Atomic and Ionic Impact Phenomena on Metal Surfaces

ISBN-13: 9783642460272 / Angielski / Miękka / 2012 / 402 str.

M. Kaminsky

Opis

The collisions of neutral or charged gaseous particles with solid surfaces govern many physical and chemical phenomena, as has been The gas/solid phenomena in turn depend on a recognized for a long time. great variety of processes such as the charge transfer of the gas/solid interface, adsorption and desorption, the energy transfer between an incident particle and the surface, etc. Our knowledge of these processes, however, is only fragmentary. This is partly due to the difficulty in adequately controlling the ex- perimental conditions. Consequently, until recently the data were usually so complex that reliable information about a particular elementary process could not be deduced. Within the last five to ten years, however, the techniques of ultra-high vacuum and surface preparation have developed rapidly and there has been a booming and widespread interest in the role of gas/solid interactions in such diverse fields as plasma physics, thermonuclear reactions, thermionic energy conversion, ion propulsion, sputtering corrosion of the surface of satellites and ion engines, ion getter pumps, deposition of thin films, etc. This led to extensive investigations of numerous gas/solid phenomena, such as surface ionization, sputtering, emission of secondary electrons and ions from surfaces under atom and/or ion impact, ion neutralization, and the thermal accomodation of gaseous particles on surfaces. As a result, it has become possible to gather a variety of valuable information.

Spis treści

1. The Nature of the Metal Surface.- 1.1. The Heterogeneous Surface.- 1.1.1. Physical Heterogeneity.- 1.1.1.1. Lattice Defects and Interstitial Positions.- 1.1.1.2. Occurrence of Different Crystal Planes on the Surface.- 1.1.2. Chemical Heterogeneity.- 1.1.3. Induced Heterogeneity.- 1.2. Theoretical Description of Metal Surfaces. The Work function.- 2. Determination of the Work Function of Metal Surfaces.- 2.1. Thermal Emission of Electrons.- 2.2. Thermal Emission of Ions.- 2.3. Photoelectric Method.- 2.4. Method Based on the Field Emission of Electrons.- 2.5. Measurements of Contact Potential.- 2.6. Electron Reflection Method.- 3. Preparation of Metal Surfaces.- 3.1. Thermal Desorption; the Flash-Filament Method.- 3.2. Ion Bombardment of the Surface.- 3.3. Evaporation of Thin Layers.- 3.4. Galvanotechnic Procedures.- 4. Binding Forces Effective in the Collision of Atoms and Molecules with Metal Surfaces.- 4.1. vanderWaals Forces—Physical Adsorption.- 4.1.1. Homogeneous Surfaces.- 4.1.2. Heterogeneous Surfaces.- 4.2. Exchange Forces—Weak Chemisorption on Homogeneous and Heterogeneous Surfaces.- 4.3. Heteropolar Binding Forces—Strong Chemisorption.- 4.3.1. Atoms on Homogeneous Surfaces.- 4.3.2. Polar Molecules on Homogeneous Surfaces.- 4.3.3. Heterogeneous Surfaces.- 5. Energetics of Surface Reactions.- 5.1. General Remarks and Definitions.- 5.2. Heats of Adsorption for Physical Adsorption.- 5.3. Heats of Adsorption for Weak Chemisorption.- 5.4. Heats of Adsorption for Strong Chemisorption.- 6. Inelastic Collisions of Atoms and Molecules with Metal Surfaces: The Accommodation Coefficient.- 6.1. Definition and General Remarks.- 6.2. Methods for Measuring Accommodation Coefficients.- 6.2.1. Measurements in the Low-Pressure Range.- 6.2.1.1. Molecular-Beam Method.- 6.2.1.2. Heat-Conductivity Method.- 6.2.1.3. Recoil Methods.- 6.2.2. Measurements at High Pressures: the Temperature Jump.- 6.3. Experimental Results on Accommodation Coefficients.- 6.3.1. Monatomic Gases.- 6.3.1.1. Experimental Data.- 6.3.1.2. Theoretical Considerations.- 6.3.2. Diatomic Gases.- 6.3.2.1. Experimental Data.- 6.3.2.2. Theoretical Considerations.- 6.3.3. Polyatomic Gases.- 6.3.3.1. Experimental Data.- 6.3.3.2. Theoretical Considerations.- 6.4. Determination of Relaxation Times for the Process of Energy Exchange between the Normal Vibrational States of the System Comprising Adsorbed Molecule and Metal Surface.- 7. Elastic Collisions of Atoms and Molecules with Metal Surfaces.- 8. Emission of Positive Ions Formed at Metal Surfaces (Surface Ionization).- 8.1. Theoretical Considerations.- 8.1.1. Equation for Emission from a Homogeneous Surface in the Absence of External Electrical Fields.- 8.1.2. Equation for Emission from a Homogeneous Surface in an External Electrical Field.- 8.1.3. Equation for Emission from Heterogeneous Surfaces in the Absence of External Electrical Fields.- 8.1.4. Equation for Emission from Heterogeneous Surfaces in an External Electrical Field.- 8.2. Relation of the Saha-Langmuir Equation to the Frenkel Equation and to Charge-Transfer Probabilities.- 8.3. Experimental Investigation of Positive Surface Ionization (PSI).- 8.3.1. Experimental Methods.- 8.3.1.1. “Bulb” Method without Mass Spectrometric Analysis.- 8.3.1.2. Single Filament Ion Source with Mass Spectrometer: Plain Emitter—Porous Emitter.- 8.3.1.3. Multiple-Filament Source with Mass Spectrometer.- 8.3.1.4. Beam Methods.- 8.3.1.5. Pulsed-Beam Methods.- 8.3.2. Experimental Results.- 8.3.2.1. Positive Surface Ionization for Alkali Metal Atoms in Weak Electric Fields.- 8.3.2.2. Positive Surface Ionization of Some Alkali-Salt Molecules on Metal Surfaces in Weak External Fields.- 8.3.2.3. Positive Surface Ionization of Alkaline Earth Elements and Compounds in Weak External Fields.- 8.3.2.4. Positive Surface Ionization of Other Elements and Compounds in Weak External Fields.- 8.3.2.5. Positive Surface Ionization in Strong External Electric Fields—Field Desorption.- 9. Formation and Emission of Negative Ions at Metal Surfaces (NSI).- 9.1. Theoretical Considerations.- 9.1.1. Emission Equation for a Homogeneous Surface.- 9.1.2. Emission Equation for Heterogeneous Surfaces.- 9.2. Experimental Methods.- 9.3. Experimental Results.- 10. Sputtering of Metal Surfaces by Ion Bombardment.- 10.1. Introduction.- 10.2. Experimental Methods.- 10.2.1. Methods for Producing the Incident Ion.- 10.2.1.1. Glow Discharge.- 10.2.1.2. Low-Pressure Gas Discharge in a Magnetic Field.- 10.2.1.3. Supplemented Low-Pressure Arc.- 10.2.1.4. Ion Beams (Not Mass Analyzed).- 10.2.1.5. Mass-Analyzed Ion Beams.- 10.2.2. Methods of Determining the Sputtering Yield.- 10.2.2.1. Weight Change of Target and/or Collector.- 10.2.2.2. Optical Transmission through Sputtered Layers.- 10.2.2.3. Radioactive-Tracer Method.- 10.2.2.4. Surface-Ionization.- 10.2.2.5. Mass-Spectrometric Detection.- 10.2.2.6. Optical Spectroscopy.- 10.3. Experimental Results.- 10.3.1. Sputtering of Neutral Target Atoms from Polycrystalline Targets.- 10.3.1.1. Threshold Values for Sputtering.- 10.3.1.2. Sputtering Yields in the Hard-Sphere Collision Region.- 10.3.1.2.1. Dependence on the Energy of the Incident Ion.- a) Energy Range 0.1–1.0 keV.- b) Energy Range 1–60 keV.- 10.3.1.2.2. Dependence on Angle of Incidence.- 10.3.1.2.3. Dependence on Target Temperature.- 10.3.1.2.4. Self-Sputtering.- 10.3.1.2.5. Dependence on the Incident-Ion Current Density.- 10.3.1.2.6. Dependence on Residual Gas Pressure.- 10.3.1.2.7. Angular Distribution of Sputtered Particles.- 10.3.1.2.8. Mean Velocity of Sputtered Particles.- 10.3.1.3. Sputtering Yields in the Weak-Screening Region.- 10.3.1.3.1. Dependence on the Incident-Ion Energy.- 10.3.1.3.2. Angular Distribution of Sputtered Particles.- 10.3.1.4. Sputtering Yields in the Rutherford-Collision Region.- 10.3.2. Sputtering of Neutral Target Atoms from Monocrystalline Targets.- 10.3.2.1. Atom Ejection Pattern for Face-Centered Cubic Metals.- 10.3.2.1.1. The (100) Surface.- 10.3.2.1.2. The (110) Surface.- 10.3.2.1.3. The (111) Surface.- 10.3.2.2. Atom Ejection for Body-Centered Cubic Metals.- 10.3.2.2.1. The (100) Surface.- 10.3.2.2.2. The (110) Surface.- 10.3.2.2.3. The (111) Surface.- 10.3.3. Sputtering of Target Particles in an Excited Neutral or Ionized State from Polycrystalline and Monocrystalline Targets.- 10.3.3.1. Treshold Values for the Sputtering of Charged Particles.- 10.3.3.2. Species of Sputtered Positive and Negative Ions.- 10.3.3.3. Dependence on the Energy of the Primary Ion.- 10.3.3.4. The Effect of Target Temperature.- 10.3.3.5. Energy Distribution of Sputtered Ions.- 10.3.4. Etching of Surfaces by Sputtering.- 10.3.4.1. Etching of Polycrystalline Metal Surfaces.- 10.3.4.2. Etching of Single-Crystal Surfaces.- 10.3.5. Structural Changes in Pure Metals or Alloys as a Result of Ion Bombardement.- 10.4. Theoretical Treatments of the Sputtering Process.- 10.4.1. “Hot-Spot” Model—“Heated Spike” Model.- 10.4.2. Collision Models.- 10.4.2.1. Collision Theories for the Energy Range E < EA (Hard-Sphere-Region).- 10.4.2.2. Collision Theories for the Energy Range EA Collision Theories for the Energy Range E >EB (Rutherford-Collision Region).- 11. Ion Scattering from Metal Surfaces.- 11.1 Definitions: Ion-Reflection Coefficient and Secondary-Emission Coefficient.- 11.2 Experimental Techniques.- 11.3. Experimental Ion-Reflection and Secondary-Emission Coefficients.- 11.3.1. Dependence on the Incident Ion Energy.- 11.3.1.1. Incident Noble-Gas Ions.- 11.3.1.2. Incident Alkali Ions.- 11.3.1.3. Incident Protons, Deuterons, and Various Other Atomic and Molecular Ions.- 11.3.2. Dependence on the Mass and Electronic Configuration of the Incident Ion.- 11.3.3. Dependence on the Mass and Work Function of the Target Material.- 11.3.4. Dependence on the Angle of Incidence.- 11.3.5. Energy Distribution of Reflected and Secondary Ions.- 11.3.6. Dependence on the Target Temperature and on Surface Contamination.- 11.4. Theoretical Treatment of Ion Scattering from Metal Surfaces.- 12. Neutralization of Ions on Metal Surfaces (Potential Emission of Secondary Electrons).- 12.1. Introductory Remarks and Definitions.- 12.2. Auger Neutralization; Resonance Neutralization.- 12.2.1. Experimental Methods.- 12.2.2. Experimental Results.- 12.2.2.1. Singly-Charged Ions.- 12.2.2.1.1. Secondary-Electron Yield ? and its De pendence on the Energy E of the Incident Ion.- 12.2.2.1.2. Energy Distribution of Secondary Elec trons and its Dependence on the Incident-Ion Energy.- 12.2.2.1.3. Influence of Surface Contamination on the Yield and Energy Distribution of the Secondary Electrons.- 12.2.2.2. Multiply-Charged Ions.- 12.2.2.2.1. Secondary Electron Yield ? and its Dependence on the Energy E of the Incident Ion.- 12.2.2.2.2. Energy Distribution of Secondary Elec trons.- 12.2.2.2.3. Influence of Surface Contamination on the Electron Yield and the Electron Distribution.- 12.2.3. Theory of Auger Neutralization.- 12.2.3.1. General Definitions of the Total Transition Rate and Related Probability Functions.- 12.2.3.2. Total Transition Rate and the Probability for Auger Neutralization.- 12.2.3.3. The Probability of Emission of an Excited Electron from the Metal Surface.- 12.2.3.4. Effects which Broaden the Electron Energy Distri bution.- 12.2.3.5. Comparison of Experimental and Theoretical Values for the Energy Distribution and Yield of Secondary Electrons.- 13. De-excitation of Metastable Atoms and Ions on Metal Surfaces.- 13.1. Introductory Remarks and Description of Experimental Methods.- 13.2. Experimental Data for the Total Yield and Energy Distribution of Secondary Electrons from De-excitation of Metastable Atoms and Ions on Metal Surfaces.- 13.3. Theoretical Aspects of the Auger De-excitation of Metastable Atoms on Metal Surfaces.- 14. The Emission of Electrons from Metal Surfaces by Bombardment with Charged and Uncharged Particles (Kinetic Emission).- 14.1. Introduction.- 14.2. Experimental Methods.- 14.3. Experimental Results.- 14.3.1. Dependence of Secondary-Electron Yield ? on the Energy or Velocity of an Incident Ion or Neutral Atom.- 14.3.1.1. Medium Energy Range.- 14.3.1.1.1. Atoms and Ions of Noble Gases.- 14.3.1.1.2. Alkali or Alkaline Earth Metal Ions.- 14.3.1.1.3. Ions of Various Kinds.- 14.3.1.2. High-Energy Range.- 14.3.1.2.1. Noble-Gas Ions.- 14.3.1.2.2. Alkali and Alkaline Earth Metal Ions.- 14.3.1.2.3. Various Kinds of Ions.- 14.3.2. Effects of Surface Coverage on the Secondary Electron Yield ?.- 14.3.3. Dependence of the Electron Yield ? on the Mass of the Incident Ion (Isotope Effect).- 14.3.4. Dependence of the Electron Yield ? on the Charge State of the Incident Particle.- 14.3.5. Temperature Dependence of the Secondary Electron Yield ?.- 14.3.6. Variation of ? with the Angle of Incidence ?.- 14.3.7. Energy Distribution of Secondary Electrons.- 14.4. Theoretical Aspects of the Kinetic Emission of Secondary Electrons.- Literature.- Author Index.