Three-dimensional atom probe (3DAP) has been developed in our laboratory. In our instrument, the position-sensitive detector with a diameter of 120 mm following a pair of microchannel plates (MCP) was set up at a distance of 110 mm in front of the apex of the sample. Our original preset-type sample stage with a local microelectrode was adopted. The pulse laser, or voltage pulse, was used as a trigger for field evaporation. The pulse width of the laser was 180 fs at a wavelength of 1030 nm. The pulse width of the voltage pulse was less than 10 ns. The performance of our instrument was widely tested with the pure tungsten samples fabricated by the electropolishing and focused ion beam methods. The flight path compensation of detected ions, including the small inclination of MCP assembly, led to the good mass resolution approximately 220 (FWHM). By this compensation, we realized full 0.75 sr acceptable angle 3DAP. The detection efficiency of emitted ions was estimated to be about 50% from the three-dimensional reconstruction images of samples.

A wide-angle laser-assisted three-dimensional atom probe (3DAP) was developed, with a wide angle (0.75 sr) and short flight distance (110 mm) adopted to enlarge the analysis area of the tip. However, the short flight distance of ions resulted in the degradation of mass resolution. Therefore, flight path compensation was examined to improve the mass resolution in the 3DAP with a flight distance of 110 mm. With geometric compensation based on a simple concentric sphere model, the detected ions could be identified. By the compensation of the flight path for a small inclination on the microchannel plate (MCP) in the direction normal to the tip axis, the isotopes of detected ions were identified and high mass resolution was attained for a very short flight distance.

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.

Recently, laser pulses on a three-dimensional atom probe have been used to induce field evaporation. The advantages of laser-pulse atom probes are application to higher resistivity materials such as semiconductors and high mass resolution. Early studies of laser-pulse atom probes were performed with laser pulses of nanosecond duration. All evidence from these early studies and most recent studies using sub-picosecond laser pulses have indicated that the field evaporation of atoms by laser pulses occurred by a thermal pulsing mechanism. On the other hand, some recent experiments with sub-picosecond laser pulses have resulted in the proposal of athermal mechanisms (e.g., optical rectification) of field evaporation. Thus, the mechanism of field evaporation at the apex of a needle specimen by sub-picosecond laser pulses has not yet been established. We report the dependence of field evaporation voltage on the polarization angle of femtosecond laser pulses for metal specimens.

In our previous study, we introduced a new specimen preparation method for the three-dimensional atom probe in which the materials were pared off from oblique back by Ga-FIB. It was suggested that there was a possibility of reducing the gallium implantation in the analyzable regions by using the method. In this study, the gallium implantation level of the method was evaluated with better statistical accuracy by extending the analyzed volume and improving the mass resolution. The specimens were fabricated by means of the conventional and our new methods, and analyzed by atom probe with voltage or laser pulses. The mass spectra with the larger analyzed volume or counts of detected ions and the higher mass resolution than those of our previous study were obtained. Then, the ratio of gallium ions to all detected ions was calculated with better statistical accuracy and it was confirmed that the gallium ion concentration at the surface area was reduced close to or less than the detection limits of our instrument by our new method.