py4DSTEM: a software package for multimodal analysis of four-dimensional scanning transmission electron microscopy datasets

Scanning transmission electron microscopy (STEM) allows for imaging, diffraction, and spectroscopy of materials on length scales ranging from microns to atoms. By using a high-speed, direct electron detector, it is now possible to record a full 2D image of the diffracted electron beam at each probe position, typically a 2D grid of probe positions. These 4D-STEM datasets are rich in information, including signatures of the local structure, orientation, deformation, electromagnetic fields and other sample-dependent properties. However, extracting this information requires complex analysis pipelines, from data wrangling to calibration to analysis to visualization, all while maintaining robustness against imaging distortions and artifacts. In this paper, we present py4DSTEM, an analysis toolkit for measuring material properties from 4D-STEM datasets, written in the Python language and released with an open source license. We describe the algorithmic steps for dataset calibration and various 4D-STEM property measurements in detail, and present results from several experimental datasets. We have also implemented a simple and universal file format appropriate for electron microscopy data in py4DSTEM, which uses the open source HDF5 standard. We hope this tool will benefit the research community, helps to move the developing standards for data and computational methods in electron microscopy, and invite the community to contribute to this ongoing, fully open-source project

In-situ TEM Lithiation of Alternative Battery Electrode Materials

The world-wide effort to produce and use cleaner energy also necessitates more advanced energy storage capabilities. For example, clean sources of electricity, such as wind or solar, are intermittent and require load leveling. Electric vehicles require more energy- and power-dense batteries in order to truly compete with fossil-fuel-based combustion engines. Lithium-ion batteries (LIBs) currently dominate the secondary battery market. However, in order to build a better LIB, there is a clear need for a better understanding of the fundamentals of lithiation processes. Transmission electron microscopy (TEM) is unique in its ability to correlate structural data with chemical information; as such, in-situ TEM techniques can provide vital, fundamental data on alternative electrode materials that will support the development of advanced batteries. In general, lithium storage in a host material may be accomplished by one of two mechanisms. The first is intercalation of layered materials, which is minimally disruptive to the host structure at the cost of Li storage capacity. The second is alloying, which in many cases allows the uptake of several Li atoms per host atom, but rapid structural evolution and expansion occur during the reaction. MoS2 and Sn were the materials chosen for this work, to represent both Li storage mechanisms and to demonstrate the power of in-situ TEM experimentation for identifying atomic-scale processes that contribute to the lithiation of an electrode material. MoS2 is a layered material with a high specific capacity and excellent rate capability, while elemental Sn forms several intermetallics with Li, storing up to 4.25 Li atoms per Sn atom in its fully-lithiated phase. Solid-state half-cells were constructed inside the TEM using a holder designed to perform simultaneous scanning-tunneling microscopy (STM) and TEM. Li metal was used as the counter/reference electrode, with either MoS2 or Sn as the working electrode and solid Li2O on the surface of the Li metal acting as an electrolyte. Real-time observations of the structural evolution of the working electrode materials, as well as post mortem analysis, are presented and discussed

Laser Direct Write Synthesis of Lead Halide Perovskites

Lead halide perovskites are increasingly considered for applications beyond photovoltaics, for example, light emission and detection, where an ability to pattern and prototype microscale geometries can facilitate the incorporation of this class of materials into devices. Here we demonstrate laser direct write of lead halide perovskites, a remarkably simple procedure that takes advantage of the inverse dependence between perovskite solubility and temperature by using a laser to induce localized heating of an absorbing substrate. We demonstrate arbitrary pattern formation of crystalline CH₃NH₃PbBr₃ on a range of substrates and fabricate and characterize a microscale photodetector using this approach. This direct write methodology provides a path forward for the prototyping and production of perovskite-based devices

Coupling In Situ TEM and Ex Situ Analysis to Understand Heterogeneous Sodiation of Antimony

We employed an in situ electrochemical cell in the transmission electron microscope (TEM) together with ex situ time-of-flight, secondary-ion mass spectrometry (TOF-SIMS) depth profiling, and FIB–helium ion scanning microscope (HIM) imaging to detail the structural and compositional changes associated with Na/Na⁺ charging/discharging of 50 and 100 nm thin films of Sb. TOF-SIMS on a partially sodiated 100 nm Sb film gives a Na signal that progressively decreases toward the current collector, indicating that sodiation does not proceed uniformly. This heterogeneity will lead to local volumetric expansion gradients that would in turn serve as a major source of intrinsic stress in the microstructure. In situ TEM shows time-dependent buckling and localized separation of the sodiated films from their TiN-Ge nanowire support, which is a mechanism of stress-relaxation. Localized horizontal fracture does not occur directly at the interface, but rather at a short distance away within the bulk of the Sb. HIM images of FIB cross sections taken from sodiated half-cells, electrically disconnected, and aged at room temperature, demonstrate nonuniform film swelling and the onset of analogous through-bulk separation. TOF-SIMS highlights time-dependent segregation of Na within the structure, both to the film-current collector interface and to the film surface where a solid electrolyte interphase (SEI) exists, agreeing with the electrochemical impedance results that show time-dependent increase of the films’ charge transfer resistance. We propose that Na segregation serves as a secondary source of stress relief, which occurs over somewhat longer time scales

py4DSTEM: a software package for multimodal analysis of four-dimensional scanning transmission electron microscopy datasets

Scanning transmission electron microscopy (STEM) allows for imaging, diffraction, and spectroscopy of materials on length scales ranging from microns to atoms. By using a high-speed, direct electron detector, it is now possible to record a full 2D image of the diffracted electron beam at each probe position, typically a 2D grid of probe positions. These 4D-STEM datasets are rich in information, including signatures of the local structure, orientation, deformation, electromagnetic fields and other sample-dependent properties. However, extracting this information requires complex analysis pipelines, from data wrangling to calibration to analysis to visualization, all while maintaining robustness against imaging distortions and artifacts. In this paper, we present py4DSTEM, an analysis toolkit for measuring material properties from 4D-STEM datasets, written in the Python language and released with an open source license. We describe the algorithmic steps for dataset calibration and various 4D-STEM property measurements in detail, and present results from several experimental datasets. We have also implemented a simple and universal file format appropriate for electron microscopy data in py4DSTEM, which uses the open source HDF5 standard. We hope this tool will benefit the research community, helps to move the developing standards for data and computational methods in electron microscopy, and invite the community to contribute to this ongoing, fully open-source project