Christopher S. Own

Precession electron diffraction 1: multislice simulation.

Precession electron diffraction (PED) is a method that considerably reduces dynamical effects in electron diffraction data, potentially enabling more straightforward solution of structures using the transmission electron microscope. This study focuses upon the characterization of PED data in an effort to improve the understanding of how experimental parameters affect it in order to predict favorable conditions. A method for generating simulated PED data by the multislice method is presented and tested. Data simulated for a wide range of experimental parameters are analyzed and compared to experimental data for the (Ga,In)(2)SnO(4) (GITO) and ZSM-5 zeolite (MFI) systems. Intensity deviations between normalized simulated and kinematical data sets, which are bipolar for dynamical diffraction data, become unipolar for PED data. Three-dimensional difference plots between PED and kinematical data sets show that PED data are most kinematical for small thicknesses, and as thickness increases deviations are minimized by increasing the precession cone semi-angle phi. Lorentz geometry and multibeam dynamical effects explain why the largest deviations cluster about the transmitted beam, and one-dimensional diffraction is pointed out as a strong mechanism for deviation along systematic rows. R factors for the experimental data sets are calculated, demonstrating that PED data are less sensitive to thickness variation. This error metric was also used to determine the experimental specimen thickness. R(1) (unrefined) was found to be about 12 and 15% for GITO and MFI, respectively.

Quantitative analyses of precession diffraction data for a large cell oxide.

Kinematical and two-beam calculations have been conducted and are compared to experimental precession data for the large unit cell crystal La4Cu3MoO12. Precession electron diffraction intensities are found to exhibit approximate two-beam behavior and demonstrate clear advantages over conventional SADP intensities for use in structure solution.

Electron precession: A guide for implementation

The design approach for electron precession systems designed at Northwestern University is described, and examples of systems retrofitted onto two different transmission electron microscopes using this method are demonstrated. The precession diffraction patterns from these instruments are of good quality while simultaneously being very easy to acquire. A 15-minute procedure for aligning these instruments is described in the appendix. Partnering this user-friendly and inexpensive hardware implementation with fast and user-friendly crystallography software offers potentially speedy and routine solution of crystal structures.

Aberration-corrected Precession Electron Diffraction

Precession electron diffraction (PED) is a promising technique for collecting high quality diffraction patterns for rapid nanoscale structural characterization [1]. It is able to reduce dynamical scattering effects, improving the interpretability of diffraction intensities over those obtained by conventional electron diffraction techniques. When used on a microscope that can produce a fine probe, the method simplifies symmetry identification and enables more straightforward phase recovery (using statistical inversion techniques) for small phases on the order of tens of nanometers. Several studies have reported remarkable improvements to dataset quality: R-factors of just above 10% have been reported for fairly thick metal oxide phases solved using PED data, as compared to 20%-40% typical for conventional selected area patterns (for reference, typical synchrotron X-ray R-factors are under 10%) [2-6].

Cone‐angle Dependence of Ab‐initio Structure Solutions Using Precession Electron Diffraction

Precession electron diffraction (PED) is a technique which is gaining increasing interest due to its ease of use and reduction of the dynamical scattering problem in electron diffraction, leading to more direct structure solutions. We have performed a systematic study of the effect of precession angle for the mineral andalusite on kinematical extinctions and direct methods solutions where the semiangle was varied from 6.5 to 32 mrad in five discrete steps. We show that the intensities of kinematically forbidden reflections decay exponentially as the precession semiangle (φ) is increased and that the amount of information provided by direct methods increases monotonically but non‐systematically as φ increases. We have also investigated the zeolite‐framework mineral mordenite with PED and have found a direct methods solution where the 12‐ring is clearly resolved for the first time.

STEM Aberration Correction: an Integrated Approach

Progress in aberration correction of electron microscopes has been rapid in the last decade. CEOS and Nion, the two companies chiefly responsible for the advent of practical aberration correctors, were started 12 and 11 years ago, respectively, at a time when aberration correction still seemed an impractical dream to many electron microscopists. The first sub-A resolution, directly interpretable aberration-corrected images were published in 2002 [1]. Today, there are more than 100 aberration-corrected electron microscopes in the world, and several more are installed each month. The resolution attained has reached 50 pm (0.5 A) in both STEM and TEM, and the electron current in an atom-sized electron probe can now be such that atomic-resolution STEM/EELS elemental maps can be acquired in less than one minute [2].

Portable Electron Microscopy and Microanalysis in Extreme Environments

Electron microscopy (EM) is a highly attractive tool for many applications due to its unique blend of strong optical scattering, high native resolution, large depth of focus, and variety of signals including characteristic Xray emission, enabling high-magnification structural imaging and chemical analysis. Despite high optical performance and versatility supporting a wide variety of industries from basic science research to industrial process monitoring, EM has through its ~100-year history been widely regarded as a high-end tool with limited reach outside the laboratory, in particular due to inherent complexity and need for vacuum. Making EM accessible outside constrained laboratory environments will bring EM’s performance and versatility to a much broader range of scientific and engineering endeavors.

Developments in Reel-to-Reel Electron Microscopy Infrastructure

An increasing need for structural imaging at small length scales and simultaneous demand for data from larger volumes in research and commercial applications such as gene sequencing, neuroanatomy, and industrial process monitoring has encouraged new developments in electron microscopy (EM) technology, in particular high throughput tools. We previously reported on construction of a new serial sample imaging tool called the GridStageTM produced by us at Voxa, which enables direct imaging of serial sequential samples loaded onto tape via transmission electron microscopy (TEM), with capacity exceeding 10,000 samples per tape reel [1]. We have used tape delivery in ssDNA sequencing by EM and more recently in 3D serial section reconstruction of tissue, providing neuroanatomy at resolution and detail orders of magnitude greater than ever before. GridStage and its smaller sibling SpriteTM, a simple cartridge-based sample imaging platform able to load and image sixteen 3 mm disc samples at a time (see Fig. 1), are deployed and currently in use at Allen Institute for Brain Sciences. These novel stages are installed onto arrayed JEOL 1200 EX microscopes configured to obtain large montage datasets >1 petabyte in size at speeds exceeding 100 MPixels/s per tool. Others have developed parallel imaging systems based on scanning electron microscopy (SEM) for a similar application [2]. Reel-to-reel (R2R) imaging has the advantages of rapid automated sequential imaging of samples, random access by virtue of sample indexing, and easy storage at air in desiccant chambers or in vacuum chambers ready for future re-imaging. New powerful imaging capabilities necessitate new methods for sample preparation, which has traditionally been a complex and demanding aspect of high-resolution biological tissue imaging. As development of serial sectioning tools for SEM and TEM [3] opened the path to novel high-throughput serial imaging, experience with serial imaging indicates new types of serial sample post-processing steps that can enhance image acquisition pipeline throughput. We report here on new industrial automation tools we have produced supporting high-throughput continuous automated R2R imaging. Sample throughput in serial section imaging of cortical tissue is limited in part by the quality of tissue staining protocols. A popular manual protocol for contrast enhancement of structures for EM is double-staining using uranyl acetate in tissue block form followed by post-staining after sectioning with lead citrate. Lead citrate enhances contrast by binding primarily with proteins and glycogens. However, it also forms a water-insoluble toxic lead carbonate white precipitate if exposed to CO2. This necessitates a controlled environment to prevent unwanted high-Z precipitates that can cause staining artifacts as well as absorb beam energy and catalyze catastrophic damage in suspended tissue sections imaged under high beam currents. While commercial systems are available for applying liquid processes on multiple TEM grids simultaneously using a CO2-free flow cell or novel TEM carrier systems connected to pipettors [4-5], these do not scale to more than about 50 separate samples per batch; high-throughput R2R based processes require efficiently staining >1000 samples at a time. We have constructed a new R2R fluid staining system called StriderTM that is equipped to precisely apply stains directly to serial tissue samples mounted on continuous tape (Fig. 2). Strider has room for six customizable computer-controlled modular fluid stations, each capable of applying and draining a fluid without damaging thin supported membranes (Fig. 3). Strider incorporates an environment chamber fillable with purge gas, which when used in conjunction with a solid CO2 getter material such as NaOH prevents carbonate precipitation. Strider’s process rate is similar to that of tissue sectioning machines, thereby lending it to imaging pipeline use for either TEM or SEM tape-based serial 32 doi:10.1017/S1431927617000848 Microsc. Microanal. 23 (Suppl 1), 2017

Democratizing the micro-scale: A simplified, miniaturized SEM for K-12 and informal student scientists

Learners in K-12 schools and informal learning environments have historically had significantly less access to critical technologies than practicing scientists. They can observe pollen grains in basic light microscopes while studying plants, but cannot observe the surface structures that affect the pollens’ dispersal. They can learn about structure-function relationships in insect anatomy, but not observe mechanosensory bristles on the eye of a fly they caught in their own classroom or learning space, nor the nanostructures enabling moths to hang upside-down on the ceiling. While today’s student scientists have access to a great wealth of microand nano-scale images via the internet, they have so far been unable to take those images themselves. For K-12 student scientists and informal learners, direct observation of a great range of scientific phenomena has been impossible.

Field-Portable Nano-Imaging: A New Tool for On-Demand Microscopy

Electron microscopy is widely regarded as a high-end laboratory science tool, where substantial resources are pooled to collect image data of exquisite quality. Electron microscopes (EM’s) are uniquely able to produce detailed structural images that support discoveries from basic science to monitoring of industrial process. The strong scattering, large depth of focus, and unique blend of signals including elemental analysis are attractive in many applications. Being difficult to operate relative to many other common laboratory tools, EM’s are traditionally housed in centers at universities and large research institutions where ample laboratory space, support staff, supplies, and skilled operators come together, or at industrial sites for organizations with research or quality control needs that justify the substantial cost. For those who do not have access to an on-site EM, many larger institutions and service centers accept samples sent in to be imaged, at great expense and often delay of weeks to months for complex analyses. The complexity, high cost, and significant maintenance associated with collecting EM image data has until now severely limited the fields in which EM can be realistically used [1]. This is exemplified in the number of EM instruments deployed (in the tens of thousands) to the number of deployed light microscopes (in the hundreds of millions) [2].