The Beauty and Clarity of a Well Designed Experiment (original) (raw)
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New techniques in electron energy-loss spectroscopy and energy-filtered imaging
Micron, 2003
This article is a survey of hardware and software advances that promise to increase the power and sensitivity of electron energy-loss spectroscopy (EELS) and energy-filtered imaging (EFTEM) in a transmission electron microscope. Recent developments include electron-gun monochromators, lens-aberration correctors, and software for spectral sharpening, spectral processing and interpretation of fine structure. Future improvements could include the deployment of new electron sources. The expected enhancements in energy and spatial resolution are compared with fundamental limitations that arise from the natural widths of spectral peaks, the delocalization of inelastic scattering and the problem of electron-irradiation damage.
Limits to the spatial, energy and momentum resolution of electron energy-loss spectroscopy
Ultramicroscopy, 2007
We discuss various factors that determine the performance of electron energy-loss spectroscopy (EELS) and energy-filtered (EFTEM) imaging in a transmission electron microscope. Some of these factors are instrumental and have undergone substantial improvement in recent years, including the development of electron monochromators and aberration correctors. Others, such as radiation damage, delocalization of inelastic scattering and beam broadening in the specimen, derive from basic physics and are likely to remain as limitations. To aid the experimentalist, analytical expressions are given for beam broadening, delocalization length, energy broadening due to core-hole and excited-electron lifetimes, and for the momentum resolution in angleresolved EELS.
Atomic resolution electron energy-loss spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 2005
Electron energy-loss spectroscopy (EELS) has been successfully used to measure the electronic structure of materials with atomic (i.e. sub-nanometer) spatial resolution. Furthermore, the combination of incoherent Z-contrast imaging and EELS allows us to correlate structural features, such as defects or interfaces directly with the changes in the local electronic structure. In this review, we will discuss the theoretical aspects and experimental procedures for achieving atomic-resolution EELS. In particular, we will describe the practicalities of the combination of Z-contrast imaging and EELS, used in the scanning transmission electron microscopy mode and also describe some of our recent results where column-by-column EELS has helped solve important material science problems.
Performance of a new high-resolution electron energy-loss spectroscopy microscope
Microscopy Microanalysis Microstructures, 1991
2014 We have been developing a new instrument for high resolution electron energy-loss spectroscopy (EELS). It is composed of a JEM-1200EX transmission electron microscope-the basic component-and two Wien filters (a monochrometer and an analyzer) with retardation lenses and acceleration lenses. The stigmatic focus has been achieved by a special design of the Wien filter. A spatial resolution of 190nm, and a momentum resolution (203C0/03BB) of 0.069Å-1 have been obtained. The energy resolution has attained so far to a value of 81 meV. 1. Introduction.
High resolution energy-loss spectroscopy
Ultramicroscopy, 1989
In principle, Electron Energy-Loss Spectroscopy in the Scanning Transmission Electron Microscope can obtain information related to the electronic structure of single defect structures in semiconductors. The instrumental requirements necessary to accomplish this are discussed. Examples include: Si and GaAs interband excitations, graphite EXELFS analysis, and surface and defect induced structure at the SiL2. 3 edge.
A computer aided approach to electron energy loss spectroscopy and imaging
Computer Methods and Programs in Biomedicine, 1992
In this paper we present the design and configuration of an imaging system for electron energy loss spectroscopy (EELS) and electron spectrographic imaging (ESI). The interfacing of commercial off-the-shelf hardware, custom software and a transmission electron microscope containing integrated spectrographic capabilities produces results that are well suited for clinical applications. The custom design and integration of this system allows for full control over all of the methods and procedures employed. This full control and knowledge of the procedures used is not always possible with commercial packages. This custom software allowed for the definition and testing of a new procedure for the determination of the theoretical background image, and hence the ability to refine the overall sensitivity for elemental detection. To further the proof of elemental detection, a procedure for continuous scan of an area of interest while varying delta E can also be performed with this system.
Ultramicroscopy, 2003
We present experimental measurements of the C K-ELNES of high temperature pyrolysed graphite and related crystalline materials as a function of collection angle and sample tilt. These results together with a corresponding theoretical analysis indicate that the so-called ''magic angle'' for EELS measurements of an anisotropic crystal such as graphite, where spectra are independent of sample orientation, is approximately two times the characteristic scattering angle. We briefly discuss the implications of this result for the experimental measurement of anisotropic structures, including interfaces, as well as for the detailed modelling of ELNES structures using advanced electronic structure calculations. r
Physical Review B, 2008
An electron reaching the detector after being backscattered from a solid surface in a reflection electron energy loss spectroscopy ͑REELS͒ experiment follows a so-called V-type trajectory if it is reasonable to consider that it has only one large elastic scattering event along its total path length traveled inside the solid. V-type trajectories are explicitly assumed in the dielectric model developed by Yubero et al. ͓Phys. Rev. B 53, 9728 ͑1996͔͒ for quantification of electron energy losses in REELS experiments. However, the condition under which this approximation is valid has not previously been investigated explicitly quantitatively. Here, we have studied to what extent these REELS electrons can be considered to follow near V-type trajectories. To this end, we have made Monte Carlo simulations of trajectories for electrons traveling at different energies in different experimental geometries in solids with different elastic scattering properties. Path lengths up to three to four times the corresponding inelastic mean free paths have been considered to account for 80-90% of the total electrons having one single inelastic scattering event. On this basis, we have made detailed and systematic studies of the correlation between the distribution of path lengths, the maximum depth reached, and the fraction of all electrons that have experienced near V-type trajectories. These investigations show that the assumption of V-type trajectories for the relevant path lengths is, in general, a good approximation. In the rare cases, when the detection angle corresponds to a scattering angle with a deep minimum in the cross section, very few electrons have experienced true V-type trajectories. However, even in these extreme cases, a large fraction of the relevant electrons have near V-type trajectories.