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Low-magnification and zoomed-in SEM images of large (a) and (b), medium (c) and (d), and small (e) and (f) CdS NBs on different locations of the mica substrate. Notice the difference of the scale bar in Figs. 1(b)–1(f).
(a) The normalized differential transmitted THz probe pulse (−ΔE/E) as a function of time delay of the three different sized CdS NBs and bulk CdS with pump fluence of 20 μJ/cm2. (b) Pump fluence dependent for the three CdS NB samples. (c) Real (open circle) and (d) imaginary (open square) components of the photoconductivity spectra at 5 ps after photoexcitation. The solid lines for NBs samples are the best-fit by the Drude-Smith model. For bulk sample, the fitting is done with Drude model.
Time dependence of the best-fit parameters with Drude-Smith model: (a) carrier density n, (b) parameter c, and (c) from 5 to 500 ps for the transient complex photoconductivities of large (black square), medium (red circle), and small (blue triangle) sized NBs after photoexcitation with the pump fluence of 20 μJ/cm2. (d) The extracted time dependent percentage of depletion layer in NBs. Inset is the schematic picture of the time evolution of depletion layer.
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