First-Principles Study of Metal Adatom Adsorption on Black

Mar 27, 2015 - Open Access ...... Orion will install emissions technology. Carbon black maker Orion Engineered Carbons will install Haldor Topsoe's SN...
0 downloads 0 Views 5MB Size
Download PDF
Article pubs.acs.org/JPCC

First-Principles Study of Metal Adatom Adsorption on Black Phosphorene Tao Hu and Jisang Hong* Department of Physics, Pukyong National University, Busan 608-737, Korea

ABSTRACT: We have investigated the structure, adsorption energy, growth mode, diffusion barrier, magnetic property, dipole moment, and work function of Li, Na, Mg, Al, Cr, Fe, Co, Ni, Mo, Pd, Pt, and Au adsorption on phosphorene using firstprinciples density-functional theory. We have found that all the adatoms favor the hollow site of hexagonal. It seems that the Mg, Cr, Mo, and Au adatoms may have three-dimensional (3D) growth mode on phosphorene substrate, whereas all other adatoms prefer two-dimensional (2D) growth mode. The metallic state is observed in Li, Na, Al, and Cr doped systems, and the Cr doped phosphorene displays magnetic state. The other eight metal doped systems still preserve semiconducting band gap. Among them, we obtained spin polarized band structures in Fe, Co, and Au doped systems with a band gap. In particular, the Fe doped phosphorene can be a potential candidate for dilute magnetic semiconductor material because no clustering problem will take place. We found a variation in dipole moment and work functions in each impurity doped layer. Both dipole moment and the shift of the Fermi level could account for the change of work function semiquantitatively.

1. INTRODUCTION Two-dimensional (2D) structure has a very small volume to surface ratio, and the surface is exposed to the exterior environment. Thus, the surface property can be manipulated by introducing capping layer, impurity doping, or defect formation.1 As a result, 2D materials display remarkable physical, chemical, mechanical, and electrical properties, not found in bulk materials. Various types of 2D materials such as graphene, 2 h-BN, 3,4 transition metal dichalcogenides (TMDs),5,6 g-C3N4,7,8 and g-C4N39,10 are receiving extensive research interest due to their unique physical properties for innovative potential device applications. Among them, the graphene has attracted extensive research interest owing to its peculiar properties such as high mobility, good conductivity, quantum hall effect, and massless Dirac fermion feature. Very recently, a new 2D material phosphorene named after its parent black phosphorus was mechanically exfoliated by scotch tape based microcleavage method.11−14 In addition, a single layer phosphorene was also obtained by plasma-assisted fabrication process. This newly emerging 2D layer structured material is now attracting research interest in physics, chemistry, and material science due to potential device applications.15 Compared with the graphene, the most striking difference is the existence of an energy band gap in the © XXXX American Chemical Society

phosphorene layer. Unlike the zero gap of graphene, the phosphorene has an intrinsic direct band gap. Indeed, the band gap of black phosphorus depends on its dimensionality. In bulk structure, the bulk black phosphorus has a gap of 0.31−0.35 eV, but this value varies with 2D geometry. In this regard, many reports reveal that the band gap in 2D phosphorene strongly depends on the number of layers12,16 and the in-layer strain.17,18 Because of this semiconducting feature, the phosphorene may be superior to the graphene for device applications in many ways. Along with this band gap, the phosphorene layer has also a peculiar geometric characteristic. Unlike many other two-dimensional layer structured materials, the atoms in a single layer black phosphorene are not residing in a flatland. Instead, they form a puckered hexagonal structure by covalence bonds. Besides, the phosphorene layer displays strongly anisotropic features in transport and optical properties along armchair and zigzag directions,16,19 and these features are not found in a graphene layer. It seems that the structural property results in the anisotropy of physical properties and Received: February 8, 2015 Revised: March 19, 2015

A

DOI: 10.1021/acs.jpcc.5b01300 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

Figure 1. (a) Illustration of top and side view of phosphorene and three adsorption sites: hollow (H), bridge (B), and on-top (T). The upper and lower sublayers of phosphorene are indicated in different colors, and the black balls represent metal adatoms. (b) Band structure of pristine phosphorene. (c) Density of states of pristine phosphorene.

2. COMPUTATIONAL DETAILS We have performed spin polarized first-principles calculation based on density functional theory with the generalized gradient approximation (GGA) of Perdew−Burke−Ernzerhof.33 The Vienna ab initio simulation package (VASP)34−37 is used. A plane-wave basis set with an energy cutoff of 500 eV is employed. All calculations are chosen to converge the total energy to 0.01 eV. Phosphorene has four P atoms arranged in orthorhombic primitive unit cell, and lattice constant of the primitive unit cell is 3.35 × 4.62 Å. A 4 × 3 orthorhombic phosphorene supercell (containing 48 P atoms) is modeled for adatom−phosphorene systems. Thus, this is equivalent to the impurity concentration of 2.08% and the corresponding supercell’s dimension is 13.40 × 13.86 Å. Because of this large lattice constant, the artificial interaction with neighboring unit cell can be ignored. We use a vacuum distance of 20 Å in the z direction. Entire calculations have been performed with a (5 × 5 × 1) k-mesh scheme. Since the impurity atom is adsorbed on one side, the hybridized system can maintain a dipole moment. Thus, the dipole correction has been considered for local electrostatic potential and total energy.

that these intriguing physical properties may lead to nextgeneration novel device applications. The study on phosphorene is a rapidly growing field. So far, various physical properties have been investigated in 2D sheets. For instance, mechanical,20 electronic,21,22 transport,11,23 and optical properties24,25 were already explored in the last year. Magnetic state of phosphorene induced by nonmagnetic atoms has been reported as well.26 In one-dimensional nanoribbon geometry, both zigzag and armchair structures have been considered.27,28 Moreover, phosphorus nanotubes have been studied as well.29 Indeed, these kinds of works have been performed in the graphene study. However, the systematic studies of metal adatom or cluster adsorption on phosphorene layer are still lacking although the studies on Li adatom30,31 and metal-phosphorene contacts32 have been reported recently. Thus, it will be of interest to explore the fundamental physics such as adsorption energy, adsorption geometry, density of states (DOS), electronic band structure, magnetic moment, dipole moment, and work function. In this work, we have considered 12 adatom impurities from alkaline metal to 5d elements. More specifically, we have considered Li, Na, Mg, Al, Cr, Fe, Co, Ni, Mo, Pd, Pt, and Au atoms on phosphorene layer.

3. RESULTS AND DISCUSSION 3.1. Geometry and Adsorption Energy. In Figure 1, we first showed a schematic illustration of adatom adsorbed on phosphorene layer, band structure, and density of states (DOS) B

DOI: 10.1021/acs.jpcc.5b01300 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

energy (Ea) and bulk cohesive energy (Ec).40 We used the experimental cohesive energy per atom of the bulk metal (Ec) from ref 41. Usually, a large value of Ea/Ec implies that a metal adatom prefers 2D growth mode on a substrate, whereas a small value indicates that a 3D island growth mode is more favorable rather than forming 2D layer on the substrate. Along with the relationship between adsorption energy and a cohesive energy, the diffusion barrier is also an important physical quantity because this value affects the metal island density and size. The island density will be higher if the diffusion barrier is larger and vice versa. We estimated this diffusion barrier under the assumption that the diffusion path between favorable sites will be through the high-symmetry direction. Thus, the diffusion barrier height became the energy difference of adsorption energies between the lowest and the next lowest adsorption energy site. Of course, it is necessary to do more accurate calculation to find complete potential surface using such as the nudged elastic band method.42 We compared the diffusion energy barrier obtained by our estimation with the only available result. It is reported that the diffusion energy barrier of Li is 0.76 eV.31 We obtained an energy barrier of 0.63 eV. Our result is well comparable with the previous work. However, the thermal stability of metal island is also a key factor for understanding the growth mode, and the difference of cohesive energy and adsorption energy (Ec − Ea) can control this thermal stability. A large value of Ec − Ea indicates that high thermal energy is required to make the impurity islands coarsening. In contrast, impurity island coarsening will take place easily for the small value of Ec − Ea even at low temperature because the impurity atom can be easily detached from a small island and move to a bigger island. Figure 2 displays the summarized results. As presented in Figure 2a, the alkali metals had Ea/Ec values larger than 1, and a similar behavior was found in both Co and Ni adsorption. For 4d and 5d elements, we still found large values in Pd and Pt although they were smaller than 1. However, relatively small values were observed in Mg, Cr, Mo, and Au adsorptions. Thus, we suggest that these four atoms (Mg, Cr, Mo, and Au) may prefer 3D island growth mode while other systems will have 2D growth mode. In particular, in the Li adsorption case, the large Ea/Ec ratio prevents from aggregation or segregation at even high concentration, and this may bring an interesting issue regarding the Li ion battery problem. As shown in Figure 2b, the diffusion barrier height strongly depended on the specific impurity atom. In most of the elements, except for Mg, the diffusion barrier on phosphorene is larger than on graphene, and in particular, we found very large diffusion barrier height in 3d transition metal atoms and Mo. Besides, the diffusion barrier for 3d transition metal adatoms was higher than that of groups I−III metals. However, the Mg adatom may have large mobility on the surface of phosphorene and large island size because of very low diffusion barrier. Figure 2c displays the energy difference of Ec and Ea. One can find that the Cr, Mo, and Au metal islands will show higher thermal stability against island coarsening. In contrast, we expect that the island coarsening for Mg, Al, Fe, and Pt will take place at lower temperature. This thermal stability is also related to the catalysis applications. To this end, it is highly desirable to have 3D nanostructure with high thermal stability. In this regard, Mo and Au doped phosphorene can be used for potential surface-supported catalysis applications. 3.2. Electronic Structure and Density of States. The electronic band structure strongly depends on the specific

of pristine layer. The phosphorene layer has a direct band gap of 1 eV, and this agrees with another result.12 Based on this pristine phosphorene layer, we doped impurity atom on three different adsorption sites, namely, hollow (H), bridge (B), and on-top (T). We calculated adsorption energy (Ea) for each site using the relation given by Ea = E P + EM − EM − P

(1)

where EM−P is the total energy of the adatom−phosphorene system, EM is the total energy of an isolated metal atom, and EP is the total energy of the pristine phosphorene layer. Table 1 Table 1. Adsorption Energy (Ea) and Vertical Height (h) of Adatoms for the Hollow (H), Bridge (B), and Top (T) Sites for the 12 Adatoms Ea

h (Å)

atoms

H

B

T

H

B

T

Li Na Mg Al Cr Fe Co Ni Mo Pd Pt Au

1.823 1.291 0.613 1.988 1.721 3.129 4.381 4.482 3.305 3.505 4.842 1.636

1.193 0.921 0.312 1.305 0.912 1.355 2.994 3.033 0.956 2.134 2.972 1.052

1.148 0.885 0.278 1.248 0.791 1.122 2.121 2.360 0.817 2.059 3.032 1.197

1.51 2.04 2.00 1.78 1.40 1.21 1.07 1.01 1.44 1.20 1.12 1.37

2.22 2.62 2.72 2.37 2.27 2.00 1.20 1.31 2.33 2.03 1.97 2.27

2.27 2.66 2.78 2.40 2.39 2.21 1.99 1.95 2.43 2.21 2.19 2.35

shows the calculated results. Besides, the vertical distance (h) from the basal plane to the adatom position is also presented. Here, we estimated the vertical distance as a difference between the height of the adatom and the average height of the three nearest P atoms. Among the three possible adsorption sites in our calculations, the hollow site (H) became the most stable adsorption position. This is consistent with a very recent study.38 Generally, the adatoms have the smallest height in the hollow site with the strongest adsorption energy, while the adatoms on the T site have the largest height with the smallest adsorption. Therefore, the general trend of a geometric configuration and adsorption energy agreed with each other. For the two alkali metal atoms Li and Na, the adsorption energies are 1.823 and 1.291 eV, respectively. In the case of Li, both adsorption energy and vertical distance were in good quantitative agreement with previous calculations.31 Within 3d transition metals, the adsorption energy became stronger and stronger with decreasing atomic radii, and the adsorption energy is generally larger than groups I−III metals, except for Cr adatom. A similar trend was found for 4d and 5d transition metals adatoms, except for adatom Au. As compared with the metal adsorption on graphene, we observed enhanced adsorption energies in most of the elements on the phosphorene layer.39,40 Experimentally, it is an important issue to understand the growth mode of metal on a specific substrate. For instance, the metal elements will have two-dimensional (2D) or threedimensional (3D) growth morphology depending on various conditions in vapor deposition growing process. Many factors can affect the growth morphology such as energetics, kinetics, and more factors. Nonetheless, we can extract useful information to understand this from the ratio of adsorption C

DOI: 10.1021/acs.jpcc.5b01300 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

polarized states appeared. In addition, both Li and Na doped systems had very similar band structures because Li and Na have only one 3s valence electron. In Al doped case, the impurity band still crossed the Fermi level, but the bandwidth was narrower than Li and Na doped cases. In Cr adsorption, we found a spin polarized band structure. In these four metallic systems, we observed a charge transfer from impurity atom to a phosphorus atom. Thus, the Fermi level of phosphorene is upshifted due to reception of charge. Consequently, these four impurities behave as donor elements. In other impurity doped systems, the semiconducting feature was still preserved although a size of the band gap depends on the impurity type. The calculated band gaps are presented in Table 2. Table 2. Properties for the Favored Adsorption Site (Hollow) for the 12 Adatoms; the Properties Listed Are the Magnetic Moment (m) per Adatom of the Adatom− Phophorene System, Band Gap in Each System, Work Function (Φ) for the Hybrid System, and Dipole Moment (DM)

Figure 2. (a) Ratio of the adsorption energy to the bulk cohesive energy of adatoms (Ea/Ec). (b) Estimated diffusion barrier energy (Eb) of metal adatoms on phosphorene substrate. (c) Energy difference (Ec − Ea) between the bulk cohesive energy and the adsorption energy.

impurity type. Interestingly, Li, Na, Al, and Cr doped systems showed metallic band structures because we found impurity bands crossing the Fermi level, and Figure 3a−d shows the calculated results. For Li, Na, and Al doped systems, no spin

atom

m (μB)

band gap (eV)

Φ (eV)

DM (Debye)

Li Na Mg Al Cr Fe Co Ni Mo Pd Pt Au

0 0 0 0 4.89 2 1 0 0 0 0 1

0 0 0.54 0 0 0.68 0.26 0.89 0.93 0.95 0.94 0.08

3.37 3.01 4.19 3.98 4.17 4.33 4.51 4.88 4.29 4.66 4.81 4.43

2.31 3.88 0.94 0.28 1.51 1.34 0.68 0.59 2.35 0.62 0.28 0.08

As shown in Table 2, the impurity adsorption tended to suppress the band gap of a pristine layer although it varied with

Figure 3. Calculated band structures of metallic adatom−phosphorene systems. (a) Li doped phosphorene. (b) Na doped phosphorene. (c) Al doped phosphorene. (d) Cr doped phosphorene. D

DOI: 10.1021/acs.jpcc.5b01300 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

Figure 4. Calculated band structures of semiconducting adatom−phosphorene systems. (a) Mg doped phosphorene. (b) Fe doped phosphorene. (c) Co doped phosphorene. (d) Ni doped phosphorene. (e) Mo doped phosphorene. (f) Pd doped phosphorene. (g) Pt doped phosphorene. (h) Au doped phosphorene.

specific impurity atom. Figure 4 shows the band structures of semiconducting systems. The spin polarized band structures appeared in Cr, Fe, Co, and Au doped systems. The first three atoms belong to typical 3d transition metal elements, and it is not a surprising result. However, we found no spin polarized state in the Ni doped case, whereas the Au doped system showed spin polarized band structure. Indeed, the magnetic moment of Ni is about 0.6 μB in bulk structure, and this rather small magnetic moment can be easily vanished due to hybridization effect with substrate material. Thus, the suppression of the magnetic moment in Ni atom can be understood. However, in general, the Au does not show a magnetic moment in a bulk system. However, interestingly, we found a magnetic moment in Au. Among the four spin polarized systems with band gap, the Fe doped system had a sizable band gap. Because of this band gap, the Fe doped

system may bring an interesting issue regarding the spintronics applications. For instance, one of the technical problems in conventional dilute magnetic semiconductors was the clustering issue. However, as displayed in Figure 2a, the ratio Ea/Ec for Fe doped phosphorene suggests that the Fe impurity may form a 2D structure. This tells that the Fe doped phosphorene can be a potential dilute magnetic system. In other magnetic systems, the band gap or the ratio Ea/Ec was rather small. Figure 5 shows the calculated density of states (DOS). Here, we only presented the DOS of magnetic systems. It is obvious that the magnetic moment stems from the 3d orbitals in Cr, Fe, and Co. However, in Au case, the 5d orbitals did not contribute to the magnetic moment because the Au had filled 5d shells. Interestingly, the spin polarization originated from the 5s orbital. In general, the 5s orbital has very broad bandwidth and does not show meaningful spin polarization in most of the E

DOI: 10.1021/acs.jpcc.5b01300 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

Figure 5. Spin polarized projected density of states of (a) Cr, (b) Fe, (c) Co, and (d) Au.

we also explored the correlation between the work function shift and the dipole moment. The most common definition of work function is given by

cases. In our Au doped phosphorene system, we found a charge transfer from P atom to Au. Thus, this resulted in high DOS peak near the Fermi level in nonmagnetic state. According to the Stoner criterion, the nonmagnetic state becomes unstable if the Fermi level is located in the high peak of DOS and then the spin polarization takes place. Consequently, this Stoner criterion can account for the magnetic moment in Au doped system. Generally, the results related to magnetic and electronic properties match well with the previous work38 in the case of the same adatoms. 3.3. Dipole Moment and Work Function. The adsorption of metal atoms on phosphorene can cause charge redistribution by means of charge transfer. However, the charge transfer is an ambiguous quantity, and it is not easy to determine quantitatively from calculations and experiments. Instead, the dipole moment is a more proper way to illustrate the charge transfer or charge redistribution. We, thus, calculated the dipole moment. The phosphorene sheet was placed in the x−y plane, and the dipole moment (DM ) along the perpendicular direction to the layer was calculated by the following equation: DM = −

∫ ρ(z)zdz + ∑ Nez i i i

Φ = Evac − E F

(3)

where Evac is the vacuum energy and EF is the Fermi energy. We extracted the vacuum energy from the electrostatic potential in the z direction. Since the phosphorene had an impurity atom only on one side, the vacuum energies of two sides will be different from each other, and this vacuum energy difference is related to the magnitude of dipole moment. Thus, a larger surface dipole moment will produce larger vacuum energy difference. We chose the vacuum energy of the side with metal atoms attached to calculate the work function. We found a work function of 5.03 eV for a pristine phosphorene layer and this was consistent with recent calculation.32 This calculated value was underestimated approximately by ∼5% as compared with the experimental result (5.3 eV).21 The work function in each case was also presented Table 2. The Li and Na created relatively larger dipole moments, and the work functions were significantly decreased in Li and Na doped systems. In transition metal doped layer, the Cr, Fe, and Mo also generated very large dipole moments, especially for Mo. A dipole moment of 2.35 D was induced by Mo. However, the change of work function by transition metals was more complex. To explore more details, we employed the expression for the work function given by

(2)

where ρ(z) is the valence electron density, z is the coordinate, Ni is the atomic number of ion i, and e is the charge of one proton. The dipole moment induced by the adsorption of metal atoms can change the work function of phosphorene. Indeed, the study of work function of material can provide very useful information for various physical and chemical device applications. So, we calculated the work function. Furthermore,

Φ = eVexchange + eVdipole − E F

(4)

where Vexchange is determined by the bulk electron density and Vdipole is the surface dipole potential that electrons must F

DOI: 10.1021/acs.jpcc.5b01300 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C overcome so that electrons can escape from the surface. By combining eqs 3 and 4, we can express the change in the work function (ΔΦ) in terms of dipole moment and the Fermi level shift. For instance, we can write in the following way ΔΦ = eΔVdipole − ΔE F

(5)

Then, ΔΦ = kDM − ΔE F

(6)

where k is a constant determined by the system property. This equation shows that both the dipole moment (DM) and the shift of the Fermi level can affect the work function. Figure 6

Figure 7. Scattered plot of the work function shift (ΔΦ) as a function of IP of metal atoms. The red dashed line is obtained from eq 7

level. Thus, the shift in ΔΦ will be larger in lower IP impurity case. As displayed in Figure 7, the phenomenological expression seemed reasonable. Overall, our results showed that the shift in work function could be explained in terms of the dipole moment and the shift of the Fermi level.

4. CONCLUSION In summary, we explored various physical properties of metal adatoms adsorption on phosphorene layer using first-principles calculations. All the adatoms considered in this study preferred the hollow site of the hexagonal structure of phosphorus. As compared with the metal adsorption on graphene, we found enhanced adsorption energies in most of the elements on phosphorene layer. Besides, the diffusion barrier was also larger on phosphorene than on graphene. The study of ratio Ea/Ec suggests that the Mg, Cr, Mo, and Au adatoms prefer 3D island growth, while the other eight adatoms may show 2D growth mode. We propose that the Cr, Mo, and Au metal islands have higher thermal stability against island coarsening. However, the island coarsening will be observed in Mg, Al, Fe, and Pt doped systems. However, it seems that the Mo and Au doped phosphorene can be used for potential surface-supported catalysis applications. The electronic band structure was sensitive to the specific impurity atom. For instance, we observed metallic band structure in Li, Na, Al, and Cr adsorption, whereas all other systems possessed semiconducting band gap. However, the spin polarized state appeared in Cr, Fe, Co, and Au doped systems. Among them, in particular, we found that the Fe doped phosphorene could be a potential dilute magnetic semiconductor material. A variation in dipole moment and work function was observed in each impurity doped layer. In metallic systems, the correlation of Fermi level shift and work function was clearly observed. However, the work functions deviated from the simple linear relationship in semiconducting systems. Nonetheless, our results show that the shift in work function can be explained in terms of the dipole moment and the shift of the Fermi level in a semiqualitative manner. Besides, we presented that the work function had a phenomenological relationship with ionization potential energy.

Figure 6. Scattered plot of the work function shift (ΔΦ) as a function of the dipole moment. The red dashed line is for the four metallic systems.

shows the calculated results. Interestingly, the metallic systems such Li, Na, Al, and Cr doped phosphorene can be well fitted by this formula. The Fermi level shift ΔEF of 0.95 eV was obtained from the extrapolation, and indeed, this was very close to the Fermi level shift found in four metallic systems. In Chan’s work,39 they also reported such a linear relation for metal adatoms on graphene. We also investigated the Fermi level shift in other eight semiconducting systems as well. However, it was system dependent so that a simple linear relationship was no longer held. Nonetheless, we observed that the magnitude of the Fermi level shift was smaller than that found in metallic systems. This implies that the work function change for four conducting systems should be above the red dashed line and we found such a trend. In addition, we also investigated the phenomenological relation with the experimental ionization potential (IP), and Figure 7 show the calculated result using the relationship ΔΦ = 0.45IP − 4.14eV

(7)

By definition, the IP is an energy required to remove an electron from the impurity−phosphorene hybrid. In ionic bonding scheme, we expect larger dipole moment for a smaller IP impurity adsorption because a charge transfer will take place relatively easily. Thus, the change in Φ will be more noticeable in a lower IP impurity adsorption. In general, the magnitude of ΔΦ shows increasing tendency as the IP decreases. In ionic bonding scheme, the charge transfer will take place relatively easier with lower IP impurity, and this will result in larger dipole moment and upshift of the Fermi level to the vacuum

■

AUTHOR INFORMATION

Notes

The authors declare no competing financial interest. G

DOI: 10.1021/acs.jpcc.5b01300 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C

■

(19) Fei, R.; Yang, L. Strain-Engineering the Anisotropic Electrical Conductance of Few-Layer Black Phosphorus. Nano Lett. 2014, 14 (5), 2884−2889. (20) Wei, Q.; Peng, X. Superior Mechanical Flexibility of Phosphorene and Few-Layer Black Phosphorus. Appl. Phys. Lett. 2014, 104 (25), 251915. (21) Takahashi, T.; Tokailin, H.; Suzuki, S.; Sagawa, T.; Shirotani, I. Electronic Band Structure of Black Phosphorus Studied by AngleResolved Ultraviolet Photoelectron Spectroscopy. J. Phys. C: Solid State Phys. 1985, 18 (4), 825. (22) Li, Y.; Yang, S.; Li, J. Modulation of the Electronic Properties of Ultrathin Black Phosphorus by Strain and Electrical Field. J. Phys. Chem. C 2014, 118, 23970−23976. (23) Das, S.; Zhang, W.; Demarteau, M.; Hoffmann, A.; Dubey, M.; Roelofs, A. Tunable Transport Gap in Phosphorene. Nano Lett. 2014, 14 (10), 5733−5739. (24) Tran, V.; Yang, L. Scaling Laws for the Band Gap and Optical Response of Phosphorene Nanoribbons. Phys. Rev. B 2014, 89 (24), 245407. (25) Low, T.; Rodin, A. S.; Carvalho, A.; Jiang, Y.; Wang, H.; Xia, F.; Castro Neto, A. H. Tunable Optical Properties of Multilayer Black Phosphorus Thin Films. Phys. Rev. B 2014, 90 (7), 075434. (26) Khan, I.; Hong, J. Manipulation of Magnetic State in Phosphorene Layer by Non-Magnetic Impurity Doping. New J. Phys. 2015, 17 (2), 023056. (27) Ramasubramaniam, A.; Muniz, A. R. Ab Initio Studies of Thermodynamic and Electronic Properties of Phosphorene Nanoribbons. Phys. Rev. B 2014, 90 (8), 085424. (28) Carvalho, A.; Rodin, A. S.; Neto, A. H. C. Phosphorene Nanoribbons. Europhys. Lett. 2014, 108 (4), 47005. (29) Guo, H.; Lu, N.; Dai, J.; Wu, X.; Zeng, X. C. Phosphorene Nanoribbons, Phosphorus Nanotubes, and van Der Waals Multilayers. J. Phys. Chem. C 2014, 118 (25), 14051−14059. (30) Li, Q.-F.; Wan, X. G.; Duan, C.-G.; Kuo, J.-L. Theoretical Prediction of Hydrogen Storage on Li-Decorated Monolayer Black Phosphorus. J. Phys. Appl. Phys. 2014, 47 (46), 465302. (31) Zhao, S.; Kang, W.; Xue, J. The Potential Application of Phosphorene as an Anode Material in Li-Ion Batteries. J. Mater. Chem. A 2014, 2 (44), 19046−19052. (32) Gong, K.; Zhang, L.; Ji, W.; Guo, H. Electrical Contacts to Monolayer Black Phosphorus: A First-Principles Investigation. Phys. Rev. B 2014, 90 (12), 125441. (33) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77 (18), 3865− 3868. (34) Kresse, G.; Hafner, J. Ab Initio Molecular Dynamics for Liquid Metals. Phys. Rev. B 1993, 47 (1), 558−561. (35) Kresse, G.; Hafner, J. Ab Initio Molecular-Dynamics Simulation of the Liquid-Metal−amorphous-Semiconductor Transition in Germanium. Phys. Rev. B 1994, 49 (20), 14251−14269. (36) Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6 (1), 15−50. (37) 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. (38) Kulish, V. V.; Malyi, O. I.; Persson, C.; Wu, P. Adsorption of Metal Adatoms on Single-Layer Phosphorene. Phys. Chem. Chem. Phys. 2014, 17 (2), 992−1000. (39) Chan, K. T.; Neaton, J. B.; Cohen, M. L. First-Principles Study of Metal Adatom Adsorption on Graphene. Phys. Rev. B 2008, 77 (23), 235430. (40) Liu, X.; Wang, C. Z.; Hupalo, M.; Lu, W. C.; Tringides, M. C.; Yao, Y. X.; Ho, K. M. Metals on Graphene: Correlation between Adatom Adsorption Behavior and Growth Morphology. Phys. Chem. Chem. Phys. 2012, 14 (25), 9157. (41) Kittel, C. Introduction to Solid State Physics, 8th ed.; Wiley: Hoboken, NJ, 2005.

ACKNOWLEDGMENTS This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 2013R1A1A2006071) and by the Supercomputing Center/Korea Institute of Science and Technology Information with supercomputing resources including technical support (KSC-2014-C3-052)

■

REFERENCES

(1) Butler, S. Z.; Hollen, S. M.; Cao, L.; Cui, Y.; Gupta, J. A.; Gutiérrez, H. R.; Heinz, T. F.; Hong, S. S.; Huang, J.; Ismach, A. F.; et al. Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene. ACS Nano 2013, 7 (4), 2898−2926. (2) 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. (3) Paine, R. T.; Narula, C. K. Synthetic Routes to Boron Nitride. Chem. Rev. 1990, 90 (1), 73−91. (4) Lin, Y.; Connell, J. W. Advances in 2D Boron Nitride Nanostructures: Nanosheets, Nanoribbons, Nanomeshes, and Hybrids with Graphene. Nanoscale 2012, 4 (22), 6908−6939. (5) Xu, M.; Liang, T.; Shi, M.; Chen, H. Graphene-Like TwoDimensional Materials. Chem. Rev. 2013, 113 (5), 3766−3798. (6) Tan, C.; Zhang, H. Two-Dimensional Transition Metal Dichalcogenide Nanosheet-Based Composites. Chem. Soc. Rev. 2014, DOI: 10.1039/C4CS00182F. (7) Zheng, Y.; Liu, J.; Liang, J.; Jaroniec, M.; Qiao, S. Z. Graphitic Carbon Nitride Materials: Controllable Synthesis and Applications in Fuel Cells and Photocatalysis. Energy Environ. Sci. 2012, 5 (5), 6717− 6731. (8) Wang, X.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen, K.; Antonietti, M. A Metal-Free Polymeric Photocatalyst for Hydrogen Production from Water under Visible Light. Nat. Mater. 2009, 8 (1), 76−80. (9) Du, A.; Sanvito, S.; Smith, S. C. First-Principles Prediction of Metal-Free Magnetism and Intrinsic Half-Metallicity in Graphitic Carbon Nitride. Phys. Rev. Lett. 2012, 108 (19), 197207. (10) Hashmi, A.; Hong, J. Metal Free Half Metallicity in 2D System: Structural and Magnetic Properties of G-C4N3 on BN. Sci. Rep. 2014, 4, 4374. (11) Li, L.; Yu, Y.; Ye, G. J.; Ge, Q.; Ou, X.; Wu, H.; Feng, D.; Chen, X. H.; Zhang, Y. Black Phosphorus Field-Effect Transistors. Nat. Nanotechnol. 2014, 9 (5), 372−377. (12) Liu, H.; Neal, A. T.; Zhu, Z.; Luo, Z.; Xu, X.; Tománek, D.; Ye, P. D. Phosphorene: An Unexplored 2D Semiconductor with a High Hole Mobility. ACS Nano 2014, 8 (4), 4033−4041. (13) Lu, W.; Nan, H.; Hong, J.; Chen, Y.; Zhu, C.; Liang, Z.; Ma, X.; Ni, Z.; Jin, C.; Zhang, Z. Plasma-Assisted Fabrication of Monolayer Phosphorene and Its Raman Characterization. Nano Res. 2014, 7 (6), 853−859. (14) Castellanos-Gomez, A.; Vicarelli, L.; Prada, E.; Island, J. O.; Narasimha-Acharya, K. L.; Blanter, S. I.; Groenendijk, D. J.; Buscema, M.; Steele, G. A.; Alvarez, J. V.; et al. Isolation and Characterization of Few-Layer Black Phosphorus. 2D Mater. 2014, 1 (2), 025001. (15) Liu, H.; Du, Y.; Deng, Y.; Ye, P. D. Semiconducting Black Phosphorus: Synthesis, Transport Properties and Electronic Applications. Chem. Soc. Rev. 2014, DOI: 10.1039/C4CS00257A. (16) Tran, V.; Soklaski, R.; Liang, Y.; Yang, L. Layer-Controlled Band Gap and Anisotropic Excitons in Few-Layer Black Phosphorus. Phys. Rev. B 2014, 89 (23), 235319. (17) Rodin, A. S.; Carvalho, A.; Castro Neto, A. H. Strain-Induced Gap Modification in Black Phosphorus. Phys. Rev. Lett. 2014, 112 (17), 176801. (18) Peng, X.; Wei, Q.; Copple, A. Strain-Engineered Direct-Indirect Band Gap Transition and Its Mechanism in Two-Dimensional Phosphorene. Phys. Rev. B 2014, 90 (8), 085402. H

DOI: 10.1021/acs.jpcc.5b01300 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C (42) Henkelman, G.; Jónsson, H. Improved Tangent Estimate in the Nudged Elastic Band Method for Finding Minimum Energy Paths and Saddle Points. J. Chem. Phys. 2000, 113 (22), 9978−9985.

I

DOI: 10.1021/acs.jpcc.5b01300 J. Phys. Chem. C XXXX, XXX, XXX−XXX