Institut des Sciences Moléculaires d'Orsay




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Home page > Research Teams > Molecular Nanoscience Group > Silicene wires and sheets

Silicene : wires and sheets


Leader: Hamid Oughaddou

Participants: Hanna Enriquez, Andrew Mayne & Gérald Dujardin

Students: Khalid Quertite & Wei Zhang

Silicene is a honeycomb structure of silicon which grows as single layers or nanowires on silver surfaces. Although theorists had speculated about the existence and possible properties of silicene, the first experimental observations were reported by B. Lalmi, H. Oughaddou, H. Enriquez, et al. in 2010. Using the STM, self-assembled silicene nanoribbons and silicene sheets deposited on a silver crystal are studied with atomic resolution. The honeycomb structure observed in the STM images is reminiscent of the honeycomb structure of graphene. Density Functional Theory calculations show that silicon atoms form stable honeycomb but buckled structures on silver.

Techniques: RT STM - LT STM - Surface X-Ray Diffraction (SXRD) - ALE - Auger Electron Spectroscopy (AES) - LEED - Synchrotron Radiation


Dirac cone in 2D silicene The remarkable properties of graphene stem from its two-dimensional (2D) structure, with a linear dispersion of the electronic states at the corners of the Brillouin zone (BZ) forming a Dirac cone. Since then, other 2D materials have been suggested based on boron, silicon, germanium, phosphorus, tin, and metal di-chalcogenides. Here, we present an experimental investigation of a single silicon layer on Au(111) using low energy electron diffraction (LEED), high resolution angle-resolved photoemission spectroscopy (HR-ARPES), and scanning tunneling microscopy (STM). The HR-ARPES data show compelling evidence that the silicon based 2D overlayer is responsible for the observed linear dispersed feature in the valence band, with a Fermi velocity of vF = 10+6 m.s−1 comparable to that of graphene. The STM images show extended and homogeneous domains, offering a viable route to the fabrication of silicene-based opto-electronic devices.

Article: S. Sadeddine, H. Enriquez, A. Bendounan, P.K. Das, I. Vobornik, A.J. Mayne, G. Dujardin, F. Sirotti, A. Kara, H. Oughaddou, “Compelling experimental evidence of a Dirac cone in the electronic structure of a 2D Silicon layer”, Scientific Reports 7, 44400 (2017)

Silicene : A promising new 2D material. Silicene is emerging as a two-dimensional material with very attractive electronic properties for a wide range of applications ; it is a particularly promising material for nano-electronics in silicon-based technology. Over the last decade, the existence and stability of silicene has been the subject of much debate. Theoretical studies of free-standing silicene predicted a puckered honeycomb structure with electronic properties resembling those of graphene. However, experimental fabrication of silicene has been achieved only through epitaxial growth on crystalline surfaces. Since the first experimental evidence of the formation of silicene on Ag(110) and Ag(111) in 2010, this very active field has developed with the recent growth of silicene on Ir(111), ZrB2(0001) and Au(110) substrates. In this review, we discuss the experimental and theoretical studies of silicene performed to date. Special attention is given to different experimental studies of the electronic properties of silicene on metal substrates. New avenues for the growth of silicene on other substrates with different chemical characteristics are presented along with foreseeable applications such as nano-devices and novel batteries.

Review : H. Oughaddou, H. Enriquez, M.R. Tchalala, H. Yildirim, A.J. Mayne, A. Bendounan, G. Dujardin, M. Ait Ali, A. Kara, “Silicene : A promising new 2D material”, Prog. Surf. Science 90, 46-83 (2015)

Atomic and electronic structures of the (√13x√13)R13.9° of silicene sheet on Ag(111). Using scanning tunneling microscopy, low energy electron diffraction measurements, and ab initio calculations based on density functional theory, we present atomic models of the (√13×√13)R13.9◦ silicene superstructure grown on Ag(111). The STM images reveal two co-existing atomic arrangements with two different orientations of the silicene sheet relative to the Ag(111) surface. DFT calculations with and without the inclusion of van der Waals interactions show corrugated Si atomic positions for both orientations implying a significant interaction with Ag(111) surface. The electronic structure of both silicene and Ag(111) surface are sufficiently affected that new interface states emerge close to the Fermi level.

Article : M. R. Tchalala, H. Enriquez, H. Yildirim, A. Kara, A. Mayne, G. Dujardin, M. Ait Ali and H. Oughaddou, "Atomic and electronic structures of the (√13x√13)R13.9° of silicene sheet on Ag(111)", Appl. Surf. Sci. 303, 61–66 (2014)

Atomic structure of silicene nanoribbons on Ag(110). The growth of silicene nano-ribbons (NRs) on Ag(110) substrate is re-investigated using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Deposition of one silicon monolayer at 230°C induces the formation of one-dimensional 1.6 nm wide silicene nanoribbons into a well-ordered compact array with a nanometer-scale pitch of just 2 nm. Based on the STM analysis we derived an atomic model of the silicene nanoribbons (NRs) where they are substantially buckled, and quantum confinement of the electrons in the NRs contribute to electronic density of states.

article : M. R. Tchalala, H. Enriquez, A. Mayne, A. Kara, G. Dujardin, M. Ait Ali and H. Oughaddou, "Atomic structure of silicene nanoribbons on Ag(110)", Journal of Physics : Conference Series 491, 012002 (2014)

Silicon Sheets by Redox Assisted Chemical Exfoliation. In this paper, we report the direct chemical synthesis of silicon sheets in gram-scale quantities by chemical exfoliation of pre-processed calcium disilicide (CaSi2). We have used a combination of x-ray photoelectron spectroscopy, transmission electron microscopy and energy-dispersive x-ray spectroscopy to characterize the obtained silicon sheets. We found that the clean and crystalline silicon sheets show a two-dimensional hexagonal graphitic structure.

article: M.R. Tchalala, M. Ait Ali, H. Enriquez, A. Kara, A. Lachgar, S. Yagoubi, E. Foy, E. Vega, A. Bendounan, M. Silly, F. Sirroti, S. Nitshe, D. Chaudanson, H. Jamgotchian, B. Aufray, A.J. Mayne, G. Dujardin, H. Oughaddou, “Silicon Sheets by Redox Assisted Chemical Exfoliation”, J. Phys. Condens. Mat. 25, 442001 (2013)

First NC-AFM images of silicene. We present the first non-contact atomic force microscopy (nc-AFM) of a silicene on a silver (Ag) surface, obtained by combining non-contact atomic force microscopy and scanning tunneling microscopy (STM). STM images over large areas of silicene grown on the Ag(111) surface show both (root13 x root13)R13.9 and (4 x 4) superstructures. For the widely observed (4 x 4) structure, the observed nc-AFM image is very similar to the one recorded by STM. The structure resolved by nc-AFM is compatible with only one out of two silicon atoms being visible. This indicates unambiguously a strong buckling of the silicene honeycomb layer.

Article : Z. Majzik, M. R. Tchalala, M. Švec, P. Hapala, H. Enriquez, A. Kara, A.J. Mayne, G. Dujardin, P. Jelínek, H. Oughaddou, "Combined AFM and STM measurements of a silicene sheet grown on the Ag(111) surface", J. Phys. Condens. Mat. 25, 225301 (2013)

Formation of one-dimensional self-assembled silicon nanoribbons on Au(110)-(2x1). We report results on the self-assembly of silicon nanoribbons (NRs) on the (2x1) reconstructed Au(110) surface under ultra-high vacuum conditions. Upon adsorption of 0.2 monolayer (ML) of silicon the (2x1), reconstruction of Au(110) is replaced by an ordered surface alloy. Above this coverage, a new superstructure is revealed by low energy electron diffraction (LEED), which becomes sharper at 0.3 Si ML. This superstructure corresponds to Si nanoribbons all oriented along the (110) direction as revealed by LEED and scanning tunneling microscopy (STM). STM and high- resolution photoemission spectroscopy indicate that the nanoribbons are flat and predominantly 1.6 nm wide. In addition, the silicon atoms show signatures of two chemical environments corresponding to the edge and center of the ribbons.

Article : M.R. Tchalala, H. Enriquez, A.J. Mayne, A. Kara, S. Roth, M.G. Silly, A. Bendounan, F. Sirroti, Th. Greber, B. Aufray, G. Dujardin, H. Oughaddou, "Formation of one-dimensional self-assembled silicon nanoribbons on Au(110)-2x1", Appl. Phys. Lett. 102, 083107 (2013)

Adsorption of silicon on Au(110) : an ordered 2D surface alloy. We show experimental evidence for the formation of a two dimensional Si/Au(110) surface alloy. In this study, we have used a combination of scanning tunneling microscopy, low energy electron diffraction, Auger electron spectroscopy, and ab initio calculations based on density functional theory. A highly ordered and stable Si-Au surface alloy is observed subsequent to growth of a sub-monolayer of silicon on an Au(110) substrate kept above the eutectic temperature.

Article: H. Enriquez, A.J. Mayne, A. Kara, S. Vizzini, S. Roth, B. Lalmi, A.P. Seitsonen, B. Aufray, Th. Greber, R. Belkhou, G. Dujardin, H. Oughaddou Appl. Phys. Lett. 101, 021605 (2012)