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Nano Research

, Volume 11, Issue 3, pp 1193–1203 | Cite as

Aqueous and mechanical exfoliation, unique properties, and theoretical understanding of MoO3 nanosheets made from free-standing α-MoO3 crystals: Raman mode softening and absorption edge blue shift

  • Hongfei LiuEmail author
  • Yongqing Cai
  • Mingyong Han
  • Shifeng Guo
  • Ming Lin
  • Meng Zhao
  • Yongwei Zhang
  • Dongzhi Chi
Research Article

Abstract

Crystalline α-MoO3 belts consisting of nanosheets stacked along their [010] axes were synthesized via thermal vapor transport of MoO3 powders at elevated temperatures. The MoO3 belts were millimeters in length along their [001] axes and tens to hundreds of micrometers in width along their [100] axes. Mechanical and aqueous exfoliations of the belts to form two-dimensional (2D) nanosheets were processed via the scotch-tape and bovine serum albumin (BSA) assisted methods, respectively. Upon scotch-tape exfoliation, the Raman features of MoO3 exhibited monotonic decreases in intensity as the thickness was gradually fell to approach that of a 2D nanosheet. Most Raman features eventually disappeared when a monolayer nanosheet was produced, except for the Mo–O–Mo stretching mode (Ag) at ~818 cm−1, which was accompanied by mode-softening of up to 5 cm−1. This mode softening, hitherto not reported for 2D α-MoO3 nanosheets, can be attributed to lattice relaxations that are validated here via theoretical density functional perturbation theory calculations. The BSA-assisted exfoliation products exhibited a blueshift in the α-MoO3 nanosheet absorption edge; they also revealed an absorption peak at 3.98 eV that can be attributed to their intrinsic exciton absorptions. These observations, together with the facile synthesis of high-purity α-MoO3 crystals, illuminate the possibility of further 2D α-MoO3 nanosheet production and lattice dynamic studies.

Keywords

α-MoO3 two-dimensional materials exfoliations lattice vibrational dynamics micro-Raman scattering 

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Notes

Acknowledgements

The authors would like to acknowledge B. Li for his setting-up of the tube-furnace and Coryl J. J Lee for collecting the SEM/EDX/XRD data. This research is supported by A*STAR Science and Engineering Research Council Pharos 2D Program (SERC Grant No. 152-70-00012).

Supplementary material

12274_2017_1733_MOESM1_ESM.pdf (1.4 mb)
Aqueous and mechanical exfoliation, unique properties, and theoretical understanding of MoO3 nanosheets made from free-standing α-MoO3 crystals: Raman mode softening and absorption edge blue shift

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Copyright information

© Tsinghua University Press and Springer-Verlag GmbH Germany 2018

Authors and Affiliations

  • Hongfei Liu
    • 1
    Email author
  • Yongqing Cai
    • 2
  • Mingyong Han
    • 1
  • Shifeng Guo
    • 1
  • Ming Lin
    • 1
  • Meng Zhao
    • 1
  • Yongwei Zhang
    • 2
  • Dongzhi Chi
    • 1
  1. 1.Institute of Materials Research and Engineering (IMRE)A*STAR (Agency for Science, Technology and Research)SingaporeSingapore
  2. 2.Institute of High Performance Computing (IHPC)A*STAR (Agency for Science, Technology and Research)SingaporeSingapore

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