Elemental analysis of telatively thick specimens by EELS

1992 ◽  
Vol 50 (2) ◽  
pp. 1248-1249
Author(s):  
R.F. Egerton ◽  
S.C. Cheng
Keyword(s):  
Function Approximation ◽  
Core Loss ◽  
Delta Function ◽  
Mean Free Path ◽  
Specimen Thickness ◽  
Low Loss ◽  
Amorphous Silicon Dioxide ◽  
Edge Profile ◽  
Data Points ◽  
Inelastic Mean Free Path

Core-loss spectra of thicker specimens are strongly influenced by plural scattering. Plural inelastic events increase the background Ib underneath an ionization edge by an amount dependent on t/λ, t being the specimen thickness and λ the total-inelastic mean free path. However, plural scattering also contributes to the integral core-loss signal Ic. In fact, if the latter were integrated over a sufficiently large energy window Δ, the signal/background ratio (SBR=IC/Ib) might be expected to be independent of t.Figure 1 shows K-edge signal/background ratios for elemental carbon and silicon, presented as measured data points (for a collection semi-angle of l0mrad, 120keV incident energy and Δ=100eV) and as solid curves calculated by convolving a power-law edge profile with a delta-function approximation of the low-loss region. For silicon, SBR falls off more slowly with increasing t/λ, as expected from its higher edge energy. This trend is confirmed by measurements on amorphous silicon dioxide depicted in Fig.2, which shows the signal/background ratios of the oxygen and silicon K-edges as a function of thickness.

Quantitative energy-filtered tem imaging of interfaces

1996 ◽  
Vol 54 ◽  
pp. 542-543 ◽  
Author(s):  
J. Bentley ◽  
E. A. Kenik ◽  
K. Siangchaew ◽  
M. Libera
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Unit Volume ◽  
Core Loss ◽  
Mean Free Path ◽  
Slit Width ◽  
Elemental Mapping ◽  
Low Loss ◽  
Transmission Electron ◽  
Inelastic Mean Free Path

Quantitative elemental mapping by inner shell core-loss energy-filtered transmission electron microscopy (TEM) with a Gatan Imaging Filter (GIF) interfaced to a Philips CM30 TEM operated with a LaB6 filament at 300 kV has been applied to interfaces in a range of materials. Typically, 15s exposures, slit width Δ = 30 eV, TEM magnifications ∼2000 to 5000×, and probe currents ≥200 nA, were used. Net core-loss maps were produced by AE−r background extrapolation from two pre-edge windows. Zero-loss I0 (Δ ≈ 5 eV) and “total” intensity IT (unfiltered, no slit) images were used to produce maps of t/λ = ln(IT/I0), where λ is the total inelastic mean free path. Core-loss images were corrected for diffraction contrast by normalization with low-loss images recorded with the same slit width, and for changes in thickness by normalization with t/λ, maps. Such corrected images have intensities proportional to the concentration in atoms per unit volume. Jump-ratio images (post-edge divided by pre-edge) were also produced. Spectrum lines across planar interfaces were recorded with TEM illumination by operating the GIF in the spectroscopy mode with an area-selecting slit oriented normal to the energy-dispersion direction. Planar interfaces were oriented normal to the area-selecting slit with a specimen rotation holder.

Quantitative Composition Maps of Magnetic Recording Media by EFTEM

1999 ◽  
Vol 5 (S2) ◽  
pp. 634-635 ◽  
Author(s):  
J. Bentley ◽  
J.E. Wittig ◽  
T.P. Nolan
Keyword(s):  
Magnetic Recording ◽  
Core Loss ◽  
Mean Free Path ◽  
Model Material ◽  
Quantitative Composition ◽  
Specimen Thickness ◽  
Recording Media ◽  
Magnetic Recording Media ◽  
Plan View ◽  
Inelastic Mean Free Path

Elemental mapping of Co-Cr-X based magnetic recording media at resolutions approaching 1 nm by energy-filtered transmission electron microscopy (EFTEM) can provide quantitative measurements of intergranular Cr segregation for correlation with magnetic properties and materials processing. The thin-film media present many challenges for EFTEM methods, such as diffraction contrast and closelyspaced edges. The goal of this work was to provide robust methods for mapping quantitative compositions in such materials. Results presented here are for a model material of 60 nm of Co84Cr12Ta4 on a 75 nm Cr underlayer; both films were d.c. magnetron sputtered onto a NiP-plated Al substrate pre-heated to 250°C. Other compositions and thinner layers (∼30 nm) have also been studied. EFTEM was performed on back-thinned, plan-view specimens with a Gatan Imaging Filter (GIF) interfaced to a 300 kV LaB6 Philips CM30. Optimized acquisition conditions have been detailed elsewhere. Besides core-loss image series, zero-loss I0 (slit width Δ=10eV), low-loss Ik (Δ=30eV), and unfiltered IT images were recorded, and maps of t/λ. = ln(IT / I0), where t is specimen thickness and λ. is the total inelastic mean free path, were produced.

Determination of Inelastic Mean Free Path by Electron Energy-Loss Spectroscopy in TEM: A Model Study Using Si and Ge

2006 ◽  
Vol 982 ◽  
Author(s):  
Chongmin Wang ◽  
Bret D. Cannon
Keyword(s):  
Free Path ◽  
Mean Free Path ◽  
Thickness Measurement ◽  
Least Square ◽  
Specimen Thickness ◽  
Low Loss ◽  
Diffraction Profile ◽  
Key Factor ◽  
Inelastic Mean Free Path

ABSTRACTAlthough the inelastic mean free path for Si and Ge have been measured previously, reported experimental values for silicon range from 121 nm to 160 nm for 200 keV and a large collection angle. A key factor responsible for this uncertainty is the lack of an accurate measurement of the specimen thickness at the point at which the EELS spectra are obtained. In this research, we have evaluated a systematic methodology for determination of the specimen thickness. In the thickness measurement based on converging beam electron diffraction, CBED, instead of the classic “trial and error” straight-line-fitting method to either the maxima or minima, a non-linear least square fitting of the theoretical diffraction profile to the energy filtered two-beam CBED is used. The low-loss EELS spectrum is also obtained from the same location. The inelastic mean free path was determined using the measured thickness and EELS data. Furthermore, attempt is also made to obtain the dielectric function from the low-loss spectrum. The established method will be extended to other materials and the results will be compared with numerical simulations.

Local thickness determination by Electron Energy Loss Spectroscopy

1994 ◽  
Vol 52 ◽  
pp. 944-945
Author(s):  
Suichu Luo ◽  
John R. Dunlap ◽  
Richard W. Williams ◽  
David C. Joy
Keyword(s):  
Energy Loss ◽  
Analytical Electron Microscopy ◽  
Mean Free Path ◽  
Single Scattering ◽  
Specimen Thickness ◽  
Three Dimension ◽  
Angular Correction ◽  
Electron Intensity ◽  
Image Position ◽  
Inelastic Mean Free Path

In analytical electron microscopy, it is often important to know the local thickness of a sample. The conventional method used for measuring specimen thickness by EELS is:where t is the specimen thickness, λi is the total inelastic mean free path, IT is the total intensity in an EEL spectrum, and I0 is the zero loss peak intensity. This is rigorouslycorrect only if the electrons are collected over all scattering angles and all energy losses. However, in most experiments only a fraction of the scattered electrons are collected due to a limited collection semi-angle. To overcome this problem we present a method based on three-dimension Poisson statistics, which takes into account both the inelastic and elastic mixed angular correction.The three-dimension Poisson formula is given by:where I is the unscattered electron intensity; t is the sample thickness; λi and λe are the inelastic and elastic scattering mean free paths; Si (θ) and Se(θ) are normalized single inelastic and elastic angular scattering distributions respectively ; F(E) is the single scattering normalized energy loss distribution; D(E,θ) is the plural scattering distribution,

Determination of Mean Free Path for Inelastic Scattering in Poly(2-Vinyl Pyridine) by Low-Loss Spectrum Imaging

2000 ◽  
Vol 6 (S2) ◽  
pp. 224-225
Author(s):  
A. Aitouchen ◽  
T. Chou ◽  
M. Libera ◽  
M. Misra
Keyword(s):  
Free Path ◽  
Free Fall ◽  
Mean Free Path ◽  
Specimen Thickness ◽  
Thickness Determination ◽  
Vinyl Pyridine ◽  
Integrated Intensity ◽  
Inelastic Mean Free Path ◽  
Electron Energy Loss

The common experimental method to determine the total inelastic mean free path i by electron energy-loss spectroscopy (EELS) is by the relation : t/λi= ln(It/IO) [1] where t is the specimen thickness, It, is the total integrated intensity, and Io is the intensity of the zero-loss peak. The accuracy of this measurement depends on the thickness determination. Model geometries like cubes, wedges, and spheres enable accurate thickness determination from transmission images.Spherical polymers with diameters of order 10-200nm can be made from a number of high-Tg polymers by solvent atomization. This research studied atomized spheres of poly(2-vinyl pyridine) [PVP]. A solution of 0.1% PVP in THF was nebulized. After solvent evaporation during free fall within the chamber atmosphere, solid spherical polymer particles with a range of diameters were collected on holey-carbon TEM grids at the bottom of the atomization chamber.

Thickness measurements by Electron Energy Loss Spectroscopy (EELS)

1993 ◽  
Vol 51 ◽  
pp. 434-435
Author(s):  
Ruoya Ho ◽  
Lijie Zhao ◽  
Yun-Yu Wang ◽  
Zhifeng Shao ◽  
Andrew P. Somlyo
Keyword(s):  
Energy Loss ◽  
Mean Free Path ◽  
Finite Energy ◽  
Specimen Thickness ◽  
Essential Requirement ◽  
High Loss ◽  
Image Position ◽  
Inelastic Mean Free Path ◽  
Thickness Measurements ◽  
Electron Energy Loss

An estimate of specimen mass-thickness is an essential requirement for evaluate with EELS the absolute elemental concentration in biological specimens. The conventional method used for measuring specimen thickness by EELS is: where t is the specimen thickness, λi is the total inelastic mean free path, It is the total count in an EELS spectrum and I0 is the count in the zero loss peak. This equation is rigorously correct, only if the electrons are collected over all scattering angles and the spectrum covers all energy losses. But in most experiments with a finite energy loss region, because of the limited collection semi-angle, we can only collect a fraction of scattered electrons. Omitting the high loss electrons will result in a cut-off error that is usually less than 5%, if we use an energy window from 0 eV to 150 eV or above. But the effect of the limited semi-angle is more serious. Fig. 1 shows the ln(It/I0) measured on the same specimen in both TEM and STEM mode at 80 keV with a magnetic sector spectrometer equipped with a parallel detector on Philips 400 FEG.

scholarly journals Benchmarking ideal sample thickness in cryo-EM using MicroED

2021 ◽  
Author(s):  
Michael W. Martynowycz ◽  
Max T. B. Clabbers ◽  
Johan Unge ◽  
Johan Hattne ◽  
Tamir Gonen
Keyword(s):  
Free Path ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Mean Free Path ◽  
Sample Thickness ◽  
Proteinase K ◽  
Specimen Thickness ◽  
Quality Of Data ◽  
Inelastic Mean Free Path

The relationship between sample thickness and quality of data obtained by microcrystal electron diffraction (MicroED) is investigated. Several EM grids containing proteinase K microcrystals of similar sizes from the same crystallization batch were prepared. Each grid was transferred into a focused ion-beam scanning electron microscope (FIB/SEM) where the crystals were then systematically thinned into lamellae between 95 nm and 1650 nm thick. MicroED data were collected at either 120, 200, or 300 kV accelerating voltages. Lamellae thicknesses were converted to multiples of the calculated inelastic mean free path (MFP) of electrons at each accelerating voltage to allow the results to be compared on a common scale. The quality of the data and subsequently determined structures were assessed using standard crystallographic measures. Structures were reliably determined from crystalline lamellae only up to twice the inelastic mean free path. Lower resolution diffraction was observed at three times the mean free path for all three accelerating voltages but the quality was insufficient to yield structures. No diffraction data were observed from lamellae thicker than four times the calculated inelastic mean free path. The quality of the determined structures and crystallographic statistics were similar for all lamellae up to 2x the inelastic mean free path in thickness, but quickly deteriorated at greater thicknesses. This study provides a benchmark with respect to the ideal limit for biological specimen thickness with implications for all cryo-EM methods.

scholarly journals Benchmarking the ideal sample thickness in cryo-EM

2021 ◽  
Vol 118 (49) ◽  
pp. e2108884118
Author(s):  
Michael W. Martynowycz ◽  
Max T. B. Clabbers ◽  
Johan Unge ◽  
Johan Hattne ◽  
Tamir Gonen
Keyword(s):  
Free Path ◽  
Ion Beam ◽  
Mean Free Path ◽  
Sample Thickness ◽  
Proteinase K ◽  
Specimen Thickness ◽  
Quality Of Data ◽  
Inelastic Mean Free Path ◽  
The Ideal

The relationship between sample thickness and quality of data obtained is investigated by microcrystal electron diffraction (MicroED). Several electron microscopy (EM) grids containing proteinase K microcrystals of similar sizes from the same crystallization batch were prepared. Each grid was transferred into a focused ion beam and a scanning electron microscope in which the crystals were then systematically thinned into lamellae between 95- and 1,650-nm thick. MicroED data were collected at either 120-, 200-, or 300-kV accelerating voltages. Lamellae thicknesses were expressed in multiples of the corresponding inelastic mean free path to allow the results from different acceleration voltages to be compared. The quality of the data and subsequently determined structures were assessed using standard crystallographic measures. Structures were reliably determined with similar quality from crystalline lamellae up to twice the inelastic mean free path. Lower resolution diffraction was observed at three times the mean free path for all three accelerating voltages, but the data quality was insufficient to yield structures. Finally, no coherent diffraction was observed from lamellae thicker than four times the calculated inelastic mean free path. This study benchmarks the ideal specimen thickness with implications for all cryo-EM methods.

scholarly journals Determining On-Axis Crystal Thickness with Quantitative Position-Averaged Incoherent Bright-Field Signal in an Aberration-Corrected STEM

2012 ◽  
Vol 18 (4) ◽  
pp. 720-727 ◽  
Author(s):  
Huolin L. Xin ◽  
Ye Zhu ◽  
David A. Muller
Keyword(s):  
Accurate Determination ◽  
Analytical Electron Microscopy ◽  
Mean Free Path ◽  
Specimen Thickness ◽  
Crystal Thickness ◽  
Bright Field ◽  
Analytical Electron ◽  
Inelastic Mean Free Path ◽  
Electron Energy Loss

AbstractAn accurate determination of specimen thickness is essential for quantitative analytical electron microscopy. Here we demonstrate that a position-averaged incoherent bright-field signal recorded on an absolute scale can be used to determine the thickness of on-axis crystals with a precision of ±1.6 nm. This method measures both the crystalline and the noncrystalline parts (surface amorphous layers) of the sample. However, it avoids the systematic error resulting from surface plasmon contributions to the inelastic mean-free-path thickness estimated by electron energy loss spectroscopy.

Comparison of Calculated and Recorded Electron Energy-Loss Spectra of Aluminium and Carbon

1990 ◽  
Vol 48 (2) ◽  
pp. 64-65
Author(s):  
L. Reimer ◽  
R. Oelgeklaus
Keyword(s):  
Fourier Transform ◽  
Energy Loss ◽  
Electron Energy ◽  
Rotational Symmetry ◽  
Mean Free Path ◽  
Single Scattering ◽  
Specimen Thickness ◽  
Two Dimensional ◽  
Image Position ◽  
Electron Energy Loss

Quantitative electron energy-loss spectroscopy (EELS) needs a correction for the limited collection aperture α and a deconvolution of recorded spectra for eliminating the influence of multiple inelastic scattering. Reversely, it is of interest to calculate the influence of multiple scattering on EELS. The distribution f(w,θ,z) of scattered electrons as a function of energy loss w, scattering angle θ and reduced specimen thickness z=t/Λ (Λ=total mean-free-path) can either be recorded by angular-resolved EELS or calculated by a convolution of a normalized single-scattering function ϕ(w,θ). For rotational symmetry in angle (amorphous or polycrystalline specimens) this can be realised by the following sequence of operations :(1)where the two-dimensional distribution in angle is reduced to a one-dimensional function by a projection P, T is a two-dimensional Fourier transform in angle θ and energy loss w and the exponent -1 indicates a deprojection and inverse Fourier transform, respectively.

Sign in / Sign up

Export Citation Format

Share Document