Towards compositional imaging using auger electron signals

1991 ◽  
Vol 49 ◽  
pp. 6-7
Author(s):  
M M El Gomati ◽  
M Prutton ◽  
R H Roberts ◽  
I R Barkshire ◽  
P G Kenny ◽  
...  
Keyword(s):  
Electron Beam ◽  
Auger Electron ◽  
Elemental Distribution ◽  
Beam Diameter ◽  
Surface Distribution ◽  
Analytical Technique ◽  
Electron Production ◽  
Distribution Of Elements ◽  
Low Efficiency ◽  
Surface Analytical Technique

Auger electron spectroscopy (AES) is a well established, quantitative surface analytical technique with reasonable accuracy of the order of 1% of an atomic monolayer. When it is combined with a small electron beam diameter, high resolution concentration maps of the surface distribution of elements can be obtained. This has been demonstrated to be a useful and powerful method in surface analysis. However, because of the rather low efficiency of Auger electron production (∼ 10-5 - 10-4 per incident electron) long frame scan times (of the order of hours) have to be employed in the case of multi-element composite samples. The raw images often reflect not only surface elemental distribution but also electron beam fluctuations. In addition, subsurface atomic number variations as well as local surface topography are known to alter the contrast of these images. In order to quantify Auger maps to give concentration distribution of the surface elements, sample and instrumental effects have to be separated.

scholarly journals Auger Electron Spectroscopy-A Review

2019 ◽  
Vol 7 (3) ◽  
pp. 100-103
Author(s):  
K. Bhavyasri ◽  
M. Sreshta ◽  
R. Swethasri
Keyword(s):  
Electron Beam ◽  
Auger Electron Spectroscopy ◽  
Electron Spectroscopy ◽  
Auger Electron ◽  
Excess Energy ◽  
Analytical Technique ◽  
Corrosion Science ◽  
Characterization Of Materials ◽  
Sensitive Analytical Technique

Auger electron spectroscopy (AES) is surface sensitive analytical technique mainly,it provides quantitative elemental and chemical state information from surfaces of solid materials.It utilizes a high current, finely focused electron beam as an excitation source.In AES,A sample is probed with electron beam with energy between 3 to 3o Kev which results in ejection of electron in core level, filled by an outer level electron with excess energy being used then, this excess energy used to emit an electron this, emitted electron is said as Auger electron. That result as function of auger electron energy. The resulting spectra is obtained used to determine the composition of samples. The Auger electron kinetic energies are characteristic of emitting atoms and the measurement of their energies is used to identify the elements variation of composition with depth can be determined by ion sputtering technique. Lastly,AES is applicable for detection of thin films, characterization of materials, metallurgy and corrosion science.  

scholarly journals Mapping the Surface Distribution of Elements on Ap Stars Using the Maximum Entropy Method

1993 ◽  
Vol 138 ◽  
pp. 258-271
Author(s):  
Artie P. Hatzes
Keyword(s):  
Maximum Entropy ◽  
Rotation Period ◽  
Entropy Method ◽  
Elemental Distribution ◽  
Surface Distribution ◽  
Horizontal Diffusion ◽  
Distribution Of Elements ◽  
Characteristic Features ◽  
Magnetic Poles ◽  
Ap Stars

AbstractA technique for deriving the distribution of elements on the surface of Ap stars using maximum entropy reconstruction principles is described. The technique is applied to deriving the silicon distribution on 56 Ari, CU Vir, 11 Ori and the chromium distribution on ϒ2 Ari. Silicon on these stars is depleted at the magnetic poles and is enhanced in regions between the magnetic equator and poles. The chromium distribution on ϒ2 Ari is markedly different than the chromium distribution seen on other Ap stars. It shows depletions at one of the magnetic poles (as do other Ap stars) but it does not show the depleted band at the equator as has been seen on θ Aur, 45 Her, and ω Her. The silicon distribution on 11 Ori also differs from that found on other stars in that it shows evidence for a depleted band, similar to what has been seen in the chromium distribution is some stars. Characteristic features in the abundance maps such as spots or bands appear to mark the location of the magnetic poles or equator so that these maps can be used to infer the magnetic field geometries on these stars. Dipole decentering parameters derived from the abundance maps yield decentering parameters of about 0.2 stellar radii. The amount of decentering seems to be correlated with rotation period (longer period Ap stars have less decentering). Horizontal diffusion can complicate the use of abundance maps to determine the field geometry. The effects of horizontal diffusion can only be understood by a proper theoretical study of its effects or by mapping the elemental distribution on Ap stars of known age.

Application of Improved Voltage Compensation in the SEM to Imaging of Organic Materials

1973 ◽  
Vol 31 ◽  
pp. 444-445
Author(s):  
P.J. Killingworth ◽  
M. Warren
Keyword(s):  
Electron Beam ◽  
Organic Materials ◽  
Operating Parameters ◽  
Low Density ◽  
Beam Diameter ◽  
Incident Electron Beam ◽  
Specimen Material ◽  
Voltage Compensation ◽  
Selection Of ◽  
Scanning Electron

Ultimate resolution in the scanning electron microscope is determined not only by the diameter of the incident electron beam, but by interaction of that beam with the specimen material. Generally, while minimum beam diameter diminishes with increasing voltage, due to the reduced effect of aberration component and magnetic interference, the excited volume within the sample increases with electron energy. Thus, for any given material and imaging signal, there is an optimum volt age to achieve best resolution.In the case of organic materials, which are in general of low density and electric ally non-conducting; and may in addition be susceptible to radiation and heat damage, the selection of correct operating parameters is extremely critical and is achiev ed by interative adjustment.

Reduction of Specimen Contamination in Electron-Beam Instruments

1976 ◽  
Vol 34 ◽  
pp. 576-577
Author(s):  
G. Lehmpfuhl ◽  
P. J. Smith
Keyword(s):  
Electron Beam ◽  
Cold Trap ◽  
Beam Diameter ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Hydrocarbon Molecules ◽  
Electron Microscopes ◽  
Combination Of Methods ◽  
Convergent Beam ◽  
Very High

Specimens being observed with electron-beam instruments are subject to contamination, which is due to polymerization of hydrocarbon molecules by the beam. This effect becomes more important as the size of the beam is reduced. In convergent-beam studies with a beam diameter of 100 Å, contamination was observed to grow on samples at very high rates. Within a few seconds needles began forming under the beam on both the top and the underside of the sample, at growth rates of 400-500 Å/s, severely limiting the time available for observation. Such contamination could cause serious difficulty in examining a sample with the new scanning transmission electron microscopes, in which the beam is focused to a few angstroms.We have been able to reduce the rate of contamination buildup by a combination of methods: placing an anticontamination cold trap in the sample region, preheating the sample before observation, and irradiating the sample with a large beam before observing it with a small beam.

Spatially Resolved Photoelectron Spectroscopy: Recent Progress and Future Plans

1990 ◽  
Vol 48 (2) ◽  
pp. 388-389
Author(s):  
A. M. Bradshaw
Keyword(s):  
Photoelectron Spectroscopy ◽  
Chemical Reactivity ◽  
Target Material ◽  
Orbital Energy ◽  
Light Sources ◽  
Analytical Technique ◽  
Hartree Fock ◽  
Spatially Resolved ◽  
Koopmans Theorem ◽  
Surface Analytical Technique

X-ray photoelectron spectroscopy (XPS or ESCA) was not developed by Siegbahn and co-workers as a surface analytical technique, but rather as a general probe of electronic structure and chemical reactivity. The method is based on the phenomenon of photoionisation: The absorption of monochromatic radiation in the target material (free atoms, molecules, solids or liquids) causes electrons to be injected into the vacuum continuum. Pseudo-monochromatic laboratory light sources (e.g. AlKα) have mostly been used hitherto for this excitation; in recent years synchrotron radiation has become increasingly important. A kinetic energy analysis of the so-called photoelectrons gives rise to a spectrum which consists of a series of lines corresponding to each discrete core and valence level of the system. The measured binding energy, EB, given by EB = hv−EK, where EK is the kineticenergy relative to the vacuum level, may be equated with the orbital energy derived from a Hartree-Fock SCF calculation of the system under consideration (Koopmans theorem).

X-ray mapping without STEM

1994 ◽  
Vol 52 ◽  
pp. 508-509
Author(s):  
Judith M. Brock ◽  
Max T. Otten
Keyword(s):  
Life Science ◽  
Materials Science ◽  
Chemical Elements ◽  
Full Description ◽  
Scanning System ◽  
Elemental Distribution ◽  
X Ray ◽  
Transmission Electron ◽  
Distribution Of Elements ◽  
Made In

A knowledge of the distribution of chemical elements in a specimen is often highly useful. In materials science specimens features such as grain boundaries and precipitates generally force a certain order on mental distribution, so that a single profile away from the boundary or precipitate gives a full description of all relevant data. No such simplicity can be assumed in life science specimens, where elements can occur various combinations and in different concentrations in tissue. In the latter case a two-dimensional elemental-distribution image is required to describe the material adequately. X-ray mapping provides such of the distribution of elements.The big disadvantage of x-ray mapping hitherto has been one requirement: the transmission electron microscope must have the scanning function. In cases where the STEM functionality – to record scanning images using a variety of STEM detectors – is not used, but only x-ray mapping is intended, a significant investment must still be made in the scanning system: electronics that drive the beam, detectors for generating the scanning images, and monitors for displaying and recording the images.

scholarly journals Compositional Variation of Eudialyte-Group Minerals from the Lovozero and Ilímaussaq Complexes and on the Origin of Peralkaline Systems

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 548
Author(s):  
Lia N. Kogarko ◽  
Troels F. D. Nielsen
Keyword(s):  
Linear Trend ◽  
Major And Trace Elements ◽  
High Tech ◽  
Compositional Variation ◽  
Elemental Distribution ◽  
Magma Chambers ◽  
Eudialyte Group ◽  
System A ◽  
Distribution Of Elements ◽  
World Class

The Lovozero complex, Kola peninsula, Russia and the Ilímaussaq complex in Southwest Greenland are the largest known layered peralkaline intrusive complexes. Both host world-class deposits rich in REE and other high-tech elements. Both complexes expose spectacular layering with horizons rich in eudialyte group minerals (EGM). We present a detailed study of the composition and cryptic variations in cumulus EGM from Lovozero and a comparison with EGM from Ilímaussaq to further our understanding of peralkaline magma chambers processes. The geochemical signatures of Lovozero and Ilímaussaq EGM are distinct. In Lovozero EGMs are clearly enriched in Na + K, Mn, Ti, Sr and poorer Fe compared to EGM from Ilímaussaq, whereas the contents of ΣREE + Y and Cl are comparable. Ilímaussaq EGMs are depleted in Sr and Eu, which points to plagioclase fractionation and an olivine basaltic parent. The absence of negative Sr and Eu anomalies suggest a melanephelinitic parent for Lovozero. In Lovozero the cumulus EGMs shows decrease in Fe/Mn, Ti, Nb, Sr, Ba and all HREE up the magmatic layering, while REE + Y and Cl contents increase. In Lovozero EGM spectra show only a weak enrichment in LREE relative to HREE. The data demonstrates a systematic stratigraphic variation in major and trace elements compositions of liquidus EGM in the Eudialyte Complex, the latest and uppermost part of Lovozero. The distribution of elements follows a broadly linear trend. Despite intersample variations, the absence of abrupt changes in the trends suggests continuous crystallization and accumulation in the magma chamber. The crystallization was controlled by elemental distribution between EGM and coexisting melt during gravitational accumulation of crystals and/or mushes in a closed system. A different pattern is noted in the Ilimaussaq Complex. The elemental trends have variable steepness up the magmatic succession especially in the uppermost zones of the Complex. The differences between the two complexes are suggested to be related dynamics of the crystallization and accumulation processes in the magma chambers, such as arrival of new liquidus phases and redistributions by mush melts.

AIN/GaN and AIGaN/GaN Heterostructures Grown by HVPE on SiC Substrates

1997 ◽  
Vol 482 ◽  
Author(s):  
Yu. V. Melnik ◽  
A. E. Nikolaev ◽  
S. I. Stepanov ◽  
A. S. Zubrilov ◽  
I. P. Nikitina ◽  
...  
Keyword(s):  
Growth Rate ◽  
Electron Beam ◽  
Vapor Phase ◽  
Electron Spectroscopy ◽  
Auger Electron ◽  
Hydride Vapor Phase Epitaxy ◽  
X Ray Diffraction ◽  
Electrical Measurements ◽  
X Ray ◽  
Micro Analysis

AbstractGaN, AIN and AIGaN layers were grown by hydride vapor phase epitaxy. 6H-SiC wafers were used as substrates. Properties of AIN/GaN and AIGaN/GaN structures were investigated. AIGaN growth rate was about 1 μm/min. The thickness of the AIGaN layers ranged from 0.5 to 5 μm. The AIN concentration in AIGaN layers was varied from 9 to 67 mol. %. Samples were characterised by electron beam micro analysis, Auger electron spectroscopy, X-ray diffraction and cathodoluminescence.Electrical measurements performed on AIGaN/GaN/SiC samples indicated that undoped AIGaN layers are conducting at least up to 50 mol. % of AIN.

scholarly journals Advanced test of the model stellar atmospheres: the nature of the light variability of magnetic chemically peculiar stars

2008 ◽  
Vol 4 (S252) ◽  
pp. 347-348
Author(s):  
J. Krtička ◽  
Z. Mikulášek ◽  
J. Zverko ◽  
J. Žižňovský ◽  
P. Zvěřina
Keyword(s):  
Chemical Elements ◽  
Horizontal Distribution ◽  
Stellar Atmospheres ◽  
Silicon Iron ◽  
Surface Distribution ◽  
Chemically Peculiar ◽  
Peculiar Stars ◽  
Distribution Of Elements ◽  
Chemically Peculiar Stars ◽  
Light Variability

AbstractThe magnetic chemically peculiar stars exhibit both inhomogeneous horizontal distribution of chemical elements on their surfaces and the light variability. We show that the observed light variability of these stars can be successfully simulated using models of their stellar atmospheres and adopting the observed surface distribution of elements. The most important elements that influence the light variability are silicon, iron, and helium.

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