Elastic properties and intrinsic strength of two-dimensional InSe flakes

Abstract

The mechanical properties of two-dimensional (2D) materials are critical for their applications in functional devices as well as for strain engineering. Here, we report the Young's modulus and breaking strength of multilayered InSe, an emerging 2D semiconductor of the layered group III chalcogenide. Few-layer InSe flaks were exfoliated from bulk InSe crystal onto Si/SiO 2 substrate with microfabricated holes, and indentation tests were carried out using an atomic force microscopy probe. In combination with both continuum analysis and finite element simulation, we measured the Young's modulus of multilayer 2D InSe (>5 L) to be 101.37±17.93 GPa, much higher than its bulk counterpart, while its breaking strength is determined to be 8.68 GPa, approaching the theoretical limit of 10.1 GPa. Density functional theory calculations were also carried out to explain the insensitivity of Young's modulus to the layer count. It is found that 2D InSe is softer than most 2D materials, and exhibits breaking strength higher than that of carbon fiber, yet remaining more compliant, making it ideal for flexible electronics applications. The reliability of our method is also validated by measurement of graphene.

Out-of-Plane Deformations Determined Mechanics of Vanadium Disulfide (VS2) Sheets

“…We note that VS 2 appears to be the softest among the 2D transition metal dichalcogenides (TMDs) library (Figure c). For instance, the Young’s moduli are approximated to be 100 GPa for MoTe 2 and increase to ∼170 GPa for MoSe 2 and WSe 2 . − MoS 2 and WS 2 typically exhibit higher values ranging from 200 to 330 GPa. ,,− Young’s moduli of graphene and hBN can be even one magnitude larger than that of VS 2 . ,,,,,− It is also found that the compliance of VS 2 is comparable to that of some main group metal chalcogenides, such as InSe, GaTe, and Bi 2 Te 3 . − As the Young’s modulus reflects the change in elastic energy associated with the deformation of the atomic bonds, the softness of VS 2 can be hence explained by the relatively weaker V–S bonds compared to atomic bonding in other 2D materials. Particularly, while the V–S bond length (∼2.36 Å) is similar to the Mo–S bond length (∼2.31 Å), the larger V–S bond angle (∼85.0°) in contrast to the Mo–S bond angle (∼81.5°) enables VS 2 with a lower resistance to stretching (see more details in Tables S1 and S2).…”

Enhanced Optical Emission from 2D InSe Bent onto Si‐Pillars

“…The corresponding shift of the Raman peaks (Figure 3) supports a strain‐induced change of vibrational and electronic properties. [ 16–25,31 ] The bent layers are subject to a weak tensile and compressive strain in the outer and inner surfaces, respectively, which reduces the band gap energy (Figure S5, Supporting Information). Our calculated reduction of the band gap energy is in line with the measured energy shift (<5 meV) of the PL peak in the bent flakes.…”

“…[ 4,14,15 ] Thus, band edge excitons tend to couple preferentially to light polarized along the z‐direction (or c‐axis), rather than along the xy‐plane as for TMDCs. [ 4 ] Mechanical strain can modify these properties: [ 16–20 ] 2D vdW crystals can sustain high strain in reversible fashion due to their large mechanical flexibility [ 21–23 ] and, amongst them, InSe is one of the most flexible systems with a small Young's modulus (23.1 ± 5.2 GPa) [ 24 ] and a bandgap energy that is very sensitive to strain. [ 25 ] Thus, InSe represents a promising system to explore and exploit the effects of strain on electronic and optical properties.…”

Anomalous Low Thermal Conductivity of Atomically Thin InSe Probed by Scanning Thermal Microscopy

“…Amongst the 2D materials in the metal chalcogenide class, indium selenide (InSe) has emerged as a promising semiconductor. [ 5–14 ] It has a band edge absorption energy that increases with decreasing layer thickness; [ 5,6 ] high broad‐photoresponsivity from the infrared to the ultra‐violet range; [ 7–9 ] low‐mass conduction band electrons and high electron mobility even in atomically thin films (i.e., larger than in silicon‐based field‐effect transistors (FETs)); [ 10,11 ] high mechanical strength; [ 12,13 ] a strain‐sensitive band structure [ 14,15 ] with 1D van Hove singularities, [ 16 ] etc. Thanks to this unique set of physical properties, 2D InSe holds promise for a wide range of applications, from ultra‐thin and flexible electronics to next‐generation quantum metrology and photosensing.…”