16 ADVANCED MATERIALS & PROCESSES | JANUARY/FEBRUARY 2024 required, the simulations are currently prepared ahead of time and stored in a database accessible from the Holo- Microscope application. The simulations are accessed via the wireless network connection from the HoloLens 2. This allows the simulation database to archive a significant number of results that can be referenced without overwhelming the onboard storage of the HoloLens 2. Figure 2 demonstrates the workflow of the HoloMicroscope: (1) elements are selected in a periodic table of elements, (2) candidate crystal structures that contain these elements are chosen from materials in the NHI database, (3) the specific zone axes and image types are chosen by the user, and (4) previously simulated images are displayed on a holographic board. The next generation HoloMicroscope application will enable users to select elements in a periodic table, but the candidate crystal structures will be pulled from the Materials Project API, abTEM simulations will be completed on the fly, and then users can choose which images to view. Other techniques can also be simulated and included, such as energy dispersive spectro- scopy (EDS) or electron energy loss spectroscopy (EELS). Ni-W ALLOY CASE STUDY To illustrate the HoloMicroscope application’s usefulness, let’s compare the traditional process in a case study on the Ni-W alloy system. While studying electro- deposited Ni-W, one of the authors (CJM) obtained the high-resolution STEM images in Fig. 3 from three different zone axes of an unknown phase in a Ni-W alloy. After a lengthy and time-consuming manual identification process, including multiple TEM data collection sessions, diffraction pattern analysis, and EDS analysis, the unknown phase was eventually identified as the eta-carbide Ni6W6C[6]. In this case, carbon was an impurity element, which was A common situation that arises during TEM analysis is the need to identify unexpected crystalline phases during development of new alloys and compounds. These unknown phases may result from novel alloy compositions, unusual heat treatments, or “unintended impurities.” This situation was the inspiration for the HoloMicroscope application as its creators longed for a tool to help identify unknown phases in structural materials while conducting TEM analysis. The process of accurately identifying unidentified phases is quite extensive and typically involves multiple TEM sessions interspersed with manual post-session analysis of data gathered during the TEM sessions. The data may include low- and high-resolution images, diffraction patterns, and energy dispersive x-ray (EDX) spectra. In addition to manual analysis, the microscopist may run computer simulations based on known crystalline phases to help identify the unknown phases. However, not all microscopists are comfortable running such simulations, and those who are comfortable sometimes lack the programming expertise necessary to quickly reach their goal. All in all, the traditional process of identifying unknown phases is time-consuming and can significantly delay research progress. The focus of the current HoloMicroscope application is to provide a set of rapid and interactive holograms for identifying unknown crystalline phases. The user interface consists of several interactive holographic buttons and selection menus that allow the user to efficiently view/ complete simulations that are relevant to the material under study. The foundation of this capability is a database of computer simulations of high- resolution scanning transmission electron microscope (STEM) images and electron diffraction patterns. The simulations are produced using the abTEM simulation package[3], the PRISM algorithm[4], and crystal data from the Materials Project[5]. These simulations include high-angle annular dark field, low-angle annular dark field, and bright field micrographs of selected crystal structures on low-index zone axes. Given the computational run time Fig. 2 — A process for identifying Ni6W6C using the HoloMicroscope: (1) The user selects elements of interest; (2) the user is presented with a list of materials containing those elements; (3) the user selects the viewing mode, i.e., the type of simulations to view; (4) the user examines the simulations and discovers a simulated HAADF-STEM image of interest.
RkJQdWJsaXNoZXIy MTYyMzk3NQ==