In the annual dark field (ADF) imaging mode, diffraction intensities inside the ADF detector cutoff angle are discarded. This results a significant loss of the available information. By simultaneous recording the diffraction patterns, we can gain additional information about the specimen, while the ADF image gives the precise position of the probe. This paper describes how to extract the local lattice parameters or to measure the strain field from the zero diffraction disk. The accurate measurement of strain field close to an interface provide the complementary information about the composition and the structure of the interface. An example is the oxygen deficiency in high Tc superconductor of YBa2Cu3O7-δ. The level of oxygen deficiency is too small to be detected by x-ray spectroscopy but affect the lattice parameters significantly that can be experimentally measured [1].

Modern TEM's are not suited for the taking of diffraction-contrast images of defects. Figures in books and papers taken more than a quarter century ago show defects (dislocations, small precipitates and so on) against a uniform background, reflecting constant diffraction conditions across the field of view. Such pictures can not be taken today. Even if the sample is quite flat, TEM images are crossed by “bend contours” which arise, not from the bending of the sample, but from the changing orientation of the beam. In modern TEM's, the objective lens is an immersion lens. The sample sits deep within the magnetic field of the lens and, thus, the electrons are travelling in a helical pattern as they strike the sample. Even with a so-called parallel beam, at different places across the image, the electrons strike the sample at different angles (see figure 1).

The increased demand in the microelectronics industry for higher spatial resolution in the analysis of device defects has focused attention on the use of transmission electron microscopy(TEM). However, in contrast to scanning electron microscopes(SEM), the number of TEM units in the microelectronics industry is still limited. This is because TEM operation and TEM specimen preparation are rather complicated and the results dependent upon operator experience.

A innovative solution using a dedicated ultra thin film evaluation system(HD-2000) based upon a 200kV cold field emission scanning transmission electron microscopy(STEM) technique has been developed[1]. The system has STEM image resolution of 0.24nm and 0.3nm spatial resolution for elemental analysis using energy dispersive X-ray(EDX) spectroscopy with 0.3sr collection solid angle. The system therefore allows materials characterization to be performed at atomic resolution. Another advantage of the system is the ease of use due to newly developed PC-SEM operation software.

In this paper, we use a Bloch wave approach to show that the elastically scattered electrons from neighbouring atomic columns in a zone-axis oriented crystal contribute incoherently to a Z-contrast image regardless of the fact that we have coherent dynamical scattering from a stationary lattice with no absorption. This incoherent nature of the elastic scattering means that through the filtering of the ls-type Bloch states by the detector geometry we approach the Rutherford Z2 dependence of the column intensity for sufficiently large inner detector angle. Thus, annular dark-field (ADF) imaging provides us with a direct incoherent structure image of the atomic-column positions in a zone-axis oriented crystal.

Bloch wave simulations were carried out at 300 kV for the 〈110〉 orientation of InAs (a = 6.06Å) with full, half and empty columns of In atoms. Calculations including 411-beams were carried out for each of the above structural configurations for a single incident partial plane wave vector parallel to the optic axis.

The demand for the higher performance of semiconductor devices, for instance IC functionality, has stimulated industry to further scale the critical dimensions of the semiconductor devices [6]. Also, as parasitic capacitances are reduced in small device structures, the energy loss in these devices is consequently reduced. [1] Achieving the desired performance from such reduced device structures requires optimization of both the interface properties and dopant redistribution processes, such as diffusion and segregation, under various processing conditions. Only through a careful and accurate characterization of these properties on the atomic scale in the electron microscope we can achieve the understanding of the materials interactions during processing necessary to optimize these properties [2].

Conventional imaging and microanalysis techniques in transmission electron microscopy (TEM), such as phase contrast imaging and energy dispersive X-ray spectroscopy (EDS), lack either the spatial resolution or require extensive simulations and through focal series reconstructions to reveal the structure and composition of such interfaces/doping layers (and in the case of simulations may still not give a unique solution).

Recent success of spherical aberration (Cs) correctors for TEM and STEM opened a new generation of microscopy. In order to achieve sub Å resolution in experiment, however, it is necessary to use a monochromator to reduce the effect of chromatic aberration due to the energy spread of the electron source. The monochromator is also necessary for the high energy-resolution EELS (HREELS). Three microscopes - sub Å TEM, 1 Å STEM and HREELS - and those combinations are considered to bring the high performance electron microscopes of the next generation. Among those three, 1 Å STEM has the highest technical difficulties from the point of view of electron optics instrumentation. In this investigation, we will describe the main electron optical problems, which we should solve within a few years, to achieve 1 Å STEM.

The main reason, why 1 Å STEM is so difficult, is the spread of the beam due to the second order aberrations of the energy filter used as the monochromator.

Using parallel beam illumination, electron beam-induced structural transformation has been studied as radiation damages for decades. Recently, however, more attention may need to be paid to beam-induced chemical transformation which happens under illumination by a finely focused beam. Such a small probe is often used in analytical electron microscopy, particularly the core-electron energy loss spectroscopy (EELS). Since the signal for the spectroscopy is very weak long radiation is required and makes the induced chemical reactions happen. Therefore, without attentions to the reactions, the acquired data could lead to misinterpretation of specimen properties. In the present study, using a single crystal calcium fluoride (CaF2), we demonstrated by time-resolved EELS that radiation with a nanometer electron probe could induce chemical reactions between the specimen and the typical residual gases in a microscope column.

The thin films of CaF2 were fabricated by vaporizing flakes of single crystal CaF2 with an electron beam and by dissolving the vapors onto a (001) surface of sodium chloride (NaCl) heated at 300°C.

Recently there has been considerable interest in developing nanometer- and sub-nanometer-scale electronic devices. Of particular interest in this regard is whether individual molecules or molecular complexes can be employed as electronic device elements. Aviram et al. have reported switching and rectification in an organic thin film. More recently, Potember et al. have shown a field-induced conductance transition on a 500 nm scale, but did not demonstrate local reversibility of the transition. The reverse transition was induced only by application of a broad laser pulse or heat. We have observed and replicated reversible conductance transitions in a fully-organic crystalline complex, on a scale close to the dimensions of the unit cell.

A crystalline thin-film organic complex of 3-nitrobenzal malononitrile and 1,4-phenylenediamine (NBMN-pDA), exhibits reversible conductance transitions on the sub-nanometer scale when exposed to local electric field pulses from an STM tip.

FeAl alloys with 40 to 50 at % Al have an impressive combination of oxidation and sulfidation resistance, low density, and low cost and are thus considered as possible substitutes for stainless steels. However, before these materials can be used in structural applications, the fracture characteristics of the alloy's grain boundaries need to be improved. Small additions of carbon and boron have been considered and the resulting properties have been reported. Boron is found to prevent intergranular fracture in iron-rich alloys and to mitigate environmental embrittlement although the improvement is not as dramatic as is seen with Ni3Al alloyed with boron. Boron segregates to the grain boundaries in Fe-Al alloys and boride precipitates at the boundaries and within the grains have been observed.

In this paper, we report the composition and atomic arrangement in a recently discovered phase (designated v phase) found in Fe-Al alloys containing small boron additions using a combination of Z-contrast imaging and electron energy-loss spectroscopy.

The energy-loss spectrum of transmitted electrons contains a wealth of information regarding the physical, chemical and electronic properties of the medium under analysis. It provides a powerful means for materials characterisation in the TEM by use of electron energy-loss spectroscopy (EELS) or its spatially parallel counterpart, energy-selective imaging (ESI). Essentially, both analyses probe the same core-loss information, recording transmitted intensity / as a function of energy-loss E and spatial position x, y, to yield a three-dimensional data set I(E, x, y). Acquisition of an extended series of energy-selected images across the energy-loss range of interest has been shown to provide useful spectral as well as spatial information, with the resolution of extracted ‘image-spectra’ being determined by the energy interval between acquisitions and the width of the energy-selecting slit, as illustrated in Figure la . This mode of analysis, termed ‘image-spectroscopy’ is directly analogous to spectrum-imaging in the STEM, and offers many advantages over conventional two- or three-window elemental mapping techniques .

Crystal structure refinement by the convergent-beam electron diffraction (CBED) method has the following advantages: (i) Nanometer-size crystal structure refinement: CBED patterns can be obtained from specimen areas of a few nanometer in diameter, (ii) Dynamical diffraction effect: the CBED intensities contain phase information of crystal structure factors through the strong dynamical effect. (iii) Site-selective analysis: the use of Bloch states formed by incident electrons allows structure determination weighted for specific atom sites. Energy-filtering (EF) to revome inelastically scattered background is now getting necessary for such quantitative analysis of CBED patterns. Especially for the determination of atom positions and Debye-Waller factors, the use of energy-filtered higher-order Laue zone (HOLZ) CBED patterns is essential because small displacements of atoms can be sensitively detected using HOLZ reflections with large reciprocal vectors. For this purpose, we developed a new fl-filter transmission electron microscope (JEM-2010FEF) with a high acceptance angle [2] and a new analysis program “mbfit” to refine structural parameters using many-beam Bloch-wave calculations and least-square fitting [1].

Many of the electrical, mechanical, and electrochemical properties of diamond-like carbon (DLC) coatings are determined by the amount of sp3 bonding. Correlations of bonding and properties are important in efforts to optimize coatings for specific applications. DLC thin films were grown at LANL by plasma deposition and subsequently ion implanted with N or Ar. Cross-sectioned TEM specimens were characterized with a Gatan imaging filter (GIF) interfaced to a LaB6 Philips CM30T at the ORNL SHaRE User Facility. For elemental distribution maps the following conditions were used: incident beam divergence α = 2.9 mrad, collection angle β = 4.8 mrad, slit width ΔE = 30 eV, exposure times of typically 5 s, 2x-binned 512×512 images, and TEM magnification ∼2000. The standard 3-window method was used for producing elemental maps with AE-r background extrapolation; 2-window jump-ratio images were also produced.

When acquiring energy-filtered TEM (EFTEM) images of a crystalline material, the detrimental effects of diffraction contrast can often be seen in raw energy-filtered images (EFI) (i.e., pre-edge and post-edge images), jump-ratio images and elemental maps as residual diffraction contrast. Residual diffraction contrast occurs in raw EFI because of plural scattering (i.e., inelastic-elastic and elastic-inelastic electron scattering) and in jump-ratio images and elemental maps because background removal procedures often are unable to completely account for intensity changes due to dynamical effects (elastic scattering) that occur between pre-edge and post-edge images acquired at different energy losses.

It is demonstrated in these experiments that, when examining a planar interface, EFTEM images have increased compositional contrast and decreased residual diffraction contrast when the sample is oriented so that the interface is parallel to the electron beam, but not directly on a zone axis.

Spectroscopy and imaging techniques based on electron energy-losses (EELS), which are accessible through energy-filtering transmission electron microscopes (EFTEMs), have proven to be important tools in both materials and life science investigations.

The two most widely used techniques on commercially available EFTEMs are elastic imaging and elemental mapping. Elastic imaging enhances image resolution and contrast by extracting the zero-loss signal and eliminating the inelastic background, whereas elemental mapping, which involves signals coming from element-specific inner-shell ionization edges, is employed to form two dimensional elemental distribution images. In both cases relatively large energy windows of a range of 10 to 30eVare typically used to form energy-filtered images with usually low to moderately high magnifications.

There is however much more information available in an EELS spectrum, which is contained in the detailed fine structure within 0-20eV of a core excitation edge (ELNES) or in the very low energy-loss up to 5eV.

Electron energy loss spectrum-imaging (EELSI) in the energy filtering transmission electron microscope (EFTEM) can provide more accurate analysis of elemental distributions than that obtainable by the standard two-window or three-window background subtraction techniques. Spectra containing many channels can be extracted from regions of interest and analyzed using established methods for quantitation. For example, the pre-edge background can be fitted by an inverse power law and subtracted from the post-edge spectrum. EELSI in the EFTEM is often superior to spectrum-imaging in the scanning transmission electron microscope for mapping specimen regions of size greater than 1 μm. This is due the much larger total beam current that is available at the specimen in a fixed-beam microscope relative to a scanned-beam microscope. Our aim here is demonstrate the advantages of such EELSI measurements for analysis of biological specimens. However, we also indicate some potential pitfalls in acquiring elemental maps in the EFTEM, which can be attributed to specimen instabilities during the acquisition.

In the context of biological specimens, it is in principle desirable to quantitatively map, rather than just point analyze, the distribution of physiologically important elements, and to do so at subcellular resolution. Presently, this can be accomplished by electron energy loss spectrum-imaging (EELSI) in both the scanning transmission electron microscope (STEM) and the energy-filtering transmission electron microscope (EFTEM). Until recently, this approach has been of limited value for mapping the particularly important element Ca, mainly because intracellular total Ca concentrations are normally quite low (<5 mmol/kg dry weight) and because the background in the vicinity of the Ca L23 edge is complex and requires precise background modeling to extract the very weak Ca signals. As a result, the Ca signal is usually not high enough to reach detection threshold during a practical EELSI acquisition time.

Electron energy-loss spectrometry and energy-filtered imaging allow the possibility of detecting, quantifying and mapping of boron. Boron spatial distribution in biological tissue is of particular interest for boron neutron capture therapy (BNCT) for cancer. We have studied the limits of boron quantification and mapping using electron energy-loss spectroscopy and energy-filtered imaging.

To evaluate the concentration limits for boron mapping and quantification three types of specimens were used. First, a uniform boron layer of well known thickness deposited onto of 50 nm-thick carbon film was used to determine the limits for boron quantification. Second, samples for boron mapping with non-uniform boron distribution were prepared by electron-beam evaporation of boron onto a shadow-masked 50 nm-thick carbon film. Third, tobacco mosaic virus (TMV) in a water solution of boronophenylalanine fructrose (BPA-F) was deposited onto a 2 nm—thick carbon film.

Imaging of sample regions with a thickness significantly larger than the extinction length and strong thickness variations introduces two major problems for transmission electron microscopy (TEM) : (i) inelastic scattering increases the energy width of the transmitted electrons and therefore the resolution decreases (ii) the contrast differences caused by thickness variations can be higher than the dynamic range of the detector system.

Both problems can be solved by using energy filtering techniques. The advantage here is that for energy filtered imaging the resolution limit is not determined by the sample thickness but by the width of the energy selection aperture. Fig. 1 shows three envelope functions of the temporal coherence calculated for different values of the energy width. The functions were plotted for an acceleration voltage of 200 kV and a high voltage stability of 2 ppm.

EELS with a TEM is an established spectroscopic technique that is used to provide both qualitative and quantitative chemical information. Analysis of EELS spectral shapes provides information on the coordination, oxidation state, and spin states of atoms in minerals. Despite the availability of parallel EELS detectors for almost fifteen years, geological applications are relatively rare, mainly because of the high level of expertise required by the operator in both acquiring and analyzing the data. For example, core-loss edges can be difficult to see on the background and elemental quantification is not yet routine.

The goal of this review is to discuss the uses and interpretations of the EELS spectra of a range of minerals. We will focus on the interpretation of the electron-loss near-edge structures (ELNES) of the core-loss edges and concentrate primarily on: a) determination of the oxidation state of transition elements and other metals, and b) identification of local anion and cation coordinations. In addition, we will explore the potential of ELNES as a bonding probe.

The resolution in Electron Energy Loss Spectroscopy (EELS) in (S)TEM is presently limited by the instabilities of the high voltage supply (typically 0.2 eV), by the resolution of the spectrometer (typically 0.7 eV), and by the energy spread of the electron source (typically 0.7 eV for a Schottky field emitter). An increase of this resolution to better than 0.1 eV would enable chemical analysis on a nanometer scale. We are presently following hardware as well as software approaches in order to reach this energy resolution in a 200 kV (S)TEM.

The hardware side of our project focuses on the three limiting factors mentioned in the previous paragraph. The instabilities of the high voltage supply are mostly noise and drift, which can be reduced significantly by isolating the high voltage tank, thermally as well as acoustically. In addition, Gatan is developing an imaging filter for this project, which has sub-0.1 eV resolution.