Three dimensional atom probe tomography (3DAPT) is a unique tool in the arsenal of nanoscale characterization methods.1, 2 It can uniquely provide information about both the structure and composition of materials at near atomic-scale resolution. Although generally used for the characterization of three-dimensional metal and metal alloy phases, recent developments now allow atom probe tomography to be applied to soft materials and interfacial films. The work presented here focuses on the application of 3DAPT to electrochemical interfaces, in particular those formed via adsorption of simple ions on microelectrode surfaces and by electrodeposition of thin polymer layers and nanoparticule-encapsulated films.
The 3DAPT functions by pulse-mode field evaporation of a sample and projection of the resulting evaporated ions or molecular fragments into a position sensitive time of flight mass spectrometer. The location and identity of the projected fragments can then be resolved and reconstructed into a three-dimensional image of the sample at nanometer-scale or better resolution.
In this talk, I will describe several examples of the application of 3DAPT to electrochemical interfaces. Samples typically are in the form of nanometer sized microelectrode tips, which have been constructed by electropolishing of pure metal wires. Analysis of electrodeposited coatings can then be achieved following deposition of thin layers onto the end of the electrode tip.
We have exploited the 3DAPT to characterize several thin electrode interfaces. Monolayer coatings of adsorbed ions, such as iodide, chloride or bromide anions, have been imaged on gold electrode surfaces. Various electrodeposited polymers, including poly(aniline) and poly(phenylene oxide), have been analyzed as thin films on palladium surfaces. The 3DAPT provides information about the chemical composition of the polymer films through the mass of the evaporated fragments and information about the structure of the polymer layer as well as details about the polymer-metal interface can be resolved. Complex coatings that consist of metal nanoparticles encapsulated within electrodeposited polymer films have also been imaged.