Ultrafast light-induced softening of chalcogenide thin films above the rigidity percolation transition

Abstract

Little is known about the role of network rigidity in light-induced structural rearrangements in network glasses due to a lack of supporting experiments and theories. In this article, we demonstrate for the first time the ultrafast structural rearrangements manifested as induced absorption (IA) over a broad spectral range in a-GexAs35-xSe65 thin films above the mean-field rigidity percolation transition, quantified by the mean coordination number ⟨r⟩ = 2.40. The IA spectrum arising from self-trapped excitons, induced structural rearrangements by softening the glass network that strikingly reveal two relaxation mechanisms which differ by one order of magnitude. The fast kinetics of electron-lattice interaction occurs within 1 ps, exhibits a weak dependence on rigidity and dominates in the sub-bandgap region. In a stark contrast, the slow kinetics are associated with the structural changes in the bandgap region and depends strongly on network rigidity. Our results further demonstrate that amplitude of IA scales a linear relationship with excitation fluence which provides a unique way to induce structural rearrangements in over-coordinated network to exploit it for practical purposes. Our results modify the conventional concept of rigidity dependence of light-induced effects in network glasses, when excited with an ultrafast laser.

Pulse-duration dependence of saturable and reverse saturable absorption in ZnCo2O4 microflowers

“…From the best fit to the experimental data (Inset), the optical bandgap is found to be 1.72 and 2.73 eV, in accordance with the work by Guo [25] and Yu [26]. To obtain the intersystem crossing lifetime for ZCO, we perform femtosecond pumpprobe TA measurements [27]. The TA spectra is measured from 1.65 to 2.25 eV for 400 nm excitation wavelength up to a probe delay of 600 ps.…”

Light-Induced Effects in Amorphous Chalcogenide Glasses: Femtoseconds to Seconds

“…We have seen earlier that ns TA in Ge x As 35-x Se 65 thin films decreases from floppy to rigid networks in accordance with network rigidity theory [37,38]. To prove the validity of the theory under ultrafast pulsed excitation, we performed femtosecond pump-probe measurements in Ge x As 35-x Se 65 thin films of thickness 700 nm with 400 nm, 120 fs laser, and the TA data for the samples are shown in Figure 11a at probe delay of 1 ps [63]. TA decreases when MCN increases from 2.4 to 2.6; however, interestingly, even beyond the rigidity percolation threshold, the sample with MCN = 2.6 shows significant TA, which was not predicted by network rigidity theory.…”

Lightinduced Effects in Amorphous Chalcogenide Glasses: Femtoseconds to Seconds

“…To prove the validity of the theory under ultrafast pulsed excitation we performed femtosecond pump-probe measurements in GexAs35-xSe65 thin films with 400 nm, 120 fs laser and the TA data for the samples are shown in Fig. 6(e) at probe delay of 1 ps [64]. Clearly, TA decreases when MCN increases from 2.4 to 2.6, however interestingly even beyond the rigidity percolation threshold the sample with MCN=2.6 shows significant TA which was not pedicted by network rigidity theory.…”