Biaxial strain engineering of CVD and exfoliated single- and bi-layer MoS₂ crystals

Abstract

Single- and bi-layer MoS2 are two-dimensional semiconductors able to withstand very large deformations before failure, standing out as suitable templates for strain engineering applications and flexible electronics. It is imperative, for the proper integration of this material in practical applications, that the relationship between material property and strain is well understood. Two dimensional MoS2 crystals fabricated by chemical vapor deposition or micromechanical exfoliation are transferred onto flexible substrates and subjected to biaxial tension on a carefully designed and assessed loading stage with high accuracy and control. The successful stress transfer from substrate to the overlying 2D crystal is identified by in-situ monitoring of the strain-induced phonon frequency and photoluminescence peak shifts. Reliable values for the mode Grüneisen parameters and exciton deformation potentials were obtained by studying a significant number of crystals. The experimental results are backed by density functional theory calculations and are in good agreement with the experiments. This work highlights the potential of these materials in strain engineering applications and gives accurate values for single- and bi-layer MoS2 thermomechanical parameters.

Biaxial versus uniaxial strain tuning of single-layer MoS2

“…During the elaboration of this manuscript we became aware of the work of Michail et al [73] where they use the cruciform bending/indentation method developed by Androulidakis et al [61], similar to this work, to study the effect of biaxial strain in the photoluminescence and Raman spectra of exfoliated and chemical vapour deposited single-and bi-layer MoS2.…”

Local strain and tunneling current modulate excitonic luminescence in MoS2 monolayers

“…This modulation rate is in good agreement with the result obtained by diffraction-limited photoluminescence of CVD monolayer MoS 2 upon biaxial strain (a value of −76 ± 10 meV/%). 48 Considering the absence of a trend on the bare Au substrate and the electronic decoupling of monolayer MoS 2 from the Au substrate by a thin water spacer, the observed linear modulation of A exciton energy can be assigned to the local strain variations in MoS 2 , induced by the corrugated surface. Moreover, spectra acquired on other monolayer MoS 2 flakes wet-transferred from the same CVD-synthesis have closely matching values for the strain modulation rates (Fig.…”

“…Assuming that shear strain components are negligible, biaxial strain 3 b takes the simple form of 3 xx + 3 yy , where 3 xx and 3 yy are the strain components in the x and y directions. 48,49 To derive the sum of these two strain components from local surface topography, we compare the actual surface area of MoS 2 and its projected area, as shown in Fig. S7.…”

Strain Switching in van der Waals Heterostructures Triggered by a Spin‐Crossover Metal–Organic Framework

“…[10] Here, we introduce a novel technique for triggering strain on 2D materials by using thin SCO van der Waals layers. Current state-of-the-art regarding strain engineering on 2D materials includes the thermal variation or bending of the substrate where the 2D material is located, [12][13][14][15] inducing ripples and bubbles, [16,17] applying hydrostatic pressure, [18,19] or the use of piezoelectric and microheater actuators, [20][21][22] among others. Most of these approaches allow variation of the degree of strain, although they are technically complex and not easy to integrate, for example, with low-temperature measurements.…”