Intrinsic Piezoelectricity in Two-Dimensional Materials

Abstract

We discovered that many of the commonly studied two-dimensional monolayer transition metal dichalcogenide (TMDC) nanoscale materials are piezoelectric, unlike their bulk parent crystals. On the macroscopic scale, piezoelectricity is widely used to achieve robust electromechanical coupling in a rich variety of sensors and actuators. Remarkably, our density-functional theory calculations of the piezoelectric coefficients of monolayer BN, MoS 2 , MoSe 2 , MoTe 2 , WS 2 , WSe 2 , and WTe 2 reveal that some of these materials exhibit stronger piezoelectric coupling than traditionally employed bulk wurtzite structures. We find that the piezoelectric coefficients span more than 1 order of magnitude, and exhibit monotonic periodic trends. The discovery of this property in many twodimensional materials enables active sensing, actuating, and new electronic components for nanoscale devices based on the familiar piezoelectric effect. SECTION: Physical Processes in Nanomaterials and Nanostructures

Observation of piezoelectricity in free-standing monolayer MoS2

“…0.5 C m −2 when normalized by the layer thickness), close to a reported result calculated by density functional theory 7 . The measured piezoelectric coefficient is comparable to the bulk values of standard piezoelectric crystals such as ZnO or AlN.…”

“…7). Figure 3a shows the fitting of experimental data on a monolayer MoS 2 device with Y 2D = (1.2 ± 0.1) × 10 2 N m −1 and σ 2D = 45 ± 5 mN m −1 , which agrees well with previous ab initio calculations and experimental results 7,28 . The repeatable load-indentation curves demonstrated the quality of the atomic crystalline film and the effectiveness of the clamp.…”

“…Transition-metal dichalcogenides can retain their atomic structures down to the single-layer limit without lattice reconstruction, even under ambient conditions 6 . Recent calculations have predicted the existence of piezoelectricity in these two-dimensional crystals due to their broken inversion symmetry 7 . Here, we report experimental evidence of piezoelectricity in a free-standing single layer of molybdenum disulphide (MoS 2 ) and a measured piezoelectric coefficient of e 11 = 2.9 × 10 -10 C m −1 .…”

“…The rapidly growing demand for high-performance and miniaturized devices in micro-electro-mechanical systems (MEMS) and electronics 10-12 calls for nanoscale piezoelectric materials, motivating theoretical investigations into novel low-dimensional systems such as nanotubes and single molecules 13,14 . Transition-metal dichalcogenides (TMDCs) are ideal candidates as low-dimensional piezoelectric materials because of their structural non-centrosymmetry 7 . Although there has been extensive research interest in the unique properties originating from such symmetry breaking, including circular dichroism and second harmonic generation (SHG) [15][16][17][18][19] , experimental quantitative determination of the intrinsic piezoelectric properties of these two-dimensional crystals has yet to be demonstrated.…”

Piezoelectricity of Functionalized Graphene: A Quantum-Mechanical Rationalization

“…[6][7][8] When it comes to low-dimensional systems, graphene would clearly be the most promising material to work with in the fabrication of electronic, optoelectronic and spintronic nano-devices due to all of its well-known remarkable properties, including extraordinarily high electron mobility, mechanical stiffness and flexibility. [9][10][11][12][13][14][15] The exploitation of piezoelectricity of graphene would indeed lead to a new branch of possible applications in nano-electro-mechanical systems (NEMS) devices requiring high electromechanical coupling.…”