Sub-Micron Spatial Resolution Edx Microchemical Analysis Of Bulk Specimens In The Sem At Low Beam Voltages

1990 ◽  
Vol 48 (2) ◽  
pp. 234-235
Author(s):  
E D Boyes ◽  
D L Smith
Keyword(s):  
Spatial Resolution ◽  
Normal Incidence ◽  
Substantial Contribution ◽  
Beam Specimen ◽  
Plan View ◽  
X Ray ◽  
Interaction Volume ◽  
Beam Voltage ◽  
Microchemical Analysis ◽  
Probe Size

The spatial resolution of data in the SEM depends on the the original probe size of the instrument, the beam-specimen interaction volume and the signal escape range. The first two terms are strong functions of the beam voltage. The range [R] of the beam-specimen interaction for chemical microanalysis by x-ray spectroscopy [EDX] has a general dependence given by R ∝ E05/3. The data in Fig.1 were obtained in plan view with a beam at normal incidence using evaporated thin films of aluminum [Z=13] of various thicknesses on a silicon substrate of similar atomic number [Z=14]. The voltage at which the film and the substrate contribute equally to the [EDX] x-ray spectrum [Fig.2] can be measured with an accuracy of only a few volts. The experiment was designed to measure the depth of the interaction volume. In this geometry the data are independent of the probe size which makes a substantial contribution to the lateral resolution of analysis with a simple SEM operated at low voltages [E0 <5kV].

High spatial resolution x-ray microanalysis of interfaces

1995 ◽  
Vol 53 ◽  
pp. 284-285
Author(s):  
J. R. Michael
Keyword(s):  
Spatial Resolution ◽  
Electron Probe ◽  
Solid Angle ◽  
Collection Efficiency ◽  
Spatial Scales ◽  
Energy Dispersive Spectrometer ◽  
X Rays ◽  
X Ray ◽  
Probe Size ◽  
Brightness Field

X-ray microanalysis in the analytical electron microscope (AEM) refers to a technique by which chemical composition can be determined on spatial scales of less than 10 nm. There are many factors that influence the quality of x-ray microanalysis. The minimum probe size with sufficient current for microanalysis that can be generated determines the ultimate spatial resolution of each individual microanalysis. However, it is also necessary to collect efficiently the x-rays generated. Modern high brightness field emission gun equipped AEMs can now generate probes that are less than 1 nm in diameter with high probe currents. Improving the x-ray collection solid angle of the solid state energy dispersive spectrometer (EDS) results in more efficient collection of x-ray generated by the interaction of the electron probe with the specimen, thus reducing the minimum detectability limit. The combination of decreased interaction volume due to smaller electron probe size and the increased collection efficiency due to larger solid angle of x-ray collection should enhance our ability to study interfacial segregation.

Practical Importance of Spatial Resolution and Analytical Sensitivity in AEM X-ray Microanalysis

1990 ◽  
Vol 48 (2) ◽  
pp. 432-433
Author(s):  
J. Zhang ◽  
D.B. Williams ◽  
J.I. Goldstein
Keyword(s):  
Spatial Resolution ◽  
Practical Importance ◽  
Beam Current ◽  
Specimen Thickness ◽  
Analytical Sensitivity ◽  
Related Factors ◽  
X Ray ◽  
Probe Size ◽  
Excitation Volume ◽  
Two Parameters

Analytical sensitivity and spatial resolution are important and closely related factors in x-ray microanalysis using the AEM. Analytical sensitivity is the ability to distinguish, for a given element under given conditions, between two concentrations that are nearly equal. The analytical sensitivity is directly related to the number of x-ray counts collected and, therefore, to the probe current, specimen thickness and counting time. The spatial resolution in AEM analysis is determined by the probe size and beam broadening in the specimen. A finer probe and a thinner specimen give a higher spatial resolution. However, the resulting lower beam current and smaller X-ray excitation volume degrade analytical sensitivity. A compromise must be made between high spatial resolution and an acceptable analytical sensitivity. In this paper, we show the necessity of evaluating these two parameters in order to determine the low temperature Fe-Ni phase diagram.A Phillips EM400T AEM with an EDAX/TN2000 EDS/MCA system and a VG HB501 FEG STEM with a LINK AN10 EDS/MCA system were used.

Low-voltage EDS of magnesium ferrite Dendrites in a FEG-SEM

1996 ◽  
Vol 54 ◽  
pp. 478-479
Author(s):  
Matthew T. Johnson ◽  
Ian M. Anderson ◽  
Jim Bentley ◽  
C. Barry Carter
Keyword(s):  
Monte Carlo ◽  
Quantitative Analysis ◽  
Monte Carlo Simulations ◽  
Cross Section ◽  
Spatial Resolution ◽  
Low Voltage ◽  
Magnesium Ferrite ◽  
X Ray ◽  
Interaction Volume ◽  
Ferrite Spinel

Energy-dispersive X-ray spectrometry (EDS) performed at low (≤ 5 kV) accelerating voltages in the SEM has the potential for providing quantitative microanalytical information with a spatial resolution of ∼100 nm. In the present work, EDS analyses were performed on magnesium ferrite spinel [(MgxFe1−x)Fe2O4] dendrites embedded in a MgO matrix, as shown in Fig. 1. spatial resolution of X-ray microanalysis at conventional accelerating voltages is insufficient for the quantitative analysis of these dendrites, which have widths of the order of a few hundred nanometers, without deconvolution of contributions from the MgO matrix. However, Monte Carlo simulations indicate that the interaction volume for MgFe2O4 is ∼150 nm at 3 kV accelerating voltage and therefore sufficient to analyze the dendrites without matrix contributions.Single-crystal {001}-oriented MgO was reacted with hematite (Fe2O3) powder for 6 h at 1450°C in air and furnace cooled. The specimen was then cleaved to expose a clean cross-section suitable for microanalysis.

Quantification Of Segregation Levels Using Xeds In The Stem

1999 ◽  
Vol 5 (S2) ◽  
pp. 146-147
Author(s):  
V. J. Keast ◽  
D. B. Williams
Keyword(s):  
Grain Boundary ◽  
Boundary Segregation ◽  
Scanning Transmission Electron Microscope ◽  
Factor V ◽  
X Ray ◽  
Interaction Volume ◽  
Probe Size ◽  
Scanning Transmission ◽  
The Matrix ◽  
Image Position

The quantification of grain boundary segregation levels, as measured with X-ray energy dispersive spectroscopy (XEDS) in a scanning transmission electron microscope (STEM), is dependent on the size and shape of the interaction volume. The segregation level T (in atoms/nm2) is related to the intensities of the characteristic peaks in the X-ray spectrum, Is and Im, bywhere ρ is the density of the matrix in atoms/nm3, Am and As are the atomic masses of the matrix and segregant respectively and ksm is the usual k-factor. The geometric factor, V/A, is the ratio of the volume of interaction to the area of the grain boundary inside in the interaction volume. Different models have been used to describe the interaction volume and these are illustrated in Fig. 1 and the appropriate expression for V/A is given in each case. In the simplest case, beam broadening is neglected and the interaction volume can be described as a cylinder with diameter equal to the probe size, d.

On Low Voltage Scanning Electron Microscopy and Chemical Microanalysis

2000 ◽  
Vol 6 (4) ◽  
pp. 307-316 ◽  
Author(s):  
E.D. Boyes
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Spatial Resolution ◽  
Low Voltage ◽  
Energy Dispersive ◽  
Beam Specimen ◽  
Topographic Analysis ◽  
X Ray ◽  
Voltage Scanning ◽  
Scanning Electron

AbstractThe current status and general applicability of scanning electron microscopy (SEM) at low voltages is reviewed for both imaging (low voltage scanning electron microscopy, LVSEM) and chemical microanalysis (low voltage energy-dispersive X-ray spectrometry, LVEDX). With improved instrument performance low beam energies continue to have the expected advantages for the secondary electron imaging of low atomic number (Z) and electrically non-conducting samples. They also provide general improvements in the veracity of surface topographic analysis with conducting samples of all Z and at both low and high magnifications. In new experiments the backscattered electron (BSE) signal retains monotonic Z dependence to low voltages (<1 kV). This is contrary to long standing results in the prior literature and opens up fast chemical mapping with low dose and very high (nm-scale) spatial resolution. Similarly, energy-dispersive X-ray chemical microanalysis of bulk samples is extended to submicron, and in some cases to <0.1 μm, spatial resolution in three dimensions at voltages <5 kV. In favorable cases, such as the analysis of carbon overlayers at 1.5 kV, the thickness sensitivity for surface layers is extended to <2 nm, but the integrity of the sample surface is then of concern. At low beam energies (E0) the penetration range into the sample, and hence the X-ray escape path length out of it, is systematically restricted (R = F(E05/3)), with advantages for the accuracy or elimination of complex analysis-by-analysis matrix corrections for absorption (A) and fluorescence (F). The Z terms become more sensitive to E0 but they require only one-time calibrations for each element. The new approach is to make the physics of the beam–specimen interactions the primary factor and to design enabling instrumentation accordingly.

On Low Voltage Scanning Electron Microscopy and Chemical Microanalysis

2000 ◽  
Vol 6 (4) ◽  
pp. 307-316
Author(s):  
E.D. Boyes
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Spatial Resolution ◽  
Low Voltage ◽  
Energy Dispersive ◽  
Beam Specimen ◽  
Topographic Analysis ◽  
X Ray ◽  
Voltage Scanning ◽  
Scanning Electron

Abstract The current status and general applicability of scanning electron microscopy (SEM) at low voltages is reviewed for both imaging (low voltage scanning electron microscopy, LVSEM) and chemical microanalysis (low voltage energy-dispersive X-ray spectrometry, LVEDX). With improved instrument performance low beam energies continue to have the expected advantages for the secondary electron imaging of low atomic number (Z) and electrically non-conducting samples. They also provide general improvements in the veracity of surface topographic analysis with conducting samples of all Z and at both low and high magnifications. In new experiments the backscattered electron (BSE) signal retains monotonic Z dependence to low voltages (<1 kV). This is contrary to long standing results in the prior literature and opens up fast chemical mapping with low dose and very high (nm-scale) spatial resolution. Similarly, energy-dispersive X-ray chemical microanalysis of bulk samples is extended to submicron, and in some cases to <0.1 μm, spatial resolution in three dimensions at voltages <5 kV. In favorable cases, such as the analysis of carbon overlayers at 1.5 kV, the thickness sensitivity for surface layers is extended to <2 nm, but the integrity of the sample surface is then of concern. At low beam energies (E0) the penetration range into the sample, and hence the X-ray escape path length out of it, is systematically restricted (R = F(E05/3)), with advantages for the accuracy or elimination of complex analysis-by-analysis matrix corrections for absorption (A) and fluorescence (F). The Z terms become more sensitive to E0 but they require only one-time calibrations for each element. The new approach is to make the physics of the beam–specimen interactions the primary factor and to design enabling instrumentation accordingly.

The spatial resolution of x-ray microanalysis in thin foils

1991 ◽  
Vol 49 ◽  
pp. 472-473
Author(s):  
D. B. Williams ◽  
J. R. Michael ◽  
J. I. Goldstein ◽  
A. D. Romig
Keyword(s):  
Spatial Resolution ◽  
Thin Foil ◽  
Beam Specimen ◽  
Beam Diameter ◽  
Worst Case ◽  
X Ray ◽  
Thin Foils ◽  
Elastic Scatter ◽  
Electron Beam Diameter ◽  
Beam Broadening

The spatial resolution of x-ray microanalysis in a thin foil is determined by the size of the beam-specimen interaction volume. This volume is a combination of the incident electron beam diameter (d) and the beam broadening (b) due to elastic scatter within the specimen. Definitions of spatial resolution have already been proposed on this basis but all present a worst case value for the resolution based on the dimensions of the beam emerging from the exit face of the foil.

Applications of high spatial resolution hicroanalysis to materials problems using dedicated STEM

1978 ◽  
Vol 36 (1) ◽  
pp. 418-419
Author(s):  
Ernest L. Hall ◽  
John B. Vander Sande
Keyword(s):  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Profile Analysis ◽  
Scanning Transmission Electron Microscope ◽  
Dramatic Improvement ◽  
X Ray ◽  
Transmission Electron ◽  
Probe Size ◽  
Scanning Transmission ◽  
Compositional Variations

The scanning transmission electron microscope has afforded a dramatic improvement in the spatial resolution of X-ray microanalysis of thin specimens, allowing the investigation of extremely localized compositional variations in materials systems. In this paper, the results of high resolution composition profile analysis in several materials are presented. The materials were analyzed in a 100 kV field emission STEM manufactured by VG Microscopes, Ltd., and fitted with an energy dispersive X-ray spectrometer. The specimens were held in a double-tilt graphite cartridge which allowed X-ray detection in the tilt range 0°-20° about each axis. The vacuum in the specimen chamber was ∿ 2 x 10-9 torr during analysis. Electron probe spot sizes of 5-10 Å were used, corresponding to probe currents in the range of 10-10-10-9 amps.For a given specimen composition, the spatial resolution of X-ray microanalysis in thin specimens is a function of probe size, accelerating voltage, specimen atomic number, and thickness.

Low Voltage Topographic Imaging of Biological Samples in the SEM

2000 ◽  
Vol 6 (S2) ◽  
pp. 760-761
Author(s):  
Paul Walther
Keyword(s):  
Spatial Resolution ◽  
Surface Coating ◽  
Electron Probe ◽  
Low Voltage ◽  
Sample Surface ◽  
Primary Beam ◽  
Beam Specimen ◽  
Interaction Volume ◽  
Topographic Imaging ◽  
The Impact

Joy and Pawley (1992) defined the limitations of spatial resolution in the SEM as follows. “The spatial resolution of the scanning electron microscope is limited by at least three factors: the diameter of the electron probe, the size and shape of the beam/specimen interaction volume with the solid for the mode of imaging employed and the Poisson statistics of the detected signal.” The interaction volume of the primary beam in the sample increases with increasing accelerating voltage (Vo), because electrons with higher energy penetrate deeper into the sample. The interaction volume affects the spatial resolution, because the electrons that finally form the image do not only originate from the impact point of the primary beam, but from the much larger interaction volume. It is not simple to understand how this affects spatial resolution, since resolution is also heavily influenced by the properties of the sample surface (the surface coating) and it is the issue of ongoing debates.

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