Designing artificial 2D crystals with site and size controlled quantum dots

Xuejun Xie,Pulickel M Ajayan,Wei Cao,Jiahao Kang,Jae Hwan Chu,Kaustav Banerjee,Yongji Gong

doi:10.1038/s41598-017-08776-3

Xuejun Xie, Pulickel M Ajayan + Show 5 more

Open Access

https://doi.org/10.1038/s41598-017-08776-3

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Abstract

Ordered arrays of quantum dots in two-dimensional (2D) materials would make promising optical materials, but their assembly could prove challenging. Here we demonstrate a scalable, site and size controlled fabrication of quantum dots in monolayer molybdenum disulfide (MoS2), and quantum dot arrays with nanometer-scale spatial density by focused electron beam irradiation induced local 2H to 1T phase change in MoS2. By designing the quantum dots in a 2D superlattice, we show that new energy bands form where the new band gap can be controlled by the size and pitch of the quantum dots in the superlattice. The band gap can be tuned from 1.81 eV to 1.42 eV without loss of its photoluminescence performance, which provides new directions for fabricating lasers with designed wavelengths. Our work constitutes a photoresist-free, top-down method to create large-area quantum dot arrays with nanometer-scale spatial density that allow the quantum dots to interfere with each other and create artificial crystals. This technique opens up new pathways for fabricating light emitting devices with 2D materials at desired wavelengths. This demonstration can also enable the assembly of large scale quantum information systems and open up new avenues for the design of artificial 2D materials.

Highlights

The evolution of information technology is approaching the quantum era
Figure 1. 1T phase quantum dot superlattice created on 2H phase monolayer MoS2 at room temperature. (a) Schematic of electron beam irradiation on 2H phase MoS2 to trigger the transition of 1T phase triangular MoS2 quantum dots, where L is the lattice spacing and a is the side length of the 1T phase triangle. (b) Raman spectra before and after electron beam irradiation
As the electron beam irradiation dose increases, the intensities of E12g peak at 381.56 cm−1 and A1g peak at 404.82 cm−1 decrease, and E12g peak moves to lower wavenumbers and A1g peak moves to higher wavenumbers, which is different from the Raman peaks of MoS2′s defects[24, 25]

Summary

Introduction

The evolution of information technology is approaching the quantum era. Quantum dots or artificial atoms are promising medium for quantum information teleportation and processing[1,2,3], and they represent the state-of-art of human capability to manipulate matter[4]. Quantum dot superlattices have been widely investigated for creating materials with tunable bandgaps[18, 19] They were all made by bottom-up methods that make it inherently hard to design the lattice structure as desired, and their performance get smeared by energetic and positional disorders[20]. We report the first successful demonstration of a top-down method for creating large area quantum dot superlattice on monolayer MoS2 at room temperature by focused electron beam irradiation with sub-nanometer precision in large scale (30 μm × 30 μm). (a) Schematic of electron beam irradiation on 2H (semiconducting) phase MoS2 to trigger the transition of 1T (metallic) phase triangular MoS2 quantum dots, where L is the lattice spacing (or pitch) and a is the side length of the 1T phase triangle. Large-scale quantum information systems, as well as opens up new pathways for fabricating light emitting devices with 2D materials at desired wavelengths

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