Deposition of Functional, Alloy Based Nanowires Via Pulse Plating Methods
Authors: Hansal Wolfgang E.G. , Sandulache Gabriela , Hansal Selma 
Published: February 2020

The electrochemical deposition of various nanowires is well described in recent scientific publications and focus of the research of a significant number of research groups worldwide. Deposited on a micro/nano porpous aluminum substrate on top of a silicon wafer the level of filling of the pores with the electrodeposit and the homogeneity of the filling over the substrate are key quality factors that will determine the output of nano wires per wafer substrate. With the introduction of alloys the alloy composition and ist alteration over the length of the substrate will be additional critical criteria.

DC plating faces strong limitation in the filling grade as well as in the homogeneity of the alloy composition. Pulse and Pulse Reverse Plating has been introduced as an optimization step for the production of nano-wires.

This presentation gives a report of the results of an sucessful international research project (FP7-ICT-2011-C, MANAQA) describing a technological breakthrough by developing a new method for biological single-molecule measurements. The major technological aim has been the development of single-molecule assays by integrating micro-scale cantilevers with magnetic nanowires (NW) electromagnetically controlled along multiple degrees-of-freedom. For enabling such assays, existing cutting-edge technologies – Atomic Force Microscopy (AFM), nanofabrication, nanowires, and magnetic manipulation – were combined in an integrated approach .

This focus of this paper will is the aspect of the electrodeposition of these magnetic nanostructures. Two main lines of magnetic alloys (soft or hard magnetic) were followed, developing the appropriate electrolyte systems as well as the pulse deposition processes. The fundament of these developments has been a comprehensive work package investigating the electrochemical dependencies and reaction mechanisms for controlled alloy deposition. The effect of general plating factors such as pH, alloying metal concentrations in the electrolyte and temperature has been studied.

For the electrodeposition of CoNi nanowires, a mixed sulfate-chloride has been used. As substrate, aluminum coated silicon wafer have been nanostructured using pulse anodising processes. After deposition, the AAO templates were mechanically broken to observe the nanowire growth using back-scatter electron-microscopy. The alloy composition of the nanowires were investigated via SEM-EDX. Alternative systems such as NiCoFe were deposited and compared with the CoNi nanowires. The pulse sequence applied had an influence on the composition of the deposited nanowires. Beside the pulse sequence the pH of the solution as well as the presence of complex agents (for the alloy formation) were found to be critical parameters for the stability and reproducibility of the alloy deposition process. The deposit properties, e.g. even filling of pores and a homogenous alloy composition along the nanowires were substantially improved by the introduction of pulse plating techniques. The magnetic properties and the reproducibility of those were demonstrated in respect to the application targeted.

For both European research projects, high quality nanowires were received, modified accordingly to the application and tested. The aimed development of single-molecule assays by integrating micro-scale cantilevers with magnetic nanowires electromagnetically controlled along multiple degrees-of-freedom was successfully demonstrated.