Micromechanism study on electronic and magnetic properties of silicene regulated by oxygen

doi:10.1016/j.jmst.2019.03.032

Abstract

Abstract:

Silicene, a two-dimensional (2D) silicon counterpart of graphene with attractive electronic properties, has attracted increasing attention. Understanding of its interaction with oxygen is of fundamental importance for nano-electronics in silicon-based technology. Here, we have systematically studied the structural, electronic and magnetic properties of silicene with oxygen atoms adsorption by using an unbiased structure search method coupled with First-principles calculations. The results show that the most favorable oxygen adsorption site on silicene surface is bridge site and oxygen atoms tend to chemisorb on silicene. A detailed analysis of the electronic band structure and density of state (DOS) suggests that there is a band gap opening near Fermi level after oxygen adsorption, which lead to pristine silicene changing from a gapless semiconductor to a direct or indirect bandgap semiconductor. The important finding is that two and six oxygen atoms adsorbed silicene are more advantageous due to the relatively large direct band gaps at the K point. The calculated magnetic moments and spin density isosurfaces reveal that the total magnetic moments are mostly localized on silicene sheet. This finding provides new insights for further materials design based on two-dimensional silicon systems.

Key words: Silicene, CALYPSO method, Band gap, Oxygen adsorption

Li-Ping Ding, Peng Shao, Lin-Tai Yang, Wei Guo Sun, Fang-Hui Zhang, Cheng Lu. Micromechanism study on electronic and magnetic properties of silicene regulated by oxygen[J]. J. Mater. Sci. Technol., 2019, 35(8): 1803-1808.

Figures/Tables 6

Fig. 1. (a) Top and (b) side views of the geometry of pristine silicene. The yellow and green ball represent the top and valley silicon atoms, respectively. (c) The corresponding electronic band structure.

Fig. 2. Structures of silicene with two and six oxygen atoms adsorption together with their relative energies. 2 and 6 represent the numbers of adsorbed oxygen atoms.

Table 1 Average Si-Si bond lengths (in Å), the shortest and longest O-Si bond lengths (in Å), the average buckling parameter Δ (in Å), adsorption energy Ead (in a.u.), and band gap Eg (in meV) for the lowest-energy structures of On-silicene (n = 0, 2-8). The subscript from 2 to 8 stand for the number of oxygen atoms adsorbed on silicene. The superscript I and II stand for the shortest and longest O–Si bond lengths, respectively.

Structures	Si–Si	O–Si^I	O–Si^II	Δ	E_ad	E_g
Silicene	2.27	-	-	0.47	-	1.46
O₂-Silicene	2.29	1.65	1.74	0.53	-0.51	612
O₃-Silicene	2.29	1.63	1.83	0.49	-0.76	30
O₄-Silicene	2.31	1.64	1.78	-	-0.96	13
O₅-Silicene	2.31	1.62	1.75	-	-1.19	157
O₆-Silicene	2.36	1.68	1.86	-	-1.37	244
O₇-Silicene	2.32	1.52	1.90	-	-1.63	175
O₈-Silicene	2.32	1.64	1.86	-	-1.82	144

Fig. 3. Electronic band structures and electronic density states (DOS) of O2-silicene (a) (c) and O6-silicene (b)(d).

Table 2 Spin total magnetic moments of On-silicene (n = 0, 2-8), as well as the local magnetic moments of silicene sheet and the corresponding α and β spin electronic configurations on silicene sheet. The superscripts from 2 to 8 stand for the number of oxygen atoms adsorbed on silicene.

Structures	μ (μ_B)		Natural electron configuration
	T	L	α	β
Silicene	4	4.34	3s^23.343p^40.483d^0.304p^0.22	3s^22.73p^36.943d^0.304p^0.06
O₂-Silicene	4	4.35	3s^23.263p^40.423d^0.314p^0.18	3s^22.893p^36.433d^0.304p^0.19
O₃-Silicene	4	4.02	3s^23.333p^40.213d^0.314p^0.205p^0.01	3s^22.933p^36.713d^0.314p^0.085p^0.01
O₄-Silicene	2	1.98	3s^23.013p^39.063d^0.344p^0.155p^0.02	3s^22.723p^37.403d^0.334p^0.055p^0.02
O₅-Silicene	2	1.88	3s^23.043p^38.223d^0.344p^0.145p^0.02	3s^22.853p^36.543d^0.344p^0.135p^0.02
O₆-Silicene	2	1.94	3s^23.653p^36.933d^0.314p^0.185p^0.03	3s^23.553p^35.093d^0.314p^0.185p^0.03
O₇-Silicene	4	3.92	3s^23.343p^37.663d^0.344p^0.135p^0.04	3s^22.943p^34.263d^0.304p^0.075p^0.02
O₈-Silicene	4	4.02	3s^23.493p^36.993d^0.344p^0.135p^0.01	3s^23.123p^33.543d^0.344p^0.095p^0.01

Fig. 4. Spin density isosurfaces of O2-silicene and O6-silicene.

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