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The successful use of a microband electrode printed on a silicon internal reflection element to perform time resolved infrared spectroscopy is described. Decreasing the critical dimension of the microband electrode to several hundred micrometers provides a sub-microsecond time constant in a Kretschmann configured spectroelectrochemical cell. The high brilliance of synchrotron sourced infrared radiation has been combined with a specially designed horizontal attenuated total reflectance (ATR) microscope to focus the infrared beam on the microband electrode. The first use of a sub-microsecond time constant working electrode for ATR surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) is reported. Measurements show that the advantage afforded by the high brilliance of the synchrotron source is at least partially offset by increased noise from the experimental floor. The test system was the potential induced desorption of an adsorbed monolayer of 4-methoxypyridine (MOP) as measured using step-scan interferometry. Based on diffusion considerations alone, the expected time scale of the process was less than 10 microseconds but was experimentally measured to be three orders of magnitude slower. A defect-mediated dissolution of the condensed film is speculated to be the underlying cause of the unexpected slow kinetics. Key words: ATR-SEIRAS, microband electrode, electrochemical time constant, step-scan interferometry, synchrotron infrared radiation. Nous decrivons l'emploi d'une electrode a microbande imprimee sur un element de reflexion interne en silicium que nous avons appliquee a la spectroscopie infrarouge a resolution temporelle. La reduction de la dimension critique de l'electrode a microbande a quelques centaines de micrometres donne lieu a une constante de temps de l'ordre de l'inframi-croseconde dans une cellule spectroelectrochimique de configuration Kretschmann. La forte brillance du rayonnement synchrotron infrarouge a ete conjuguee a un microscope en reflexion totale attenuee (RTA) horizontal specialement concu pour concentrer le faisceau infrarouge sur l'electrode a microbande. Nous faisons etat de la premiere utilisation d'une electrode de travail a constante de temps dans l'inframicroseconde destinee a la spectroscopie d'absorption infrarouge exaltee de surface en RTA (ATR-SEIRAS ou Attenuated Total Reflectance-Surface Enhanced InfraRed Absorption Spectroscopy). Selon les resultats que nous avons obtenus, l'avantage qu'offre la forte brillance de la source synchrotron est annule, du moins partiellement, par l'augmentation du bruit provenant du plancher de l'environnement experimental. L'eventuelle desorption d'une monocouche de 4methoxypyridine (MOP) adsorbee, mesuree par interferometrie a balayage progressif, constituait le systeme de mise a l'epreuve. Sur la base de considerations centrees uniquement sur la diffusion, le processus aurait du se produire sur une echelle de temps inferieure a 10 microsecondes, mais les mesures experimentales ont revele qu'il etait plus lent de trois ordres de grandeur. Nous posons l'hypothese selon laquelle une dissolution du film condense regie par la presence de defauts pourrait etre la cause sous-jacente de la cinetique etonnamment lente. [Traduit par la Redaction] Mots-cles : ATR-SEIRAS, electrode a microbande, constante de temps electrochimique, interferometrie a balayage progressif, rayonnement synchrotron infrarouge., Introduction The electrochemical RC cell constant, the product of the electrolyte resistance and the capacitance of the working electrode, determines the minimum time required for an electrified interface to respond [...]

The adsorption of arsenic on an amorphous iron oxy(hydroxides) (ferrihydrite) under reductive conditions is reported. The fabrication of an ATR--IR spectroelectrochemical cell that allows the vibrational characterization of arsenate and arsenite adsorbed on a thin film of ferrihydrite is described. The cell is shown to allow the application of reductive conditions through the introduction of a working electrode that is positioned adjacent to the mineral phase. ATR--IR spectra reveal that increasingly negative solution potentials ([E.sub.h]) leads to the loss of adsorbed arsenate prior to the reductive dissolution of Fe(III) in the ferrihydrite. Under the experimental conditions, there is no evidence of reduction of arsenate to arsenite. Through the use of a miniaturized pH probe, the desorption of arsenate through electrochemical biasing is shown to arise solely from competitive adsorption from hydroxide ions produced by electrolysis of water. The results indicate that, within the time frame accessible in these measurements, only extreme reductive conditions are detrimental to arsenic sequestration in mine tailings facilities. Key words: arsenite, arsenate, ferrihydrite, reductive conditions, electrochemistry, ATR--IR. Nous faisons etat de l'adsorption de l'arsenic sur un (oxy)hydroxyde de fer amorphe (ferrihydrite) en conditions reductrices. Nous decrivons la fabrication d'une cellule spectroelectrochimique infrarouge a reflectance totale attenuee (ATR--IR) permettant la caracterisation vibrationnelle de l'arseniate et de l'arsenite adsorbes sur une couche mince de ferrihydrite. Nous avons montre que la cellule permet d'employer des conditions reductrices en y introduisant une electrode de travail placee de maniere adjacente a la phase minerale. Les spectres ATR--IR revelent qu'une augmentation du potentiel de la solution ([E.sub.h]) vers des valeurs de plus en plus negatives entraine une desorption de l'arseniate avant que la dissolution reductrice du Fe(III) present dans le ferrihydrite ne se produise. En conditions experimentales, nous n'observons aucun signe de reduction de l'arseniate en arsenite. A l'aide d'une sonde de pH miniaturisee, nous avons montre que la desorption de l'arseniate par polarisation electrochimique est le resultat direct de l'adsorption competitive d'ions hydroxyde produits par electrolyse de l'eau. Les resultats indiquent que, dans le cadre temporel d'execution de ces mesures, seules des conditions reductrices extremes peuvent nuire a la sequestration de l'arsenic dans les residus d'installations minieres. [Traduit par la Redaction] Mots-cles : arsenite, arseniate, ferrihydrite, conditions reductrices, electrochimie, ATR--IR., Introduction Understanding the process, mechanism, and stability of arsenic sequestration is of critical importance in the design and oversight of wastewater produced by mining activities. Arsenic is highly polymorphic and [...]

Micro electro-mechanical systems (MEMS) combining sensing and microfluidics functionalities, as are common in Lab-on-Chip (LoC) devices, are increasingly based on polymers. Benefits of polymers include tunable material properties, the possibility of surface functionalization, compatibility with many micro and nano patterning techniques, and optical transparency. Often, additional materials, such as metals, ceramics, or silicon, are needed for functional or auxiliary purposes, e.g., as electrodes. Hybrid patterning and integration of material composites require an increasing range of fabrication approaches, which must often be newly developed or at least adapted and optimized. Here, a microfabrication process concept is developed that allows one to implement attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and electrochemistry on an LoC device. It is designed to spatially resolve chemical sensitivity and selectivity, which are instrumental for the detection of chemical distributions, e.g., during on-flow chemical and biological reaction chemistry. The processing sequence involves (i) direct-write and soft-contact UV lithography in SUEX dry resist and replication in polydimethylsiloxane (PDMS) elastomers as the fluidic structure; (ii) surface functionalization of PDMS with oxygen plasma, 3-aminopropyl-triethoxysilane (APTES), and a UV-curable glue (NOA 73) for bonding the fluidic structure to the substrate; (iii) double-sided patterning of silicon nitride-coated silicon wafers serving as the ATR-FTIR-active internal reflection element (IRE) on one side and the electrode-covered substrate for microfluidics on the back side with lift-off and sputter-based patterning of gold electrodes; and (iv) a custom-designed active vacuum positioning and alignment setup. Fluidic channels of 100 μm height and 600 μm width in 5 mm thick PDMS were fabricated on 2" and 4" demonstrators. Electrochemistry on-chip functionality was demonstrated by cyclic voltammetry (CV) of redox reactions involving iron cyanides in different oxidation states. Further, ATR-FTIR measurements of laminar co-flows of H2O and D2O demonstrated the chemical mapping capabilities of the modular fabrication concept of the LoC devices. [ABSTRACT FROM AUTHOR]

Using Schwarzschild objectives, a thin section of a fruit berry seed was chemically imaged with infrared spectromicroscopy, revealing domains of phospholipid rich regions from the cell walls forming the seed's [...]

The surface stress response of micromechanical cantilever-based sensors was studied as a function of the morphology, adhesion, and cleanliness of the gold sensing surface. Two model systems were investigated: the adsorption of alkanethiol self-assembled monolayers at the gas--solid interface and the potential-controlled adsorption of anions at the liquid--solid interface. The potential-induced surface stress, on a smooth and continuous polycrystalline Au(111)-textured microcantilever in 0.1 M HCl[O.sub.4], is in excellent agreement with macroscopic Au(111) single-crystal electrode results. It is shown that ambient contaminants on the sensing surface dramatically alter the surface stress-potential response. This observation can be misinterpreted as evidence that for polycrystalline Au(111) microcantilever electrodes, surface stress is dominated by surface energy change. Results for anions adsorption on gold are in contrast to the gas-phase model system. We demonstrate that the average grain size of the gold sensing surface strongly influences the magnitude of the surface stress change induced by the adsorption of octanethiol. A 25-fold amplification of the change in surface stress is observed on increasing the average gold grain size of the sensing surface from 90 to 500 nm.

Palladium nanoparticles have been electrodeposited on the surfaces of conductive indium tin oxide (ITO) modified silicon internal reflection elements. The resulting films are shown to be excellent platforms for attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies of palladium surfaces. Monitoring the mid-infrared reflectivity of the interface during the constant potential electrodepostion of a Pd2+ precursor reveals a distinct and reproducible minimum that corresponds to the onset of the electronic percolation threshold of the deposited metal islands as confirmed by scanning electron microscopy. Effective medium theory (EMT) is used to model the reflectivity of the Si/ITO/Pd interface as a function of the volume fraction of the deposited metal and to calculate the ATR-SEIRA spectra of an adsorbed monolayer of organic molecules. EMT calculations are in qualitative agreement with most aspects of the experimental spectra which show that the intensities and spectral line shapes are highly dependent on the amount of deposited palladium. The methodology is applied to the potential dependent adsorption of 4-methoxypyridine on palladium. The experimental results show that the pyridine derivative adopts an edge-tilted orientation on oxide covered Pd and undergoes an orientation change in the hydrogen adsorption region that increases both the degree of edge-tilt and the extent of π-bonding between the pyridine ring and the metal. [ABSTRACT FROM AUTHOR]

We show that a microgrooved ATR-SEIRAS optimized Si ATR wafer designed to allow high angles of incidence at the electrode-solution interface provides improved signal-to-noise in electrochemical ATR-SEIRAS. Microgrooved Si ATR [...]

The synthesis and structural characterization of aluminum- and gallium-bridged [1.1]chromarenophanes and [1.1]molybdarenophanes are reported. These compounds are shown to contain two pairs of inner [alpha] protons that are oriented toward each other.

We monitor potential-induced changes at a Au film electrode using the ATR-SEIRAS sampling technique. Benefits are discussed. Attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) provides in situ surface-sensitive IR [...]

Pitting corrosion of reinforcing steel bar (rebar) imbedded in concrete by chloride ions can cause concrete degradation. It is thus necessary to develop methods to mitigate concrete corrosion which could include using a protective polymer rebar coating. Corrosion studies of polyvinyl butyral‐carbon black polymer‐coated rebar using soft X‐ray fluorescence (XRF) microprobe and micro‐X‐ray absorption near edge spectroscopy (μ‐XANES) are reported in this study. After removal of the polyvinyl butyral‐carbon black polymer coating, Fe Lα1, Mn Lα1, and O Kα1 XRF maps were collected as well as Fe and Mn L3‐edge μ‐XANES spectra from different regions across the whole rebar surface by collection of total electron yield (TEY) and partial XRF yield (PFY) spectra. The distribution of metallic Fe and Fe corrosion products was determined by analysis of the Fe XRF map. The μ‐XANES spectra indicated a higher fraction of Fe (III) phases on the corroded rebar surface, while Fe (II/III) phases were the major corrosion products beneath the surface region. In addition, Mn (II) and Mn (III) were determined as the valence states of the manganese corrosion products. [ABSTRACT FROM AUTHOR]

Reported herein is an analysis of accelerated corrosion of a commercially coated fusion‐bonded epoxy rebar sample using an X‐ray spectromicroscopy methodology that involves the combination of X‐ray fluorescence mapping (XRF) and micro X‐ray absorption near‐edge spectroscopy (μ‐XANES). XRF maps collected using an excitation energy of 7115 eV reveal a sharp contrast between corroded and noncorroded sample areas after correction for topography effects that can be confirmed by Fe K‐edge μ‐XANES. This X‐ray spectromicroscopy methodology allows for the study of corrosion through commercially prepared polymer‐coated rebar coatings without any modification to the polymer film prior to analysis and is suitable for long‐term testing of the corrosion of these materials under real‐world conditions. [ABSTRACT FROM AUTHOR]

The adsorption of a model quaternary ammonium surfactant, octyltrimethylammonium triflate, on Au(111) has been studied using capacity and chronoculometry methods. The surfactant adsorbs on the metal surface as a non-dissociated ion pair at moderate potentials but can be desorbed by either positive or negative polarization. Within the adsorption region, two states are observed which correspond to a horizontal monolayer and a higher coverage vertically oriented film. Measurements of capacity transients upon potential steps reveal a slow organization of the molecular film. Although it is possible to equate the transients to known surfactant film aggregate geometries, the results are in disagreement with thermodynamic results. In comparison with other studies, the results indicate that the states of surfactant adsorption depend on surfactant chain length and electrode crystallography. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A description of a coupled electrochemical and spectrometer interface using synchrotron infrared radiation is provided. The interface described allows for the precise and accurate timing needed for time-resolved IR spectroscopic studies of electrochemical systems. The overall interface uses a series of transistor-transistor logic trigger signals generated from the commercial FTIR spectrometer to regulate the recording of control, electrochemical, and IR signals with reproducible and adjustable timing. The instrument has been tested using a thin-layer electrochemical cell with synchrotron light focused through microscope optics. The time-resolved response of the benzoquinone/dihydroxybenzoquinone redox couple is illustrated as an example of the instrument's capability. [ABSTRACT FROM AUTHOR]

Abstract: Although substantial information can be obtained from electrochemical measurements, much greater detail concerning molecular structure can be obtained by coupling such measurements with molecular spectroscopy. To this end, electrochemical and in situ surface enhanced infrared spectroscopy (SEIRAS) was performed to analyze 1,4-benzoquinone (BQ) terminated self-assembled monolayers. Monolayers were derived via the Michael addition of BQ to a pre-formed mixed monolayer composed of methyl and thiol terminated functionalities. This approach resulted in relatively robust but non-ideal redox-active monolayers. Spectroscopic and electrochemical measurements have allowed us to determine the pH dependence of both the apparent formal potential and the heterogeneous standard rate constant for proton coupled electron transfer (PCET) for this 2e−/2H+ redox system. While the former is in excellent agreement with predictions of step-wise PCET, the latter deviates from the expected kinetic response. [Copyright &y& Elsevier]

The step-wise proton coupled electron transfer (SW-PCET) model has been expanded to describe instances where three protons are transferred with either one or two electrons. Expressions have been derived describing the pH dependence of the apparent formal potential, apparent standard rate constant, apparent transfer coefficient, and reaction pathway. The expressions can be applied to both Marcus density of states theory as well as Butler-Volmer kinetics depending on the assumptions made about the individual transfer coefficients. An example of 2e3H has been provided for an aminobenzoquinone monolayer system and experimental measurements have been compared to model predictions. Although the large reorganization energy of the benzoquinone system prevents differentiation between Butler-Volmer and Marcus DOS kinetic behaviour, results are consistent with the SW-PCET model. These results indicate how acid/base substituents on tethered organic molecules can participate in PCET even though they themselves are redox inactive. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of a quaternary ammonium surfactant (octyltrimethylammonium triflate, OTATf) on Au(100) has been studied using cyclic voltammetry and chronocoulometry. The adsorption of the cationic surfactant does not lift either the thermal or charge-induced Au(100)-5×20 reconstruction. The adsorption of OTATf has also been studied on the unreconstructed, Au(100)-1×1, surface. Both crystallographic surfaces demonstrate similar behaviour characterized by a single state of adsorption yielding a positive shift in the potential of zero charge, E pzc. No evidence of ion-pairing is observed on these very negatively charged surfaces. Unlike similar zwitterionic and anionic surfactants the measured Gibbs surface excesses for OTATf indicate that this cationic surfactant does not aggregate into hemi-micelle structures on Au(100). A slightly higher capacity and a smaller positive shift in the E pzc is observed for the organic film formed on the unreconstructed surface compared to the reconstructed surface which indicates subtle differences in the two states of adsorption. On a rational potential scale, OTATf adsorbs on the Au(100)-5×20 surface at more negative potentials. This indicates that there is a stronger specific interaction between the aliphatic quaternary ion and the reconstructed substrate. [ABSTRACT FROM AUTHOR]

The heterogeneity of metal island films electrodeposited on conductive metal oxide modified internal reflection elements is shown to provide a variable attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) response. A self-assembled monolayer of a ferrocene-terminated thiol monolayer (FcC11SH) was formed on the gold islands covering a single substrate, which was measured using both a conventional spectrometer and a custom-built horizontal microscope. Cyclic voltammetry and ATR-SEIRAS results reveal that the FcC11SH-modified substrate undergoes a reversible electron transfer and an associated re-orientation of both the ferrocene/ferrocenium headgroup and the hydrocarbon backbone. The magnitude of the absorption signal arising from the redox changes in the monolayer, as well as the IR signature arising from the ingress/egress of the perchlorate counterions, is shown to depend significantly on the size of the infrared beam spot when using a conventional Fourier transform infrared spectrometer. By performing equivalent measurements on a horizontal microscope, the primary cause of the differences in the signal level is found to be the heterogeneity in the density of gold islands on the conductive metal oxide. Graphical Abstract [ABSTRACT FROM AUTHOR]

• Shell-isolated nanoparticle enhanced Raman spectroscopy was applied on a mineral's surface. • The adsorption of flotation collectors onto pyrite surface was investigated by in-situ electrochemical SHINERS. • Both of xanthate and MBT adsorption were enhanced by cathodic stripping of the pre-oxidized products. • Compared to xanthate, MBT shows a broader potential window for adsorption. In this paper, shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) has been applied to investigate the adsorption of typical collectors, butyl xanthate and 2-mercaptobenzothiazole (MBT), on pyrite surface. With the help of inert shell isolated gold nanoparticles as electric field enhancers, high quality electrochemical spectra were obtained in relation to real-world flotation conditions, enabling the quantitative identification of the chemical reactions occurring only on the mineral surface. It has been found that polysulphide anions are predominant oxidation product of pyrite after abrading and above 0 mV vs Ag/AgCl. Both the adsorption of xanthate and MBT are suppressed on pre-oxidized pyrite surface. The pre-formed polysulphide is diminished at negative potentials, which are favourable for collector's adsorption. Compared to xanthate, MBT shows greater resistance to pyrite oxidation and a broader potential window for adsorption due to the presence of two "minerophilic" groups (endocyclic nitrogen atom bonding in addition to the interaction through the exocyclic S atom). Single exocyclic S atom bonding is predominant in more favarouble adsorption environments. Dithiolate, the oxidation products of xanthate and MBT, has been precluded due to the high stability of adsorbed collector. This is inconsistent with the ex-situ XPS measurement where air exposure may induce oxidation. [ABSTRACT FROM AUTHOR]