Highly Conductive Metallic State and Strong Spin–Orbit Interaction in Annealed Germanane

Abstract

Similar to carbon, germanium exists in various structures such as three-dimensional crystalline germanium and germanene, a two-dimensional germanium atomic layer. Regarding the electronic properties, they are either semiconductors or Dirac semimetals. Here, we report a highly conductive metallic state in thermally annealed germanane (hydrogen-terminated germanene, GeH), which shows a resistivity of ∼10–7 Ω·m that is orders of magnitude lower than any other allotrope of germanium. By comparing the resistivity, Raman spectra, and thickness change measured by AFM, we suggest the highly conductive metallic state is associated with the dehydrogenation during heating, which likely transforms germanane thin flakes to multilayer germanene. In addition, weak antilocalization is observed, serving as solid evidence for strong spin–orbit interaction (SOI) in germanane/germanene. Our study opens a possible new route to investigate the electrical transport properties of germanane/germanene, and the large SOI might provide the essential ingredients to access their topological states predicted theoretically.

Synthesis of 2D Germanane (GeH): a New, Fast, and Facile Approach

“…These characteristics hold great promise for electronic and optoelectronic applications and recently we reported the first realization of germanane field effect transistors,f abricated from multilayer single crystal flakes, which demonstrated transport in both electron and hole doped regimes,w ith an on/off current ratio of up to 10 5 (10 4 ) and carrier mobilities of 150 cm 2 V À1 s À1 (70 cm 2 V À1 s À1 )a t 77 K( room temperature). [9] Moreover,i naseparate study [10] we found evidence for ah ighly conductive metallic state that develops with the dehydrogenation during heating, ap rocess,w hich seems to transform germanane thin flakes into multilayer germanene. These results as well as many other recently proposed applications of germanane [8a,11] and germanene [12] in (opto)electronics,e nergy production and storage as well as in (photo)catalysis leave no doubt that alarge scale,low cost and fast synthesis for very high quality and thermally stable germanane flakes is urgently required in order to fully explore the scientific and technological potential of 2D germaniumbased materials.…”

Synthesis of 2D Germanane (GeH): a New, Fast, and Facile Approach

“…Partially refined atomic coordinates and isotropic displacement factors for germanane at 295 K. Hydrogen positions were generated by geometrical considerationsand not refined.Space group C2: a = 6.789-(10) , b = 4.035(5) , c = 11.24(4) , b = 105.5(2)8 8.…”

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...…”