steven higgins, ph.d. - vita
208 Oelman Hall
Department of Chemistry
3640 Colonel Glenn Hwy.
Dayton, OH 45435
B.A., Chemistry, 1991, Saint Olaf College, Northfield, Minnesota
Ph. D., Analytical Chemistry, 1996, University of Wisconsin-Madison
Minor Fields: Quantum Chemistry, Solid State Physics, Computer Science
Research Advisor: Professor Robert J. Hamers, Thesis: Microscopic investigations of chemical and electrochemical reactions at the galena (PbS)/water interface.
Postdoctoral, Environmental and Surface Chemistry, Dept. of Geology and Geophysics, University of Wyoming, 1996-1997, with Prof. Carrick M. Eggleston.
Assistant Professor, Chemistry Department, Wright State University, 2002-present
Research Scientist, Dept. of Geology and Geophysics, University of Wyoming, 1997-2002
Intern Chemist, 3M Corporation, St. Paul, Minnesota, 1991
Intern Chemist, The Dow Chemical Company, Midland, Michigan, 1990
My research interests cover a broad range of environmental, technological and fundamental problems at solid surfaces and are directed at understanding kinetics and thermodynamics of chemical reactions at solid-liquid interfaces. From an environmental perspective, there are numerous materials-related problems that arise in chemical monitoring and sensing, mineralization processes, long-term radioactive waste storage, restoration of contaminated groundwater and sediments, pollution prevention and greenhouse gas sequestration. Underlying the broad issues encompassed in these environmental areas are fundamental reactions at the surfaces of solid materials and the liquid environment. In many technologies, there is an increasing demand for process optimization, cost control, and ultimately, better products. The materials and chemical industries face problems involving reactions at solid-liquid interfaces including scale formation and inhibition, corrosion inhibition, electroplating, surfactant performance, crystal growth, and thin film deposition, to name just a few. All of these problems involve chemistry at solid-liquid interfaces and represent the key motivating factor behind my research direction.
My current research projects focus on the study of interfacial chemical dynamics related to problems in environmental chemistry. Understanding the complex surface processes (e.g., diffusion, adsorption/desorption, dissolution/precipitation, and charge transfer reactions) that occur at the boundary between solid and fluid phases is the general goal of my laboratory experiments. Past and present work has involved the use of scanning probe microscopy (SPM) to obtain in-situ, atomic-scale information on dissolving mineral surfaces. The real-space high-resolution images obtained by SPM provide structural information related to microscopic dissolution and growth mechanisms. We are in an unique position to perform ground-breaking research on solid-liquid interface dynamics with the development of the world's first hydrothermal atomic force microscope (HAFM). This SPM system, which is designed to operate at high temperatures and pressures in a wide variety of corrosive fluids, gives us the opportunity to study surface and elementary step dynamics on materials whose exchange kinetics are too sluggish for study under ambient conditions. The knowledge gained from this work can be applied to problems in mineral-water interface geochemistry, crystal growth, corrosion inhibition, and nanotechnological applications of quantum dots.
Crystal Growth and Dissolution: A major project in my group will focus on understanding inorganic and bio-mineralization processes that influence the chemistry of fragile ecosystems such as those found in marine environments and will also have a direction toward understanding crystallization in solid-phase carbon management strategies and long-term radioactive waste immobilization. My approach to a better understanding of these problems will involve detailed in-situ Atomic Force Microscopy (AFM), and hydrodynamic (e.g., channel-flow cell, and wall-jet flow cell) studies of heterogeneous kinetics under well-defined chemical and transport conditions. Since the quality and properties of many materials, and the heterogeneous kinetics of surface reactions depend on defect and impurity content, my research will provide a new level of understanding of the interaction and influence of inorganic as well as organic contaminants on processes ranging from surface dynamics of non-linear optical materials such as Potassium Dihydrogen Phosphate (KDP) to growth and dissolution kinetics of scaling minerals such as alkaline earth sulfates, phosphates, and carbonates and molecular-scale step dynamics and chemistry of solid surfaces.
Adsorption at Solid-Liquid Interfaces: Many problems in aqueous geochemistry, corrosion and scaling inhibition involve adsorptive interaction between organic molecules and solid surfaces. By choosing appropriate non-linearly active molecules, it is possible to determine adsorption free energies, and in some cases, information on the molecular orientation at the surface may be determined through optical second harmonic generation. It is my intent to utilize this surface sensitive approach to determine relationships between the concentration of adsorbed molecules and the kinetics of a particular process (i.e., dissolution, precipitation). This approach will incorporate a new hydrodynamic experimental design to ensure well-defined and controllable mass transport in these dynamic systems. With the fluid chemistry and transport conditions under experimental control and means for simultaneously characterizing the surface chemistry and reaction flux, this very powerful methodology can be utilized in the interrogation of specific heterogeneous reaction mechanisms.
Chemical Sensing: All of these research projects require the use of chemical sensors to provide homogeneous chemical information pertinent to the heterogeneous problems. A project that will begin in Fall 2002 is the development of new types of polymeric chemical sensors and incorporate these into thin films. The films will be formed by electropolymerization of monomeric sensing units from solution onto the substrate, or by spin casting of dissolved polymers and sols. Film properties (chemical, physical and mechanical) will be characterized by electrochemical methods and AFM. The key objectives are (1) to develop the fundamental chemical syntheses and characterization of monomeric materials, including transition metal complexes containing vinyl-pyridine and vinyl-bipyridine ligands, that display species-specific binding or that may be useful in molecularly imprinted films, (2) to develop a fundamental understanding of film formation mechanisms and of the relation between formation conditions and chemical specificity, sensitivity and stability of the film; (3) to design and construct sensor devices consisting of the polymeric or sol-gel matrix containing embedded analyte recognition sites deposited on various substrates; (4) to deploy sensor prototype devices for field validation studies by comparison of the obtained data to results from established analytical methods.
These sensors will be deployed in hydrothermal systems ranging from Yellowstone National Park thermal springs to Deep Sea Hydrothermal Vents (DSHVs), in addition to being used in the laboratory studies outlined above. Sensors for Fe(II)/Fe(III), SO3-, SO42-, S2O3-, NO3-, and O2, are of particular interest for long-term environmental monitoring. Over the past year, the sensors project has grown into an inter-institutional and interdisciplinary effort comprised of the nominee and collaborators with expertise ranging from inorganic synthesis to sensor technology through mineral surface science to field geochemistry.
Instrumentation: The observation of molecular scale reactions with scanning probe microscopy represents one of my key research areas. I have developed a Hydrothermal AFM (HAFM) that operates in highly corrosive fluids and significantly extends the pressure and temperature range of AFM technologies. There are two major reasons why this development is important to materials-related and environmental problems. First, in situ observations are usually required to describe the underlying mechanism in a reaction of interest. Second, the AFM is a valuable structural characterization tool, but has poor detection limits when used to observe dynamics. It is difficult to discuss mechanisms without kinetic experimental data to interrogate. To surmount this shortcoming of the AFM, elevated temperatures assist by accelerating heterogeneous reaction rates. My research will continue to push the limits of temperature and pressure in the AFM that will expand our research base to include studies under supercritical CO2, which is important in many materials formation processes and is gaining increased attention as a replacement for some organic solvents. With the capability to study surfaces with the AFM under supercritical fluids, we may begin to observe polymerization reactions in real time at the macromolecular level. These studies will be the first of their kind and may lead to a better understanding, and ultimately, a better control over the formation of new polymeric materials.
Publications and Patents:
Higgins S. R., Boram L. H., Eggleston C. M., Coles B. A., Compton R. G. and Knauss K. G. (2002) Dissolution kinetics, step and surface morphology of magnesite (104) surfaces in acidic aqueous solution at 60 oC by atomic force microscopy under defined hydrodynamic conditions, Journal of Physical Chemistry B, 106, 6696-6705.
Eggleston C. M., Stack A. G., Rosso K. M., Higgins S. R., Stack A., Bice A. M., Boese S. W., Pribyl R. D., and Nichols J. J. (2002) The structure of hematite (-Fe2O3) (001) surfaces in aqueous media: Scanning tunneling microscopy and resonant tunneling calculations of coexisting O and Fe terminations, Geochimica et Cosmochimica Acta, in review.
Stack A. G., Higgins S. R., and Eggleston C. M. (2002) Response to Comment on "Point of Zero Charge of a Corundum-Water Interface Probed with Optical Second Harmonic Generation (SHG) and Atomic Force Microscopy (AFM): New Approaches to Oxide Surface Charge", Geochimica et Cosmochimica Acta, in press.
Higgins S. R., Stack A. G., Knauss K. G., Eggleston C. M., and Jordan G. (2002) Probing molecular scale adsorption and dissolution-growth processes using nonlinear optical and scanning probe methods suitable for hydrothermal applications. In Water-Rock Interactions, Ore Deposits, and Environmental Geochemistry: A Tribute to David A. Crerar, Special Publication No. 7 (ed. R. Hellmann and S. A. Wood), pp. 111-128. The Geochemical Society.
Stack A., Higgins S. R. and Eggleston C. M. (2001) Point of zero charge of a corundum-water interface probed with optical second harmonic generation (SHG) and atomic force microscopy (AFM): Non-stoichiometric approaches to oxide surface charge, Geochimica et Cosmochimica Acta, 65, 3055-3063.
Jordan G., Higgins S. R., Eggleston C. M., Knauss K. G. and Schmahl W. W. (2001) Dissolution kinetics of magnesite in acidic aqueous solution, a hydrothermal atomic force microscopy (HAFM) study: Step orientation and kink dynamics. Geochimica et Cosmochimica Acta, 65, 4257-4266.
Higgins S. R., Jordan G., and Eggleston C. M. (2002) Dissolution kinetics of magnesite in acidic aqueous solution, a hydrothermal atomic force microscopy (HAFM) study: Step kinetics and dissolution flux. Geochimica et Cosmochimica Acta, in press.
Higgins S. R., Bosbach D., Eggleston C. M. and Knauss K. G. (2000) Kink dynamics and step growth on barium sulfate (001): A hydrothermal atomic force microscopy study, Journal of Physical Chemistry B, 104, 6978-6982.
Jordan G., Higgins S. R., Eggleston C. M., Swapp S. M., Janney D. M. and Knauss K. G. (1999) Acidic dissolution of plagioclase. In-situ observations by hydrothermal scanning force microscopy. Geochimica et Cosmochimica Acta, 63, 3183-3191.
Higgins S. R., Eggleston C. M., Knauss K. G. and Boro C. O. (2002) A hyperbaric hydrothermal flow-through fluid cell atomic force microscope. Patent # 6,437,328.
Eggleston C. M., Higgins S. R. and Maurice P. (1998) Scanning Probe Microscopy of Environmental Interfaces. Environmental Science and Technology, 32, 456A-459A.
Higgins S. R., Jordan G., Eggleston C. M. and Knauss K. G. (1998) Dissolution kinetics of the barium sulfate (001) surface by hydrothermal atomic force microscopy. Langmuir, 14, 4967-4971.
Higgins S. R., Eggleston C. M., Jordan G., Knauss K. G. and Boro C. O. (1998) In-situ observation of oxide and silicate mineral dissolution by hydrothermal scanning force microscopy: Initial results for hematite and albite. Mineralogical Magazine , 62, 618-619.
Jordan G., Higgins S. R., Eggleston C. M., Knauss K. G., and Boro C. O. (1998) Dissolution of barite(001) observed by hydrothermal scanning force microscopy. Mineralogical Magazine , 62, 725-726.
Jordan G., Higgins S. R. and Eggleston C. M. (1998) Dissolution of the periclase (001) surface. A scanning force microscope study. American Mineralogist, 84, 144-151.
Higgins S. R., Eggleston C. M., Knauss K. G. and Boro C. O. (1998) A hydrothermal atomic force microscope for imaging in aqueous solution up to 150 oC. Review of Scientific Instruments , 69, 2994-2998.
Higgins S. R., Stack A., Eggleston C. M. and dos Santos Afonso M. (1998) Proton and ligand adsorption at silica- and alumina-water interfaces studied by optical second harmonic generation (SHG). Mineralogical Magazine , 62, 616-617.
Higgins S. R. and Hamers R. J. (1996) Chemical dissolution of the galena(001) surface observed using electrochemical scanning tunneling microscopy. Geochimica et Cosmochimica Acta 60, 3067-3073.
Higgins S. R. and Hamers R. J. (1996) Morphology and dissolution processes of metal sulfide minerals observed with the electrochemical scanning tunneling microscope. Journal of Vacuum Science and Technology B 14, 1360-1364.
Hamers R. J., Chen X., Frank E. R., Higgins S. R., Shan J., and Wang Y. (1996) Atomically-resolved investigations of surface reaction chemistry by scanning tunneling microscopy. Israel Journal of Chemistry 36, 11-24.
Higgins S. R. and Hamers R. J. (1995) Spatially-resolved electrochemistry of the lead sulfide (galena) (001) surface by electrochemical scanning tunneling microscopy. Surface Science 324, 263-281.