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Theory Seminar:Theoretical and Experimental Exploration of Two-Dimensional Silicon Structures
Title : Theory Seminar:Theoretical and Experimental Exploration of Two-Dimensional Silicon Structures
Date :
Time :
2014/10/31(Fri)
4:00 PM - 5:00 PM 
Place : Seminar Room 5 (A615), 6th Floor, ISSP   
Lecturer : Prof. Taisuke Ozaki
Affiliation : Center of Computational Materials Science, Institute for Solid State Physics, The University of Tokyo
Summary : Although it is believed that two-dimensional honeycomb structures consisting of silicon atoms do not exist experimentally due to relative instability of its hybridized sp2 orbitals, a recent experiment clearly demonstrates that silicene, honeycomb structure of silicon atoms, can be fabricated on ZrB2 (0001) thin films [1]. Here, we report on detailed studies for geometrical and electronic structures of silicene on ZrB2 and a related two-dimensional structure by means of electronic structure calculations based on density functional theories (DFT), guided by a close collaboration with experiments performed by the Yamada-Takamura group of JAIST [1-6]. Theoretical chemical shift of Si-2p states [1] and band structure calculations [4] strongly support the formation of silicene having a planar-like structure. The stability of the planar-like structure over the regularly buckled structure can be understood by interaction between states of the silicene and surface states consisting of the d-orbital of the top Zr atoms [2]. We also propose a possible mechanism for the formation of the domain structure of silicene on ZrB2 [1,5]. It is inferred that the domain structure is induced by an instability of a phonon having a nearly zero frequency, and is formed in such a way that the k-points having the zero frequency can be removed from the first Brillouin zone. The mechanism is verified by performing large-scale total energy calculations. We further explore a possible structure of multi-layer silicene, and find that the MoS2 structure consisting of silicon atoms is stabilized with atoms in the inner layer having a sixfold coordination, which results in cigar-shaped nematic orbitals originating from the Si-sp2 orbitals [6].

[1] A. Fleurence, R. Friedlein, T. Ozaki, H. Kawai, Y. Wang, and Y. Yamada-Takamura, Phys. Rev. Lett. 108, 245501 (2012).
[2] C.-C. Lee, A. Fleurence, R. Friedlein, Y. Yamada-Takamura, and T. Ozaki, Phys. Rev. B 88, 165404 (2013).
[3] A. Fleurence, Y. Yoshida, C.-C. Lee, T. Ozaki, Y. Yamada-Takamura, and Y. Hasegawa, Appl. Phys. Lett. 104, 021605 (2014).
[4] C.-C. Lee, A. Fleurence, Y. Yamada-Takamura, T. Ozaki, and R. Friedlein, Phys. Rev. B 90, 075422 (2014).
[5] C.-C. Lee, A. Fleurence, R. Friedlein, Y. Yamada-Takamura, and T. Ozaki, submitted to Phys. Rev. Lett.; arXiv:1408.2588.
[6] F. Gimbert, C.-C. Lee, R. Friedlein, A. Fleurence, Y. Yamada-Takamura, and T. Ozaki, Phys. Rev. B, in press; arXiv:1401.0142.
Committee Chair : Taisuke Ozaki (ext.63582)
e-mail: t-ozaki :at: issp.u-tokyo.ac.jp