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<p>An investigation of the local structure of MoS<sub>2</sub> colloidal quantum dots (QDs) through extended X-ray absorption fine structure (EXAFS) spectroscopy is presented. The solvent-assisted sonication-centrifugation method is used to prepare MoS<sub>2</sub> QDs with sizes ranging from 4 to 70 nm. We determine the structural parameters of the first-nearest-neighbour shell as a function of dot size using EXAFS analysis. The coordination number and average Mo–S bond length are found to decrease as the size of QD decreases from 70 to 4 nm. It is also observed from EXAFS analysis that the S-vacancy, i.e., the number of edge states, increases significantly as the S:Mo ratio decreases with downsizing of the QDs. The increase in edge state density facilitates the efficacy of surface oxidation and some photoabsorption-dependent properties, such as photoresponse and photocatalytic degradation. Efficacy of these processes enhances significantly with scaling down of the MoS<sub>2</sub> QDs. The rate of atmospheric oxidation significantly enhances in MoS<sub>2</sub> QDs as the dot size reduces. A fivefold increase in photocatalytic degradation efficacy of the QDs is observed when the dot size scales down from 70 to 4 nm. Further, photoresponse as well as external quantum efficiency of the photodetectors fabricated with these QDs exhibit more than four times enhancement when the size is reduced from ~70 to ~4 nm.</p>

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An EXAFS study of the size effect on the local structure of MoS2 colloidal quantum dots and its correlation with chemical and optoelectronic properties

  • 期刊论文

  • 发表日期：

    2026年5月27日

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  • Suparna Pal,
  • Parasmani Rajput,
  • B Tirumala Rao,
  • Neha Sharma,
  • Subhrajit Mukherjee

摘要

An investigation of the local structure of MoS2 colloidal quantum dots (QDs) through extended X-ray absorption fine structure (EXAFS) spectroscopy is presented. The solvent-assisted sonication-centrifugation method is used to prepare MoS2 QDs with sizes ranging from 4 to 70 nm. We determine the structural parameters of the first-nearest-neighbour shell as a function of dot size using EXAFS analysis. The coordination number and average Mo–S bond length are found to decrease as the size of QD decreases from 70 to 4 nm. It is also observed from EXAFS analysis that the S-vacancy, i.e., the number of edge states, increases significantly as the S:Mo ratio decreases with downsizing of the QDs. The increase in edge state density facilitates the efficacy of surface oxidation and some photoabsorption-dependent properties, such as photoresponse and photocatalytic degradation. Efficacy of these processes enhances significantly with scaling down of the MoS2 QDs. The rate of atmospheric oxidation significantly enhances in MoS2 QDs as the dot size reduces. A fivefold increase in photocatalytic degradation efficacy of the QDs is observed when the dot size scales down from 70 to 4 nm. Further, photoresponse as well as external quantum efficiency of the photodetectors fabricated with these QDs exhibit more than four times enhancement when the size is reduced from ~70 to ~4 nm.