High-resolution Elemental Mapping Research Articles

Advantages of elemental mapping by high-voltage EFTEM

Elemental mapping is one of the most important capabilities of energy-filtering transmission electron microscopy (EFTEM), which can be carried out in several types of TEM instruments. The recently developed post-column imaging filter makes it possible to perform the EFTEM in a high-voltage electron microscope without modifying the column of the microscope. The high-voltage EFTEM offers the possibility of performing high-resolution elemental mapping. Improvement in spatial resolution and collection efficiency specific to elemental mapping in the high-voltage EFTEM are due to the inelastically scattered electrons being concentrated into smaller scattering angles and due to relativistic effects.

Microstructure Evolution During Solid-State Reactions in Polycrystalline Nb/Al and Ti/Ai Multilayer Thin-Films

ABSTRACTThe microstructural changes that occur during the reaction of sputter-deposited Nb/Al and Ti/Al multilayer thin-films with bilayer thicknesses ranging from 10 nm to 333 nm have been studied. The films were deposited with an overall stoichiometry of XAl3 (X = Nb,Ti) and subsequently annealed to different stages of the reaction in a differential scanning calorimeter (DSC). Data obtained from cross-sectional transmission electron microscopy (XTEM), and in situ synchrotron X-ray diffraction (XRD) experiments have provided evidence for a two-stage reaction mechanism for the formation of NbAl3. Microscopy results from a film with a bilayer period of 333 nm showed a microstructure that was consistent with two-dimensional growth in the plane of the interface. A uniform, 10 nm thick continuous layer of the product phase was formed followed by growth normal to the interface that initially consisted of larger, faceted grains. By the end of the reaction, an equiaxed NbAl3 grain structure was observed. High resolution elemental mapping using a scanning transmission electron microscope (STEM) revealed penetration of Nb into the Al layer and enhanced growth in regions where Al grain boundaries intersected the interface. Characterization of microstructure evolution in the Ti/Al system was complicated by the formation of two metastable structures consisting of cubic Ll2 followed by tetragonal DO23, and finally the equilibrium, tetragonal DO22 structure. However, the metastable phase transition temperatures were clearly isolated using the in situ XRD technique.

Electron spectroscopic imaging and fine probe EDX analysis of liquid phase sintered ceramics

This paper is focussed on high resolution imaging and microanalysis of two classes of liquid phase sintered ceramic materials, α and duplex α/β sialons and α-SiC ceramics. The microstructures were characterized in a FEGTEM equipped with surrounding interactive instrumentation for EDX and EELS analysis and electron energy filtering, and special attention was paid to the intergranular microstructure and the variation in local chemical composition. The α and duplex α/β sialon ceramics had been fabricated from balanced starting powder mixtures corresponding to the α-sialon composition R 0·4Si 10·2Al 1·8O 0·6N 15·4 (R=Sm, Dy or Yb) and the β-sialon composition Si 5·4Al 0·6O 0·6N 7·4. The α-SiC ceramics had been pressureless sintered or hot isostatically pressed with smaller additions of Al 2O 3 and Y 2O 3. Combined high resolution analytical and spatial information was obtained from electron spectroscopic images recorded around the C K, N K, O K, Al L 2,3 and rare earth element N 4,5 edges in the electron energy loss spectrum. Residual glassy grain boundary films rich in O and cations originating from the metal oxide/nitride additives were present at all characterized grain boundaries. High resolution imaging and elemental maps computed from the electron energy filtered images showed intergranular film thicknesses in the range 1·5 to 2·3 nm. The results imply that the intergranular film thickness in the sialon microstructures is dependent upon the particular grain boundary and the local chemistry as well as the α′ stabilizing cation. Elemental concentration profiles obtained by stepwise fine probe EDX analysis across α′/α′, α′/β′ and β′/β′ sialon grain boundaries revealed significant variations in the local α′ and β′ substitution levels, both within and between analysed grains. Concentration gradients within the sialon and α-SiC grains, associated with the different grain boundaries, were not detected.

High-spatial resolution compositionally-sensitive imaging of metallic particles using plasmon energy-loss electrons in TEM

High spatial resolution elemental maps have been demonstrated in studies of Y + implanted alumina and Al/Ti multilayer specimens using energy-filtered transmission electron microscopy. A spatial resolution of ≈2nm is achieved. Aluminum containing particles formed in Y + implanted alumina have been identified using energy-filtered images formed with plasmon energy-loss electrons. Noncrystalline aluminum containing particles in specimens implanted at lower ion energies are also observed and the image contrast can be reasonably interpreted using a compositional shell model.

1 nm resolution x-ray elemental mapping using a 300kV field emission TEM

The characteristics of advanced semiconductor devices are affected by contamination due to impurity atoms with sizes at the nanometer level, so it is very important to evaluate such contamination with nanometer-level resolution. In order to cope with this task, we have developed an x-ray elemental mapping system, attached to a 300-kV FE-TEM, with an information limit of 0.11 nm.Both small spot size and sufficient probe current are necessary for high-resolution and highsensitivity x-ray elemental mapping. The elemental mapping is performed with the scanning transmission electron microscope(STEM) mode. For high-resolution STEM imaging, the objective lens works with high excitation as a condenser-objective single lens where the aberrations of the other illuminating lenses are demagnified to negligible level, allowing the extremely small spot size to be obtained. The probe current, however, decreases in proportion to the square of the demagnification of the illuminating system. In this study, the optimum illuminating condition for elemental mapping is examined.

Application of imaging TOF-SIMS to the study of some coal macerals

Four areas on the surface of a high organic sulphur coal specimen (S o,daf=10.59%, R o,max=1.48%) from Guidin, Guizhou province, southwest China, were examined using the novel and powerful microprobe technique of imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS). The high resolution elemental and chemical maps and ion fragments obtained made it possible to distinguish the various organic and inorganic phases in the areas and determine the in situ elemental and organic distributions among the different phases of the coal sample. Moreover, the affinity mode (organic or inorganic) in which some elements occurred was investigated. The study indicates that imaging TOF-SIMS is a very useful technique for coal analysis in that it integrates the conventional petrographical examination with chemical analysis.

Some problems and solutions in electron energy loss spectroscopy of cryosections

Electron energy loss spectroscopy (EELS) has been a powerful tool for high resolution studies of elemental distribution, as well as electronic structure, in thin samples. Its foundation for biological research has been laid out nearly two decades ago, and in the subsequent years it has been subjected to rigorous, but by no means extensive research. In particular, some problems unique to EELS of biological samples, have not been fully resolved. In this article we present a brief summary of recent methodological developments, related to biological applications of EELS, in our laboratory. The main purpose of this work was to maximize the signal to noise ratio (S/N) for trace elemental analysis at a minimum dose, in order to reduce the electron dose and/or time required for the acquisition of high resolution elemental maps of radiation sensitive biological materials.Based on the simple assumption of Poisson distribution of independently scattered electrons, it had been generally assumed that the optimum specimen thickness, at which the S/N is a maximum, must be the total inelastic mean free path of the beam electron in the sample.

Auger electron spectroscopy and microscopy with probe-size limited resolution

High spatial resolution Auger electron spectra and images have been obtained by optimizing secondary electron collection efficiency in a scanning transmission electron microscope (STEM). We describe an ultrahigh vacuum, 100 keV STEM which is capable of collecting Auger electron spectra and images with edge resolutions of ≤5 nm. Typical spectra and images from the Ge/Si(100) and Ag/Si(100) film growth systems are presented and discussed. These images demonstrate high-resolution elemental mapping which can be used in the study of surface processes on the nanometer scale.

Determination of ionization cross section by electron spectroscopic imaging

Electron energy loss spectroscopy (EELS) has become a significant technique for high resolution elemental microanalysis and mapping. Theoretically, quantitative analysis requires only one simple equation:Eqn.(1)where N is the number of atoms per unit area analysed; I(net)(a,δ) is the core loss intensity integrated over an energy range δ beyond the ionization edge and with a collection angle a; I(total) is the total intensity integrated beneath the whole spectrum; σ(a,δ) is the corresponding ionization cross section.To obtain I(net) according to current convention and some theoretical justification, the simplest way of removing the background beneath an ionization edge is simply fitting at least two pre-edge measurements to the equation of I=AE-r, where I is the intensity of electrons that have energy loss E; A and r are constants to be determined from the fitted pre-edge region. Several other methods have also been derived for better accuracy in specific applications.