Mixed-dimensional heterostructures integrate the advantages of materials with various dimensional ranges, offering a useful framework for multiple technological developments. In a study published in the journal ACS Applied Materials & Interfaces, a novel method for engineering anisotropic behavior and light-matter interaction of monolayer MoS2 by fusing it with a one-dimensional (1D) AlGaAs nanowire (NW) has been presented.
Study: Inducing Strong Light–Matter Coupling and Optical Anisotropy in Monolayer MoS2 with High Refractive Index Nanowire. Image Credit: spainter_vfx/Shutterstock.com
Mixed-Dimension van der Waals Heterostructures
The distinctive optical, topological, electrical, and magnetic features of two-dimensional (2D) van der Waals (vdW) substances have drawn considerable attention and significantly influenced the landscape of essential research in chemistry, physics, and material sciences.
Interestingly, the dangling-bond-free characteristics in 2D materials allow for noncovalent interactions to combine them with non-2D substances (like 0-, 1-, or 3 D materials) to create new mixed-dimensional vdW heterostructures.
These structures can integrate the synergistic benefits of multiple dimensional materials, making them a preferable platform compared to simple 2D substances for various advanced applications, from nanolasers to on-chip photodetectors.
The Problem with 2D Materials
Due to a relatively short light-matter interaction length and defect-mediated nonradiative electron-hole recombination compared to bulk crystals, atomically thin two-dimensional layered substances, such as transition metal dichalcogenides (TMDCs), typically have low luminescence quantum output.
These characteristics lead to 2D TMDC-based optoelectronic tools with low performance. The enhancement of the light-matter interaction in 2D materials has been proposed using a wide range of techniques, such as incorporating Fabry-Perot optical cavities, meta-surfaces, plasmonic structures, and waveguides.
In terms of modifying light-matter interactions in 2D materials, plasmonic nanostructures consisting of noble metals (such as Au and Ag NWs) are the most developed. However, the methods and structures used to produce them are usually complicated, suffering from optical losses brought on by metals, and cannot be merged with methods used to fabricate semiconductors.
Semiconducting Nanowires Could be the Solution
High refractive index semiconductor NWs can help solve these problems and open new possibilities for the functionalization of 2D materials.
Due to its great integration ability, direct band gap, precise control in doping, and easy and economical manufacturing, III-V semiconducting 1D NWs have recently been identified as potential candidates for a variety of optoelectronic applications.
AlGaAs NW, as a III-V semiconducting material with a strong refractive index, produces intensely concentrated optical fields in its 1D structure. Due to their developed transfer and growth mechanisms, these nanowires are also suited for integration with optical circuits, nanophotonic components, or other dimensional materials.
By facilitating strong light-matter interactions, a simple fusion of two-dimensional TMDCs with 1D NWs can easily modify the excitonic sensitivity of TMDCs. In addition to these light-matter interactions, a monolayer TMDC's hexagonal lattice formation features naturally broken inversion and 3-fold (C3) rotational symmetry.
Generally, the C3 structure of these substances can be disrupted by applying strain, bending, and a decrease in dimensionality. These materials exhibit robust anisotropic vibrational, strong light-matter interactions, and electrical and optical responses.
What did the Researchers Do?
This study presents a novel method for combining monolayer MoS2 with 1D AlGaAs NW to design the light-matter interaction and symmetry. MoS2 photoluminescence (PL), compared to that in a bare monolayer MoS2 flake, greatly rises in the mixed-dimensional heterostructure due to their robust electromagnetic (EM) field confined in the NW.
Strong anisotropic optical effects are produced because this structure explicitly breaks the 3-fold rotational symmetry of MoS2. Additionally, we[MC1] [the author] created phototransistors based on mixed-dimensional heterostructures and compared their effectiveness to monolayer MoS2 phototransistors.
Main Results of the Study
By fusing monolayer MoS2 with high refractive index AlGaAs NW, the work shows how these materials can be used to enhance and excite polarization-sensitive optoelectronic and optical capabilities.
Comparing MoS2/NW heterostructures to bare monolayer MoS2 samples, the PL and Raman intensity of MoS2 improves approximately by 3 and 9 times, respectively. Due to the loss of rotational symmetry brought on by the NW, a substantial anisotropic reaction in the PL with a degree of anisotropy of about 60% was also observed.
Excitation polarization-dependent EM field constriction of NWs is the key cause of these optical responses following numerical simulations. The polarization sensitivity of the mixed-dimensional photodetectors offers increased device performance.
The specific sensitivity of MoS2/NW devices are approximately five and three times higher than those of bare monolayer MoS2 phototransistors. These findings open the door for high-performance optoelectronic and photonic devices based on 2D/1D mixed-dimensional heterostructures.
Shafi, A. M., Ahmed, F. et al. (2022). Inducing Strong Light–Matter Coupling and Optical Anisotropy in Monolayer MoS2 with High Refractive Index Nanowire. ACS Applied Materials & Interfaces. Available at: https://doi.org/10.1021/acsami.2c07705
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