Strongly enhanced electromechanical coupling in atomically thin transition metal dichalcogenides

• Published in: Materials today (Kidlington, England) England), 2021-07, Vol.47, p.69-74
• Main Authors: Haque, Md Farhadul, Snapp, Peter, Kim, Jin Myung, Wang, Michael Cai, Bae, Hyung Jong, Cho, Chullhee, Nam, SungWoo
• Format: Article
• Language: English
• ISSN: 1369-7021; 1873-4103
• DOI: 10.1016/j.mattod.2020.12.021

Out-of-plane converse flexoelectric response of atomically thin MoS2 and WSe2 is obtained by piezoresponse force microscopy. The atomically thin MoS2 and WSe2 not only show 700% (MoS2) and 400% (WSe2) enhanced converse flexoelectric response than their bulk structures, but also surpass the intrinsic in-plane piezoresponse. The effect of puckering on the measurement technique is investigated for the monolayer transition metal dichalcogenide and the highest converse flexoelectric response (8.14 pm/V) is shown in WSe2 by inducing a built-in in-plane tension to reduce puckering. [Display omitted] Flexoelectricity in thin films has emerged as an effective electromechanical response owing to appealing scaling law and universal existence. However, current studies show limited out-of-plane converse flexoelectric effect (CFE) of ultra-thin transition metal dichalcogenides (TMDs) when compared to their conventional in-plane piezoresponse. Here, we report converse flexoresponse of atomically thin TMDs such as molybdenum disulfide (MoS2) and tungsten diselenide (WSe2) which exceeds their intrinsic in-plane piezoresponses. Our piezoresponse force microscopy (PFM) measurements revealed strongly enhanced CFE of the atomically thin MoS2 and WSe2 than their bulk counterpart (∼700% enhancement in MoS2, ∼400% enhancement in WSe2). We observed an anomalous reduction in converse flexoresponse in the monolayer structure attributed to a puckering deformation. By inducing a built-in in-plane tension to reduce puckering, we estimated the CFE of monolayer WSe2 to be 8.14 pm/V, the highest among the atomically thin TMDs.