Density control of electrodeposited Ni nanoparticles/nanowires inside porous anodic alumina templates by an exponential anodization voltage decrease

Abstract

Porous alumina templates have been fabricated by applying an exponential voltage decrease at the end of the anodization process. The time constant η of the exponential voltage function has been used to control the average thickness and the thickness distribution of the barrier layer at the bottom of the pores of the alumina structure. Depending on the η value, the thickness distribution of the barrier layer can be made very uniform or highly scattered, which allows us to subsequently fine tune the electrodeposition yield of nickel nanoparticles/nanowires at low voltage. As an illustration, the pore filling percentage with Ni has been varied, in a totally reproducible manner, between ∼3 and 100%. Combined with the ability to vary the pore diameter and repetition step over ∼2 orders of magnitude (by varying the anodization voltage and electrolyte type), the control of the pore filling percentage with metal particles/nanowires could bring novel approaches for the organization of nano-objects.

Porous Alumina Template based Versatile and Controllable Direct Synthesis of Silicon nanowires

“…Ni was prefilled inside nanopores prior to Au deposition. As already reported [11,12], Ni can be well electrodeposited inside PAA template (~ 100%), so it was expected that Au filling fraction will be enhanced by Ni prefilling approach yielding multi-layered metal nanowires. Moreover, usually, introducing barrier layer thinning process results in branched structure at the bottom of nanopores [11,16].…”

“…As already reported [11,12], Ni can be well electrodeposited inside PAA template (~ 100%), so it was expected that Au filling fraction will be enhanced by Ni prefilling approach yielding multi-layered metal nanowires. Moreover, usually, introducing barrier layer thinning process results in branched structure at the bottom of nanopores [11,16]. Even though, very well filled small gold nanoparticles could be successfully located inside nanopores as shown in figure 1, one can notice that some of such nanoparticles are placed inside each of the branched structure at the bottom of nanopores.…”

“…Depending on desired pore diameter and interpore distance, anodization voltage was varied. After anodization process, barrier layer thinning process socalled exponential voltage decrease was carried out subsequently in order to thin barrier oxide layer at the bottom of nanopores [11]. Then, wet-chemical pore widening process was carried out for a removal of residual barrier oxide layer at the bottom of pores in 0.3M phosphoric acid (H 3 PO 4 ) at 30 °C for 25 min.…”

“…For catalyst filling process, pulsed electrodeposition (PED) process was introduced [11,12]. Here, gold was used as a catalyst for SiNW growth and several influencing parameters on PED process was varied for successful Au filling inside PAA template.…”

“…Recently, we have introduced barrier layer thinning process by voltage decrease method [11] and this controllable method allows ones to fill uniformly metal nanoparticles inside of pores.…”