We are interested in the detailed dynamics of reactions at well-characterized surfaces and interfaces. The following paragraphs describe some of these studies:
Chirality is a well known property of organic molecules. The study of three dimensional chirality dates from the work of Pasteur. Chirality is exhibited in two dimensions as well, in particular in the adsorption of chiral and achiral organic molecules on solid surfaces. Scanning probe microscopy has made the structural study of these two dimensional chiral layers possible with atomic and molecular resolution. We have studied the formation of chiral monolayers from the adsorption of long chain substituted hydrocarbons on highly oriented pyrolytic graphite (HOPG) surfaces. The goal of our work in this project is to understand the complex interactions that govern the structures that form when long chain organic molecules adsorb on HOPG, and to develop predictive capability for the formation of chiral monolayers of particular nanoscale structure. This understanding will be useful for the design of chirally active sensors, chiral catalytic materials, and chiral separations media. A detailed understanding of two dimensional chiral structures is also relevant for unraveling the mystery of homochirality in biological molecules.
The bonding between an organometallic species and an oxide or nitride supporting substrate is important to the chemistry of supported catalysts, electronic device processing, and adhesion and lubrication phenomena. This bonding may be investigated with the aid of photoelectron spectroscopy (UPS and XPS). When combined with other surface probes such as thermal desorption spectroscopy (TDS), AES, LEED, and vibrational spectroscopic characterization by high resolution electron energy loss spectroscopy (HREELS) or reflection-absorption infrared spectroscopy (RAIRS), a relatively complete picture of the surface properties of the adsorbed species becomes available. We are exploring, in collaboration with Professor Jeffrey Schwartz, the interaction of a number of transition metal organometallic and phosphonate complexes with well characterized oxide surfaces. In this work electron spectroscopic measurements are correlated with the chemical behavior of the supported complex, as studied by conventional heterogeneous catalysis methods and mass sensitive kinetic methods. This approach is also extended to the study of important oxide and nitride bound metallic layers, which are of interest in electronic materials chemistry, in bio-compatible materials chemistry, and in adhesion and corrosion inhibition applications.
HREELS and TDS in combination provide a very detailed view of the kinetics and mechanisms of small molecule reactions on well-characterized solid surfaces. We have studied a number of small molecule reactions on the clean and adsorbate modified Fe(100) surface. This surface exhibits a very rich and complex chemistry, and serves as a useful model for the investigation of structure-reactivity correlations in surface chemistry. Currently, we are using these methods to examine the interaction of a number of sulfur, nitrogen, and phosphorous containing molecules, which are promising candidates for corrosion inhibitors on the iron surface. We are also using electron spectroscopy to examine the detailed mechanism of oxidation of complex alloy surfaces with the goal of understanding the corrosion process in extreme environments. These surface spectroscopic studies are correlated with electrochemical impedance spectroscopy and corrosion rate evaluation studies.
The detection of small magnetic fields is a problem of great importance with application in vehicle detection, security sensors, and mineral and petrochemical prospecting. Laser addressed magnetometers detect magnetic fields by monitoring the spin precession of laser prepared spin polarized atoms in the gas phase. The cells that contain these spin polarized atoms (usually rubidium or cesium atoms) are often coated with paraffin wax on the interior surfaces in an attempt to prevent the wall-collision relaxation of the spin polarization. These coatings are very empirical, and little is known about how or why they work to improve the sensitivity of these laser addressed magnetometer devices. In a collaborative research project with researchers in the Department of Physics at Princeton University and at the University of California, Berkeley, we are working to develop an understanding of these anti-relaxation coatings, and to develop new “designer” coatings that will enhance the sensitivity of these devices. We are carrying out detailed studies of the physical and chemical properties of functional anti-relaxation coatings, using electron spectroscopy and scanning probe microscopy to understand the electronic structure and morphology of these layers. We are using our self-assembled monolayer methodology developed in our earlier work to develop coatings to improve the anti-relaxation nature of these surfaces. These fundamental studies will provide the basic underpinning for the rational use of surface chemistry to improve the sensitivity and lifetime of these micromagnetometer systems.
The collision of a gas molecule with a surface, followed by trapping of the molecule on the surface, must precede any surface reactions which might take place. Some knowledge of this fundamental process, along with the accompanying energy transfer to the surface, is essential to a complete understanding of heterogeneous reaction dynamics. We have used infrared spectroscopic methods to investigate the detailed dynamics of a very important prototype surface reaction, the catalytic oxidation of CO and related molecules on platinum. This reaction, which is essential in the control of pollution from automobile exhaust, has generated an enormous number of studies. In spite of all this work, the detailed dynamics of the reaction are just starting to become clear. Using a diode laser absorption spectrometer, we have probed the dynamics of this process in detail. We have used this method to map out the detailed ro-vibrational populations of the product CO2 and changes in these populations with changing surface reaction conditions. These studies have been extended to the reaction of CO with NO and methanol with O2, as well as studies of related molecules such as formaldehyde and formic acid.
Selected Recent Publications
- F. Tao and S.L. Bernasek, “Self-assembly of 5-Octadecyloxyisophthalic Acid and Its Coadsorption with Terephthalic Acid”, Surface Sci., 601, 2284 (2007).
- J.E. McDermott, M. McDowell, I.G. Hill, J. Hwang, A. Kahn, S.L. Bernasek, J. Schwartz, “Organophosphonate Self-Assembled Monolayers for Gate Dielectric Surface Modification of Pentacene-Based Organic Thin-Film Transistors: A Comparative Study”, J. Phys. Chem. A, 11, 12333 (2007).
- G. Bhargava, I. Gouzman, T.A. Ramanarayanan, C.M. Chun, and S.L. Bernasek, “Characterization of the “Native” Surface Thin Film on Pure Polycrystalline Iron: a High Resolution XPS and TEM Study”, Appl. Surf. Sci., 253, 4322 (2007).
- G. Bhargava, T.A. Ramanarayanan, I. Gouzman, E. Abelev, and S.L. Bernasek, “Inhibition of Iron Corrosion by Imidazole: An Electrochemical and Surface Science Study”, Corrosion, 65, 308 (2009).
- N. Oncel and S.L. Bernasek, “The effect of molecule-molecule and molecule-substrate interaction in the formation of Pt-octaethyl porphyrin self-assembled monolayers”, App. Phys. Lett., 92, 133305 (2008).
- F. Tao, Y. Cai, Y. Ning, G-Q Xu, and S.L. Bernasek, “Transfer of Electron Density and Formation of Dative Bonds in Chemisorption of Pyrrolidine on Si(111)7x7”, J. Phys. Chem. C., 112, 15474 (2008).
- S.J. Seltzer, D.M. Rampulla, S. Rivillon-Amy, Y.J. Chabal, S.L. Bernasek, and M.V. Romalis, “Testing the Effects of Surface Coatings on Alkali Atom PolarizationLifetimes”, J. App. Phys., 104, 103116 (2008).
- D.M. Rampulla, N. Oncel, E. Abelev, Y.W. Yi, S. Knappe, and S.L. Bernasek, “Effects of Organic Film Morphology on the Formation of Rb Clusters on Surface Coatings Used in Alkali Metal Atom Magnetometer Cells”, App. Phys. Lett., 94, 1 (2009).
- T.L. Peng and S.L. Bernasek, “The Internal Energy of CO2 Produced by the Catalytic Oxidation of CH3OH by O2 on Polycrystalline Platinum”, J. Chem. Phys., 131, 154701 (2009).
- N. Oncel and S.L. Bernasek, “Comparison of Ni(II) and Vanadyl-Octaethylporphyrin Self-assembled Monolayers Formed on Bare and 5-(octadecyloxy) Isophthalic Acid Covered HOPG”, Langmuir, 25, 9290 (2009).
- E. Abelev, T.A. Ramanarayanan, and S.L. Bernasek, “Iron Corrosion in 3% NaCl solution in CO2 and Low Concentration H2S Environments at Ambient Temperature and Pressure: An Electrochemical and Surface Science Study”, J. Electrochem. Soc., 156, C331 (2009).
- E. Abelev, J. Sellberg, T.A. Ramanarayanan, and S.L. Bernasek, “Effect of H2S on Fe corrosion in CO2-saturated Brine”, J. Materials Science, 44, 6167 (2009).
- F. Tao, G.-Q. Xu, and S.L. Bernasek, “Electronic and Structural Factors in Modification and Functionalization of Semiconductor Surfaces with Aromatic Systems”, Chemical Reviews, 109, 3991 (2009).
- M. Dubey, A. Raman, E.S. Gawalt, and S.L. Bernasek, “Differential Charging in X-ray Photoelectron Spectroscopy for Characterizing Organic Thin Films”, J. Electron Spec. Rel. Phen., 176, 18 (2010).
- S. Suzer, E. Abelev, and S.L. Bernasek, “Impedance-Type Measurements Using XPS”, Applied Surface Sci., 256, 1296 (2009).
- G. Bhargava, T.A. Ramanarayanan, and S.L. Bernasek, “Imidazole-Fe Interaction in Aqueous Chloride Medium: Effect of Cathodic Reduction of the Native Oxide”, Langmuir, 26, 215 (2010).