Tunneling Spectroscopy: Capabilities, Applications, and New Techniques

This book has been compiled to give specialists, in areas that could be helped by tunneling spectroscopy, a rounded and relatively painless intro­ duction to the field. Why relatively painless? Because this book is filled with figures-A quick glance through these figures can give one a good idea of the types of systems that can be studied and the quality of results that can be obtained. To date, it has been somewhat difficult to learn about tunneling spectroscopy, as papers in this field have appeared in a diversity of scientific journals: for example. The Journal of Adhesion, J(}urnal (}f Catalysis, Surface and Interface Analysis, Science, Journal of the American Chemical Society, Physical Review-over 45 different ones in all, plus numerous conference proceedings. This diversity is, however, undoubtedly healthy. It indicates that the findings of tunneling spectroscopy are of interest and potential benefit to a wide audience. This book can help people who have seen a few papers or heard a talk on tunneling spectroscopy and want to learn more about what it can do for their field. Tunneling spectroscopy is presently in a transitional state. Its experi­ mental methods and theoretical basis have been reasonably well developed. Its continued vitality will depend on the success of its applications. Crucial to that success, as pointed out by Ward Plummer, is the adoption of tunneling spectroscopy by specialists in the areas of application.

1. Introduction.- 1. Why? Why? Why?.- 1.1. Why Do Vibrational Spectroscopy?.- 1.2. Why Do Tunneling Spectroscopy?.- 1.3. Why Not Do Infrared, Raman, or Electron Loss Spectroscopy Instead?.- 2. A Water Analogy for Tunneling Spectroscopy.- 2.1. Water Flow.- 2.2. Tunneling.- 3. Strengths of Tunneling Spectroscopy.- 3.1. Spectral Range.- 3.2. Sensitivity.- 3.3. Resolution.- 3.4. Selection Rules.- 4. Weaknesses of Tunneling Spectroscopy.- 4.1. Junction Geometry.- 4.2. Top Metal Electrode.- 4.3. Cryogenic Temperatures.- 5. General Experimental Techniques.- 5.1. Introduction.- 5.2. Sample Preparation.- 5.2.1. The Substrates.- 5.2.2. The Vacuum Evaporator.- 5.2.3. Junction Fabrication.- 5.2.4. Care and Handling of Completed Junctions.- 5.2.5. Cryogenics.- 5.2.6. Characterizing Junctions and Obtaining Spectra.- 5.2.7. Calibration and Measuring Peak Positions.- 6. Conclusions.- References.- 2. The Interaction of Tunneling Electrons with Molecular Vibrations.- 1. Introduction.- 2. Elastic Tunneling.- 3. Inelastic Tunneling.- 3.1. Simple Long-Range Models.- 3.2. Complex Long-Range Models.- 3.3. Short-Range Models.- 4. Conclusions.- References.- 3. Tunneling Spectroscopies of Metal and Semiconductor Phonons.- 1. Introduction.- 2. Threshold Spectroscopy of Normal State Phonons.- 2.1. Semiconductors.- 2.2. Metals.- 3. Superconductive Tunneling: The Effective Phonon Spectrum ?2F(?).- 3.1. Superconductivity.- 3.2. The Tunneling Density of States in C—I—S Junctions.- 3.3. McMillan—Rowell Inversion for ?2F(?).- 4. Proximity Tunneling Methods.- 4.1. C — I — NS Junctions in the Thin-N Limit.- 4.2. Phonons in the Superconductor S.- 4.3. Phonons in the Proximity Layer N.- 5. Conclusions.- References.- 4. Electronic Transitions Studied by Tunneling Spectroscopy.- 1. Introduction.- 2. Experimental.- 3. Results.- 3.1. Rare Earth Oxides.- 3.2. Large Molecules.- 4. What Are Not Electronic Transitions?.- 5. Conclusions.- References.- 5. Light Emission from Tunnel Junctions.- 1. Introduction.- 2. Planar Tunnel Junctions and Surface Polaritons.- 3. Light Emission from Tunnel Junctions: The Theoretical Picture and Examples.- 3.1. General Remarks.- 3.2. Light Emission from Slightly Roughened Junctions.- 3.3. Light Emission from Junctions Grown on Holographic Gratings.- 3.4. Light Emission from Small-Particle Junctions.- 3.5. Summary.- 4. Conclusions.- References.- 6. Comparisons of Tunneling Spectroscopy with Other Surface Analytical Techniques.- 1. Introduction.- 2. Major Surface Analytical Techniques: A Brief Survey.- 2.1. Techniques for Studying Surface Chemical Composition.- 2.1.1. X-Ray Photoelectron Spectroscopy.- 2.1.2. Auger Electron Spectroscopy.- 2.1.3. Secondary Ion Mass Spectrometry.- 2.2. Determination of Surface Electronic Structure.- 2.2.1. Ultraviolet Photoelectron Spectroscopy.- 2.2.2. Electron Energy Loss Spectroscopy.- 2.3. Techniques for Surface Structural Analysis.- 2.3.1. Surface Extended X-Ray Absorption Fine Structure.- 2.3.2. Low-Energy Electron Diffraction.- 2.3.3. Transmission Electron Microscopy.- 2.3.4. Gas Adsorption.- 2.3.5. Scanning Electron Microscopy.- 2.4. Observation of Surface Vibrational Modes.- 2.4.1. Infrared Spectroscopy.- 2.4.2. Surface Raman Spectroscopy.- 2.4.3. High-Resolution Electron Energy Loss Spectroscopy.- 2.4.4. Inelastic Neutron Scattering Spectroscopy.- 3. The Application of Modern Surface Analytical Techniques to the Characterization of Carbon Monoxide Adsorbed on Alumina Supported Rhodium.- 3.1. Sample Preparation and Morphology.- 3.1.1. High-Surface-Area Samples.- 3.1.2. Low-Surface-Area Samples.- 3.2. Vibrational Spectroscopic Analysis.- 3.3. 13C Nuclear Magnetic Resonance Studies.- 3.4. Adsorbate Structure and Bonding from Studies of Model Systems.- 4. Conclusions.- References.- 7. The Detection and Identification of Biochemicals.- 1. Introduction.- 2. IET Spectra of Biological Compounds.- 2.1. Amino Acids.- 2.2. Pyrimidine and Purine Bases.- 2.3. Nucleotides and Nucleosides.- 3. Surface Adsorption and Orientation Effects on the IETS of Nucleotides.- 4. uv Radiation Damage Studies with IETS.- 5. Conclusions.- References.- 8. The Study of Inorganic Ions.- 1. Introduction.- 2. Why Study Inorganic Ions by Tunneling Spectroscopy?.- 2.1. Direct Observation of Transitions Forbidden in Photon Spectroscopy.- 2.1.1. Vibrational Transitions.- 2.1.2. Electronic Transitions.- 2.2. Impregnation Catalysts.- 2.3. Speciation of Metal Ions in Natural Waters.- 3. Doping Techniques and Insulator Surfaces.- 3.1. Solution Phase Doping of Alumina Barriers.- 3.2. AlOx and MgO Supported OySiHx Barriers.- 4. Solution Phase versus Gas Phase Adsorption.- 5. Representative Spectra.- 5.1. Metal Cyanide Complexes.- 5.2. Metal Glycinates.- 5.3. Other Inorganic Systems.- 6. The Role of Counterions.- 7. Oxidation and Reduction Processes.- 8. What’s Next?.- 9. Conclusions.- References.- 9. Studies of Electron-Irradiation-Induced Changes to Monomolecular Structure.- 1. Introduction.- 1.1. Why Study Irradiation-Induced Molecular Structure Changes?.- 1.2. Why Use Tunneling Spectroscopy?.- 1.3. Scope of this Chapter.- 2. Present State-of-the-Art Experiments.- 2.1. Electron Irradiation Experiments.- 2.2. Underlying Assumptions.- 2.3. Determination of “Damage” Cross-Sections.- 2.4. General Trends.- 3. Suggestions for Future Experiments.- 3.1. Review of Zeroth-Order Experiments.- 3.2. First-Order Experiments.- 3.3. Second-Order Experiments.- 4. Conclusions.- References.- 10. Study of Corrosion and Corrosion Inhibitor Species on Aluminum Surfaces.- 1. Introduction.- 1.1. General Remarks.- 1.2. Corrosion of Aluminum in Organic Media.- 1.3. Corrosion by Chlorinated Hydrocarbons.- 1.4. Corrosion Inhibitors for Aluminum in Chlorinated Solvents.- 1.5. Corrosion and Inhibitor Surface Species.- 2. Corrosion of Aluminum by Carbon Tetrachloride.- 2.1. Proposed Reactions.- 2.2. Tunneling Spectroscopy Studies.- 2.2.1. Experimental Procedure.- 2.2.2. Surface Species.- 3. Inhibition of Corrosion by Formamide.- 3.1. Surface Species.- 3.2. Inhibition Mechanism.- 4. Corrosion of Aluminum by Trichloroethylene.- 4.1. Reaction with Aluminum.- 4.2. Surface Species and Reactions.- 4.3. Corrosion Mechanism.- 5. Corrosion Inhibitors for Aluminum in Hydrochloric Acid.- 5.1. Acridine Surface Species.- 5.2. Orientation of Thiourea on Aluminum Oxide.- 6. Conclusions.- References.- 11. Adsorption and Reaction on Aluminum and Magnesium Oxides.- 1. Introduction.- 2. Clean Aluminum Oxide.- 3. Dirty Aluminum Oxide.- 4. Doped Aluminum Oxide.- 4.1. Formic Acid.- 4.2. Acetic Acid and Closely Related Molecules.- 4.3. Higher Acids.- 4.4. Unsaturated Acids.- 4.5. Unsaturated Hydrocarbons.- 4.6. Phenols.- 4.7. Aromatic Alcohols and Amines.- 4.8. Bifunctional Molecular Species.- 4.9. Chemical Mixtures.- 5. Clean Magnesium Oxide.- 6. Doped Magnesium Oxide.- 6.1. Benzaldehyde.- 6.2. Formic, Acetic, and Propionic Acids.- 6.3. Phenol.- 6.4. Carboxylate Mode Shift.- 6.5. Benzyl Alcohol.- 6.6. Unsaturated Hydrocarbons.- 6.7. Diketone.- 7. Technical Postscript.- 8. Conclusions.- References.- 12. The Structure and Catalytic Reactivity of Supported Homogeneous Cluster Compounds.- 1. Introduction.- 2. Experimental Procedures.- 3. Results and Discussion.- 3.1. Zr(BH4)4 on Al2O3 at 300 K.- 3.2. Zr(BH4)4 on Al2O3 at 475 K.- 3.3. The Interaction of Zr(BH4)4 on Al2O3 with D2, D2O, and H2O.- 3.4. The Interaction of Zr(BH4)4 on Al2O3with C2H4, C3H6, and C2H2.- 3.5. The Interaction of Zr(BH4)4 on Al2O3 with Cyclohexene, 1,3-Cyclohexadiene and Benzene.- 3.6. Ru3(CO)12 on Al2O3.- 3.7. [RhCl(CO)2]2 on Al2O3.- 3.8. Fe3(CO)12 on Al2O3.- 4. Conclusions.- References.- 13. Model Supported Metal Catalysts.- 1. Introduction.- 2. Special Techniques.- 3. Experimental Results.- 3.1. Carbon Monoxide on Rhodium.- 3.1.1. Chemisorption of CO on Rhodium.- 3.1.2. Hydrogenation of CO on Rhodium.- 3.2. Carbon Monoxide on Iron.- 3.3. Carbon Monoxide and Hydrogen on Nickel.- 3.4. Carbon Monoxide on Cobalt.- 3.5. Ethanol on Silver.- 4. Future Areas of Study.- 4.1. Acetylene on Palladium.- 4.2. Carbon Monoxide on Ruthenium.- 4.3. Carbon Monoxide on Platinum.- 4.4. Other Molecules; Other Reactions.- 4.5. Low-Temperature Adsorption.- 5. Conclusions.- References.- 14. Computer-Assisted Determination of Peak Profiles, Intensities, and Positions.- 1. Introduction.- 2. Measurement of Tunneling Conductance and Its Derivatives.- 2.1. Modulation Spectroscopy.- 2.2. A Survey of Measuring Circuits.- 2.3. Calibration of Tunnel Conductance and Its Derivatives.- 3. Interfacing with a Computer.- 3.1. General Considerations.- 3.2. Analog-to-Digital Conversion.- 3.3. Digital Data Transmission from Analog Instrumentation.- 3.3.1. IEEE 488 Standard Interface.- 3.3.2. The BCD Interface.- 3.3.3. The Serial Interface (RS-232C).- 3.3.4. The Parallel Interface.- 4. Peak Profile Determination.- 4.1. General Remarks.- 4.2. Factors Affecting Peak Profile.- 4.3. Peak Profiles of Junctions with Composite Barriers.- 4.4. Peak Intensities.- 4.5. Peak Positions.- 5. Data Handling.- 5.1. General Comments.- 5.2. Data Calibration.- 5.3. Data Storage.- 5.4. Data Analysis.- References.- 15. Infusion Doping of Tunnel Junctions.- 1. Introduction.- 1.1. Doping Requirements.- 1.2. Review of Other Doping Methods.- 1.2.1. Vapor Phase Doping.- 1.2.2. Liquid Phase Doping.- 1.2.3. Infusion Doping.- 2. Experimental Description of Infusion.- 2.1. Junction and Film Preparation.- 2.2. Infusion Techniques.- 2.3. Infusion Monitoring—Resistance and Capacitance.- 3. Experiments Relating to Physical Mechanisms of Infusion.- 3.1. Resistance and Capacitance Behavior.- 3.2. Film Porosity.- 3.3. Water Infusion and Organic Molecules.- 3.4. Masking Experiments.- 3.5. Sn and Au Overlay Films.- 4. Examples of Molecules Infused.- 4.1. Acids and Bases.- 4.2. Solvents and Alcohols.- 4.3. Solid Phase Molecules.- 5. Applications of Infusion.- 5.1. Hydrogenation and Deuteration of Propiolic Acid.- 5.2. Solid-State Anodization of Aluminum.- 5.3. Other Applications.- 6. Conclusions.- References.- 16. Vibrational Spectroscopy of Subnanogram Samples with Tunneling Spectroscopy.- References.