Abstract
Piezoelectric response in two-dimensional (2D) materials has evoked immense interest in using them for various applications involving electromechanical coupling. In most of the 2D materials, piezoelectricity is coupled along the in-plane direction. Here, we propose a technique to probe the in-plane piezoelectric coupling strength in layered nanomaterials quantitively. The method involves a novel approach for in-plane field excitation in lateral Piezoresponse force microscopy (PFM) for 2D materials. Operating near contact resonance has enabled the measurement of the piezoelectric coupling coefficients in the sub pm/V range. Detailed methodology for the signal calibration and the background subtraction when PFM is operated near the contact resonance of the cantilever is also provided. The technique is verified by estimating the in-plane piezoelectric coupling coefficients (d11) for freely suspended MoS2 of one to five atomic layers. For 2D-MoS2 with the odd number of atomic layers, which are non-centrosymmetric, finite d11 is measured. The measurements also indicate that the coupling strength decreases with an increase in the number of layers. The techniques presented would be an effective tool to study the in-plane piezoelectricity quantitatively in various materials along with emerging 2D-materials.
Highlights
Zhu et al.[11] have experimentally verified the piezoelectric response in an odd number of layers of M oS2
Device architecture and characterization Suspended MoS2 devices are fabricated on Si/SiO2 substrates for the Piezoresponse force microscopy (PFM) measurements
To quantify the contribution from electrostatic drive near contact resonance frequency, we propose a method involving a separate set of measurements called pseudo-piezoresponse measurements
Summary
Zhu et al.[11] have experimentally verified the piezoelectric response in an odd number of layers of M oS2 They have calculated piezoelectric stress coefficients (e11) using the nano-indentation method and have indicated that lateral PFM cannot be performed on MoS2. The methods allow us to perform lateral PFM on 2D materials with in-plane excitation These measurements can be performed on most commercially available AFMs using commercial AFM tips. PFM is one of the application modules in AFM, which is utilized to characterize the piezoelectric and ferroelectric properties of the material[17] It is widely used for the measurement of piezo coupling c oefficients[18,19,20]. To measure the d11 coefficient for 2D materials, lateral PFM with in-plane field excitation is required
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