Three-Dimensional Atom Probe Tomography of Oxide, Anion, and Alkanethiolate Coatings on Gold

Abstract

We have used three-dimensional atom probe tomography to analyze several nanometer-thick and monomolecular films on gold surfaces. High-purity gold wire was etched by electropolishing to create a sharp tip suitable for field evaporation with a radius of curvature of <100 nm. The near-surface region of a freshly etched gold tip was examined with the atom probe at subnanometer spatial resolution and with atom-level composition accuracy. A thin contaminant layer, primarily consisting of water and atmospheric gases, was observed on a fresh tip. This sample exhibited crystalline lattice spacings consistent with the interlayer spacing of {200} lattice planes of bulk gold. A thin oxide layer was created on the gold surface via plasma oxidation, and the thickness and composition of this layer was measured. Clear evidence of a nanometer-thick oxide layer was seen coating the gold tip, and the atomic composition of the oxide layer was consistent with the expected stoichiometry for gold oxide. Monomolecular anions layers of Br− and I− were created via adsorption from aqueous solutions onto the gold. Atom probe data verified the presence of the monomolecular anion layers on the gold surface, with ion density values consistent with literature values. A hexanethiolate monolayer was coated onto the gold tip, and atom probe analysis revealed a thin film whose ion fragments were consistent with the molecular composition of the monolayer and a surface coverage similar to that expected from literature. Details of the various coating compositions and structures are presented, along with discussion of the reconstruction issues associated with properly analyzing these thin-film systems.

A New Approach to Understand the Adsorption of Thiophene on Different Surfaces: An Atom Probe Investigation of Self-Assembled Monolayers

“…Our goal is to use APT to determine surface coverage, desorption energy, and dissociation properties. There have been only a small number of previous studies in which APT has been used to analyze SAMs. − Unlike previous work, which was conducted on other systems or using different experimental conditions, here we have used the voltage pulsing mode for better control over the evaporation sequence and detected fragments, and, crucially, to avoid possible effects caused by the laser illumination on the specimen’s structure or its field evaporation behavior . This is the first time the field evaporation behavior of thiophene has been compared for different substrate types.…”

Atom Probe Tomographic Mapping Directly Reveals the Atomic Distribution of Phosphorus in Resin Embedded Ferritin

“…From this information, a unique 3-dimensional reconstruction can be formed revealing the atomic scale composition along with impurity distributions up to a part-per-million sensitivity and subnanometer spatial resolution 6 7 . APT continues to make major contributions in the materials science of structural 8 9 and electronic materials 8 10 , and recently has been demonstrated in geological 11 , bio-mineralogical 12 13 14 , soft organic 15 16 17 and bio-organic 4 18 19 materials. However the regular application of APT to soft biological materials is lacking in large part due to difficulties in specimen preparation.…”

Organic Materials and Organic/Inorganic Heterostructures in Atom Probe Tomography

“…Laser pulsing heats the specimen tip surface, lowering the required electric field for field evaporation and, consequently, reducing premature specimen failure from stresses generated by the electric field. We discuss here the rapidly improving analysis capabilities for self-assembled monolayers [11][12][13], polymers [14][15][16], and the complex architecture of a tooth biomineral nanocomposite [17].…”