grain boundary and its hydrogenated effect in stanene

Grain boundary and its hydrogenated effect in stanene Zhili Zhu, Qiang Sun, and Yu Jia Citation: AIP Advances 6, 035012 (2016); doi: 10.1063/1.4944621 View online: http://dx.doi.org/10.1063/1.4944621 View Table of Contents: http://aip.scitation.org/toc/adv/6/3 Published by the American Institute of Physics AIP ADVANCES 6, 035012 (2016) Grain boundary and its hydrogenated effect in stanene Zhili Zhu,a Qiang Sun, and Yu Jiaa International Joint Research Laboratory for Quantum Functional Materials of Henan, and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001, China (Received December 2015; accepted March 2016; published online 16 March 2016) The geometric and electronic properties of grain boundary (GB) in two-dimensional (2D) stanene have been investigated by first-principles calculations Four typical GB structures with particularly low formation energies were found These extended defects act as quasi-one-dimensional semiconductor or metallic wires depending on their geometric structures Moreover, they are reactive and the adsorption of H atoms at the GB region is more stable than the stanene bulk region A single H adsorption poses a drastic effect on the electronic behavior of GB defects, and the band structures can be tuned by the coverages of H adsorption at these GB defects in stanene The present results indicate that GBs are important defects in stanene which may be useful for nanomaterial devices C 2016 Author(s) All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/) [http://dx.doi.org/10.1063/1.4944621] Two-dimensional (2D) materials, such as graphene, silicone and germanene belonging to group-IV 2D materials, and transition metal dichalcogenides for MX2 (M = Mo, W; X = S, Se), have been paid extensive attentions in recent years due to their outstanding properties for spintronics and nanodevice applications Most recently, a 2D stanene with graphene-like structure has been fabricated by molecular beam epitaxy.1 It is a biatomic layer of α-Sn(111) which contains two atoms per unit cell They occupy two triangular sublattices stacking together with a buckled honeycomb structure In the family of 2D group-IV materials, stanene is of special interest because of its prominent properties It is assumed as the candidate of quantum spin hall insulators with large bandgap2–4 with the addition of quantum anomalous Hall effect near-room-temperature.5 Stanene may also be a promising thermoelectric material6 and topological superconductor.7 Nevertheless, to realize such proposed applications in 2D materials, it is necessary to tune their properties at the nanoscale Introducing extended defects into these 2D materials may be an effective way to modulate the charge distribution in one dimension of several atoms For instance, grain boundary (GB) defect observed in graphene is found to be a metallic wire,8 and it presents a tunable magnetism by GB lattice distortion,9 which may be crucial to the device application Recent experiments also reveal a variety of dislocations and GBs in MoS2 samples,10,11 which can actually improve the performance by generating qualitative magnetism, a new property that is not present in the original MoS2.12 While GB has been found to be critical in graphene and MoS2, to the best of our knowledge, there has no any investigations on the GB defects in stanene Thus, in this letter we explore the GB structures in stanene, examine the relative stabilities and electronic properties as well as their hydrogenated effects by means of ab initio calculations Four typically GBs were found, and they pose obvious influences on the electronic structure of stanene Furthermore, these GBs are reactive and the adsorption of H atoms is more stable at the defect than in the stanene bulk region Our results strongly suggest that GBs may play important roles in tuning the properties of stanene The geometric and electronic properties are calculated using the VASP code.13 A periodic supercell is constructed to simulate stanene The vacuum layer is set to 15 Å to eliminate interactions a Authors to whom correspondence should be addressed Electronic mail: zlzhu@zzu.edu.cn jiayu@zzu.edu.cn 2158-3226/2016/6(3)/035012/6 6, 035012-1 © Author(s) 2016 035012-2 Zhu, Sun, and Jia AIP Advances 6, 035012 (2016) FIG Optimized geometries of four typical GB structures: (a) GB1(5-7), (b) GB2(5-7), (c) GB3(5-7) and (d) GB4(5-8) The dashed-lines indicate the unit cell, and the solid lines define the misorientation angle of the two symmetric large-angle grain boundaries, respectively between two stanene layers The Perdew-Burke-Ernzerhof (PBE)14 is used for exchange-correlation functional The projector augmented wave (PAW) basis set15,16 with the kinetic energy cutoff of 400 eV are chosen All structures are fully relaxed until the residual forces are converged within 0.01 eV/Å Figure indicates the proposed four typical GB defects in stanene from the DFT calculations Two symmetric large-angle GBs were found, shown in Fig 1(a) and 1(b), respectively The misorientation angle between the left and right crystalline domains can be described by θ = θ + θ 2, which 035012-3 Zhu, Sun, and Jia AIP Advances 6, 035012 (2016) FIG Band structures of stanene with GB defects: (a) GB1(5-7), (b) GB2 (5-7), (c) GB3(5-7) and (d) GB4(5-8), without (black lines) and with (red lines) spin-orbital coupling, respectively is bisected by the GB lines in symmetric GB structures The adjacent crystalline domains rotae ±θ/2 with respect to their perfect interface The optimized tilt angles for GB1(5-7) and GB2(5-7) are 21.8◦and 32.2◦, respectively, which are the same as that of GBs in graphene.17 Fig 1(c) presents the GB3(5-7) which joins a zigzag and an armchair edge together to form a hybrid zigzag-armchair stanene Fig 1(d) shows the GB4(5-8) structure formed between the zigzag edges of two stanene domains by sharing the Sn atoms along the edge The formation energies were calculated to investigate the relative stability of these GB structures The formation energy Eform along the boundary per unit length are defined as: Eform = (EGB − N × Est)/2L where EGB is the total energy of stanene with GB defects, Est is the energy of Sn atom in perfect stanene, N indicates the total number of Sn atoms in supercell, L is the periodic length of supercell along the boundary, the factor is added since two boundaries are included in one supercell The calculated formation energies are 0.50, 0.58, 1.11 and 0.52 eV/nm for GB1(5-7), GB2(5-7), GB3(5-7) and GB4(5-8), respectively They are particularly small which indicate these kinds of GB structures can be easily realized in experiment To explore the effects of GB defects on the electronic properties of stanene, the band structures of different GB systems were calculated and presented in Fig It is found that the GB1(5-7) and GB3(5-7) systems are gapless when spin-orbital coupling (SOC) is not included, and have a gap of 0.08 eV when SOC effects are considered In comparison, the GB2(5-7) defect induces a band gap about 0.1 eV in stanene with negligible effect by the SOC However, the GB4(5-8) system is metallic These extended defects act as quasi-one-dimensional semiconductor or metallic wires relevant to the GB structures Such wires may form building blocks for atomic-scale electronics In addition to the fact that the GB defect itself has a significant effect on the electronic structure of stanene, it may also provide an accessible path for tuning the charge distribution in one dimension of several atoms widths and effectively tailor the functionality of stanene sheets It has been suggested that the GBs defects play unique roles in ruling impurity doping18 and adatom adsorption19 in graphene Thus, the properties of H adsorption at the GB defects in stanene are further examined We first examine the energetic stability of H atoms adsorbed at stanene with GB defects, H/GB A single H atom adsorbed on the top of Sn atoms was considered The nonequivalent adsorption sites at the defect region are indicated by the letters A, B, C, D, E, and F, as shown in Fig The letter G denotes the stanenelike region (not shown) Table I presents the calculated adsorption energies It is obvious that the adsorption energy at the GB defect is smaller than that at stanene-like bulk region for all investigated adsorption sites The results suggest that H atoms serve as a favorable process in energy adsorbed at the GB regions 035012-4 Zhu, Sun, and Jia AIP Advances 6, 035012 (2016) FIG Adsorption sites (in green) at the defect regions for (a) GB1(5-7), (b) GB2(5-7), (c) GB3(5-7) and (d) GB4(5-8), respectively TABLE I Adsorption energies (eV) of a single H atom adsorbed at stanene with different GB defects The letters denote the adsorption sites (see Fig 3) Site G A B C D E F H/GB1(5-7) H/GB2(5-7) H/GB3(5-7) H/GB(5-8) -1.69 -1.89 -1.87 -1.79 -1.66 -1.70 -1.53 -1.88 -1.76 -1.68 -1.86 -1.81 -1.74 -1.69 -1.92 -1.74 -1.78 -1.72 -1.71 -1.67 -1.96 -1.89 -1.86 -1.77 -1.73 The hydrogen adsorption energies at the most stable sites are 1.89, 1.88, 1.92 and 1.96 eV for GB1(5-7), GB2(5-7), GB3(5-7) and GB4(5-8), respectively These reactive GB defects can serve as nucleation regions for the formation of a narrow stanene strip embedded in the bulk stanene region To pursue the effects posed by a single H adsorption, the band structures of different H/GB systems were calculated The calculated band structures of H/GB1(5-7), H/GB2(5-7), H/GB3(5-7) and H/GB4(5-8) corresponding to the most stable configurations are shown in Figs 4(a)-4(d), respectively Comparing them with that of prisitine GB systems, it is clear that the single H adsorption has a drastic effect on the electronic properties of GB defects All the systems become metallic, and the Dirac points of prisitine GB1(5-7), H/GB2(5-7) systems disappear in the hydrogen adsorbed systems To further examine the coverage effects of H adsorption at these GB defects in stanene, the full and half hydrogenated GB defects were investigated For the half hydrogenated GB defect, only the 035012-5 Zhu, Sun, and Jia AIP Advances 6, 035012 (2016) FIG Band structures of hydrogenated GB defects with a single H adsorption in stanene: (a) H/GB1(5-7), (b) H/GB2 (5-7), (c) H/GB3(5-7) and (d) H/GB4(5-8), respectively FIG Band structures of full (red line) and half (blue line) hydrogenated GB defects in stanene: (a) H/GB1(5-7), (b) H/GB2 (5-7), (c) H/GB3(5-7) and (d) H/GB4(5-8), respectively GB atoms of one sublattice are H-saturated The calculated band structures are shown in Fig It was found that the full hydrogenated GB1(5-7) and GB4(5-8) defects keep the systems metallic, while the GB2 (5-7) and GB3(5-7) systems are semiconductor The GB2 (5-7) system has a direct band gap of 0.1 eV, and GB3 (5-7) system is gapless In contrast, the half hydrogenated GB1(5-7) leads to the system semiconductor with a band gap of 0.15 eV The GB2(5-7) system maintains the similar semiconducting feature to that of full hydrogenated defects However, the GB3(5-7) and GB4(5-8) systems become metal and gapless semiconductor, respectively It is worth noting that they are gapless semiconductor and metal in their full hydrogenated cases, respectively The results suggest that the band structures can be tuned by the coverages of H adsorption at the GB defects in stanene In summary, the geometric and electronic properties of grain boundaries in stanene have been investigated using the first-principles calculations Four typical GB structures with particularly low formation energies were found They act as quasi-one-dimensional semiconductor or metallic wires relevant to their geometric bulk structures Furthermore, they are reactive and the adsorption of H atoms is more stable at the defect sites than in the stanene bulk region The electronic properties are strongly affected by the single H adsorption at the GB defects, and could be tuned by the coverages These reactive GB defects may serve as a nucleation region for the formation of a narrow stanene strip embedded in the bulk stanene region 035012-6 Zhu, Sun, and Jia AIP Advances 6, 035012 (2016) Z.L Zhu, and Y Jia gratefully acknowledge financial support from the National Natural Science Foundation of China (No 11504332) and the Natural Science Foundation of Henan Province of China (No 152300410049) The calculations were performed on the High Performance Clusters of Zhengzhou University F Zhu, W Chen, Y Xu, C Gao, D Guan, C Liu, D Qian, S Zhang, and J Jia, Nat Mater 14, 1020 (2015) C C Liu, H Jiang, and Y Yao, Phys.Rev B 84, 195430 (2011) Y Xu, B Yan, H J Zhang, J Wang, G Xu, P Tang, W Duan, and S C Zhang, Phys Rev Lett 111, 136804 (2013) G F Zhang, Y Li, and C J Wu, Phys Rev B 90, 075114 (2014) S C Wu, G Shan, and B H Yan, Phys Rev Lett 113, 256401 (2014) Y Xu, Z Gan, and S C Zhang, Phys Rev Lett 112, 226801 (2014) J Wang, Y Xu, and S C Zhang, Phys.Rev B 90, 054503 (2014) J Lahiri, Y Lin, P Bozkurt, I I Oleynik, and M Batzill, Nat Nanotechnol 5, 326 (2010) L Kou, C Tang, W Guo, and C Chen, ACS Nano 5, 1012 (2011) 10 Y.-H Lee, X.-Q Zhang, W Zhang, M.-T Chang, C.-T Lin, K.-D Chang, Y.-C Yu, J T.-W Wang, C.-S Chang, L.-J Li, and T.-W Lin, Adv Mater 24, 2320 11 Y Shi, W Zhou, A Y Lu, W Fang, Y H Lee, A L Hsu, S M Kim, K K Kim, H Y Yang, L J Li, J C Idrobo, and J Kong, Nano Lett 12, 2784 (2012) 12 Z Zhang, X Zou, V H Crespi, and B I Yakobson, ACS Nano 7, 10475 (2013) 13 G Kresse and J Furthmüller, Phys Rev B 54, 11169 (1996) 14 J P Perdew, K Burke, and M Ernzerhof, Phys Rev Lett 77, 3865 (1996) 15 P E Blöchl, Phys Rev B 50, 17953 (1994) 16 G Kresse and D Joubert, Phys Rev B 59, 1758 (1999) 17 O.V Yazyev and S G Louie, Phys Rev B 81, 195420 (2010) 18 W H Brito, R Kagimura, and R H Miwa, Phys.Rev B 85, 035404 (2012) 19 W H Brito, R Kagimura, and R H Miwa, Appl.Phys Lett 98, 213107 (2011) ... 035012 (2016) Grain boundary and its hydrogenated effect in stanene Zhili Zhu,a Qiang Sun, and Yu Jiaa International Joint Research Laboratory for Quantum Functional Materials of Henan, and School... gapless when spin-orbital coupling (SOC) is not included, and have a gap of 0.08 eV when SOC effects are considered In comparison, the GB2(5-7) defect induces a band gap about 0.1 eV in stanene with... any investigations on the GB defects in stanene Thus, in this letter we explore the GB structures in stanene, examine the relative stabilities and electronic properties as well as their hydrogenated