Auger Scanning Electron Microscopy Research Articles

Scanning Auger microscopy study of lanthanum partitioning in sphene-based glass‐ceramics

Abstract Glass-ceramics are being investigated as possible hosts for the radioactive wastes that would result from recycling irradiated nuclear fuels. For a glass‐ceramic to be a superior waste form to a single-phase glass, some of the long-lived actinides and fission products must be preferentially incorporated into the lattice of the crystalline phase. The partitioning of lanthanum in sphene-based glass‐ceramics has been studied by scanning Auger electron microscopy for lanthanum concentrations from 0.2 to 2.0 mol.%. Sphene crystals (CaTiSiOs) were located in the silica-rich glass matrix by recording digital Auger images of the calcium and titanium distributions. The sphene crystals .were typically 0.5 to 5 μn in size and occupied approximately 40% of the total specimen volume. Auger spot analyses revealed that lanthanum was strongly partitioned (by at least a factor of 10) into the sphene phase of phosphorus-free glass-ceramics; however, when a small amount of phosphorus (0.7 mol.%) was included in the...

Scanning auger microanalysis study of 304 stainless steel surface irradiated with helium and argon ions

Microanalysis of 304 stainless steels whose surfaces were irradiated with 100 keV He and 2 keV Ar ions was performed by means of a scanning Auger electron microscopy technique. Many blisters and exfoliated layers appeared on the surfaces with the He irradiation. Auger analysis revealed that the surface of exfoliated layers was enriched with Cr-oxide. The thickness of the enriched layer was observed to be more than 10 nm in depth. The result suggests that the irradiation induced segregation of Cr-oxide was associated with the exfoliation of blister skins. The surfaces with the Ar irradiation showed many sputter-cones. The Auger analysis of these sputter-cones revealed that C atoms were deposited at the top of the sputter-cones. The result suggested that the sputter-cones were formed due to the deposition of C atoms whose sputtering yield was smaller than the stainless steel.

Instrumental effects in quantitative Auger electron spectroscopy

Experiments used to determine the energy resolution, field of view, depth of field and instrumental response of a concentric hemispherical analyser (CHA) are described. The effect of analysis energy on the size and shape of the field of view is investigated using a procedure which employs the imaging facilities of a scanning Auger electron microscope. The transmission of the CHA, for different input lens retardation ratios, is found, firstly, in an experiment using a thermionic electron source and, secondly, using the departure from linearity of spectra plotted in a log N ( E) vs log E form. Such a plot is found to provide a convenient and sensitive method of detecting possible sources of error, such as mispositioning of the sample surface or electrostatic charging of material in the specimen region. These findings indicate the need for careful mechanical alignment of the spectrometer and for the sample surface to be positioned reproducibly within ±200 μm of the centre of the CHA field of view to ensure an accuracy of better than ±10% in estimates of Auger current. A procedure for repositioning the specimen to give a reproducibility of ca +2% in signal measurement is deduced. Computer techniques, to correct for effects of both spectrometer transmission and detector efficiency, are described.

The influence of X‐ray‐induced Auger electrons in quantitative electron‐induced Auger spectroscopy

AbstractThe X‐ray‐induced Auger electron intensities are often neglected in quantitative electron‐induced Auger electron spectroscopy. For the first time, analytical expressions are given for these relative intensities (induced by continuous or characteristic X‐rays). The influence of the operating voltage and the effects of the bulk and surface compositions are also discussed. Some numerical values show that at high operating voltages these intensities can reach several tens of percent of the Auger intensity directly created by the incident electron beam. Such contributions increase the apparent backscattering parameter r, therefore, they cannot be neglected when accurate quantitative analysis is required. Though such influences are troublesome for the analysis of small precipitates in scanning Auger electron microscopy, they can also give additional information on the bulk composition of a sample.

Weld Metal Fracture Modes in a Series of HSLA Steel Weldments

A series of welds were made by the Submerged Arc Welding process using a single base plate but different flux and wire combinations. The microstructure-mechanical property relationship of the welds was studied. In addition to the normal ductile and cleavage fracture modes expected for weld metals of the composition range studied, extensive grain boundary fracture (along prior austenite grain boundaries) was found in one weld that had a fully acicular ferrite microstructure. Scanning Auger and conventional scanning electron microscopy were used to characterize the composition and microstructure at the grain boundaries in the weld metal. Résumé Une série de soudures a été réalisée en employant un arc submergé pour différentes combinaisons de fondants et de tiges à souder. La relation entre la microstructure et les propriétés mécaniques des soudures a été déterminée. En plus des modes normaux de rupture pour ce type de soudure, une fracture intergranulaire prononcée a été observée dans une soudure qui possédait une microstructure de ferrite aciculaire. Les techniques de microscopie électronique à balayage et d'Auger en balayage ont été utilisées pour caractériser la composition et la microstructure aux joints de grains de la soudure.

Mathematical and physical considerations on the spatial resolution in scanning Auger electron microscopy

A simple mathematical model is used to evaluate the spatial resolution in scanning Auger microscopy (SAM). This model includes for the first time all the possible causes of Auger electron production and broadening (impact parameter effect, backscattering effect, X-ray induced Auger electron production). The conclusions depend greatly upon the criteria of resolution used (Δ(50) or δ(10–90)). Physical limitations due to the impact parameter and influence of X-ray-induced electron production are established. This model is in good agreement with the experimental data. Applications to scanning electron microscopy and other microanalysis techniques are also suggested.

Techniques for the correction of topographical effects in scanning Auger electron microscopy

A number of ratioing methods for correcting Auger images and linescans for topographical contrast are tested using anisotropically etched silicon substrates covered with Au or Ag. Thirteen well-defined angles of incidence are present on each polyhedron produced on the Si by this etching. If N1 electrons are counted at the energy of an Auger peak and N2 are counted in the background above the peak, then N1, N1−N2, (N1−N2)/N2, and (N1−N2)/(N1+N2) are measured and compared as methods of eliminating topographical contrast. The latter method gives the best compensation but can be further improved by using a measurement of the sample absorption current. Various other improvements are discussed.

Software for scanning Auger microscopy

SUMMARYThe procedures embodied in a program suite designed for use with a computer controlled digital scanning Auger electron microscope are elucidated. These include techniques for the collection and subsequent processing of spectra, linescans and images. Schemes found to be the most efficient for the normalization of data to correct for both incident beam current fluctuations and sample surface topography are explained. Averaging and economical smoothing algorithms are considered as a means of improving the signal‐to‐noise ratio when working with high spatial resolution (probe diameter less than 150 nm), which necessarily limits the available beam current to less than about 3 nA. Emphasis is laid upon the desirability of obtaining quantitative information and to this end software routines for use in ascertaining surface chemical composition from spectra are described. These include numerical differentiation of spectra and modelling and subtraction of the secondary electron background from beneath an Auger feature. The transfer of data to a faster computer and more lengthy processing operations, for improving the quality of Auger maps, are also discussed.

Scanning auger electron microscopy with high spatial or high energy resolution

An all-electrostatic, computer controlled, high spatial and high energy resolution, scanning Auger electron microscope incorporating a RHEED camera is described. The electron column has a 50 nm spatial resolution at 55 mm working distance. The energy analyser allows high energy resolution of up to 630 or constant energy windows of down to 1 eV over the energy range of 20 eV to 1000 eV. A system software allowing flexibility of the computer control is described. 128 × 128 pixel Auger images of Al and SiO 2, with frame scan times of the order of 8 min, are presented.

Strong oxide-oxide interactions in silica-supported Fe 3O 4: III. Water-induced migration of silica on geometrically designed catalysts

Geometrically designed catalysts were prepared by evaporating silica onto part of the surface of an oxidized iron foil. These model catalysts allowed scanning Auger electron microscopy to be used to study the mobility of silica in different gas environments at ca. 670 K and atmospheric pressure. For the iron oxide/silica model catalyst, silica migration was observed upon treatment in H 2 O CO or H 2 O H 2 gas mixtures, while significant migration was not observed upon treatment in CO 2 CO or O 2. In particular, that portion of the iron oxide surface, initially free of Si, became covered by Si after treatment in H 2 O CO or H 2 O H 2 , while it remained essentially free of Si after treatment in CO 2 CO or O 2. Preliminary investigation of a similarly prepared Pt SiO 2 catalyst indicated that the phenomenon of SiO 2 mobility at ca. 660 K and atmospheric pressure may be of importance for other silica-supported catalyst systems.

Observation of surface segregation of sulphur in CuNi alloys at elevated temperature with scanning Auger electron microscope

Surface segregations of Cu and S in a CuNi (50wt%) alloy at elevated temperatures of ∼600°C were studied under scanning Auger electron microscope, JAMP-3. Scanning images of S, Cu and Ni Auger signals have revealed that the surface segregations of both Cu and S take place preferentially depending on grains and the contrasts in S and Cu Auger images are complementary. This leads to another confirmation of the previous work, namely, that the surface segregation of Cu is considerably suppressed by the existence of S at the outermost atom layer.

Observation of surface segregation of sulphur in Cu-Ni alloys at elevated temperature with scanning auger electron microscope

Surface segregations of Cu and S in a Cu-Ni (50wt%) alloy at elevated temperatures of ∼600°C were studied under scanning Auger electron microscope, JAMP-3. Scanning images of S, Cu and Ni Auger signals have revealed that the surface segregations of both Cu and S take place preferentially depending on grains and the contrasts in S and Cu Auger images are complementary. This leads to another confirmation of the previous work, namely, that the surface segregation of Cu is considerably suppressed by the existence of S at the outermost atom layer.

Scanning electron-stimulated desorption microscopy of model-biological surfaces.

Electron-stimulated desorption (ESD) of ions and neutrals from surfaces has been used to study chemisorption in many simple gas–solid systems1,2, but there has been much less effort devoted to ESD studies with significant spatial resolution3–7. ESD contrasts with scanning electron microscopy because ESD signals depend sensitively on the coverage and binding of an adsorbed species1. Applying scanning ESD to biological surfaces permits the surface chemical variations to be mapped using simple low mass adsorbates8 in comparison with conventional electron microscopy of biological matters which relies on heavy-metal stain technology9. We show here how scanning ESD can complement scanning Auger electron microscopy in mapping the surface chemistry of biological substrates. A model biological substrate constructed from a deposited synthetic polypeptide monolayer (polymethyl-glutamate) is used as the controlled sample surface. Micrographs display a spatial variation in H+ desorption with a resolution of 10−4 cm. We also discuss limitations to resolution as dictated by signal-to-noise considerations. The contrast mechanism would be useful for studying the important biological surface problems such as membrane morphology, cell-interfacial composition, and cell-to-cell adhesion.

Development of a Scanning Auger Electron Microscope Equipped with a Field Emission Gun

Development of a Scanning Auger Electron Microscope Equipped with a Field Emission Gun

Monte Carlo calculation approach to quantitative Auger electron spectroscopy

A Monte Carlo calculation technique based on both the partial wave expansion method for elastic scattering and Krefting and Reimer’s treatment for inelastic scattering was applied for quantitative study by Auger electron spectroscopy. The theory has described the experiment of energy and angular distributions of backscattered electrons with considerable success. Dependence of the Auger signal generation on primary electron energy was investigated with a scanning Auger electron microscope, and the result was compared with the theory for a number of elements of practical interest. Through this, we have found that the present Monte Carlo approach allows us to evaluate contributions of backscattered electrons to Auger signal generation leading to more comprehensive quantitative AES study.

Probing multicomponent materials by Auger-electron-spec-trometry

In quantitative Auger electron spectroscopy (AES) analysis, the emphasis is generally laid on the vertical variation in signal from an element versus the variation in composition from the surface to the bulk. In such a framework, a quantitative method has been previously developed by the authors, which provides such information as the thickness of a segregated layer or the initial growth process of a thin film. Here, this method is applied to study a horizontal variation of composition, i.e. the signal variation of a scanning Auger electron microscope (SAM) when the incident electron beam is scanned across the boundary of grains of different composition. In order to evaluate the SAM resolution, for the case of an ideal step boundary, calculations are carried out by taking into account the influence of angular distributions, of attenuation length of primary, secondary and Auger electrons, of secondary electron yield and of the beam shape (point, Gaussian or columnar). The results for the cases of Ag-Au, Si-Ag and Be-Cu, lead to a SAM spatial resolution of ≈30 Å for a primary beam of 2–3 keV with an infinitesimal diameter and a resolution of the order of the beam size for Gaussian and columnar beams. Extrapolation of this method to a primary beam energy of 20 keV is discussed and leads to results similar to those obtained by Monte Carlo simulation.

Synchronous modulation in scanning Auger electron microscopy. (USA)

Synchronous modulation in scanning Auger electron microscopy. (USA)

Characterization of AlxGa1−xAs–GaAs layer structures by scanning Auger electron microscopy

Crater-edge and conventional depth profiling have been used to characterize epitaxial films of AlxGa1−xAs grown by LPE on GaAs (100) substrates. In order to reduce damage low energy (?500 eV) argon ions were used. From the high energy Auger transitions values of x were derived with an accuracy Δx=0.01. Minimum chemical interface widths were observed of 2.5 nm, independent of depth below the surface.

角度研摩法を用いた深さ方向高分解能オージェ分析とその半導体素子への応用

The element in-depth profiles have been measured by scanning Auger electron microscopy in conjunction with the angle-lap profiling method, instead of the conventional Auger sputter profiling method. The angle-lap profiling method has advantages that the depth resolution is independent of depth below the surface and that there is no necessity for taking account of sputter broadening effect which complicates the sputter profiling analysis. It is shown that the actual interface width can be obtained by the correction taking account of several broadening factors such as Auger electron escape depth, incident electron beam diameter and surface roughness induced by angle-lapping. This profiling method has applied to the analysis of InGaAsP/InP double-hetero interface and GaAs ohmic contact reaction.

Digital integrator in scanning Auger electron microscopy

A digital integration technique based on the use of V/F and D/A converters accompanied by the digital scanning and the synchronous square-wave modulation has been introduced in the scanning Auger electron microscopy. This integrator allows us to perform integration in very high efficiency leading to high signal to noise ratio and to high spatial resolution of the Auger pictures.