Feasibility of a New Atom Probe Specimen Preparation Method Using a Focused Ion Beam

Abstract

Specimens for three-dimensional atom probe (3DAP) analysis must be needle-shaped and the apex of specimen is primarily fabricated by focused ion beam (FIB). In the specimen preparation by FIB, the gallium ions are generally implanted into the surface region of the specimen during the irradiations of the ions. Therefore, the surface structure of the specimen is disarranged and amorphous. This phenomenon makes it difficult to reconstruct a three-dimensional image of the specimen. The implantation is caused by irradiating the apex of the specimen with FIB. In this study, we propose a new specimen preparation method in which FIB is irradiated from behind the needle specimen due to avoids the implantation of gallium ions. The assembly in this method was installed in the FIB instrument. The specimens were fabricated by means of the conventional and proposed methods and analyzed by atom probe in our laboratory. It was shown that not only the gallium implantation but also the rupture of specimen were inhibited by the proposed method.

A New Specimen Preparation Method for Three-Dimensional Atom Probe

“…The gallium ion concentration at the surface area for the specimen C was close to or less than the detection limits of our instrument, and it was confirmed strictly that the gallium implantation was suppressed by our new method as it had been shown in our previous study (The ratios of gallium ions to all detected ions in our previous study were 6% and 1%) [4] V. CONCLUSION The multi-sided pyramidal specimen was fabricated by using the stepping motor. The gallium atom density distribution against the cumulated number of detected ions from surface to interior of the specimen was determined from the specimen fabricated by the conventional annular milling method.…”

“…The electropolished specimen was fixed on the stepping motor with the homemade jig after the positions of the specimen, the jig and the motor were adjusted so that the rotation wobble of the specimen apex was reduced to <100 µm [4]. The specimen fixed on the motor was set to FIB stage holder parallel to the holder surface.…”

“…The specimen was set parallel to the beam axis of FIB and FIB was irradiated in a circular pattern from the direction of the specimen apex. The specimen C was fabricated by a present method [4]. The specimen was set parallel to the stage holder surface, the stage holder was tilted to 45…”

“…Then this gallium implantation has a great effect on reconstructing an atomic scale image of the specimen. To avoid this gallium implantation, we proposed a new specimen preparation method in which the materials were pared off from oblique back by FIB [4]. It was suggested that there was a possibility of reducing the gallium implantation in the analyzable regions by using the present method.…”

“…However, the gallium implantation level was not evaluated with sufficient statistical accuracy, because the analyzed volume or the counts of detected ions were too small. In addition, the specimens were analyzed with only voltage-pulsed 3DAP in our laboratory which had relatively low mass resolution, then gallium isotopes cannot be resolved [4].…”