Multi-Component Functional Nanostructures
Ferroelectric nanolithography exploits polarization dependent surface interactions to pattern nanoparticles, but the factors that control the particle size and distribution are not sufficiently well understood to produce hybrid nanostructures. Here the effects of photon energy, photon flux, and polarization vector orientation on ferroelectric domain specific photoreactions are quantified, leading to an understanding of the nanoparticle deposition mechanism. Patterned nanoparticle arrays functionalized with optically active porphyrin complexes are configured into optoelectronic devices.
Fig. a illustrates SPM polarization patterning schematically, while Fig. b shows the relationship between the surface potential and the orientation of the domains. Fig. c compares the topographic structure and the surface potential after a pattern is poled with a biased tip. Fig. d and Fig. e are examples of domain induced production of silver and gold nanoparticles on patterned PZT surfaces.
The reactions associated with the AuNPs formation are seen in the equations here. Fig. f and g show the influence of the FE domains and photon flux of the AuNPs deposition respectively. Fig. h shows the reaction process on the surface schematically. Initial reduction occurs in the absence of a barrier for electron transfer. As the nanoparticles increase in size, an interface barrier forms and causes an electron depletion region below the particle, indicated by the shaded region. The reaction will stop (the nanoparticle will stop growing) once the interfacial barrier is large enough that the depletion depth is larger than the tunneling distance.
We take advantage of FE lithography here to fabricate NP devices. Here a schematic diagram of a patterned hybrid nanostructure device and the structure of dithiol-terminated meso-to-meso ethyne-bridged tris[(porphinato)zinc(II)] supermolecule (dithiol-PZn3) is shown in Fig. i. Fig j and k are comparisons of dark current and photoconduction with 533 nm (green) and 655 nm (red) light for two devices. Enhancement of photocurrent compared to the dark current are shown in Fig. l. The photocurrent in this device arises predominantly from the interaction of the transverse plasmon induced current.