Annemie Adriaens

Static secondary ion mass spectrometry : (S-SIMS). Part 1. Methodology and structural interpretation

Static secondary ion mass spectrometry (S-SIMS) allows the chemical characterization of the constituents in the upper monomolecular layer of a solid sample. Within the range of micro-analytical methods, S-SIMS occupies a rather unique position in that it combines monolayer sensitivity with the capability to generate molecular information. In general, elemental ions, structural fragments, molecular and adduct ions are generated from both inorganic and organic molecules, including polymers. The chemical analysis of the upper monolayer makes S-SIMS especially suited to the study of the interface chemistry in a variety of materials. Polymer applications take an important place because S-SIMS allows a lot of information on these often intractable materials, e.g., identification, detection of surface functionalities, study of segregation of copolymer components and molecular weight (MW) distributions. In addition to the qualitative identification, S-SIMS allows high reproducibility and thereby permits quantitative studies with the aid of standards. Finally, S-SIMS offers imaging capabilities to visualize directly the distribution of given components within the upper surface layer of solids. Mapping with high lateral resolution is feasible for elemental ions and in favorable cases also for organic compounds. This review aims at a comprehensive coverage of the S-SIMS literature of the past decade. It comprises two parts, of which the first part deals with the more general aspects of the technique. It begins with a brief tutorial review of instrumentation, methodology and current concepts of ion formation. Particular attention is given to the link and difference with the matured dynamic SIMS method. Finally, imaging in S-SIMS is discussed. Application of S-SIMS to complex materials makes the interpretation of signals, in terms of the sample composition, intricate but crucial. Therefore, the features of inorganic and organic mass spectra are surveyed to assess the structure specificity and the kind of information obtainable. The second part of this review focuses on a variety of applications, primarily in the field of material sciences. Detailed studies on the surface chemistry of catalysts are discussed. The increasing importance of surface modification and tailoring to improve the interface properties has generated a wide range of applications. Examples from different technologies and industrial processes, such as semiconductors, paint, composite materials and corrosion protection of metals, are highlighted. Attention is devoted to the complementarity between S-SIMS and other micro-analytical surface techniques. The review aims at being of interest on the one hand to the S-SIMS users looking for interesting application areas and on the other hand, to the application chemists searching a method, potentially capable of yielding specific information for their material analysis problem.

Surface characterization of artificial corrosion layers on copper alloy reference materials

Abstract This paper describes the surface characterization of artificial patina layers on five different copper alloys. The chemical composition of the examined bronzes covers the major families of archaeological copper alloys from antiquity until the Roman period. The patina layers of the five samples were formed under identical conditions by electrochemical means. Light microscopy, scanning electron microscopy with energy dispersive X-ray micro analysis (SEM–EDX) and Fourier transform infrared spectroscopy (FTIR) were used to describe the main properties of the patina layers. The results were interpreted and classified according to an existing corrosion model for copper alloys.

A comparison of microbeam techniques for the analysis of corroded ancient bronze objects

This paper describes the use of several microbeam analysis techniques for the chemical characterization of corrosion compounds on ancient bronze objects. They include optical microscopy, SEM-EDX, TOF-SIMS, SR-FTIR, SR-XRD, and XANES. The objective is to investigate which combination of analysis methods is most suitable for this type of application, taking into account aspects such as limited sampling and the ability of obtaining spatial information. Results show that SR-XRD in combination with optical microscopy and SEM-EDX is able to provide a complete description of the layered structure both on elemental and molecular level.

Electrochemical determination of hydrogen peroxide with cytochrome c peroxidase and horse heart cytochrome c entrapped in a gelatin hydrogel

A novel and versatile method, based on a membrane-free enzyme electrode in which both the enzyme and a mediator protein are entrapped in a gelatine hydrogel was developed for the fabrication of biosensors. As a proof of principle, we prepared a hydrogen peroxide biosensor by successfully entrapping both horse heart cytochrome c (HHC) and Saccharomyces cerevisae cytochrome c peroxidase (CCP) in a gelatin matrix which is immobilized on a gold electrode. This electrode was first pretreated with 6-mercaptohexanol. The biosensor displayed a rapid response and an expanded linear response range from 0 to 0.3 mM (R = 0.987) with a detection limit of 1 × 10(-5)M in a HEPES buffer solution (pH 7.0). This method of encapsulation is now further investigated for industrial biosensor applications.

Self-Assembled Supramolecular Array of Polymeric Phthalocyanine on Gold for the Determination of Hydrogen Peroxide

This Article describes for the first time the formation of a supramolecular self-assembled monolayer of polymeric phthalocyanine (poly(CuPc)) onto a gold substrate. The latter is established through the interaction of the cyano group, belonging to the poly(CuPc), with the metal substrate. The functionalized gold substrate was characterized using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and electrochemical methods. Results clearly demonstrated the interaction between gold and the nitrogen atom of cyano group and showed at the same time the formation of a completely covered polymeric monolayer on the gold surface. In addition, the modified gold surface seems to exhibit a reversible redox behavior and is found to act as an electronic conductor, which allows rapid electron transfer. Electrochemical impedance spectroscopy (EIS) analyses in the presence of [Fe(CN)(6)](3-/4-) as a redox couple revealed that the modified electrode showed a much lower electron transfer resistance compared with bare gold. In addition, the modified electrode is found to catalyze the H(2)O(2) reduction very effectively, showing a catalytic current that varies linearly with the peroxide concentration in the range of 0.35 to 70 μM with a detection limit of 0.25 μM.

Investigation of grain boundary segregation in acceptor and donor doped strontium titanate

Abstract Grain boundary segregation in electronic ceramics is often responsible for dictating the grain boundary properties, which in turn dictate the macroscopic electronic properties of the material. Consequently, it is important to understand the nature of segregation phenomena in these materials. Here we present results from a combination of diverse analytical techniques used to investigate the character of grain boundary segregation in acceptor (Fe, Mn) and donor (Nb) doped strontium titanate. X-ray emission spectroscopy (XES) and electron energy loss spectroscopy (EELS) analysis consistently show segregation of both acceptor (Fe, and Mn) and donor (Nb) dopant species to the grain boundaries. Within the spatial resolution of the techniques, the segregation profiles for these dopants are found to be limited to less than 5 nm about the grain boundaries. Furthermore secondary ion mass spectroscopy shows that the segregation is ubiquitous throughout the samples, and not limited to selected grain boundaries.

Electrochemical study of gelatin as a matrix for the immobilization of horse heart cytochrome c

The aim of this paper is to emphasize the strength of gelatin as a stable matrix for redox enzymes. Cyclic voltammetry has been applied for a detailed electrochemical study of horse heart cytochrome c (HHC) entrapped in a gelatin matrix immobilized on a gold electrode. The influence of the HHC concentration, the mass percentage of the gelatin and the nature of the gelatin on the electrochemical behaviour of HHC have been described in detail. In addition, attenuated total reflection infrared (ATR-IR) spectroscopy was used to prove the immobilization on a qualitative and conformational level. The thickness of the gelatin film was determined using a non-contact optical profiler. These results open up new perspectives in the development of stable, biocompatible matrices for redox enzymes. The latter has its relevance in the field of biosensor development.

Electrochemical quantification of copper-based alloys using voltammetry of microparticles: optimization of the experimental conditions

Voltammetry of microparticles has been used in this work for the qualitative and quantitative analyses of zinc, tin, lead and copper in binary, ternary or quaternary alloy samples. The analyses were carried out by spiking small amounts of the metals into a carbon paste electrode, after which they were anodically stripped off using differential pulse voltammetry. The work involved four separate experiments. The first one examined the type of electrolyte, which is suitable to identify the four elements. More specifically, the aim was to examine in which electrolyte all elements can be measured simultaneously–as would be the case in a quaternary copper alloy–without seeing any overlap in their current peaks. The second experiment focused on optimizing the measurement conditions with the aim of having the current peaks of each element well separated from the others. For this part, we made use of the central composite design. The aims were to: (i) maximize the separation between current peaks, (ii) determine which variable has a higher impact on the response, (iii) give an insight in the robustness of the method close to the optimum conditions and (iv) eventually show interactions between variables. In the third experiment, the four elements were quantified in their binary mixtures. Here, the percentage of the oxidation current for each metal, which is directly related to the ratio of the metal in the binary matrices, was employed for the calibration. Finally, in the last experiment, the elements were quantified in two real quaternary samples: a brass and a lead bronze.

Microscopical speciation analysis with laser microprobe mass spectrometry and static secondary ion mass spectrometry

This paper presents a set of data which compares the potential and limitations of laser microprobe mass spectrometry (TOF-LMMS and FT-LMMS) and static secondary ion mass spectrometry (S-SIMS) for inorganic speciation at a microscopical level. In general LMMS yields prominent signals of adduct ions consisting of the intact molecule combined with a stable ion, which allows a direct identification of the analyte. S-SIMS also yields abundant diagnostic signals to specify the molecular composition. However, adduct ions are not always present, which means that the identification often relies on fingerprinting. Results further indicate that the potential and the application area of S-SIMS and FT-LMMS are complementary to one another.

Influence of pH and Chloride Concentration on the Corrosion Behavior of Unalloyed Copper in NaCl Solution: A Comparative Study Between the Micro and Macro Scales

The effects of pH and chloride concentration on the electrochemical corrosion of copper in aqueous sodium chloride (NaCl) media were studied at the micro scale using a microcapillary droplet cell and at the macro scale using a conventional large scale cell. Using an experimental design strategy, electrochemical response surface models of copper versus pH and NaCl concentration were constructed with the minimum number of experiments required. Results show that the electrochemical behavior of copper under corrosive media shows significant differences between the micro and macro scale experiments. At the micro scale, the pit initiation of copper occurs at more negative potentials for high NaCl concentrations and alkaline pH values. Also, the micro scale potentiostatic measurements indicate higher stabilised passive currents at high NaCl concentrations and low (acidic) pH values. At the macro scale, the pH is shown to have a greater influence on the corrosion potential. The chloride concentration is the most significant factor in the passive current case while at the micro scale the effect of these two factors on the passive current was found to be the same. The surface morphology of the formed patina on the corroded copper in both micro and macro systems reveal a more significant role of the chloride concentration on the structure and the grain size of the patinas. Finally, micro and macro electrochemical impedance spectroscopy of copper at various NaCl concentrations and pH values demonstrates a different behavior of copper after several potentiodynamic polarization cycles.