The measurement of the fluorescence of Si K x-rays by Au M x-rays

1990 ◽  
Vol 48 (2) ◽  
pp. 198-199
Author(s):  
John A. Small ◽  
Scott A. Wight ◽  
Robert L. Myklebust ◽  
Dale E. Newbury
Keyword(s):  
Electron Beam ◽  
Electron Probe ◽  
Primary Electron ◽  
Characteristic Line ◽  
X Rays ◽  
Limited Information ◽  
Primary Electron Beam ◽  
X Ray ◽  
Image Position ◽  
Critical Excitation

The characteristic fluorescence correction is used in electron probe microanalysis to account for the x-ray intensity excited in element “a” by the x-rays from the characteristic line of another element, “b”, in the sample. Since the excited intensity is not generated by the primary electron beam, it is necessary to apply the fluorescence correction for quantitative elemental analysis. This correction can be significant particularly when element “b” is a major component of the sample and the characteristic line for element “b” is slightly higher in energy than the critical excitation energy for the excited line of element “a”.The fluorescence correction, which is used in the various analytical programs, is described in equation 1.where I'*fa/I'*pa is the ratio of the emitted “a” intensity excited by “b” x-rays to the emitted intensity excited by the primary electron beam. The various parameters in this equation are accurately known for the K x-ray lines, but only very limited information is available for the M x-ray lines.

Effects of chamber pressure and accelerating voltage on X-RAY resolution in the ESEM

1992 ◽  
Vol 50 (2) ◽  
pp. 1324-1325 ◽  
Author(s):  
Brendon J. Griffin
Keyword(s):  
Electron Beam ◽  
Primary Electron ◽  
Chamber Pressure ◽  
X Rays ◽  
Viewing Angle ◽  
Primary Electron Beam ◽  
Specific Data ◽  
X Ray ◽  
Working Distance ◽  
Eds Microanalysis

Chamber pressure, accelerating voltage and working distance have been shown to control the relative diameter of the scattered skirt of the primary electron beam at the specimen surface in the ESEM. Inital x-ray studies indicate that at 3 torr, 30 kV and a WD=15mm, 45% of the beam comes from beyond 25 μm of the incidence point and 4% from beyond 1.5mm. At 5 torr 66% of the beam is scattered beyond 25 μm2. No specific data was available on the spatial resolution of x rays and this study aimed to improve that situation. The results also form the basis for establishing a mechanism for and defining the potential limits of quantitative EDS microanalysis in the ESEM.The negative viewing angle of the EDS x-ray detector in the current ESEM (model E-3) requires at least a 15 degree tilt on a flat sample for microanalysis. This geometry places a narrow limit on the working distance range that can be used, due to the collimation of the detector, thereby effectively eliminating working distance as a variable in x-ray microanalysis.

X-Ray Energy Dispersive Spectroscopy in the Environmental Scanning Electron Microscope

1998 ◽  
Vol 4 (S2) ◽  
pp. 182-183
Author(s):  
John F. Mansfield ◽  
Brett L. Pennington
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Energy Dispersive Spectroscopy ◽  
Primary Electron ◽  
Environmental Scanning ◽  
Primary Electron Beam ◽  
X Ray ◽  
Environmental Sem ◽  
Scanning Electron

The environmental scanning electron microscope (Environmental SEM) has proved to be a powerful tool in both materials science and the life sciences. Full characterization of materials in the environmental SEM often requires chemical analysis by X-ray energy dispersive spectroscopy (XEDS). However, the spatial resolution of the XEDS signal can be severely degraded by the gaseous environment in the sample chamber. At an operating pressure of 5Torr a significant fraction of the primary electron beam is scattered after it passes through the final pressure limiting aperture and before it strikes the sample. Bolon and Griffin have both published data that illustrates this effect very well. Bolon revealed that 45% of the primary electron beam was scattered by more than 25 μm in an Environmental SEM operating at an accelerating voltage of 30kV, with a water vapor pressure of 3Torr and a working distance of 15mm.

Quantitative EDS analysis in the environmental ESEM using a bremstrahlung intensity-based correction for primary electron beam variation and scatter

1996 ◽  
Vol 54 ◽  
pp. 842-843 ◽  
Author(s):  
B.J. Griffin ◽  
C.E. Nockolds
Keyword(s):  
Electron Beam ◽  
Beam Current ◽  
Primary Electron ◽  
Primary Beam ◽  
Minimum Condition ◽  
Chamber Pressure ◽  
Primary Electron Beam ◽  
Faraday Cage ◽  
X Ray ◽  
Eds Analysis

Quantitative EDS analysis of bulk samples in the scanning electron microscope (SEM) or electron microprobe requires, as a fundamental parameter, a stable and reproducible primary electron beam current Beam current is usually measured with a Faraday cage positioned in the electron column below the objective aperture or in the specimen holder. Reproducibility and stability within 1%/hour is a minimum condition.Primary beam current measurement in the ESEM or any high pressure SEM is difficult to measure. Electron-gas interaction in the biased chamber generates a positive ion flow highly amplified relative to the primary beam (Danilatos, 1990) and generates an x-ray signal from the gas. The latter signal amplitude is dependent on primary beam current, chamber pressure and backscatter electron signal from the specimen (Griffin et al. 1993). These interactions prevent quantification of EDS data standardised to Faraday cage primary beam current measurements or x-ray counts from a reference standard.

Factors Affecting Quantitative Analysis Error in ESEM-EDS

2000 ◽  
Vol 6 (S2) ◽  
pp. 790-791
Author(s):  
R. A. Carlton ◽  
C. E. Lyman ◽  
J. E. Roberts
Keyword(s):  
Electron Beam ◽  
Target Location ◽  
Primary Electron ◽  
Environmental Scanning ◽  
X Rays ◽  
Factors Affecting ◽  
X Ray ◽  
Carbon Coated ◽  
Sample Chamber ◽  
Analysis Error

Standard Reference Material (SRM) 482 of the National Institute of Standards and Technology is a set of 6 gold/copper wires, ranging in concentration from 0 to 100% Cu in 20% steps, intended for calibration studies of electron beam microanalyzers. This is an appropriate standard to test the accuracy of energy dispersive x-ray spectrometry (EDS) in the Environmental Scanning Electron Microscope (ESEM). While the presence of the gas in the sample chamber gives the ESEM its unique capabilities, it also is the source of complications to x-ray spectrometry. The gas can spread the primary electron beam into a wide skirt of electrons with the consequent production of x-rays many micrometers from the target location of the beam.The six wires (∼ 500 jam in diameter) were embedded and polished in one epoxy mount. The mount was carbon coated in one set of experiments. The coating was removed and the sample retested.

Phosphor Imaging Plate Measurement of Electron Scattering in the Environmental Scanning Electron Micrsoscope

2000 ◽  
Vol 6 (S2) ◽  
pp. 798-799
Author(s):  
S.A. Wight ◽  
C.J. Zeissler
Keyword(s):  
Electron Beam ◽  
Direct Measurement ◽  
Electron Scattering ◽  
Measurement Data ◽  
Primary Electron ◽  
Environmental Scanning ◽  
Imaging Plate ◽  
X Rays ◽  
Primary Electron Beam ◽  
Scanning Electron

In this work, phosphor imaging plate technology is applied to measure electron scattering directly in the environmental scanning electron microscope (ESEM) specimen chamber. The scattering of electrons from the primary electron beam, under relatively high-pressure conditions (266 Pa) in the ESEM sample chamber, degrades the analytical accuracy of elemental analysis. The degree of this degradation is poorly known. To date, attempts to measure experimentally the spatial distribution of the scattered electrons have been limited to observing secondary effects such as the intensity of x-rays produced from copper targets positioned at various distances from the primary electron beam interaction point. A more accurate distribution of the scattered electron intensity can be obtained from a direct measurement of both the scattered and unscattered electrons over a large area with single electron sensitivity. Improvements to the accuracy of Monte Carlo models of the scattering process will be made possible by the direct measurement data.

Characteristic and Continuum Fluorescence in Electron Beam X-ray Microanalysis

1999 ◽  
Vol 5 (S2) ◽  
pp. 562-563
Author(s):  
C.E. Nockolds
Keyword(s):  
Electron Beam ◽  
Electron Probe Microanalysis ◽  
Electron Probe ◽  
Mathematical Framework ◽  
X Rays ◽  
Correction Procedure ◽  
X Ray ◽  
Exponential Term ◽  
Accurate Expression ◽  
Original Formula

Of the different aspects of electron probe microanalysis(EPMA)which were studied by Castaing during his doctorate the work on characteristic x-ray fluorescence was the most definitive. In his thesis, which was completed in 1951, Castaing established the physical and mathematical framework for a correction procedure for fluorescence which is essentially still used in EPMA today. Much of the effort since then has been in refining and improving the accuracy of the correction and extending the scope of the correction to a wider range of specimen types. The Castaing formula was developed for the case of a K x-ray from element A being excited by a K xray from element B (K-K fluorescence) and in 1965 Reed extended the range of the correction by including the K-L, L-L and L-K interactions. In the same paper Reed also introduced the expression from Green and Cosslett for the calculation of K intensities, which was believed to be more accurate than the expression used by Castaing. The original formula included a somewhat unrealistic exponential term to allow for the depth of the production of the primary x-rays and a number of workers have tried replacing this term with a more accurate expression, however, in general this has led to only small changes in the final correction. Reed also simplified the formula in order to make the calculation easier in the days before fast computers; in particular he replaced the jump ratio variable by two constants, one for the K-shell and one for the L-shell. Much later Heinrich showed that this simplification was no longer necessary and that the jump ratio could in fact be calculated directly.

Improving the Analtical Accuracy in the Analysis of Particles by Employing Low Voltage Analysis:

2000 ◽  
Vol 6 (S2) ◽  
pp. 924-925
Author(s):  
JA Small ◽  
JT Armstrong
Keyword(s):  
Electron Beam ◽  
Electron Probe ◽  
Low Voltage ◽  
X Rays ◽  
Relative Uncertainty ◽  
Particle Volume ◽  
X Ray ◽  
Uncertainty Estimates ◽  
Corrected Data ◽  
Particle Geometry

The energy of the electron beam, in conventional electron probe microanalysis, is generally in the range of 15-25 keV which provides the necessary overvoltage to excite efficiently the K and L x-ray lines for elements with atomic numbers in the range of about 5-83. One of the primary microanalytical methods for obtaining compositional information on particles is X-ray analysis in the electron probe and these same voltage criteria have been applied to the procedures developed for this purpose. The main difference in analytical procedures for bulk samples and particles is that corrections have to be applied to the particle k-ratios or calculated compositions to compensate for: 1) the penetration or scattering of electrons out of the particle volume and 2) variations in the absorption due to particle geometry of x-rays less than about 3 keV. In general, particle corrections improve the accuracy and reduce the relative uncertainty estimates from several tens of percent for uncorrected data to about 10% for corrected data.

Spatial Resolution of SEM Signals

1972 ◽  
Vol 30 ◽  
pp. 436-437
Author(s):  
H. Soezima
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Primary Electron ◽  
Resolving Power ◽  
X Rays ◽  
Primary Electron Beam ◽  
Scanning Electron Microscope Analysis ◽  
Electron Microscope Analysis ◽  
Scanning Electron

There are few investigations discussed on resolution of the signals as spatial resolving power, at the scanning electron microscope analysis. There remains misunderstanding that better resolution is obtained only by making a primary electron beam diameter small. At the scanning electron microscope analysis, there are such signals as secondary electron, back scattered electron, absorbed electron, transmitted electron, auger electron, cathode luminescence and X-rays. The spatial resolutions of these signals are effected not only by primary electron diameter but also by accelerating voltage, sample density, electro conductivity of the sample, surface condition of the sample, relative position among the primary electron optics, sample and detection system, energy of the signals, potential and magnetic distribution, and current density distribution of primary electron beam.Some examples of the X-rays, that have the poorest resolving power in the signals, are shown below.

Operating Conditions For Quantitative X-Ray Analysis In The Environmental SEM

1998 ◽  
Vol 4 (S2) ◽  
pp. 294-295
Author(s):  
R. A. Carlton ◽  
C. E. Lyman ◽  
J. E. Roberts
Keyword(s):  
Electron Beam ◽  
Target Location ◽  
Primary Electron ◽  
Operating Conditions ◽  
Environmental Scanning ◽  
X Rays ◽  
X Ray ◽  
Sample Chamber ◽  
Low Pressures ◽  
Environmental Sem

Standard Reference Material (SRM) 482 of the National Institute of Standards and Technology is a set of 6 gold/copper wires, ranging in concentration from 0 to 100% Cu in 20% steps, intended for calibration studies of electron beam microanalyzers. This is an appropriate standard to test the accuracy of energy dispersive x-ray spectrometry (EDS) in the Environmental Scanning Electron Microscope (ESEM). While the presence of the gas in the sample chamber gives the ESEM its unique capabilities, it also is the source of complications to x-ray spectrometry. The gas can spread the primary electron beam into a wide skirt of electrons with the consequent production of x-rays many micrometers from the target location of the beam. In spite of the difficulties, at least two methods have been proposed to correct high pressure data to that expected at low pressures.

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