Paul J. Sides - US grants

This project deals with the processing of primary metals such as aluminum alloys. Liquid metals are employed as cathodes in molten salt electrolysis. The cathodic part is reduced into the molten metal, e.g. aluminum into the aluminum pad of Hall-Heroult cells or into the floating aluminum laser of a three layer aluminum refining cell. In this work metals that are normally solid will be reduced into and onto liquid metal substrates, both at ambient temperatures and in molten salt systems at elevated temperature. Electrolytic reduction of metals from aqueous solution at mercury and amalgam electrodes will also be studied and extended to cover low-melting metal mixtures and gallium in non aqueous media. The metal deposition at liquid silver and aluminum, using the established see- in technique, will also be studied. The research conducted includes a study of the nature of solid products electrocystallized on an atomically smooth substrate and the establishment of the conditions under which alloying or film deposition occurs.

This is an interdisciplinary project to study the chemical engineering aspects of organometallic vapor phase epitaxy (OMVPE). It involves an interdisciplinary team of two chemical engineers and two materials scientists. The team has selected a known but important system, the homo- and heteroepitaxial growth of cadmium telluride onto cadmium telluride and gallium arsenide surfaces. There are three aspects of the study: 1. Modeling of the deposited films as a function of temperature, alkyl mixture, and flow in an impinging jet reactor with uniform heat and mass transfer characteristics. 2. Study of the surface chemical kinetics by thermogravimetric analysis to develop surface kinetic constants to feed into the model developed in the first study. 3. Evaluation of the electronic and structural quality of the films as they are formed under different conditions, as identified with the help of the model. The great value of this project is in the combination of well thought-out reactor geometry and materials selections, with adequate tools for materials characterization, together with a well-planned, fundamental approach to understanding and controlling the physics and chemistry of the OMVPE process. Processes of this type will play a central role in the development of future high-tech industries, which richly justifies the investment necessary to understand these processes in as full a manner as possible. This improved understanding will translate into improved quality of products and into greater efficiencies in the industries which employ them.

9319186 Sides This is an investigation of the kinetics of organometallic vapor- phase epitaxy (OMVPE) of homoepitaxial cadmium telluride at both the macroscopic and microscopic levels. Macroscopic experiments explore the effect of misorientation of substrates on the morphology of OMVPE-deposited material. Rate laws for step growth and for hillock growth are developed in order to test the hypothesis that steps are critical sites of reactions of the commonly used sources dimethlycadmium and diisopropyltellurium. A methodology will be developed to use rate laws to predict conditions under which high-quality epitaxial films can be grown. The effect of substrate surface microstructure on the elementary reactions in the deposition mechanism is also investigated. Scanning tunneling microscopy, low-energy electron diffraction, and other surface science techniques are employed. Thin films of cadmium telluride and related compounds are attractive for fabrication of devices involving light emitters, radiation detectors, and optical switching. At present, they are prepared by molecular beam epitaxy (MBE), a method that is slow, cumbersome, and expensive. Perfection of OMVPE techniques should permit higher-volume, lower-cost production of these films, making them acceptable for consumer applications. It is to this end that this effort is ultimately directed. ***

Professors Paul Sides and David Sholl will investigate the origin of the morphological instability occurring during homoepitaxial chemical vapor deposition of CdTe thin films from organometallic precursors. They will use Monte Carlo Simulations and continuum growth models as well as experiments of CdTe deposition on (100), (110), (111)CD and (111)Te. Morphology will be determined with nomarsky and scanning tunneling microscopy in a time-resolved manner, and the observations will be compared with the simulations. A new monoloayer-sentitive technique will be developed based on scattered total internal reflection infrared spectroscopy. Radiaiton below 900 nm will be directed through the crystal towards the CdTe-vapor interface with the purpose of detecting the appearance of steps. The hypothesis that Schwoebel barriers are responsible for the morphological instability of CdTe deposited by OMVPE will be tested.

Proposal # 9980759
PI Dr. James H. Garrett
Title: NMR on a Chip: a Micro-NMR Device for in situ Detection of
Chloride in Concrete


The goal of this Engineering Microsystems: "XYZ" on a Chip project is to investigate the hypothesis that a micro nuclear magnetic resonance (NMR) based detector, defined as all aspects of an NMR other than the magnet and power supply, can detect chloride ion in concrete. The coils, oscillator, and essential electronics of an NMR, typically a large expensive device, are being created on a single chip with the CMOS process. The coil turns are one micron thick and one to two millimeters in diameter. The team includes faculty from civil engineering, chemical engineering, electrical engineering, and physics. The project's first stage is modeling and theoretical analysis of a micro NMR. The second stage consists of experiments aimed at demonstrating that the micro NMR can detect protons. This is a useful intermediate objective because the response of protons is 100 times larger than chloride and the signal can be used for calibration of the chloride detection. The third stage is measuring the concentration of free chloride in concrete. The results of this work underpin a sensor technology that could have a substantial impact on the nation's civil infrastructure. For example, an economical chloride sensor based on NMR and dispersed throughout a bridge deck can trigger remediation that prevents loss of the structure due to corrosion of the steel reinforcement. The broader impact of the project is creation of a technology that could find biomedical and other applications.

0079416
Hanon

Low-Energy Electron Microscopy (LEEM) is used to generate real-time images of surfaces with a lateral resolution of better than 10 nanometer. Surfaces can be imaged at arbitrarily high temperatures, and during growth. Contrast in LEEM arises because of differences in electron reflectivity at the surface, which reflect variations in the structural, chemical and magnetic properties of the surface. This award will help establish a LEEM facility at Carnegie Mellon University for use by an interdisciplinary group of researchers spanning four University departments. Proposed research projects include investigations of phase transitions at surfaces, two-dimensional coarsening and growth, step and phase boundary fluctuations, GaN growth, wetting of organic films, surface magnetism, growth at chiral surfaces, and texture development in thin film growth.

Low-Energy Electron Microscopy (LEEM) is used to generate real-time images of surfaces with a lateral resolution of better than ten nanomters, during growth, and at arbitrarily high temperatures. These unique features allow growth at surfaces to be studied in unprecedented detail. A LEEM facility will be established at Carnegie Mellon University for use by an interdisciplinary group of researchers. LEEM will be applied to a wide range of growth problems, from fundamental investigations of the chemistry and physics of surfaces, to process optimization in the development of new magnetic media.

Abstract
CTS-0089875
J. L. Anderson, Carnegie Mellon University

Electrophoretic deposition is the procress where charged colloid particles are driven by an applied
electrical field towards the surface of an electrode and deposited there. Under certain conditions, the particles will still be mobile and self assemble before being depositedat a fixed surface location. There is a variety of desirable applications for this procedure, depending on the colloids, the electrodes and also the applied electrical field; in particular, the results obtained differ radically for direct currents and for alternating ones. The goal of this proposal is first to assess the currentlyavailable theoretical models (e.g. electrohydrodynamic, electrokinetic) and their limitaions. It is then to develop a theory and perform experiments which would include all the aspects of self-ordered aggregation for the alternating current case (e.g. Brownian motion, electrokinetice, colloid forces). Specifically, the expected to increase accuracy substantially above what has been obtained elsewhere with layer-averaged modeling.

Abstract
CTS-0338089
Paul Sides, Carnegie Mellon University


The field of this research is electrochemically stimulated self-assembly. A hypothesis about the mechanism behind an experimentally observed anomalous motion of a colloidal particle near an electrode will be tested. The experimental observation is that a colloidal particle resides on average closer to an electrode than its equilibrium position during ac polarization when the electrolyte is KOH; conversely, the particle resides on average farther away from its equilibrium position when the electrolyte is NaHCO3. The reason for this solution dependent behavior remains unknown.

Three possible candidate forces due to electrically stimulated flow arise from
electrokinetic, electrohydrodynamic, and electroosmotic effects. Electrokinetic effects are defined as arising from the interaction of electric fields with the charge on the particle. Electrohydrodynamic effects are defined as arising from the interaction of electric fields with unbalanced charge in a diffusion layer generated by the passage of faradaic current. Electroosmotic effects are defined as arising from the interaction of electric fields with the diffuse charge of the double layer of the electrode. Preliminary calculations have shown that electrokinetic effects are present but cannot account for the observations. Electrohydrodynamic effects can in principle account move the particle downward or upward on average but are not strong enough to account for the observation. Electroosmotic effects are strong enough and under some circumstances can account for the experimentally observed results; therefore the hypothesis to be tested involves modeling and experimentation related to this effect.

The work will consist of four thrusts. The first thrust is thorough modeling of the electroosmotic effect with a finite element analysis. The second thrust is introduction of rigorous techniques of electrochemistry into the Total Internal Reflection Microscopy experiments by which we observe the behavior of the particle. The third thrust is a novel experiment by which the diffuse layer potential, i.e. the zeta potential of the electrode, will be measured. A disk electrode oscillating (not rotating) at several kilohertz produces a quasi-superconducted sheet of alternating current due to the mobile charge of the diffuse layer. This sheet of current will be detected by its induced electromotance in a surrounding coil. This design allows the measurement of the zeta potential of a single surface of an electrode pair even during passage of faradaic current. The fourth thrust is elaboration of a model for the dependence of the diffuse layer potential on faradaic current.

The research will improve knowledge of forces important in the formation of ordered layers of particles on surfaces. The potential application areas are sensor and optical technology.

Proposal Title: Investigation of Enantioselective Adsorption on Chiral Mineral Surfaces
Proposal Number: CTS-0521719
Principal Investigator: Paul Sides
Institution: Carnegie Mellon University

The objective of this proposal is to demonstrate that chiral surfaces of minerals can function as enantioselective analysis and separations media. Many common inorganic materials have chiral bulk structures. Fundamental evidence for the enantiospecific adsorption of amino acids on single crystalline quartz and calcite will be produced. Ultra-high vacuum surface science tools will be used to quantify the differences in the adsorption energies of R- and S- amino acids onto chiral surfaces of quartz and calcite. The extent of the adsorption will be evaluated in vacuum by temperature programmed desorption and in aqueous solutions by detection of the zeta potential differences between surfaces of opposite handedness when amino acids are adsorbed. The zeta potential measurements will be made using a novel technique recently developed at Carnegie Mellon University. This technique will be adapted to make a differential measurement of enantioselective adsorption on R- and S- surfaces. Enantioselective adsorption on mineral surfaces has never before been studied under the controlled conditions possible in ultrahigh vacuum. The second novel feature is the use of a rotating disk method recently invented for measuring changes in zeta potential of inorganic surfaces associated with adsorption of charged molecules such as amino acids; this method makes possible a true differential measurement of enantioselectivity. The proposed investigation will contribute to the fundamental understanding of the enantiospecific adsorption of chiral compounds on inorganic chiral surfaces. In terms of the broader impacts, the proposed investigation will foster dissemination of knowledge about chirality, a subtle aspect of molecular structure that engineering disciplines such as materials science and chemical engineering have largely ignored. A new experiment based on enantiospecific adsorption will be incorporated in an existing laboratory course. This work could lead to better processes for performing separations of chiral molecules for use in pharmaceuticals, artificial flavors, and agrochemicals.

National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415)


Proposal Number: 0730391
Principal Investigators: Sides, Paul
Affiliation: Carnegie Mellon University
Proposal Title: Investigation of the Zeta Potential of Electrically Polarized
Inrterfaces

The field of this research is electrochemically directed self-assembly of colloidal particles on electrodes. A hypothesis about the mechanism behind an experimentally observed electrolyte-dependent motion of colloidal particles near an electrode will be tested. The experimental observation is that a correlation between a phase angle and the aggregation or separation of two particles during ac polarization exists. The expected angle is 90o. The observed angles are less than 90o for KOH and greater than 90o for bicarbonate solution. The particles separate in KOH and aggregate in KOH. This correlation between the phase angle relative to 90o and whether the particles aggregate or separate has been verified for several combinations of electrolyte and electrode. The reason for this solution dependent correlation remains unknown.

The hypothesis is that the required extra force arises from a flow mechanism called "faradaically coupled electroosmosis" (FCEO) driven by interaction of lateral electric field components with charge in the electrode's double layer. FCEO breaks the symmetry of the strong force arising from the "particle based electroosmosis" (PBEO) interaction between the electric field and particles' charge. FCEO modifies the particle behavior such that the particle height and electric field do not exhibit the expected _/2 phase relationship.

The research will improve knowledge of forces important in the formation of ordered layers of particles on surfaces. The potential application areas are sensors and optical technology.

Intellectual Merit The intellectual thrust of this proposal is the hypothesis that electroosmotic flow due to interaction between electric fields and the double layers of the particle and electrode is the key to understanding not only the behavior of a single particle near a polarized electrode but also to understanding the aggregative/separative behavior of multi-particle systems. Proving this hypothesis would complete the understanding of remote assembly of particles. The problem is rich in science and engineering; it involves the combination of colloidal, electrochemical, and hydrodynamic phenomena. The proposed investigation includes novel experimentation and multiphysical electrohydrodynamic computer simulations. The propose investigation is the capstone study necessary to complete the puzzle of this most subtle effect.

Broader Impact The phenomena of this study are of fundamental interest to colloid science and technology. New display technologies employ the interaction of electric fields with particles encapsulated with liquids. Cells, given their charge, can be manipulated by electrohydrodynamic flows and even sorted. Electroosmotic flow is important in technologies beyond the details of this problem, particularly in microfluidic transport of liquids. The new perspectives gained will also support the development of laboratory experiments already inserted into the colloid science curriculum. The research will be a part of the training of a graduate student and undergraduates at Carnegie Mellon, who will become productive agents in the scientific and engineering community.

1133082
PI: Sides

Technical description: The core hypothesis of this project is that colloidal particles can function as probes of local electrochemical current density. The essence of the innovation is using scattered light from colloidal particles during polarization of electrodes. In experiments, colloidal particles will be scattered across test electrodes used in electrochemical cells. Laser radiation introduced at an angle of incidence greater than a critical angle will create evanescent radiation proximate to the electrodes. The particles scatter these evanescent waves as visible light. The particles respond dynamically to local current density, which means that the particles transduce the local current density to light having an intensity that can be measured. Theory will convert the light intensity to a determination of current density. When ensembles of particles are used, the method creates an image of current density on the electrode. Imaging the scattering of a 2D ensemble of particles on a composition spread alloy working electrode during polarization of the film will reveal the regions of high electrochemical activity over the entire sample within minutes, with a resolution of areas as small, or perhaps smaller, than 100 microns on a side. This will mean that a library made from a sample one square centimeter in area will have 104 samples in its collection. The project focuses on oxygen evolution from aqueous solution as the test electrochemical reaction. This reaction is highly irreversible and has been of considerable interest for decades.

Broader significance and importance: There is broad interest in developing high throughput methods for accelerating research. This project focuses on development of a high throughput method for investigation of an electrochemical reaction that is critical to enabling the supply of hydrogen as a fuel. The project will make possible a thousandfold increase in productivity in the search for new electrode materials for carrying out the splitting of water to produce hydrogen and pure oxygen. The concept of imaging amperometry might be the best solution to this problem; if so, the method will be adopted at other laboratories and/or a scientific instrument will be developed by an electrochemical instrument company or a startup. The proposed research has the potential for a large payoff in capability in addition to the richness of its research in education.

CBET - 1511619
PI: Schneider, James

Many products of technological importance involve suspensions of particles in liquids. This project examines the mechanisms of electrical charge formation on particles immersed in nonpolar liquids. The formation of charges on particles can create electrostatic repulsions between the particles that inhibit their aggregation, which leads to a stable suspension. Certain types of surfactants can be added to the suspension as charging agents to help stabilize the suspension electrostatically. The PI has developed a method to synthesize collections of surfactants with systematic variations in their molecular structures. The surface charging characteristics of these surfactants will be characterized by using two instruments developed by the co-PIs. Results of the project will help test theories of charging in nonpolar media and ultimately lead to the rational design of improved surfactant materials for charging and particle stabilization in nonpolars. Such systems are important in a variety of technologies, including e-readers, oil-based toners for printing, and slow-release fertilizers. The researchers will use the example of the e-reader to engage K-12 students in the basic science underlying display technology and will develop a module for use in university student instruction.

This project aims to resolve long-standing questions concerning charge formation in nonpolar solvents by creating libraries of high-purity, custom-synthesized surfactants and studying their propensity to stabilize particles. The synthesis technique gives full control of tail length, extent of branching, headgroup chemistry, and counterion composition. Surface charging will be measured on test surfaces of controlled chemistry using the ZetaSpin method, which makes zeta potential measurements without concern for particle flocculation during the measurement. Inter-particle potentials will be measured by the highly sensitive TIRM method. Elucidation of interparticle potentials will determine if the Gouy-Chapman theory or the counterion-only theory is a valid descriptor of charge screening effects in different systems. The corresponding decay lengths will give a more reliable measure of ionic strength than can be obtained from conductivity measurements. This project will provide valuable insight into the rational design of charging compounds and will help develop new theories to describe inter-particle potentials in doped nonpolars.