Water is the most abundant component of biological material, but it is systematically excluded from conventional electron microscopy. This is because water evaporates rapidly under the vacuum conditions of an electron microscope. Cryoelectron microscopy has long been seen as a possible avenue to overcome this limitation, but until recently the direct observation of frozen-hydrated specimens was relatively unsuccessful because of a number of serious difficulties. These were, in particular, due to the absence of a good cryospecimen holder, the inherently low contrast of hydrated specimens and the structural damage due to ice crystals formed during freezing. As a consequence, the cryomethods which have flourished in electron microscopy during the last 20 years were not aimed at preserving the hydration of the specimen in the electron microscope. Freezing was only used as an aid to preparation. The objects ultimately observed in the electron microscope were dry and at room temperature. Such cryomethods have recently been reviewed in detail (Robards and Sleytr 1985).

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Cryo-electron microscopy of vitrified specimens.

Publisher Summary In energy-filtering transmission electron microscopy (EFTEM), the zero-loss electrons or electrons passing an energy-loss window of the electron energy-loss spectroscopy (EELS) are used for image formation. This can be achieved by using the scanning mode in a dedicated scanning transmission electron microscope (STEM) or in a TEM with a spectrometer behind the camera chamber or by using an imaging filter lens in the column of a TEM. The conventional TEM and STEM modes can be combined in this way with the mode of electron spectroscopic imaging (ESI) and electron spectroscopic diffraction (ESD), and different modes can be used to record an EELS spectrum. An EFTEM can therefore make full use of elastic and inelastic electron-specimen interactions. This chapter provides an overview of the physical background and the possibilities of EFTEM. The relevant physics of elastic and inelastic scattering is also discussed followed by the instrumentation of EFTEM. The theoretical approaches for understanding the contrast and examples of application are presented for ESI and for ESD.

Energy-filtering transmission electron microscopy

An overview over the current state of research in the field of biaxial nematic liquid crystalline materials is given. After a short introduction, providing some general aspects and summarizing the classical approaches, the main part focuses on recent developments of new concepts for designing biaxial nematics. First, the major theoretical concepts are outlined, including the classification to different symmetries, the importance of cooperativity and cluster formation for the development of biaxial order and the conditions for the establishment of field induced and spontaneous biaxiality in nematic phases. These new concepts also require the re-evaluation of the tools used for the identification of phase biaxiality, which are discussed briefly. In the second part, recent progress in the design of potential biaxial nematic materials, especially focussing on bent-core molecules with nematic phases, is reported and, finally, comparisons with phase biaxiality as observed in smectic liquid crystals are made.

Biaxial nematic phases

Main conformer of gaseous glycine: molecular structure and rotational barrier from electron diffraction data and rotational constants

Factors influencing the precision of quantitative scanning transmission electron microscopy

New Values for the Partial Wave Electron Scattering Factor for the Elements 1≤Z≤57 and 72≤Z≤90 for Incident Electron Energies of 10, 40, 70, and 100 keV

A. C. Yates

Papers

New Values for the Partial Wave Electron Scattering Factor for the Elements 1≤Z≤57 and 72≤Z≤90 for Incident Electron Energies of 10, 40, 70, and 100 keV