Fig. 1. Characterization of NUs. (a) High-magnification TEM image, where the inset is optical photo of NUs colloidal solution; (b) low-magnification TEM image; (c) SEM image; (d) normalized extinction spectrum; (e) size distribution of NUs spikes; (f) size distribution of NUs cores

Fig. 2. Characterization of NUs-TiO₂ composite structure. (a) Energy band diagram; (b) SEM image of NUs drop cast on TiO₂ film; (c) XRD patterns of NUs-TiO₂/FTO, TiO₂/FTO and FTO; (d) transmission spectra; (e) reflection spectra; (f) absorption spectra; (g) PL images of NUs-TiO₂ and TiO₂

Fig. 3. Schematic of experimental set-up used for identifying the location of measured particles. (a) Schematic of photoelectrochemical (PEC) cell device; (b) low-magnification optical image of identified location; (c) high-magnification optical image of identified position; (d) SEM image of identified location

Fig. 4. PEC analysis of NUs-TiO₂ at microscale level. (a) Time evolution of photocurrent under chopping illumination; (b) dependence of photocurrent on applied bias; (c) dependence of photocurrent on excitation source power; (d) stability measurement of NUs-TiO₂

Fig. 5. FDTD-simulated electric filed distribution of a single NUs at different incident wavelengths. (a) 400 nm; (b) 514 nm; (c) 600 nm; (d) 800 nm