2. High Temperature UHV-STM System 264 3. Hydrogen Desorption Process on Si (111) Surface 264 4. (7x7) - (1 xl) Phase Transition on Si (111) Surface 271 Step Shifting under dc Electric Fields 275 5. 6. Conclusions 280 Acknowledgements and References 281 12. DYNAMIC OBSERVATION OF VORTICES IN SUPERCONDUCTORS USING ELECTRON WAVES 283 by Akira Tonomura 1. Introduction 283 2. Experimental Method 284 2. 1 Interference Microscopy 284 2. 2 Lorentz Microscopy 287 Observation of Superconducting Vortices 288 3. 3. 1 Superconducting Vortices Observed by Interference Microscopy 288 3. 1. 1 Profile Mode 288 3. 1. 2 Transmission Mode 291 3. 2 Superconducting Vortices Observed by Lorentz Microscopy 293 3. 3 Observation of Vortex Interaction with Pinning Centers 294 3. 3. 1 Surface Steps 295 3. 3. 2 Irradiated Point Defects 296 4. Conclusion 298 References 299 13. TEM STUDIES OF SOME STRUCTURALLY FLEXIBLE SOLIDS AND THEIR ASSOCIATED PHASE TRANSFORMATIONS 301 by Ray L. Withers and John G. Thompson 1. Introduction 301 2. Tetrahedrally Comer-Connected Framework Structures 302 3. Tetragonal a-PbO 311 4. Compositionally Flexible Anion-Deficient Fluorites and the "Defect Fluorite" to C-type Sesquioxide Transition 320 5. Summary and Conclusions 327 Acknowledgements and References 327 Author Index 331 Subject Index 333 List of Contributors A. ASEEV Institute of Semiconductor Physics, Russian Academy of Sciences Novosibirsk, 630090, pr. ac. , Lavrentjeva 13, RUSSIA E. BAUER Department of Physics and Astronomy, Arizona State University Tempe, AZ 85287-1504, U. S. A. G. H.

2. High Temperature UHV-STM System 264 3. Hydrogen Desorption Process on Si (111) Surface 264 4. (7x7) - (1 xl) Phase Transition on Si (111) Surface 271 Step Shifting under dc Electric Fields 275 5. 6. Conclusions 280 Acknowledgements and References 281 12. DYNAMIC OBSERVATION OF VORTICES IN SUPERCONDUCTORS USING ELECTRON WAVES 283 by Akira Tonomura 1. Introduction 283 2. Experimental Method 284 2. 1 Interference Microscopy 284 2. 2 Lorentz Microscopy 287 Observation of Superconducting Vortices 288 3. 3. 1 Superconducting Vortices Observed by Interference Microscopy 288 3. 1. 1 Profile Mode 288 3. 1. 2 Transmission Mode 291 3. 2 Superconducting Vortices Observed by Lorentz Microscopy 293 3. 3 Observation of Vortex Interaction with Pinning Centers 294 3. 3. 1 Surface Steps 295 3. 3. 2 Irradiated Point Defects 296 4. Conclusion 298 References 299 13. TEM STUDIES OF SOME STRUCTURALLY FLEXIBLE SOLIDS AND THEIR ASSOCIATED PHASE TRANSFORMATIONS 301 by Ray L. Withers and John G. Thompson 1. Introduction 301 2. Tetrahedrally Comer-Connected Framework Structures 302 3. Tetragonal a-PbO 311 4. Compositionally Flexible Anion-Deficient Fluorites and the "Defect Fluorite" to C-type Sesquioxide Transition 320 5. Summary and Conclusions 327 Acknowledgements and References 327 Author Index 331 Subject Index 333 List of Contributors A. ASEEV Institute of Semiconductor Physics, Russian Academy of Sciences Novosibirsk, 630090, pr. ac. , Lavrentjeva 13, RUSSIA E. BAUER Department of Physics and Astronomy, Arizona State University Tempe, AZ 85287-1504, U. S. A. G. H.