Surface-plasmon-enhanced photocurrent generation of CdTe nanoparticle/titania nanosheet composite layers on Au particulate films

Multilayer films composed of Au particle/titania nanosheet (TNS)/CdTe nanoparticle were successfully prepared using a layer-by-layer-deposition technique. CdTe nanoparticles were accumulated as the topmost layer on TNS/poly(diallyldimethylammonium) (PDDA) bilayers deposited on the substrates of an Au particle film or an F-doped SnO2 (FTO) electrode. CdTe nanoparticles were acted as a photosensitizer. The photogenerated electrons in CdTe nanoparticles were injected into the conduction band of titania nanosheets to produce anodic photocurrent at a more positive potential than −0.4 V vs. Ag/AgCl. The magnitude of photocurrent was much larger for the films prepared on the Au particle film rather than that on the FTO electrode. Furthermore, with an increase in the thickness of (TNS/PDDA) bilayers, that is, the distance between Au and CdTe nanoparticles, the photocurrent was drastically decreased. The enhancement factor of photocurrent, defined as the ratio of the magnitude of photocurrent obtained with CdTe particle layer immobilized on Au layer to that on FTO, was varied from 2 to 10 by changing the wavelength of irradiation light. The broad peak at 520 nm appeared in the action spectrum of the enhancement factor and its profile roughly corresponded to the localized surface plasmon resonance peak of Au particle layer whose peak wavelength was ca. 540 nm. These facts indicated that the photoexcitation of the surface plasmon of Au particles, which produced a locally enhanced electric field near Au particle layer, played an important role in the increase in the photoexcitation probability of CdTe nanoparticles deposited as the topmost layer.