Investigation of the synthesis and internal structure of protective oxide layers on high-purity chromium with SIMS scanning techniques

The major problem affecting the application of chromium in high temperature processes is the ongoing spallation of the protective oxide layer formed during hot-gas oxidation. This results in a continuous material erosion. To gain a deeper insight in the spallation and oxidation process, a high-purity powder-metallurgically produced chromium sample was submitted to a two-stage hot gas oxidation process. The formed oxide layers were investigated by 3D SIMS and scanning SIMS. The formation of the protective oxide layer is carried by the diffusion of chromium from the bulk through the already existing oxide layer and the reaction of the diffused chromium with the oxygen from the gaseous phase. In parallel to the growing of the oxide layer, an accumulation of impurities at the interface oxide layer – bulk can be observed. The enrichment of trace elements at the interface level (for the investigated sample Cl and N) can be explained by the low solubility of these elements in chromium oxide and therefore their inability to diffuse through the already formed protective layer. Received: 24 June 1996 / Revised: 22 January 1997 / Accepted: 26 January 1997     

The detection of oxygen in magneto-optical layers with SIMS

The detection of oxygen in magneto-optical layers is of fundamental importance for the characterization of the stability of RE-TM material. The magnetic properties are directly influenced by oxide formation. Oxygen depth profiles are carried out by using the SIMS technique. A comparison with magnetic measurements showed a clear conformity. We were able to study the oxidation behaviour of various layers at room temperature and at higher values up to 250° C for several hours. It could be shown that aluminum is a successful material for the protection of RE-films against oxidation. The difficulties of translating SIMS counting rates into concentration values were overcome by using EPMA. Specially prepared reference samples were measured by this technique and could then be used as standard samples for SIMS.     

Investigation of Asian lacquer films using ToF‐SIMS and complementary analytical techniques

Lacquer has been used in Asian countries for thousands of years as a natural coating material owing to its durable, adhesive, decorative, and protective properties. Protection and restoration of lacquer‐coated cultural remains has become an important subject, and identification of the lacquer types in old lacquer‐wares has also become very important for conservation and restoration research. This paper provides identification of several molecular species of vegetal‐source Asian lacquers with the aim of providing a methodology for application in the field of cultural heritage. Several chemical markers of the vegetal species in Asian lacquers were identified using a methodology consistent with the sampling restrictions required for cultural‐heritage objects. Surface analytical methods such as time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), X‐ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were used to characterize Korean, Chinese, and Vietnamese lacquers; avoiding time‐consuming and destructive extraction processes. These ToF‐SIMS results provided the structural characterization of a series of catechol derivatives. The ToF‐SIMS spectra of Rhus vernicifera from Korea and China, and Rhus succedanea from Vietnam indicated a series of urushiol and laccol repeat units, respectively, in the mass range of m/z 0–1800. Because of its sensitivity, specificity, and speed of analysis, the ToF‐SIMS technique can be used to investigate cultural lacquer‐coated treasures as well as to discriminate among different Asian lacquer coatings or binding mediums for the conservation or restoration of lacquer‐ware. Copyright © 2016 John Wiley & Sons, Ltd.     

SIMS investigations on the growth mechanisms of protective chromia and alumina surface scales

The oxidation behaviour of the oxide-dispersion strengthened (ODS) high-temperature alloys MA 956 (an aluminium oxide former) and MA 754 (a chromium oxide former) has been compared with that of two model alloys, Fe-20Cr-5Al and Ni-25Cr. The morphology and composition of the oxide scales were investigated by metallography, X-ray diffraction analysis and scanning electron microscopy. For analysis of the oxide layer growth mechanisms, twostage oxidation experiments with¹⁸O as tracer were used, the distribution of the oxygen isotopes in the oxide scale being determined by SIMS. The ODS alloys show a more selective oxidation than the two model alloys; moreover, the protective oxides on the ODS alloys have a lower growth rate and better adhesion than those on the two model alloys. From the SIMS investigations it can be deduced that the improved properties of the layers on the ODS alloys result from a change in the transport processes in the protective layer; whereas the aluminium and chromium oxide films on the conventional alloys grow by cation and anion transport, the scales on the ODS alloys grow almost exclusively by anion transport. It is shown that the observed properties of the oxide scales on the ODS alloys can be explained by this change in transport mechanism.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Three dimensional characterization of trace element distribution in high purity chromium

The investigation of the distribution of trace elements in two chromium samples with different corrosion resistivity is reported. The concentration of the trace elements in both samples is in the typical range of high purity chromium and did not explain the different behaviour in the corrosion test. To measure the three-dimensional distribution imaging secondary ion mass spectrometry (SIMS) was used. Fine details were measured by scanning SIMS because of the better resolution. An enrichment of nitrogen and carbon at the grain boundaries of the sample with lower corrosion resistivity was observed.     

Investigation on the influence of sulfur segregation on the adherence of protective oxide layers on high temperature materials

Summary Oxide layers of various thicknesses have been produced on Fe-15Cr and NiAl doped with sulfur. For thin oxide layers, depth profiles demonstrated that no sulfur is enriched at the oxide-metal interface. For thick oxide layers, the interface has been made accessible by bending or scratching the specimen. Sulfur has been found on the spalled area by AES. Micrographs proved that excessive void formation is responsible for the bad adherence of the oxide layers to the substrate. Sulfur segregaton decreases the surface energy, thus reducing the radius of nucleus formation and promoting void formation. Reactive elements form refractive sulfides with sulfur, thereby improving scale adherence.     

Quantitative SIMS depth profiling of Al in AlGaN/AlN/GaN HEMT structures with nanometer‐thin layers

The possibilities of quantitative secondary ion mass spectrometry (SIMS) depth profiling of Al in AlxGa1 ? xN/AlN/GaN transistor heterostructures are shown. Using a series of test structures for a TOF.SIMS‐5 time‐of‐flight mass spectrometer, we obtained a refined linear calibration dependence of the secondary‐ion yield on the composition ×, namely, Y(CsAl+)/Y(CsGa+) = K × x/(1 ? x), with a high linear correlation coefficient, Rl = 0.9996, which permits quantitative SIMS analysis of relatively thick AlGaN barrier layers. The method of profile reconstruction with allowance for the main artifacts of ion sputtering has been first applied for the analysis of GaN/AlGaN/AlN/GaN high electron mobility transistor structure. This method permits to perform quantitative analysis of the thickness and composition of a nanometer‐thin AlN sublayer and to estimate the measurement error. For the structure being studied, the AlN sublayer is 1.2 ± 0.2 nm thick. Copyright © 2016 John Wiley & Sons, Ltd.     

Surface analysis on discharged MnO2 cathode using XPS and SIMS techniques

Manganese dioxide (MnO₂) appears to be an effective cathode material for a battery system. No studies on lithium insertion in aqueous media are known to the best of our knowledge. However, in one of our previous papers we reported that lithium could be intercalated into a MnO₂ host compound using an aqueous LiOH electrolyte; however simple chemistry suggests that it should not. It is found that a battery with LiOH electrolyte functions quite differently from the cell that uses Li₂SO₄. This paper describes the surface modifications that accompany the electrochemical behavior of MnO₂ during redox (discharge) processes in the lithium hydroxide and sulfate media. XPS and SIMS techniques were used to study the resultant surface of the MnO₂ cathode and the spectra reveal that the formation of an insoluble layer of Li₂CO₃ precedes the process of reduction. SEM was used to study the microstructure of the MnO₂ cathode. Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of composition and growth mechanisms of oxide scales on high temperature alloys by SNMS,SIMS, and RBS

Composition and growth phenomena of alumina scales on a conventional wrought alloy Fe-20Cr-5Al and an yttria containing ODS alloy with the same base composition were investigated. The alloys were oxidized in a twostage oxidation process at 1000 °C in air and air containing¹⁸O-tracer. By using secondary neutrals and secondary ion mass spectrometry in combination with RBS, the in-depth concentration of main and minor alloying elements as well as the oxygen isotope distribution in the alumina scale could be determined. It is shown, that the difficulties in deriving the exact growth processes of the scales from the oxygen tracer profiles can be overcome by using the time dependance of the iron and chromium distribution in the alumina. From these results it could be derived that growth of the oxide scales formed on the ODS and the conventional alloy mainly differ in the relative contribution of aluminium diffusion. The mechanisms which lead to these differences in scale growth phenomena will be discussed.     

A comparison of the static SIMS and G‐SIMS spectra of biodegradable homo‐polyesters

Static SIMS (SSIMS) is a surface analytical technique capable of providing molecular chemical information from solids. A major barrier to the wider take‐up of the technique is the complexity associated with the interpretation of SSIMS spectra. Quality of the interpretation depends on the expertise of analysts and making references to the limited mass spectral libraries. For many materials, there are no SSIMS library spectra. A new library‐independent method, G‐SIMS, is capable of facilitating the interpretation of SSIMS data. G‐SIMS spectra contain parent fragments, which are formed without substantial degradation or rearrangements, and highlight molecular fragments, which are directly related to the surface. In our study, G‐SIMS has been tested on medically relevant biodegradable polyester series, including poly (glycolic acid) (PGA), poly‐l‐(lactic acid) (PLA), poly‐β‐(hydroxybutyrate) (PHB) and poly‐ε‐(caprolactone) (PCL). The polyester series chosen here have closely related structures, which allow us to explore the capabilities of G‐SIMS. The G‐SIMS spectra have facilitated the identification of different polyesters by exhibiting mainly characteristic ions, representative of the polymers' molecular structures. The results also indicated that for the chosen polyester series, the larger the repeating monomer structures, the smaller the maximum number of repeat units were seen in the G‐SIMS spectra. The G‐SIMS spectra for the homologous polyester series have provided an insight into the fragmentation mechanisms as a function of repeating monomer molecular weights and structures. Copyright © 2008 John Wiley & Sons, Ltd.     

Investigation of gettering effects in CZ-type silicon with SIMS

Ion implantation is a well-known standard procedure in electronic device technology for precise and controlled introduction of dopants into silicon. However, damage caused by implantation acts as effective gettering zones, collecting unwanted metal impurities. This effect can be applied for proximity gettering reducing the concentration of impurities in the active device region. In this study the consequences of high-energy ion implantation into silicon and of subsequent annealing were analysed by means of secondary ion mass spectrometry (SIMS). Depth profiles were recorded of such impurities as copper, oxygen and carbon to obtain information about their gettering behaviour. The differences in impurities gettering behaviour were studied as a function of the implanted ions, P and Si, of the implantation dose and annealing time at T=900°C. Besides impurities gettering at the mean projected range (Rp) of implanted ions, Rp-effect, defects at around half of the projected ion range, Rp/2-effect, and even in some cases beyond Rp, trans-Rp-effect, have also been found to be effective in gettering of material impurities.     

Comparison of ICP-MS and SIMS techniques for determining uranium isotope ratios in individual particles

The determination of uranium isotope ratios in individual particles is of great importance for nuclear safeguards. In the present study, an analytical technique by inductively coupled plasma mass spectrometry (ICP-MS) with a desolvation sample introduction system was applied to isotope ratio analysis of individual uranium particles. In ICP-MS analysis of individual uranium particles with diameters ranging from 0.6 to 4.2 μm in a standard reference material (NBL CRM U050), the use of the desolvation system for sample introduction improved the precision of ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope ratios. The performance of ICP-MS with desolvation was compared with that of a conventionally used method, i.e., secondary ion mass spectrometry (SIMS). The analysis of test swipe samples taken at nuclear facilities implied that the performance of ICP-MS with desolvation was superior to that of SIMS in a viewpoint of accuracy, because the problems of agglomeration of uranium particles and molecular ion interferences by other elements could be avoided. These results indicated that ICP-MS with desolvation has an enough ability to become an effective tool for nuclear safeguards.     

Statistically rigorous analysis of imaging SIMS data in the presence of detector saturation

We present a new strategy for analyzing imaging time‐of‐flight SIMS data sets affected by detector saturation. Rather than attempt to correct the measured data to remove saturation, we incorporate the detector behavior into the statistical basis of the analysis. This is performed within the framework of maximum a posteriori reconstruction. The proposed approach has several advantages over previous techniques. No approximations are involved other than the assumed model of the detector. The method performs well even when applied to highly saturated and/or single‐scan data sets. It is statistically rigorous, correctly treating the underlying statistical distribution of the data. It is also compatible with Bayesian methods for incorporating prior knowledge about sample properties. An efficient iterative scheme for solving the proposed equations is presented for the case of the bilinear model commonly used in analyses of SIMS data. The correctness of the approach and its efficacy are demonstrated on synthetic data sets. The method is found to perform better than a widely‐used data‐correction method used in combination with alternating‐least‐squares Multivariate Curve Resolution analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

SIMS of organic layers with unknown matrix parameters: Locating the interface in dual beam argon gas cluster depth profiles

Four simple methods are evaluated to determine their accuracies for establishing the interface location in secondary ion mass spectrometry intensity depth profiles of organic layers where matrix effects have not been measured. Accurate location requires the separate measurement of each ion's matrix factor. This is often not possible, and so estimates using matrix-less methods are required. Six pure organic material interfaces are measured using many secondary ions to compare their locations from the four methods with those from full evaluation with matrix terms. For different secondary ions, matrix effects cause the apparent interface positions to vary over 20 nm. The shifts in the intensity profiles on going from a layer of P into a layer of Q are in the opposite direction to that for going from Q into P, so doubling layer thickness errors. The four methods are as follows: M1, use of the median interface position in the intensity profiles for the five lightest ions for 15 ≤ m/z ≤ 150; M2, extrapolation of the position for each ion to m/z = 0 for ions with m/z ≤ 150; M3, as M2 but for m/z ≤ 300; and M4, the extreme positions for all m/z ≤ 100. Comparison with the location using matrix terms shows their ranking, from best to worst, to be M4, M3, M1, and M2 with average errors of 10%, 12%, 14%, and 17%, respectively, of the profile interface full widths at half maximum. Use of pseudo-molecular ions is very much poorer, exceeding 50%, and should be avoided.     

Investigation of non-metallic impurities in High Speed Steel using SIMS imaging and scanning techniques

Non-metallic impurities or phases are often unintentional but important constituents in steel – they primarily influence the properties and behavior of the material by forming crystallization nuclei during the solidification process of the molten material. The kind, formation and spatial distribution of these inclusions has been investigated in this work by 2D SIMS, depth profiling and scanning SIMS. These non-metallic phases can be divided into oxides, nitrides, carbides, sulfides and gas bubbles. Probably the most important phase, the oxygenic, results from reactions of the molten bath with the ambient air and from the admixture of de-oxidation components. The investigated HSS specimen exhibits two different classes of inclusions. The first class mainly contains sulfide precipitates and differs widely from the second. The latter exhibits a spherical structure with the outer sphere combining the oxygenic precipitation and the core containing nitrides and sulfides. Due to the small size of the inclusions, they have been investigated by high resolution scanning SIMS to separate the different phases. Received: 30 July 1997 / Revised: 9 February 1998 / Accepted: 15 February 1998     

Static SIMS studies of the oxides and hydroxides of aluminium

The degree of hydroxylation or hydration of aluminium surfaces has been examined by static secondary ion mass spectroscopy (SSIMS). The SSIMS spectra of a series of aluminium oxide, oxyhydroxide and hydroxide surfaces have been obtained using instruments in three configurations. Similarities were observed in both negative and positive secondary ions spectra. Even though a direct comparison of the relative intensities cannot be made from one instrument to the other, a similar ranking of the various aluminium hydroxylation states was observed. Several ranking methods are discussed, as well as the similarities and differences observed while using the three instruments. Similar secondary ions were detected whatever the degree of hydroxylation of the aluminium oxide. This argues in favour of the formation of fragments by the combination of individually sputtered atoms or clusters to form the more stable secondaries, rather than the kick-off of 'structure-related' clusters originating directly from the upper surface layer.     

Investigation of surface interactions between volatile chromium species and ceramics

Stainless steels are often used in high temperature (≥500°C) applications such as solid oxide fuel cells (SOFCs), combustion engine exhaust systems, and in power/chemical plant process equipment. At high temperature and in oxidizing conditions, chromium containing oxides, such as chromia, may form protective surface layers on the underlying alloy. Reactive evaporation of chromium, however, may occur from the protective surface layers given these conditions, resulting in the formation of volatile chromium species such as CrO₂(OH)₂. These volatile chromium species may then interact with surrounding materials, potentially resulting in hazardous compound formation, or having detrimental effects on system performance, as in the case of SOFCs. To better understand the interaction of volatile chromium condensation/deposition on material substrates, volatile chromium species were generated from chromia powder at 500°C to 900°C and flowed past coupons of alumina and mica and quartz wool at temperatures ranging from 150°C to 900°C for 24- and 100-hour exposures. The ceramic surfaces were characterized as a function of these exposures using X-ray photoelectron spectroscopy (XPS). Analysis of Cr 2p_3/2 peak positions revealed the influence of temperature, material, and exposure time on the oxidation states of surface chromium compounds and extent of chromium deposition. Potential mechanisms are proposed to help explain the observed trends.     

Growth and SIMS study of d.c.‐sputtered indium oxide films on silicon

Indium oxide thin films were grown onto Si and quartz substrates by d.c. reactive sputtering of elemental indium. X‐ray diffraction and transmission electron microscopy studies confirmed the single‐phase and polycrystalline nature of the films. Secondary ion mass spectrometry investigations of In₂O₃/Si structures showed the formation of an inhomogeneous interface region ～20 nm thick between In₂O₃ and Si. The overall feature of the interface remained the same under annealing in an oxygen atmosphere, but annealing in an argon atmosphere drastically altered the nature of the interface. The observations indicate that interface formation and stability depend critically on the availability of oxygen. Copyright © 2005 John Wiley & Sons, Ltd.     

Biphasic oxidation of diaquadichloro(1,10-phenanthroline)chromium(III) by N-bromosuccinimide and the formation of chromium(IV) and chromium(V)

The kinetics of oxidation of diaquadichloro(1,10-phenanthroline)chromium(III) complex, [Cr^III(phen)(H₂O)₂Cl₂]⁺, by N-bromosuccinimide (NBS) is biphasic. The first faster step involves the oxidation of Cr(III) to Cr(IV). The second slower step is due to the oxidation of Cr(IV) to Cr(V). The reaction product is isolated and characterized by electron spin resonance (ESR), IR, and elemental analysis. The chromium(V) product is consistent with the formula [Cr^V(phen)Cl₂(O)]Br. The rate constants k_f and k_s, for the faster and the slower steps respectively, were obtained using an Origin 9.0 software program. Values of both k_f and k_s, varied linearly with [NBS] at constant reaction conditions. The effect of pH on the reaction rate is investigated over the pH (4.11–6.01) range at 25.0°C. The rate constants k_f and k_s increased with increasing pH. This is consistent with hydroxo forms of the chromium species being more reactive than the aqua forms. Chromium(III) complexes, more often than not, are inert. The oxidation of the Cr(III) complex to Cr(IV), most likely, proceeds by an outer sphere mechanism. Since chromium(IV) is labile the mechanism of its oxidation to chromium(V) is not certain.     

Static TOF‐SIMS. A VAMAS interlaboratory study. Part II — accuracy of the mass scale and G‐SIMS compatibility

An interlaboratory study involving 32 time‐of‐flight static SIMS instruments from 13 countries has been conducted. In Part I of the analysis of data, we showed that 84% of instruments have excellent repeatabilities of better than 1.9% and that a relative instrument spectral response (RISR) can be used to evaluate variations between different generic types of instrument. Use of the RISR improves comparability between instruments by a factor of 33. Here, in Part II, we study the accuracy of the mass scale calibration in TOF‐SIMS and evaluate instrument compatibility with G‐SIMS. We show that the accuracy of calibration of the mass scale is much poorer than generally expected (?60 ppm for peaks <200 u and ?150 ppm for a large molecular peak at 647 u). This is a major issue for analysts. Elsewhere, we have developed a detailed study of the factors affecting the mass calibration and have developed a generic protocol that improves accuracy by a factor of 5. Here, this framework of understanding is used to interpret the results presented. Furthermore, we show that eight out of the ten participants submitting data for G‐SIMS could use operating conditions that generated G‐SIMS spectra of the PC reference material. This demonstrates that G‐SIMS may be conducted with a wide variety of instrument designs. © Crown Copyright 2007. Reproduced by permission of the Controller of HMSO. Published by John Wiley & Sons, Ltd.