Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Failure Mechanics of Functional Nanostructures in Advanced Technologies(2014) Jia, Zheng; Li, Teng; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The past decade has seen a surge of interest in developing novel functional nanostructures to enable advanced technologies, such as flexible electronics and high performance lithium-ion batteries. Examples of such functional nanostructures include organic/inorganic multi-layer thin films in flexible electronics and nano-sized silicon/tin-based anodes in lithium/sodium ion batteries. Widespread implementation of these advanced technologies with novel functional nanostructures in the future will broadly impact human's daily life. However, grand challenges for developing robust novel functional nanostructures still exist. During operating cycles, these functional nanostructures undergo large deformation and high stresses, which may cause fracture and pulverization of the nanostructures, thereby leading to degradation and mechanical failure of the flexible devices or battery cells. Therefore, enhancing mechanical durability of the novel functional nanostructures in a mechanically demanding environment remains a significant challenge to the nanostructure design. This dissertation aims to shed lights on capturing the characteristics of the failure mechanisms of some novel functional nanostructures by theoretical and computational mechanics approach, The novel functional nanostructures investigated in my thesis includes inorganic/organic multilayer nanostructures, polyimide-supported brittle ITO films, substrate-supported ductile metal films and nanobead/nanowall/nanowire/nanoparticle electrodes in high-performance batteries. More importantly, we also explore possible solutions to effectively enhance the mechanical durability of these functional nanostructures.Item CARBON NANOTUBE THIN FILM AS AN ELECTRONIC MATERIAL(2009) Sangwan, Vinod Kumar; Williams, Ellen D; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon nanotubes (CNT) are potential candidates for next-generation nanoelectronics devices. An individual CNT possesses excellent electrical properties, but it has been extremely challenging to integrate them on a large-scale. Alternatively, CNT thin films have shown great potential as electronic materials in low cost, large area transparent and flexible electronics. The primary focus of this dissertation is patterning, assembling, characterization and assessment of CNT thin films as electronic material. Since a CNT thin film contains both metallic and semiconducting CNTs, it can be used as an active layer as well as an electrode material by controlling the growth density and device geometry. The growth density is controlled by chemical vapor deposition and airbrushing methods. The device geometry is controlled by employing a transfer printing method to assemble CNT thin film transistors (TFT) on plastic substrates. Electrical transport properties of CNT TFTs are characterized by their conductance, transconductance and on/off ratio. Optimized device performance of CNT TFTs is realized by controlling percolation effects in a random network. Transport properties of CNTs are affected by the local environment. To study the intrinsic properties of CNTs, the environmental effects, such as those due to contact with the dielectric layer and processing chemicals, need to be eliminated. A facile fabrication method is used to mass produce as-grown suspended CNTs to study the transport properties of CNTs with minimal effects from the local environment. Transport and low-frequency noise measurements are conducted to probe the intrinsic properties of CNTs. Lastly, the unique contrast mechanism of the photoelectron emission microscopy (PEEM) is used to characterize the electric field effects in a CNT field effect transistor (FET). The voltage contrast mechanism in PEEM is first characterized by comparing measurements with simulations of a model system. Then the voltage contrast is used to probe the local field effects on a single CNT and a CNT thin film. This real-time imaging method is assessed for potential applications in testing of micron sized devices integrated in large scale.