Ultrafast Electronic Relaxation Dynamics of Atomically Thin MoS2 Is Accelerated by Wrinkling

Strain engineering is an attractive approach for tuningthe localoptoelectronic properties of transition metal dichalcogenides (TMDs).While strain has been shown to affect the nanosecond carrier recombinationdynamics of TMDs, its influence on the sub-picosecond electronic relaxationdynamics is still unexplored. Here, we employ a combination of time-resolvedphotoemission electron microscopy (TR-PEEM) and nonadiabatic ab initio molecular dynamics (NAMD) to investigate the ultrafastdynamics of wrinkled multilayer (ML) MoS2 comprising 17layers. Following 2.41 eV photoexcitation, electronic relaxation atthe & UGamma; valley occurs with a time constant of 97 & PLUSMN; 2 fs forwrinkled ML-MoS2 and 120 & PLUSMN; 2 fs for flat ML-MoS2. NAMD shows that wrinkling permits larger amplitude motionsof MoS2 layers, relaxes electron-phonon couplingselection rules, perturbs chemical bonding, and increases the electronicdensity of states. As a result, the nonadiabatic coupling grows andelectronic relaxation becomes faster compared to flat ML-MoS2. Our study suggests that the sub-picosecond electronic relaxationdynamics of TMDs is amenable to strain engineering and that applicationswhich require long-lived hot carriers, such as hot-electron-drivenlight harvesting and photocatalysis, should employ wrinkle-free TMDs.