Exceptional Tunability of Band Energy in a Compressively Strained Trilayer MoS₂ Sheet

Abstract

Tuning band energies of semiconductors through strain engineering can significantly enhance their electronic, photonic, and spintronic performances. Although low-dimensional nanostructures are relatively flexible, the reported tunability of the band gap is within 100 meV per 1% strain. It is also challenging to control strains in atomically thin semiconductors precisely and monitor the optical and phonon properties simultaneously. Here, we developed an electromechanical device that can apply biaxial compressive strain to trilayer MoS2 supported by a piezoelectric substrate and covered by a transparent graphene electrode. Photoluminescence and Raman characterizations show that the direct band gap can be blue-shifted for ~300 meV per 1% strain. First-principles investigations confirm the blue-shift of the direct band gap and reveal a higher tunability of the indirect band gap than the direct one. The exceptionally high strain tunability of the electronic structure in MoS2 promising a wide range of applications in functional nanodevices and the developed methodology should be generally applicable for two-dimensional semiconductors.

Strong Modulation of Optical Properties in Black Phosphorus through Strain-Engineered Rippling

“…The magnitude of the observed shifts, around +10% (tensile) to -30% (compressive) of the unstrained sample gap, greatly exceeds typical values measured in transition metal dichalcogenides. [20][21][22][23][24][25][26] The results of our tight-binding simulations are compatible with these observations for strains below ± 5%. Most saliently, the observed spatial modulation of the absorption edge suggests the possibility of strain-induced confinement of carriers along the ripple valleys, where the local electronic gap is smallest.…”

“…This is once more in contrast with other 2D semiconductors where an opposite sign of the strain-induced band gap change has been observed. [20][21][22][23][24][25] A deeper insight into the spatial variation of the absorption edge energy can be obtained through iso-absorption maps that represent the energy at which the local absorption at each sample position This is the post-peer reviewed version of the following article: J. Quereda et al "Strong modulation of optical properties in black phosphorus through strain-engineered rippling" Nano Letters (2016) DOI:10.1021/acs.nanolett.5b04670 Which has been published in final form at: http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b04670 7 reaches a certain value. In Figure 1c we present an iso-absorption map that shows the spatial dependence of the absorption edge onset across the rippled black phosphorus sample (see the Supporting Information for more details about the hyperspectral technique and data analysis used to build up this map).…”

Strain and structure heterogeneity in MoS2 atomic layers grown by chemical vapour deposition

“…Substrate-induced straining of 2D materials for band structure engineering has been effectively explored in previous studies 26,28 . However, these experiments have only been performed on exfoliated samples and a comprehensive study of the role of substrate and homogeneity on the transferred strain has not been explored.…”

“…However, these experiments have only been performed on exfoliated samples and a comprehensive study of the role of substrate and homogeneity on the transferred strain has not been explored. Most recently, the strain-induced bandgap changes in monolayer MoS 2 , using polymer substrates, has been demonstrated 26,[28][29][30] . However, because of the weak adhesion between MoS 2 and substrates, strain cannot be completely transferred to MoS 2 from the substrate, as exemplified in graphene strain-engineering studies 31,32 .…”

Graphene–MoS2 hybrid nanostructures enhanced surface plasmon resonance biosensors

“…Before the attachment to prism, graphene and MoS 2 layers are deposited on the top of the Au thin film coated glass slide [9,42,43]. The excitation light wavelength used for the SPR sensing is 632.8 nm.…”