Time-of-flight Secondary Ion Mass Spectrometry Study Research Articles

Evaluation of Molecular Fragmentation in Polycyclic Aromatic Hydrocarbons by Time-of-Flight Secondary Ion Mass Spectrometry

In time-of-flight secondary ion mass spectrometry (TOF-SIMS), ionized molecules and molecular fragments (secondary ions) are generated in collisions of high-energy ions (primary ions) with a solid sample surface. Mass spectra of the emitted secondary ions are typically used to identify molecular species and to determine their spatial distribution on the sample surface. Here, we extend this application in a TOF-SIMS study of a series of polycyclic aromatic hydrocarbons (PAHs) where we focus on the fragmentation of these molecules, with the purpose of better understanding the fragmentation patterns of heavy aromatic molecules in petroleum. For all PAHs, the collision process generated (i) a series of smaller cation fragments and (ii) cations close in size to the original PAH (molecular cations). Stark differences are measured for various PAHs regarding the abundance of smaller fragments versus molecular cations. Observation of hydrogen-deficient (H-deficient) cation fragments indicates the formation of polyynes and allenes. For PAHs producing higher fractions of small cation fragments, these ions are surprisingly hydrogen rich (H-rich). The H/C ratio of fragments does not scale with the fraction of Clar sextet carbon, nor with energies of low-lying electronic transitions. Free radical cation fragments tend to be suppressed. For sufficiently large fragments, aromatic cations appear to be formed and include some free radical aromatics. There is ample production of molecular ions with loss of a single carbon atom or a methine group, which corresponds to the reduction of a 6-membered aromatic ring to a 5-membered ring. There is some enhancement of free radical molecular cations due to the corresponding formation of neutral polyynes. Fragment anions are also produced with a strong preference for very H-deficient carbon clusters, in some cases being the same as carbon cluster anions observed in space. Comparisons of PAH TOF-SIMS spectra with those of asphaltenes are discussed in detail.

TOF-SIMS study of latent fingerprints on challenging substrates with the aid of transfer films.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been applied in forensic science for fingerprint detection. However, due to limitations of the instrument, it is not always possible to directly sample fingerprints on certain substrates. In this report, we indirectly sampled fingerprints using transfer films. First, we optimized the experimental conditions and identified transfer films with better results. We then explored the feasibility of revealing fingerprints after transfer and successfully transferred and revealed the detailed features of fingerprints on several common objects that could not be directly sampled. Fingerprints transferred from smooth surfaces yield clearer feature details in ion images. Additionally, we analyzed the substances in the transferred fingerprints and detected components of morphine and MDMA(3,4-methylenedioxy-n-methylamphetamine). By combining feature details with identified chemical components, the identity of a person can be determined, linking suspects to the crime scene. This work provides a new approach for sample introduction in instrumental analysis, enabling TOF-SIMS to be applied in more scenarios.

Nanostructured fluids confined into Highly Viscous Polymeric Dispersions as cleaning tools for artifacts: A rheological, SAXS, DSC and TOF-SIMS study

The development, and the structural and mechanical characterization of an new complex system composed by an oil-in-water microemulsion (μE) embedded in a aqueous 3D Highly Viscous Polymeric Dispersion (HVPD) of poly(vinyl alcohol) (PVA) cross-linked by borax, is here presented together with its possible implications in paintings conservation. The HVPD/μE was characterized by Small Angle X-Rays Scattering (SAXS), Differential Scanning Calorimetric (DSC) and rheology to obtain information about the mutual effect of the μE and of the PVA network on both the nanostructure of the μE, and on the mechanical behavior of the system. Experimental data indicate that the nanostructure of the μE is retained even in the presence of the PVA/borax network whose mechanical properties are enhanced by the presence of the nanofluid. The effect of HVPD/μE on organic molecules thin films of varnish coatings usually used on easel paintings, was studied by Attenuated Total Reflection Fourier Transform InfraRed spectroscopy (ATR-FTIR) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The results showed that an interaction occurred leading to the extraction of the organic molecules within the HVPD/μE. The applicative consequence was that the HVPD/μE complex fluid revealed itself to be a potential, very powerful and “green” tool for selective cleaning of easel paintings affected by artificial aged coatings, with very low environmental impact and leaving no residues onto the painting surface.

ToF-SIMS evaluation of markings made by the same black ballpoint pens at different times

The differentiation and relative dating of ink lines in questioned documents are important tasks in forensic science. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a surface-sensitive mass spectrometry technique with potential to distinguish inks based on chemical differences such as those caused by differences in the age of ink markings from the same pen. In this work, both positive and negative polarity ToF-SIMS spectra were evaluated for three commercial black ballpoint pen inks over an analysis time of 4 to 671 days. Changes in the spectra included demethylation of triarylmethane dyes such as crystal violet, and loss of the anionic dye metanil yellow. ToF-SIMS spectra of the black ballpoint inks continued to change up to 6 months for all inks and up to 22 months in some cases. Samples with 1-day, 1-week and 1-month drying times were also evaluated using several data processing approaches. Markings from the same pen were most likely to be distinguished by ToF-SIMS if the age difference between the markings was 1 month or longer, although some samples were distinguished with smaller differences in writing times. Furthermore, the results indicated that ToF-SIMS imaging is best performed within 3–6 months after sample preparation as differentiation becomes more difficult after longer analysis delays. This is the first systematic ToF-SIMS study of ink aging, which provides valuable information about the characteristic ions and data analysis approaches for future forensic analyses.

ToF-SIMS study of selective anchoring of Ru(tpy)2 complexes on zirconium-phosphate functionalized oxide surfaces

Polypyridine-based ruthenium complexes are among the most interesting photoactive molecular systems, in virtue of a number of outstanding (photo)physicochemical properties. To exploit such properties in solid-state applications, such as molecular electronics, optoelectronics, and photovoltaics, tailored experimental strategies are needed for the anchoring of such complexes on surfaces. At the same time, these strategies need to be investigated and validated through precise monitoring of the surface composition. In this contribution, the authors report on the application of time-of-flight secondary ion mass spectrometry (ToF-SIMS) for studying the anchoring onto transparent (semi)conducting fluorine tin-doped oxide of the polypyridinic photoactive RuDT2. This molecule is characterized by an Ru(tpy)2 core and two free terpyridinic units. The authors’ approach involves the use of a surface priming strategy based on the chemistry of zirconium phosphates and phosphonates (ZP-priming) to provide a platform for direct anchoring of RuDT2 molecules at the oxide surface. Onto patterned ZP-fluorine-doped tin oxide (FTO), the authors report selective anchoring of RuDT2 only onto ZP domains, while no binding occurs onto bare FTO areas. The latter were shown to remain available for further functionalization using functional molecules containing phosphonic moieties, and in the authors’ case, a phosphonic derivative of rhodamine B (RhB-P) was used. ToF-SIMS imaging was intensively used to monitor each reaction step and confirm the successful laterally resolved and selective adsorption of RuDT2 and RhB-P onto ZP and bare FTO domains, respectively.

TOF-SIMS study of morphology and chemical composition of wustite-based precursor and iron catalyst for ammonia synthesis

This study focuses on the application of time-of-flight secondary ion mass spectrometry (TOF-SIMS) for analysis of the morphology and chemical composition of a wustite-based precursor and iron catalyst for ammonia synthesis. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used as supplementary methods. TOF-SIMS imaging was capable of visualizing the micrometer-scale spatial distribution of elements on the surface of the catalyst precursor, which was composed of wustite crystallites separated by spaces, with high concentrations of K, Al and Ca used as promoters. Moreover, aluminum and calcium were detected in the wustite crystallites. Potassium, despite having a vanishingly low concentration in wustite phase, was able effectively to wet the wustite surfaces upon annealing at 350 °C.The potassium layer that formed on the surface of the wustite precursor had a different composition than that on the surface of the iron nanocrystallites of the iron catalyst. The most important finding concerns the composition of the surface of the iron catalyst.TOF-SIMS analysis showed a layer containing oxygen in the subsurface region of the iron catalyst obtained from the wustite-based precursor. This structure on the surface of the iron catalyst enabled the formation of active sites for the adsorption of nitrogen on iron atoms during ammonia synthesis.

ToF-SIMS study of oxide films thermally grown on nickel-base alloys

The oxidation behaviours of polycrystalline and monocrystalline Ni-base alloys (Ni-16Cr-8Fe (wt%)) were investigated in situ by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The oxide layer formed is duplex: an inner chromium-rich layer and an outer layer which is rich in nickel and iron. Time evolution of the composition of inner layer from pure Cr2O3 towards spinel (NiCr2O4) was observed. The oxidation kinetics was accelerated by alloy grain boundaries, which can favour the diffusion of chromium. Both the parabolic and volatilization constants increased with increasing temperature, with kp varying from 1.9×10−3 to 1.6×10−2 nm2.s−1, and kv from 1.0×10−3 to 2.9×10−3 nm.s−1.

Effects of silane- and MDP-based primers application orders on zirconia–resin adhesion—A ToF-SIMS study

ObjectiveTo evaluate the 3-methacryloyloxypropyltrimethoxysilane (MPS)- and 10-methacryloyloxydecyl-dihydrogen-phosphate (MDP)-base primers, in their single or sequential applications, with regard to modifying zirconia surfaces and improving resin–zirconia adhesion. MethodsZirconia disks received different treatments: without primer (Zr), MPS-base primer (S), MDP-base primer (M), MPS/MDP mixture (SMmix), MPS followed by MDP (SM), and MDP followed by MPS (MS). The compositions and chemical interactions of the coatings to zirconia were analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS) and reconstructed 3D ion images. Surface wettability of these coatings to water and resin adhesive was assessed. The shear bond strength (SBS) between resin and the treated zirconia was also examined before and after thermocycling. ResultsGroups S and MS presented substantial OH− ions in the coatings and zirconia substrate. PO2− and PO3− fragments existed in all MDP-treatment groups with various proportions and distributions, while groups M and SM showed higher proportions of PO3− and the zirconium phosphate related ions. In 3D ion images, PO3− in groups M and SM was denser and segregated to the interface, but was dispersed or overlaid above PO2− in SMmix and MS. All the primers increased the surface wettability to water and resin, with M and SM presenting superhydrophilic surfaces. All MDP-treatment groups showed improved SBS before thermocycling, while M and SM retained higher SBS after this. SignificanceThe MDP-base primer shows a relevant function in facilitating POZr bonding and enhancing resin–zirconia bonding. The co-treated MPS impairs the chemical activity of MDP, especially if it is the final coat.

ToF-SIMS study of differentiation of human bone-derived stromal cells: new insights into osteoporosis

Lipids have numerous important functions in the human body, as they form the cells' plasma membranes and play a key role in many disease states, presumably also in osteoporosis. Here, the fatty acid composition of the outer plasma membranes of cells differentiated into the osteogenic and adipogenic direction is studied with surface-sensitive time-of-flight secondary ion mass spectrometry (ToF-SIMS). For data evaluation, principal component analysis (PCA) is applied. Human (bone-derived) mesenchymal stromal cells (hMSCs) from an osteoporotic donor and a control donor are compared to reveal differences in the fatty acid composition of the membranes. The chemical information is correlated to staining and real-time quantitative polymerase chain reaction (rt-qPCR) results to provide insight into the gene expression of several differentiation markers on the RNA level. Adipogenic differentiation of hMSCs from a non-osteoporotic donor correlates with increased relative intensities of all fatty acids under investigation. After osteogenic differentiation of non-osteoporotic cells, the relative mass signal intensities of unsaturated fatty acids such as oleic and linoleic acids are increased. However, the osteoporotic cells show increased levels of palmitic acid in the plasma membrane after exposure to osteogenic differentiation conditions, which correlates to an immature differentiation state relative to non-osteoporotic osteogenic cells. This immature differentiation state is confirmed by increased early osteogenic differentiation factor Runx2 on RNA level and by less calcium mineralization spots seen in von Kossa staining and ToF-SIMS images. Graphical abstract Time-of-flight secondary ion mass spectrometry is applied to analyze the fatty acid composition of the outer plasma membranes of cells differentiated into the adipogenic and osteogenic direction. Cells from an osteoporotic and a control donor are compared to reveal differences due to differentiation and disease stage of the cells.

Detection and distribution of lithium in Mg-Li-Al based alloy by ToF-SIMS

Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) is used to investigate the surface as well as bulk microstructural features of novel Mg-Li-Al based alloy namely Mg-9Li-7Al-3Sn-1Zn (LATZ9531). ToF-SIMS study indicates that there are six multi-oxide layers present within the surface film of LATZ9531. Furthermore, The presence of Li containing phase has been qualitatively confirmed based on the high number of Li-ion counts in SIMS, and the same is verified quantitatively by using electron probe microanalysis (EPMA). The novel approach may be useful to determine the chemical composition of the phases in various alloys which has lighter alloying elements such as lithium.

Fluorine plasma treatment of bare and nitrilotris(methylene)triphosphonic acid (NP) protected aluminum: an XPS and ToF-SIMS study

Nitrilotris(methylene)triphosphonic acid (NP) is a technologically important molecule that has been used for years as a corrosion inhibitor and/or adhesion promoter on aluminum and other metal surfaces. However, to the best of our knowledge, the detailed surface characterization of NP adsorbed on aluminum, or on any other surface, has not been reported. Herein, we report an X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis of a series of untreated and NP-coated aluminum substrates that were exposed to the downstream products of a fluoroalkane + oxygen plasma for different amounts of time (from 0 to 20 s). As indicated by P 2p, N 1s, Al 2p, O 1s, and F 1s narrow scans, even a 4-s plasma treatment significantly damages the NP protective layer and converts the native aluminum oxide into aluminum oxyfluoride. Heat treatment of the fluorine plasma-treated samples in the air substantially converts the aluminum oxyfluoride back to aluminum oxide, while similar heating under vacuum results in little change to the materials. A slow loss of fluorine from the samples occurs over the course of weeks when they are stored in the air. A ToF-SIMS analysis reveals sets of signals that are consistent with no surface treatment, NP treatment, or fluorine plasma treatment. A principal component analysis of the negative ion ToF-SIMS spectra from the samples shows the expected differentiation of the samples. Copyright © 2014 John Wiley & Sons, Ltd.

A combined ToF-SIMS and XPS study for the elucidation of the role of water in the performances of a Post-Plasma Process using LaMnO3+δ as catalyst in the total oxidation of trichloroethylene

LaMnO3+δ which is an environment-friendly and inexpensive material has been previously used as catalyst in Post-Plasma Catalysis (PPC) in the total oxidation of trichloroethylene (TCE) which is a solvent widely used in dry cleaning and degreasing processes. It has been shown that the process efficiency increases in moist air (RH=18%).The issue we want to address herein is the effect of water on the location of chlorine at the surface of the catalyst as chlorine is able to alter the catalyst structure, activity and stability. Therefore, a combined Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS) study has been carried out on the fresh LaMnO3+δ catalyst (LM) and used catalysts after performing PPC with TCE diluted in dry synthetic air (LM0) or with industrial air containing water (LM18; 18 stands for the Relative Humidity) and CO2 (about 560ppmv) at a temperature of 150°C. XPS and ToF-SIMS results both show the presence of chlorine on the tested catalysts whose amount increases by exposure of the catalyst to the reactive mixture in dry synthetic air. XPS results reveal that chlorine is present as both chloride ion and covalent chlorine on LM0 while organic chlorinated residues are absent on LM18 catalyst. ToF-SIMS study indicates that lanthanum excess as oxide(hydroxide) partially covering the perovskite mainly transforms into LaOCl and to a minor extent into LaCl3. Extent of Mn chlorination seems to be favored over LM0 having a higher MnClx±/MnOCl± ionic ratio compared to LM18. Furthermore ToF-SIMS clearly identifies C1 chlorinated organic ions, mainly CH2Cl+ and CHCl2−, on LM0 which may contribute to the XPS Cl organic component. From the combined ToF-SIMS and XPS results it is found that water delays the surface degradation extent of the perovskite into related (oxy)(hydroxy)chlorinated inorganic phases by less molecular chlorine and related chlorine species on the catalyst surface. A reaction scheme of Cl removal over LaMnO3+δ emphasing the role of water is given taking into account the detection of ToF-SIMS ions representative of the successive Mn intermediate states. As a consequence water allows tuning the degradation pathways of the main intermediate of the reaction, dichloroacetyl chloride (DCAC), which decomposes to give phosgene, HCCl3 and CCl4 by a successive Cl incorporation over (oxy)(hydroxy)chorinated perovskite or/and Mn species while COx species are likely formed over the perovskite.

TOF–SIMS study of polyester/melamine resin with Ar gas cluster ion beam

A pre‐coated steel sheet for household electrical appliances needs to be highly formable and stain resistant. In recent years, secondary ion mass spectrometry (SIMS) with a time‐of‐flight (TOF) mass analyzer with an Ar gas cluster ion beam (Ar–GCIB) has been widely used as a structure analysis technology of organic molecules. In this paper, we looked into the effectiveness of Ar–GCIB–TOF–SIMS as a structure analysis technique of paint film. As a result, we could detect the trimer fragment ions of hexamethoxymethylmelamine in the range of m/z = 400–800 for the first time for the spin‐coating of HMMM on a Si wafer. By evaluation of characteristic monomer fragment ions, we could find out the different surface distributions of melamine‐formaldehyde resin with the different formulations of paint films. Copyright © 2014 John Wiley & Sons, Ltd.

A contact angle and ToF-SIMS study of SAM–thiol interactions on polycrystalline gold

A process of chemical differentiation of neighboring Au features on a substrate (for biosensing applications) involves a step, where after electrochemical removal of a self-assembled monolayer (SAM) from one feature, another SAM is deposited onto it by incubation with a different thiol. During this incubation step, other undesorbed features are also exposed to this thiol which may lead to a partial SAM–thiol exhange, the extent of which is a function of time. Here, such surface reactions were followed on polystalline Au in both directions using contact angle measurements and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The thiols involved were dodecanethiol (DDT) which forms SAM promoting adsorption of proteins and 11-mercaptoundecyl)tri(ethylene glycol) (TPEG) whose SAM prevents such adsorption. The surface reactions in both directions cannot be described by a simple pseudo-first-order kinetics. It was found that while the DDT SAM interaction with a TPEG solution leads eventually to a total replacement, the reverse process, TPEG SAM interaction with DDT, leads to no noticeable exchange over the first 3h and then asymptotically approaches ∼50% replacement.

XPS and ToF-SIMS study of Sn–Co alloy thin films as anode for lithium ion battery

Sn–Co alloy films were prepared by electroplating on copper and used as anode material of lithium ion battery. Cyclic voltammetry and galvanostatic discharge/charge measurements were combined with surface analysis by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results show the buildup of a solid electrolyte interphase (SEI) layer formed by reductive decomposition of electrolyte during the first Li–Sn alloying cycle. The layer is constituted of a mixture of Li 2CO 3, ROCO 2Li, lithium oxalates, and/or ROLi, and its chemical composition is modified during the electrochemical multi-cycling process with increase of the Li 2CO 3 content. Multi-cycling also fractures the SEI layer. ToF-SIMS results revealed an incomplete initial alloying process of lithium ion with Sn, limited by mass transport through a Co layer and dividing the Sn–Co layer alloy into a fully lithiated outer part and an essentially non-lithiated inner layer during the first discharge. The volume expansion/shrink associated with the alloying/dealloying reaction irreversibly cracks and splits up the Sn–Co alloy into particles with interstitials voids filled by the SEI layer. Multi-cycling amplifies this division of the Sn–Co layer without material loss and stabilizes discharge/charge capacity.

TOF-SIMS study of red sealing-inks on paper and its forensic applications

Red sealing-ink samples are frequently submitted to forensic laboratories for identification and comparison in a wide variety of criminal and civil cases. The non-destructive identification of sealing-inks on paper is of important to preserve as large an amount of a fraudulent check, forged document, or other such evidence as possible for use in legal proceedings. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) for the analysis of red sealing-inks on paper surfaces was investigated. TOF-SIMS spectra were employed to identify elements and organic compounds in red sealing-inks. An analysis was performed on five sealing-inks of red color manufactured in Korea, Japan, and China. Several fibers from specific sealing-ink sample on paper can be removed leaving little evidence of tampering and can be distinguished from other sealing-inks. Overlapped area of sealing-ink and ballpoint pen in the document was also investigated in order to identify the sequence of recording. Therefore, this study shows that TOF-SIMS is a useful technique for the non-destructive analysis of red sealing-inks on paper.

Photocatalytic decomposition of methylene blue and 4-chlorophenol on nanocrystalline TiO 2 films under UV illumination: A ToF-SIMS study

The photocatalytic degradation of methylene blue and 4-chlorophenol on nanocrystalline TiO 2 (nc-TiO 2) under UV irradiation was investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Nanocrystalline TiO 2 films were prepared from suspensions containing TiO 2-crystallites of different average sizes, the smallest one being 12 nm. The organic substances (either methylene blue or 4-chlorophenol) were applied to these films. The specimens were studied in the pristine state and upon UV exposure. The UV illuminations were carried out both under atmospheric conditions and in situ under ultrahigh vacuum in the ToF-SIMS instrument. Distinct mass signals from the parent molecules and from fragment ions are observed for the as-prepared samples. Upon irradiation with UV light under atmospheric conditions, the surface composition is significantly changed, an observation ascribed to photocatalytic reactions induced by UV photons: the parent molecule signals are strongly diminished whereas fragmentation products are identified to be present at the TiO 2 surfaces. UV irradiations carried out under different vacuum conditions in the ToF instrument (ultrahigh vacuum, air or oxygen adsorption) indicate that varying ambient conditions may influence the photocatalytic reaction on the nanocrystalline TiO 2 films.

ToF-SIMS study of growth behavior in all-nanoparticle multilayer films using a novel indicator layer

All-nanoparticle multilayer films found novel applications in the areas of photonics, catalysis, sensors, and biomaterials. The assembly of nanoparticles into conformal and uniform films with precise control over chemical and physical properties poses a significant challenge. Using time-of-flight secondary ion mass spectrometry (ToF-SIMS), we have investigated the growth behavior in all-nanoparticle multilayer films using a novel indicator layer. The all-nanoparticle multilayer films were prepared by dipping the polyester substrate with electrostatic charges alternatively into solutions containing three different types of nanoparticles (TiO 2, Al 2O 3, and SiO 2). Upon the deposition of each layer, ToF-SIMS was employed to determine the surface chemical composition of intermediate products. The intermixing extent of TiO 2 indicator layer was used to reveal the stratification of each layer. Combining with zeta-potential measurements, the solvation and deposition of the under-layer species in the aqueous environment during fresh layer formation was proposed as a plausible cause for mutilayers not stratified into well-defined layers but displaying a nonlinear growth behavior.

Characterisation of poly(methyl methacrylate) film deposited on iron powder particles by electropolymerization

Iron powder microparticles were coated with a poly(methyl methacrylate) (PMMA) film by electropolymerization in a fluidised bed reactor. The formation of a PMMA coating on the microparticles’ surface was studied with pyrolysis gas chromatography (Py-GC) fingerprinting as well as time-of-flight secondary ion mass spectrometry (TOF-SIMS). While Py-GC can provide information about PMMA bulk formation and quick information about PMMA deposition on iron microparticles, TOF-SIMS can give detailed information about particle surface PMMA coatings. A TOF-SIMS study was performed in both, positive and negative ion modes with Bi + and Bi 3 + primary ions. Static TOF-SIMS macroscans of powder microparticle surface resulted in the identification of the regions with species related to the PMMA fragments in the negative ion region ( Bi 3 + ) . TOF-SIMS results confirmed that PMMA coating on the iron powder microparticle surface formed an incoherent and inhomogeneous film. PMMA coating was somewhere very thin to supply a sufficient positive charged secondary ion signal. Plating of metallic powder particles by polymeric coating enables the modification of surface and structural properties of materials used in powder metallurgy. PMMA coated iron powder microparticles can be innovative as lubricants in such a way that, when they are subjected to pressure, they burst and release carbon to metal powder. The main aim of this research work is to characterise PMMA coatings deposited by electropolymerization on the surface of iron powder microparticles.

Temperature-dependent modifications in the surface composition of Finemet: A ToF-SIMS study

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was employed as an in situ tool to study the temperature-induced alteration of the surface composition of amorphous Finemet, Fe 73Si 15.8B 7.2Cu 1Nb 3. Temperature was changed reversibly by cooling from room temperature to 118 K and warming back to room temperature. As a general result, the ion intensities and, consequently, the surface concentrations of the alloy constituents were found to vary non-monotonously. Therefore segregation processes were in operation the extent of which was element-specific. Most importantly, while cycling the temperature hysteresis behaviour was observed with concentration of Fe developing just opposite to that of the alloying elements. Accordingly, on cooling the alloy, the surface enrichment with B, Si, Nb, Cu attained first a maximum in the range of 248–193 K before the segregation changed the trend to establish appreciable depletion of these elements at 118 K (as compared to room temperature). By contrast, the surface iron content developed inversely and decreased first to a minimum at ∼223 K before reaching enrichment at 118 K. During warming, a maximum segregation of boron and silicon was observed at about 223 K – similar as on cooling – so that this temperature can be considered characteristic of the segregation process. Dissociative adsorption of water from the residual atmosphere occurring at low temperatures was responsible for the formation of surface hydroxides of iron, silicon and niobium; an enhanced adsorption of molecular water was observed at temperatures below 153 K. The temperature-dependent segregation and adsorption–desorption processes were found to be largely reversible, so that the surface composition of Finemet was practically restored after finishing the cooling–warming cycle. The processes and factors governing the non-monotonous temperature dependence of the surface segregation in the amorphous alloy are discussed within the frame of segregation theory and the influence of temperature-induced tensile stress on segregation.