Grain boundary segregation of P and micro-structural changes in 12% Cr-steels

Phosphorus occurs as impurity in 12% CrMoV-steels and tends to enrich at grain boundaries. The phosphorus grain boundary segregation in a laboratory cast of the steel X 20 CrMoV 12 1 with a relatively high phosphorus content (0.057% P) was studied by Auger electron spectroscopy and the segregation kinetics and equilibria were described. Using the results phosphorus segregation could be predicted and compared to measured phosphorus concentrations in long-term annealed steels. Investigations by transmission electron microscopy showed recrystallisation and an agglomeration of carbides with aging time and the occurrence of new phases (Laves-phase Fe₂ Mo). All these processes lead first to an increase in toughness as established in notch-impact fracture tests for the laboratory cast, however, after long-term use a reduction in toughness is expected.     

The segregation of As,Sb and Bi in Cr-Ni steels and alloys with different Ni contents investigated using AES

This paper reports on an AES study of grain boundary segregation in five kinds of Cr-Ni corrosion-resistant steels and alloys with different Ni contents that were enriched by As, Sb or Bi. The results show that all mentioned impurities segregate to the grain boundaries and that the segregation level depends on the type of the impurity. The highest amount of segregant atoms was found in the case of Bi, while it appeared to be substantially lower for As and Sb. The segregation level of each impurity grows also with the Ni content. This increase is more pronounced for Bi and Sb than for As. In particular the results demonstrate that the enrichment of grain boundaries by a given impurity is strongly connected to the solubility of this element in the matrix.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

AES and LEED study of well‐ordered oxide film grown on Cu–9at.%Al(111)

An alloy of Cu–9at.%Al(111) has been oxidized in a low‐energy electron diffraction (LEED)/AES and a scanning AES instrument at elevated temperatures. Dosing with 1300 L of oxygen at 995 K gives rise to well‐ordered oxide layer formation on the Cu–9at.%Al alloy. The structure of the ordered oxide confirmed by LEED is ( ) R30°. The chemical state of the oxide was Al₂O₃. The morphology of the surface observed with SEM in the scanning AES instrument revealed flat oxide growth with triangular defects of the same orientation. The possible epitaxy between the alloy substrate and alumina layer has been discussed. Copyright © 2003 John Wiley & Sons, Ltd.     

AES study of underclad cracking

The present work deals with the occurrence of underclad cracks in three types of steels differing in the contents of the alloying elements (Cr, Ni, Mn) and in the impurities level (As, Sb, Sn). The presence of the intercrystalline fracture typical for the underclad cracks was proved to be dependent on the temperature and on the ageing time. It follows from the results of Auger electron spectroscopy, that the sulphur and phosphorus segregations accompanied by a higher number of carbide (possibly sulphide) particles cause a decrease of grain boundary strength. Segregations of other impurity elements were not detected at grain boundaries.     

Effect of surface orientation on the segregation kinetics of Sb from a Cu single crystal

In a previous theoretical study it has been suggested that the bulk vacancy formation energy near a surface depends on the orientation of the surface. It has been suggested also that this dependency of the vacancy formation energy would influence the bulk diffusion coefficient near the surface. The experimental results presented in this paper support this hypothesis. The experimental results were obtained by measuring the bulk‐to‐surface segregation of Sb for a Cu(111) single crystal with 0.088 at.% Sb and for a Cu(110) single crystal with 0.082 at.% Sb. The experimental results were fitted with the vacancy‐modified Darken model and it was clear that the bulk diffusion coefficient beneath the (110) surface is higher than the bulk diffusion coefficient beneath the (111) surface. Copyright © 2003 John Wiley & Sons, Ltd.     

X-ray photoelectron spectra and Auger studies of the surface oxidation of cobalt

Surface oxidation of Co has been investigated at different temperatures in the 300–600 K range at oxygen exposures upto 10⁶ L by XPES and AES techniques. In the XPES, both the valence band and core level bands have been employed to monitor the oxidation while in the AES, metal Auger intensity ratios as well as O(KLL)/Co(L₂₃M₄₅M₄₅) ratios have been examined. Only CoO is formed on the surface at high oxygen exposures at and above 500 K. Communication No. 62 from the Solid State and Structural Chemistry Unit.     

Quantification of grain boundary equilibrium segregation by NanoSIMS analysis of bulk samples

A technique for the quantification of equilibrium grain boundary segregation by high resolution secondary ion mass spectroscopy (NanoSIMS) on simple metallographically polished surfaces has been demonstrated for the model system of sulphur segregation to nickel grain boundaries. Samples of nickel containing 5.4 wt ppm of sulphur were annealed at different temperatures to achieve different equilibrium sulphur grain boundary concentrations, ranging from less than 1% to about 50% of a monolayer. Quantification was carried out from sulphur concentration profiles acquired across about 20 grain boundaries in each sample. An internal standard (nickel containing a known concentration of sulphur in solid solution) was used for calibration. It is found that, depending on the annealing temperature, the average grain boundary sulphur concentration ranges from 0.9 to 25.8 ng cm^–2 (or 1.7 10¹³ to 4.8 10¹⁴ atoms cm^–2), i.e. ~0.015 to ~0.43 monolayer. Thermodynamic analysis gives a segregation free energy of ?97.8 kJ mol^–1 and a grain boundary sulphur concentration at saturation of 26.7 ng cm^–2 (or 5.0×10¹⁴ atoms cm^–2), i.e. ~0.44 monolayer, in good agreement with previous measurements on this system. The limit of detection of the technique is shown to be as low as 0.24 ng cm^–2 (or 4.5×10¹² atoms cm^–2), i.e. ~0.004 monolayer, with a counting time of only 10 min. Copyright © 2012 John Wiley & Sons, Ltd.     

An AES study of Sn surface segregation in Cu single crystals

Quantitative treatment of Sn segregation data in the three low‐index planes of Cu(111), Cu(110) and Cu(100) was carried out. Auger electron spectroscopy (AES) was used to acquire the data by heating the sample linearly with time (positive linear temperature ramp, PLTR) from 450 to 900 K and immediately cooling it linearly with time (negative linear temperature ramp, NLTR) from 900 to 650 K. The experimental data were fitted using the Darken model for the PLTR profiles. Two supportive models—Fick's integral and the Bragg–Williams equations—were used to extract the starting segregation parameters for the Darken model. Fick's integral was used to fit part of the data for the PLTR profile and the Bragg–Williams equations were used for the NLTR profile, which accounts for an extended equilibrium segregation region. The Sn segregation parameters, namely the interaction energy Ω_{Cu? Sn}, the diffusion coefficient D and the segregation energy ΔG, were found as: Copyright © 2005 John Wiley & Sons, Ltd.     

Analysis of the antitarnish film on a tin surface by x-ray photoelectron spectroscopy and Auger electron spectroscopy

A corrosion-resistant complex film formed in ethylenediaminetetra(methylidenephosphonic acid) (EDTMP) solution was determined by x-ray photoelectron spectroscopy and Auger electron spectroscopy to consist of 48.0% O, 11.7% Sn, 7.7% N, 22.1% C and 10.5% P. From the differences in the binding energies of Sn, N and O before and after film formation and the RPO^2?₃ and SnN vibrations in the Raman spectrum of the film, it was deduced that N and O in EDTMP were coordinated with Sn in the film.     

Functional micropatterned surfaces prepared by simultaneous UV‐lithography and surface segregation of fluorinated copolymers

A new procedure focused on the design and preparation of structured and functional polymer surfaces by combination of two approaches acting simultaneously is developed. The elaboration of micrometer size patterned surfaces by UV‐light lithography is reported where, in addition, the surface chemical composition can be controlled by surface segregation of a fluorinated copolymer incorporated in the photopolymerizable mixture. As evidenced by contact angle and XPS measurements, the surface composition can be modified depending on such factors as with the environmental conditions or the concentration of copolymer in the blend. Moreover, the functionality of the copolymer is enhanced by the surface pattern created. As a consequence, the wettability of the films can be modified depending on the pattern and composition of the blend. By using this methodology, functional adaptive sensitive surfaces with a well‐defined topography will be obtained in one single step and without the use of tedious and time‐consuming multistep procedures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Investigation of surface and thermogravimetric characteristics of carbon-coated iron nanopowder

Demand for high-density press and sinter components is increasing day by day. Of the different ways to improve the sinter density, the addition of nanopowder to the conventional micrometer-sized metal powder is an effective solution. The present investigation is aimed at studying the surface chemistry of iron nanopowder coated with graphitic carbon, which is intended to be mixed with the conventional iron powder. For this purpose, iron nanopowder in the size range of 30 nm to submicron (less than 1 micron) was investigated using thermogravimetry at different temperatures: 400°C, 600°C, 800°C, 1000°C, and 1350°C. The X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and high-resolution scanning electron microscopy (HR-SEM) were used for characterizing the powder as well as samples sintered at different temperatures. The presence of iron, oxygen, carbon, chromium, and zinc were observed on the surface of the nanopowder. Iron was present in oxide state, although a small metallic iron peak at 707 eV was also observed in the XPS spectra obtained from the surface indicating the oxide scale to be maximum of about 5 nm in thickness. For the sample treated at 600°C, presence of manganese was observed on the surface. Thermogravimetry results showed a two-step mass loss with a total mass loss of 4 wt.% when heated to 1350°C where the first step corresponds to the surface oxide reduction.     

Quantitative surface analysis by X-ray photoelectron spectroscopy and X-ray excited auger electron spectroscopy

It is shown that X-ray excited KLL Auger electron spectra allow it to describe measured signal strengths similarly to X-ray photoelectron signals, thus offering valuable information on the quantitative surface composition of a solid sample. The principal equation and corresponding fundamental parameters are discussed. As a result Auger spectra of C, N, O, F, and Na can be easily used in a multiline approach for quantitative analysis. LMM and MNN spectra give rise to more problems, due to their more complicated structure, uncertainties with regard to the background and the influence of Coster-Kronig transitions. These problems are overcome by the use of empirical ratios of the strongest lines of 2p/LMM or 3d/MNN. Since these ratios are independent of sample composition, they allow it to transform the Auger signal into the corresponding photoelectron signal, provided that a standard sample has been measured. Thus a true additional information is obtained and moreover difficulties in cases of photoelectron spectra with overlapping lines from other chemical elements can be overcome.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

State of the Cu electrode surface studied by X-ray photoelectron and Auger spectroscopies

Annealing of the copper plate in flame was found (by XPS and X-ray Auger spectroscopy) to enrich the surface copper layers in oxygen in the forms of Cu₂O and adsorbed oxygen. The changes in the surface layers of the copper cathode due to annealing can be the origin of the earlier found enhancement of its activity in the electrocatalytic hydrogenation of citral and trans-2-allyl-6-R-1,2,3,6-tetrahydropyridines (R = Me, All, Ph). This method of the copper electrode pre-treatment provides its long durability, an insignificant decrease in the electrocatalytic activity in time, and the reproducibility of the electrocatalytic hydrogenation of unsaturated organic compounds.     

SIMS and Auger investigation of oxygen adsorption on polycrystalline nickel surface

As it is known, the secondary ion yields increase stepwise upon increasing O₂ exposure, during SIMS measurements on metal samples in an oxygen atmosphere. Taking Auger spectra at varying oxygen exposure, the variation of satellite peaks and the chemical shift has been monitored, and a similar step-like dependence at the same range of oxygen exposures was found. This shows, that the discontinuous increase in the secondary ion intensity is due to the different types of oxides formed on the metal surface. Identification of these oxides are discussed.     

Recent progress in quantitative and high spatial resolution AES

Progress in high resolution Auger electron spectroscopy (HR-AES or scanning Auger microscopy, SAM) during the past few years is characterized by the use of efficient field emission electron sources, parallel detection capabilities and improved data acquisition, storage and processing, thus enhancing spatial resolution (to about 10 nm), signal to noise figure and quantification of elements in different chemical bonding states, e.g. by routinely using factor analysis. Optimized ion sputtering facilities, particularly sample rotation, enable depth profiling with high, depth independent resolution. The basic features of SAM are discussed with respect to EPMA (electron probe micro-analysis), emphasizing fundamental limitations and future developments.     

Stereoselective 6-exo cyclization of amidyl radicals. An experimental and theoretical study

Unsaturated primary amidyl radicals of Z-configurations underwent efficient chemo- and stereoselective 6-exo cyclization reactions via chair-conformational transition states, leading to the predominant formations of 3,6-trans, 4,6-cis, or 5,6-trans substituted δ-lactams.     

Segregation and Stability in Surface Alloys: PdxRu1−x/Ru(0001) and PtxRu1−x/Ru(0001)

The stability of PdRu/Ru(0001) and PtRu/Ru(0001) surface alloys and the tendency for surface segregation of Pd and Pt subsurface guest metals in these surface alloys is studied by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). Atomic resolution STM imaging and AES measurements reveal that upon overgrowing the surface alloys with a 1–2 monolayer Ru film and subsequent annealing to the temperatures required for initial surface alloy formation, the Ru‐covered Pd (Pt) atoms float back to the outermost layer. The lateral distribution of these species is also essentially identical to that of the initial surface alloys, before overgrowth by Ru. In combination, this clearly demonstrates that the surface alloys represent stable surface configurations, metastable only towards entropically favored bulk dissolution, and that there is a distinct driving force for surface segregation of these species. Consequences of these data on the mechanism for surface alloy formation are discussed.     

Properties of alkali metal atoms deposited on a MgO surface: a systematic experimental and theoretical study

The adsorption of small amounts of alkali metal atoms (Li, Na, K, Rb, and Cs) on the surface of MgO powders and thin films has been studied by means of EPR spectroscopy and DFT calculations. From a comparison of the measured and computed g values and hyperfine coupling constants (hfccs), a tentative assignment of the preferred adsorption sites is proposed. All atoms bind preferentially to surface oxide anions, but the location of these anions differs as a function of the deposition temperature and alkali metal. Lithium forms relatively strong bonds with MgO and can be stabilized at low temperatures on terrace sites. Potassium interacts very weakly with MgO and is stabilized only at specific sites, such as at reverse corners where it can interact simultaneously with three surface oxygen atoms (rubidium and cesium presumably behave in the same way). Sodium forms bonds of intermediate strength and could, in principle, populate more than a single site when deposited at room temperature. In all cases, large deviations of the hfccs from the gas-phase values are observed. These reductions in the hfccs are due to polarization effects and are not connected to ionization of the alkali metal, which would lead to the formation of an adsorbed cation and a trapped electron. In this respect, hydrogen atoms behave completely differently. Under similar conditions, they form (H(+))(e(-)) pairs. The reasons for this different behavior are discussed.