Editors' Choice—A Methodology to Electrochemically Fabricate Fe-Ni-Co Nanotips

Abstract

Fe-Ni-Co nanotips at the end of nanowires are fabricated at the interface of two Fe-Ni-Co regions via a combination of pulse electrodeposition, anodization and chemical etching. The conditions to electrodeposit and anodize the Fe-Ni-Co nanowires in polycarbonate templates were investigated with a rotating cylinder electrode (RCE) to inspect the polarization behavior of the thin film deposition. The wires were fabricated with three, consecutive electrochemical conditions, where first an Fe-Ni-Co wire segment is deposited, followed by an anodic potential to induce growth of an iron oxide thin film, and then followed by an applied, pulse cathodic current density to reduce the oxide and deposit another layer of Fe-Ni-Co. Upon etching, tips formed at the end of the last Fe-Ni-Co region, as evidenced by SEM. Potential transients during the last applied cathodic pulse current step, suggests that both the reduction of the oxide and metal occur, and that TEM/SAED confirm changes in the crystalline Fe-Ni-Co structure at the interfacial region between steps that contributes to the tip formation. Electrodeposition conditions to fabricate nanowires using nanoporous templates have been widely examined for different applications, and several good reviews summarize the vast number of metal and alloy nanowire systems considered.1-4 Different nanowire morphologies have been reported, some directly formed within the templates, such as nanotubes, [5][6][7] and those that are subsequently etched once released from their templates, such as nanogaps, 4,8 and porous nanowires, 9,10 or through subsequent annealing or displacement reactions resulting in interesting structures, such as nanopeapods. 11,12In addition, Geng and Podlaha 13 recently, showed that Cu-Fe-Ni-Co nanowires could be etched in a preferred radial direction, thinning nanowire segments.Nanowires that are shaped into tips at one end, nanotips, have been widely researched due to their application as cantilever tips for high-resolution atomic force microscopy (AFM), 14,15 tip-enhanced near-field optical microscopy, 16 and scanning tunneling microscopy (STM), [17][18][19] and the need has recently expanded to bio/chemical sensors to measure electrical conduction as a new methodology for molecular detection and monitoring. [20][21][22][23] The reported nanotip materials used in AFM/STM are usually W and Pt/Ir, which are prepared through a "drop off" technique, where the tungsten wire is immersed in a KOH solution (etchant) acting as an anodic electrode; the highest etching rate appears just below the air/electrolyte interface, causing necking and eventual "drop off" of the bottom part of the wire, leaving a sharp tip. 14,17,19,24,25 Alternative methods for fabricating nanotips include: focused ion beam (FIB) lithography, 26 vapor-liquidsolid method (VLS), 27,28 and a novel, self-masking technique where SiC nanosized clusters are generated on top of a substrate, followed by a dry etch of the unmasked substrate regions to create nanotips where the SiC clusters reside. 29In this...

Template-Assisted Electrodeposition of Fe-Ni-Co Nanowires: Effects of Electrolyte pH and Sodium Lauryl Sulfate

“…Locally, the composition could change along the nanowire length if one of the metal rates were under mass transport control, or if the pH changes. Both Fe and Ni ion reduction are expected to be under predominately kinetic control, but Co may be influenced by mass transport changes The change in current efficiency as the nanowire grows could also change the local pH and hence composition, as reported by Geng et al 17 for the same electrolyte presented here. Deligianni and Romankiw 43 have confirmed a surface pH rise during Ni-Fe thin film deposition.…”

Patterned electromagnetic alignment of magnetic nanowires

“…FeNiCo composite nanowires were pulsed electrodeposited in a nanoporous alumina template with 0.2 μm diameter pores and up to 30 μm in length. Details on the electrodeposition process can be found in [51]. After the electrodeposition, the alumina template was dissolved with a 2 M NaOH solution overnight.…”

Activity and Regeneration of Electrodeposited Fe–Ni–Co-Based Electrocatalysts for the Alkaline Oxygen Evolution Reaction

“…Fe−Ni−Co thin films were electrodeposited galvanostatically from a sulfate/sulfamate−boric acid electrolyte (details in Supporting Information, Table S1), adapted from Kim et al 36 and Geng et al 37 Copper rotating cylinder electrodes (RCEs) having a diameter of 1 cm and length of 1.2 cm served as the working electrode with Pt as the counter electrode. The RCE is not flush with the top and bottom insulating regions of the plastic holder, but it is recessed, making a right angle between the plastic holder and the copper electrode, to facilitate a uniform current density distribution.…”