Electronic Processes on Semiconductor Surfaces During Chemisorption

1. Electrons and Holes in a Semiconductor.- 1.1. Order and Disorder in Crystals.- 1.1.1. Types of Defects.- 1.1.2. Properties of Defects.- 1.2. Electrical Conduction of Nonmetallic Crystals.- 1.2.1. Factors Influencing Conduction.- 1.2.2. Types of Electrical Conduction.- 1.3. The Mechanism of n- and p-type Conduction.- 1.3.1. Free Electrons, Holes, and Excitons in a Lattice.- 1.3.2. Energy Levels of Electrons and Holes.- 1.4. The Energy Spectrum of an Electron in an Infinite Crystal Lattice.- 1.4.1. Statement of the Problem.- 1.4.2. Eigenfunctions and Eigenvalues.- 1.4.3. A Three-Dimensional Lattice.- 1.4.4. The Energy Spectrum of a Hole.- 1.5. The Energy Spectrum of an Electron in a Finite Crystal Lattice.- 1.5.1. Statement of the Problem.- 1.5.2. Eigenfunctions and Eigenvalues.- 1.5.3. Tamm and Shockley Surface Levels.- 1.6. Statistics of Electrons and Holes in Semiconductors.- 1.6.1. The Fermi-Dirac Distribution Function.- 1.6.2. n- and p-type Semiconductors.- 1.6.3. Statistics of Local States.- 1.6.4. The Position of the Fermi Level.- 1.7. Limits of the Band Theory of Semiconductors.- 1.7.1. Characteristic Features of the Band Theory.- 1.7.2. The Validity of the Band Theory.- 1.7.3. The Valence Band.- 2. The Various Types of Adsorption.- 2.1. The Main Laws of Adsorption.- 2.1.1. The Main Prerequisites for Langmuir' s Theory.- 2.1.2. The Kinetics of Adsorption.- 2.1.3. Adsorption Equilibrium.- 2.2. Physical and Chemical Adsorption.- 2.2.1. The Difference between Physical and Chemical Adsorption.- 2.2.2. Calculating the Adsorption Minimum.- 2.2.3. Activated Adsorption.- 2.2.4. The Nature of the Activation Barrier.- 2.3. "Strong" and "Weak" Bonds in Chemisorption.- 2.3.1. "Weak" and "Strong" Donor and "Strong" Acceptor Fonns of Chemisorption.- 2.3.2. The Various Forms of Chemisorption on Jonic Crystals.- 2.3.3. Examples.- 2.4. Radical and Valence-Saturated Forms of Chemisorption.- 2.4.1. Free Valences of a Surface.- 2.4.2. The Reactivity of Chemisorbed Particles.- 2.4.3. Examples of Radical and Valence-Saturated Forms of Chemisorption.- 2.4.4. The Dissociation of Molecules in Adsorption and the Recombination of Chemisorbed Atoms.- 2.5. The One-Electron Bond in Chemisorption.- 2.5.1. Statement of the Problem.- 2.5.2. Eigenfunctions and Eigenvalues.- 2.5.3. The Polarization of a Chemisorbed Atom.- 2.6. The Two-Electron Bond in Chemisorption.- 2.6.1. Statement ofthe Problem.- 2.6.2. Eigenfunctions and Eigenvalues.- 2.6.3. Free Lattice Electrons as Adsorption Centers.- 2.6.4. Allowing for "Weak" Bonding.- 2.7. Quantum-Mechanical Calculations in Adsorption Theory.- 2.7.1. The Cluster Approximation.- 2.7.2. "Covalent" Clusters for Oxide Lattices.- 2.7.3. "Ionic" Clusters for Oxide Lattices.- 3. Electron Transitions in Chemisorption.- 3.1. Transitions between Various Forms of Chemisorption.- 3.1.1. Transitions between Energy Levels.- 3.1.2. Transitions between Adsorption Curves.- 3.1.3. Equilibrium of Various Forms of Chemisorption.- 3.1.4. The Notion of Electron Transitions in Chemisorption Theories.- 3.2. Adsorption Equilibrium.- 3.2.1. Adsorptivity of a Surface.- 3.2.2. Surface Charging in Adsorption.- 3.3. The Kinetics of Adsorption.- 3.3.1. Statement of the Problem.- 3.3.2. Adsorption at a Constant Surface Potential: The General Case.- 3.3.3. Adsorption at a Constant Surface Potential: Particular Cases.- 3.3.4. Adsorption with a Varying Surface Potential.- 3.4. The Kinetics of Desorption.- 3.4.1. Desorption with Electronic Equilibrium.- 3.4.2. Violation of Electronic Equilibrium in Desorption.- 3.4.3. Incomplete Desorption.- 3.5. The Role of the Fermi Level in Chemisorption.- 3.5.1. The Fermi Level as Regulator of the Chemisorptive Properties of a Surface.- 3.5.2. The Origin of non-Langmuiran Relations.- 3.5.3. The Approximations of the "Boundary Layer Theory".- 4. The Interaction of the Surface with the Bulk in a Semiconductor.- 4.1. The Connection between Surface and Bulk Properties of a Semiconductor.- 4.1.1. The Connection between the Position of the Fermi Levels at the Surface and in the Bulk of a Semiconductor.- 4.1.2. The Surface Potential.- 4.1.3. The Dependence of the Surface Potential on Various Factors.- 4.2. Effects due to the Charging of the Surface.- 4.2.1. Effect of Adsorption on Work Function.- 4.2.2. Surface Conduction.- 4.2.3. Effect of External Field and Adsorption on Conduction.- 4.3. The "Quasiisolated" Surface.- 4.3.1. The Notion of a "Quasiisolated" Surface.- 4.3.2. Some Properties of "Quasiisolated" Surfaces.- 4.3.3. The Continuous and Quasicontinuous Spectra of Surface States.- 4.4. Adsorptive Properties of a Charged Semiconductor.- 4.4.1. The Adsorptivity of a Charged Semiconductor.- 4.4.2. The Electroadsorptive Effect.- 4.4.3. Adsorption lons on a Semiconductor.- 4.5. The Influence of the Surface on the Impurity Distribution inside a Semiconductor.- 4.5.1. Statement of the Problem.- 4.5.2. Impurity Distribution in the Surface Layer of Semiconductors.- 4.5.3. Effect of Impurity on the Adsorptivity of Semiconductors.- 4.5.4. Irreversible Adsorption.- 4.6. The Adsorptivity of Semiconductor Films on Metals.- 4.6.1. The Variation of the Potential in the Film.- 4.6.2. The Adsorptivity of the Film for a Positively Charged Surface.- 4.6.3. The Adsorptivity of the Film for a Negatively Charged Surface.- 4.7. Growth of a Semiconductor Film on a Metal.- 4.7.1. Statement of the Problem.- 4.7.2. The Electric Field in the Film.- 4.7.3. The Logarithmic Law of Film Growth.- 4.7.4. The Parabolic and Linear Laws of Film Growth.- 4.7.5. Succession of Laws of Film Growth with Temperature and Pressure Variation.- 5. The Catalytic Effect of a Semiconductor.- 5.1. The Basics.- 5.1.1. Semiconductors as Catalysts of Chemical Reactions.- 5.1.2. The Activity and Selectivity of a Catalyst.- 5.1.3. The Activation Energy.- 5.1.4. The Electronic Theory of Catalysis.- 5.2. The Role of the Fermi Level in Catalysis.- 5.2.1. Radical Mechanisms of Heterogeneous Reactions.- 5.2.2. Acceptor and Donor Reactions.- 5.3. Electronic Mechanisms of Catalytic Reactions.- 5.3.1. Oxidation of Hydrogen.- 5.3.2. Decomposition of Alcohol.- 5.3.3. Oxidation of Carbon Monoxide.- 5.3.4. Hydrogen-Deuterium Exchange.- 5.4. The Relationship between the Catalytic Activity of a Semiconductor and Its Electronic Properties.- 5.4.1. The Origin ofthe Relationship between Catalytic Activity, Work Function, and Electrical Conductivity.- 5.4.2. Experimental Results.- 5.4.3. Variations in Electrical Conductivity and Work Function in the Course of a Reaction.- 5.4.4. Correlation between Catalytic Activity and the Forbidden Gap Width in the Energy Spectrum of a Semiconductor.- 5.5. The Effect of Various Factors on Catalytic Activity.- 5.5.1. The Effect of an Extemal Electric Field.- 5.5.2. Catalytic Properties of a Semiconductor Film on a Metal.- 5.5.3. The Mechanism of the Action of an Impurity.- 5.5.4. The Experimental Data on the Effect of Impurities.- 5.5.5. The Compensation Effect.- 6. Processes on a Real Surface.- 6.1. Deviations from Langmuir's Theory on a Real Surface.- 6.1.1. The Concept of an In homogeneous Surface.- 6.1.2. The Concept of Interaction.- 6.2. The Adsorption-Heat Distribution Function.- 6.2.1. Inhomogeneity due to Irregularities in the Impurity Distribution.- 6.2.2. The Relation between the Impurity Concentration Gradient and the Adsorption-Heat Distribution Function.- 6.2.3. Examples of Inhomogeneous Surfaces.- 6.3. The Role of Surface Structural Defe.- 6.3.1. Adsorption on a Structural Defect.- 6.3.2. Adsorption on Defects of Thermal Origin.- 6.3.3. Adsorption on the Surface of a Disordered Semiconductor.- 6.4. Adsorption on Dispersed Semiconductors.- 6.4.1. Adsorptive Properties of a Dispersed Semiconductor.- 6.4.2. The Compensation Effect on Dispersed Semiconductors.- 6.5. Controlling the Stoichiometry of Crystals.- 6.5.1. Theoretical Aspects of the Problem.- 6.5.2. Experimental Results.- 7. The Effect of Illumination on the Adsorptive and Catalytic Properties of a Semiconductor.- 7.1. The Photoadsorption Effect.- 7.1.1. Positive and Negative Photoadsorption Effects.- 7.1.2. The Photoadsorption Effect on Ideal and Real Surfaces.- 7.1.3. Review of Basic Experimental Data.- 7.2. The Photoadsorption Effect at an Ideal Surface.- 7.2.1. The Effect of Illumination on the Amount of Various Forms of Chemisorption.- 7.2.2. Allowing for the Annihilation of Excitons at Chemisorbed Particles.- 7.2.3. The Mechanism of the Influence of Illumination on the Adsorptivity of a Surface.- 7.2.4. The Magnitude of the Photoadsorption.- 7.3. The Sign and Absolute Value ofthe Photoadsorption Effect at an Ideal Surface.- 7.3.1. Statement of the Problem.- 7.3.2. Solution for a Simplified Potential Function.- 7.3.3. The Case of the Excitonic Mechanism of Light Absorption.- 7.3.4. A Graphic Representation of the Results.- 7.3.5. The Case of High Excitation.- 7.4. Adsorption Centers in Photoadsorption.- 7.4.1. The Nature of Adsorption Centers.- 7.4.2. The Concentration of Adsorption Centers.- 7.4.3. Variation of Adsorption Center Concentration under Illumination.- 7.5. The Photoadsorption Effect at a Real Surface.- 7.5.1. Adsorption after lllumination.- 7.5.2. The Sign and Magnitude of the Photoadsorption Effect.- 7.5.3. "Direct" Photodesorption.- 7.5.4. The Aftereffect.- 7.6. Comparison of the Theory of the Photoadsorption Effect with the Experimental Data.- 7.6.1. Influence of lllumination on the Adsorptivity of a Surface.- 7.6.2. "Memory" Effects in Photoadsorption.- 7.6.3. Some Theoretical Predictions.- 7.7. The Photocatalytic Effect.- 7.7.1. The Mechanism of the Photocatalytic Effect.- 7.7.2. Hydrogen-Deuterium Exchange.- 7.7.3. Oxidation ofCarbon Monoxide: The Experimental Data and the Reaction Mechanism.- 7.7.4. Oxidation of CO: Comparison of Theoretical Results with Experimental Data.- 7.7.5. Synthesis ofHydrogen Peroxide: The Experimental Data and the Reaction Mechanism.- 7.7.6. Synthesis of Hydrogen Peroxide: Comparison of Theoretical Results with Experimental Data.- 8. Adsorption and Luminescence.- 8.1. Basic Facts on Luminescence of Crystals.- 8.1.1. The Various Types of Luminescence.- 8.1.2. Luminescence Center.- 8.1.3. Traps and Quenching Centers.- 8.2. The Effect of Adsorption on Luminescence.- 8.2.1. The Various Mechanisms of Influence of Adsorption on Photoluminescence.- 8.2.2. Recombination Luminescence: Statement of the Problem.- 8.2.3. Recombination Luminescence: Limiting Cases.- 8.2.4. Recombination Luminescence: Experimental Data.- 8.2.5. Excitonic Luminescence: Statement of the Problem.- 8.2.6. Excitonic Luminescence: A Discussion.- 8.3. The Basic Laws of Radical-Recombination Luminescence.- 8.3.1. The Spectral Composition ofRadical-Recombination Luminescence Emission.- 8.3.2. The Effect of Temperature on Intensity of RRL Spectra.- 8.3.3. The Effect of Electric Field on Intensity of RRL Spectra.- 8.3.4. The Effect of lllumination on RRL Intensity.- 8.4. The Mechanism of Radical-Recombination Luminescence.- 8.4.1. The Excitation Mechanism.- 8.4.2. The Mechanism of Luminescence.- 8.4.3. The Dependence of RRL Intensity on the Position of the Fermi Level.- 8.4.4. The Dependence of RRL Intensity on an External Electric Field.- 8.4.5. The Temperature Dependence of RRL Intensity.- 8.4.6. Radical Photoluminescence.- 8.5. Adsorption Luminescence.- 8.5.1. The Fundamentals of Adsorption Luminescence.- 8.5.2. The Mechanism and Kinetics of Adsorption Luminescence.- 8.5.3. Adsorption Luminescence at Adsorption Equilibrium.- 8.5.4. Adsorption Luminescence and the Adsorption Emission of Electrons.- 8.5.5. Luminescence Emission Accompanying Catalytic Reactions at Surfaces.- 9. Conclusion.- 9.1. The "Local" and "Collective" Effects in Chemisorption and Catalysis.- 9.2. The Basic Concepts of the Electronic Theory of Chemisorption.- 9.3. The Electronic Theory of Chemisorption and Experiment.- References.