Leigh Stephenson

Characterizing solute hydrogen and hydrides in pure and alloyed titanium at the atomic scale

Abstract Ti and its alloys have a high affinity for hydrogen and are typical hydride formers. Ti-hydride are brittle phases which probably cause premature failure of Ti-alloys. Here, we used atom probe tomography and electron microscopy to investigate the hydrogen distribution in a set of specimens of commercially pure Ti, model and commercial Ti-alloys. Although likely partly introduced during specimen preparation with the focused-ion beam, we show formation of Ti-hydrides along α grain boundaries and α/β phase boundaries in commercial pure Ti and α+β binary model alloys. No hydrides are observed in the α phase in alloys with Al addition or quenched-in Mo supersaturation.

An atomic-scale view at the composition of amyloid-beta fibrils by atom probe tomography

Amyloid-beta (Aβ) proteins play an important role in a number of neurodegenerative diseases. Aβ is found in senile plaques in brains of Alzeimer’s disease patients. The 42 residues of the monomer form dimers which stack to fibrils gaining several micrometers in length. Using Aβ fibrils with 13C and 15N marker substitution, we developed an innovative approach to obtain insights to structural and chemical information of the protein. We deposited the modified protein fibrils to pre-sharped aluminium needles with >100-nm apex diameters and, using the position-sensitive mass-to-charge spectrometry technique of atom probe tomography, we acquired the chemically-resolved three dimensional information for every detected ion evaporated in small fragments from the protein. We also discuss the influence of experimental parameters such as pulse energy and pulse frequency of the used Laser beam which lead to differences in the size of the gained fragments, developing the capability of localising metal atom within Aβ plaques.

Applications, Technical Challenges, and Recent Implementation of a UHV/Cryogenic Specimen Transfer System for Atom Probe Tomography

The ability to control or prevent the change of a sample from its native state prior to analysis is a desire of nearly every microscopy technique. For a wide variety of microscopies and associated applications, changes related to exposed surfaces or the bulk temperature history have little or no effect on the goal of the analysis, e.g. characterization of stainless steel grain size. For other studies, a very carefully controlled environment (temperature, pressure, atmosphere, etc.) is critical, e.g. recording the oxidation state of an exposed lithium metal sample. For atom probe tomography (APT), sample preparation is critical as the region of interest must be placed within a needle geometry with a typical diameter of less than 200 nm at the apex. Like transmission electron microscopy, the surface-area-to-volume ratio of a typical APT sample (Figure 1) can be tens of orders of magnitude larger than a typical metallographic mount [1].