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A scanning precession electron diffraction system has been integrated with a direct electron detector to allow the collection of improved quality diffraction patterns. This has been used on a two-phase α–β titanium alloy (Timetal® 575) for phase and orientation mapping using an existing pattern-matching algorithm and has been compared to the commonly used detector system, which consisted of a high-speed video-camera imaging the small phosphor focusing screen. Noise is appreciably lower with the direct electron detector, and this is especially noticeable further from the diffraction pattern center where the real electron scattering is reduced and both diffraction spots and inelastic scattering between spots are weaker. The results for orientation mapping are a significant improvement in phase and orientation indexing reliability, especially of fine nanoscale laths of α-Ti, where the weak diffracted signal is rather lost in the noise for the optically coupled camera. This was done at a dose of ~19 e−/Å2, and there is clearly a prospect for reducing the current further while still producing indexable patterns. This opens the way for precession diffraction phase and orientation mapping of radiation-sensitive crystalline materials.

A model-based fitting algorithm for electron energy-loss spectroscopy spectra is introduced, along with an intuitive user-interface. As with Verbeeck & Van Aert, the measured spectrum, rather than the single scattering distribution, is fit over a wide range. An approximation is developed that allows for accurate modeling while maintaining linearity in the parameters that represent elemental composition. Also, a method is given for generating a model for the low-loss background that incorporates plural scattering. Operation of the user-interface is described to demonstrate the ease of use that allows even nonexpert users to quickly obtain elemental analysis results.

In recent years there has been a great upsurge of applications involving quantitative high-resolution electron microscopy, in particular comparing experimental micrographs with image simulations for determination of defect structures. Emphasis has been given to the determination of experimental parameters, the utilization of slow-scan CCD cameras for digital recording and extraction of quantitative structural and chemical information. More attention to surface cleanliness is needed to improve signal quality and the possibility of electron irradiation damage should not be overlooked. Issues related to adoption of a reliability of R -factor are briefly discussed.

The phase of an electron wave is altered by electric and magnetic fields as it passes through a specimen. This phase change can be accurately quantified from off-axis electron holograms acquired using a slow-scan CCD camera, and small changes can be observed over small dimensions. Expressions for the precision of the phase estimate, which is limited by shot noise, have been developed. These include most of the real experimental parameters. It is found that the typical precision of practical phase measurements is better than π/100 for spatial resolutions of 1–3 nm, in good agreement with the theoretical optimal phase precision. In order to attain such small errors the effects of geometric distortion, which can introduce phase differences of up to π, must be carefully corrected.

The mean inner potential of a solid is a fundamental property of the material and depends on both composition and structure. By using cleaved crystal wedges of known angle, combined with dogital recording of off-axis electron holograms and with theoretical calculations of dynamical effects, the mean inner potential of Si (9.26±0.08 V), MgO (13.01±0.08 V), GaAs (14.53±0.17 V) and PbS (17.19±0.12 V) is measured with high accuracy of about 1%. Dynamical contributions to the phase of the transmitted beam are found by Bloch wave calculations to be less than 5% when the crystal wedges are titled away from zone-axis orientations and from major Kikuchi bands. The accuracy of the present method is a factor of 3 better than previously achieved by reflection high-energy electron diffraction and electron interferometry. The major causes of uncertainty were specimen imperfections and errors in phase measurement and magnification calibration.

New ways to measure detection properties of slow‐scan charge‐coupled device (CCD) cameras suitable for electron microscopy, mainly based on the statistics of single‐electron events, are discussed. The experiments concentrate on the newly introduced Gatan 679 slow‐scan CCD camera. It has been established that for this instrument (if equipped with a thin YAG scintillator) 20% of the true intensity is recorded at the highest detectable spatial frequency (Nyquist frequency), limited mostly by the modulation transfer function of the YAG scintillator. The detection quantum efficiency is 0.45 for single 100‐kV electrons and 0.15 for single 400‐kV electrons, and is approaching unity for intensities higher than ten electrons. Furthermore, nonlinearity of the response is smaller than deviations in the image intensity due to shot noise. Examples are presented illustrating the detection properties of slow‐scan CCD cameras for electron imaging, which also include high dynamic range and negligible geometric distortion.

The modern analytical transmission electron microscope gives signals from both elastically and inellastically scattered electrons at rates up to a few magabytes per second. A flexible multiasking system is needed to effectively integrate the information from a microscope with multiple detectors while synchronously controlling selected optical parameters of the instrument. We describe a system based on a Digital Equipment LSI-11 microcomputer equipped with a frame buffer and show how it has been used to develop new experimental capabilities such as time-resolved spectroscopy and multi-spectroscopy elemental mapping.

The optics of the illuminating system of a TEM/STEM equipped with a high-brightness field emission source has been studied in order to determine the current density distributions of small electron probes used for microanalysis. The experimental distributions were measured from high-magnification TEM images of the small probes, and compared to theoretical distributions calculated using both coherent and incoherent optics. The microscope was shown to be capable of producing an electron probe with a FWHM diameter of 1.7 nm and a current of 1 nA. The size of the probe is limited by electrical and mechanical instabilities.

This letter presents results of rapid processing for X-ray absorption correction in quantitative X-ray microanalysis using an analytical electron microscope. A computer-based system developed for analytical electron microscopy is used to assist in the extrapolation method, which does not require thickness measurement but only the recording of characteristic X-rays for absorption correction.

Electron holography is necessarily a two-step process. First, the object and reference waves must be coherently superimposed in recording the electron hologram. Second, reconstruction of the hologram is required in order to extract the desired phase and/or amplitude of the electron wave which has passed through the object. Historically, hologram recording has been carried out photographically, and the subsequent reconstruction has been done optically.261,451 In addition to inevitable time delays, the use of these techniques in electron holography can result in unsuspected artefactual information, thus motivating the utilization of alternative recording and processing methods that offer greater reliability and the possibility of more accurate quantification.

In the 3-dimensional (3-D) reconstruction of protein crystals with variable thicknesses the electron images and diffraction patterns can only be merged if the crystal thickness is known. Measurement of the thickness using the ratio of the number of inelastically scattered electrons to the number of electrons in the zero loss peak can be accomplished with parallel electron energy loss spectrometry (PEELS). A theoretical analysis of the accuracy of the technique on paraffin crystals of different thicknesses is presented. Our experimental studies with paraffin crystals show the feasibility of measuring a single layer of 47 A with good accuracy under low dose and low temperature conditions. A simple experimental apparatus is proposed to obtain thicknesses from small regions of unstained protein crystals prior to collecting the 3-D data sets from the unexposed area of the same crystal.

The continuing remarkable progress of computer technology is dramatically changing how electron optical instrumentation is being used. Instead of concentrating on taking just one spectrum or one image at a time, it now has become possible to design complete experiments aimed at solving the problems at hand more rapidly and more directly.We have designed a PC-based acquisition system that aims to innovate and simplify both TEM and STEM operation. The first advance this system represents is integrated data acquisition from all detectors commonly found on electron microscopes: TV and slow-scan CCD cameras, different flavors of STEM detectors, and EDX, CL, Auger and EELS spectrometers. The new system allows experiments combining microscope control with the acquisition capabilities of all these detectors. The second advance is the implementation of “live” processing. Most common processing tasks can be executed on-the-fly, even at video-rate acquisition speeds.

Shadow images are obtained on the detector plane when the specimen in a STEM instrument is illuminated by a stationary beam formed with a very large or no objective aperture. It has been recognized for some time that the shadow image formed after a thin crystal specimen in the diffraction plane of a STEM instrument with a field emission gun can be treated as an in-line hologram. Since the transmitted and diffracted beams are added to give interference effects, all the information on the relative phase of the scattered beams is recorded in the shadow image. In fact, this is basically equivalent to the original scheme envisioned by Gabor, where he proposed that a reconstruction could be made from a hologram so that the imperfection due to spherical aberration of the objective lens could be corrected and improved resolution could be achieved.

Interfacial structure is a controlling parameter in the behavior of many materials. Electron microscopy methods are widely used for characterizing such features as interface abruptness and chemical segregation at interfaces. The problem for high resolution microscopy is to establish optimum imaging conditions for extracting this information. We have found that off-axis electron holography can provide useful information for the study of interfaces that is not easily obtained by other techniques.Electron holography permits the recovery of both the amplitude and the phase of the image wave. Recent studies have applied the information obtained from electron holograms to characterizing magnetic and electric fields in materials and also to atomic-scale resolution enhancement. The phase of an electron wave passing through a specimen is shifted by an amount which is proportional to the product of the specimen thickness and the projected electrostatic potential (ignoring magnetic fields and diffraction effects). If atomic-scale variations are ignored, the potential in the specimen is described by the mean inner potential, a bulk property sensitive to both composition and structure. For the study of interfaces, the specimen thickness is assumed to be approximately constant across the interface, so that the phase of the image wave will give a picture of mean inner potential across the interface.

The new parallel detection EELS systems have opened up the possibility of performing time-resolved studies of compositional changes and the evolution of near-edge structure caused by radiation damage or positional changes across heterogeneous interfaces. Zaluzec has described a system using a 2-D CCD array in which one axis corresponds to time. Such a system can acquire 100 512-channel spectra in a time limited by the CCD readout and digitization time. Our system is an extension of an existing data acquisition system using modified software and a Gatan 666 parallel EELS equipped with a 1024-element 1-D photodiode array. We have taken advantage of the computer’s memory architecture to stack a time series of multiple spectra (or any portion of these spectra) in the extended memory space above 256 K-bytes. The 4 M-bytes of system memory enables storage of up to 1920 spectra 1024 channels long. For inner-shell edges, a 100-500 msec signal integration time per spectrum is typical. After acquisition the series of spectra are recovered from extended memory and are stored on disk. They can then be retrieved for post processing or can be played back through the display, from which VCR recordings can be directly made.