Anomalous piezoelectricity in two-dimensional graphene nitride nanosheets

Abstract

Piezoelectricity is a unique property of materials that permits the conversion of mechanical stimuli into electrical and vice versa. On the basis of crystal symmetry considerations, pristine carbon nitride (C 3 N 4 ) in its various forms is non-piezoelectric. Here we find clear evidence via piezoresponse force microscopy and quantum mechanical calculations that both atomically thin and layered graphitic carbon nitride, or graphene nitride, nanosheets exhibit anomalous piezoelectricity. Insights from ab inito calculations indicate that the emergence of piezoelectricity in this material is due to the fact that a stable phase of graphene nitride nanosheet is riddled with regularly spaced triangular holes. These non-centrosymmetric pores, and the universal presence of flexoelectricity in all dielectrics, lead to the manifestation of the apparent and experimentally verified piezoelectric response. Quantitatively, an e 11 piezoelectric coefficient of 0.758 C m À 2 is predicted for C 3 N 4 superlattice, significantly larger than that of the commonly compared a-quartz.

Observation of a giant two-dimensional band-piezoelectric effect on biaxial-strained graphene

“…Benefitting from its ultrathin and easily bendable structure, the graphene membrane presents an ultrahigh direct piezoelectric coefficient (~37 nC N − 1 , approximately two orders of magnitude higher than traditional piezoelectric materials and functional graphene [16][17] ), although the converse piezoelectric coefficient is small (~12.5 μm V − 1 ) due to graphene's semi-metallic property and large quantum capacitance.…”

“…15 Achievement of piezoelectricity in previous pioneering works requires the functionalization or nanopatterning of graphene to break this centrosymmetry. 16,17 Furthermore, in its intrinsic (semi-)metallic states, graphene is clearly non-piezoelectric and/or non-flexoelectric. 17 In addition, its singleatom thickness leads to an ill-defined out-of plane strain gradient and a questionable breakage of the centrosymmetric flexoeletricity.…”

Advanced Scanning Probe Microscopy of Graphene and Other 2D Materials

“…The calculated vertical piezocoefficient was found to be about 1.4 nm/V, which is much higher than that of conventional piezoelectric materials [135]. Atomically-thin graphene nitride also exhibits anomalous piezoelectricity, due to the fact that a stable phase of a sheet features regularly spaced triangular holes, as indicated by ab initio calculations [136]. Directional dependent piezoelectric effects in chemical vapor deposited MoS 2 monolayers were measured through lateral PFM when an electric field was applied laterally across the flakes [131].…”

The memristive behavior of non-uniform strained carbon nanotubes

“…Previously, we have experimentally shown that vertically aligned CNTs exhibit a memristive switching associated with their strain and polarization [1][2][3]. Analysis of the literature [4][5][6] has shown that non-uniform strain in carbon nanostructures can lead to the appearance of a piezoelectric effect and the corresponding internal electric field in them. We put forward a proposal that the non-uniform strain of the CNT acts as an additional source of resistance which depends on the value of the current flowing.…”