Auger Images Research Articles

New methods for image collection and analysis in scanning Auger microscopy

While scanning Auger micrographs are used extensively for illustrating the stoichiometry of complex surfaces and for indicating areas of interest for fine point Auger spectroscopy, there are many problems in the quantification and analysis of Auger images. These problems include multiple contrast mechanisms and the lack of meaningful relationships with other Auger data. Collection of multielemental Auger images allows some new approaches to image analysis and presentation. Information about the distribution and quantity of elemental combinations at a surface are retrievable, and particular combinations of elements can be imaged, such as alloy phases. Results from the precipitate hardened alloy A1-2124 illustrate multispectral Auger imaging.

Surface compositions of the two phases of differently prepared Ni-Cr-Al and Ni-Cr-Al-Zr samples

The surface compositions of the α/β and γ/γ' phases of different metallographic preparations of Ni-15Cr-24Al and Ni-15Cr-24Al-0.3Zr (at%) alloys are presented. Surfaces investigated include a mechanically polished surface for both alloys, a mechanically polished acid etched surface of the Ni-Cr-Al-Zr both before heating and after heating to 600°C for several hours, and the underlying surface of this latter sample exposed by ball cratering. Both phases of all surfaces considered show depletion of Al. It is concluded that the Al depletion is not an artefact of the sample metallographic preparation or the analytical procedure. This is supported by analysis of the composition of a sample scratched in situ under UHV. It is further concluded that the Al depletion is due to oxidation during bakeout. Cr-rich features in both the α/β and γ/γ' phases are reported. An optimal two dimensionally smoothed Cr Auger image is presented showing these features which are considered to be due to the αCr solid solution particles or clustering of these particles in the α/β phase and the Ni solid solution component in the γ/γ' phase.

Chemical constituents of eroded gun surfaces

A study has been made on the distribution of chemical constituents on eroded surfaces of retired guns using the instrument, PHI Model 548 ESCA/Auger with a SAM attachment. Three eroded gun tubes in progressive stages of corrosion were examined by Scanning Auger Microprobe. The elemental constituents were first established from Auger spectra of various sampling spots using a wide primary electron beam, and then Auger images of selected elements were obtained from a beam width approximately 5 μm. The chemical elements present on the top surface layer depend largely on the propellants used in firings. The prominent features of the eroded surface were extensive oxidation and severe thermal cracking. The heterogeneous distribution and the accumulation of the major elements which participated in the surface erosion are imaged and illustrated.

Some results of investigations into relationships between a few elements of nodular graphite cast iron and nodular graphite

Some Results of Investigations Into Relationship Between a Few Elements of Nodular Graphite Cast Iron and Nodular Graphite An investigation of the fractured surfaces of pins, having a diameter of 1.5 mm, obtained during the production of commercial nodular cast irons of Meehanite types is reported. The investigation was performed using a scanning electron microsopec (SEM) with an attachment for energy dispersive analysis and scanning Auger microprobe (SAM), where the principal attention was given to SAM. Point analysis, Auger images and Auger line scans were performed on the fractured surfaces and also approximately 200 A and 1μm below the surface. The nodule/metal and intercrystalline graphite interfaces in the investigated iron were free of foreign elements.

Observation of surface diffusion by biassed secondary electron imaging: The case of Ag/W(110)

The system Ag/W(110) has been studied by SEM, AES, RHEED and a simple new technique, biassed secondary electron imaging. By depositing Ag past an edge and through a mask of holes, surface diffusion of Ag has been observed, in competition with the nucleation of crystals on top of adsorbed multilayers. The extent of surface diffusion, and of nucleation, is highly temperature dependent in the range 200–550°C. The biassed secondary electron technique is shown to have a much better signal-to-noise ratio than equivalent Auger electron line-scans or images; the contrast arises from changes in secondary electron production and detection, especially changes in work function and backscattering. The qualitative conclusions of the results for interactions between Ag atoms on W(110) are discussed.

Brittle fracture of polycrystalline tungsten

A comparative study of the brittle fracture of three varieties of polycrystalline tungsten has been carried out using mainly impact tests, scanning electron microscopy and Auger spectroscopy. It indicates the occurrence of two modes of brittle fracture, namely cleavage and intergranular fractures, whose proportions depend on temperature and on phosphorus segregation at the grain boundaries. Scanning Auger images indicate unambiguously that phosphorus is only located on the intergranular surfaces. No phosphorus is observed on cleavage planes. Fracture surfaces are the result of the propagation of a crack through the whole sample. As the propagation follows the path which requires the lowest expenditure of energy, it depends both on a geometrical factor and on the respective values of the cleavage (γcl) and intergranular (γl) works of fracture. Our results indicate an increase in γcl and γl with temperature (the effect being more marked in the case of γcl) and a large decrease in γl with phosphorus segregation at the grain boundaries. This impurity produces an intergranular embrittlement of the tungsten.

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...

Ratioed scatter diagrams. An erotetic method for phase identification on complex surfaces using scanning Auger microscopy

By ratioing multiple Auger intensities and plotting a two-dimensional occupational scatter diagram while digitally scanning across an area, the number and elemental association of surface phases can be determined. This can prove a useful tool in scanning Auger microscopic analysis of complex materials. The technique is illustrated by results from an anomalous region on the reaction zone of a SiC/Ti–6A1–4V metal matrix composite material. The anomalous region is shown to be a single phase associated with sulphur and phosphorus impurities. Imaging of a selected phase from the ratioed scatter diagram is possible and may be a useful technique for presenting multiple scanning Auger images.

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.

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.

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.

A SIMS and AES examination of a Cu/Co/Si alloy

AbstractThe present paper deals with SIMS and AES examination of the layer structure developing during the annealing of a Cu/Co/Si alloy. It was discovered from the spectra and Auger images that there is a significant local increase of the concentration of the alloying materials. A surface layer develops during heat treatment of the alloy sample. We prove the presence of CoSi clusters and the joint enrichment of Si and Co.

Synchronous modulation in scanning Auger electron microscopy

The modulation frequency on the cylindrical mirror analyzer of a scanning Auger microscope has been synchronized to the digital scanning system. This technique allows one to obtain an Auger image free from moire patterns which arise from the beat between scanning and modulation frequencies, and permits operation at frequency settings which optimize use of the electronics in the detection system.

Effects of backscattering on the resolution of scanning Auger Microscopy

We have previously shown that the combination of a UHV SEM with a field emmission gun and a CMA for Auger detection is a valuable tool for surface microanalysis /1,2 3/, and we have demonstrated 30nm resolution using conventional N'(E) detection /4/. Although Auger images can be produced in some circumstances with the resolution of the beam diameter, the size of the analysis volume is influenced by backscattered electrons, and this resolution limit has not previously been experimentally determined. In the present preliminary experiments we have observed Auger line scans across abrupt chemical boundaries as a function of incidence angle, ø, and beam energy, Ep. These intensity profiles show reasonable agreement with Monte Carlo calculations /5, 6, 7, 8/ of the spatial distribution of backscattered electrons. For near-normal incidence, most of the Auger current will be emitted from within the primary beam area.A polycrystalline tungsten surface was flashed clean by electron bombardment heating and 2-5pm diam

A digital scanning Auger electron microscope incorporating a concentric hemispherical analyser

A scanning electron microscope with a field-emitting electron gun, digitally controlled scanning and a concentric hemispherical energy analyser is described and compared with different types of energy dispersive scanning electron microscopes. The advantages of hemispherical analysers accessed by electrostatic lenses are flexible electron optical control of working distances and resolving power. A 4 element lens is described which results in an analyser with a 2 eV window over an energy range of 20 eV to 800 eV. Auger images of calcium and sulphur on titanium are given. Spatial resolutions of 50 nm and frame scan times of a few minutes are possible.

Comparison of electron sources for high-resolution Auger spectroscopy in an SEM

The effect of primary beam current and electron spot size on the Auger image resolution and signal-to-noise ratio (S/N) have been determined for field emission and thermionic emission sources. It is demonstrated that by use of a FE source and nA primary beam currents, an Auger image resolution of less than 1000 Å can be obtained. The major limitation to Auger spatial resolution is attributed to backscattered electrons. A LaB6 source is clearly superior to FE sources at primary beam currents of greater than 1×10−8 A.

New SEM–Auger microanalyzer with UHV capability

The design and performance of a new Auger microanalyzer (EMAS) with the capability of UHV scanning electron microscope (SEM) is described. The incident electron beam is focused by a magnetic lens system, and the spatial resolution is below 0.5 μm for the Auger analysis mode and on the order of 100 Å in the SEM mode. Possible modes of analysis include point analysis, line analysis, and Auger image mapping, in addition to secondary electron and absorbed current imaging. The depth profiling of chemical composition in submicron structures is also provided by use of ion beam etching. An air‐locked sample changer is employed to keep the vacuum of the system at 10−7 Pa during specimen loading and unloading. Three examples of applications to microelectronics devices are presented.

Abstract: Scanning microspot Auger spectroscopy and microscopy as a device diagnostic technique

Auger spectroscopy with a focused electron beam in the scanning electron microscope (SEM) has been applied as a diagnostic technique for solid state devices. The focused electron beam in a SEM allows one to determine the surface topography (SEM mode) of the specimen and then determine the Auger spectra of selected areas. In addition, a scanning Auger image may be obtained by using the amplitudes of the Auger peaks for intensity or amplitude modulation of the cathode ray tube. In the present system, a SEM designed with a dry-pump UHV system and equipped with an Auger electron detector and sputter etching capability has been applied to device failure diagnostics. Vacuum levels of 3×10−9 Torr (4×10−7 Pa) at the specimen stage have been obtained with an electro-ion-titanium sublimation pumping system. A secondary electron image resolution of less than 2000 Å with Auger spectra of features less than 1 μm have been attained. Gray-scale images from Auger electrons have been obtained at beam currents of 10−6 to 10−8 A. The Auger electron detector used has an energy resolution of 0.5% and transmission of 10%. A sputter-etching capability for sputter cleaning of specimen surfaces prior to analysis is provided. The energy source of the SEM is a triode electron gun with a high-emission filament (3.5×105 A cm−2 sr−1 at 20 kV). The relationship between probe current and diameter for a fixed working distance was measured in order to determine the optimum spatial resolution for AES. For optimum conditions and high beam currents (10−6 A) spatial resolution is essentially determined by the probe diameter. For low beam currents, it is shown that parameters such as escape depth, atomic number, surface area, and beam energy affect spatial resolution. AES recording time and its variation with signal-to-noise ratio has also been determined. The normal modes for microspot AES investigations in the SEM include spot analysis, line scan, and Auger electron imaging. For Auger imaging the vacuum levels and probe currents are shown to be the critical parameters since the time to record such an image is usually greater than five minutes.