Abstract
AbstractControlling the propagation and intensity of an optical signal is central to several technologies ranging from quantum communication to signal processing. These require a versatile class of functional materials with tailored electronic and optical properties, and compatibility with different platforms for electronics and optoelectronics. Here, the inherent optical anisotropy and mechanical flexibility of atomically thin semiconducting layers are investigated and exploited to induce a controlled enhancement of optical signals. This enhancement is achieved by straining and bending layers of the van der Waals crystal indium selenide (InSe) onto a periodic array of Si‐pillars. This enhancement has strong dependence on the layer thickness and is modelled by first‐principles electronic band structure theory, revealing the role of the symmetry of the atomic orbitals and light polarization dipole selection rules on the optical properties of the bent layers. The effects described in this paper are qualitatively different from those reported in other materials, such as transition metal dichalcogenides, and do not arise from a photonic cavity effect, as demonstrated before for other semiconductors. The findings on InSe offer a route to flexible nano‐photonics compatible with silicon electronics by exploiting the flexibility and anisotropic and wide spectral optical response of a 2D layered material.
Highlights
The fundamental science of 2D indium selenide (InSe) is an exciting research field with recent breakthroughs emerging from its unique elec-Atomically thin layers of van der Waals crystals and their tronic band structure
Our data and analysis for InSe layers bent onto Si-pillars reveal that the orbital symmetry of the band-edge states and light polarization dipole selection rules play the main role in the enhancement of the optical signal
We have demonstrated the deterministic positioning of 2D InSe flakes of different thickness onto a periodic array of Si-pillars
Summary
Thin layers of van der Waals (vdW) crystals and their tronic band structure. We show a site-specific, reproducible bending of individual flakes onto the pillars and corresponding enhancement of the Raman and photoluminescence (PL) signals We explain these findings by first-principles calculations of the electronic band structure of 2D InSe, revealing the role of the strain and geometrical shape of the bent flakes. Our approach to this optical enhancement differs from previous works that used randomly distributed nanoparticles or wrinkles to texture the layers.[14,15] The effects described in this paper are qualitatively different from those reported in other materials: they do not arise from localization of carriers and/or non-homogeneous strain intentionally created by transferring the layers onto dielectric pillars; and they do not arise from a photonic cavity effect, that is, from light interactions with subwavelength dielectric cavities. The measured enhancement of the optical signal by more than a factor of 10 in the thinnest layers (≈2 nm) offers a route to the controlled modulation of the optical properties of atomically thin semiconductors for flexible optoelectronics, compatible with complementary metal oxide semiconductor technology and planar optical waveguides
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