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Articles 1 - 30 of 39
Full-Text Articles in Engineering
Epitaxially Grown Collagen Fibrils Reveal Diversity In Contact Guidance Behavior Among Cancer Cells, Juan Wang, Joseph W. Petefish, Andrew C. Hillier, Ian C. Schneider
Epitaxially Grown Collagen Fibrils Reveal Diversity In Contact Guidance Behavior Among Cancer Cells, Juan Wang, Joseph W. Petefish, Andrew C. Hillier, Ian C. Schneider
Andrew C. Hillier
Invasion of cancer cells into the surrounding tissue is an important step during cancer progression and is driven by cell migration. Cell migration can be random, but often it is directed by various cues such as aligned fibers composed of extracellular matrix (ECM), a process called contact guidance. During contact guidance, aligned fibers bias migration along the long axis of the fibers. These aligned fibers of ECM are commonly composed of type I collagen, an abundant structural protein around tumors. In this paper, we epitaxially grew several different patterns of organized type I collagen on mica and compared the morphology …
High Rate Detection Of Volatile Products Using Differential Electrochemical Mass Spectrometry: Combining An Electrode-Coated Membrane With Hydrodynamic Flow In A Wall-Tube Configuration, Subramanian Venkatachalam, Robert J. Angelici, L. Keith Woo, Andrew C. Hillier
High Rate Detection Of Volatile Products Using Differential Electrochemical Mass Spectrometry: Combining An Electrode-Coated Membrane With Hydrodynamic Flow In A Wall-Tube Configuration, Subramanian Venkatachalam, Robert J. Angelici, L. Keith Woo, Andrew C. Hillier
Andrew C. Hillier
We present an experimental system that combines differential electrochemical mass spectrometry with hydrodynamic flow consisting of an impinging jet in a wall-tube configuration. This assembly allows simultaneous detection of electrochemical signals along with monitoring of dissolved gas species using differential electrochemical mass spectrometry under well-defined hydrodynamic conditions and over a wide range of mass transfer rates. The working electrode is deposited directly onto a thin, hydrophobic membrane, which also serves as the inlet to the mass spectrometer. This inlet provides extremely rapid mass detection as well as a high flux of products from the electrode surface into the mass spectrometer. …
Angle-Tunable Enhanced Infrared Reflection Absorption Spectroscopy Via Grating-Coupled Surface Plasmon Resonance, Joseph W. Petefish, Andrew C. Hillier
Angle-Tunable Enhanced Infrared Reflection Absorption Spectroscopy Via Grating-Coupled Surface Plasmon Resonance, Joseph W. Petefish, Andrew C. Hillier
Andrew C. Hillier
Surface enhanced infrared absorption (SEIRA) spectroscopy is an attractive method for increasing the prominence of vibrational modes in infrared spectroscopy. To date, the majority of reports associated with SEIRA utilize localized surface plasmon resonance from metal nanoparticles to enhance electromagnetic fields in the region of analytes. Limited work has been performed using propagating surface plasmons as a method for SEIRA excitation. In this report, we demonstrate angle-tunable enhancement of vibrational stretching modes associated with a thin poly(methyl methacrylate) (PMMA) film that is coupled to a silver-coated diffraction grating. Gratings are fabricated using laser interference lithography to achieve precise surface periodicities, …
Electrochemically Modulated Permeability Of Poly(Aniline) And Composite Poly(Aniline)−Poly(Styrenesulfonate) Membranes, D. L. Pile, Y. Zhang, Andrew C. Hillier
Electrochemically Modulated Permeability Of Poly(Aniline) And Composite Poly(Aniline)−Poly(Styrenesulfonate) Membranes, D. L. Pile, Y. Zhang, Andrew C. Hillier
Andrew C. Hillier
The influence of oxidation state on the permeability of several probe molecules through conducting polymer membranes comprising composites of poly(aniline) and poly(styrenesulfonate) was examined in aqueous solution. Pure poly(aniline) membranes displayed a characteristic increase in permeability between reduced and half-oxidized states for neutrally charged phenol and negatively charged 4-hydroxybenzenesulfonate. In contrast, positively charged pyridine experienced decreased permeability through the membrane when poly(aniline) was switched from the reduced to the half-oxidized state. This behavior can be explained by a combination of oxidation-induced film swelling and the anion-exchange character of the positively charged membrane. The membrane composition was modified to include a …
Rapid And Reversible Generation Of A Microscale Ph Gradient Using Surface Electric Fields, Eric L. May, Andrew C. Hillier
Rapid And Reversible Generation Of A Microscale Ph Gradient Using Surface Electric Fields, Eric L. May, Andrew C. Hillier
Andrew C. Hillier
We report a method for the rapid and reversible generation of microscale pH gradients using a spatially varied electric field. A linear gradient in electrochemical potential is produced on an electrode surface consisting of a platinum catalyst layer on indium−tin oxide-coated glass by the application of two different potential values at spatially distinct surface locations. The resulting potential gradient drives the oxidation and reduction of water at different rates along the surface, as dictated by the local applied potential. A nonuniform distribution of pH in the neighboring solution results due to the variation in surface reaction rates. The extent and …
Scanning Electrochemical Mapping Of Spatially Localized Electrochemical Reactions Induced By Surface Potential Gradients, Shrisudersan Jayaraman, Erin L. May, Andrew C. Hillier
Scanning Electrochemical Mapping Of Spatially Localized Electrochemical Reactions Induced By Surface Potential Gradients, Shrisudersan Jayaraman, Erin L. May, Andrew C. Hillier
Andrew C. Hillier
The influence of a surface potential gradient on the location and extent of electrochemical reactions was examined using a scanning electrochemical microscope. A linear potential gradient was imposed on the surface of a platinum-coated indium tin oxide electrode by applying two different potential values at the edges of the electrode. The applied potentials were used to control the location and extent of several electrochemical reactions, including the oxidation of Ru(NH3)62+, the oxidation of H2, and the oxidation of H2 in the presence of adsorbed CO. Scanning electrochemical mapping of these reactions was achieved by probing the feedback current associated with …
Organic Materials And Organic/Inorganic Heterostructures In Atom Probe Tomography, Derk Joester, Andrew C. Hillier, Yi Zhang, Ty J. Prosa
Organic Materials And Organic/Inorganic Heterostructures In Atom Probe Tomography, Derk Joester, Andrew C. Hillier, Yi Zhang, Ty J. Prosa
Andrew C. Hillier
Nano-scale organic/inorganic interfaces are key to a wide range of materials. In many biominerals, for instance bone or teeth, outstanding fracture toughness and wear resistance can be attributed to buried organic/inorganic interfaces. Organic/inorganic interfaces at very small length scales are becoming increasingly important also in nano and electronic materials. For example, functionalized inorganic nanomaterials have great potential in biomedicine or sensing applications. Thin organic films are used to increase the conductivity of LiFePO4 electrodes in lithium ion batteries, and solid electrode interphases (SEI) form by uncontrolled electrolyte decomposition. Organics play a key role in dye-sensitized solar cells, organic photovoltaics, and …
Combinatorial Synthesis And Reactivity Screening Of Electro-Oxidation Catalyst Gradients, Shrisudersan Jayaraman, Andrew C. Hillier
Combinatorial Synthesis And Reactivity Screening Of Electro-Oxidation Catalyst Gradients, Shrisudersan Jayaraman, Andrew C. Hillier
Andrew C. Hillier
Combinatorial methods represent an appealing experimental method for the discovery of heterogeneous catalysts. One can efficiently identify candidate materials or sample vast regions of composition space using a combination f dense catalyst libraries and high-throughput reactivity screening techniques. This is particularly appealing for the discovery of novel catalysts for low temperature fuel cells where multi-component systems have shown improved performance.
Directed Electrodeposition Of Polymer Films Using Spatially Controllable Electric Field Gradients, Erin L. Ratcliff, Andrew C. Hillier
Directed Electrodeposition Of Polymer Films Using Spatially Controllable Electric Field Gradients, Erin L. Ratcliff, Andrew C. Hillier
Andrew C. Hillier
We report a method for the directed electrodeposition of polymer films in various patterns using spatially controllable electric field gradients. One- and two- dimensional surface electric field gradients were produced by applying different potential values at spatially distinct locations on an electrode surface. Variations in the resulting local electrochemical potentials were used to spatially manipulate the rate of electrodeposition of several polymers. By controlling the electric field gradient in the presence of sequentially varying deposition solutions, complex polymer patterns could be produced. One-dimensional structures consisting of alternating bands of polyaniline and either poly(phenylene) oxide or poly(aminophenylene) oxide were produced, as …
Resonance Quenching And Guided Modes Arising From The Coupling Of Surface Plasmons With A Molecular Resonance, Wei-Hsun Yeh, Joseph W. Petefish, Andrew C. Hillier
Resonance Quenching And Guided Modes Arising From The Coupling Of Surface Plasmons With A Molecular Resonance, Wei-Hsun Yeh, Joseph W. Petefish, Andrew C. Hillier
Andrew C. Hillier
In this paper, we describe experimental and modeling results that illucidate the nature of coupling between surface plasmon polaritons in a thin silver film with the molecular resonance of a zinc phthalocyanine dye film. This coupling leads to several phenomena not generally observed when plasmons are coupled to transparent materials. The increased absorption coefficient near a molecular resonance leads to a discontinuity in the refractive index, which causes branching of the plasmon resonance condition and the appearance of two peaks in the p-polarized reflectance spectrum. A gap exists between these peaks in the region of the spectrum associated with the …
Grating-Coupler Assisted Infrared Reflection Absorption Spectroscopy For The Characterization Of Organic Thin Films, Bipin K. Singh, Andrew C. Hillier
Grating-Coupler Assisted Infrared Reflection Absorption Spectroscopy For The Characterization Of Organic Thin Films, Bipin K. Singh, Andrew C. Hillier
Andrew C. Hillier
We demonstrate how grating-coupler assisted infrared reflection absorption spectroscopy can be used to simultaneously determine the chemical identity and relative thickness of organic thin films. With a grating substrate, a threshold anomaly associated with passing off of the −1 diffracted order occurs at grazing angles of incidence, resulting in a sharp absorbance in the infrared. The position of this peak is sensitive to the grating geometry as well as the dielectric environment near its surface. Thus, shifts in the peak position can be used to determine the relative thickness of adsorbed films or quantify molecular adsorption events. To illustrate the …
Three-Dimensional Atom Probe Tomography Of Oxide, Anion, And Alkanethiolate Coatings On Gold, Yi Zhang, Andrew C. Hillier
Three-Dimensional Atom Probe Tomography Of Oxide, Anion, And Alkanethiolate Coatings On Gold, Yi Zhang, Andrew C. Hillier
Andrew C. Hillier
We have used three-dimensional atom probe tomography to analyze several nanometer-thick and monomolecular films on gold surfaces. High-purity gold wire was etched by electropolishing to create a sharp tip suitable for field evaporation with a radius of curvature of layer, primarily consisting of water and atmospheric gases, was observed on a fresh tip. This sample exhibited crystalline lattice spacings consistent with the interlayer spacing of {200} lattice planes of bulk gold. A thin oxide layer was created on the gold surface via plasma oxidation, and the thickness and composition of this layer was measured. Clear evidence of a nanometer-thick oxide …
Wavelength Tunable Surface Plasmon Resonance-Enhanced Optical Transmission Through A Chirped Diffraction Grating, Wei-Hsun Yeh, Justin Kleingartner, Andrew C. Hillier
Wavelength Tunable Surface Plasmon Resonance-Enhanced Optical Transmission Through A Chirped Diffraction Grating, Wei-Hsun Yeh, Justin Kleingartner, Andrew C. Hillier
Andrew C. Hillier
We report the construction and testing of a chirped diffraction grating, which serves as a substrate for surface plasmon-enhanced optical transmission. This grating possesses a spatial variation in both pitch and amplitude along its surface. It was created by plasma oxidation of a curved poly(dimethoxysilane) sheet, which resulted in nonuniform buckling along the polymer surface. A gold-coated replica of this surface elicited an optical response that consisted of a series of narrow, enhanced transmission peaks spread over the visible spectrum. The location and magnitude of these transmission peaks varied along the surface of the grating and coincided with conditions where …
High Rate Detection Of Volatile Products Using Differential Electrochemical Mass Spectrometry: Combining An Electrode-Coated Membrane With Hydrodynamic Flow In A Wall-Tube Configuration, Subramanian Venkatachalam, Robert J. Angelici, L. Keith Woo, Andrew C. Hillier
High Rate Detection Of Volatile Products Using Differential Electrochemical Mass Spectrometry: Combining An Electrode-Coated Membrane With Hydrodynamic Flow In A Wall-Tube Configuration, Subramanian Venkatachalam, Robert J. Angelici, L. Keith Woo, Andrew C. Hillier
Andrew C. Hillier
We present an experimental system that combines differential electrochemical mass spectrometry with hydrodynamic flow consisting of an impinging jet in a wall-tube configuration. This assembly allows simultaneous detection of electrochemical signals along with monitoring of dissolved gas species using differential electrochemical mass spectrometry under well-defined hydrodynamic conditions and over a wide range of mass transfer rates. The working electrode is deposited directly onto a thin, hydrophobic membrane, which also serves as the inlet to the mass spectrometer. This inlet provides extremely rapid mass detection as well as a high flux of products from the electrode surface into the mass spectrometer. …
Diffraction-Based Tracking Of Surface Plasmon Resonance Enhanced Transmission Through A Gold-Coated Grating, Wei-Hsun Yeh, Joseph W. Petefish, Andrew C. Hillier
Diffraction-Based Tracking Of Surface Plasmon Resonance Enhanced Transmission Through A Gold-Coated Grating, Wei-Hsun Yeh, Joseph W. Petefish, Andrew C. Hillier
Andrew C. Hillier
Surface plasmon resonance enhanced transmission through metal-coated nanostructures represents a highly sensitive yet simple method for quantitative measurement of surface processes and is particularly useful in the development of thin film and adsorption sensors. Diffraction-induced surface plasmon excitation can produce enhanced transmission at select regions of the visible spectrum, and wavelength shifts associated with these transmission peaks can be used to track adsorption processes and film formation. In this report, we describe a simple optical microscope-based method for monitoring the first-order diffracted peaks associated with enhanced transmission through a gold-coated diffraction grating. A Bertrand lens is used to focus the …
Use Of Dispersion Imaging For Grating-Coupled Surface Plasmon Resonance Sensing Of Multilayer Langmuir–Blodgett Films, Wei-Hsun Yeh, Andrew C. Hillier
Use Of Dispersion Imaging For Grating-Coupled Surface Plasmon Resonance Sensing Of Multilayer Langmuir–Blodgett Films, Wei-Hsun Yeh, Andrew C. Hillier
Andrew C. Hillier
We report grating-coupled surface plasmon resonance measurements involving the use of dispersion images to interpret the optical response of a metal-coated grating. Optical transmission through a grating coated with a thin, gold film exhibits features characteristic of the excitation of surface plasmon resonance due to coupling with the nanostructured grating surface. Evidence of numerous surface plasmon modes associated with coupling at both front (gold/air) and back (gold/substrate) grating interfaces is observed. The influence of wavelength and angle of incidence on plasmon coupling can be readily characterized via dispersion images, and the associated image features can be indexed to matching conditions …
Surface Plasmon Resonance Imaging Of Biomolecular Interactions On A Grating-Based Sensor Array, Bipin K. Singh, Andrew C. Hillier
Surface Plasmon Resonance Imaging Of Biomolecular Interactions On A Grating-Based Sensor Array, Bipin K. Singh, Andrew C. Hillier
Andrew C. Hillier
A surface plasmon resonance sensor array based upon a grating substrate was developed for the detection of biomolecular interactions. The substrate consisted of a gold grating prepared by wet chemical treatment of a commercial recordable compact disk. A custom-built floating pin microspotter was constructed to deliver solutions containing ω-functionalized linear alkanethiols to the grating surface and produce an array of sensor elements with different exposed functional end groups. This array platform can be used to study biomolecular interactions in a label-free, sensitive, and high-throughput format. To illustrate the performance of this device, a test protein (bovine serum albumin) was exposed …
Combined Electrochemical Surface Plasmon Resonance For Angle Spread Imaging Of Multielement Electrode Arrays, Andrew C. Hillier, Chang Hoon Choi
Combined Electrochemical Surface Plasmon Resonance For Angle Spread Imaging Of Multielement Electrode Arrays, Andrew C. Hillier, Chang Hoon Choi
Andrew C. Hillier
A surface plasmon resonance imaging system combined with a multielement electrode array is described. An optical system with shaping optics is used to direct a wedge of light onto a gold-coated sample. The reflected light is detected in the form of an angle-spread image of the surface, with one direction denoting a variable incident angle and the other showing a span of locations along one lateral direction of the sample surface. At the proper incident angle, the angle-spread image shows the complete surface plasmon resonance curve over a span of locations on the surface. This imaging system is combined with …
Surface Plasmon Resonance Enhanced Transmission Of Light Through Gold-Coated Diffraction Gratings, Bipin K. Singh, Andrew C. Hillier
Surface Plasmon Resonance Enhanced Transmission Of Light Through Gold-Coated Diffraction Gratings, Bipin K. Singh, Andrew C. Hillier
Andrew C. Hillier
Narrow peaks are observed in the transmission spectra of p-polarized light passing through a thin gold film that is coated on the surface of a transparent diffraction grating. The spectral position and intensity of these peaks can be tuned over a wide range of wavelengths by simple rotation of the grating. The wavelengths where these transmission peaks are observed correspond to conditions where surface plasmon resonance occurs at the gold−air interface. Light diffracted by the grating couples with surface plasmons in the metal film to satisfy the resonant condition, resulting in enhanced light transmission through the film. Notably, this phenomenon …
A Multi-Electrode Electrochemical And Scanning Differential Electrochemical Mass Spectrometry Study Of Methanol Oxidation On Electrodeposited Ptxruy, K. Jambunathan, S. Jayaraman, Andrew C. Hillier
A Multi-Electrode Electrochemical And Scanning Differential Electrochemical Mass Spectrometry Study Of Methanol Oxidation On Electrodeposited Ptxruy, K. Jambunathan, S. Jayaraman, Andrew C. Hillier
Andrew C. Hillier
Methanol electro-oxidation was studied on a series of electrodeposited PtxRuy catalysts constructed as multielement band electrodes. A combination of electrochemical and scanning differential electrochemical mass spectrometry measurements were performed to evaluate the composition-dependence of methanol oxidation, methanol decomposition, CO2 current efficiency, and the product distribution at 25 and 50 °C. At 25 °C, cyclic voltammetry revealed that the presence of Ru led to enhanced methanol oxidation rates over that of pure Pt. Methanol decomposition showed a similar composition-dependence. Mass spectrometry measurements revealed the evolution of HCOOH and CO2 during methanol oxidation and allowed indirect determination …
Construction And Reactivity Screening Of A Surface Composition Gradient For Combinatorial Discovery Of Electro-Oxidation Catalysts, Shrisudersan Jayaraman, Andrew C. Hillier
Construction And Reactivity Screening Of A Surface Composition Gradient For Combinatorial Discovery Of Electro-Oxidation Catalysts, Shrisudersan Jayaraman, Andrew C. Hillier
Andrew C. Hillier
Materials possessing gradients in composition or structure are of interest for a range of applications, including the construction of functionally graded structural materials, as novel sensor and actuator platforms, and to control the site-specific binding of proteins and cells on surfaces. Gradients can also be used as sample libraries for combinatorial materials discovery that present an extremely dense sample set.
Construction Of A Tethered Poly(Ethylene Glycol) Surface Gradient For Studies Of Cell Adhesion Kinetics, K. Mougin, A. S. Ham, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier
Construction Of A Tethered Poly(Ethylene Glycol) Surface Gradient For Studies Of Cell Adhesion Kinetics, K. Mougin, A. S. Ham, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier
Andrew C. Hillier
Surface gradients can be used to perform a wide range of functions and represent a novel experimental platform for combinatorial discovery and analysis. In this work, a gradient in the coverage of a surface-immobilized poly(ethylene glycol) (PEG) layer is constructed to interrogate cell adhesion on a solid surface. Variation of surface coverage is achieved by controlled transport of a reactive PEG precursor from a point source through a hydrated gel. Immobilization of PEG is achieved by covalent attachment of the PEG molecule via direct coupling chemistry to a cystamine self-assembled monolayer on gold. This represents a simple method for creating …
Construction Of Cell-Resistant Surfaces By Immobilization Of Poly(Ethylene Glycol) On Gold, K. Mougin, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier
Construction Of Cell-Resistant Surfaces By Immobilization Of Poly(Ethylene Glycol) On Gold, K. Mougin, M. B. Lawrence, E. J. Fernandez, Andrew C. Hillier
Andrew C. Hillier
Considerable effort has been expended in efforts to create surfaces that resist the adsorption of proteins and cells for biomedical applications. The majority of such work has focused on surfaces constructed from bulk polymers or thin polymer films. However, the fabrication of surfaces via self-assembled monolayers (SAMs) has attracted considerable interest because of the robustness, versatility, and wide-ranging applicability of these materials. SAMs are particularly appealing for biological systems where well-defined surface chemistries can be created to facilitate coupling, biorecognition, or cell adhesion along with a host of other applications in biochemistry and biotechnology.
Atom Probe Tomography Characterization Of Thin Copper Layers On Aluminum Deposited By Galvanic Displacement, Yi Zhang, Jiahe Ai, Andrew C. Hillier, Kurt R. Hebert
Atom Probe Tomography Characterization Of Thin Copper Layers On Aluminum Deposited By Galvanic Displacement, Yi Zhang, Jiahe Ai, Andrew C. Hillier, Kurt R. Hebert
Andrew C. Hillier
″Ultrathin″ metallization layers on the order of nanometers in thickness are increasingly used in semiconductor interconnects and other nanostructures. Aqueous deposition methods are attractive methods to produce such layers due to their low cost, but formation of ultrathin layers has proven challenging, particularly on oxide-coated substrates. This work focused on the formation of thin copper layers on aluminum, by galvanic displacement from alkaline aqueous solutions. Analysis by atom probe tomography (APT) showed that continuous copper films of approximately 1 nm thickness were formed, apparently the first demonstration of deposition of ultrathin metal layers on oxidized substrates from aqueous solutions. The …
A Combined Triboelectrochemical Qcm For Studies Of The Cmp Of Copper, Wenquan Lu, Jian Zhang, Frank Kaufman, Andrew C. Hillier
A Combined Triboelectrochemical Qcm For Studies Of The Cmp Of Copper, Wenquan Lu, Jian Zhang, Frank Kaufman, Andrew C. Hillier
Andrew C. Hillier
In order to improve our understanding of the fundamental surface processes associated with the chemical mechanical planarization ~CMP! of metals, we have developed an experimental tool that combines the high resolution mass sensing capabilities of the quartz crystal microbalance ~QCM! with a triboelectrochemical testing system. A electrochemical QCM is combined with a polishing tool and force sensor in order to perform controlled surface abrasion while simultaneously monitoring mass changes and electrochemical signals at the metal/solution interface. This system can be used to simulate a metal polishing process with in situ surface measurement capabilities. Typical parameters that can be measured include …
Measuring Electrocatalytic Activity On A Local Scale With Scanning Differential Electrochemical Mass Spectrometry, K. Jambunathan, Andrew C. Hillier
Measuring Electrocatalytic Activity On A Local Scale With Scanning Differential Electrochemical Mass Spectrometry, K. Jambunathan, Andrew C. Hillier
Andrew C. Hillier
This paper describes a new technique entitled scanning differential electrochemical mass spectrometry ~SDEMS! that combines a quadrupole mass spectrometer with a membrane-covered capillary inlet and a high resolution positioning system that is designed to perform spatial mapping in solution near an electrode interface. Potential applications of this technique include the local characterization of anode catalysts for fuel cells as well as a range of analytical measurements and combinatorial screening studies. The capabilities of this technique are demonstrated by monitoring product evolution in several model electrocatalytic reactions, including the hydrogen evolution reaction, carbon monoxide oxidation, and the direct oxidation of methanol …
Screening The Reactivity Of Ptxruy And Ptxruymoz Catalysts Toward The Hydrogen Oxidation Reaction With The Scanning Electrochemical Microscope, S. Jayaraman, Andrew C. Hillier
Screening The Reactivity Of Ptxruy And Ptxruymoz Catalysts Toward The Hydrogen Oxidation Reaction With The Scanning Electrochemical Microscope, S. Jayaraman, Andrew C. Hillier
Andrew C. Hillier
We report an application of the scanning electrochemical microscope that exploits its ability to spatially map the kinetics of heterogeneous electron-transfer reactions in order to perform screening measurements for combinatorial studies of electrooxidation catalysts. The ability to measure the activity of catalyst surfaces toward the hydrogen oxidation reaction via tip−sample feedback is used to characterize the activity of PtxRuy and PtxRuyMoz catalysts as a function of composition and electrode potential. Multielement band electrodes containing various compositions of PtxRuy and PtxRuyMoz deposits are created via pulsed electrochemical deposition onto patterned substrates. Catalyst compositions are verified through a combination of Auger electron …
Construction And Reactivity Mapping Of A Platinum Catalyst Gradient Using The Scanning Electrochemical Microscope, Shrisudersan Jayaraman, Andrew C. Hillier
Construction And Reactivity Mapping Of A Platinum Catalyst Gradient Using The Scanning Electrochemical Microscope, Shrisudersan Jayaraman, Andrew C. Hillier
Andrew C. Hillier
Wedescribe a method for the characterization of electro-oxidation catalysts that involves the fabrication and reactivity mapping of samples possessing a catalyst gradient. The objective of this work is to demonstrate a method for catalyst preparation and screening that directly measures the activity of spatially localized catalyst samples toward electro-oxidation reactions relevant to the fuel cell anode in an effort to discover and characterize new catalyst formulations. In this report, a well-defined gradient in the surface coverage of platinum is created on an electronically conductive but catalytically inactive indium-tin-oxide (ITO) substrate by the application of a nonuniform electric field during platinum …
Imaging The Reactivity Of Electro-Oxidation Catalysts With The Scanning Electrochemical Microscope, Biren C. Shah, Andrew C. Hillier
Imaging The Reactivity Of Electro-Oxidation Catalysts With The Scanning Electrochemical Microscope, Biren C. Shah, Andrew C. Hillier
Andrew C. Hillier
We describe an application of the scanning electrochemical microscope that utilizes tip-sample feedback to characterize the reactivity of electro-oxidation catalysts. The kinetics of hydrogen oxidation are probed at a platinum electrode as a function of applied potential in aqueous sulfuric acid solution. Tip-sample feedback generates a tip response that reflects the rate of hydrogen oxidation at the substrate. The ability to directly measure the rate constant for hydrogen oxidation is, subsequently, used to perform reactivity mapping of heterogeneous electrodes consisting of catalytic and noncatalytic domains. Differences in reaction kinetics clearly distinguish surface composition variations based upon their reactivity toward hydrogen …
Nanometer-Scale Probing Of Potential-Dependent Electrostatic Forces, Adhesion, And Interfacial Friction At The Electrode/Electrolyte Interface, Shane D. Campbell, Andrew C. Hillier
Nanometer-Scale Probing Of Potential-Dependent Electrostatic Forces, Adhesion, And Interfacial Friction At The Electrode/Electrolyte Interface, Shane D. Campbell, Andrew C. Hillier
Andrew C. Hillier
The atomic force microscope (AFM) was used to examine the influence of an applied electrochemical potential on the interfacial properties of the electrode/electrolyte interface. Measurements of electrostatic force, adhesion, and friction coefficient were performed at two different electrode surfaces: glassy carbon anda thin film of sulfonate-derivatized poly(aniline) (SPANi). At the carbon electrode, changes in electrostatic force between probe and substrate exhibited a potential-dependent transition from repulsive to attractive values at potentials negative and positive of the potential of zero charge (Epzc). Simultaneous measurements of tip-substrate adhesion and friction coefficient showed a change from low to high values over the same …