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Owing to the complete spin-polarization of electronic states near Fermi energy, half-metallic ferromagnets, especially two-dimensional half-metallic ferromagnets, have garnered significant attention in the field of spintronics. However, the practical applications of these materials are greatly hindered by their low Curie temperatures. Therefore, the exploration of high Curie temperature half-metallic ferromagnets poses a necessary and challenging task. In this study, we predict a two-dimensional transition metal oxide, CrO2 monolayer, and employ first-principles calculations to investigate the crystal structure, electronic properties, magnetic ground state, and ferromagnetic phase transition. The calculations of phonon spectrum, elastic constant, and molecular dynamics simulations indicate that CrO2 monolayer is dynamically, mechanically, and thermally stable. The convex hull diagram of Cr-O systems shows that the hull energy of the predicted CrO2 layer is only 0.18 eV, further confirming the structural stability and large possibility for experimental fabrication. More importantly, the electronic and magnetic properties of CrO2 monolayer demonstrate that it is a two-dimensional ferromagnetic half-metal with wide band gap. Five d suborbitals are divided into Eg and T2g orbitals because of the crystal field of Cr atom in the center of O tetrahedron, and the spin-polarizations of Eg orbitals make a major contribution to the moment around Cr atom. The ferromagnetic coupling along Cr-O-Cr chain is dominated by the superexchange interaction bridged by O 2p orbitals, similar to the typical Mn-O-Mn superexchange model. The magnetic behavior of the Cr spin lattice in a CrO2 monolayer is described by a two-dimensional Heisenberg model, in which the exchange coupling anisotropy is ignored and the single ion anisotropy is the main consideration. By solving the Heisenberg model through using the Monte Carlo simulation method, the Curie temperature is determined to be over 400 K. The high Curie temperature ferromagnetism is rare in two-dimensional ferromagnetic materials and even rarer in semi-metallic materials, which makes it an ideal material for fabricating spintronic devices and studying spin quantum effects.
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Keywords:
- transition metal oxide /
- two-dimensional ferromagnetic half-metal /
- Curie temperature /
- first-principles theory
[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 666Google Scholar
[2] Zhang H 2015 ACS Nano 9 9451Google Scholar
[3] Gong C, Li L, Li Z L, Ji H W, Stern A, Xia Y, Cao T, Bao W, Wang C Z, Wang Y, Qiu Z Q, Cava R J, Louie S G, Xia J, Zhang X 2017 Nature 546 265Google Scholar
[4] Huang B, Clark G, Navarro-Moratalla E, Klein D R, Cheng R, Seyler K L, Zhong D, Schmidgall E, McGuire M A, Cobden D H, Yao W, Xiao D, Jarillo-Herrero P, Xu X 2017 Nature 546 270Google Scholar
[5] Gong C, Zhang X 2019 Science 363 eaav4450Google Scholar
[6] Balan A P, Radhakrishnan S, Woellner C F, Sinha S K, Deng L, de los Reyes C, Rao B M, Paulose M, Neupane R, Apte A, Kochat V, Vajtai R, Harutyunyan A R, Chu C W, Costin G, Galvao D S, Martí A A, van Aken P A, Varghese O K, Tiwary C S, Iyer A M M R, Ajayan P M 2018 Nat. Nanotechnol. 13 602Google Scholar
[7] Balan A P, Radhakrishnan S, Kumar R, Neupane R, Sinha S K, Deng L Z, de los Reyes C A, Apte A, Rao B M, Paulose M, Vajtai R, Chu C W, Costin G, Martí A A, Varghese O K, Singh A K, Tiwary C S, Anantharaman M R, Ajayan P M 2018 Chem. Mater. 30 5923Google Scholar
[8] Zhang Y, Chu J W, Yin L, Shifa T A, Cheng Z Z, Cheng R Q, Wang F, Wen Y, Zhan X Y, Wang Z X, He J 2019 Adv. Mater. 31 1900056Google Scholar
[9] Wang H D, Lei P H, Mao X Y, Kong X, Ye X Y, Wang P F, Wang Y, Qin X, Meijer J, Zeng H L, Shi F Z, Du J F 2022 Chin. Phys. Lett. 39 047601Google Scholar
[10] Feng P J, Zhang X H, Zhang S, Liu D P, Gao M, Ma F J, Yan X W, Xie Z Y 2022 ACS Omega 7 43316Google Scholar
[11] Liu D P, Zhang S, Gao M, Yan X W, Xie Z Y 2021 Appl. Phys. Lett. 118 223104Google Scholar
[12] Feng P J, Zhang S, Liu D P, Gao M, Ma F J, Yan X W, Xie Z Y 2022 J. Phys. Chem. C 126 10139Google Scholar
[13] Liu D P, Feng P J, Gao M, Yan X W 2021 Phys. Rev. B 103 155411Google Scholar
[14] Zhang S, Feng P J, Liu D P, Wu H F, Gao M, Xu T S, Xie Z Y, Yan X W 2022 Phys. Rev. B 106 235402Google Scholar
[15] Wang Y, Guo Y, Wang Z K, Fu L, Zhang Y, Xu Y J, Yuan S J, Pan H Z, Du Y W, Wang J L, Tang N J 2021 ACS Nano 15 12069Google Scholar
[16] Wang Y, Xu W, Fu L, Zhang Y, Wu Y Z, Wu L T, Yang D Y, Peng S Z, Ning J, Zhang C, Cui X, Zhong W, Liu Y, Xiong Q H, Han G Q, Hao Y 2023 ACS Appl. Mater. Interfaces 15 54797Google Scholar
[17] Wang Y, Xu W, Yang D Y, Zhang Y, Xu Y J, Cheng Z X, Mi X K, Wu Y Z, Liu Y, Hao Y, Han G Q 2023 ACS Nano 17 24320Google Scholar
[18] Zha H M, Li W, Zhang G J, Liu W J, Deng L W, Jiang Q, Ye M, Wu H, Chang H X, Qiao S 2023 Chin. Phys. Lett. 40 087501Google Scholar
[19] Huang P, Zhang P, Xu S G, Wang H D, Zhang X W, Zhang H 2020 Nanoscale 12 2309Google Scholar
[20] Lin Z C, Peng Y X, Wu B C, Wang C S, Luo Z C, Yang J B 2022 Chin. Phys. B 31 087506Google Scholar
[21] Cava R J 2000 J. Am. Ceram. Soc. 83 5Google Scholar
[22] Wilson R M 2019 Phys. Today 72 19Google Scholar
[23] Chen H H, Yang Y F, Zhang G M, Liu H Q 2023 Nat. Commun. 14 5477Google Scholar
[24] Rasmussen F A, Thygesen K S 2015 J. Phys. Chem. C 119 13169Google Scholar
[25] Topsakal M, Cahangirov S, Bekaroglu E, Ciraci S 2009 Phys. Rev. B 80 235119Google Scholar
[26] Yang J, Jiang Y L, Li L J, Muhire E, Gao M Z 2016 Nanoscale 8 8170Google Scholar
[27] Zhang F, Zhu J J, Zhang D L, Schwingenschlögl U, Alshareef H N 2017 Nano Lett. 17 1302Google Scholar
[28] de Groot R A, Mueller F M, van Engen P G, Buschow K H J 1983 Phys. Rev. Lett. 50 2024Google Scholar
[29] Wolf S A, Awschalom D D, Buhrman R A, Daughton J M, von Molnár S, Roukes M L, Chtchelkanova A Y, Treger D M 2001 Science 294 1488Google Scholar
[30] Schwarz K 1986 J. Phys. F: Met. Phys. 16 L211Google Scholar
[31] Dedkov Yu S, Rüdiger U, Güntherodt G 2002 Phys. Rev. B 65 064417Google Scholar
[32] Ji Y, Strijkers G J, Yang F Y, Chien C L, Byers J M, Anguelouch A, Xiao G, Gupta A 2001 Phys. Rev. Lett. 86 5585Google Scholar
[33] Xie W H, Liu B G, Pettifor D G 2003 Phys. Rev. B 68 134407Google Scholar
[34] 程志梅, 王新强, 王风, 鲁丽娅, 刘高斌, 段壮芬, 聂招秀 2011 物理学报 60 096301Google Scholar
Cheng Z M, Wang X Q, Wang F, Lu L Y, Liu G B, Duan Z F, Nie Z X 2011 Acta Phys. Sin. 60 096301Google Scholar
[35] Kobayashi K I, Kimura T, Sawada H, Terakura K, Tokura Y 1998 Nature 395 677Google Scholar
[36] Alijani V, Winterlik J, Fecher G H, Naghavi S S, Felser C 2011 Phys. Rev. B 83 184428Google Scholar
[37] 许佳玲, 贾利云, 靳晓庆, 郝兴楠, 马丽, 侯登录 2019 物理学报 68 157501Google Scholar
Xu J L, Jia L Y, Jin X Q, Hao X N, Ma L, Hou D L 2019 Acta Phys. Sin. 68 157501Google Scholar
[38] Zhao J T, Zhao K, Wang J J, Yu X Q, Yu J, Wu S X 2012 Acta Phys. Sin. 61 213102 (in Chinses) [赵建涛, 赵昆, 王家佳, 余新泉, 于金, 吴三械 2012 物理学报 61 213102]Google Scholar
Zhao J T, Zhao K, Wang J J, Yu X Q, Yu J, Wu S X 2012 Acta Phys. Sin. 61 213102 (in Chinses)Google Scholar
[39] Kresse G, Hafner J 1993 Phys. Rev. B 47 558Google Scholar
[40] Kresse G, Furthmüller J 1996 Phys. Rev. B 54 11169Google Scholar
[41] Blöchl P E 1994 Phys. Rev. B 50 17953Google Scholar
[42] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865Google Scholar
[43] Sun J, Ruzsinszky A, Perdew J P 2015 Phys. Rev. Lett. 115 036402Google Scholar
[44] Dudarev S L, Botton G A, Savrasov S Y, Humphreys C J, Sutton A P 1998 Phys. Rev. B 57 1505Google Scholar
[45] Togo A, Tanaka I 2015 Scr. Mater. 108 1Google Scholar
[46] Martyna G J, Klein M L, Tuckerman M 1992 J. Chem. Phys. 97 2635Google Scholar
[47] Born M, Huang K, Lax M 1955 Am. J. Phys. 23 474Google Scholar
[48] Wooster W A, Wooster N 1931 Nature 127 782Google Scholar
[49] Dufek V, Petrů F, Brožek V 1967 Monatsh. Chem. 98 2424Google Scholar
[50] Zhang Q, Xu M K, Shen Z R, Wei Q 2017 J. Mater. Sci. Mater. Electron. 28 12056Google Scholar
[51] Zhou S M, Zhu G Y, Wang Y Q, Lou S Y, Hao Y M 2011 Chem. Eng. J. 174 432Google Scholar
[52] Bärnighausen H, Brauer G, Schultz N 1965 Z. Anorg. Allg. Chem. 338 250Google Scholar
[53] Cococcioni M, de Gironcoli S 2005 Phys. Rev. B 71 035105Google Scholar
[54] Henkelman G, Arnaldsson A, Jónsson H 2006 Comput. Mater. Sci. 36 354Google Scholar
[55] Graf T, Felser C, Parkin S S P 2011 Prog. Solid. State Ch. 39 1Google Scholar
[56] Zhang Y H, Wang B, Guo Y, Li Q, Wang J L 2021 Comput. Mater. Sci. 197 110638Google Scholar
[57] Ma F J, Lu Z Y, Xiang T 2008 Phys. Rev. B 78 224517Google Scholar
[58] Xu C, Feng J, Xiang H, Bellaiche L 2018 NPJ Comput. Mater. 4 57Google Scholar
[59] Šabani D, Bacaksiz C, Milošević M V 2020 Phys. Rev. B 102 014457Google Scholar
[60] 张杰 2023 博士学位论文 (北京: 中国科学院物理研究所)
Zhang J 2023 Ph. D. Dissertation (Beijing: Institute of Physics, Chinese Academy of Sciences
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图 1 CrO2单层的原子结构图 (a)俯视图; (b)侧视图; (c)立体图, 黑色虚线框表示原胞; (d) CrO2单层的声子谱; (e) CrO2单层在1000 K下总势能随时间的演化曲线, 时间范围为5 ps, 插图为经过5 ps分子动力学模拟后CrO2最终构型的俯视图和侧视图
Figure 1. Atomic structure of CrO2 monolayer: (a) Top view; (b) side view; (c) oblique view, the unit cell is marked by the black dashed line square; (d) phonon spectra of CrO2 monolayer; (e) total energy evolution with time at 1000 K. The illustration shows a top and side view of the final configuration of CrO2 after 5 ps molecular dynamics simulation.
图 2 (a) Cr-O系统的凸包图, 五角星表示本工作中的CrO2单层结构; (b) Cr原子的d轨道电子数对Hubbard U的响应关系, 红线和蓝线表示自洽计算和非自洽计算的结果
Figure 2. (a) Convex hull of formation energy of the Cr-O systems, the star is the CrO2 monolayer in this work; (b) the response of d electron number to the small U perturbation, red and blue symbols correspond to the results from the self-consistent and non-self-consistent calculations.
图 5 (a) CrO2单层结构的俯视图, J1和J2分别表示最近邻和次近邻Cr原子间的交换耦合系数; (b) FM序; (c) AFM-I序; (d) AFM-II序, 不同磁序下的原胞用黑色虚线框表示, 红色箭头和蓝色箭头表示相反的磁矩指向
Figure 5. (a) Nearest and next-nearest neighbor exchange couplings, J1 and J2, represented by the double arrows; (b) ferromagnetic order; (c) antiferromagnetic order I (AFM-I); (d) antiferromagnetic order II (AFM-II), the magnetic unit cells are marked with the dashed line, red and blue arrows indicate the opposite directions of Cr magnetic moments.
表 1 CrO2在FM, AFM-Ⅰ和AFM-Ⅱ磁序的能量, 单个Cr原子的局域磁矩, 交换耦合系数J1和J2, 单离子磁各向异性能A和居里温度TC. FM能量设置为零
Table 1. Energies in the FM, AFM-I, and AFM-II orders, the nearest and next-nearest neighbor exchange couplings J1 and J2, the anisotropic energy, the Curie temperature. The FM energy is set to zero.
Method EFM/meV EAFM-Ⅰ/meV EAFM-Ⅱ/meV Moment/μB J1/(meV·S–2) J2/(meV·S–2) A/(meV·S–2) TC/K GGA + U 0 120.23 167.96 2.4 –41.99 –9.06 –0.195 461 SCAN 0 109.71 191.43 2.2 –47.86 –3.50 –0.103 422 -
[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 666Google Scholar
[2] Zhang H 2015 ACS Nano 9 9451Google Scholar
[3] Gong C, Li L, Li Z L, Ji H W, Stern A, Xia Y, Cao T, Bao W, Wang C Z, Wang Y, Qiu Z Q, Cava R J, Louie S G, Xia J, Zhang X 2017 Nature 546 265Google Scholar
[4] Huang B, Clark G, Navarro-Moratalla E, Klein D R, Cheng R, Seyler K L, Zhong D, Schmidgall E, McGuire M A, Cobden D H, Yao W, Xiao D, Jarillo-Herrero P, Xu X 2017 Nature 546 270Google Scholar
[5] Gong C, Zhang X 2019 Science 363 eaav4450Google Scholar
[6] Balan A P, Radhakrishnan S, Woellner C F, Sinha S K, Deng L, de los Reyes C, Rao B M, Paulose M, Neupane R, Apte A, Kochat V, Vajtai R, Harutyunyan A R, Chu C W, Costin G, Galvao D S, Martí A A, van Aken P A, Varghese O K, Tiwary C S, Iyer A M M R, Ajayan P M 2018 Nat. Nanotechnol. 13 602Google Scholar
[7] Balan A P, Radhakrishnan S, Kumar R, Neupane R, Sinha S K, Deng L Z, de los Reyes C A, Apte A, Rao B M, Paulose M, Vajtai R, Chu C W, Costin G, Martí A A, Varghese O K, Singh A K, Tiwary C S, Anantharaman M R, Ajayan P M 2018 Chem. Mater. 30 5923Google Scholar
[8] Zhang Y, Chu J W, Yin L, Shifa T A, Cheng Z Z, Cheng R Q, Wang F, Wen Y, Zhan X Y, Wang Z X, He J 2019 Adv. Mater. 31 1900056Google Scholar
[9] Wang H D, Lei P H, Mao X Y, Kong X, Ye X Y, Wang P F, Wang Y, Qin X, Meijer J, Zeng H L, Shi F Z, Du J F 2022 Chin. Phys. Lett. 39 047601Google Scholar
[10] Feng P J, Zhang X H, Zhang S, Liu D P, Gao M, Ma F J, Yan X W, Xie Z Y 2022 ACS Omega 7 43316Google Scholar
[11] Liu D P, Zhang S, Gao M, Yan X W, Xie Z Y 2021 Appl. Phys. Lett. 118 223104Google Scholar
[12] Feng P J, Zhang S, Liu D P, Gao M, Ma F J, Yan X W, Xie Z Y 2022 J. Phys. Chem. C 126 10139Google Scholar
[13] Liu D P, Feng P J, Gao M, Yan X W 2021 Phys. Rev. B 103 155411Google Scholar
[14] Zhang S, Feng P J, Liu D P, Wu H F, Gao M, Xu T S, Xie Z Y, Yan X W 2022 Phys. Rev. B 106 235402Google Scholar
[15] Wang Y, Guo Y, Wang Z K, Fu L, Zhang Y, Xu Y J, Yuan S J, Pan H Z, Du Y W, Wang J L, Tang N J 2021 ACS Nano 15 12069Google Scholar
[16] Wang Y, Xu W, Fu L, Zhang Y, Wu Y Z, Wu L T, Yang D Y, Peng S Z, Ning J, Zhang C, Cui X, Zhong W, Liu Y, Xiong Q H, Han G Q, Hao Y 2023 ACS Appl. Mater. Interfaces 15 54797Google Scholar
[17] Wang Y, Xu W, Yang D Y, Zhang Y, Xu Y J, Cheng Z X, Mi X K, Wu Y Z, Liu Y, Hao Y, Han G Q 2023 ACS Nano 17 24320Google Scholar
[18] Zha H M, Li W, Zhang G J, Liu W J, Deng L W, Jiang Q, Ye M, Wu H, Chang H X, Qiao S 2023 Chin. Phys. Lett. 40 087501Google Scholar
[19] Huang P, Zhang P, Xu S G, Wang H D, Zhang X W, Zhang H 2020 Nanoscale 12 2309Google Scholar
[20] Lin Z C, Peng Y X, Wu B C, Wang C S, Luo Z C, Yang J B 2022 Chin. Phys. B 31 087506Google Scholar
[21] Cava R J 2000 J. Am. Ceram. Soc. 83 5Google Scholar
[22] Wilson R M 2019 Phys. Today 72 19Google Scholar
[23] Chen H H, Yang Y F, Zhang G M, Liu H Q 2023 Nat. Commun. 14 5477Google Scholar
[24] Rasmussen F A, Thygesen K S 2015 J. Phys. Chem. C 119 13169Google Scholar
[25] Topsakal M, Cahangirov S, Bekaroglu E, Ciraci S 2009 Phys. Rev. B 80 235119Google Scholar
[26] Yang J, Jiang Y L, Li L J, Muhire E, Gao M Z 2016 Nanoscale 8 8170Google Scholar
[27] Zhang F, Zhu J J, Zhang D L, Schwingenschlögl U, Alshareef H N 2017 Nano Lett. 17 1302Google Scholar
[28] de Groot R A, Mueller F M, van Engen P G, Buschow K H J 1983 Phys. Rev. Lett. 50 2024Google Scholar
[29] Wolf S A, Awschalom D D, Buhrman R A, Daughton J M, von Molnár S, Roukes M L, Chtchelkanova A Y, Treger D M 2001 Science 294 1488Google Scholar
[30] Schwarz K 1986 J. Phys. F: Met. Phys. 16 L211Google Scholar
[31] Dedkov Yu S, Rüdiger U, Güntherodt G 2002 Phys. Rev. B 65 064417Google Scholar
[32] Ji Y, Strijkers G J, Yang F Y, Chien C L, Byers J M, Anguelouch A, Xiao G, Gupta A 2001 Phys. Rev. Lett. 86 5585Google Scholar
[33] Xie W H, Liu B G, Pettifor D G 2003 Phys. Rev. B 68 134407Google Scholar
[34] 程志梅, 王新强, 王风, 鲁丽娅, 刘高斌, 段壮芬, 聂招秀 2011 物理学报 60 096301Google Scholar
Cheng Z M, Wang X Q, Wang F, Lu L Y, Liu G B, Duan Z F, Nie Z X 2011 Acta Phys. Sin. 60 096301Google Scholar
[35] Kobayashi K I, Kimura T, Sawada H, Terakura K, Tokura Y 1998 Nature 395 677Google Scholar
[36] Alijani V, Winterlik J, Fecher G H, Naghavi S S, Felser C 2011 Phys. Rev. B 83 184428Google Scholar
[37] 许佳玲, 贾利云, 靳晓庆, 郝兴楠, 马丽, 侯登录 2019 物理学报 68 157501Google Scholar
Xu J L, Jia L Y, Jin X Q, Hao X N, Ma L, Hou D L 2019 Acta Phys. Sin. 68 157501Google Scholar
[38] Zhao J T, Zhao K, Wang J J, Yu X Q, Yu J, Wu S X 2012 Acta Phys. Sin. 61 213102 (in Chinses) [赵建涛, 赵昆, 王家佳, 余新泉, 于金, 吴三械 2012 物理学报 61 213102]Google Scholar
Zhao J T, Zhao K, Wang J J, Yu X Q, Yu J, Wu S X 2012 Acta Phys. Sin. 61 213102 (in Chinses)Google Scholar
[39] Kresse G, Hafner J 1993 Phys. Rev. B 47 558Google Scholar
[40] Kresse G, Furthmüller J 1996 Phys. Rev. B 54 11169Google Scholar
[41] Blöchl P E 1994 Phys. Rev. B 50 17953Google Scholar
[42] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865Google Scholar
[43] Sun J, Ruzsinszky A, Perdew J P 2015 Phys. Rev. Lett. 115 036402Google Scholar
[44] Dudarev S L, Botton G A, Savrasov S Y, Humphreys C J, Sutton A P 1998 Phys. Rev. B 57 1505Google Scholar
[45] Togo A, Tanaka I 2015 Scr. Mater. 108 1Google Scholar
[46] Martyna G J, Klein M L, Tuckerman M 1992 J. Chem. Phys. 97 2635Google Scholar
[47] Born M, Huang K, Lax M 1955 Am. J. Phys. 23 474Google Scholar
[48] Wooster W A, Wooster N 1931 Nature 127 782Google Scholar
[49] Dufek V, Petrů F, Brožek V 1967 Monatsh. Chem. 98 2424Google Scholar
[50] Zhang Q, Xu M K, Shen Z R, Wei Q 2017 J. Mater. Sci. Mater. Electron. 28 12056Google Scholar
[51] Zhou S M, Zhu G Y, Wang Y Q, Lou S Y, Hao Y M 2011 Chem. Eng. J. 174 432Google Scholar
[52] Bärnighausen H, Brauer G, Schultz N 1965 Z. Anorg. Allg. Chem. 338 250Google Scholar
[53] Cococcioni M, de Gironcoli S 2005 Phys. Rev. B 71 035105Google Scholar
[54] Henkelman G, Arnaldsson A, Jónsson H 2006 Comput. Mater. Sci. 36 354Google Scholar
[55] Graf T, Felser C, Parkin S S P 2011 Prog. Solid. State Ch. 39 1Google Scholar
[56] Zhang Y H, Wang B, Guo Y, Li Q, Wang J L 2021 Comput. Mater. Sci. 197 110638Google Scholar
[57] Ma F J, Lu Z Y, Xiang T 2008 Phys. Rev. B 78 224517Google Scholar
[58] Xu C, Feng J, Xiang H, Bellaiche L 2018 NPJ Comput. Mater. 4 57Google Scholar
[59] Šabani D, Bacaksiz C, Milošević M V 2020 Phys. Rev. B 102 014457Google Scholar
[60] 张杰 2023 博士学位论文 (北京: 中国科学院物理研究所)
Zhang J 2023 Ph. D. Dissertation (Beijing: Institute of Physics, Chinese Academy of Sciences
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