coletti, C.; Iwasaki, T.; Zakharov, A. A.; Starke, U. Quasi-Free-Standing Epitaxial Graphene on SiC Obtained by Hydrogen Intercalation. Phys. Rev. Lett. 2009, 103 (24), 246804. (50) Houssa, M.; Pourtois, G.; Afanas’ev, V. V.; Stesmans, A. Can Silicon Behave Like Graphene? A First-Principles Study. Appl. Phys. Lett. 2010, 97 (11), 112106.


22

Page 23 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(51) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using A Plane-Wave Basis Set. Phys. Rev. B 1996, 54 (16), 11169-11186. (52) Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to The Projector Augmented-Wave Method. Phys. Rev. B 1999, 59 (3), 1758-1775. (53) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77 (18), 3865-3868. (54) Grimme, S. Semiempirical GGA-Type Density Functional Constructed with A Long-Range Dispersion Correction. J. Comput. Chem. 2006, 27 (15), 1787-1799. (55) Bučko, T.; Hafner, J.; Lebègue, S.; Ángyán, J. G. Improved Description of The Structure of Molecular and Layered Crystals: Ab Initio DFT Calculations with van der Waals Corrections. J. Phys. Chem. A 2010, 114 (43), 11814–11824. (56) Kim, K. K.; Hsu, A.; Jia, X.; Kim, S. M.; Shi, Y.; Hofmann, M.; Nezich, D.; RodriguezNieva, J. F.; Dresselhaus, M.; Palacios, T. et al. Synthesis of Monolayer Hexagonal Boron Nitride on Cu Foil Using Chemical Vapor Deposition. Nano Lett. 2012, 12 (1), 161-166. (57) Park, Y. S. SiC Materials and Devices; Academic Press: Virginia, USA, 1998. (58) Lebègue, S.; Eriksson, O. Electronic Structure of Two-Dimensional Crystals from Ab Initio Theory. Phys. Rev. B 2009, 79 (11), 115409. (59) Henkelman, G.; Arnaldsson, A.; Jónsson, H. A fast and robust algorithm for Bader decomposition of charge density. Comput. Mater. Sci. 2006, 36 (3), 354-360.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 25

(60) Sanville, E.; Kenny, S. D.; Smith, R.; Henkelman, G. Improved grid-based algorithm for Bader charge allocation. J. Comput. Chem. 2007, 28 (5), 899-908. (61) Tang, W.; Sanville, E.; Henkelman, G. A grid-based Bader analysis algorithm without lattice bias. J. Phys.: Condens. Matter 2009, 21 (8), 084204. (62) Zhou, Z.; Zhao, J.; Chen, Z.; Gao, X.; Lu, J. P.; Schleyer, P. v. R.; Yang, C.-K. True Nanocable Assemblies with Insulating BN Nanotube Sheaths and Conducting Cu Nanowire Cores. J. Phys. Chem. B 2006, 110 (6), 2529-2532.


24

Page 25 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC


25

Silicene on Substrates - American Chemical Society

Recommend Documents