Contrast in the electron spectroscopic imaging mode of a TEM. I. Influence of zero-loss filtering on scattering contrast

Measured values of the transmission of amorphous films as a function of the objective aperture and film thickness can be described by a single-scattering theory for unfiltered and zero-loss filtered images in the electron spectroscopic imaging mode of a transmission electron microscope. The theory can be applied to estimate the gain of contrast by zero-loss filtering for specimen structures larger and smaller than the chromatic aberration disc.     

Energy filtering transmission electron microscopy using the new JEM-2010FEF

The new JEM-2010FEF electron microscope provides useful techniques based on energy filtering as an omega-type energy filter is integrated into a thermal field-emission 200 kV transmission electron microscope. For example, the zero-loss imaging improves the contrast of high resolution lattice images as well as images of precipitates or lattice defects in alloys. The acquisition time for elemental mapping with core-loss electrons is one order in magnitude shorter than with energy-dispersive X-ray spectroscopy. The removal of inelastically scattered electrons enables us to observe weak lines in convergent-beam electron diffraction patterns from a thicker specimen with a probe size 1–2 nm in diameter. A combination of the field emission gun and sensitive recording media such as an imaging plate and a slow-scan CCD camera makes the energy filtering more powerful.     

Image analysis of macroporous polystyrene sorbents using electron spectroscopic imaging to enhance mass contrast. The architectural relationship between polymer porosity and absorption capacity

We describe the microscopical analysis of two polystyrene divinylbenzene copolymers (PS-DVB) made using 20 and 55% (v/v) DVB cross-linker respectively, in which the hydrated structure of each polymeric material solvated in water is preserved by employing very rapid freezing and low-temperature freeze-drying techniques. Using the zero-loss mode of electron spectroscopic imaging to enhance the contrast of unstained polymer sections, we introduce some novel methods for the application of computer-assisted image analysis for routine examination of polymer pore structure. We also relate these parameters to the ability of the two polymers to absorb nanometre-sized particles—neutral colloidal gold particles and cationized ferritin. Both methods will be invaluable in the structural analysis of porous polymers, but particularly for comparative analyses of macroporous sorbents.     

Contrast in the electron spectroscopic imaging mode of a TEM

The ratio of inelastic-to-elastic total cross-sections has been measured in an energy-filtering electron microscope for different elements. Formulae for the transmission of elastically and inelastically scattered electrons in part I were used to calculate the optimum conditions for a Z-ratio contrast in the electron spectroscopic imaging mode. Structure-sensitive contrast can be observed for all non-carbon atoms in biological sections when filtering with an energy loss at ΔE ～ 250 eV below the carbon K edge. Model experiments with evaporated layers of different elements on a carbon film allow measurement of the contrast increase. Filtering with the carbon plasmon loss shows a lower phase contrast than with zero-loss filtering. This can be explained by calculating contrast transfer functions for inelastically scattered electrons.     

Quantitative high resolution transmission electron microscopy: the need for energy filtering and the advantages of energy-loss imaging

Evidence is presented that inelastically scattered electrons contribute significant detail at the atomic level to high resolution images, particularly in high voltage instruments. The implications for quantitative image interpretation are shown to be serious and a case is made for incorporating facilities for energy-filtered imaging in future high resolution electron microscopes.     

Mapping of ELNES on a nanometre scale by electron spectroscopic imaging

The amorphous interfacial layer between Si substrates and diamond films grown by plasma-assisted chemical vapour deposition has been studied by electron spectroscopic imaging. The amorphous layer consists mainly of carbon, which can only be distinguished from the diamond film by analysis of the near-edge structure (ELNES) of the carbon K edge. Series of electron spectroscopic images were acquired across the carbon K edge and were analysed in order to reveal the presence of the π*- and σ*-excitations. After background removal from the corresponding images, phase maps for the distribution of sp² and sp³ hybridized carbon can be obtained. From the whole series of images, electron energy-loss spectra can be extracted for any given area in the images. The results show that the amorphous layer covers large areas along the interface and that regions with only 1–2 nm layer thickness can clearly be analysed. The results obtained with the electron spectroscopic imaging technique will be compared with results obtained on a field emission gun scanning transmission electron microscope.