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TD-EFISH measurements on a 4 nm as-deposited sample for two different incident photon energies. The unique decay of EFISH is resonantly enhanced near the incident photon energy of 1.6 eV (inset).
TD-EFISH measurements on a 4 nm as-deposited sample at different incident laser powers. (Inset) Log-log scale plot of the EFISH decay vs incident laser power. The slope of indicates a two-photon absorption process and is responsible for EFISH decay mechanism.
TD-EFISH hysteresis measurements on a 4 nm as-deposited sample. Scan 2 is distinguished from scan 1 by temporarily blocking the incident laser, while the accumulated surface negative charge is wiped clear with methanol. The EFISH decay and hysteresis is not observed for annealed or samples (inset).
Schematic band diagram representation of the different charge transport mechanisms leading to the TD-EFISH results. The localized 3.2 eV negatively charged defect within is believed to be responsible for the EFISH decay.
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