Formation, Stability, Geometry and Band Structure of Organically Surface-Modified Germanane

doi:.10.1016/j.jmst.2016.01.019

Abstract

Abstract:

Surface modification may be an effective means for controlling the properties of germanane, i.e., hydrogenated germanene. In this work, we investigate the formation, stability, structure and electronic properties of surface-modified germanane that results from the hydrogermylation, alkoxylation, aminization or phenylation of germanane. By assuming the typical organic surface coverage of ~33%, we have compared organically surface-modified germanane with germanene and germanane in the framework of density functional theory. It is found that organically surface-modified germanane may all stably exist despite the endothermic nature of organic surface modification. Organic surface modification leads to the decrease of the Ge59/img_1.tif0.00.0Ge bond length and the Ge59/img_2.tif0.00.0Ge59/img_3.tif0.00.0Ge bond angle of germanane, while causing the buckling distance of germanane to increase. Hydrogenation makes germanene change from a semimetal to a direct-bandgap semiconductor. Organic surface modification further impacts the band structure of the resulting germanane. Hydrogermylated/alkoxylated germanane is a direct-bandgap semiconductor, while aminated/phenylated germanane is an indirect-bandgap semiconductor. All the organic surface modification gives rise to the increase of the bandgap of germanane.

Key words: Surface modification, Grain boundaries, Density functional theory, Band structure

Jia Hui,Wang Rong,Ni Zhenyi,Liu Yong,Pi Xiaodong,Yang Deren. Formation, Stability, Geometry and Band Structure of Organically Surface-Modified Germanane[J]. J. Mater. Sci. Technol., 2017, 33(1): 59-64.

Figures/Tables 5

Fig.1 Optimized structures of (a) germanene, (b) germanane, (c) hydrogermylated germanane, (d) alkoxylate germanane, (e) aminated germanane and (f) phenylated germanane. Both top (left) and side (right) views of these structures are shown. Ge, H, C, O and N atoms are denoted by green, white, grey, red and blue balls, respectively

Table 1 Formulas, structural properties, binding energies (Eb), formation energies (Ef) and bandgaps (Eg) of germanene, germanane and organically surface-modified germanane. The structural properties include the buckling distance (Δ), the Ge-Ge bond length (<Ge-Ge>) and the Ge-Ge-Ge angle (∠(Ge-Ge-Ge)). The superscripts of i and d stand for the indirect and direct bandgaps, respectively

	Germanene	Germanane	Hydrogermylated germanane	Alkoxylated germanane	Aminated germanane	Phenylated germanane
Formula	Ge₁₈	Ge₁₈H₁₈	Ge₁₈C₁₈H₅₄	Ge₁₈C₁₂O₆H₄₂	Ge₁₈C₁₂N₆H₄₂	Ge₁₈C₃₆H₄₂
<Ge Ge> (?)	2.44	2.44	2.42(0.8%)	2.42(0.8%)	2.42(0.8%)	2.41(1.2%)
∠(Ge Ge Ge)(°)	112	109	109	106-108	107-108	105-106
△(?)	0.69	0.81	0.90(11.1%)	0.93(14.8%)	0.90(11.1%)	0.95(17.3%)
Ge X(?)	-	1.59	1.99	1.96	1.96	1.99
E_f(eV)	-	-4.4	48.7	37.0	39.6	74.4
E_b(eV)	-	3.7	4.8	4.8	4.8	5.5
E_g(eV)	0	0.9^d	1.8^d	1.2^d	1.6ⁱ	1.1ⁱ

Fig.2 Bond distributions of (a) hydrogermylated germanane, (b) alkoxylated germanane, (c) aminated germanane and (d) phenylated germanane at 0, 300 and 600 K after 2000 ps of molecular dynamics. For clarity, the probability density is set at 1 for each bond length at 0 K

Fig.3 Band structures of (a) germanene, (b) germanane, (c) hydrogermylated germanane, (d) alkoxylated germanane, (e) aminated germanane and (f) phenylated germanane. Energy is shifted so that the Fermi level is at 0 eV

Fig.4 Partial density of states (pDOS) of (a) germanene, (b) germanane, (c) hydrogermylated germanane, (d) alkoxylated germanane, (e) aminated germanane and (f) phenylated germanane. Energy is shifted so that the Fermi level is at 0 eV

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