Self-assembly of gold nanoparticles on poly(allylamine hydrochloride) nanofiber: A new route to fabricate "necklace" as single electron devices

Fabrication of a percolating conductive device exhibiting "necklace-like morphology" is being reported utilizing a new route. This device was fabricated by exploiting the electrostatic self-assembly of citrate capped negatively charged Au nanoparticles (NPs) (60 nm diameter) over positively charged poly(allylamine hydrochloride) (PAH) fibrous scaffold and followed by synthesis of small Au NPs (∼10 nm) on the PAH surface. These 10 nm Au NPs were selectively synthesized over the PAH fiber surface using the surface catalyzed reduction of Au precursor (HAuCl₄), leading to a continuous conducting network. This conducting device demonstrated a room temperature (RT) Coulomb-blockade characteristic, which is indicative of "single electron device". The deposition of Au NPs was directed by the diameter of PAH fibers and UV-irradiation exposure time used during the synthesis process. The average diameter of the fibers was in the ∼100-150 nm range, and the polyelectrolyte (PAH) was fabricated using the electrospinning technique. The size of these fibers was controlled by tuning the physical properties of PAH solution. Exposure of UV-irradiation for 25 min was sufficiently enough to deposit Au NPs in close proximity to each other. Longer exposure time (∼60 min) resulted in a device which showed linear Ohmic current-voltage (I-V) behavior. The present process is reproducible, efficient, and resulted in a structurally stable and robust device.