First principles simulations of nanomaterials for nanoelectronics and spintronics

First-principles Simulations of Nanomaterials for Nanoelectronics and Spintronics CAI YONGQING (B.Sc., Northwestern Polytechnical University) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF PHYSICS NATIONAL UNIVERSITY OF SINGAPORE 2011 Acknowledgements First of all, I would like to thank my supervisor, Prof. Feng Yuan Ping. Prof. Feng has given me lots of guidance and encouragement during the past years. I am grateful to him for his word-by-word corrections of my manuscript and thesis, and his support for me to attend the conference at ICTP. I would like to thank my co-supervisor Dr. Zhang Chun, who has provided a lot of help and suggestions on my research work. I got many insights from discussions with his sharp mind and plenty of experience in the computational physics. I would like to thank the previous and current members in the group. At the early stage of my research, I got a lot of help from Wu Rongqin, Peng Guowen, and Lu Yunhao. I had many useful discussions with them and other group members including Ge MinYuan, Yang Ming, Zhou Miao, Sha Zhendong, Shen Lei, Bai Zhaoqiang, Dai Zhenxiang, Zhang Aihua, and Yang Kesong. At last, I would like to thank my parents, relatives and friends. Especially i thank my parents for their support and love, and thanks Ke Qingqing for being patient and enlightening with me in the past three years. i Table of Contents Acknowledgements i Abstract v Publications vii List of Tables x List of Figures xi Introduction 1.1 Quasi one-dimensional (1D) nanomaterials as building blocks of nanoelectronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Molecular electronic devices: molecular diode and molecular switch 1.2.1 Molecular diode . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.2 Molecular switch . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Highly spin-polarized materials for spintronics . . . . . . . . . . . . 1.4 Objectives and scope of the thesis . . . . . . . . . . . . . . . . . . . 12 1.2 First-principles Methods 2.1 Density functional theory . . . . . . . . . . . . . . . . . . . . . . . . 15 16 ii 2.2 2.3 2.1.1 Hohenberg-Kohn theory and Kohn-Sham equation . . . . . . 17 2.1.2 LDA and GGA . . . . . . . . . . . . . . . . . . . . . . . . . 20 Implementation of density functional theory . . . . . . . . . . . . . 22 2.2.1 Pseudopotential . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.2.2 Planewave Basis . . . . . . . . . . . . . . . . . . . . . . . . . 25 Non-equilibrium Green’s function method . . . . . . . . . . . . . . 26 2.3.1 Green’s function . . . . . . . . . . . . . . . . . . . . . . . . 26 2.3.2 Open systems and NEGF . . . . . . . . . . . . . . . . . . . 28 2.3.3 Implementation of NEGF combined with DFT . . . . . . . . 30 Switching and rectification of a single light-sensitive diarylethene molecule sandwiched between graphene nanoribbons 33 3.1 Computational details . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.2 Photochromic switching . . . . . . . . . . . . . . . . . . . . . . . . 37 3.2.1 Molecular electronic structure . . . . . . . . . . . . . . . . . 37 3.2.2 Linear conductance and molecular switch . . . . . . . . . . . 38 3.3 Rectification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Functionalization of gold nanotubes and carbon nanotubes 4.1 54 Adsorbate and defect effects on electronic and transport properties of gold nanotubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 4.1.1 Computational details . . . . . . . . . . . . . . . . . . . . . 55 4.1.2 Structures and energetics of adsorbates on gold nanotubes . 55 4.1.3 Electronic structures of CO and O adsorbed gold nanotubes 60 4.1.4 Conductance of CO and O absorbed Au tubes . . . . . . . . 64 iii 4.1.5 4.2 4.3 Defect effects on conductance of Au tubes: Au adsorbate and vacancy . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Mechanically and chemically tuning of the work function of CNT . 68 4.2.1 Work function of CNT . . . . . . . . . . . . . . . . . . . . . 68 4.2.2 Computational details . . . . . . . . . . . . . . . . . . . . . 69 4.2.3 Strain effects on work function of pristine CNT . . . . . . . 71 4.2.4 Work function of potassium-adsorbed CNT . . . . . . . . . . 74 4.2.5 Strain effect on work function of potassium-decorated CNT . 75 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Strain effect on the spin injection and electronic tunneling of Co2 CrAl/NaNbO3 /Co2 CrAl 82 5.1 Computational details . . . . . . . . . . . . . . . . . . . . . . . . . 83 5.2 Energetics and electronic structure analysis . . . . . . . . . . . . . . 84 5.3 Strain effects on the spin injection and tunnel magnetoresistance . . 88 5.4 Strain effects on the tunnel magnetoresistance . . . . . . . . . . . . 91 5.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Conclusions and perspectives 95 References 98 iv Abstract Rapid developments of nanoelectronics and spintronics call for the design of new materials for building blocks of nanoscale electronic devices. In this thesis, first principles calculations were carried out to study the physical properties of various kinds of nanomaterials and investigate their potential applications in nanoelectronics and spintronics. Firstly, we studied coherent electronic transport through a single light sensitive diarylethene molecule sandwiched between two graphene nanoribbons (GNRs). The “open” and “closed” isomers of the diarylethene molecule that can be converted between each other upon photo-excitation were found to have drastically different current-voltage characteristics. More importantly, when one GNR is metallic and another one is semiconducting, strong rectification behavior of the “closed” diarylethene isomer with the rectification ratio >103 was observed. The results open possibilities for the design of a new class of molecular electronic devices. Secondly, electronic and/or transport properties of gold nanotubes and carbon nanotubes (CNTs) were studied. For gold nanotubes, effects of adsorbates (CO molecule and O atom) and defects on the electronic and transport properties of v Au (5,3) and Au (5,5) nanotubes were investigated. After CO adsorption, the conductance of Au (5,3) decreases by 0.9 G0 , and the conductance of Au (5,5) decreases by approximately 0.5 G0 . For O adsorbed Au tubes, O atoms strongly interact with Au tubes, leading to around G0 of drop of conductance for both Au tubes. When a monovacancy defect is present, the conductance decreases by around G0 for both tubes. For CNT, strain dependence of work functions of both pristine and potassium doped CNTs was calculated. We found that for pristine cases, the uniaxial strain has strong effects on the work functions of CNTs, and the responses of work functions of CNT (5,5) and (9,0) to the strain are distinctly different. When coated with potassium, for both CNTs, work functions can be reduced by more than 2.0 eV, and the strain dependence of work functions changes drastically. Finally, effects of strain on transport properties of Co2 CrAl/NaNbO3 /Co2 CrAl magnetic tunneling junction (MTJ) were studied. Both spin polarization and tunnel magnetoresistance (TMR) of the MTJ were found to respond to positive (tensile) and negative (compressive) strains asymmetrically. While a compressive strain up to 4% causes slight increases in the spin polarization and small fluctuations in TMR, a tensile strain of a few percent significantly reduces the TMR. This study provides a theoretical understanding on relationship between transport properties through a MTJ and interface atomic structural changes induced by an external strain. vi Publications [1] Yongqing Cai, Miao Zhou, Minggang Zeng, Chun Zhang, Yuan Ping Feng, “Adsorbate and defect effects on electronic and transport properties of gold nanotubes”, Nanotechnology 22, 215702 (2011). [2] Yongqing Cai, Aihua Zhang, Yuan Ping Feng, Chun Zhang, Hao Fatt Teoh, Ghim Wei Ho, “Strain effects on work functions of pristine and potassium-decorated carbon nanotubes”, J. Chem. Phys., 131, 224701 (2009). [3] M. G. Zeng, L. Shen, Y. Q. Cai, Z. D. Sha, Y. P. Feng, “Perfect spin-filter and spin-valve in carbon atomic chains”, Appl. Phys. Lett. 96, 042104 (2010). [4] M. Zhou, Y. Q. Cai, M. G. Zeng, C. Zhang, Y. P. Feng, “Mn-doped thiolated Au-25 nanoclusters: Atomic configuration, magnetic properties, and a possible high-performance spin filter”, Appl. Phys. Lett. 98, 143103 (2011). [5] Yongqing Cai, Chun Zhang, Yuan Ping Feng, “Dielectric properties and lattice dynamics of α-PbO2-type TiO2 : The role of soft phonon modes in pressure-induced phase transition to baddeleyite-type TiO2 ”, Phys. Rev. B 84, 094107 (2011). [6] Yongqing Cai, et. al., “Strain effect on the spin injection and electronic conductance of Co2 CrAl/NaNbO3 /Co2 CrAl magnetic tunneling junction”, Manuscript vii finished for Phys. Rev. B submission. [7] Yongqing Cai, Aihua Zhang, Yuan Ping Feng, and Chun Zhang, “Switching and Rectification of a Single Light-sensitive Diarylethene Molecule Sandwiched between Graphene Nanoribbons”, J. Chem. Phys. 135, 184703 (2011). [8] Y. H. Lu, R. Q. Wu, L. Shen, M. Yang, Z. D. Sha, Y. Q. Cai, P. M. He, Y. P. Feng, “Effects of edge passivation by hydrogen on electronic structure of armchair graphene nanoribbon and band gap engineering”, Appl. Phys. Lett. 94, 122111 (2009). [9] Z. D. Sha, R. Q. Wu, Y. H. Lu, L. Shen, M. Yang, Y. Q. Cai, Y. P. Feng, Y. Li, “Glass forming abilities of binary Cu(100-x)Zr(x) (34, 35.5, and 38.2 at. %) metallic glasses: A LAMMPS study”, J. Appl. Phys. 105, 043521 (2009). [10] M. Yang, R. Q. Wu, W. S. Deng, L. Shen, Z. D. Sha, Y. Q. Cai, Y. P. Feng, J. S. Wang, “Electronic structures of beta-Si(3)N(4)(0001)/Si(111) interfaces: Perfect bonding and dangling bond effects”, J. Appl. Phys. 105, 024108 (2009). [11] R. Q. Wu, L. Shen, M. Yang, Z. D. Sha, Y. Q. Cai, Y. P. Feng, Z. G. Huang, Q. Y. Wu, “Enhancing hole concentration in AlN by Mg : O codoping: Ab initio study”, Phys. Rev. B 77, 073203 (2008). [12] R. Q. Wu, L. Shen, M. Yang, Z. D. Sha, Y. Q. Cai, Y. P. Feng, Z. G. Huang, Q. Y. Wu, “Possible efficient p-type doping of AlN using Be: An ab initio study”, Appl. Phys. Lett. 91, 152110 (2007). [13] Zhaoqiang Bai, Yongqing Cai, Lei Shen, Ming Yang, Viloane Ko, Guchang Han, and Yuanping Feng, Magnetic and transport properties of Mn3−x Ga/MgO/Mn3−x Ga viii magnetic tunnel junctions: A first-principles study, Appl. Phys. Lett. 100, 022408 (2012). ix Chapter 6. Conclusions and perspectives to the band gap of the semiconducting GNR. Therefore, the appropriate choice of the band gap of the semiconducting electrode and the alignment of the molecule’s frontier orbitals with the semiconducting gap are important for achieving the high rectification ratio. Moreover, the interface states localized in molecule-GNR contacts were found to play important roles in electron tunneling. The reported rectification mechanism provides a new way to achieve high rectification ratio (>>100) in single-molecule based devices, and the asymmetric G-D-G junctions may form the basis for a new class of high-performance molecular rectifiers. For gold nanotube and CNTs, chemical modification and mechanical loading are found to be two effective ways of tuning the properties of these nanotube systems. For gold nanotubes, the influence of adsorbates (CO molecule and O atom) on the electronic and transport properties of Au (5,3) and Au (5,5) nanotubes was investigated. For CO adsorption, the calculation predicts that the drop of conductance of Au(5,5) (0.5 G0 ) is about a half of that of Au(5,3) (0.9 G0 ). The backdonation mechanism exists for both tubes which is manifested in the variations of the C-O bond length and stretching frequency of CO molecule on the tubes with different amounts of the occupancy of the antibonding 2π ∗ orbital. Our conductance calculations show that the adsorption of O atom strongly distorts the Au tubes, which blocks two channels for transmission for both tubes. In addition, the metallic bonding nature of Au-Au bond and high mobility of Au atoms suggest that these systems are prone to be defective. Effect of defects either arising from the Au adsorption or Au vacancy, which are unavoidable during the production, on conductance and transport has been calculated. The result shows that Au adatoms can be deposited on the tubes with relatively large adsorption energies. For both 96 Chapter 6. Conclusions and perspectives tubes the vacancy leads to about 20% decrease of conductance. For CNTs, variations of work functions with strain for both pristine and potassium coated CNT (5,5) and CNT (9,0) are calculated. For pristine cases, the strain shows strong effects on work functions of both CNTs, and the work function of CNT (5,5) behaves quite differently with strain from that of CNT (9,0). We also found that the strain has great influence on K-coated CNTs. Work functions of K-coated CNTs show drastically different strain dependence from that of pristine cases. Our findings strongly suggest that tuning of strain may be a powerful method in controlling work functions of CNT-based systems. The last part of this thesis is devoted to the spin polarization and spin injection of Co2 CrAl/NaNbO3 /Co2 CrAl MTJ. The electronic structure and variations of spin polarization and TMR ratio with strain for Co2 CrAl/NaNbO3 /Co2 CrAl MTJ are investigated. Both the SP and TMR present asymmetrical responses to positive and negative strains. It is well accepted that chemical defect such as vacancy and antisite which can destroy the half-metallic character of Heusler alloy, however, our study shows that strain can lead to huge modifications of properties of Heulser/semiconductor junctions. Future work may be carried out to study the effect of coexistence of strain and chemical defects at the interface on TMR properties. 97 References [1] H. Ohnishi, Y. Kondo, and K. Takayanagi, Nature (London) 395, 780 (1998). [2] V. Rodrigues, J. Bettini, A. R. Rocha, L. G. C. Rego, and D. Ugarte, Phys. Rev. B 65, 153402 (2002). [3] G. Sclauzero, A. Dal Corso, A. Smogunov, and E. Tosatti, Phys. Rev. B 78, 085421 (2008). [4] A. Bogozi, O. Lam, H. X. He, C. Z. Li, N. J. Tao, L. A. Nagahara, T. Amlani, R. Tsui, J. Am. Chem. Soc. 123, 4585 (2001). [5] S. L. Elizondo and J. W. Mintmire, Phys. Rev. B 73, 045431 (2006). [6] R.T. Senger, S. Dag, and S. Ciraci, Phys. Rev. Lett. 93, 196807 (2004). [7] N. Agra¨ıt, A. L. Yeyati, J. M. van Ruiten beek, Phys. Rep. 377, 81 (2003). [8] Y. Oshima, A. Onga, and K. Takayanagi, Phys. Rev. Lett. 91, 205503 (2003). [9] T. Ono, and K. Hirose, Phys. Rev. Lett. 94, 206806 (2005). [10] D. Z. Manrique, J. Cserti, and C. J. Lambert, Phys. Rev. B 81, 073103 (2010). [11] C. Z. Li, H. Sha, and N. J. Tao, Phys. Rev. B 58, 6775 (1998). 98 References [12] H. Hakkinen, R. N. Barnett, U. Landman, J. Phys. Chem. B 103, 8814 (1999). [13] A. Calzolari, C. Cavazzoni, and M. B. Nardelli, Phys. Rev. Lett. 93, 096404 (2004). [14] S. Iijima, Nature 354, 56 (1991) [15] K. I. Bolotin, K. J. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, P. Kim, and H. L. Stormer, Solid State Commun. 146, 351 (2008). [16] M. G. Zeng, L. Shen, Y. Q. Cai, Z. D. Sha, Y. P. Feng, Appl. Phys. Lett. 96, 042104 (2010). [17] J. Kong, E. Yenilmez, T. W. Tombler, W. Kim, H. Dai, R. B. Laughlin, L. Liu, C. S. Jayanthi, and S. Y. Wu, Phys. Rev. Lett. 87, 106801 (2001). [18] P. Kim, L. Shi, A. Majumdar, and P. L. McEuen, Phys. Rev. Lett. 87, 215502 (2001). [19] M. Horibe,M. Nihei, D. Kondo, A. Kawabata, and Y. Awano, Jpn. J. Appl. Phys. 43, 7337 (2004). [20] S. J. Tans, M. H. Devoret, H. Dai, A. Thess, R. E. Smalley, L. J. Geerligs, and C. Dekker, Nature (London) 386, 474 (1997). [21] H. W. Ch. Postma, T. Teepen, Z. Yao, M. Grifoni, and C. Dekker, Science 293, 76 (2001). [22] V. Derycke, R. Martel, J. Appenzeller, and Ph. Avouris, Nano Lett. 9, 453 (2001). [23] S. J. Tans, A. R. M. Verschueren, and C. Dekker, Nature 393, 49 (1998). 99 References [24] D. Kang, N. Park, J.-h. Ko, E. Bae and W. Park, Nanotechnology 16, 1048 (2005). [25] M. Bockrath, J. Hone, A. Zettl, P. L. McEuen, A. G. Rinzler, and R. E. Smalley, Phys. Rev. B 10606, 61 (2000). [26] V. Derycke, R. Martel, J. Appenzeller, and P. Avouris, Nano Lett. 1, 453 (2001). [27] Y. Nosho, Y. Ohno, S. Kishimoto, and T. Mizutani: Appl. Phys. Lett. 86, 073105 (2005). [28] Z. Y. Zhang, et. al., Nano Lett. 7, 3603 (2007). [29] L. M. Zhang, M. M. Fogler, Phys. Rev. Lett. 100, 116804 (2008). [30] A. Ossipov, M. Titov, C. W. J. Beenakker, Phys. Rev. B 75, 241401 (2007). [31] A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, A. K. Geim, Rev. Mod. Phys. 81, 109-162 (2009). [32] D. V. Kosynkin, A. L. Higginbotham, A. Sinitskii, J. R. Lomeda, A. Dimiev, B. K. Price, J. M. Tour, Nature 458, 872 (2009). [33] Y. Yoon and J. Guo, Appl. Phys. Lett 91, 73103 (2007). [34] D. Basu, M. J. Gilbert, L. F. Register, S. K. Banerjee, and A. H. MacDonald, Appl. Phys. Lett 92, 042114 (2008). [35] Y. B. Zhang, T.-T. Tang, C. Girit, Z. Hao, M. C. Martin, A. Zettl, M. F. Crommie, Y. R. Shen, and F. Wang, Nature (London) 459, 820 (2009). 100 References [36] S. Y. Zhou, D. A. Siegel, A. V. Fedorov, and A. Lanzara, Phys. Rev. Lett. 101, 086402 (2008). [37] S. K. Saha, R. Ch. Chandrakanth, H. R. Krishnamurthy, and U. V. Waghmare, Phys. Rev. B 80, 155414 (2009). [38] F. Guinea, M. I. Katsnelson, and A. K. Geim, Nat. Phys. 6, 30 (2009). [39] C. H. Park, L. Yang, Y. W. Son, M. L. Cohen, and S. G. Louie, Nat. Phys. 4, 213 (2008). [40] H. Min, B. Sahu, S. K. Banerjee, and A. H. MacDonald, Phys. Rev. B, vol. 75, 155115 (2007). [41] A. Aviram, M. A. Ratner, Chem. Phys. Lett. 29, 277 (1974). [42] N. J. Geddes, J. R. Sambles, D. J. Jarvis, W. G. Parker, D. J. Sandman, Appl. Phys. Lett. 56, 1916 (1990). [43] R. M. Metzger, Acc. Chem. Res. 32, 950 (1999). [44] M.-K. Ng, and L. Yu, Angew. Chem. Int. Ed. 41, 3598 (2002). [45] M. Elbing, et al. Proc. Natl Acad. Sci. USA 102, 8815 (2005). [46] B. Song, D. A. Ryndyk, G. Cuniberti, Phys. Rev. B 76, 045408 (2007). [47] E. G. Petrov, Y. R. Zelinsky, V. May, P. H¨anggi, J. Chem. Phys. 127, 084709 (2007). [48] A. Broo, M. C. Zerner, Chem. Phys. 196, 423 (1995). 101 References [49] J. Reichert, R. Ochs, D. Beckmann, H. B. Weber, M. Mayor, and H. von L¨ohneysen, Phys. Rev. Lett. 88, 176804 (2002) [50] B. Larade, and A. M. Bratkovsky, Phys. Rev. B 68, 235305 (2003). [51] A. Troisi and M. A. Ratner, J. Am. Chem. Soc. 124, 14528 (2002). [52] R. M. Metzger, Chem. Phys. 326, 176-187 (2006). [53] K. Stokbro, J. Taylor, M. Brandbyge, J. Am. Chem. Soc. 125, 3674-3675 (2003). [54] N. Armstrong, R. C. Hoft, A. McDonagh, M. B. Cortie, M. J. Ford, Nano Lett. 7, 3018-3022 (2007). [55] D. Q. Andrews, G. C. Solomon, R. P. Van Duyne, M. A. Ratner, J. Am. Chem. Soc. 130, 17309 (2008). [56] W. Y. Kim and K. S. Kim, Acc. Chem. Res. 43, (2010). [57] C. Zhang, M. H. Du, H. P. Cheng, X. G. Zhang, A. E. Roitberg, J. L Krause, Phys. Rev. Lett. 92, 158301 (2004). [58] S. Kawata, Y. Kawata, Chem. Rev. 100, 1777 (2000). [59] N. Weibel, S. Grunder, M. Mayor, Org. Biomol. Chem. (2007). [60] T. Kudernac, S. J. van der Molen Molen, B. J. van Wees, B. L. Feringa, Chem. Commun. 34 (2006). [61] M. Ikeda, N. Tanifuji, H. Yamaguchi, M. Irie, K. Matsuda, Chem. Commun. 13 (2007). 102 References [62] S. J. van der Molen, H. van der Vegte, T. Kudernac, I. Amin, B. L. Feringa, B. J. van Wees, Nanotechnology, 17, 310 (2006). [63] S. J. van der Molen, J. Liao, T. Kudernac, J. S. Agustsson, L. Bernard, M. Calame, B. J. van Wees, B. L. Feringa, C. Sch¨onenberger, Nano Lett. 9, 76-80 (2009). [64] W. R. Browne, B. L. Feringa, Annu. Rev. Phys. Chem. 60 (2009). [65] D. Dulic, S. J. van der Molen, T. Kudernac, H.T. Jonkman, J. J. D. de Jong, T. N. Bowden, J. van Esch, B. L. Feringa, B. J. van Wees, Phys. Rev. Lett. 91, 207402 (2003). [66] M. Zhuang, M. Ernzerhof, Phys. Rev. B 72, 073104 (2005). [67] J. He, F. Chen, P. A. Liddell, et. al., Nanotechnology, 16, 695 (2005). [68] F. Mott, Proc. Roy. Soc. A 153, 699 (1936). [69] R. Meservey and P. M. Tedrow, Phys. Rev. Lett. 26, 192 (1971). [70] M. Julli`ere, Phys. Lett. A 54, 225 (1975). [71] M. N. Baibich, J. M. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff, P. Etienne, G. Creuzet, A. Friederich, and J. Chazelas, Phys. Rev. Lett. 61, 2472 (1988). [72] G. Binash, P. A. Grnberg, F. Saurenbach, and W. Zinn, Phys. Rev. B 39, 4828 (1989). [73] S. Yuasa et al., Nature Mater. 3, 868 (2004). 103 References [74] K. D. Belashchenko, E. Y. Tsymbal, I. I. Oleynik, and M. van Schilfgaarde, Phys. Rev. B 71, 224422 (2005). [75] A. Yanase and K. Siratori, J. Phys. Soc. Jpn. 53, (1984). [76] K. Schwartz, J. Phys. F, Met. Phys. 16, (1986). [77] K. Kobayashi, T. Kimura, H. Sawada, K. Terakura, and Y. Tokura, Nature 395, 6703 (1998). [78] H. Akinaga, M. Mizuguchi, K. Ono, M. Oshima, J. Magn. Soc. Jpn. 22, 451 (2000). [79] K. Inomata, N. Ikeda, N. Tezuka, R. Goto, S. Sugimoto, M. Wojcik, and E. Jedryka, Sci. Technol. Adv. Mater. (2008). [80] M. Yamamoto, T. Ishikawa, T. Taira, G.-f. Li, K.-i Matsuda and T. Uemura, J. Phys. Condens. Matter 22, 164212(2010). [81] H. L. Yu, et al., Appl. Phy. Lett. 98, 011910 (2011). [82] T. Block, M. J. Carey, B. A. Gurney, and O. Jepsen, Phy. Rev. B 70, 205114 (2004) [83] B. Botters, F. Giesen, J. Podbielski, P. Bach, G. Schmidt, L. W. Molenkamp, and D. Grundler, Appl. Phys. Lett. 89, 242505 (2006) [84] M. J. Pechana, C. Yua, D. Carrb, C. J. Palmstrøm, Journal of Magnetism and Magnetic Materials 286 (2005) 340C345 [85] J. S. Moodera, X. Hao, G. A.Gibson, and R. Meservey, Phys. Rev. Lett. 61, 637 (1988). 104 References [86] A. R. Rocha, el. al. Nature materials, (2006). [87] L. Bogani and W. Wernsdorfer, Nature materials, (2008). [88] M. Born and J. R. Oppenheimer, Ann. Physik 84, 457 (1927). [89] P. Hohenberg and W. Kohn, Phys. Rev. B 136, 864 (1964). [90] W. Kohn and L. J. Sham, Phys. Rev. A 140, 1133 (1965). [91] D. R. Hartree, Proc. Camb. Phil. Sco. 24, 89 (1928). [92] V. Fock, Z. Phys. 61, 126 (1930). [93] A. B. Adib, Density functional theory: Why and how, (2004). [94] D. M. Cepeley and B. J. Alder, Phys. Rev. Lett. 45, 566 (1980). [95] J. P. Perdew and A. Zunger, Phys. Rev. B 23, 5048 (1981). [96] J. P. Perdew and Y. Wang, Phys. Rev. B 45, 13244 (1992). [97] J. P. Perdew, K, Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3867 (1996). [98] D. J. Singh, L. Nordstrom, Planewaves, Pseudopotentials and the LAPW Method, Springer (2006). [99] G. B. Bachelet, D. R. Hamann and M. Schluter, Phys. Rev. B 26, 4199 (1982). [100] D. Vanderbilt, Phys. Rev. B 41, 7892 (1990). [101] P. E. Bl¨ochl, Phys. Rev. B 50, 17953 (1994). [102] N. A. W. Holzwarth, G. E. Matthews, R. B. Dunning, A. R. Tackett, and Y. Zeng, Phys. Rev. B 55, 2005 (1997). 105 References [103] S. Datta, Quantum transport: atom to transistor, (2005). [104] S. Datta, Superlattices and Microstructures, 28, 253 (2000). [105] J. Taylor, H. Guo, J. Wang, Phys. Rev.B 63, 121 104 (2001). [106] M. Brandbyge, J.L. Mozos, P. Ordejon, J. Taylor, K. Stokbro, Phys. Rev. B 65, 165 401 (2002). [107] G. Cuniberti, G. Fagas, K. Richter, Introducing Molecular Electronics, Springer (2005). [108] J. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996). [109] G. Kresse, Furthmller, Phys. Rev. B 54, 11169 (1996). [110] M. Brandbyge, J. -L. Mozos, P. Ordejn, J. Taylor, K. Stokbro, Phys. Rev. B 65, 165401 (2002). [111] N. D. Mermin, H. Wagner, Phys. Rev. Lett. 17, 1133 (1966). [112] Q. Yan, B. Huang, J. Yu, F. Zheng, J. Zang, J. Wu, B. Gu, F. Liu, W. Duan, Nano Lett. 7, 1469 (2007). [113] A. J. Kronemeijer, H. B. Akkerman, T. Kudernac, B. J. Van Wees, B. L. Feringa, P. W. M. Blom, B. De Boer, Adv. Mater. 20, 1467-1473 (2008). [114] J. Li, G. Speyer, O. F. Sankey, Phys. Rev. Lett. 93, 248302 (2004). [115] R. Stadler, V. Geskin, J. Cornil, Adv. Funct. Mater. 18, 1119-1130 (2008). [116] S. Lenfant, C. Krzeminski, C. Delerue, G. Allan, D. Vuillaume, Nano Lett. 3, 741-746 (2003). 106 References [117] P. E. Kornilovitch, A. M. Bratkovsky, R. S. Williams, Phys. Rev. B 66, 165436 (2002). [118] C. Krzeminski, C. Delerue, G. Allan, D. Vuillaume, R. M. Metzger, Phys. Rev. B 64, 085405 (2001). [119] D. Vuillaume, S. Lenfant, Microelectr. Eng. 70, 539-550 (2003). [120] V. Mujicaa, M. A. Ratnerb, A. Nitzan, Chem. Phys. 281,147-150 (2002). [121] W. Y. Kim, K. S. Kim, Acc. Chem. Res. 43,111-120 (2010). [122] H. Cheraghchi, K. Esfarjani, Phys. Rev. B 78, 085123 (2008). [123] S. S. Datta, D. R. Strachan, S. M. Khamis, A. T. Charlie Johnson, Nano Lett. 8,1912-1915 (2008). [124] L. Ci, Z. Xu, L. Wang, W. Gao, F. Ding, K. F. Kelly, B. I. Yakobson, P. M. Ajayan, Nano Res. 1, 116-122 (2008). [125] M. del Valle, R. Gutierrez, C. Tejedor, G. Cuniberti, Nat. Nanotechnol. 2, 176-179 (2007). [126] A. C. Whalley, M. L. Steigerwald, X. Guo, C. Nuckolls, J. Am. Chem. Soc. 129, 12590 (2007). [127] X. Guo, J. P. Small, J. E. Klare, Y. Wang, M. S. Purewal, I. W. Tam, B. H. Hong, R. Caldwell, L. Huang, S. O’Brien, J. Yan, R. Breslow, S. J. Wind, J. Hone, P. Kim, C. Nuckolls, Science 311 (2006). [128] G. Kresse, Furthmller, J. Comput. Mater. Sci. 6, 15 (1996). 107 References [129] J. M. Soler, E. Artacho, J. D. Gale, A. Garca, J. Junquera, P. Ordejn, D. Snchez-Portal, J. Phys. Condens. Matter 14, 2745 (2002). [130] J. Taylor, H. Guo, J. Wang, Phys. Rev. B 63, 245407 (2001). [131] B. Delley, J. Chem. Phys. 92, 508 (1990). [132] B. Delley, J. Chem. Phys. 113, 7756 (2000). [133] R. T. Senger, S. Dag, and S. Ciraci, Phys. Rev. Lett. 93, 196807 (2004). [134] B. Yoon, H. H¨akkinen, U. Landman, A. S. W¨orz, J.-M. Antonietti, S. Abbet, K. Judai, U. Heiz, science 307, 403 (2005). [135] G. Blyholder, J. Phys. Chem. 68, 2772 (1964). [136] M. Kiguchi, D. Djukic, and J. M. van Ruitenbeek, Nanotechnology 18, 035205 (2007). [137] H.-J. Freund and G. Pacchioni, Chem. Soc. Rev. 37, 2224(2008). [138] R. Martel, T. Schmidt, H. R. Shea, T. Hertel, and Ph. Avouris, Appl. Phys. Lett. 73, 17 (1998) [139] H. M. Manohara, E. W. Wong, E. Schlecht, B. D. Hunt, and P. H. Siegel, Nano Letters 5, 1469 (2005) [140] J. Zhao, J. Han, and J. P. Lu, Phys. Rev. B 65, 194301 (2002) [141] B. Shan, K. Cho, Phys. Rev. Lett. 94, 236602 (2005) [142] W. S. Su, T. C. Leung, and C. T. Chan, Phys. Rev. B 76, 235413 (2007) 108 References [143] Y. Cho, C. Kim, H. Moon, Y. Choi, S. Park, C.-K. Lee, S. Han, Nano Letters 8, 81 (2008) [144] Jien Cao, Qian Wang, and Hongjie Dai, Phys. Rev. Lett. 90, 15 (2003) [145] T. W. Tombler, C. Zhou, L. Alexseyev, J. Kong, H. Dai, L. Liu, C. S. Jayanthi, M. Tang, S.-Y. Wu, Nature, 405, 15 (2000) [146] Y. He, C. Zhang, C. Cao, and H.-P. Cheng, Phys. Rev. B, 75, 235429 (2007) [147] S. Sreekala, X.-H. Peng, P. M. Ajayan, and S. K. Nayak, Phys. Rev. B 77, 155434 (2008) [148] J.-Q. Lu, J. Wu, W. Duan, B.-L. Gu, H.T.Johnson, J. Appl. Phys. 97, 114314 (2005) [149] D. Vanderbilt, Phys. Rev. B 41, 7892 (1990) [150] G. Kresse, J. Furthm¨ uller, Comput. Mater. Sci. 6, 15 (1996) Phys. Rev. B 54, 11169 (1996) [151] Y. Wang and J.P. Perdew, Phys. Rev. B 43, 8911 (1991) [152] H.J. Monkhorst and J. D. Pack, Phys. Rev. B 13, 5188 (1976) [153] M.F. Yu, O. Lourie, M.J. Dyer, K. Moloni, T.F. Kelly, R.S. Ruoff, Science 287, 5453(2000) [154] B.G. Demczyk, et al. Sci. Eng. A, 173, 334 (2002) [155] V. Vitale, A. Curioni, and W. Andreoni, J. Am. Chem. Soc.,130 18 (2008) [156] L. Yang, J. Han, Phys. Rev. Lett. 85, (2000) 109 References [157] A. Maiti, Nature Materials, 2, (2003) [158] G. Zhao, Q. Zhang, H. Zhang, G. Yang, O. Zhou, and L.-C. Qin, and J. Tang, Appl. Phys. Lett. 89, 263113 (2006) [159] E. Durgun, S. Dag, V. M. K. Bagci, O. G¨ ulseren, T. Yildirim, and S. Ciraci, Phys. Rev. B 67, 201401 (2003) [160] S. Suzuki, C. Bower, Y. Watanabe, O. Zhou, Appl. Phys. Lett. 76, 26 (2000) [161] G. Henkelman, A. Arnaldsson, Hannes J´onsson, Comput. Mater. Sci. 36, (2006) [162] U. Martinez, L. Giordano, and G. Pacchionia, J. Chem. Phys. 128, 164707 (2008) [163] I. I. Oleinik, et al., Phy. Rev. B 65, 020401(R) (2001). [164] M. Jullie‘re, Phys. Lett. A 54, 225 (1975). [165] Y. Miura, et al., Phy. Rev. B 78, 064416 (2008). [166] M. Nobori, T. Nakano, J. Hasegawa, G. Oomi, Y. Sakuraba, K. Takanashi, Y. Miura, Y. Ohdaira and Y. Ando, Phy. Rev. B 83, 104410 (2011) 110 First-principles Simulations of Nanomaterials for Nanoelectronics and Spintronics CAI YONGQING NATIONAL UNIVERSITY OF SINGAPORE 2011 [...]... band structure of the semiconducting or insulating layer However, strain effect on spin polarization and TMR of MTJ has not been systematically investigated Motivated by the above issues, the aim of this thesis is to study physical properties of various kinds of nanomaterials for applications in nanoelectronics and spintronics devices and to analyze new effects arising from variations such as strain and. .. characteristics of molecules may lead to new devices Building an electronic device on top of individual molecules is one of the ultimate goals in nanoelectronics Recently, spintronics is a particularly promising technology, where the spin states 1 Chapter 1 Introduction of carriers are utilized as an additional degree of freedom for information processing and storage Combination of technologies in spintronics and. .. denote bonds formed by O, N, C and S, respectively Note that hydrogen atoms are not shown in the figure The shadowed area denotes portions in the supercell chosen as electrodes (b) Band structures of 10-, 12-, and 14-aGNR and 6-zGNR The calculated band gaps are 1.21, 0.54, 0.22 eV for 10-aGNR, 12aGNR and 14-aGNR respectively Ca and Cz are the lattice constant of the unit cell of the aGNR and zGNR, respectively... spintronics and nanoelectronics could lead to a new generation of devices with novel functionalities and superior performance 1.1 Quasi one-dimensional (1D) nanomaterials as building blocks of nanoelectronics Quasi 1D nanomaterials such as metallic nanowires and nanotubes are quite promising in nanoelectronics due to their high current density and conductivity.[1–6] As the dimension of materials reduces...List of Tables 4.1 Energetics and structures of adsorbates (CO, O, Au) on Au (5,3) and Au (5,5) nanotubes d is the shortest length of the bonds formed by Au and adsorbates; δQx (x =CO, O, Au) and δQAu are the net partial charge transfers of the adsorbates and the Au atom with the shortest distance from the adsorbates 5.1 58 Calculated cohesive energies and interface bond lengths for. .. structure and transport properties of a single light sensitive diarylethene molecule sandwiched between two GNRs were investigated In Chapter 4, factors that influence the properties of two types of nanotube (gold nanotube and CNT) are discussed For the gold nanotube, the effects of adsorbates (CO molecule and O atom) and defects on the electronic structures and 13 Chapter 1 Introduction conductances of Au... offers a new route towards spintronics, and a new field of molecular spintronics that combines spintronics and molecular electronics is emerging.[86, 87] Among all the molecules, organic molecules are quite promising since they exhibit weak spin-orbit 11 Chapter 1 Introduction Figure 1.3: Schematic pictures of density of states (DOS) of paramagnet, ferromagnet, and half metal and hyperfine interactions... nanotechnology, a variety of nanomaterials, such as nanowires and nanotubes, have been successfully produced, which triggers the emergence of nanoelectronics and provides new opportunities to achieve continuing performance improvement in post-Si technology Among all the produced nanomaterials, carbon based nanomaterials such as carbon nanotubes (CNTs) and graphene are strong candidates in replacing Si... ( . First-principles Simulations of Nanomaterials for Nanoelectronics and Spintronics CAI YONGQING (B.Sc., Northwestern Polytechnical University) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF. 94 6 Conclusions and perspectives 95 References 98 iv Abstract Rapid developments of nanoelectronics and spintronics call for the design of new materials for building blocks of nanoscale electronic. (b) Band structures of 10-, 12-, and 14-aGNR and 6-zGNR. The calculated band gaps are 1.21, 0.54, 0.22 eV for 10-aGNR, 12- aGNR and 14-aGNR respectively. Ca and Cz are the lattice constant of the