Diao Mengjuan, Li Hui, Sun Yanhui, Liang Ying, Yu Zhiyang, Boukhvalov Danil W, Huang Zhipeng, Zhang Chi
School of Chemical Science and Engineering, Tongji University, Shanghai 200092, P. R. China.
State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, Fuzhou 350002, P. R. China.
ACS Appl Mater Interfaces. 2021 Jan 27;13(3):4211-4219. doi: 10.1021/acsami.0c20741. Epub 2021 Jan 13.
The knowledge concerning the influence of defects on the nonlinear optical response of materials remains scarce so far. In this work, we have successfully introduced defects into SnS nanosheets by plasma treatment and shown that a defect generation is an effective approach to significantly improve the reverse saturable absorption of SnS. The SnS nanosheets treated with Ar plasma for 40 s exhibit a nonlinear absorption coefficient (β) as large as (2.9 ± 0.12) × 10 cm GW, which is nearly 9 times that of the untreated sample. The influence of Ar-plasma-treatment time, defect type, and defect number on the nonlinear absorption of SnS nanosheets are also studied. Structure and spectroscopy characterization confirms the introduction of S and Sn vacancies with Ar-plasma etching. Surface photovoltage spectroscopy and density functional theory calculation indicate that S vacancies can induce in-gap states in the band gap. These in-gap states act as intermediate states for the successive absorption of photons during femtosecond laser excitation (namely, excited-state absorption). In contrast, Sn defects cannot lead to in-gap states and have a limited contribution to nonlinear absorption. Our result would provide a promising way to improve optical nonlinearities.
到目前为止，关于缺陷对材料非线性光学响应影响的知识仍然匮乏。在这项工作中，我们通过等离子体处理成功地在硫化锡纳米片中引入了缺陷，并表明缺陷的产生是显著提高硫化锡反饱和吸收的有效方法。用氩等离子体处理40秒的硫化锡纳米片表现出高达(2.9±0.12)×10 cm GW的非线性吸收系数(β)，这几乎是未处理样品的9倍。还研究了氩等离子体处理时间、缺陷类型和缺陷数量对硫化锡纳米片非线性吸收的影响。结构和光谱表征证实了氩等离子体蚀刻引入了硫和锡空位。表面光电压光谱和密度泛函理论计算表明，硫空位可以在带隙中诱导带隙内的状态。这些带隙内的状态在飞秒激光激发期间作为连续吸收光子的中间状态（即激发态吸收）。相比之下，锡缺陷不会导致带隙内的状态，并且对非线性吸收的贡献有限。我们的结果将为改善光学非线性提供一条有前景的途径。
