调控缺陷实现二维硫化钼的饱和与反饱和吸收特性研究

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在"可控缺陷工程下的硫化钼二维材料分散体和薄膜的饱和及反饱和吸收研究"中，论文阐述了对二维材料中的缺陷进行理解和调控对于线性和非线性光电子器件的重要性，尤其是在调整非线性光学吸收性能方面。研究者们利用了尺寸较小的原子缺陷，通过分级离心法成功制备出不同尺寸的钼硫化物纳米片。高分辨率的X射线光电子能谱（XPS）显示出与尺寸相关的硫空位缺陷，这表明材料的非线性光学性质可能随尺寸变化而变化。作者 Chunhui Lu、Hongwen Xuan 等来自陕西联合石墨烯实验室、国家光电技术与功能材料重点实验室、国际光电技术和纳米功能材料合作研究中心，以及西北大学物理学院和西安邮电大学科学学院的研究团队，他们通过细致的实验揭示了小尺寸缺陷如何影响二维材料的特性。他们的工作展示了如何通过控制缺陷来设计具有特定饱和和反饱和吸收特性的钼硫化物分散体和薄膜，这对于开发新型光电子设备，如调制器、激光器或开关等，具有潜在的应用价值。这项研究强调了在设计下一代高性能光电器件时，对材料缺陷的精细调控是至关重要的。它不仅涉及基础科学原理，如尺寸效应与缺陷结构对光吸收行为的影响，也包括了实际应用中的可操控性，即通过改变材料的缺陷分布，能够实现对光信号处理的动态控制。因此，这一发现为二维材料在光子学领域的未来发展奠定了坚实的基础，特别是在非线性光学器件的设计和优化上。

Saturable and reverse saturable absorption in

molybdenum disulfide dispersion and film by

defect engineering

CHUNHUI LU,

HONGWEN XUAN,

*YIXUAN ZHOU,

XINLONG XU,

QIYI ZHAO,

AND JINTAO BAI

Shaanxi Joint Laboratory of Graphene, State Key Laboratory of Photoelectric Technology and Functional Materials, International Collaborative

Center on Photoelectric Technology and Nano Functional Materials, Institute of Photonics & Photon-Technology, School of Physics,

Northwest University, Xi’an 710069, China

School of Science, Xi’an University of Posts and Telecommunications, Xi’an 710121, China

*Corresponding author: hwxuan@nwu.edu.cn

Received 22 April 2020; revised 14 June 2020; accepted 23 June 2020; posted 24 June 2020 (Doc. ID 395870); published 27 August 2020

Understanding and controlling defect in two-dimensional materials is important for both linear and nonlinear

optoelectronic devices, especially in terms of tuning nonlinear optical absorption. Taking advantage of an atomic

defect formed easily by smaller size, molybdenum disulfide nanosheet is prepared successfully with a different size

by gradient centrifugation. Interestingly, size-dependent sulfur vacancies are observed by high-resolution

X-ray photoelectron spectroscopy, atomic force microscopy, and transmission electron microscopy. The defect

effect on nonlinear absorption is investigated by Z-scan measurement at the wavelength of 800 nm. The results

suggest the transition from saturable absorption to reverse saturable absorption can be observed in both disper-

sions and films. First principle calculations suggest that sulfur vacancies act as the trap state to capture the

excited electrons. Moreover, an energy-level model with the trap state is put forward to explain the role of

the sulfur vacancy defect in nonlinear optical absorption. The results suggest that saturable absorption and reverse

saturable absorption originate from the competition between the excited, defect state and ground state absorp-

tion. Our finding provides a way to tune the nonlinear optical performance of optoelectronic devices by defect

engineering.

https://doi.org/10.1364/PRJ.395870

1. INTRODUCTION

Unavoidable defects in the growth process of two-dimensional

(2D) materials can dramatically affect the performance of the

corresponding device. Defect-associated nonradiative recombi-

nation will lead to low quantum efficiency (<0.6%)[1], and

structure defects will result in lower carrier mobility [2].

Defects can also be a source of merit; for instance, photolumi-

nescence enhancement induced by sulfur (S) vacancy [3] and

oxygen bonding at the defect sites [4] in monolayer molybde-

num disulfide (MoS

) and catalytic efficiency in hydrogen evo-

lution reaction improved by S vacancies [5] at edge defects [6].

However, the contribution of these defects to the nonlinear op-

tical (NLO) properties, such as saturable absorption (SA) and

reverse saturable absorption (RSA), is not completely clear so

far. Recently, different defect types, including effective two-

photon absorption (TPA) from zinc (Zn) vacancy [7], tunable

NLO absorption derived from the concentration of manganese

doping [8], and enhanced modulation depth [9] from localized

defect states at grain boundaries, have been introduced to im-

prove the performance of nonlinear photonic devices. Actually,

these defects act as different trap centers to capture electrons

[10], holes [11], or excitons [12,13], which make it crucial

to confirm the type of defect-induced localized states in 2D

materials.

MoS

is a typical 2D material to design linear optoelectronic

devices due to its excellent optical and electronic properties,

including high current on/off ratio (∼10

), high electron

mobility (10

· V

−1

· s

−1

)[14], strong catalytic activity [15],

and photoluminescence [16,17]. Importantly, a size-dependent

few-layer MoS

can be achieved easily using ultrasonic exfolia-

tion [18] combined with the gradient centrifugation method

[19]. On the other hand, nonlinear photonic applications in-

cluding Q-switching [20], mode-locking [21,22], and an op-

tical limiter [23] have also been designed based on SA and

RSA behavior. For example, MoS

and graphene were reported

with stronger SA [24] than those of MoTe

and MoSe

, while

BN exhibited a strong RSA effect [25]. SA and RSA can be

interpreted as a transmission increasing and decreasing accord-

ing to pump intensity, respectively. It is determined by a smaller

absorption cross section in excited state compared with that in

1512

Vol. 8, No. 9 / September 2020 / Photonics Research

Research Article

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