This book is based on the results of many years of experimental work by the author and his colleagues, dealing with the electronic properties of organic crystals. E. Silinsh has played a leading role in pOinting out the importance of the polarization energy by an excess carrier, in determining not only the character of the carrier mobility in organic crystals, but in determining the band gap and the nature of the all-important trapping site in these crystals. The one-electron model of electronic conductivity that has been so successful in dealing with inorganic semiconductors is singular ly unsuccessful in rationalizing the unusual physical properties of organic crystals. A many-body theory is required, and the experimental manifestation of this is the central role played by the crystal polarization enerqies in transferring the results obtained with the isolated molecule, to the solid. The careful studies of E. Silinsh in this field have shown tn detail how this polarization energy develops around the excess carrier (and also the hole-electron pair) sitting on a molecular site in the crystal. As with all insulators, trapping sites playa dominant role in reducing the magnitude of ~he current that can theoretically pass through the organic crystal. It is usually the case that these trapping sites are energetically distributed within the forbidden band of the crystal. For many years, an exponential distribution has shown itself to be useful and reasonably correct: However,' E.

Inhalt

1. Introduction: Characteristic Features of Organic Molecular Crystals.- 1.1 Interaction Forces in Molecular Crystals.- 1.2 The Atom-Atom Potential Method.- 1.3 Aromatic Hydrocarbons Model Compounds of Organic Molecular Crystals.- 1.4 Specific Properties of Electronic States in a Molecular Crystal.- 1.5 Basic Characteristics of Electronic Conduction States in Molecular Crystals.- 2. Electronic States of an Ideal Molecular Crystal.- 2.1 Neutral Excited States in a Molecular Crystal.- 2.2 Ionized States in a Molecular Crystal.- 2.3 Electronic Polarization of a Molecular Crystal by a Charge Carrier.- 2.4 Electrostatic Methods of Electronic Polarization Energy Calculation in Molecular Crystals.- 2.5 Determination of Molecular Polarizability Tensor.- 2.6 Selection of Molecular Polarizability Components bi. for Electronic Polarization Energy Calculations.- 2.7 Extended Polarization Model of Ionized States in Molecular Crystal s.- 2.8 Charge Transfer (CT) States in Molecular Crystals.- 2.9 Experimental Determination of Energy Structure Parameters in Molecular Crystals.- 2.10 Energy Structure of an Anthracene Crystal.- 2.11 Energy Structure of Aromatic and Heterocyclic Molecular Crystals.- 3. Role of Structural Defects in the Formation of Local Electronic States in Molecular Crystals.- 3.1 Statistical Aspects of the Formation of Local States of Polarization Origin.- 3.2 General Considerations on the Role of Specific Structural Defects.- 3.3 Point Defects (Vacancies) in Molecular Crystals, Their Crystallographic and Electronic Properties.- 3.4 Dislocation Defects, Their Role in Local State Formation.- 3.5 Energetics of Dislocations in Molecular Crystals.- 3.6 Atomic and Molecular Models of the Dislocation Core.- 3.7 Dislocation Alignments and Aggregations, TheirConfigurational and Energetic Properties.- 3.8 Grain Boundaries, Their Energetic Characteristics.- 3.9 Stacking Faults in Molecular Crystals.- 3.10 Formation of Predimer States in the Regions of Extended Structural Defects of Anthracene-Type Crystals.- 3.11 Some More Complex Two- and Three-Dimensional Lattice Defects in Molecular Crystals.- 3.12 Observation of Structural Defects in Molecular Crystals.- 3.13 Main Characteristics of Dislocation Defects in Some Model Molecular Crystals.- 4. Local Trapping Centers for Excitons in Molecular Crystals.- 4.1 Theory of Exciton States in a Deformed Molecular Crystal.- 4.2 Electron Level Shifts in Hydrostatically Compressed Molecular Crystal s.- 4.3 Formation of Local Exciton Trapping Centers in Structural Defects of a Crystal.- 5. Local Trapping States for Charge Carriers in Molecular Crystals.- 5.1 Electronic Polarization Energy of a Compressed Anthracene Crystal.- 5.2 Formation of Local Trapping Centers for Charge Carriers in Structural Defects of a Real Molecular Crystal.- 5.3 Energy Spectrum of Local States of Polarization Origin in Stacking Faults of an Anthracene Crystal.- 5.4 Local Surface States of Polarization Origin in Molecular Crystals.- 5.5 Local States of Polarization Origin in the Vicinity of a Lattice Vacancy.- 5.6 Local Charge Carrier Trapping in Covalent, Ionic and Molecular Crystal s.- 5.7 Randomizing Factors Determining Gaussian Distribution of Local States of Structural Origin.- 5.8 Investigation of Local Trapping States by Method of Space Charge Limited Currents (SCLC).- 5.9 Phenomenological SCLC Theory for Molecular Crystals with Gaussian Distribution of Local Trapping States.- 5.10 Gaussian SCLC Approximations of Experimental CV Characteristics.- 5.11 SCLC Theory for Spatially Nonuniform Trap Distribution.- 5.12 Investigation of Local Trapping States by Thermally Activated Spectroscopy Techniques.- 5.13 Other Experimental Methods for Local Trapping State Study.- 5.14 Correlations Between Distribution Parameters of Local Trapping States and Crystalline Structure.- 5.15 Local Lattice Polarization by Trapped Charge Carrier in Molecular Crystals.- 5.16 Guest Molecules as Trapping Centers in a Host Lattice.- 6. Summing Up and Looking Ahead.- References.- Additional References with Titles.