Study on Quantitative Analysis of Carbon and Nitrogen in Stoichiometric θ-Fe3C and γ′-Fe4N by Atom Probe Tomography

The quantitative analysis performance of carbon and nitrogen was investigated using stoichiometric θ-Fe3C (25 at% C) and γ′-Fe4N (~20 at% N) precipitates in pulsed voltage and pulsed laser atom probes. The dependencies of specimen temperature, pulse fraction, and laser pulse energy on the apparent concentrations of carbon and nitrogen were measured. Good coincidence with 25 at% carbon concentration in θ-Fe3C was obtained for the pulsed voltage atom probe by considering the mean number of carbon atoms per ion at 24 Da and the detection loss of iron, while better coincidence was obtained for the pulsed laser atom probe by considering only the mean number of carbon at 24 Da. On the other hand, a lack of nitrogen concentration in γ′-Fe4N was observed for the two atom probes. In particular, the pulsed laser atom probe showed a significant lack of nitrogen concentration. This implies that a large amount of 14N2+ was obscured by the main iron peak of 56Fe2+ at 28 Da in the mass-to-charge spectrum. Regarding preferential evaporation or retention, carbon in θ-Fe3C exhibited little of either, but nitrogen in γ′-Fe4N exhibited definite preferential retention. This result can be explained by the large difference in ionization energy between carbon and nitrogen.

On the Field Evaporation Behavior of Dielectric Materials in Three-Dimensional Atom Probe: A Numeric Simulation

As a major improvement in three-dimensional (3D) atom probe, the range of applicable material classes has recently been broadened by the establishment of laser-assisted atom probes (LA-3DAP). Meanwhile, measurements of materials of low conductivity, such as dielectrics, ceramics, and semiconductors, have widely been demonstrated. However, besides different evaporation probabilities, heterogeneous dielectric properties are expected to give rise to additional artifacts in the 3D volume reconstruction on which the method is based. In this article, these conceivable artifacts are discussed based on a numeric simulation of the field evaporation. Sample tips of layer- or precipitate-type geometry are considered. It is demonstrated that dielectric materials tend to behave similarly to metals of reduced critical evaporation field.

PREDICTION OF THE DELAMINATION IN THE PEARLITIC STEEL FILAMENTS BY 3 DIMENAIONAL ATOM PROBE TOMOGRAPHY

We have tried to find out the critical factor governing the delamination in the pearlitic steel filaments. Steel filaments were fabricated depending on the carbon content from 0.72 to 1.02 wt.%. The delamination was identified by a torsion tester specially designed for thin-sized wires and scanning electron microscopy. The results showed that as the carbon content increased, the number of twists to fracture decreased, and the delamination only occurred in the filament with 1.02 wt .% C . In order to elucidate this behavior, the microstructure of the filaments was observed using advanced analysis techniques such as 3 dimensional atom probes tomography (3-DAPT).

First Data from a Commercial Local Electrode Atom Probe (LEAP)

The first dedicated local electrode atom probes (LEAP [a trademark of Imago Scientific Instruments Corporation]) have been built and tested as commercial prototypes. Several key performance parameters have been markedly improved relative to conventional three-dimensional atom probe (3DAP) designs. The Imago LEAP can operate at a sustained data collection rate of 1 million atoms/minute. This is some 600 times faster than the next fastest atom probe and large images can be collected in less than 1 h that otherwise would take many days. The field of view of the Imago LEAP is about 40 times larger than conventional 3DAPs. This makes it possible to analyze regions that are about 100 nm diameter by 100 nm deep containing on the order of 50 to 100 million atoms with this instrument. Several example applications that illustrate the advantages of the LEAP for materials analysis are presented.

Atom Probes Leap Ahead

Since early times, the collective understanding of our microscopic universe has been directly tied to the quality of our microscopies. This has been true from the advent of light microscopes through to modern electron microscopes. Indeed, if one is to work on a given scale, one must be able to “see” at that scale. At the beginning of the 21st century, human inquiry is focused on the atomic scale.