Scanning Auger Microscope Research Articles

X-ray induced vanadium L3M23M45 auger electron spectra as tool to trace vanadium oxidation state: Study of surface stoichiometry recovery of V2O3 film

Ratio of two peaks in X-ray induced vanadium L3M23M45 Auger electron spectra has been used to monitor oxidation state of V2O3 thin film surface followed by vacuum annealing. The V2O3 film was grown with sol-gel method on the Al2O3 (0001) substrate. The O 1s, V 2p core-level X-ray photoelectron spectra and V L3M23M45 Auger electron spectra were measured from the film as function of annealing temperature. Brief exposure of the film to the air turned surface vanadium to 4+ oxidation state. Annealing in UHV at 455 K completely converted vanadium to 3+. The binding energy (BE) difference between O 1s and V 2p3/2 core-level changed from 14.0 eV to 14.9 eV as annealing temperature increased from room temperature to 455 K. Intensity ratio of the two peaks in V L3M23M45 Auger electron spectra, peak originated from O 2p region to that from V 3d region, changes from 0.91 to 0.63. In combination with measurement from VO2 film, relation between intensity ratio of V L3M23M45 doublet and the oxidation state of vanadium was established by comparison with BE difference between O 1s and V 2p3/2 core-level. V L3M23M45 Auger electron spectra can be useful tool for scanning Auger microscope (SAM) to get high spatial resolution vanadium ion distribution. A few points to consider for application toward SAM mapping have been discussed.

Investigation of the final stages of a P4-like coliphage infection in Escherichia coli through scanning, transmission and nano-scanning-auger electron microscopy (NanoSAM)

Enlargement of bacterial cells during bacteriophage replication has been observed in the past with T-even, Lambda and N4 bacteriophages by the use of transmission electron microscopy (TEM) and light microscopy techniques and hypotheses explaining the enlargement of bacteriophage-infected cells have been postulated in literature. In this study, enlarged Escherichia coli cells were observed using scanning electron microscopy (SEM) after 45 min of a P4-like bacteriophage infection. These bacteria were also studied using scanning auger microscopy (SAM) in combination with anthe Argon-ion gunof a scanning Auger microscope (SAM) by which the bacteria were etched. Neither SEM nor SAM have been used during the analysis of bacteriophage infected enlarged host cells, making this study unique. The use of SAM on bacteriophage-related investigations is also novel. Small phage-like particles were observed inside the etched enlarged and etched normal bacteriophage-exposed host cells. The presence of bacteriophage-like particles inside both types of cells confirmed that the enlarged cells, which were scarce in this sample, were not artifacts of some kind such as contamination by other microorganisms. Due to the scarcity of these enlarged cells, it was concluded that a previous hypothesis on tThe enlargement of bacteriophage infected host cells coincides with previous studies reported in literature, did not apply to thebut never before with P4-like bacteriophages. used in this study. Key words: Bacteriophage, coliphage, replication cycle, Esherichia coli, Nano scanning electron microscopy.

Phase separation behavior of Ge2Sb2Te5 line structure during electrical stress biasing

We report the breakdown behavior of a patterned Ge2Sb2Te5 multiline structure during the voltage-driven electric stress biasing. Scanning Auger microscope analysis shows that the breakdown process accompanies with a phase separation of Ge2Sb2Te5 into an Sb, Te-rich phase and a Ge-rich phase. The phase separation is explained by the incongruent melting of Ge2Sb2Te5 based on the pseudobinary phase diagram between Sb2Te3 and GeTe. It is claimed that this phase separation behavior by incongruent melting provides one of the plausible mechanisms of the device failure in a phase change memory.

Application of high spatial resolution scanning work function spectroscopy to semiconductor surfaces and interfaces

Work function can be measured from the onset energy of secondary electron (SE) emission spectra in a scanning Auger microscope. In this article, the authors demonstrate the potential of such high spatial resolution work function spectroscopy in probing the Fermi-level position at semiconductor surfaces and the band bending at semiconductor interfaces. Using in situ cleaved cross-sectional GaAs and SiC p-n junctions, they show that the SE onset energy is very sensitive to the surface Fermi-level position and can also be used to measure electron affinity. By measuring the widths of the transition regions, the doping densities and built-in potential can be quantitatively obtained at a spatial resolution of ∼10nm. This technique can also be applied to a wide range of semiconductor heterojunctions. The influences of air cleaving, Ar ion sputtering, contamination, and primary electron beam are studied. They also discuss the advantages, limitations, and possible future improvements of this technique.

Evaluation of the shapes of Auger- and secondary-electron line scans across interfaces with the logistic function

We report on the use of the extended logistic function for fitting Auger-electron (AE) and secondary-electron (SE) line scans. Such fits provide convenient and objective measures of parameters describing the interface width and possible asymmetry of a line scan. We show examples of fits to AE and SE line scans for three types of samples. Fits to AE and SE data for a gold island on a carbon substrate gave useful measures of the lateral resolution of a scanning Auger microscope and “tails” present in the line scans showed evidence of imperfect alignment of the microscope. Fits to AE spectra obtained as the primary beam was scanned across an edge of Cr∕Cr2O3 lines on an indium tin oxide substrate showed similar tails due to the effect of backscattered electrons on the generation of Auger electrons for primary energies between 15 and 25keV. Fits with the logistic function to SE line scans across a fractured Ni∕Cr multilayer sample and to AE and SE line scans across a sputtered crater of this sample provided useful measures of the interface width.

Influence of thickness of Hf buffer layer on the interfacial structures of sputtered HfO 2 on SiO 2/Si

The influence of thickness of Hf–metal buffer layer on the interfacial diffusion and reaction was investigated using in situ X-ray photoelectron spectroscopy, scanning Auger microscope and grazing incident X-ray reflectivity. Hf–metal firstly reacted with native Si oxide forming Hf silicates, and all Si–O was further reduced to be Si 0 after 1 nm Hf–metal deposition. The Hf–metal and Hf-suboxide in Hf(1 nm)/SiO 2/Si structure were further oxidized to be Hf 4+ during HfO 2 sputtering deposition and post-deposition annealing. Si diffused out and reacted with HfO 2 during annealing. The Hf(1 nm) buffer layer exhibited a better performance than the Hf(0.3 nm) buffer layer in suppressing the diffusion of Si and the reaction between diffused Si and HfO 2.

The composition of the boundary region of MnS inclusions in stainless steel and its relevance in triggering pitting corrosion

Recently, controversy has arisen on the presence of a Cr-depleted zone around MnS inclusions in stainless steels and the relevance of such zones to pit initiation events. In the present work, we use a scanning Auger microscope (SAM) combined with simple pitting immersion tests to elucidate this question in more detail. The SAM analysis of 27 inclusions of a high S-containing DIN 1.4305 stainless steel indicated no Cr-depletion at the inclusion/matrix-interface with a lateral resolution of ±20 nm. A scanning electron microscope (SEM) characterization of the sample surface after an exposure to 10% FeCl 3 solution shows that pitting attack in all cases initiates at inclusion sites. Different pit initiation morphologies were observed (inside the inclusion, around the inclusion, mixed attack morphology). However, even the attack morphology “around an inclusion” cannot be ascribed to Cr depletion at the inclusion. Although in special cases (special composition or heat treatment history of the steel) a Cr-depleted may be induced at the matrix/inclusion-interface, the present work shows that this approach does not generally hold and therefore the presence of such a depletion zone cannot be the general explanation for pitting of stainless steels in the vicinity of inclusions.

Surface electromigration of In-covered Si high-index surfaces

To clarify the role of facet in electromigration on the vicinal Si(001), we investigated in this study surface mass transport of In on Si high-index (103) and vicinal (001) surfaces, using scanning Auger microscope, low energy electron diffraction (LEED) and atomic force microscope (AFM). In parallel with (103), we also investigated similarly the most stable high-index (113) of Si for reference. Specimens with a large area of these surfaces were prepared from Si(001) wafer by cutting, grinding and polishing. No surface electromigration of In on Si(103) surface was observed at any temperature, while In overlayer exhibited a typical Stranski–Krastanov mode of growth. This fact strongly suggests that In adatoms move around over the intermediate layer, but there is no driving force of electromigration on them. The electromigration on the vicinal Si(001) depended upon the off-angle. It was most enhanced with the off-angle of around 4°. Based upon these results a model is proposed to explain the puzzling electromigration of In on vicinal Si(001). We found out that In on Si(113) exhibited a normal surface electromigration towards cathode.

From LEED to MULSAM

This account gives an outline of the work done in the Department of Physics, University of York since 1965. The Surface Physics Group has been particularly active in the development and application of electron probes of solid surfaces with strong emphasis upon low-energy electron diffraction and scanning electron microscopy using Auger electrons to form images. A scanning Auger microscope using multi-imaging (MULSAM) has been particularly fruitful for the study of a variety of heterogeneous materials. Examples are given of the application of MULSAM to the minimization of topographic contrast artefacts, to the study of multilayers of magnetic materials, to the characterization of very rough PtRh catalyst surfaces, to the interpretation of the shapes of electron spectra and to the angular dependence of both Auger electron and energy-dispersive x-ray signals. Copyright © 2000 John Wiley & Sons, Ltd.

Diffusion of sulphur on to oxidised free surface of polycrystalline nickel via emergent grain boundaries

Specimens of polycrystalline nickel have been annealed at ∼700°C and oxidised in situ within a scanning Auger microscope. Auger spectroscopy has been used to monitor the chemical composition of the free surface, and real time secondary electron imaging used to observe the specimen surface. A novel segregation effect has been recorded whereby sulphur emerges on to the free surface via emergent grain boundaries in the form of sulphurous bands, displacing the established oxide overlayer. The kinetics of the broadening of these bands depends on the tenacity of the oxide which, in turn, depends on the levels of sulphur present on the specimen surface before oxidation. Qualitative mechanisms are proposed for the observed effects.

Scanning Auger microscopy study of electromigration induced failure in submicrometric microelectronic devices

Scanning Auger microscopy is a powerful tool to investigate elemental and chemical composition of surfaces, interfaces and thin films. Thanks to its high lateral resolution (better than 10 nm at 20 keV using the last generation of Schottky field emission tip) and to the surface sensitivity of the Auger electrons (between 5 and 30 Å, depending on the investigated element), it is very useful in microelectronics laboratories, where the size of the components is often less than 200 nm. In this work we shall present the analysis performed by means of a scanning Auger microscope on the elemental and chemical distribution on a defective submicrometric via contact (about 200×500 nm) connecting two metal lines of a 64 Mb DRAM chip before and after an extreme electric test, in order to study the effect of a huge current passing through the contact. The analysis has been performed with very high spatial resolution (better than 20 nm) onto samples that showed different electrical behaviour after the test. Our measurements have allowed us to describe the bad behaviour of the circuit due to a migration of some metal atoms induced by electron flow.

Tip cleaning and sharpening processes for noncontact atomic force microscope in ultrahigh vacuum

Tip cleaning and sharpening processes for noncontact atomic force microscope (AFM) operated in ultrahigh vacuum (UHV) were carried out and evaluated by a scanning Auger microscope (SAM) with a field emission electron gun and a noncontact AFM in UHV combined with a scanning tunneling microscope and a field emission microscope. The cantilever used in this study was piezoresistive, which can be heated by passing a current through the resistive legs of the cantilever. As a pretreatment, the tip was irradiated with ultraviolet light in oxygen to remove carbon contaminants. It was heated at about 750°C to form a clean oxide layer in oxygen of 5×10 −5 Torr in an SAM chamber. The desorption of the layer can make a remained tip apex sharper by heating under electron beam irradiation. A thermally oxidized layer was also eliminated by HF etching to sharpen the tip apex. The procedures are useful to obtain a well-defined Si tip suitable for a noncontact AFM.

Investigation of Interactions Between Polymer-coated Nano-Y-TZP Particles by AFM

It is well known that copolymers of polyacrylic acid (PAA) and polymethacrylic acid (PMAA) are strongly adsorbed on the surfaces of alumina and zirconia [1]. For this reason, inorganic oxides such as alumina, silica, and zirconia were surfacemodi®ed by polymers to improve their compatibility with the organic phase in many important applications [2, 3]. Recently, PAA and NH4PAA were applied to prepare core-shell alumina nanocomposite particles by their interparticle-bridging capability [4, 5]. The kinetics and equilibrium of the process have been studied in detail and it was widely claimed that polymer coatings can balance the interactions between particles by inducing repulsive force to prevent the agglomeration of particles, hence, to promote the homogeneity of the particle surfaces [2, 6]. However, until recently the mechanism was probed in submicrosized Al2O3 [7]; nanosized particles differ from submicroparticles naturally, they are ready to agglomerate, and the interactions between them may demonstrate some diversity in comparison with submicroparticles. Although atomic force microscopy (AFM) is attractive for imaging surface topographies of insulating materials because of its exible nature, until recently, the use of the AFM as a force sensing tool has been limited [7±9]. For the ®rst time, we employ AFM to probe interactions between nano-Y-TZP (yttria stabilized tertragonal zirconia, Y2O3 3 mol %), which is a prospective structural ceramic in many critical environments [10]. In a typical procedure, nanosized Y-TZP powder with a speci®c surface area of 31.55 m gy1 (BET) was synthesized by chemical precipitation [10]; TEM shows that the particle size is about 20 nm (Fig. 1). Polymer dispersants used are NH4PAA (ammonium polyacrylate) and NH4PMAA (ammonium polymethacrylate) (Mw ˆ 10 000). Y-TZP suspensions were prepared by ball milling at least 24 h, the suspensions were adjusted to pH 10 by (CH3)4NOH, dispersant concentration was 2 % dwb (dry weight basis of the powder) for NH4PAA and NH4PMAA, respectively. The suspension was ball milled and then equilibrated for 24 h. The particles were separated by using an LG-10 centrifuge at 2000 rpm for 1 h and the supernatant was removed. The polyelectrolytes-coated nano-Y-TZP particles were dried in vacuo prior to surface characterization and interaction analysis. The surface of the powder was characterized by using a Microlab-310F scanning auger microscope (SAM), indium particles were employed as a template for the anchoring of Y-TZP powder. The interaction was analyzed by AFM (Topometrix explorer, commercial silicon nitride tip with a radius around 50 nm) in dried environment, the force curve is the force between the tip, and the surface of the thin plates formed by high pressure from the powders [7, 8]. Fig. 2 shows the SAM spectra of nano-Y-TZP powder. It is easy to ®nd out from the SAM results that the polymer coated nano-YTZP powder has a carbon peak at about 270 eV, which indicates that the surfaces of the nanoparticles were successfully

Observation of Si(111) Surfaces Using Energy-analyzed Electrons.

A stepped Si(111) surface consisted of atomically flat terraces and step bands where atomic steps bunched was prepared by direct-current heating in UHV. An electron-emission spectrum, generated with a field-emission-type electron gun, was observed in situ with a scanning Auger microscope (SAM). The electron-emission spectrum obtained in the direct mode included only characteristic Auger electron (AE) peaks of silicon and a secondary-electron (SE) peak. The AE/SE spectrum obtained from the atomically flat Si(111) terrace between the steps was different from the spectra from sputtered clean silicon (111) and (100) surfaces as to the background shape and the relative intensities of the characteristic peaks. We also found that the stepped surface morphology could be imaged by using only the energy-analyzed SEs when the intensity was defined as the difference between the peak height and the background intensity.

PISAM: a photon-induced scanning Auger microscope

Abstract A high-flux, scanning microspectroscope using the very intense, direct radiation from an undulator is introduced and its performance is discussed with various examples. This instrument utilizes the quasi-monochromatic beam from the first undulator at BESSY without monochromatization. Thus, X-ray induced Auger spectroscopy using all available photons above the respective threshold or photoemission using the 2-eV-wide first harmonic of this undulator can be performed. Spatial resolution is achieved in different ways, either simply by an adjustable aperture in front of the sample, yielding a diffraction-limited resolution of, for example, 3–4 μm for the C-Auger spectra, or by two mirrors, a toroidal condenser mirror and a demagnifying ellipsoidal mirror, which focus the aperture onto the sample yielding a resolution in the submicrometer range. Photoemission spectra from a selected spot can be obtained in seconds, or structures can easily be written using photon-induced reactions, because of the extremely high photon density of 1013 photons μm−2. Finally, line scans or 2D images can be recorded by scanning the sample across the focused beam.

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.

Auger electron microscopy study of transfer film induced in an aircraft braking tribosystem

Microchemical analysis was carried out using a scanning Auger microscope on the transfer film induced in an aircraft brake tribosystem. The focus was placed on the study of the distribution of major elements in the transfer film, as well as the extent and uniformity of surface oxidation. Results showed that the as-worn surface of the transfer film consisted of large amounts of contaminant elements, primarily carbon and oxygen, along with minor quantities of S, Ca, Na, N and Cl. The transferred elements were distributed nonuniformly. The scale of the nonuniformity depended on the domain (particle) size of each component in the friction material. The high concentration and nonuniform distribution of oxygen indicated that the slideinduced oxidation process was severe and nonuniform. The carbon concentration was lower and metallic elements oxidized more severely in the high oxygen region than in the low oxygen region. With sputter time the Cu/Fe ratio continued to decrease, while the C/Cu ratio increased, suggesting that carbon was easier than copper to transfer and/or adhere to the steel suface.

Surface Characterization of RuO2 ‐ SnO2 Coated Titanium Electrodes

coatings supported on titanium were characterized in morphology using a high resolution scanning electron microscope and an atomic force microscope and in composition using a scanning Auger microscope. Ruthenium was segregated in island‐like deposits in the case of ‐rich electrodes and along cracks for ‐rich electrodes where tin was localized in the macroscopically flat plane consisting of ultrafine particles. The ultrafine particles found on ‐rich electrodes, which were smaller than those found for ‐rich electrodes, contributed to the large active surface area of the electrode.

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.

Direct writing of Mo microstructures using high brilliance synchrotron radiation

Direct deposition of Mo microstructures on Si is demonstrated by photolytic decomposition of condensed Mo(CO)6 using the aperture-limited, high-intensity radiation from an undulator at the BESSY storage ring. A particular advantage of the instrument, a new photon-induced scanning Auger microscope, is the possibility of quasisimultaneous exposure (writing) and analysis employing photoemission (PES) or x-ray induced Auger spectroscopy (XAES) with sufficient energy resolution for detection of chemical differences. The present spatial resolution is 20–30 μm (for PES and writing) and 3 μm (for XAES), but this will be improved by adding focusing mirrors.