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.

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.

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,

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.

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.

Elemental analysis in a V-Ti-C alloy using electron energy loss spectroscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 552-553
Author(s):  
Hamish L. Fraser
Keyword(s):  
Binary Systems ◽  
Analytical Electron Microscopy ◽  
Scanning Transmission Electron Microscope ◽  
High Temperature Materials ◽  
Transmission Electron ◽  
Interstitial Component ◽  
Analytical Electron ◽  
Scanning Transmission ◽  
Electron Energy Loss

There has been considerable interest in the recent past concerning the application of refractory metal-interstitial systems as high temperature materials. it is important to understand the behavior of the interstitial component, and thus the determination of precipitation processes has been an area of study. in addition to making observations in simple binary systems, there is a need to characterize the changes that occur when other substitutional alloying elements are added. recently, bruemmer has studied the precipitation of carbides in a v-8Ti-c alloy over a range of temperatures. it is particularly interesting to characterize the carbides that precipitate at temperatures when the ti can diffuse rapidly (e.g. 1000°c), and determine not only the structure of the carbide but also perform microchemistry on as fine a scale as possible using analytical electron microscopy. bruemmer used a scanning transmission electron microscope (stem) (jeol jsem 200) coupled with an ortec energy dispersive x-ray analyzer to make measurements of the v:ti ratio in the carbide.

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.

Fast calibration of CBED patterns for quantitative analysis

1993 ◽  
Vol 51 ◽  
pp. 674-675
Author(s):  
M.A. Gribelyuk ◽  
M. Rühle
Keyword(s):  
Reciprocal Lattice ◽  
Accurate Determination ◽  
Incident Beam ◽  
Crystal Thickness ◽  
Structure Model ◽  
Beam Direction ◽  
Transmitted Beam ◽  
Reciprocal Vector ◽  
On Line

A new method is suggested for the accurate determination of the incident beam direction K, crystal thickness t and the coordinates of the basic reciprocal lattice vectors V1 and V2 (Fig. 1) of the ZOLZ plans in pixels of the digitized 2-D CBED pattern. For a given structure model and some estimated values Vest and Kest of some point O in the CBED pattern a set of line scans AkBk is chosen so that all the scans are located within CBED disks.The points on line scans AkBk are conjugate to those on A0B0 since they are shifted by the reciprocal vector gk with respect to each other. As many conjugate scans are considered as CBED disks fall into the energy filtered region of the experimental pattern. Electron intensities of the transmitted beam I0 and diffracted beams Igk for all points on conjugate scans are found as a function of crystal thickness t on the basis of the full dynamical calculation.

The Use of ELNES for Microanalysis

1999 ◽  
Vol 5 (S2) ◽  
pp. 664-665
Author(s):  
A.J. Craven ◽  
M. MacKenzie
Keyword(s):  
Electron Microscopy ◽  
Energy Loss ◽  
Electron Energy ◽  
Analytical Electron Microscopy ◽  
Local Environment ◽  
Edge Structure ◽  
Similar Shape ◽  
Analytical Electron ◽  
Electron Energy Loss ◽  
Combining Information

The performance of many materials systems depends on our ability to control the distribution of atoms on a nanometre or sub-nanometre scale within those systems. This is as true for steels as it is for semiconductors. A key requirement for improving their performance is the ability to determine the distribution of the elements resulting from processing the material under a given set of conditions. Analytical electron microscopy (AEM) provides a range of powerful techniques with which to investigate this distribution. By combining information from different techniques, many of the ambiguities of interpretation of the data from an individual technique can be eliminated. The electron energy loss near edge structure (ELNES) present on an ionisation edge in the electron energy loss spectrum reflects the local structural and chemical environments in which the particular atomic species occurs. Thus it is a useful contribution to the information available. Since a similar local environment frequently results in a similar shape, ELNES is useful as a “fingerprint”.

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