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采用基于密度泛函理论的第一性原理平面波赝势方法, 计算了单层GeTe、表面氢化及氟化单层GeTe的晶体结构、稳定性、电子结构和光学性质. 计算结果表明, 经过修饰后, GeTe的晶格常数、键角、键长增大, 且均具有较好的稳定性. 电子结构分析表明, 单层GeTe为间接带隙半导体, 全氢化修饰、全氟化修饰以及氢氟共修饰(F, Ge同侧; H, Te同侧)则转变为直接带隙半导体, 且修饰后的能隙均不同程度减小. 载流子有效质量表明, 全氢化、全氟化以及氢氟共修饰GeTe (F, Ge同侧; H, Te同侧)的有效质量减小, 其载流子迁移率增强. 带边势分析结果显示, 单层GeTe能够光裂解水制氢和析氧, 而修饰后的GeTe的价带带边势明显下移, 其氧化性明显增强, 能够光裂解水析O2, H2O2, O3以及OH·等产物. 光学性质表明, 修饰后的GeTe对可见光区和红、紫外区的光谱吸收效果明显增强, 表明其在光催化领域有着广阔的应用前景.Using the first principle calculation based on the density functional theory, we have systematically investigated the structure stability, electronic structure and photocatalytic properties of two-dimensional single-layered GeTe crystal structure modified by H and F. The results show that the lattice constant, bond angle and bond length of GeTe increase after being modified. The stability analysis shows that all the materials have excellent dynamical, mechanical, and thermal stabilities. The electronic structure analysis shows that the two-dimensional GeTe is an indirect bandgap semiconductor with an energy gap of 1.797 eV, and its energy band is mainly composed of Ge-4p and Te-5p, while it is converted into a direct bandgap semiconductor by H or F modification and H-F co-modification (F and Ge on one side, H and Te on the other), and their corresponding energy gaps are reduced to 1.847 eV (fH-GeTe), 0.113 eV (fF-GeTe) and 1.613 eV (hF-GeTe-hH). However, hH-GeTe-hF is still an indirect band gap semiconductor, and its energy gap is reduced to 0.706 eV. The results of the density of states show that part of the Ge-4p and Te-5p electrons are transferred to a deeper level due to the adsorption of H or F atoms, resulting in a strong orbital hybridization between them and the adsorbed atoms. The effective mass shows that the effective mass of H or F modified and H-F co-modified GeTe (F and Ge on one side, H and Te on the other) decrease, and their carrier mobilities increase. The carrier recombination rates of all modified GeTe materials are lower than that of the intrinsic GeTe, so the semiconductor will be more durable. The electron density difference shows that due to the electronegativities of atoms being different from each other, when H or F is used to modify GeTe, some electrons transfer to H and F atoms, resulting in the weakening of covalent bond between Ge and Te atoms and the enhancement of ion bond. The results of band-edge potential analysis show that GeTe can produce hydrogen and oxygen by photolysis of water. However, the valence band edge potential of the modified GeTe decreases significantly, and its oxidation ability increases considerably, the photocatalytic water can produce O2, H2, O3, OH·, etc. Optical properties show that the modified GeTe can enhance the absorption of visible and ultraviolet spectrum, which indicates that they have great application prospects in the field of photocatalysis.
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Keywords:
- two-dimensional GeTe /
- electronic structure /
- effective mass /
- photocatalysis
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图 1 优化后的晶胞模型 (a) GeTe侧视图; (b) fH-GeTe俯视图; (c) fH-GeTe侧视图; (d) hH-GeTe-hF侧视图; (e) hF-GeTe-hH侧视图; (f) K点路径
Fig. 1. The optimized geometric structures: (a) side view of GeTe; (b) top view of fH-GeTe; (c) side view of fH-GeTe; (d) side view of hH-GeTe-hF; (e) side view of hF-GeTe-hH; (f) K point path.
图 2 声子谱 (a) GeTe; (b) fH-GeTe; (c) fF-GeTe; (d) hH-GeTe-hF; (e) hF-GeTe-hH
Fig. 2. Phonon dispersion: (a) GeTe; (b) fH-GeTe; (c) fF-GeTe; (d) hH-GeTe-hF; (e) hF-GeTe-hH.
图 3 分子动力学模拟计算的能量随时间的变化, 插图表示加热到500 K温度下最后的结构图 (a) GeTe; (b) fH-GeTe; (c) fF-GeTe; (d) hH-GeTe-hF; (e) hF-GeTe-hH
Fig. 3. Variation of the total energy in the molecular dynamics simulation at 500 K for: (a) GeTe; (b) fH-GeTe; (c) fF-GeTe; (d) hH-GeTe-hF; (e) hF-GeTe-hH, during a timescale of 2.5 ps. The insets are the top (left panel) and side (right panel) views of the atomic structure snapshots taken from the molecular dynamics simulation.
图 4 能带图和态密度 (a) GeTe; (b) fH-GeTe; (c) fF-GeTe; (d) hH-GeTe-hF; (e) hF-GeTe-hH
Fig. 4. Band structure and density of states: (a) GeTe; (b) fH-GeTe; (c) fF-GeTe; (d) hH-GeTe-hF; (e) hF-GeTe-hH.
图 5
$\langle 0, 0, 1 \rangle$ 截面差分电荷密度图 (a) GeTe; (b) fH-GeTe; (c) fF-GeTe; (d) hH-GeTe-hF; (e) hF-GeTe-hHFig. 5. Electron density difference
$\langle 0, 0, 1 \rangle$ : (a) GeTe; (b) fH-GeTe; (c) fF-GeTe; (d) hH-GeTe-hF; (e) hF-GeTe-hH.
图 6 半导体的导带与价带的带边电势示意图
Fig. 6. Reduction and oxidation potentials of CB and VB edges of all chemically decorated GeTe.
表 1 晶体的结构参数及吸附能
Table 1. Structural parameters for all chemically decorated GeTe.
Structure (a/b)/Å θ/(°) l/Å l1/Å l2/Å σ/Å Ef/eV GeTe 3.95 91.22 2.76 — — 1.56 — fH-GeTe 5.09 119.92 2.94 1.60 1.69 –0.08 –5.80 fF-GeTe 4.18 93.08 2.88 1.79 2.04 1.58 –7.45 hH-GeTe-hF 4.02 92.04 2.97 1.59 2.08 1.56 –5.79 hF-GeTe-hH 5.21 119.99 3.01 1.81 1.69 –0.03 –7.74 
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表 2 半导体的载流子有效质量
Table 2. The effective mass for all chemically decorated GeTe.
Effective mass GeTe fH-GeTe fF-GeTe hH-GeTe-hF hF-GeTe-hH $ m_{\rm h}^*/m_0 $ 0.54 0.24 0.23 1.50 0.30 $ m_{\rm e}^*/m_0 $ 0.52 0.39 0.27 0.91 0.49 D 1.04 1.63 1.17 1.65 1.63
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表 3 半导体的导带和价带的带边电势
Table 3. Reduction and oxidation potentials of CB and VB edges of all chemically decorated GeTe.
Structure GeTe fH-GeTe fF-GeTe hH-GeTe-hF hF-GeTe-hH $ \chi $ 5.03 6.01 7.23 6.59 6.59 CB/eV –0.37 0.76 2.68 1.74 1.28 VB/eV 1.42 2.25 2.79 2.44 2.90
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[1] Novoselov K S, Geim A K, Morozov S V, Jiang D, Zhang Y, Dubonos S V, Grigorieva I V, Firsov A A 2004 Science 306 666
Google Scholar
[2] Bolar S, Shit S, Kumar J S, Murmu N C, Genesh R S, Inokawa H, Kuila T 2019 Appl. Catal., B-environ. 254 432
Google Scholar
[3] Hu W, Yang J L 2017 J. Mater. Chem. C 5 12289
Google Scholar
[4] Yao L H, Cao M S, Yang H J, Liu X J, Fang X Y, Yuan J 2014 Comput. Mater. Sci. 85 179
Google Scholar
[5] Molle A, Grazianetti C, Tao L, Taneja D, Alam M H, Akinwande D 2018 Chem. Soc. Rev. 47 6370
Google Scholar
[6] Cao M S, Wang X X, Zhang M, Shu J C, Cao W Q, Yang H J, Fang X Y, Yuan J 2019 Adv. Funct. Mater. 29 1807398
Google Scholar
[7] Wang L J, Wang W Z, Chen Y L, Yao L Z, Zhao X, Shi H L, Cao M S, Liang Y J 2018 Acs. Appl. Mater. Interfaces 10 11652
Google Scholar
[8] Chen P F, Li N, Chen X Z, Ong W J, Zhao X J 2018 2D Mater. 5 014002
[9] Zhao J, Li Y L, Ma J 2016 Nanoscale 8 9567
[10] Chen Y L, Wang L J, Wang W Z, Cao M S 2017 Appl. Catal. B-Environ. 209 110
Google Scholar
[11] Wong S L, Khoo K H, Quek S Y, Wee A T S 2015 J. Phys. Chem. C 119 29193
Google Scholar
[12] Zeng Q S, Sun B, Du K Z, Zhao W Y, Yu P, Zhu C, Xia J, Chen Y, Cao X, Yan Q Y, Shen Z X, Yu T, Long Y, Koh Y K, Liu Z 2019 2D Mater. 6 045009
[13] Zhang S L, Yan Z, Li Y F, Chen Z F, Zeng H B 2015 Angew. Chem.-Int. Edit. 54 3112
Google Scholar
[14] Fonseca J J, TonGey S, Topsakal M, Chew A R, Lin A J, Ko C, Luce A V, Salleo A, Wu J Q, Dubon O D 2016 Adv. Mater. 28 6465
Google Scholar
[15] Fedorenko Y G 2015 Semiconductors 49 1640
Google Scholar
[16] Gelca A C, Sava F, Simandan I D, Bucur C, Dumitru V, Porosnicu C, Mihai C, Velea A 2016 J. Non-Cryst. Solids 499 1
[17] Qiao M, Chen Y L, Wang Y, Li Y F 2018 J. Mater. Chem. A 6 4119
Google Scholar
[18] Singh A K, Hennig R G 2014 Appl. Phys. Lett. 105 042103
Google Scholar
[19] Wan W H, Liu C, Xiao W D, Yao Y G 2017 Appl. Phys. Lett. 111 132904
Google Scholar
[20] Zhang P P, Zhao F L, Long P, Wang Y, Yue Y C, Liu X Y, Feng Y Y, Li R J, Hu W P, Li Y, Feng W 2018 Nanoscale 10 34
Google Scholar
[21] Tang W C, Sun M L, Ren Q Q, Wang S K, Yu J 2016 Appl. Surf. Sci. 376 286
Google Scholar
[22] Zhang D B, Zhou Z P, Wang H Y, Yang Z X, Liu C 2018 Nanoscale Res. Lett. 13 400
Google Scholar
[23] Yuan J H, Xie Q X, Yu N N, Wang J F 2017 Appl. Surf. Sci. 394 625
Google Scholar
[24] SeGell M D, Lindan P J D, Probert M J, Pickard C J, Hasnip P J, Clark S J, Payne M C 2002 J. Phys.-Condes. Matter 14 2717
Google Scholar
[25] Xie Q X, Yuan J H, Yu N N, Wang L S, Wang J F 2017 Comput. Mater. Sci. 135 160
Google Scholar
[26] Yuan J H, Yu N N, Xue K H, Miao X S 2017 RSC Adv. 7 8654
Google Scholar
[27] Zhang J F, Wageh S, Al-Ghamdi A, Yu J G 2016 Appl. Catal. B-Environ. 192 101
Google Scholar
[28] Tian Y L, Hua H L, Yue W W, Chen M N, Hu G C, Ren J F, Yuan X B 2017 Mod. Phys. Lett. B 31 1750335
Google Scholar
[29] 王胜楠, 毛启楠, 袁倩敏, 李鹤, 季振国 2016 材料科学与工程学报 34 702
Wang S N, Mao Q N, Yuan Q M, Li H, Ji Z G 2016 Journal of Materials Science and Engineering 34 702
[30] Yu W L, Zhang J F, Peng T Y 2016 Appl. Catal. B-Environ. 181 220
Google Scholar
[31] Yu N N, Yuan J H, Li K X 2018 Appl. Surf. Sci. 427 0169
Google Scholar
[32] Goclon J, Winkler K 2018 Appl. Surf. Sci. 462 134
Google Scholar
[33] Zhou Y H, Peng Z B, Chen Y D, Luo K, Zhang J, Du S Y 2019 Comput. Mater. Sci. 168 137
Google Scholar
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