The Electronic Properties of SiC Graphene-Like: Doped and No-Doped Case

Transcription

1 Copyright 2011 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Computational and Theoretical Nanoscience Vol. 8, 1 5, 2011 The Electronic Properties of SiC Graphene-Like: Doped and No-Doped Case E. Chigo Anota 1, H. Hernández Cocoletzi 1, A. Bautista Hernández 2, and J. F. Sánchez Ramírez 3 1 Cuerpo Académico de Ingeniería en Materiales-Facultad de Ingeniería Química-BUAP, C. U. San Manuel, C. P , Puebla, México 2 Facultad de Ingeniería-BUAP, C. U. San Manuel, C. P , Puebla, México 3 Unidad Profesional Interdisciplinaria en Ingeniería y Tecnologías Avanzadas-IPN, Av. Instituto Politécnico Nacional 2580, Barrio Laguna Ticomán, 07340, México, DF Using first principles calculations, within GGA (PBE) approximation for the exchange-correlation term, we investigated the structural and electronic properties of graphene like silicon carbide doped with N; the study was done employing a C n H m cluster and considering two types of doping, sustitutional and interstitial. Both cases are stable and a transition from semiconductor (Si 12 C 12 H 12 sheet) to semimetal (Si 12 C 11 NH 12 sheet) is observed. The cohesive energy is almost the same for both structures, which indicates enough stability in order to synthesize this kind of systems. Additionally, a high increment in the polarity when substituting C by N is observed, a change from inert to covalent system happens. Keywords: C n H m Cluster, Silicon Carbide, DFT Theory. 1. INTRODUCTION Based on the discovery of graphene, 1 many compounds were experimentally 2 and theoretically 3 proposed. An excellent review on graphene has been done by Geim. 4 Efforts have been directed to understand the essentials and applications of systems with similar structure. For example, using first principles calculations, Hou and Song, 5 studied the structure and electronic structure of Si n C n n = 1 10 clusters; they found a transition from two dimensional to three dimensional structure as n increases. Bekaroglu et al. 6 found a honeycomb structure for SiC and with behavior of semiconductor, gap equal to 2.53 ev. Additionally, Luxmi and coworkers 7 have studied the formation of graphene on a SiC (0001) surface, giving good conditions of growing; the group of Oida 8 has shown that it is possible to grow graphene using a SiC surface as substrate. As we can see, SiC clusters may be the base for the fabrication of novel materials in the nanoelectronics. 9 Moreover, it would be interesting to modify its properties in order to open the possibilities of usage; this can be done Author to whom correspondence should be addressed. through a doping in two different ways, substitionally or interstitially. In this work we investigate these two effects using first principles calculations within the molecular simulation scheme; the study is done on a coronene like cluster (C 24 H 12, and considering atomic N as the dopant. This model has been successfully used by Chigo 10 to study 2D carbon structures, the boron nitride oxide 11 and a series of nitrides; 3 the Li and F doping process 12 and the adsorption of water, and ozone of boron nitride have been explained too. We obtain the optimum geometry (angle and bond length), the dipole moment, and the vibrational frequencies, as well as binding energy and the difference between HOMO and LUMO (gap). The details of calculations are given in Section 2; Section 3 is devoted to the results and discussion. Finally, conclusions are given. 2. COMPUTATIONAL DETAILS The calculations were done using the Density Functional Theory (DFT) developed by Walter Kohn in the 60 s, and as implemented in the DMOL 3 code available from Accelrys Inc. 19 We utilized the GGA approximation for the exchange-correlation term within the parameterization of Perdew-Burke-Ernzerhof (BBE). 20 Taking J. Comput. Theor. Nanosci. 2011, Vol. 8, No /2011/8/001/005 doi: /jctn

2 The Electronic Properties of SiC Graphene-Like: Doped and No-Doped Case Anota et al. we used charge = 0 and multiplicity = 1. The limit for the orbital was of 0.40 nm; the convergence for the SCF cycles was Ha. The obtainment of non-negative frequencies was the criterion for structural stability. 22 Additional details on the calculations can be found in Refs RESULTS AND DISCUSSION Fig. 1. Cluster model for silicon carbide (Si 12 C 12 H 12. Si 12 C 12 H 12 (Fig. 1) as the initial configuration, we did a substitutional and an interstitial doping. For the first case, Si 12 C 12 x N x H 12 (x = 1 3 (Figs. 2(a and b)) and Si 11 NC 12 H 12 (Fig. 2(c)) structures were analyzed, and for the second one, the configuration Si 12 C 12 NH 12 (Fig. 2(d)) was considered. The double numeric plus polarization (DNP) all electron atomic base for the core, in the singlet ground state was used; this base includes a p orbital for hydrogen, and a d orbital for carbon and silicon atoms. For the substitutional doping we used charge = 0 and multiplicity = 2 and for interstitial one Si 12 C 11 NH 12 (a) Figure 1 depicts the optimum structure of the SiC cluster; we observe a planar geometry with a Si-C bond length of 1.79 Å, very similar to the value for the monomer and the 2D SiC, as indicated in Table I. When a C atom is substituted by an N atom (Fig. 2(a)), the cluster remains unmodified with a N-Si bond length equal to 1.78 Å, the Si-C bond length is unchanged. The former and this cluster poses positive frequencies, this means that both structures are structurally stable. The substitution with three N atoms (Si 12 C 9 N 3 H 12, 12.48% of doping), Figure 2(b), maintains the shape of the mesh and bond lengths, but the cluster becomes structurally. If a Si atom is replaced by a N atom (Si 11 NC 12 H 12 Fig. 2(c)), the system is and the hexagons around the N atom are a little deformed, with variations in the Si-C bonds (Fig. 2(c)). Finally, the interstitial doping (Fig. 2(d)), gave rise to a deformation of the cluster with a planar geometry; the N atom interacts with the mesh forming a heptagon, a pentagon and a tetragon. The C-N bond length has a value of 1.34 Å while the Si-C bond is of 1.67 Å, both with a sp 2 bond like (the original mesh has a sp bond like). Figure 3 shows the HOMO and LUMO for the stable structures; the isosurfaces of molecular orbital for the Initial and final geometry stable (doping at 4.16 %) Si 12 C 11 NH 12 Si 12 C 9 N 3 H 12 (b) Inittial and final geometry (doping at %) Si 12 C 9 N 3 H 12 Fig. 2. Continued. 2 J. Comput. Theor. Nanosci. 8, 1 5, 2011

3 Anota et al. The Electronic Properties of SiC Graphene-Like: Doped and No-Doped Case Si 11 NC 12 H 12 (c) Final geometry] (doping at 4.16 %) Si 12 C 12 NH 12 (d) Initial geometry Final geometry Fig. 2. Cluster models for doped silicon carbide with nitrogen. other clusters are not included because they are. The contribution to the molecular orbital in the SiC (Si 12 C 12 H 12 is due to the carbon p z orbital with a little hybridization with the s and p z orbitals of the silicon atom, for both, the HOMO and the LUMO (Fig. 3(a)). The difference between the HOMO and LUMO has a value of 2.62 ev, only 3.5% different from another theoretical result reported in the literature (Table I). For the Si 12 C 11 N 1 H 12 (4.16% of doping) cluster the HOMO is completely due to p z orbital of Si and in the LUMO there exists hybridization between the C p z orbital and the s and p z orbitals of the Si (Fig. 3(b)); in this case, the gap has Table I. a value of 0.25 ev i.e., a transition from a semiconductor to a semimetal is found when a C atom substitution occur. For x = 3 (12.48% of doping) the gap is 0.23 ev. When the Si is substituted by N, the structure remains as a semiconductor. All these results are summarized in Table I. The dipole moment was also calculated. The value for this parameter when x = 1is Debye, which is bigger than the value for SiC (x = 0), Debye. The polarity for x = 3 is almost the same as for x = 0; for the other cases, this quantity is incremented respect to the x = 0 case. Optimal distance (Å), dipole moment (Debye), energy gap (difference HOMO and LUMO), and binding energy (ev). Bond length (Å) Cluster Si-C C-H Si-H C-N N-Si Dipole moment (Debye) 10 3 Gap (ev) Binding energy (ev) Monomer (exp.) Si 12 C 12 H this work SiC 2D Si 12 C 11 NH stable Si 12 C 9 N 3 H Si 11 NC 12 H a a a Si 12 C 12 NH a a a Irregular hexagons (Figs. 2(c and d)). J. Comput. Theor. Nanosci. 8, 1 5,

4 The Electronic Properties of SiC Graphene-Like: Doped and No-Doped Case Anota et al. HOMO LUMO (a) 4.95 ev 2.32 ev (b) 2.65 ev 2.39 ev Fig. 3. Isosurfaces of molecular orbitals for stable cases (a) silicon carbide and (b) silicon carbide doped with N replacing C (4.16% of doping). 4. CONCLUSIONS In this work, we have theoretically studied the structural and electronic properties of SiC clusters as well as the polarity. Taking the Si 12 C 12 H 12 as the initial cluster, the effect of different kinds of doping was also investigated. We used the Density Functional Theory within de the GGA approximation. The main findings were that SiC and the substitution of a C atom by one N atom (Si 12 C 11 NH 12 are the unique stable structures, all of them with planar geometry; other kind of doping gives rise to systems. According to the binding energy, the Si 12 C 11 NH 12 cluster posses the higher stability. The gap between the HOMO and LUMO is also affected by the doping, it undergoes a transition from a semiconductor (2.62 ev) to a semimetal (0.25 ev) character when C atoms are substituted for N atoms; when the Si atom is substituted, the system remains as a semiconductor but with a small gap (0.73 ev) however, this cluster is. The inclusion of one N atom in the center of the central hexagon of the cluster, favor the formation of a heptagon, a pentagon and a tetragon in the mesh. Finally, when the doping take place, a change from ionic to covalent behavior is observed; this and the other properties are not influenced by the increment of N atoms. Acknowledgments: This work was partially supported by VIEP BUAP (CHAE-ING10-I), FIQ-BUAP ( ), Cuerpo Académico Ingeniería en Materiales (BUAP-CA-177) and CONACyT, Mexico (Grant No ). References 1. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A. A. Firsov, Science 306, 666 (2004). 2. K. S. Novoselov, D. Jiang, F. Schedin, T. J. Booth, V. V. Khotkevich, S. V. Morozov, and A. K. Geim, Proc. Natl Acad. Sci. USA 102, (2005). 3. E. Chigo Anota, M. Salazar Villanueva, and H. Hernández Cocoletzi, Phys. Status Solidi C (2010). 4. A. K. Geim, Science 324, 1530 (2009). 5. J. Hou and B. Song, J. Chem. Phys. 128, (2008). 6. E. Bekaroglu, M. Topsakal, S. Cahangirov, and S. Ciraci, Phys. Rev. B 81, (2010). 7. Luxmi, N. Srivastava, and R. M. Feenstra, J. Vac. Sci. Technol. B 8. S. Oida, F. R. McFeely, J. B. Hannon, R. M. Tromp, M. Copel, Z. Chen, Y. Sun, D. B. Farmer, and J. Yurkas, Mater. Sci. 9. P. Melinon, B. Masenelli, F. Tournus, and A. Perez, Nat. Mater. 6, 480 (2007). 10. E. Chigo Anota, Sup y Vac. 22, 19 (2009). 11. E. Chigo Anota, M. Salazar Villanueva, and H. Hernández Cocoletzi, J. Nanosci. Nanotechnol. (2010). 4 J. Comput. Theor. Nanosci. 8, 1 5, 2011

5 Anota et al. The Electronic Properties of SiC Graphene-Like: Doped and No-Doped Case 12. E. Chigo Anota, M. Salazar Villanueva, and H. Hernández Cocoletzi, Phys. Status Solidi (2010). 13. E. Chigo Anota and M. Salazar Villanueva, Sup. y Vac. 22, 23 (2009). 14. E. Chigo Anota, H. Hernández Cocoletzi, and E. Rubio Rosas, LDA Approximation Based Analysis of the Adsorption the O 3 by Boron Nitride Cluster, Submitted. 15. W. Kohn, A. D. Becke, and R. G. Parr, J. Phys. Chem. 100, (1996). 16. R. O. Jones and O. Gunnarsson, Rev. Modern Phys. 61, 689 (1989). 17. W. Kohn, Rev. Mod. Phys. 71, 1253 (1999). 18. E. Chigo Anota and J. F. Rivas Silva, Col. Fís. 37, 405 (2005). 19. B. Delley, J. Chem. Phys. 92, 508. (1990). 20. J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996). 21. B. Delley, J. Phys. Chem. 100, 6107 (1996); B. Delley, J. Chem. Phys. 113, 7756 (2000). 22. J. B. Foresman and Æ. Frisch, 2nd edn., Exploring Chemistry with Electronic Structure Methods, Gaussian Inc., USA (1996), p. 70. Received: 1 May Accepted: 15 May J. Comput. Theor. Nanosci. 8, 1 5,