Correlative Approach for Atom Probe Sample Preparation of Interfaces Using Plasma Focused Ion Beam Without Lift-Out

Fabrication of Specimens for Atom Probe Tomography Using a Combined Gallium and Neon Focused Ion Beam Milling Approach

We demonstrate a new focused ion beam sample preparation method for atom probe tomography. The key aspect of the new method is that we use a neon ion beam for the final tip-shaping after conventional annulus milling using gallium ions. This dual-ion approach combines the benefits of the faster milling capability of the higher current gallium ion beam with the chemically inert and higher precision milling capability of the noble gas neon ion beam. Using a titanium-aluminum alloy and a layered aluminum/aluminum-oxide tunnel junction sample as test cases, we show that atom probe tips prepared using the combined gallium and neon ion approach are free from the gallium contamination that typically frustrates composition analysis of these materials due to implantation, diffusion, and embrittlement effects. We propose that by using a focused ion beam from a noble gas species, such as the neon ions demonstrated here, atom probe tomography can be more reliably performed on a larger range of materials than is currently possible using conventional techniques.

Efficient preparation of microtip arrays for atom probe tomography using fs-laser processing

Microtip arrays, also called microtip coupons, are routinely used in atom probe tomography (APT) as specimen carriers. They are commercially available consumables, usually made of Si with high electrical conductivity, produced via dedicated shaping techniques. Their purpose is to act as a specimen mount after focused ion beam (FIB) based lift-out procedures. Within this work, an alternative approach to prefabricated microtip coupons is presented, by directly creating a microtip array on the sample to be investigated utilizing fs-laser processing. An exemplary array of microtip posts was fs-laser processed from a TiN coating on Si substrate and subjected to final preparation via annular FIB milling. Subsequently, APT specimen of the TiN coating as well as of the Si substrate were successfully measured in laser assisted mode, using a commercial local electrode APT system. To further emphasize the versatility of the proposed approach, additional voltage measurements of highly conductive B doped Si arrays as well as exemplarily fs-laser processed microtip arrays of various other materials are provided as supplementary material to this article. The presented methodology bypasses the lift-out and avoids the necessity of a Pt weld between specimens and coupon posts which is frequently considered to represent a weak spot. It reduces consumables consumption and provides a high number of specimens in short time, while it is applicable for a wide range of materials and has thus the potential to revolutionize APT specimen preparation.

Anisotropic wet-chemical etching for preparation of freestanding films on Si substrates for atom probe tomography: A simple yet effective approach

A major drawback of atom probe tomography (APT) experiments of complex samples is the demanding and rather time consuming specimen preparation via the lift-out process. It usually requires a skilled operator for focused ion beam (FIB) preparation, and frequently overbooked FIB workstations represent a major bottleneck in sample throughput. Within this work, the authors present an alternative approach for APT specimen preparation of functional films and coatings on Si substrates via anisotropic wet-chemical etching. Utilizing this simple, yet effective approach, a freestanding section of the film to be investigated can be fabricated in a few steps. After the etching procedure, freestanding film posts and subsequently APT specimen can be easily prepared by basic FIB milling operations without the need for a lift-out process. Hence, this approach reduces FIB efforts to a minimum in terms of complexity and required machine utilization.