Rapid advances in chemical synthesis and fabrication techniques have led to novel nano-sized materials that exhibit original and often unforeseen properties. One of the greatest advantages of these nano-systems is that their electronic and optical properties can be controlled, not only by the material's inherent features, but also by the sample's size, shape, and topology. This flexibility makes them ideal for applications in several fields, ranging from electronics and optoelectronics to biology and medicine. However, in order to design nanoelectronic devices, a clear understanding of their fundamental properties is needed. Semiconductor quantum dots (QDs) and single-walled carbon nanotubes (SWCNTs) are two of the most promising examples of low-dimensional nanomaterials. These two types of nano-systems have been chosen for the extensive studies presented in this book. The book investigates QDs and SWCNTs using quantum-chemical calculations that describe intricate details of excited state phenomena, and provides information about the mechanisms that occur on the atomic level and that are extremely difficult if not impossible to probe experimentally. It delivers, consistently and coherently, a novel approach to the nanomaterials which is promising for today's technologies as well as their future. This approach elegantly overcomes computational difficulties known in the field, and shares ways to reach top performance in description of combined quantum effects of molecular vibrations and exciton formation on the realistic size numerical models. The reader will acquire the pioneering methodology supported by most recent original results, prospectively applicable to the design of new nano-devices.
Author(s): Svetlana V. Kilina, Bradley F. Habenicht
Publisher: Pan Stanford Publishing
Year: 2009
Language: English
Pages: 202
Tags: Специальные дисциплины;Наноматериалы и нанотехнологии;
Contents......Page 10
Preface......Page 8
1. Introduction......Page 14
1.1 Common Features of Low-Dimensional Nanomaterials......Page 15
1.2 Intriguing Phenomena in Quantum Dots and Potential Applications......Page 17
1.3 Advantages and Challenges of Technological Applications of Carbon Nanotubes......Page 21
1.4 Excitonic Character and Numerical Approaches to QDs and SWCNTs......Page 24
2. Electronic Structure and Phonon-Induced Carrier Relaxation in CdSe and PbSe Quantum Dots......Page 30
2.1.1 Theoretical Considerations of Electronic and Optical Properties of Quantum Dots......Page 31
2.1.2 Dependence of Electronic Structure on a Host Material: CdSe and PbSe Quantum Dots......Page 36
2.1.3 Experimental Rates of Carrier Relaxation in Quantum Dots: Phonon Bottleneck Problem......Page 40
2.2 Simulations of Nonadiabatic Dynamics: Trajectory Surface Hopping (TSH) in Density Functional Theory (DFT)......Page 43
2.2.1 Time-Dependent Kohn-Sham Theory (TDKS)......Page 44
2.2.2 Fewest Switches Surface Hopping in the Kohn-Sham Representation......Page 46
2.2.3 Simultion Details.......Page 48
2.3.1 Electronic Structure at Zero Kelvin: Effects of Surface Reconstructions and Passivation.......Page 51
2.3.2 Evolution of Electronic Structure upon Temperature......Page 58
2.3.3 Optical Spectra of CdSe and PbSe Quantum Dots.......Page 61
2.3.4 Active Phonon Modes......Page 65
2.3.5 Phonon-Induced Electron and Hole Relaxation......Page 68
2.3.6 Simulated Rates and Regimes of Carrier Relaxation......Page 72
2.4 Conclusions......Page 75
3. Phonon-Induced Free Carrier Dynamics in Carbon Nanotubes......Page 78
3.0.1 Dynamics in Nanotubes: Optical Experiments......Page 79
3.0.2 Electronic Structure......Page 83
3.1.1 Semiclassical Model of Dephasing......Page 85
3.1.2 Decoherence Effects......Page 86
3.1.3 Simultion Details.......Page 87
3.2.1 Phonon-Induced Intraband Relaxation.......Page 89
3.2.2 Estimates of Dephasing Timescales in SWCNTs......Page 92
3.2.3 Nonradiative Recombination in a Semiconducting SWCNT......Page 98
3.3 Conclusions......Page 103
4. Including Electron-Hole Correlations: Excitonic and Vibrational Properties of Carbon Nanotubes......Page 106
4.1.1 Eexperimental Evidence of Excitons and Strong Exciton-Phonon Copuling in SWCNTs......Page 107
4.1.2 Available Theoretical Approaches Calculating Excitonic and Vibrational Effects.......Page 110
4.2 Computational ESMD Methodology......Page 112
4.2.1 Hamiltonian Model and Electronic Correlations.......Page 113
4.2.2 Exciton-Vibrational Dynamics and Relaxation......Page 115
4.2.3 Real-Space Analysis......Page 117
4.2.4 Simultion Details.......Page 118
4.3.1 Heat of Formation and Energy Gaps.......Page 123
4.3.2 Cross- and Parallel-Polarized Excitons from the Lowest Band......Page 128
4.3.3 Bright Excitons at Ground and Excited Geometries......Page 138
4.3.4 Photoexcited Vibronic Dynamics: Peierls Distortions......Page 144
4.3.5 Electron-Phonon Coupling: Huang-Rhys Factor, Stokes Shift, and Vibrational Relaxation Energies.......Page 147
4.4 Conclusions......Page 152
5. Carbon Nanotube Technological Implementations......Page 154
Color Index......Page 160
Bibliography......Page 174
Index......Page 198
