by Siu Wing Hon. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references. / by Siu Wing Hon. / Acknowledgement --- p.i / Abstract --- p.ii / Publication List --- p.iv / Chapter 1 --- Introduction --- p.1 / References --- p.6 / Chapter 2 --- Real-Space Renormalization Group (RG) Theory in Electrical Conduction --- p.9 / Chapter 2.1 --- Scale Invariance --- p.10 / Chapter 2.2 --- Critical Exponents --- p.14 / Chapter 2.3 --- Alternative View-Point of RG Theory --- p.15 / References --- p.18 / Chapter 3 --- "Weakly Nonlinear Composites: Critical Behavior, Flicker Noise and Crossover Behavior" --- p.19 / Chapter 3.1 --- Introduction --- p.19 / Chapter 3.2 --- Formalism --- p.20 / Chapter 3.3 --- Critical Exponents by RG Method --- p.22 / Chapter 3.4 --- Connection to Flicker Noise Problem and Crossover Behavior --- p.25 / Chapter 3.5 --- Discussions and Conclusions --- p.27 / References --- p.28 / Chapter 4 --- Critical Behavior of Strongly Nonlinear Composites --- p.30 / Chapter 4.1 --- Introduction --- p.30 / Chapter 4.2 --- Formalism --- p.31 / Chapter 4.3 --- Applications of RG Theory to Strongly Nonlinear Composites --- p.32 / Chapter 4.4 --- Connections with Links-Nodes-Blobs picture --- p.36 / Chapter 4.5 --- Discussions and Conclusions --- p.39 / References --- p.41 / Chapter 5 --- "Enhanced Nonlinear Response of Superconductor-Normal-conductor Composite Wires, Strips and Rods" --- p.43 / Chapter 5.1 --- Introduction --- p.43 / Chapter 5.2 --- Formalism --- p.45 / Chapter 5.3 --- Linear and Nonlinear Responses of Composite Wires --- p.46 / Chapter 5.4 --- Linear and Nonlinear Response of Composite Strips --- p.49 / Chapter 5.5 --- Linear and Nonlinear Responses of Composite Rods --- p.56 / Chapter 5.6 --- Scaling Behaviors --- p.59 / Chapter 5.7 --- Discussions and Conclusions --- p.63 / References --- p.64 / Chapter 6 --- Renormalized Effective Medium Theory for Weakly Nonlinear Composites --- p.66 / Chapter 6.1 --- Introduction --- p.66 / Chapter 6.2 --- Weakly Nonlinear Conductance Network --- p.69 / Chapter 6.3 --- Simulation --- p.70 / Chapter 6.4 --- Effective Medium Approximation --- p.76 / Chapter 6.5 --- Renormalized Effective Medium Approximation --- p.79 / Chapter 6.6 --- Discussion and Conclusions --- p.81 / References --- p.83 / Chapter 7 --- Conclusions --- p.86 / Chapter A --- Derivation of Voltage-Summation Formulas --- p.88 / Chapter B --- Effective Linear and Nonlinear Response of 2 x 2 cell --- p.92 / Chapter C --- Duality Symmetry in 2D Network --- p.97 / Chapter D --- Derivation of Effective-Medium Approximation --- p.99

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The development of electronics has been growing at a fast rate in recent years. More and more ideas have been searched and are increasing at a faster rate. However, there is more detail work in the nanolevel or nanostructure yet to be understood. Thus, more and more semiconductor physicists have move to the new field of study in nanostructures. Nanostructures are the future of electronic devices. By understanding nanostructure electronic devices, electronics is the key for the progress of any modern equipment and advancement. This comes about when electronic transport of a nanostructure is thoroughly understood. Thus, future electronic devices can utilize the development of conductance through components having dimensions on the nanometer scale.The objective of the proposed research project is to study electronic transport in a ring with an infinite potential barrier at the center and a modulated external potential in one of the arms. The relative phase between the two paths in this structure can be controlled by applying electrostatic potential in one of the arms. One can compare these types of systems with optical interferometers, where the phase difference between the two arms is controlled by changing the refractive index of one arm through the electro-optic effect. By modulating the potential in one arm of the ring, we will study the interference effect on conductance. The method of finding the conductance of a nanostructure will be using the recursive Green's function method. This includes finding transverse eigenvalues, eigenfunctions, and hopping integrals to determine Green's propagators. A FORTRAN 77 computer program is used for numerical calculations.These remarkable ultra-small and ultra-clean quantum systems are currently achieved due to significant technological advancement in fabrication. For ultra-small quantum devices, the theoretical understanding of device performance must be based on quantum carrier transport of confined electrons and holes in the channel. This theoretical research will lead to the understanding of the effects of geometry and impurities on transport of the carriers in the nanochannels. / Department of Physics and Astronomy

The key challenge for a nanomaterial based sensor is how to synthesize in bulk quantity and fabricate an actual device with insightful understanding of operational mechanisms during performance. I report here effective, controllable methods that exploit the concepts of the "green approach" to synthesize two different one-dimensional nanostructures, including tin oxide nanowires and carbon nanotubes. The syntheses are followed by product characterization and sensing device fabrications as well as sensor performance understanding at the molecular level. Sensor-analyte response and recovery kinetics are also presented. The first part of the thesis describes bulk-scale synthesis and characterization of tin oxide nanowires by the molten salt synthetic method and the nanowire doping with antimony (n-types) and lithium. The work builds on the success of using n-doped SnO2 nanoparticles to selectively detect chlorine gas at room temperature. Replacing n-doped nanoparticles with n-doped nanowires reduces the number of inter-particle electron hops between sensing electrodes. The nanowire based sensors show unprecedented 5 ppb detectability of corrosive Cl2 gas concentration in air. At the higher range, 10 ppm of Cl2 gas leads to a 250 fold increase in the device resistance. During sensor recovery, FT-IR studies show that dichlorine monoxide (Cl2O) and chlorine dioxide (ClO2) are the desorbing species. Long term stability of devices is affected by lattice oxygen vacancies replaced by chlorine atoms. Bulk-scale synthesis of multiwall carbon nanotube (MWCNTs) was achieved by a novel inexpensive synthetic method. The green chemistry method uses the non-toxic and easy to handle solid carbon source naphthalene. The synthesis is carried out by simply heating naphthalene and organometallic precursors as catalysts in a sealed glass tube. Synthesis at 610º C leads to MWCNTs of 50 nm diameter and lengths exceeding well over microns. MWCNT doping is attempted with nitrogen (n-type) and boron (p-type) precursors. Palladium nanoparticles decorated on as-synthesized MWCNTs are employed for specific detection of explosive hydrogen gas with concentrations far below the explosive concentration limits. During performance, the sensor exhibits abnormal response behaviors at hydrogen gas concentrations higher than 1%. A model of charge carrier inversion, brought about by reduction of MWCNT by hydrogen molecules dissociated by Pd nanoparticles is proposed.

Wong Yuk Chun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 71-74). / Abstracts in English and Chinese. / Abstract --- p.ii / Acknowledgments --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Motivation --- p.2 / Chapter 1.2 --- The Scope of the Project --- p.2 / Chapter 1.3 --- An Outline of the Thesis --- p.3 / Chapter 2 --- Related Work --- p.5 / Chapter 2.1 --- Percolation Effect --- p.5 / Chapter 2.2 --- Percolation Models --- p.6 / Chapter 2.2.1 --- Site Percolation --- p.6 / Chapter 2.2.2 --- Bond Percolation --- p.8 / Chapter 2.3 --- Simulated Annealing --- p.8 / Chapter 3 --- Electrical Property --- p.11 / Chapter 3.1 --- Electrical Conductivity --- p.11 / Chapter 3.2 --- Physical Model --- p.13 / Chapter 3.3 --- Algorithm --- p.16 / Chapter 3.3.1 --- Simulated Annealing --- p.18 / Chapter 3.3.2 --- Neighborhood Relation and Objective Function --- p.19 / Chapter 3.3.3 --- Configuration Space --- p.21 / Chapter 3.3.4 --- Annealing Schedule --- p.22 / Chapter 3.3.5 --- Expected Time Bound --- p.23 / Chapter 3.4 --- Results --- p.26 / Chapter 3.5 --- Discussion --- p.27 / Chapter 4 --- Thermal Properties --- p.30 / Chapter 4.1 --- Thermal Expansivity --- p.31 / Chapter 4.2 --- Physical Model --- p.32 / Chapter 4.2.1 --- The Physical Properties --- p.32 / Chapter 4.2.2 --- Objective Function and Neighborhood Relation --- p.37 / Chapter 4.3 --- Algorithm --- p.38 / Chapter 4.3.1 --- Parallel Simulated Annealing --- p.39 / Chapter 4.3.2 --- The Physical Annealing Schedule --- p.42 / Chapter 4.4 --- Results --- p.43 / Chapter 4.5 --- Discussion --- p.47 / Chapter 5 --- Scaling Properties --- p.48 / Chapter 5.1 --- Problem Define --- p.49 / Chapter 5.2 --- Physical Model --- p.50 / Chapter 5.2.1 --- The Physical Properties --- p.50 / Chapter 5.2.2 --- Bond Stretching Force --- p.50 / Chapter 5.2.3 --- Objective Function and Configuration Space --- p.51 / Chapter 5.3 --- Algorithm --- p.52 / Chapter 5.3.1 --- Simulated Annealing --- p.52 / Chapter 5.3.2 --- The Conjectural Method --- p.54 / Chapter 5.3.3 --- The Physical Annealing Schedule --- p.56 / Chapter 5.4 --- Results --- p.57 / Chapter 5.4.1 --- Case I --- p.59 / Chapter 5.4.2 --- Case II --- p.60 / Chapter 5.4.3 --- Case III --- p.60 / Chapter 5.5 --- Discussion --- p.61 / Chapter 6 --- Conclusion --- p.62 / Chapter A --- An Example on Studying Electrical Resistivity --- p.64 / Chapter B --- Theory of Elasticity --- p.67 / Chapter C --- Random Number Generator --- p.69 / Bibliography

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Avraham Benatar. / B.S.