ABSTRACT
In this chapter, the fabrication of metal nano-spaced electrodes for electronic nanodevices by electro and electroless plating is discussed. The necessary reagents, conditions, and processes required to obtain nano and atomic gaps between soft and clean surfaces electrodes are described. In the electroless method, the plating process is performed catalytically after immersing the sample in a solution which contains the same metal ions. In the electrodeposition technique, metal ions of an electrolyte move towards the sample under an applied voltage.
Both techniques are explained with examples, the first technique is described by demonstrating the formation of gold nanogap electrodes using common medical solutions as reactants, whereas the second technique is described by showing electrodeposition of nickel electrodes in a conventional electrochemical cell. Current voltage characteristics are also presented to evaluate possible applications of the nanogap electrodes in electronic nanodevices. 8.1 IntroductionNano and molecular electronics devices require the fabrication of symmetric metal electrodes separated by a nanogap (“nanogap electrodes”) in which a specific molecule or crystal can be placed in order to connect them to the macroscopic world. In the last two decades, vertical structures in which a self-assembled monolayer (SAM) of molecules is electrically connected on one side with a scanning tunneling microscope (STM) [1,2] or conductive probe atomic force microscope (C-AFM) [3] and on the other side by a metallic surface have been demonstrated. Even though this approach has yielded many important results, it suffers from limitations such as the enormous asymmetry of the electrodes, the requirement of high vacuum environment, difficulties in mass production, and difficulty in maintaining a stable chemical bond between the molecule and the microscope tip due to mechanical vibrations. To solve these problems, more recently, new coplanar metal/molecule/metal devices have been proposed. Nanogap electrodes are fabricated before the molecular components, and they are subsequently inserted. This methodology has the advantage that the junction can be characterized with and without the presence of the molecule, thus, allowing the characterization of the molecule. Among others, there are three most remarkable new approaches for making in-plane nanogaps: (i) controlling a break junction mechanically, (ii) electrical breakdown of thin metal wire via electromigration, and (iii) electroless and electrochemical plating. These techniques are schematically represented in Fig. 8.1. The first technique was first developed by Moreland and Ekin [4]. An Nb-Sn wire mounted on a flexible glass beam can be broken to form an electron tunneling junction between the fracture elements. The method was later improved by other researchers. Notched wires of different metals are obtained first with lithography, by bending the substrate with
