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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.

Electron coincidence spectroscopy in an ultrahigh vacuum scanning transmission electron microscope has been used to study the generation pathways for secondary (SE) and Auger electrons (AE) excited by high‐energy incident electrons. Energy and momentum transfer of inelastically scattered 100 keV primary electrons have been correlated with energy selected SE and AE for both thin 〈111〉 oriented Si crystals and amorphous C films. Coincidence spectra from the valence excitation region indicate that bulk plasmon decay is not the primary production channel for SE in Si(111) and that SE result partially from the decay of ionizations from deep in the valence band. Energy deposition by the primary beam is responsible for SE production at excitation energies above the valence region. At most one SE is emitted from the entrance surface of a thin film for each inelastically scattered 100 keV primary electron. An enhancement in both the SE yield and generation probability is observed at the C K ionization edge. Correl...

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.

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 effects of beam precession on the Electron Energy Loss Spectroscopy (EELS) signal of the carbon K edge in a 2 monolayer graphene sheet are studied. In a previous work, we demonstrated the use of precession to compensate for the channeling-induced reduction of EELS signal when in zone axis. In the case of graphene, no enhancement of EELS signal is found in the usual experimental conditions, as graphene is not thick enough to present channeling effects. Interestingly, though it is found that precession makes it possible to increase the collection angle, and, thus, the overall signal, without a loss of signal-to-background ratio.

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.

The production of secondary electrons by fast (100 keV) electrons is investigated by analyzing the time coincidence between inelastically scattered incident electrons and energy-filtered secondary electrons. Thin conducting and semiconducting films show differences in both the coincidence and generation spectra at energies near the bulk-plasmon excitation, suggesting that plasmon decay does not play a central role in the production of secondary electrons in Si. At primary energy losses greater than 35 eV, the secondary-electron production rate is proportional to the energy deposited by the incident electrons

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 secondary electron generation process is studied in an ultra-high vacuum scanning transmission electron microscope using electron coincidence spectroscopy. Production pathways for secondary electrons are determined by analyzing coincidences between secondary electrons and individual excitation events. The ultimate spatial resolution available in scanning electron microscopy is limited by the delocalization of the secondary electron generation process. This delocalization is studied using momentum resolved coincidence electron spectroscopy. The fraction of secondary electrons resulting from localized excitations can explain the high spatial resolution observed in secondary electron microscopy images.