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Unit cell (denoted by dotted lines) of C4-asym-unzip GO. The inset table lists the a and b lattice parameters for -asym-unzip GO and pristine graphene, as well as the associated ab initio k-point grids. C and O atoms are represented by small-silver and large-purple spheres, respectively.
Electromechanical actuation of GO and pristine graphene due to positive (hole) and negative (electron) charge injection. Inset: close-up of the charge–strain results between −0.15 and 0.075 e/C-atom charge injection.
(a) The interatomic and a-axis resolved deformations of -asym-unzip GO upon electron injection show that whilst the QM effect leads to interatomic bond length expansion, an increase in the degree of rippling results in an overall contraction of the unit cell along the a-axis. The excess charge density distribution of -asym-unzip shows the origin of the very high electron-induced contraction, where orange (blue) regions represent excess electron (hole) concentrations. All results correspond to an electron injection level of −0.05 e/C-atom.
Partial DOS ((a) and (b)) of -asym-unzip GO for 0, 0.075, and 0.15 e/C-atom hole injection. The partial DOS are decomposed into both orbital (s and p) and site (C and O atom) projections, where the C atom DOS shown are for the O atom's nearest neighbour. Excess charge density distributions are also shown for (c) 0.075 and (d) 0.15 e/C-atom hole injection. Blue (orange) regions signify excess hole (electron) concentrations. The excess charge density isosurfaces in (c) and (d) are equivalent (normalised against the injected charge).
Total strain, C–O interatomic bond strain, and C–O–C bond angle change as a function of charge injection. All hole injection levels reduce the C–O bond length, while the C–O–C bond angle initially decreases for low (0.025 e/C-atom) hole injection and then increases for higher (>0.05 e/C-atom) hole injection.
Electromechanical strain ϵ (%), strain-voltage coefficient S v (%/V), and volumetric work density W vol (J/cm3) comparison between GO and other materials.
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