Hardware and Techniques for Cross- Correlative TEM and Atom Probe Analysis

Abstract

IntroductionAtom probe tomography has primarily been used for atomic scale characterization of high electrical conductivity materials [1]. A high electrical field applied to needle-shaped specimens evaporates surface atoms, and a time of flight measurement determines each atom's identity. A 2-dimensional detector determines each atom's original position on the specimen. When repeated successively over many surface monolayers, the original specimen can be reconstructed into a 3-dimensional representation. In order to have an accurate 3-D reconstruction of the original, the field required for atomic evaporation must be known a-priori. For many metallic materials, this evaporation field is well characterized, and 3-D reconstructions can be achieved with reasonable accuracy.Compared with conventional atom probes, the use of a local electrode has been shown to increase the sustainable evaporation rate and field of view [2]. The localized electric field produced by the local electrode enables arrays of specimens to be analyzed, as opposed to a single, electropolished wire needle. Specimen arrays increase throughput by minimizing exchange to UHV and cryogenic temperatures, as well as increasing material statistics through analysis of many specimens. In order to take advantage of these specimen arrays, preparation techniques utilizing in-situ FIB liftout techniques were developed [3]. These techniques allow routine preparation of nominally 100nm diameter specimens. The FIB also enables much improved control of the specimen diameter so the atom probe experiments can be tuned accordingly.The maturation of local electrode and laser pulsed atom probe hardware, as well as FIB specimen preparation techniques, have enabled atom probe analysis of non-traditional materials such as semiconductors, ceramics, and some organic materials to become more commonplace [4]. For most of these materials, the evaporation field is not well characterized. For example, oxides and III-V materials tend to evaporate in clusters of atoms, rather than individual atoms [5]. The physics of cluster evaporation in atom probe experiments are not well understood, and the evaporation field required is also not well characterized. In order to increase the accuracy of the 3-D reconstructions in non-traditional materials, the evaporation field and its progression during an atom probe experiment should be calculated using the specimen geometric features, such as tip radius and shank angle.While a combination FIB and SEM can give some information about atom probe specimen structure, higher resolution characterization of specimens using TEM and STEM can further increase reconstruction accuracy. TEM can image not only the specimen radius and shank angle with higher precision, but also can give the internal structure of interfaces and precipitates. Diffraction and high resolution imaging can give information about the orientation of crystallographic axes with respect to the specimen, and thus allow accurate scaling of the reconstruction in the z-direction. Analyti...

Correlative Microscopy—Novel Methods and Their Applications to Explore 3D Chemistry and Structure of Nanoscale Lattice Defects: A Case Study in Superalloys

“…As recently reviewed by Herbig,8 full electron microscopy characterization of specific features can be carried out on needle-shaped specimens prior to APT analysis by utilizing specially designed holders. This approach has, for example, led to a better understanding of diffusional mechanisms resulting in local solute segregation at crystalline imperfections [9][10][11][12][13][14] that critically impact the macroscopic material behavior. APT had previously revealed details of the composition of structural imperfections, 15 the presence of which were confirmed by field ion microscopy 16 or TEM.…”

Nanoscale Compositional Analysis of a Thermally Processed Entropy-Stabilized Oxide via Correlative TEM and APT

“…However, study of the multi-phase material that results from controlled cooling of the single phase material can provide insight into the destabilization mechanisms and methods of manipulating the microstructure. The correlated use of transmission electron microscopy (TEM) and atom probe tomography (APT) is well-suited for such analyses [3,4].Here, the previously presented Mg0.2Ni0.2Co0.2Cu0.2Zn0.2O (E1) sample [1] is explored after air quenching from 1000 °C to room temperature and after slow cooling in a furnace at 2 °C/min to room temperature. APT specimens were prepared from the bulk samples using a modified focused ion beam (FIB) lift-out technique [5] where specimens were mounted on TEM grids in holders compatible with the FIB, TEM, and APT instruments [3].…”

“…The correlated use of transmission electron microscopy (TEM) and atom probe tomography (APT) is well-suited for such analyses [3,4].…”

“…APT specimens were prepared from the bulk samples using a modified focused ion beam (FIB) lift-out technique [5] where specimens were mounted on TEM grids in holders compatible with the FIB, TEM, and APT instruments [3]. This allowed for TEM imaging of the specimens both before and after APT analysis as shown in Figure 1.…”

Mediation of Electrostatic Discharge Induced Morphological Damage in Atomically Precise Tips

“…In order to fully characterize the tip geometry, hardware was developed that allows for cross sectional tomographic imaging of W wire shaped tips in a modern TEM or STEM, along with FIM, Atom Probe Tomography, and imaging in a UHV STM [4]. During characterization of the tip geometries using SEM, TEM, FIM, and atom probe, it was found that the tip radius was several orders of magnitude larger than expected (Fig 1).…”