16.2 - Template deposition of metals

Abstract

This chapter discusses the main characteristics and fabrication techniques used for obtaining templating membranes and depositing metal nanostructures by suitable electroless and electrochemical procedures. The chapter also discusses the electrochemical properties of the fabricated nanomaterials with emphasis on the characteristics and applications of nanoelectrode ensembles (NEEs). Templating membranes such as aluminum oxide films with regular pore distribution can be formed by electrooxidation of high-purity aluminum substrates in acidic electrolytes. Nanoporous polymeric membranes can be prepared by the track-etch method. Template deposition of metals can be achieved by two methods: electrochemical deposition and electroless deposition. Electrochemical deposition of metals in the pores of templating membranes requires that one side of the membrane be in direct contact with a metallic layer. This can be produced by plasma or vacuum deposition of a metal layer on one side of the membrane and requires that the membrane film be robust enough to tolerate this kind of manipulation. In electrochemical template deposition, the coated film is placed in an electrochemical cell where the template membrane acts as the cathode and a counter electrode is the anode. Final products of the electrochemical deposition are solid nanoparticles, typically nanowires. Electroless metal deposition involves the use of chemical reducing agents to plate a metal from a solution onto a surface. The key requirement for this process is to arrange the chemistry so that the kinetics of homogeneous electron transfer from the reducing agent to the metal ion is very slow. Scanning or transmission electron microscopy is typically used for performing morphological characterization of nanomaterials obtained by template synthesis. Nanometals have interesting optical properties. NEEs find their application in a variety of fields ranging from electroanalysis to sensors and electronics.