Boosting Second-Harmonic Generation in Monolayer Rhenium Disulfide by Reversible Laser Patterning

Betül Küçüköz,Battulga Munkhbat,Timur O Shegai

doi:10.1021/acsphotonics.1c01358

Betül Küçüköz, Battulga Munkhbat + Show 1 more

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https://doi.org/10.1021/acsphotonics.1c01358

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Journal: ACS Photonics	Publication Date: Jan 24, 2022
Citations: 9	License type: CC BY 4.0

Affiliation: Chalmers University of Technology

Abstract

Active modification and control of transition metal dichalcogenides (TMDs) properties are highly desirable for next-generation optoelectronic applications. In particular, controlling one of the most important characteristics of TMDs─their crystal structure and symmetry─may open means for manipulating their optical nonlinearities and electrical transport properties. Here, we show that a monolayer ReS2, which does not have a broken inversion symmetry due to its stable 1T′-distorted phase and correspondingly shows only weak second-harmonic generation (SHG), can produce a significantly enhanced (∼2 orders of magnitude) SHG upon reversible laser patterning. This enhancement can be explained by the laser-induced transition from centrosymmetric 1T′ to noncentrosymmetric 2H-phase. This hypothesis is confirmed by polarization-resolved SHG measurements, which reveal a gradual change from the 2-fold to 6-fold symmetry profiles upon laser patterning. Additionally, we found that laser patterning of the bilayer ReS2 samples, contrary to the monolayers, leads to a substantially reduced SHG signal. This result corroborates the 1T′-to-2H laser-induced phase transition. Finally, we show that the laser-induced patterning is reversible by heat. These results open a possibility to actively and reversibly control the crystal structure of mono- and few-layer ReS2 and thus its optical and electronic properties.

Highlights

Crystal structure and symmetry play an important role in determining key material properties, such as the electrical transport behavior and the level of optical nonlinearities.[1−4] Many group VI transition metal dichalcogenides (TMDs), including MoS2, WS2, and WSe2, follow the 2H crystalline structure in their most stable configuration and possess a broken inversion symmetry in the monolayer form
Strain can be used to enhance the second-harmonic generation (SHG) from symmetric TMD structures.[19−22] the even order optical nonlinearity, mechanical stress, and broken inversion symmetry in monolayer TMDs are inherently related to the piezoelectric effect, which has been recently reported for MoS2.3,23
The behavior is opposite for the bilayer ReS2, which is noncentrosymmetric in the unpatterned form

Summary

Introduction

Crystal structure and symmetry play an important role in determining key material properties, such as the electrical transport behavior and the level of optical nonlinearities.[1−4] Many group VI transition metal dichalcogenides (TMDs), including MoS2, WS2, and WSe2, follow the 2H crystalline structure in their most stable configuration and possess a broken inversion symmetry in the monolayer form This leads to a pronounced second-harmonic generation (SHG) signal due to the high second-order susceptibility, χ(2).[5−7] the values of χ(2) nonlinear coefficient for monolayer MoS2 are among the highest reported to date up to 10−7 m/V at 810 nm excitation.[6,8] significant research attention is devoted to studying these nonlinear optical effects.[9−13]. Several previous studies demonstrated that ReS2 has a weak interlayer coupling and a randomly stacked geometry due to in-plane distortion.[25−29] In contrast, several other studies claimed the layers are coupled and stacked in an orderly fashion as evidenced by the appearance of interlayer shear and breathing modes measured by ultralow frequency Raman spectrosco-

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