Structure of Electroplated Hard Gold Observed by Transmission Electron Microscopy

Abstract

Transmission electron micrographs of gold films plated in baths containing cobalt or nickel as the hardening agent showed the presence of uniformly distributed nonmetallic objects with diameters ranging from 20 to 70Å. These objects are believed to represent single molecules, and their agglomerates, of the so‐called "polymer" which has been isolated by several investigators in the form of a transparent film upon dissolution of gold deposits in aqua regia. Micrographs of gold films plated in room temperature baths containing no hardening agents revealed the presence of much larger nonmetallic objects (up to 150Å), which appeared to be gas bubbles, in addition to the features attributable to polymer molecules. Based on a comparison of the polymer content, estimated from the analysis of electron micrographs, with the total carbon content, it is suggested that the polymer is not the only source of carbon contamination in electroplated hard gold films. Possible effects of the codeposition of polymer on grain size are also briefly discussed.