Intrinsic magnetism and spontaneous band gap opening in bilayer silicene and germanene

Abstract

It has been long sought to create magnetism out of simple non-magnetic materials, such as silicon and germanium. Here we show that intrinsic magnetism exists in bilayer silicene and germanene with no need to cut, etch, or dope. Unlike bilayer graphene, strong covalent interlayer bonding formed in bilayer silicene and germanene breaks the original π-bonding network of each layer, leaving the unbonded electrons unpaired and localized to carry magnetic moments. These magnetic moments then couple ferromagnetically within each layer while antiferromagnetically across two layers, giving rise to an infinite magnetic sheet with structural integrity and magnetic homogeneity. Furthermore, this unique magnetic ordering results in fundamental band gaps of 0.55 eV and 0.32 eV for bilayer silicene and germanene, respectively. The integration of intrinsic magnetism and spontaneous band gap opening makes bilayer silicene and germanene attractive for future nanoelectronics as well as spin-based computation and data storage.

Emerging two-dimensional ferromagnetism in silicene materials

“…Silicene spintronics has become a vast field of theoretical research 20 with applications exemplified by an ideal spin filter 21 . FM order in silicene sheets is predicted to arise as long as they are asymmetrically functionalized as in partially hydrogenated 22 and bilayer 23 silicene. However, the high reactivity of silicene poses considerable difficulties to any experimentation: free-standing silicene is yet to be demonstrated and only one silicene-based device of note is reported to date 24 .…”

Diverse magnetic quantization in bilayer silicene

“…5(c)) and [n v and n v ↓1 + 2] (purple and red curves). Here, the n v = 10 (n v = 12) LLs acquire a side mode of 12 (10), leading to the anti-crossings for (n v ↑1 = 10 and n v ↓2 = 12) and (n v ↑2 = 10 and n v ↓1 = 12) LLs, as indicated by the blue circle in Fig. 5(c The DOS of the conduction LLs presents the ordering of n c ↓2 -, n c ↓1 -, n c ↑1 -and n c ↑2 -dominated peaks (green, red, blue and purple in Fig.…”

Nanoscale Assembly of 2D Materials for Energy and Environmental Applications

“…Apart from the most widely investigated material, graphene (monolayer of sp 2 carbon), there are a host of 2D materials that have garnered interest, including transition metal dichalcogenide (MX 2 ), MXene (M n+1 AX n ), silicene, phosphorene (i.e., black phosphorous), and germanene. Table 1 summarizes the typical electronic properties (bandgap (eV) [27][28][29][30][31][32] and work function (eV)), [33][34][35][36][37][38] structural property (bond length (Å)), [39][40][41][42][43][44] transport properties (electrical conductivity (S cm −1 ) [45][46][47][48][49][50] and thermal conductivity (W m −1 K −1 ) [51][52][53][54][55] ), mechanical in-plane stiffness (Young's modulus (GPa) [56][57][58][59][60][61] ), and surface energy (mJ m −2 ) [62][63][64][65][66] of these representative 2D materials.…”

“…Mater. 2020, 32,1907006 [28] ≈1.80 (Sc 2 CO 2 ) [28] ≈0.88 (Zr 2 CO 2 ) [28] ≈1.0 (Hf 2 CO 2 ) [28] ≈1.27 (ML) [29] ≈0.55 (BL) [30] ≈1.88 (ML) [31] 0 (ML) [32] ≈0.05 (BL) [32] Work function a) [Φ, eV] ≈4.5 ≈5.1 (ML, BL, MoS 2 ) [33,34] ≈4.3 (ML, WS 2 ) [34] ≈4.6 (ML, WSe 2 ) [34] ≈4.37 (Ti 3 C 2 T X ) [35] ≈3.35 (Sc10C9) [36] ≈4.76 [37] ≈5.16 (ML) [38] ≈4.56 (FL) [38] 4.66 [37] Bond length [Å] 1.42 (C-C) ≈3.15-4.03 [39] ≈2.10 (Ti-C) [40] ≈1.99 (Ti-O) [41] ≈2.15 (Ti-F) [41] ≈2.25 (Si-Si) [42] ≈2.22 (P-P) [43] 2.49-2.56 (Ge-Ge) [44] Electroconductivity [S cm −1 ] ≈10 6 [45] ≈5.0 (MoS 2 ) [46] ≈10 4 [47] 6.5 kΩ b) [48] ≈300 (with graphene) [49] ≈10 5 [50] Thermal conductivity [W m −1 K −1 ] 5300 [51] ≈19.5 (MoS 2 ) [46] ≈55.2 (Ti 3 C 2 T X ) [52] ≈16 [53,54] 2000-5000 [55] ≈15.95 [54] Young's modulus [GPa] ≈1000 [56] ≈270 (MoS 2 ) [57] ≈330 ± 30 (Ti 3 C 2 T X ) [58] ≈82...…”