Probing Effective Out‐of‐Plane Piezoelectricity in van der Waals Layered Materials Induced by Flexoelectricity

Abstract

Many van der Waals layered 2D materials, such as h‐BN, transition metal dichalcogenides (TMDs), and group‐III monochalcogenides, have been predicted to possess piezoelectric and mechanically flexible natures, which greatly motivates potential applications in piezotronic devices and nanogenerators. However, only intrinsic in‐plane piezoelectricity exists in these 2D materials and the piezoelectric effect is confined in odd‐layers of TMDs. The present work is intent on combining the free‐standing design and piezoresponse force microscopy techniques to obtain and directly quantify the effective out‐of‐plane electromechanical coupling induced by strain gradient on atomically thin MoS2 and InSe flakes. Conspicuous piezoresponse and the measured piezoelectric coefficient with respect to the number of layers or thickness are systematically illustrated for both MoS2 and InSe flakes. Note that the promising effective piezoelectric coefficient (deff33) of about 21.9 pm V−1 is observed on few‐layered InSe. The out‐of‐plane piezoresponse arises from the net dipole moment along the normal direction of the curvature membrane induced by strain gradient. This work not only provides a feasible and flexible method to acquire and quantify the out‐of‐plane electromechanical coupling on van der Waals layered materials, but also paves the way to understand and tune the flexoelectric effect of 2D systems.

Up-scalable emerging energy conversion technologies enabled by 2D materials: from miniature power harvesters towards grid-connected energy systems

“…View Article Online h-BN, TMDCs, group III and IV monochalcogenides and even chemically modified graphene. 26,30,31,79,80,[193][194][195][196][197][198][199][200][201][202] Single or few layers of them exhibit piezoelectricity, a property missing from their 3D precursors. It is attributed to the lattice distortion caused by strain and the consequent charge polarization in the crystal.…”

“…The spatial quantum confinement effects anticipated at 2D limit provide a perfect platform to investigate unconventional device architectures with unprecedented characteristics and unique functionalities. [22][23][24][25][26][27][28][29][30][31][32][33] Small-scale energy conversion IoT devices enabled by GMR, have with their manufacturing compatibility with large-scale printing or wafer-level GRM transferring processes promises to set new standards in on-grid electricity generation. 21,39,44,45,[63][64][65][66][67][68][69][70][71][72][73] In this review, we summarize the recent developments on the utilisation of GRM in emerging energy conversion device applications, mainly highlighting the high potential of this approach towards on-grid energy generation.…”

Emerging Targets in Type 2 Diabetes and Diabetic Complications

“…Adeno associated virus (AAV) mediated hepatic reconstitution of CFLAR improves glucose tolerance and alleviates liver fibrosis both in mice and monkeys, rendering it an attractive target for development of novel therapies against NASH. [209] In addition to hepatocytes, hepatic stellate cells also play an important role in development of NASH and liver fibrosis. When stimulated by inflammatory cytokines or growth factors such as TGF 1, stellate cells get activated and undergo epithelial to mesenchymal transition, gain fibroblastic features and start to proliferate.…”

Large-scale Domain Engineering in Two-Dimensional Ferroelectric CuInP2S6 via Giant Flexoelectric Effect

“…The flexoelectric effect (or flexoelectricity) refers to the formation of net electric polarization inside a crystal when an inhomogeneous strain is applied 32,33 . This effect is universal for all materials with arbitrary lattice symmetry and thus has been utilized to generate many extraordinary phenomena and functionalities, such as enhanced piezoelectricity [34][35][36][37] , the nanoscale polar vortices 38 , and anomalous photovoltaics [39][40][41] . To utilize flexoelectricity in polarization reorientation, the key is the generation of giant strain gradients 42,43 .…”