Auger Imaging Research Articles

Cross-section Auger imaging: A suitable tool to study aging mechanism of conversion type electrodes

To date, the study of conversion type reactions at both the nanometer and electrode scales over long term cycling still remains very challenging. Here, we show that combining Auger imaging with electrodes cross-section preparation by ion-milling is a suitable tool to study the aging mechanism of conversion type electrodes. Importantly, for NbSnSb-based electrodes, cycled at 25 °C and 60 °C without and with additives, this innovative approach reveals a micron scale spreading of the NbSnSb particles. It thus proves the electrochemical conversion reaction even after 400 cycles and highlights the role of the inactive Nb element in the long term reversibility, which was unexpected. Interestingly, a shell to core expansion/break up of NbSnSb particles is observed and the large and highly porous structures formed led to the electrodes porosity filling and electrodes thickness increase. The formation of the SEI is located inside the porous NbSnSb shells. At 25 °C without additive, this phenomenon is so important that the ionic and/or electronic conductivities are completely altered, which explains the rapid capacity drop to zero. Overall, cross-section Auger imaging will benefit not only to the study of conversion/alloying based batteries but also to all-solid-state batteries aging mechanism for which buried interfaces have to be reached.

Neon isotopes in individual presolar low-density graphite grains from the Orgueil meteorite.

We present He and Ne isotopes of individual presolar graphite grains from a low-density separate from Orgueil. Two grain mounts were analyzed with the same techniques but in a different sequence: The first one was measured with NanoSIMS followed by noble gas mass spectrometry, and the second one in reverse order. No grain contained 4He and only one grain on the second mount contained 3He. On the first mount, the grains had been extensively sputtered with NanoSIMS ion beams prior to noble gas analysis; we found only one grain out of 15 with presolar 22Ne above detection limit. In contrast, we found presolar 22Ne in six out of seven grains on the second mount that was not exposed to an ion beam prior to noble gas analysis. All 22 grains on the two mounts were imaged with scanning electron microscopy (SEM) and/or Auger microscopy. We present evidence that this contrasting observation is most likely due to e-beam-induced heating of the generally smaller grains on the first mount during SEM and Auger imaging, and not primarily due to the NanoSIMS analysis. If thermal contact of the grains to the substrate is absent, such that heat can only be dissipated via radiation, then the smaller, sputter-eroded grains are heated to higher temperatures such that noble gases can diffuse out. We discuss possible gas loss mechanisms and suggest solutions to reduce heating during e-beam analyses by minimizing voltages, beam currents, and dwell times. We also found small amounts of 21Ne in five grains. Using isotope data we determined that the dominant sources of most grains are core-collapse supernovae, congruent with earlier studies of low-density presolar graphite from Murchison. Only two of the grains are most likely from AGB stars, and two others have an ambiguous origin.

Nucleation of Sn and Sn–Cu alloys on Pt during electrodeposition from Sn–citrate and Sn–Cu–citrate solutions

The initial stages of Sn and Sn–Cu electrodeposition from Sn–citrate and Sn–Cu–citrate solutions on Pt were studied using both current-controlled and potential-controlled electrochemical techniques. For both Sn–citrate and Sn–Cu–citrate solutions, when the current density is controlled to lower than 15 mA/cm 2, potentials remain almost constant which is appropriate to plate dense and uniform films. When the current density is controlled to between 25 and 35 mA/cm 2, potentials drop quickly initially, followed by a gradual increase to a constant value. When current density is controlled to higher than 50 mA/cm 2, potential oscillation happens, and significant hydrogen evolution prevents the formation of dense and continuous Sn and Sn–Cu films. A constant transition time constant indicates a diffusion-controlled process. The diffusion coefficient calculated from the Sand equation is about 3.8 × 10 −6 cm 2/s for the Sn–citrate solution and 4.1 × 10 −6 cm 2/s for the Sn–Cu–citrate solution. The morphology of both Sn and Sn–Cu deposits plated under different potentials was examined by atomic force microscopy (AFM) and the distribution of each element were analyzed using Auger imaging. Analysis of both the electrochemical results at −0.72, −1.1 and −1.5 V and AFM images for both Sn and Sn–Cu deposits at −1.1 and −1.5 V suggested progressive nucleation controlled by diffusion for both Sn and Sn–Cu electrodeposition. Tin reacted with Pt to form PtSn 4, and co-deposited with Cu to form Cu 6Sn 5 during nucleation, with more Sn forming at higher applied potentials.

Ion etching methods for depth profiling of complex three-dimensional samples in combination with scanning Auger electron microscopy

Ion etching of surfaces combined with detection of secondary events (particles or radiation emitted) are used for depth profiling of samples with interesting features at-, near-, or somewhat below the surface. These methods are destructive and relatively slow, and compete with non-destructive methods like Rutherford backscattering spectroscopy, energy-dispersive X-ray spectroscopy in the scanning electron microscope or angle-resolved photoemission spectroscopy, which are non-destructive and relatively faster methods. In this work we have concentrated on the use of noble gas ion sputtering with low-energy beams in combination with electron excited Auger electron spectroscopy and imaging for analysis of nanostructured and microstructured samples. No attempt will be made here to justify this method over the other methods, as their relative merits depend on the nature of the sample and the problem at hand. We have thus chosen to study samples and problems for which this technique would be obvious to use. This work is also aimed at providing practical standards and guidelines (“metrology”) for the use of the technique in the context of industrial nanotechnology. The use of Auger electron spectroscopy instead of photoemission spectroscopy is preferred for laterally non-uniform samples due to the presently better resolution capabilities of electron beams and narrower information depths of typical Auger electron transitions. The use of Auger electrons for concentration sampling, and low-energy beams of noble gas ions for sputtering, reduces the adverse influence of atomic mixing. In this report two systems are intensively studied with sputter profiling in combination with Auger electron spectroscopy and scanning electron imaging: a hard disk and a surface of a stainless-steel sample.

Spatial control over atomic layer deposition using microcontact-printed resists

Area-selective thin film growth by atomic layer deposition (ALD) has been achieved on octadecyltrichlorosilane (ODTS) patterned substrates. Patterned hydrophobic self-assembled monolayers (SAMs) were first transferred to silicon and yttria-stabilized zirconia (YSZ) substrates by microcontact printing. Subsequently, films of either HfO 2 or Pt were grown selectively on the SAM-free regions of the surface, while ALD was blocked in regions where ODTS was present. The deposited pattern was readily observed through scanning electron microscopy and scanning Auger imaging, demonstrating that soft lithography is a simple and promising method to achieve area-selective ALD. The selectivity of the soft lithography-based method and the subsequent pattern resolution was compared for Pt versus HfO 2. It was found that using ODTS films, it is easier to achieve complete deactivation of Pt than HfO 2.

Area Selective Atomic Layer Deposition by Soft Lithography

AbstractArea selective HfO2 thin film growth through atomic layer deposition (ALD) has been achieved on octadecyltrichlorosilane (ODTS) patterned Si substrates. Patterned hydrophobic self-assembled monolayers (SAMs) were first transferred to Si substrates by micro-contact printing. Using hafnium-tetrachloride or tetrakis(dimethylamido) hafnium(IV) and water as ALD precursors, amorphous HfO2 layers were then grown selectively on the SAM-free regions of the surface where native hydroxyl groups nucleate growth from the vapor phase. The HfO2 pattern was readily observed through scanning electron microscopy and scanning Auger imaging, demonstrating that soft lithography is a simple and promising method to achieve area selective ALD. To evaluate the selectivity, the resolution of the soft lithography based method was compared with that of area selective ALD of HfO2 by selective surface modification of patterned silicon oxide obtained using long-time SAM exposure. It was found that the selective surface modification showed much higher spatial resolution and selectivity, an observation consistent with previous studies indicating that highly ordered and densely packed ODTS films were important to achieve complete deactivation.

Use of Auger imaging for three‐dimensional visualization of interface morphology at isoconcentration

AbstractDepth or line profiles on polished sections only provide partial and local information about the chemical distribution at the interface between two solids. Germination and growth, which happen during the reaction phase, can only be explored by a three‐dimensional in‐situ visualization. The most powerful means presently at our disposal are: (i) for non‐destructive analysis, synchrotron microtomography, with a maximum lateral resolution of 0.29 µm (ESRF, European Synchrotron Radiation Facility, Grenoble, France), and, (ii) for destructive analysis, SIMS image reconstruction (resolution 0.2 µm), with a difficult quantitative interpretation.The object of this paper is to demonstrate that a 3D analysis of a series of AES images is possible at an unrivalled spatial resolution (lateral and depth) and coupled with chemical analysis.The interaction between titanium and carbon at moderate temperatures is considered here to illustrate the method. The sample is elaborated from a polished substrate of carbon on which a thin layer of titanium is deposited by PVD. Thereafter the sample has been thermally treated under secondary vacuum.The data set comprises 50 images (squares of side 7 µm) separated by 20 nm, yielding to an analysis volume corresponding to a parallelepiped of 7 × 7 × 1 µm3. On a sample maintained at 450 °C for 30 min, the formation of TiC islands on a thickness of about 100 nm has been observed. Copyright © 2004 John Wiley & Sons, Ltd.

Evidence for Localization of Reaction upon Reduction of Carbon Tetrachloride by Granular Iron

The distribution of reaction sites on iron particles exposed to water containing carbon tetrachloride has been examined by measuring the locations of reaction products. The uniformity or localization of reaction sites has implications for understanding and modeling the reduction of environmental contaminants by iron in ground water systems. Granular iron surfaces similar to those being used for environmental remediation applications were studied using surfaces analysis techniques to develop an understanding of the physical and chemical structure of the surface and oxide films. Scanning Auger microscopy and imaging time-of-flight secondary ion mass spectrometry revealed that granular iron exposed to carbon tetrachloride-saturated water exhibits chloride-enriched regions occurred at pits rather than on the passive oxide film on the metal. Understanding the nature of the local solute reduction sites will play an important role in modeling the kinetics of reaction at passive iron oxide films in environmental systems.

Transfer films and friction under boundary lubrication

The role of transfer phenomena in the mechanisms of friction reduction by organic molybdenum compounds is studied with the aid of ultrahigh vacuum (UHV) analytical tribometry. Additives used are zinc dithiophosphate (Zndtp), molybdenum dithiophosphate (Modtp), molybdenum dithiocarbamate (Modtc) and Modtc/Zndtp combinations. Experiments involve UHV friction tests on tribofilms formed previously and in situ surface analyses by Auger electron spectroscopy (AES) and imaging. In the presence of Modtc, friction reduction was found to be associated with the transfer of highly dispersed MoS 2 as isolated sheets, from the tribofilm to the slider. In the presence of Modtp (or the mixture Modtc/Zndtp), a two-step tribochemical reaction is generally observed. First, phosphate from the film is transferred to the oxide on the pin and the friction coefficient is about 0.3, after an induction period of a few cycles, pure MoS 2 single sheets are transferred to the pin and the phosphate is eliminated as wear debris from the contact zone. Friction is then at its lowest value (0.02). The chemistry of the transfer phenomena is modeled using the hard and soft acid and base (HSAB) principle as described by Pearson. The overall data suggest that friction behavior under boundary lubrication with additives may be directly related to molecular scale transfer mechanisms in general.

XPS, AES and ToF‐SIMS investigation of surface films and the role of inclusions on pitting corrosion in austenitic stainless steels

Chemical inhomogeneities (inclusions) present in the alloy are known to affect the stability of the passive film on stainless steels in the presence of chloride ions. In this work, three surface analytical techniques— XPS, AES and time-of-flight SIMS (ToF-SIMS)— have been used to characterize the surface films formed on stainless steels following mechanical polishing and immersion in an aggressive 6% FeCl3 solution, which is utilized for testing the pitting corrosion resistance of stainless steels. Two 18Cr8Ni stainless steels were investigated: one with a low sulphur content, DIN 1.4301 (0.003% S), and one with a high sulphur content, DIN 1.4305 (0.29% S). The XPS results show that the surface films on both steels are composed of mixed iron–chromium oxyhydroxides with a higher chromium content compared to the bulk composition. The average passive film composition and the film thickness remained unchanged despite increasing sulphur content in the steel after mechanical polishing. Angle-resolved XPS results suggest the presence of hydroxides in the outer layer of the passive film, which is confirmed by ToF-SIMS its high surface sensitivity. Auger and ToF-SIMS imaging with high lateral resolution allow the inclusions to be characterized: sulphur and manganese maps show the power of imaging SIMS for studying the distribution of elements that are present in very low concentrations. It is shown that on the MnS part of the inclusions no (protective) oxide or hydroxide film is formed after mechanical polishing. This might be the reason for the well-documented role of these inclusions as pit initiation sites. Copyright © 2000 John Wiley & Sons, Ltd.

XPS, AES and ToF-SIMS investigation of surface films and the role of inclusions on pitting corrosion in austenitic stainless steels

Chemical inhomogeneities (inclusions) present in the alloy are known to affect the stability of the passive film on stainless steels in the presence of chloride ions. In this work, three surface analytical techniques— XPS, AES and time-of-flight SIMS (ToF-SIMS)— have been used to characterize the surface films formed on stainless steels following mechanical polishing and immersion in an aggressive 6% FeCl3 solution, which is utilized for testing the pitting corrosion resistance of stainless steels. Two 18Cr8Ni stainless steels were investigated: one with a low sulphur content, DIN 1.4301 (0.003% S), and one with a high sulphur content, DIN 1.4305 (0.29% S). The XPS results show that the surface films on both steels are composed of mixed iron–chromium oxyhydroxides with a higher chromium content compared to the bulk composition. The average passive film composition and the film thickness remained unchanged despite increasing sulphur content in the steel after mechanical polishing. Angle-resolved XPS results suggest the presence of hydroxides in the outer layer of the passive film, which is confirmed by ToF-SIMS its high surface sensitivity. Auger and ToF-SIMS imaging with high lateral resolution allow the inclusions to be characterized: sulphur and manganese maps show the power of imaging SIMS for studying the distribution of elements that are present in very low concentrations. It is shown that on the MnS part of the inclusions no (protective) oxide or hydroxide film is formed after mechanical polishing. This might be the reason for the well-documented role of these inclusions as pit initiation sites. Copyright © 2000 John Wiley & Sons, Ltd.

3D characterization of a W/TiN/ Ti/Si contact structure using MULSAM

The W/TiN/Ti/Si contact structures needed for ultra-large-scale integrated circuits have been studied using cross-sectional transmission electron microscopy (TEM) and multi-spectral Auger electron microscopy. Access to the Ti/Si interface for chemical characterization using SEM, Auger and electron energy-loss imaging and spectroscopy has been achieved by using a novel method of bevelled polishing of the silicon substrate material. Cross-sectional TEM was used to calibrate the depth scale in the MULSAM image sets, so allowing measurements of the thicknesses of various interfacial layers and the penetration of the ohmic contacts into the silicon. The TiN layer, providing adhesion of the tungsten as well as acting as a diffusion barrier, appears to have a domed shape, which penetrates the tungsten overlayer to a greater extent in the contact centres. The results of this work, combined with earlier, related, studies, enable a three-dimensional characterization of the bottom and sidewall structures in these contacts. © 1998 John Wiley & Sons, Ltd.

3D characterization of a W/TiN/ Ti/Si contact structure using MULSAM

The W/TiN/Ti/Si contact structures needed for ultra-large-scale integrated circuits have been studied using cross-sectional transmission electron microscopy (TEM) and multi-spectral Auger electron microscopy. Access to the Ti/Si interface for chemical characterization using SEM, Auger and electron energy-loss imaging and spectroscopy has been achieved by using a novel method of bevelled polishing of the silicon substrate material. Cross-sectional TEM was used to calibrate the depth scale in the MULSAM image sets, so allowing measurements of the thicknesses of various interfacial layers and the penetration of the ohmic contacts into the silicon. The TiN layer, providing adhesion of the tungsten as well as acting as a diffusion barrier, appears to have a domed shape, which penetrates the tungsten overlayer to a greater extent in the contact centres. The results of this work, combined with earlier, related, studies, enable a three-dimensional characterization of the bottom and sidewall structures in these contacts. © 1998 John Wiley & Sons, Ltd.

High Resolution Auger Imaging Combined with Focused Ion Beam for the Investigation of Metal/GaAs Contacts in High Power Transistors

ABSTRACTInspecting and understanding the thermal stability of metal contacts in the context of reliability testing on high power transistors (especially in the GaAs technology) often necessitates to view atomic concentration profiles at deep interfaces. One common method for this purpose is the combined Auger spectroscopy/ion etching technique, where the region to be investigated is etched sequentially (with a “low” etch rate, typically in the Å/second regime) and Auger electron spectra (AES) are recorded at each step of the etching process. The 3 major resolution drawbacks of this approach are first that it is time-consuming, second that the spatial resolution is limited (atomic profiles on contact regions with lateral dimensions smaller that I R~m are difficult to obtain) and third that the interface of interest is “smoothed” during the etch process. The third point yields atomic concentration profiles with an apparent inter-mixing, which sometimes hinders observation of the details of interest for the interface under investigation.We have used a different approach for this aspect of metal contact testing, in which the interface to be studied is first “revealed” by focused ion beam (FIB) micro-sectioning. After this preparation step, chemical images of the interface are directly obtained by high resolution Auger electron spectra mapping. The different operating conditions for the FIB process (orientation of the cross-section with respect to the transistor surface, preliminary procedures to eliminate residual roughness as well as surface contamination) have been optimized in order to produce Auger spectra free of any artifact. The approach is demonstrated on Au/GeNiAu ohmics contacts to the emitter electrode of GaAs-based hererostructure bipolar transistor, designed for high power amplification in the microwave regime. Ultimate spatial resolution of 20 to 30 nm on the Ayuger chemical images is demonstrated on an Auger microscope equipped with a Schottky field emitting tip.

The application of a low energy loss electron detector in conjunction with scanning Auger microscopy: an aid to quantitative surface microscopy

The application of a low loss detector is demonstrated as a quantification aid in scanning Auger microscopy. The low loss detector collects only those electrons that have lost less than a few hundred electron volts during their passage within, and escape from the specimen. The signal thus generated originates from within a comparable information depth to that of the Auger signal and the contrast is predominantly due to the average atomic number within this information depth. Calibration of the detector using elemental standards enables rapid identification of the position of, and the local atomic number of the various phases present at the surface of the specimen. This allows rapid identification of the regions for subsequent Auger spectroscopy or imaging. The low loss detector is deemed superior to conventional secondary or backscattered electron detectors for this purpose. The methodology is demonstrated on a W/TiN/Ti/Si system of trenches and contact holes that had been back polished in order to generate a bevelled cross-section through the structure.

High resolution imaging and analysis of grain boundaries in steel using a field emission auger microprobe

A standard cast low alloy steel sample, with known levels of grain boundary phosphorus and tin segregation, has been analysed after impact-fracture in a dedicated Auger microprobe. The instrument utilised a thermally assisted, Schottky diode field emission electron source. The examination illustrates the extra information that can be obtained by the high spatial resolution, in both secondary electron imaging and Auger electron spectroscopy and imaging, offered by this kind of source, when compared with more conventional tungsten and lanthanum hexaboride filaments. Cavities, with diameters of less than 1 μm, are observed on a proportion of the grain surfaces. Where cavitation occurs, tin is found to be present within the cavities and phosphorus on the areas of smooth grain boundary surface between them. During previous examinations of the same material, in a number of different laboratories, these features had not been resolved. In addition, elemental Auger mapping and analysis with a spatial resolution down to a few tens of nanometres are demonstrated by elemental imaging and spectroscopy of individual boron nitride particles on the cavitated grain boundary surfaces. It is suggested that, in the material examined, localised creep cavitation occurs during heat treatment. This is driven by residual stresses from the initial solution treatment and water quenching.

Quantitative surface microanalysis of samples with extreme topography utilising image interpretation by scatter diagrams and principal component analysis

Quantitative surface analysis (by Auger imaging, SIMS, EPMA, etc.) of many samples of technological interest is not possible due to the image artefacts arising from surface topography or other features of the sample. A methodology is presented for the identification and removal of regions within an image where artefacts dominate the contrast. This enables meaningful quantification of the regions not dominated by artefacts. The method employs multi-variate statistical techniques including 3D scatter diagrams and principal component analysis (PCA). PCA proves to be a powerful method for measuring the extent of any remnant artefact within image sets. The methodology is applied to the characterisation of a Pt Rh catalyst using the multi-spectral scanning Auger microscope at York.

Surface and interface microchemistry of archaeological objects studied with x ray photoemission spectroscopy and scanning Auger microscopy

We report x ray photoemission spectroscopy (XPS) and scanning Auger microscopy (SAM) studies of a Roman lead pipe ‘fistula’ and a Roman bronze sample. SAM analysis shows that the lead is much more oxidized in the original patina than in the naked surface of the fistula. Comparisons performed between large-area XPS measurements and microscopic SAM measurements indicate that there is a huge lateral chemical inhomogeneity in the surface composition of the bronze. Auger point spectra and elemental Auger imaging reveal, with a sub-micron spatial resolution, that tin is exclusively associated with oxygen in both materials, and the lateral distribution of these two elements is complementary to that of chlorine.

Quantitative surface chemical mapping with Auger and backscattered electron signals

The objective of surface analytical imaging methods is to map the quantitative distribution of the elements in the surface of a solid. Auger spectroscopy and imaging are often used for this purpose but the contrast in scanning Auger microscope (SAM) images of inhomogeneous, rough, surfaces show some features which are not due to the spatial variations of the surface chemical composition. Various schemes devised to reduce the effects on the image contrast of roughness and sub-surface inhomogeneity are reviewed in this paper. A model sample with a range of known surface inclinations and with known surface and sub-surface composition variations is used to demonstrate the effects of two general classes of correction schemes intended to reduce the contrast of such artefacts. The first class is based upon various arithmetic combinations of the number of electrons detected by a spectrometer set at the energy of an Auger peak and then at an energy (or a number of energies) on the spectral background above the peak. The extent to which these different combinations are successful in reducing topographical contrast and revealing otherwise hidden chemical contrast is summarised. It will be shown how a simple estimate of the Auger peak height leaves large topographical effects in the image contrast and that ratios of measurements at two energies provide a good first approximation for the removal of topographical artefacts. However, even those ratios which provide the best topographic compensation can overcorrect for variations in the sub-surface composition and its effects upon the Auger backscattering factor. In addition, they can introduce new problems for quantitative surface microanalysis. A second class of corrections involves the use of the signals from a set of four backscattered electron (BSE) detectors which collect BSE imaes at the same time as the energy-analysed images. The sum and difference signals from these detectors can be used, together with appropriate calibration, to compute three images in which the pixel intensities give the local surface inclinations and effective atomic numbers of the sub-surface material. These images can be used, in turn, to derive correction images for the Auger maps so as to yield a more accurate map of the surface chemical composition. The combination of the correlated Auger and BSE signals for each place on the surface requires the use of an instrument which collects these signals simultaneously from several detectors. Various methods of using such correlations are discussed. Surfaces with large variations in the contrast in the “raw” Auger images can be analysed with a precision of approximately ±5 at% after exploitation of such correlations.

X‐ray photoemission spectroscopy and scanning Auger microscopy studies of a Roman lead pipe ‘fistula’

AbstractWe report scanning Auger microscopy (SAM) and x‐ray photoemission spectroscopy (XPS) analysis of a Roman lead pipe ‘flstula’, the main emphasis being placed on the comparison between the surface and interface chemical composition of the joint and of the rest of the pipe. We find that the ‘tertiarium,’ a Pb–Sn alloy that the Romans used for soldering the joint, has a beneficial effect in limiting the formation of white lead, 2PbCO3·Pb(OH)2·Comparison measurements performed in the alloy and the pure separate metals show that tin markedly limits the ambient surface oxdation of lead. Conversely, tin is much more oxidized in the alloy than when analysed alone. Auger point spectra indicate that carbon is the main surface contaminant of the patina of the fistula, and Auger imaging is used to pinpoint, with a spatial resolution of ∼0.5 ∼m, the distribution of this element at the interface of a lead/tertiarium solder, performed according to the procedures described by Plinius. The diagnostic capability of Auger transitions of lead and tin for distinguishing between different phases is discussed on the basis of their chemical shifts and surface sensitivities.