We discuss the experimental studies on (i) the dynamics of charge carrier relaxation and (ii) excitation of interlayer coherent acoustic phonon and its coupling to the interband electronic transition in the photoexcited colloidal multi-layered TiS2 nanodisks of controlled thickness and diameter. The focus of the presentation is how the introduction of the lateral intralayer spatial confinement in multi-layered TiS2 nanodisks influences the relaxation dynamics of charge carriers and coherent interlayer lattice motions. Transient absorption data obtained in TiS2nanodisks (50-150 nm in diameter, ns. The rapid initial decay carrying a larger amplitude can be attributed to the combination of rapid nonradiative decay to lattice and trapping of charge carriers. The slower decay component (1-10 ns time scale), whose amplitude varies with varying dimension of the nanodisks, can be attributed to the slow recovery of the trapped charge carriers. In the transient absorption signal, we also observed oscillation of the interband transition intensity due to the excitation of coherent acoustic phonon. The frequency of coherent acoustic phonon (<1011Hz) was not sensitive to the diameter of the disk but increased with the decrease of the thickness, suggesting the excitation of interlayer phonon rather than intralayer phonon. The excitation of the coherent acoustic phonon is most likely from the impulsive heating of the lattice analogous to the case of metal nanocrystals. We estimated the periodic shift of interband absorption peak by 10-20 nm resulting from the modulation of interlayer gap by ~0.1% from the modulation depth of transient absorption signal and the estimated impulsive thermal expansion by the photoexcitation.

Charge carrier relaxation dynamics and photoexcited coherent inter-layer phonon in colloidal TiS<sub>2</sub> nanodisks of controlled thickness and diameter

247th National Meeting (2014)

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Charge carrier relaxation dynamics and photoexcited coherent inter-layer phonon in colloidal TiS2 nanodisks of controlled thickness and diameter

Charge carrier relaxation dynamics and photoexcited coherent inter-layer phonon in colloidal TiS₂ nanodisks of controlled thickness and diameter