期刊
ACS NANO
卷 10, 期 10, 页码 9370-9378出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.6b04210
关键词
ultrafast carrier dynamics; Auger carrier heating carrier cooling; femtosecond transient absorption spectroscopy; quantum wells
类别
资金
- NTU
- A*Star Science and Engineering Research Council Public Sector [122-PSF-0011]
- Computational Materials Sciences Program - U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC00014607]
- A*STAR Science & Engineering Research Council Public Sector [1421200076]
- JSPS-NUS [WBS R143-000-611-133]
Quasi-two-dimensional colloidal nanoplatelets (NPLs) have recently emerged as a class of semiconductor nanomaterials whose atomically precise monodisperse thicknesses give rise to narrow absorption and emission spectra. However, the sub-picosecond carrier dynamics of NPLs at the band edge remain largely unknown, despite their importance in determining the optoelectronic properties of these materials. Here, we use a combination of femtosecond transient absorption spectroscopy and nonadiabatic molecular dynamics simulations to investigate the early time carrier dynamics of CdSe/CdS core/shell NPLs. Band-selective probing reveals sub-picosecond Auger-mediated trapping of holes with an effective second-order rate constant of 3.5 +/- 1.0 cm(2)/s. Concomitant spectral blue shifts that are indicative of Auger hole heating are found to occur on the same time scale as the sub-picosecond trapping dynamics, whereas spectral red shifts that emerge at low excitation densities furnish an electron-cooling time scale of 0.84 +/- 0.09 ps. Finally, nonadiabatic molecular dynamics simulations relate the observed sub-picosecond Auger-mediated hole-trapping dynamics to a shallow trap state that originates from the incomplete passivation of dangling bonds on the NPL surface.
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