Transient absorption measurements of excitonic dynamics in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>3</mml:mn><mml:mi>R</mml:mi></mml:mrow><mml:mtext>−</mml:mtext><mml:msub><mml:mrow><mml:mi>MoS</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:math>
G. S. Agunbiade, Neema Rafizadeh, Ryan J. Scott, Hui Zhao
Abstract
The excitonic dynamics in ${\mathrm{MoS}}_{2}$ monolayer, bilayer, and bulk flakes with different stacking orders, namely $3R$ and $2H$, are investigated through transient absorption spectroscopy at room temperature. Samples are obtained by the mechanical exfoliation of bulk ${\mathrm{MoS}}_{2}$ crystals with $3R$ and $2H$ stacking orders. Photoluminescence spectroscopy is performed to characterize and compare the samples. Time-resolved differential reflection measurements reveal that monolayer flakes exfoliated from the $3R$ and $2H$ crystals exhibit similar exciton lifetimes of a few picoseconds. However, the exciton lifetime in the $3R$ bilayer flake is approximately 85 ps, about twice as long as that in the $2H$ bilayer. This prolonged exciton lifetime is attributed to the reduction of the electron-hole wavefunction overlap in the $3R$ bilayer due to the built-in polarization. Similarly, in bulk $3R$ ${\mathrm{MoS}}_{2}$, the exciton lifetime is around 220 ps, approximately twice as long as those in bulk $2H$ ${\mathrm{MoS}}_{2}$. The extension of the exciton lifetime in $3R$ transition metal dichalcogenides could be advantageous for their applications in optoelectronic devices.