Browsing by Author "John F. Muth, Committee Member"

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    Carbon Black Filled Electrospun Fiberweb: Electrical and Mechanical Properties
    (2007-08-22) Hwang, Jee Sang; John F. Muth, Committee Member; C. Maurice Balik, Committee Member; Tushar K. Ghosh, Committee Chair; Richard Kotek, Committee Co-Chair
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    Circuit and Integration Technologies for Molecular Electronics
    (2005-06-07) Nackashi, David Peter; John F. Muth, Committee Member; Veena Misra, Committee Member; Paul D. Franzon, Committee Chair; Gregory N. Parsons, Committee Member
    Methods for fabricating a 2D array of gold nanoparticles were investigated for the purpose of creating a cross-linked molecular network. A controllable process for quickly and easily depositing and patterning regions of gold nanoparticles was developed. This process involves first patterning gold electrodes used for electrical measurement on the wafers. Regions are then defined in photoresist where the dense gold nanoparticles are desired. Finally, the nanoparticles are deposited using a short evaporation, resulting in island formation through the Volmer-Weber growth mechanism. The resist is then stripped in a process known as liftoff, and the result is a wafer-scale substrate with well-defined regions for molecular interconnect. Before assembly, these structures conduct less than 110pA of current at submicron electrode gap distances, and often less than 20pA. As determined from SEM image analysis, it is possible to quickly and easily deposit and pattern regions on silicon dioxide containing over 4,100 per um2, each with an average area of approximately 80nm2. The number of particles, average area and fill density can be controlled to allow for a number of applications and at a variety of scales. The smaller, more numerous particles integrate into sub-500nm gaps, and the larger, meandering lines integrate into micron-scale structures.
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    Directed Assembly and Manipulation of Anisotropic Colloidal Particles by External Fields
    (2010-01-12) Gangwal, Sumit; Gregory N. Parsons, Committee Member; John F. Muth, Committee Member; Saad A. Khan, Committee Member; Orlin D. Velev, Committee Chair
    The application of external fields to anisotropic particles can be an efficient means of programmed assembly of novel materials and is a rapidly expanding research field. We report a series of studies on the assembly and manipulation of surface patterned anisotropic colloidal particles (whose surfaces are physically or chemically different) by external alternating current (AC) electric and magnetic fields. The fundamental results include the first experimental observation of induced-charge electrophoretic (ICEP) motion of asymmetric metallodielectric microspheres and the formation of novel assembled structures of these particles by dielectrophoresis (particle interaction with external AC electric ﬠeld gradients) and by magnetophoresis (migration and interaction of particles in an inhomogeneous magnetic field). The experimental and modeling techniques developed and fundamental principles uncovered could be used to engineer the processes of directed and/or programmed assembly of other types of anisotropic particles. “Janus†particles were prepared by coating dielectric, polystyrene latex microspheres with a conductive metal layer on one hemisphere. The phase space for AC electric field intensity and frequency was explored for these particles on a glass surface between two electrodes. A rich variety of metallodielectric structures and dynamics were uncovered, which are very different from those obtained from directed dielectrophoretic assembly of plain dielectric or plain conductive particles. The application of low frequency AC ﬠelds to aqueous suspensions of the Janus particles leads to unbalanced liquid flows around each half of the particle causing nonlinear, ICEP particle motion (perpendicular to the ﬠeld direction). Above 10 kHz field frequency, the metallodielectric particles assemble into new types of chain structures, where the metallized halves of neighboring particles align into lanes along the ﬠeld direction. These staggered chains were confined together to form two-dimensional metallodielectric crystals. The experimental results of the orientation of Janus particles in the electric field and the formation of staggered chains were interpreted by means of numerical simulations of the electric energy of the system. The assembly of Janus metallodielectric particles may ﬠnd applications in liquid-borne microcircuits and materials with directional electric and heat transfer. The electrokinetic motion of the particles may ﬠnd applications in microactuators and microfluidic devices. The assembly of magnetic Janus colloids (having 50% surface coating of iron on polystyrene microspheres) under the combined (and sometimes competing) dielectrophoretic and magnetophoretic forces was investigated. The structures formed by magnetic fields have the advantage that the particle interactions are bistable. They can result in permanent structures, which could be disassembled on demand by remote demagnetization and then reassembled into new stable structures, thus recycling the building blocks. The assembly of magnetic anisotropic particles may find numerous potential applications, among which are bifunctional drug delivery agents and novel flexible displays. We found that even more unusual types of new structures are formed when high frequency (> 50 kHz) AC electric fields are applied to suspensions of “patchy†particles. The microspheres, produced by glancing angle metal deposition, have either a single patch that is less than 50% of the total latex particle surface or two metallic patches on each pole of the particle. These patchy particles assemble in electric fields by interacting with each other in two or more directions, pre-programmed by the patch size and orientation. The multi-directional chains were confined together to form a percolated network of particles and lattices of unusual symmetry. Simulation results indicate that the assembly pattern of these particles into multi-directional chains is guided by quadrupolar and multipolar interactions, which allow for the future development of new strategies for highly controlled “programmed†assembly by external fields.
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    GaN MOSFETs for Low Power Giga Scale LSI Logic
    (2007-07-07) Zeng, Chang; Doug W. Barlage, Committee Chair; John F. Muth, Committee Member; Mark Johnson, Committee Member; Leda Lunardi, Committee Member; Robert M kolbas, Committee Member
    Advances in material quality and device processing have led to promising results for III-nitride electronic devices for high frequency applications. Numerous groups have report that GaN metal semiconductor field effect transistors (MESFETs) exhibit excellent device characteristics. However, a major concern of such devices is the leakage from the Schottky gate. As an alternative, the use of an insulated gate metal oxide semiconductor (MOS) structure reduces both gate leakage and power consumption. As described in this work, there are more potential advantages than reduced leakage by adopting a MOS structure in the III-N system. The scalability of this prototype device is shown with simulation to have the potential to support gate lengths below 10nm. In this Dissertation, methods to demonstrate a unique GaN based NMOS devices with minimum gate length of 0.7μm are described. Significant progress has been made on this challenging problem. The goal of this research is to introduce the processing methods and structures that will be suitable as a test vehicle for evaluating material interfaces in the GaN-Ga2O3-gate dielectric system. One of the aspects of this work is that a multi-wafer sapphire to device process time is less than one month. That enables the capacity to evaluate novel deposition schemes through electrical measurements in a timely manor. Furthermore, the process described here integrates re-grown GaN contacts. The pursuit of this is to allow maximum dopant incorporation and maximum abruptness in the source drain region to maximize the transistor's cut off frequency performance as well as the critical Ion performance. This process flow is also established as way to study hetero-geneous source drain properties. A method to analyze the n-i-n structure is presented in some detail. This n-i-n structure, along with the gate oxide, is the secondary key component to demonstrating a GaN MOS transistor with competitive performance properties for digital and RF applications. Of significance is the ability to fabricate a MOS device centered around the re-growth of N-type III-N material on intrinsically doped GaN. This method is directly related to the overall research goal to achieve a compound semiconductor MOSFET suitable for scaling below 10nm. This initial challenge of establishing a suitable experimentation vehicle has been met by the work described in this thesis. The intention of this work is to provide the experimental framework for the exploration of a variety of materials required to synthesize a complimentary GaN MOS system suitable for scaling to dimensions below 10nm.
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    Modeling and Measurement of the Differential Resistance and Ideality Factors in Heterostructure Light Emitting Diodes and Laser Diodes
    (2008-07-24) Li, Xiangming; Mark A. L. Johnson, Committee Member; Doug W. Barlage, Committee Member; Robert M. Kolbas, Committee Chair; John F. Muth, Committee Member
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    A Study on the Feasibility of Electron-based Accelerator Driven Systems for Nuclear Waste Transmutation
    (2006-08-07) Liu, Yaxi; David McNelis, Committee Co-Chair; Man-sung Yim, Committee Chair; Mohamed A. Bourham, Committee Member; John F. Muth, Committee Member
    Nuclear waste transmutation is an important option for the development of advanced fuel cycle and effective nuclear waste management. The electron accelerator driven system (ADS) was investigated in the study for nuclear waste transmutation as an alternative to proton based ADS. Target design and optimization was carried out to obtain maximum neutron generation. Subcritical core design based on single and multiple targets was investigated. System performance between electron-based ADS and proton-based ADS was compared in terms of neutron generation rate, transmutation efficiency and power generation. It was determined that the electron-based target was capable of providing high neutron flux, small target geometry size, small scale subcritical core, and low radiation damage. Multiple target design in the electron-driven ADS was also explored to flatten power distribution in the ADS subcritical core. Regarding transmutation, the power peaking factors in both the electron- and proton- ADS increase ~ 10% during the burnup period of 700 days. Thermal power in proton ADS is higher than that of electron ADS by a factor ~ 20. The transmutation effectiveness of preliminary electron-based ADS is smaller by a factor of 11 compared to preliminary proton-based ADS. Proton ADS has higher radiation damage to target materials and surrounding materials. The capital cost for electron-based and proton-based accelerator facility is fairly comparable with the cost of proton-based facilities being slightly higher by a factor of 20%. Comparing with the proton-driven ADS, the electron-driven ADS pros include small target size and small core scale, multiple target possibility for low PPF, low radiation damage to target surroundings, wide availability electron beam at ~100 MeV, and low capital cost of electron accelerator facility. There are also aspects against electron-driven ADS, including low efficiency of neutron generation rate, low transmutation efficiency, low thermal power, and electricity generation.