2008 marked the 40th anniversary of the seminal paper “Solid-State Energy-Dispersion Spectrometer for Electron-Microprobe X-ray Analysis” by Ray Fitzgerald, Klaus Kiel, and Kurt Heinrich [Science (1968), 159, 528] that introduced the Si(Li) energy dispersive spectrometer (EDS) detector as a practical analytical tool to the electron microscope community. In recognition of that anniversary, the Microscopy Society of America and the Microbeam Analysis Society organized a symposium at the 2008 Microscopy and Microanalysis Conference in Albuquerque, New Mexico to review the remarkable progress in Si(Li) EDS that has made elemental analysis available on virtually any electron beam platform.

On February 2, 1968, R. Fitzgerald, K. Keil, and K.F.J. Heinrich published a seminal paper in Science (159, 528–530) in which they described a solid-state Si(Li) energy dispersive spectrometer (EDS) for electron probe microanalysis (EPMA) with, initially, a resolution of 600 eV. This resolution was much improved over previous attempts to use either gas-filled proportional counters or solid-state devices for EDS to detect X-rays and was sufficient, for the first time, to make EDS a practically useful technique. It ushered in a new era not only in EPMA, but also in scanning electron microscopy, analytical transmission electron microscopy, X-ray fluorescence analysis, and X-ray diffraction. EDS offers many advantages over wavelength-dispersive crystal spectrometers, e.g., it has no moving parts, covers the entire X-ray energy range of interest to EPMA, there is no defocusing over relatively large distances across the sample, and, of particular interest to those who analyze complex minerals consisting of many elements, all X-ray lines are detected quickly and simultaneously.

The rapid advance and falling costs of computing power and data storage during the last 40 years have greatly enhanced the data reduction speed and analytical capacity of energy dispersive spectroscopy (EDS) systems. At the same time, the solid state X-ray detector [until recently, the Si(Li) diode] has seen performance increases due to the use of advanced materials and processing techniques. In addition, the performance of the electronic components (field effect transistor, preamp, and pulse processor) of an EDS system has been constantly improved. These technology advances have resulted in improved spectral quality, excellent light element detection, and increased count rate performance. The results have been truly remarkable and driven by the needs of the analyst. This article will summarize the progress made in these areas in the last 40 years and make a brief reference to prospects for future development in EDS system performance.

The computerized multichannel analyzer running software specifically designed for X-ray analysis appeared very early in the commercialization of the energy dispersive X-ray spectrometer (EDS) and, like the solid-state X-ray detector itself, was built on a technology foundation originally developed for nuclear spectroscopy. However, software techniques employed for gamma-ray spectra could not accommodate the continuum component of EDS spectra, and a new approach was required. Least-squares fitting with “top-hat” filtered spectra proved to be an effective solution that is still widely used today. Though modern computer technology has subsequently contributed greatly to the speed and convenience of present-day EDS software, it seems that the achievable accuracy and precision of spectrum analysis has not fundamentally improved, and most of the early challenges are still quite relevant, although they may appear in new guises. The availability of the high speed silicon drift detector, however, may provide both the incentive and the data precision to drive future advances. This article traces the formative years of EDS software from the personalized perspective of a participant. Factors that shaped the development of the industry are identified, and future directions are speculated.

A comprehensive electron energy-loss spectroscopy study of niobium (Nb) and stable Nb-oxide phases (NbO, NbO2, Nb2O5) was carried out. In this work (Part I), the plasmons and energy-loss near-edge structures (ELNES) of all relevant Nb edges (Nb-N2,3, Nb-M4,5, Nb-M2,3, Nb-M1, and Nb-L2,3) up to energy losses of about 2600 eV and the O-K edge are analyzed with respect to achieving characteristic fingerprints of Nb in different formal oxidation states (0 for metallic Nb, +2 for NbO, +4 for NbO2, and +5 for Nb2O5). Chemical shifts of the Nb-N2,3, Nb-M4,5, Nb-M2,3, and Nb-L2,3 edges are extracted from the spectra that amount to about 4 eV as the oxidation state increases from 0 for Nb to +5 for Nb2O5. Four different microscopes, including a 200 keV ZEISS Libra with monochromator, were used. The corresponding wide range of experimental parameters with respect to the primary electron energy, convergence, and collection semi-angles as well as energy resolution allows an assessment of the influence of the experimental setup on the ELNES of the different edges. Finally, the intensity of the Nb-L2,3 white-line edges is correlated with niobium 4d-state occupancy in the different reference materials.

A comprehensive electron energy-loss spectroscopy (EELS) study of niobium (Nb) and stable Nb-oxide phases (NbO, NbO2, Nb2O5) was carried out. Part II of this work is devoted to quantitative EELS by means of experimental k-factors derived from the intensity ratio of the O-K edge and the Nb-M4,5 or Nb-M2,3 edges for all three stable Nb-oxides. The precision and accuracy of the quantification are investigated with respect to the influence of intensity-measurement energy windows, background subtraction, and sample thickness. Integration-window widths allowing optimum accuracy are determined. Owing to background-subtraction errors, the Nb-M4,5 edges rather than Nb-M2,3 are preferred for quantification. Different approaches are applied to improve the precision with regard to thickness-related errors. Thus, a precision up to ±1.5% is achieved by averaging spectra from all three reference oxides to determine a k-factor using Nb-M4,5. Using the experimental k-factor, the determination of atomic concentration ratios CNb/CO in the range of 0.4 (Nb2O5) to 1 (NbO) was found to be possible with an accuracy of 0.6% (relative deviation between measured and nominal composition), whereas ratios of calculated partial ionization cross sections lead to less accurate results.

The ultrastructure of phellem cells of Quercus suber L. (cork oak) and Calotropis procera (Ait) R. Br. were analyzed using electron transmission microscopy to determine the presence or absence of plasmodesmata (PD). Different types of Q. suber cork samples were studied: one year shoots; virgin cork (first periderm), reproduction cork (traumatic periderm), and wet cork. The channel structures of PD were found in all the samples crossing adjacent cell walls through the suberin layer of the secondary wall. Calotropis phellem also showed PD crossing the cell walls of adjacent cells but in fewer numbers compared to Q. suber. In one year stems of cork oak, it was possible to follow the physiologically active PD with ribosomic accumulation next to the aperture of the channel seen in the phellogen cells to the completely obstructed channels in the dead cells that characterize the phellem tissue.

The differential accumulation of fluorescent molecules in tumorigenic versus normal cells is a well-reported phenomenon and is the basis for photodiagnostic therapy. Through the use of confocal microscopy, the kinetic uptake and accumulation of fusarochromanone (FC101) was determined in two lines of living tumorigenic cells of mesenchymal-epithelial origin and normal fibroblast cells. Like other fluorescent cationic molecules, FC101 showed increased accumulation in tumorigenic cells; however, unlike other molecules, it appeared to be accumulated in a time-dependent manner. Also, unlike traditional fluorescent cationic molecules, FC101, a potent inhibitor of cell growth, showed preferential inhibition of tumorigenic B-16 melanoma cells and MCF7 cells derived from breast cancer adenocarcinoma when compared to normal cardiac fibroblasts. Further analysis of FC101's physicochemical properties using both experimentally obtained and simulated values revealed the likelihood of membrane permeation and oral bioavailability of the compound. These physicochemical properties of FC101 were also used to predict its intracellular localization lending credence to data observed by confocal microscopy.

We have developed the focused ion beam (FIB) fold-out technique, for transmission electron microscopy (TEM) sample preparation in which there is no fine polishing or dimpling, thus saving turnaround time. It does not require a nanomanipulator yet is still site specific. The sample wafer is cut to shape, polished down, and then placed in a FIB system. A tab containing the area of interest is created by ion milling and then “folded out” from the bulk sample. This method also allows a plan-view of the sample by removing material below the wafer's surface film or device near the polished edge. In the final step, the sample is thinned to electron transparency, ready to be analyzed in the TEM. With both a cross section and plan-view, our technique gives microscopists a powerful tool in analyzing multiple zone axes in one TEM session. The nature of the polished sample edge also includes the ability to sample many areas, allowing the user to examine a very large device or sample. More importantly, this technique could make multiple site-specific e-beam transparent specimens in one polished sample, which is difficult to do when prepared by other methods.