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Structural, Electronic, and Magnetic Properties of Adatom Adsorptions on Black and Blue Phosphorene: A First-Principles Study Yi Ding, and Yanli Wang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp5114152 • Publication Date (Web): 29 Apr 2015 Downloaded from http://pubs.acs.org on May 3, 2015

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The Journal of Physical Chemistry

Structural, Electronic, and Magnetic Properties of Adatom Adsorptions on Black and Blue Phosphorene: A First-principles Study Yi Ding∗,† and Yanli Wang∗,‡ Department of Physics, Hangzhou Normal University, Hangzhou, Zhejiang 310036, People’s Republic of China, and Department of Physics, Center for Optoelectronics Materials and Devices, Zhejiang Sci-Tech University, Xiasha College Park, Hangzhou, Zhejiang 310018, People’s Republic of China E-mail: [email protected](Y.Ding); [email protected](Y.Wang)

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To whom correspondence should be addressed Hangzhou Normal University ‡ Zhejiang Sci-Tech University †

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Abstract Using first-principle calculations, we investigate the adsorption characteristics of alkali, alkaline-earth, non-metallic, transition and noble metal adatoms on phosphorene. The adsorption-induced tunable electronic structures are comparatively studied on two representative structures of phosphorene, i.e. black and blue phosphorus (P) nanosheets. Both black and blue P sheets exhibit good adsorption capability to foreign atoms, on which the binding energies of adatoms are stronger than on the BN, SiC, MoS2 , graphene sheets. On the black P sheet, most adatoms prefer to adsorb on the hollow site, while for the blue P sheet, the favourite adsorption sites are elementdependent. The majority of alkali, alkaline-earth and transition metal adatoms prefer the valley site, noble metal adatoms like the hollow site, and non-metallic ones favour the bridge and top sites instead. The semiconducting behaviours of phosphorene are modified by adatoms, which can cause p-type/n-type doping or induce mid-gap states into the P sheets. Moreover, surface adsorptions effectively functionalize the phosphorene system with versatile spintronic features: N-/P-decorated blue P sheets are halfmetals, B-/Fe-decorated ones become bipolar-semiconductors, and Co-/Au-decorated blue and black P sheets turn into spin-gapless-semiconductors. Our work demonstrates that adatom adsorption is a feasible way to the chemical functionalization of phosphorene, which brings peculiar electronic and magnetic properties for potential applications in nanoelectronics and spintronics.

Keywords Phosphorus Monolayer; Chemical Functionalization; Tunable Electronic Structure; Peculiar Spintronic Feature

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Introduction Phosphorene is the recently synthesized P nanosheet, which has attracted substantial scientific attention due to its high carrier mobility comparable to graphene. 1,2 Since a medium band gap exists in phosphorene, the fabricated P-based field-effect transistors have superior performance to other nanomaterials. 1–3 The gap size depends on the layer number of phosphorene, 4,5 and theoretical studies show the monolayer and bilayer P sheets have a suitable direct band gap for solar energy applications. 6,7 Comparing to graphene, phosphorene is much softer. 8,9 Similar to silicene, which can endure a large tensile strain, 10 the phosphorene sheet would be stretched up to 20-30 % from the equilibrium state without breaking the lattice. 8,9 Moreover, the band structures of phosphorene can be effectively modified by the strain. 11–13 Under small strains, the dispersion of bottom conduction band is changed, which alters the preferred conducting direction in phosphorene. 14 While under medium strains, an anisotropic Dirac cone would appear for phosphorene, enabling one-dimensional metallic feature. 9 When large strains are applied, a semiconductor-to-metal transition arises in phosphorene. 15 It should be noticed that the basal P plane in phosphorene is not flat. 1,2 The P atoms are buckled in a pseudo honeycomb lattice, which causes several stable structural phases for phosphorene. 16 Among them, the black and blue phosphorus nanosheets, which are named after their layered bulk materials, are the most stable structures. 16,17 The black P sheet has a washboard-like buckling, while the blue P sheet corresponds to a chair-like one. 18 Due to the structural difference, the two types of phosphorene also exhibit different electronic properties. For example, the blue P sheet has a wider band gap than the black one. 17 The blue P nanoribbons are all indirect-band-gap semiconductors, and the armchair nanoribbons have larger band gaps than the zigzag ones. 19 While for black P nanoribbons, their electronic properties are prominently determined by the edge shapes and passivations. 20,21 The bare armchair black P nanoribbons are nonmagnetic semiconductors, while the bare zigzag ones are antiferromagnetic semiconductors. 22 By edge hydrogenation, the magnetism is removed 3



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and band gaps are all transformed to direct ones. Meanwhile, the zigzag black P nanoribbons become to have lager band gaps than the armchair ones. 23,24 As a two-dimensional system, the nanosheet always has a larger surface area to volume ratio than the bulk form, which enables a high chemical activity to foreign atoms. It is expected that the surface adsorption is a feasible way to the chemical functionalization of nanosheets. For example, on the graphene sheet, the adsorbed transition metal atoms can effectively induce magnetism into the Dirac-like electronic structure, 25–29 while light nonmetallic adatoms transform graphene from a semimetal to a semiconductor with diverse n-type or p-type doping features. 30 The selective introduction of spin-polarization has also been found in the transition-metal-intercalated graphite layers. 31 Similar results have been reported on silicene and germanene sheets. 32–39 The foreign atoms are much strongly adsorbed on these buckled sheets, 32 causing versatile structural, electronic, and magnetic properties. Among the transition metal adsorptions, the Co adatom is a unique case that can achieve a quantum anomalous Hall state on silicene. 40 The functionalized systems can also exhibit metallic, half-metallic, and semiconducting behaviours depending on the adatom types. 33,34,38,39 Through adsorbing small organic molecules, the band gap of silicene is opened, which can further help to enhance the adsorption of Li atom. 41 Besides that, adatom-induced tunable electronic structures have also found in other common nanosheets, such as BN, 42,43 SiC, 44 and MoS2 . 45,46 For the recently discovered phosphorene, only the adsorption of small gas molecules, i.e. CO, CO2 , NH3 , NO, and NO2 ones, has been investigated on the black P sheet so far. 47 Detailed information about the atom adsorption on phosphorene is still unknown. Therefore, in this work, we perform a comprehensive study on the adatom adsorption on phosphorene. The surface functionalization by twenty types of adatoms, including alkali, alkaline-earth, non-metallic, transition and noble metal ones, are systematically investigated on the black and blue P sheets, for which the tunable electronic and magnetic properties are revealed in detail.

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Methods The first-principles calculations are performed by the VASP code with a plane-wave basis sets of a 400 eV cutoff energy and the Perdew-Burke-Ernzerhof (PBE) projector augmented wave pseudopotentials. 48,49 The Na pv pseudopotential, which treats the p semi-core states as valence states for Na element, is used in the calculations. In order to simulate the adsorption of isolated atoms, supercells of 3×4 and 4×4 units are adopted for black and blue phosphorene, and the vacuum space between P sheets is set to be 18 ˚ A. The Monkhorst-Pack k-meshes of 3 × 3 × 1, 6 × 6 × 1, and 9 × 9 × 1 are used to sample the Brillouin-zone in the relaxation, static, and density of states (DOS) calculations. The convergence criterion for the energy between consecutive iterations is adopted to 10−4 eV. For the adatom-decorated sheet, all the atomic coordinates are fully relaxed until the maximum force on each atom is less than 0.01 eV/˚ A. The binding energy of adatoms is defined as Ead = EP sheet + Eatom − Eadsorp , where Eadsorp / EP sheet is the total energy of phosphorene with/without adatoms, Eatom is the atomic energy of adsorbate at the spin-polarized state. By this definition, a larger Ead corresponds to a more stable adsorption. We have also performed the dispersion-corrected density functional theory (DFT+D) calculations, 50 which give consistent results with PBE ones as shown in the Supporting Information. The primitive cells of black and blue phosphorene are rectangular and hexagonal lattices as shown in Fig. 1. In our calculations, the lattice constants a and b are obtained as 4.62 and 3.30 ˚ A for the black P sheet. While for the blue P sheet, they are equal as a = b = 3.28 ˚ A. In the previous theoretical studies, Wei et al. have obtained a = 4.627, b = 3.298 ˚ A8 and Fei et al. have obtained a = 4.64, b = 3.297 ˚ A for the black P one, 14 Zhu et al. have reported a = b = 3.33 ˚ A for the blue P sheet. 17 In the experiment, Liu et al. have found the a = 4.62, b = 4.35 ˚ A in the black P multilayers. 2 Our calculated lattice constants are in good accordance with these theoretical and experimental results. The space group is 53:Pmna for the black P sheet, in which P atoms are located at the 4h site with a buckling height h of 2.19 ˚ A. While for the blue P case, the corresponding space group is 164:P-3m1 and 5



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its 2d site is fully occupied by P atoms. The buckling height h in blue P sheet is 1.22 ˚ A as shown in Fig. 1(b). These obtained structural properties also agree well with previous results. 8,9,14,16,17 Since the blue P sheet is a chair-like buckled structure akin to silicene and germanene, 32–37 there are four possible high symmetry sites for the adatoms: the hollow site (H) at the center of buckled hexagon, the bridge site (B) at the midpoint of P−P bond, the top site (T) above the upper P atom, and the valley site (V) above the lower P atom. While on the black P sheet, due to the high buckled conformation, there is not enough space for the V site to accommodate the adatoms. Thus, only the adsorptions on the H, B, and T sites are considered in the calculations. It would be noted that there are two types of P−P bonds in the black P sheet. One is the horizontal P−P bond in the zigzag line, and the other is the titled one along the armchair direction. The atom, which is initially placed on the B site of titled P−P bond, is relaxed to the H site after full structural optimization. Thus, only the midpoint of horizontal P−P bond is considered, which is marked as the B site for black P sheet as shown in Fig. 1(a).

Results and discussion Alkali and alkaline-earth adatoms Firstly, we investigate the adsorptions of Li, Na, Be, and Mg atoms on phosphorene, for which the typical adsorption structures are depicted in Fig. 2. On the black P sheet, all of them prefer the H site. The binding energies Ead are 1.93 and 1.79 eV for Li and Be adatoms, and they are decreased to 1.35 and 0.66 eV for Na and Mg ones, respectively. As shown in Tab. 1, there are smaller adsorption heights (hX ) and shorter bond lengths (lX−P ) in the Li/Be adsorption than the Na/Mg case, resulting in stronger bonding between Li/Be and the P sheet. Besides that, upon the adsorption, the displacement of adjacent P atoms (δP ) is smaller in the alkali case than the alkaline-earth one. Thus, the binding energies follow the order of Ead (Li) > Ead (Be) > Ead (Na) > Ead (Mg) on the black P 6


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sheet. When adsorbed on the blue P sheet, Li, Na, Be adatoms prefer the V site, while the Mg adatom favours the H site instead as shown in Tab.2. The binding energies are Ead (Li) = 1.78 > Ead (Na) = 1.30 > Ead (Be) = 1.16 > Ead (Mg) = 0.30 eV. The sequence is similar to the black P case except that Be adsorption is less stable than the Na one on the blue P sheet. Through checking the adsorption structures, we find the Be adatom leads to a large displacement of neighbouring P atoms on the blue P, which causes a smaller Ead than the Na one. For the same adatom, the bond lengths (lX−P ) are similar for the black and blue P sheets. However, different adatoms will prefer distinct adsorption sites, which cause various distortions of P sheets. As a result, the distances between the adsorbed atoms and P sheets (hX ) are not uniform as shown in Tabs. 1 and 2. The adsorption of alkali and alkaline-earth atoms always brings charge transfer to the substrates. Figures 3(a) and (b) depict the deformation charge distribution for the Li adatom on black and blue P sheets, which are calculated as ∆ρ = ρtotal − ρP sheet − ρLiatom , where ρtotal is the total charge density for the Li-decorated phosphorene system, ρP sheet and ρLiatom are the charge densities of isolated P sheet and Li atom at the same positions as in the adsorbed system. It can be seen that there are noticeable charge accumulation between the Li and P atoms, which indicates the covalent bonding feature for the Li adsorption. Using the Bader charge analysis, 51 we find the Li adatom transfers 0.67 and 0.53 e to black and blue P sheets, respectively. Similar results are obtained for the Na, Be, and Mg adatoms, who also loss about 0.5 − 0.6 e to the P sheets as shown in Fig. 3(c). Accordingly, the electronic structure of phosphorene is modulated by the charge transfer as shown in Figs. 3 (d) and (e). Through a comparison of DOSs in Fig. 3, it can be seen that the band gaps of black and blue P sheets, which are 0.80 and 1.79 eV by the PBE calculations, are less affected by the alkali adatoms. The Li and Na adsorptions just move the Fermi level into conduction bands, inducing the n-type doping in both black and blue P sheets. While for the alkaline-earth adatoms, the Be and Mg adsorptions bring mid-gap defect states into the black P sheet, which substantially decrease the band gap to 0.18 and 0.40 eV, respectively.

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On the blue P sheet, the Be adatom still acts as a n-type dopant as shown in Fig. 3(e), while the Mg adatom brings defect states in the band gap, reducing it to 0.38 eV for the blue P sheet. In order to gain more insights into the behaviours of adsorbed systems, the absolute energies of Li s orbital and conduction band minimum (CBM) of P sheets have been calculated, for which the zero point is set to the vacuum level. The energy of free Li s orbital is -2.91 eV, while the CBM of black/blue P sheets is -4.14/-4.19 eV. Due to the higher energy of s orbital, the Li adatom will donate its electron to the conduction bands of P sheets, causing a n-type semiconducting behaviour.

Light non-metallic (B, C, N, O) adatoms Then, we investigate the adsorptions of B, C, N and O atoms on phosphorene. Comparing to the alkali and alkaline-earth ones, these light non-metallic adatoms are more strongly adsorbed on the P sheets as shown in Tabs. 1 and 2. These adatoms form complicated adsorption structures on phosphorene as shown in Fig. 4. On the black P sheet, the B adatom prefers the H site with a Ead of 3.58 eV, while C and N adatoms prefer the B site and their binding energies Ead are 5.11 and 3.49 eV, respectively. For the O adatom, it prefers the T site with the largest Ead of 5.46 eV. As shown in Fig. 4, after full relaxation, the C adatom, which is initially placed at the B site, becomes embedded into the upper P atoms with a zero buckling height. On the other hand, the C adatom stretches three neighbouring P atoms and causes a large displacement of 0.81 ˚ A for them. Different from the C adsorption, the N adatom is still located above the P surface with a buckling height A. At the bridge site, the N adsorption breaks the underlying P-P bond and form of 0.61 ˚ a P-N-P connection instead. For the O adatom, as shown in Fig. 4(d), it forms a titled P-O bond with the beneath P atom as a T’ configure. When adsorbed on the blue P sheet, B and C adatoms prefer the B site, while the N and O ones favor the T site instead. The binding energies are Ead (B) = 3.25, Ead (C) = 3.23, Ead (N) = 3.18, and Ead (O) = 5.46 eV as listed in Tab. 2. For the B adatom, it pushes one lower P atom downward and forms 8


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a BP3 tetrahedron in the blue P sheet. The downward P atom has a high coordination number, forming nematic-like bonds with nearby B and P atoms. 52 While for the C adatom, it pulls up the lower P atom and forms two P-C bonds as shown in Fig. 4(f). For the N and O adatoms, they are located on top of an upper P atom, forming one P-N and P-O bond perpendicular to the P basal plane as shown in Figs. 4(g) and (f). Figure 5 depicts the DOSs of black P sheet decorated with B, C, N, O adatoms. The B adatom leads to a spontaneous spin-polarization in the P sheet. The magnetism is mainly from the P atoms around the B adatom and the total magnetic moment is 0.95 µB . The magnetic energy, which represents the energy gain from the spin-polarization, is calculated as ∆EM = EN M − EM AG for the decorated phosphorene. The obtained ∆EM is only 1 meV for the B adsorption, which means the magnetism may be concealed by the thermal fluctuation of surroundings. Due to the electron deficiency of B adatom, the Fermi level crosses the defect state and causes a metallic behaviour. For the C adatom, an unoccupied defect state from the C 2p orbitals appears in the gap, which significantly reduces the gap to 0.26 eV. For the N adatom, it induces a noticeable peak on the top region of valence bands, moving the Fermi level downwards. Thus, the N adatom act as a p-type dopant for the black P sheet. While for the O adatom, it introduces some small peaks into the deep valence bands between −3 ∼ −2 eV as shown in Fig. 5(d). Hence the O adsorption has negligible effect on the electronic structure of black P sheet. Diverse electronic structures are also obtained in the decorated blue P sheet. As shown in Fig. 6(a), the B adatom also causes a spin-polarization in the blue P system. The magnetism is distributed around the P atoms near the BP3 region and the magnetic energy is increased to 61 meV. Several defect states are induced in the band gap. Particularly, near the Fermi level, the occupied and unoccupied states belong to different spins, indicating a bipolar magnetic semiconducting feature 53 in the blue P sheet. For the C adatom, the adsorbed system is still nonmagnetic, but the gap value is decreased to 0.76 eV due to the mid-gap states induced by the C 2p orbitals. The N adatom also brings a spin-polarized

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phenomenon in the blue P sheet. The magnetism mainly comes from the N adatom and the magnetic energy is up to 144 meV. Moreover, the N adatom induces a 100 % spin-polarized defect state at the Fermi level, which endows a half-metallic feature for the system. It would be noted that in Fig. 6 (c), there is a sharp peak at the Fermi level, which corresponds to a localized defect state in the gap. According to the Anderson Localization theory, 54 it requires to excess a critical N coverage to achieve the insulator-metal transition. The O adsorption hardly affects the electronic structure of blue P sheet as shown in Fig. 6(d), which is similar to the black P case. Previous studies show that for the O-doped graphene, the magnetism appears in the metallic sheets, not the semiconducting ones. 55–57 Here, the O-adsorbed P sheets are all semiconductors, for which there are no localized states around the Fermi level. Thus, only the nonmagnetic behaviour is obtained in them.

Period-3 (Al, Si, P, S) adatoms The Al, Si, P, S adsorptions are also investigated in the work. Comparing to the Period-2 adatoms (B, C, N, O), the adsorption structures are simpler and binding energies are lower for Al, Si, P, S adatoms. On the black P sheet, the Al, Si, P adatoms prefer the H site, while the S one like to adsorb at the T site as a titled T’ configure akin to the O case. The binding energies are Ead (Al) = 2.00, Ead (Si) = 2.52, Ead (P ) = 1.77, and Ead (S) = 3.11 eV as listed in Tab. 1. On the blue P sheet, the Al adatom prefers the V site, Si one prefers the H site, and P and S adatoms like staying at the T site. The binding energies follow the same order to the black P case, which are Ead (P ) = 1.32 < Ead (Al) = 1.60 < Ead (Si) = 2.00 < Ead (S) = 3.27 eV. Different from the Period-2 case, the Al, Si, P, S adsorptions have similar influences on the electronic properties of black and blue P sheets. The Al 3p orbitals bring a defect peak at ∼ −1.5 eV in the DOSs. Due to the smaller band gap of black P than the blue P sheet, this peak is located in the valence bands of the former, but in the gap region of the latter. The Al adatom transfers 0.43 and 0.50 e to black and blue P sheets, making both of them 10


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n-type doped. While for the Si adatom, it just introduces defect states in the gap as shown in Figs. 7(c) and (d). These mid-gap states significantly reduce the band gaps to ∼ 0 and 0.14 eV for the black and blue P sheets, respectively. The P adsorption causes a spontaneous spin-polarization with a total magnetic moment of 1µB as shown in Figs. 7(e) and (f). The magnetic energies ∆EM are 68 and 125 meV for the black and blue sheets, respectively. On the black P sheet, the P adatom brings spin-polarized defect states in the gap. Both the top valence and bottom conduction bands belong to the same spin, resulting in a halfsemiconducting feature. 58 While on the blue P sheet, there is a 100 % spin-polarized defect state at the Fermi level, rendering a half-metallic characteristic. Upon the S adsorption, the electronic properties of phosphorene are nearly unchanged as shown in Figs. 7(g) and (f). Comparing to the O adsorption, the S adatom gives more contributions in the valence bands. Especially for the blue P sheet, the S adatom brings a new defect state on the top valence band, which slightly reduces the band gap.

Transition metal (Fe - Zn) adatoms In the following, we investigate the adsorptions of 3d transition metal atoms (Fe, Co, Ni, Cu and Zn). We find the Zn atom is not suitable to functionalize the phosphorene system. On the black P sheet, it is located at the 2.39 ˚ A above the upper P atoms with a small Ead of 0.15 eV. This situation is more pronounced on the blue P sheet, where the Zn adatom is 3.25 ˚ A higher than the top P atom and has a tiny Ead of 0.04 eV. Thus, the Zn adsorption is unstable on the phosphorene surface, which can be easily perturbed and desorbed by the surroundings. On the contrary, Fe, Co, Ni, Cu adatoms are strongly adsorbed on phosphorene with large binding energies. As shown in Tab. 1, on the black P sheet, all of them prefer the H site with Ead (F e) = 2.98, Ead (Co) = 3.75, Ead (Ni) = 4.41 and Ead (Cu) = 2.15 eV. On the blue P sheet, Co and Ni adatoms are stably adsorbed on the V site, and the Cu adatom favours the H site. The adsorption structure is a little complex for the Fe adatom, which is a V’ configure optimized from the initial B site. Such a V’ configure has a lower symmetry than 11



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the V site adsorption as shown in Fig. 8. The three P neighbours around the Fe adatom are no longer equivalent. The P1 atom is 0.54 ˚ A higher than the P2 and P3 ones, and the Fe-P1 bond length (2.09 ˚ A) is shorter than those of Fe-P2 /P3 bonds (2.15 ˚ A). For the Fe adatom, the V’ site adsorption is 0.13 eV more stable than the V site one. While for the Co, Ni, Cu adatoms, the V’ configure is unstable and it would be converged to the V site after full structural relaxation. Akin to the black P case, the binding energies on the blue P sheet obey the same order as Ead (Cu) = 1.80 < Ead (F e) = 2.57 < Ead (Co) = 3.43 < Ead (Ni) = 4.24 eV. The DOSs of 3d metal-decorated black P sheet are depicted in Fig. 9. The Fe adsorption brings several defect states in the gap, which reduces the band gap to 0.22 eV. The Co adatom also induce mid-gap states in the P sheet. More importantly, the top valence and bottom conduction states belong to different spins and touch each other at the Fermi level as shown in Fig. 9(b). Thus, the Co-decorated black P sheet becomes a bipolar spin-gaplesssemiconductor. 59 For the Ni adatom, it brings defect states in the top region of valence bands, which slightly decrease the band gap. While for the Cu adatom, it acts as a ntype dopant on the black P sheet without altering the gap as shown in Fig. 9(d). The electronic properties of blue P sheet with 3d metal adatoms are displayed in Fig. 10. Due to the large band gap of pristine blue P sheet, the 3d orbitals of Fe, Co and Ni adatoms constitute several defect states in the gap. The spin-polarization occurs in the Fe case and the magnetic energy is large up to ∆EM = 569 meV. The top valence and bottom conduction bands belong to the same spin as shown in Fig. 10(a). Hence the Fe-decorated blue P sheet is a half-semiconductor. For the Co adatom, it also brings spin-polarization in the blue P sheet with ∆EM = 193 meV. Similar to the black P case, the Co-decorated blue P is a spingapless-semiconductor but without the bipolar feature. For the Ni adsorption, the P sheets are still nonmagnetic, but the band gap is reduced from 1.79 to 1.16 eV. Whereas a weak spin-polarization appears in the Cu-decorated blue P sheet. Its magnetic energy is merely 1 meV, which will be easily destroyed by the thermal fluctuation of surroundings. As shown

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in Fig. 10(d), the Cu adatom causes a n-type doping in the blue P sheet, transforming it into a metal.

Noble metal (Ag, Au, Pt) adatoms Finally, we investigate the adsorptions of Ag, Au, Pt atoms. The H site is the most favorable adsorption sites for all these adatoms on both black and blue P sheets. As shown in Tab. 1 and 2, the binding energies are only 1 ∼ 2 eV for Ag and Au adatoms, much smaller than the 3d metal ones. While for the Pt adatom, the Ead is increased up to 4.82 and 4.13 eV on the black and blue P sheets, respectively. These values are the second highest binding energies for the investigated adatoms in this work, which are just next to the O case (5.46 eV on both P sheets). It suggests phosphorene can be used as an anchorage for the Pt atoms and nanoparticles. Figure 11 depicts the DOSs of black and blue P sheets decorated with noble metal adatoms. The Ag adatom upshifts the Fermi level into the conduction bands, causing the n-type doping in the black P sheet. While on the blue P sheet, there is a weak spin-polarization with ∆EM = 5 meV for the Ag adatom, which brings a spin-gaplesssemiconducting behaviour for it. The Au adatom induces a magnetism of 1µB in both P sheets, whose ∆EM are 25 and 35 meV for the black and blue P sheets, respectively. Further calculations by the local basis set show the magnetism of Au adatoms is robust while the Ag one is not. The spin-polarized defect states are just located in the vicinity of Fermi level, causing the bipolar spin-gapless-semiconducting feature in phosphorene as shown in Figs. 11(c) and (d). For the Pt adatom, its defect states are mainly located at -0.5 eV of the DOSs. On the black P sheet, these states are deep in the valence bands, causing negligible influence on the electronic structure. While on the blue P sheet, due to the large band gap, the defect states are located in the gap, reducing the band gap to 0.98 eV as shown in Fig. 11 (f).

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Comparison to adsorptions on other nanosheets In order to measure the adsorption capability of phosphorene, Fig. 12 generalizes the binding energies of different adatoms on black and blue P sheets, which are in comparison with the previous results on graphene, 26,60,61 BN, 42 SiC, 44 MoS2 , 46 silicene, 32–34 and germanene sheets. 38,39 It can be seen that among these nanosheets, silicene and germanene sheets have the strongest binding strength to adatoms. The phosphorene sheets also have a high adsorption capability to foreign atoms, whose binding strength is next to the silicene and germanene ones. Comparing to graphene, the phosphorene sheets exhibit a better adsorption capability to metallic adatoms, while for the nonmetallic ones, the binding energies are analogous between the graphene and phosphorene cases. It would be noted that the black P sheet has a little larger binding strength to adatoms than the blue P case. Such discrepancy is attributed to the structural difference between the two types of P sheets. The black one is a high buckled structure, while the blue sheet is a low buckled one. Previous work shows the surface corrugations enhance the chemical activity to foreign atoms. 62 The more convex region will be a more energetically favored site for adatoms. 63 Thus, the binding strength of black P sheet is slightly stronger than the blue P one. Besides that, since the surface of BN, SiC, MoS2 sheets is flat, the buckled phosphorene sheets are expected to have better adsorption capability than these semiconducting two-dimensional systems. As shown in Fig. 12(a), from the previously reported data, 46 the binding energies of C, Fe, Co adatoms on the MoS2 sheet are close to the values on the blue P sheet, while for the O, Si, S, Ni, Pt adatoms, the binding strength of MoS2 sheet is much weaker than the blue P one. While compared to the black P sheet, the MoS2 always have smaller binding strength for different adatoms. Likewise, both the BN and SiC sheets have inferior adsorption capability than the phosphorene as shown in Fig. 12. Comparing to the cohesive energies (Ecoh ) of their stable phases, Fig. 12(b) shows that only the Li, Na, O, S adatoms have Ead /Ecoh > 1, the Ni adatom has Ead /Ecoh ≈ 1, while the others have Ead /Ecoh < 1. This indicates that for most adatoms, a dispersal distribution is still a challenge on phosphorene. The isolate atom 14


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adsorption on phosphorene requires a low adsorbing concentration. However, as shown in Fig. 12 (b), comparing to graphene, BN, SiC, MoS2 ones, the Ead /Ecoh are relatively larger for black and blue P sheets, suggesting the phosphorene systems have better adsorption capabilities to adatoms. We have further performed the ab initio molecular dynamics (AIMD) simulations to check the thermodynamic stabilities of adsorptions. The AIMD results (shown in Figs. S3 of Supporting Information) demonstrate that the adatoms are strongly bound to the phosphorene surface and no desorption occurs up to 500 K. In the experiments, the black P sheets have already been fabricated, 64 and the layered bulks of blue P sheets also exist in nature. 65 Similar to graphene and other nanosheets, different functionalization methods, such as evaporation-deposition processing, ion-plasma treatment, and defect engineering, could be utilized to manufacture such atom-decorated phosphorene nanosheets.

The discussions on the Na, O, Al, Co, Au adsorptions The migration barriers of these adatoms are calculated by the nudged elastic band (NEB) method. As shown in Fig. 13 (a), due to the structural anisotropy, adatoms have two types of barriers on the black P sheet. The Ebaz one corresponds to the movement along the zigzag line, while the Ebcz one is for the atom crossing the zigzag line (detailed structural informations for the initial, transition, and final states of adatoms can be found in Figs. S1 of Supporting Information). It can be seen that the Ebaz of Na, Al, Au adatoms are small, which are only 0.043, 0.102, and 0.005 eV, respectively. While their Ebcz are relatively large, which are increased to 0.350, 0.661, and 0.586 eV. For the Co and O adatoms, their Ebaz (Ebcz ) are as large as 0.645 (2.090) and 1.092 (0.700) eV, respectively. On the blue P sheet, due to the higher structural symmetry, there is only one type of barrier for the adatom moving to the neighbouring stable site. As shown in Fig. 13 (b), the Na, Al and Au adatoms have small barriers (Eb ) of 0.032, 0.073, 0.280 eV, while the Co and O ones have large Eb up to 1.332 and 1.754 eV, respectively. It is found that the magnitudes of barriers are closely 15



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related to the adsorption energies (Ead ) and adsorption heights (hX ) of adatoms. The O and Co atoms, which have higher Ead and lower hX values, are strongly bound to the P surface. Thus, the migrations of these adatoms need to overcome a higher energy barrier. On the other hand, the Na, Al, Au atoms are weakly bound on the P surface, which would move easily at the P sheets. It should be noticed that on the black P sheet, due to the alternating zigzag buckles, the movements across the P zigzag lines are hindered. Thus, the black P sheet would be a good host substrate for the growth of one-dimensional atomic metal chains. We also investigate the possible interactions between two adatoms on P sheets. As shown in Figs. S12 of Supporting Information, there is a repulsive interaction between the Na adatoms, which prefer to be separated apart from each other. For the O adatoms, the repulsion between them is short-range and it becomes negligible when the distance is longer than 3 ˚ A. With respect to Al, Co, Au ones, there are attractions between two adatoms and the dimer-like adsorption structures would be favoured. However, in some cases (Al, Au adatoms on blue P sheet and Co adatom on black P sheet), a long-separated adsorption structure is still the local minimum on phosphorene.

The formation energies of charged Au adatom For the Au adsorption, it induces a defect state in the band gaps of black and blue P sheets. Such mid-gap defect state may acquire (lose) one electron to form a q = −1 (q = 1) charged state for the Au adatom. In order to determine the stability of neutral state, the formation energies of different charged states are calculated as ∆EAu (q) = EAu−ad (q) − EP sheet − EAu−atom + q(EV BM + EF ermi ) + Ecorr (q). 66–68 Here, q is the charged state of Au adatom, which can be adopted to the values of -1, 0, and 1 e. EAu−ad (q) is the total energy of Au-adsorbed system, EP sheet and EAu−atom are the corresponding energies of P sheet and Au atom, respectively. EV BM is the energy level of valence band maximum (VBM) and EF ermi is the tunable Fermi energy within the band gap of P sheet. Ecorr (q) is the finite-size correction for a non-neutral supercell. In the calculations, the band gaps of P sheets are 16


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adopted to the values from the Heyd-Scuseria-Ernzerhof (HSE) calculations, which are 1.59 and 2.74 eV for the black and blue P sheets, respectively. The values of Ecorr (q) are obtained by the sxdefectalign code through the Freysoldt-Neugebauer-Van de Walle (FNV) correction scheme. 69,70 The formation energies of Au adatom in different charged states are depicted in Fig. 14, in which we have also marked the charge transition level positions (ǫ(q/q ′ )) for different states. It can be seen that for the Au adatom, the ǫ(1/0) and ǫ(0/ − 1) are both beyond the band gaps of P sheets. On the black P sheet, ǫ(1/0) is below the VBM by 0.84 eV, while ǫ(0/ − 1) is above the conduction band minimum (CBM) by 0.67 eV. Similarly, on the blue P sheet, ǫ(1/0) and ǫ(0/ − 1) are EV BM − 0.22 and ECBM + 0.56 eV, respectively. Thus, as shown in Fig. 14, when the EF ermi is in the gap region of P sheets, the q = 0 state is always more stable than the q = 1/ − 1 ones. It indicates that the Au-adsorbed black and blue P sheets prefer to the neutral state rather than the p/n-type doping at finite temperatures.

Conclusion In summary, we have investigated the adsorptions of alkali, alkaline-earth, non-metallic, transition and noble metal atoms on the black and blue P sheets. We find that: (1) Various adsorption structures are obtained on phosphorene. Most adatoms prefer to occupy the H site on black P sheet except for the C, O, and S ones. While on the blue P sheet, the favourable adsorption sites are quite element-dependent. The majority of alkali, alkaline-earth and transition metal adatoms prefer the V site, and noble metal adatoms like the H site. Besides that, B and C adatoms are stably adsorbed at the B site of blue P sheet, and the N, O, P, S ones favor the T site instead. (2) Electronic properties of phosphorene are tailored by adatoms. On the black P sheet, Li, Na, Al, Cu, Ag adatoms induce n-type doping without changing the band gap, while the N adatom causes p-type doping for it. The n-type doping can also be obtained on the blue P

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sheet by Li, Na, Be, Al adatoms. For both P sheets, the O and S adsorptions have negligible effects on their electronic structures, while the other adatoms induce mid-gap defect states, significantly reducing the band gap of phosphorene. (3) Magnetism can be introduced into phosphorene by adatoms. Among the investigated adatoms, the P, Co, Au adsorptions can induce stable magnetism in black P sheet. Likewise, on the blue P sheet, B, N, P, Fe, Co, Au adtoms would cause the magnetic phenomena. Versatile spintronic features are obtained for these adsorbed systems: the N- and P-decorated blue P sheets are half-metals, the B- and Fe-decorated blue P ones are bipolar-semiconductors, and Co- and Au-decorated blue and black P sheets are spin-gapless-semiconductors. Besides that, we find that the phosphorene sheets have better adsorption capability than the BN, SiC, MoS2 and graphene ones. Due to the rich electronic and magnetic properties, surface adsorption is an effective way to functionalizing the phosphorene nanosheets, which enables the system potential applications in nano-electrics and spintronics.

Acknowledgement Authors acknowledge the supports from Zhejiang Provincial Natural Science Foundation of China (LY15A040008), National Natural Science Foundation of China (11474081, 11104249, 11104052). Parts of the calculations were performed in the Shanghai Supercomputer Center (SSC) of China and HZNU College of Science HPC Center.

Supporting Information Available The additional informations about NEB calculations, band structures of different charged adatoms, AIMD simulations, DFT+D calculations, convergence tests, symmetry effects on magnetism, work functions of Li, Na, O adsorptions, the influences of dipole corrections, HSE calculations, FHI-aims calculations, Mulliken analysis, formation energies of two adatoms, additional plots of B adatom on the blue P sheet, the DOSs of black and blue P sheets, and partial charge densities of the C adsorptions, are provided in the Supporting Information. 18


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This material is available free of charge via the Internet at http://pubs.acs.org/.

Notes The authors declare no competing financial interest.

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Table 1: The favourable adsorption sites, binding energies (Ead ), electronic and magnetic properties of adatoms on the black P sheet. The adsorption height hX is the vertical distance of adatom (X) to upper P atoms, and lX−P and δP are the minimum bond lengths of X-P bonds and maximum dispalcement of P atoms upon adsorptions. We will use the X@W to represent the adsorption structures, where X is the name of adatom and W is the adsorbed site. Atom Li Na Be Mg B C N O Al Si P S Fe Co Ni Cu Zn Ag Au Pt

Site H H H H H B→E B T→T’ H H H T→T’ H H H H H H H H

Ead (eV) 1.93 1.35 1.79 0.66 3.58 5.11 3.49 5.46 2.00 2.52 1.77 3.11 2.98 3.75 4.41 2.15 0.15 1.14 1.61 4.82

Adsorptions on the black hX (˚ A) lX−P (˚ A) δP (˚ A) 1.43 2.48 0.12 1.99 2.84 0.11 0.69 2.07 0.39 1.78 2.70 0.26 0.31 1.88 0.54 0 1.73 0.81 0.61 1.61 0.59 1.00 1.51 0.12 1.59 2.59 0.21 1.25 2.34 0.23 1.06 2.13 0.26 1.56 1.96 0.16 0.45 2.07 0.39 0.68 2.11 0.29 0.90 2.12 0.17 0.94 2.22 0.15 2.39 3.13 0.12 1.43 2.45 0.14 1.34 2.36 0.16 1.09 2.22 0.19

27

P sheet M (∆EM ) 0.95 µB (1 meV) 1 µB (68 meV) 1 µB (34 meV) 1 µB (25 meV) -


Properties n-type doping n-type doping defect states in gap defect states in gap metal defect states in gap p-type doping negligible changes n-type doping defect states in gap half-semiconductor negligible changes defect states in gap spin-gapless-SC defect states in VB n-type doping unadsorbed n-type doping spin-gapless-SC defect states in VB


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 28 of 43

Table 2: The favourable adsorption sites, binding energies (Ead ), electronic and magnetic properties of adatoms on the blue P sheet. The adsorption height hX is the vertical distance of adatom (X) to upper P atoms, and lX−P and δP are the minimum bond lengths of X-P bonds and maximum dispalcement of P atoms upon adsorptions. We will use the X@W to represent the adsorption structures, where X is the name of adatom and W is the adsorbed site. Atom Li Na Be Mg B C N O Al Si P S Fe Co Ni Cu Zn Ag Au Pt

Site Ead (eV) V 1.78 V 1.30 V 1.16 H 0.30 B→E 3.25 B 3.23 T 2.18 T 5.46 V 1.60 H 2.00 T 1.32 T 3.27 B→V’ 2.57 V 3.43 V 4.24 H 1.80 T 0.04 H 0.99 H 1.43 H 4.13

Adsorptions on hX (˚ A) lX−P (˚ A) 1.37 2.53 1.93 2.92 0.24 2.09 2.03 2.82 0 1.88 1.01 1.77 1.42 1.57 1.33 1.50 1.81 2.80 1.34 2.43 1.78 2.04 1.82 1.95 0.55 2.09 0.70 2.12 0.72 2.14 1.24 2.34 3.25 3.77 1.75 2.64 1.77 2.59 1.27 2.33

28

the blue δP (˚ A) 0.32 0.26 0.66 0.11 1.11 1.52 0.09 0.12 0.28 0.28 0.21 0.08 0.38 0.26 0.23 0.14 0.04 0.09 0.06 0.16

P sheet N (∆EM ) Properties n-type doping n-type doping n-type doping mid-gap states 1 µB (61 meV) bipolar-magnetic-SC defect states in gap 1 µB (144 meV) half-metal negligible changes n-type doping defect states in gap 1 µB (125 meV) half-metal defect states in VB 2 µB (569 meV) half-semiconductor 1 µB (193 meV) spin-gapless-SC defect states in gap 0.92 µB (1 meV) metal Unadsorbed 1 µB (5 meV) spin-gapless-SC 1 µB (35 meV) spin-gapless-SC defect states in gap


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


Graphical TOC Entry 6

Black P Blue P Gra Gra Gra BN SiC MoS Si Si Si Ge Ge a

5

Black P

Ead (eV)

Page 29 of 43

b c

4 3

2

2

d e

1

Blue P

f

0 Li NaBeMg B

g

C N O Al Si P S FeCo Ni CuAgAu Pt

Adatom

29


h


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 30 of 43

b

HB HT

HB HH

a

HT

HH

HV b a

h

h

(a) black P

(b) blue P

Figure 1: The supercells of (a) black and (b) blue P sheets, for which the primitive cell and high symmetry adsorption sites are marked.

30


Page 31 of 43

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


(a) Li@H/black P

(b) Li@V/blue P

(c) Mg@H/blue P

Figure 2: Typical adsorption structures for the alkali and alkaline-earth adatoms on the black and blue P sheets. In (a), the abbreviation of Li@H/black P indicates the Li adatom is adsorbed at the hollow (H) site of black P sheet. Similarly, in (b), (c), the Li@V/blue P and Mg@H/blue P mean the Li and Mg adatoms are adsorbed at the valley (V) and hollow (H) sites of blue P sheet, respectively. 31



0.9

black P

blue P

0.6

Q (e)

(a) Li@H/black P

0.3

0.0

Li

(b) Li@V/blue P Total

0 Li 40

Total Be

0 40 Mg

-3

DOSs (a.u.)

Total Na

0 Be 40

(d)

Total Mg

-2

Be

40 blue P

Total Li

0 Na 40

0

Na

Mg

(c)

40 black P

DOSs (a.u.)

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 32 of 43

-1

0

1

2

Total

0 Li 40

Total Li

0 Na 40

Total Na

0 Be 40

Total Be

0 40 Mg

Total Mg

0

-3

-2

-1

(e)

E(eV)

0

1

2

3

E(eV)

Figure 3: [(a) and (b)] Deformed charge densities of Li adatoms on black and blue P sheets. (c) The charge transfer from alkali and alkaline-earth adatoms to the P sheets. [(d), (e)] The DOSs of black and blue P sheets decorated with different adatoms, in which the Fermi level is set to 0 eV.

32


Page 33 of 43

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


black P

(a) B@H

(b) C@E

(c) N@B

(d) O@T

blue P

(e) B@E

(f) C@B

(g) N@T

(h) O@T

Figure 4: The adsorption structures of B−O adatoms on black and blue P sheets. Here, the abbreviation of X@W represents that the X adatom is adsorbed at the W site of P sheet. In (a)-(d), B@H means the B adatom at the hollow site, C@E means the C adatom at the embedded site, N@B means the N adatom at the bridge site, and O@T’ means the O adatom at the tilted top site of black P sheets. In (e)-(f), B@E means the B adatom at the embedded site, C@B is the C adatom at the bridge site, and N@T, O@T are the N, O adatoms at the top site of blue P sheet. 33 ACS Paragon Plus Environment


B@H/black P

Total B

20

C@E/black P

Total C

DOSs(a.u.)

DOSs (a.u)

40

0

-20 -3

-2

(a)

-1

0

1

0 -3

2

N@B/black P

-1

0

1

2

E(eV) O@T /black P

Total N

Total O

40

40

DOSs(a.u.) 0 -3

(c)

-2

(b)

E(eV)

DOSs(a.u.)

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 34 of 43

-2

-1

0

1

0 -3

2

-2

(d)

E(eV)

-1

0

1

2

E(eV)

Figure 5: The DOSs of black P sheet decorated with (a) B, (b) C, (c) N and (d) O adatoms. The inset in (a) depicts the spin charge densities of B adsorption on the black P sheet.

34


Page 35 of 43

C@B/blue P

Total B

B@E/blue P 20

Total C

DOSs(a.u.)

DOSs (a.u)

40

0

-20 -3

-2

-1

0

1

2

0 -3

3

-2

-1

Total N

N@T/blue P 20

0

1

2

3

E(eV)

(b)

E(eV)

(a)

Total O

O@T/blue P

DOSs(a.u.)

40

DOSs (a.u)

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


0

-20 -3

(c)

-2

-1

0

1

2

0 -3

3

E(eV)

-2

-1

(d)

0

1

2

3

E(eV)

Figure 6: The DOSs of blue P sheet decorated with (a) B, (b) C, (c) N and (d) O adatoms. The insets in (a) and (c) are the spin charge densities of B- and N-decorated blue P sheet.

35



Al@V/blue P

Total Al

Al@H/black P 40

DOSs(a.u.)

DOSs(a.u.) 0 -3

-2

-1

(a)

0

1

0 -3

2

-1

0

1

2

3

E(eV)

Total Si

Si@H/blue P

40

Total Si

DOSs(a.u.)

DOSs(a.u.)

40

0 -3

-2

-1

(c)

0

1

0 -3

2

-1

0

1

DOSs (a.u)

3

Total P

20

0

2

E(eV) P@T/blue P

Total P

P@H/black P

0

-20

-20 -3

-2

(d)

E(eV) 20

DOSs (a.u)

-2

(b)

E(eV) Si@H/black P

-2

-1

(e)

0

1

-3

2

-2

-1

(f)

E(eV)

0

1

3

Total S

S@T/blue P

40

2

E(eV)

Total S

S@T /black P

40

DOSs(a.u.) 0 -3

(g)

Total Al

40

DOSs(a.u.)

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 36 of 43

-2

-1

0

E(eV)

1

0 -3

2

(h)

-2

-1

0

1

2

3

E(eV)

Figure 7: The DOSs of [(a), (c), (e), (g)] black P sheet with Al−S adatoms and [(b), (d), (f), (h)] blue P sheet with Al−S adatoms. The inset in (e) and (f) present the spin charge densities of P-decorated P sheets.

36


Page 37 of 43

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


P1

Fe P1

P2/P3 Fe/P4 P4

P3

P2

(a) Fe@V /blue P P1

Co P1

P2/P3 Co/P4 P2

P3

P4

(b) Co@V/blue P

Figure 8: The adsorption structures of (a) Fe and (b) Co adatoms on the blue P sheet. Here, Co@V represents the Co adatom adsorbed at the valley site, while Fe@V’ stands for the Fe adatom at the valley site with a different local structure as shown in (a).

37



Fe@H/black P

Total Co

Co@H/black P

Total Fe

20

DOSs(a.u.)

DOSs (a.u)

40 0

-20 0 -3

-2

-1

(a)

0

1

-3

2

Ni@H/black P

-1

0

1

2

E(eV) Cu@H/black P

Total Ni

40

Total Cu

40

DOSs(a.u.) 0 -3

(c)

-2

(b)

E(eV)

DOSs(a.u.)

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 38 of 43

-2

-1

0

E(eV)

1

0 -3

2

(d)

-2

-1

0

1

2

E(eV)

Figure 9: The DOSs of black P sheet decorated with (a) Fe, (b) Co, (c) Ni and (d) Cu adatoms. The inset in (b) display the spin charge densities of Co-decorated black P sheet.

38


Page 39 of 43

Total Fe

Fe@V /blue P

Total Co

Co@V/blue P 20

DOSs (a.u)

DOSs (a.u)

20

0

0

-20

-20 -3

-2

-1

(a)

0

1

2

-3

3

-2

-1

(b)

E(eV) Ni@V/blue P

0

1

2

3

E(eV) Total Cu

Cu@H/blue P

Total Ni

20

40

DOSs (a.u)

DOSs(a.u.)

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


0

-20 0 -3

(c)

-2

-1

0

E(eV)

1

2

3

-3

(d)

-2

-1

0

1

2

3

E(eV)

Figure 10: The DOSs of blue P sheet decorated with (a) Fe, (b) Co, (c) Ni and (d) Cu adatoms. The insets in (a), (b) and (d) show the spin charge densities of Fe-, Co-, and Cu-decorated blue P sheets.

39



Ag@H/black P

Total Ag

Ag@H/blue P

Total Ag

20

DOSs (a.u)

DOSs(a.u.)

40

0

-20 0 -3

-2

-1

0

1

-3

2

0

1

0

2

3

E(eV) Total Au

20

DOSs (a.u)

DOSs (a.u)

-1

Au@H/blue P

Total Au

Au@H/black P 20

0

-20

-20 -3

-2

-1

0

1

-3

2

-2

-1

Pt@H/black P

0

1

2

3

E(eV)

(d)

E(eV)

(c)

Pt@H/blue P

Total Pt

Total Pt

40

DOSs(a.u.)

40

0 -3

(e)

-2

(b)

E(eV)

(a)

DOSs(a.u.)

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 40 of 43

-2

-1

0

1

0 -3

2

-2

-1

(f)

E(eV)

0

1

2

3

E(eV)

Figure 11: The DOSs of [(a), (c), (e)] black P sheet and [(b), (d), (f)] blue P sheet decorated with Ag, Au, Pt adatoms. The insets in (b), (c) and (d) depict the spin charge densities of Ag-, Au-decorated P sheet.

40


Page 41 of 43

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 12: The comparison of adsorption energies of different adatoms on the P, BN, SiC, MoS2 and graphene sheets. The data of binding energies of adatoms on graphene, BN, SiC, MoS2 , silicene and germanene sheets are adopted from the literature a. 60 b. 61 c. 26 d. 42 e. 44 f. 46 g. 32 h. 34 i. 33 j. 39 k. 38 , and the data of cohesive energies of different elements can be accessed from the website of http://www.knowledgedoor.com.

41



2.0

Blue P

2.0 Black P along zigzag across zigzag

1.5

Eb(eV)

1.5

Eb(eV)

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 42 of 43

1.0

0.5

0.5 0.0

1.0

Na

O

Al

Co

0.0

Au

Na

O

Al

Co

Au

(b)

(a)

Figure 13: The migration barriers of Na, O, Al, Co, Au adatoms on the (a) black and (b) blue P sheets.

42


Page 43 of 43

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 14: The formation energies of different charged states for the Au adatom on (a) black and (b) blue P sheets.

43


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