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Mechanical behavior and performance of injection molded semi-crystalline polymers.

Description: I have used computer simulations to investigate the behavior of polymeric materials at the molecular level. The simulations were performed using the molecular dynamics method with Lennard-Jones potentials defining the interactions between particles in the system. Significant effort was put into the creation of realistic materials on the computer. For this purpose, an algorithm was developed based on the step-wise polymerization process. The resulting computer-generated materials (CGMs) exhibit several features of real materials, such as molecular weight distribution and presence of chain entanglements. The effect of the addition of a liquid crystalline (LC) phase to the flexible matrix was also studied. The concentration and distribution of the second phase (2P) were found to influence the mechanical and tribological properties of the CGMs. The size of the 2P agglomerates was found to have negligible influence on the properties within the studied range. Moreover, although the 2P reinforcement increases the modulus, it favors crack formation and propagation. Regions of high LC concentration exhibit high probability of becoming part of the crack propagation path. Simulations of the tensile deformation under a uniaxial force have shown that the molecular deformation mechanisms developing in the material depend on several variables, such as the magnitude of the force, the force increase rate, and the level of orientation of the chains. Three-dimensional (3D) graphical visualization tools were developed for representation and analysis of the simulation results. These also present interesting educational possibilities. Computer simulations provide us information which is inaccessible experimentally. From the concomitant use of simulations and experiments, a better understanding of the molecular phenomena that take place during deformation of polymers has been established.
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Date: August 2003
Creator: Simoes, Ricardo J. F.

Study of Gate Electrode Materials on High K Dielectrics

Description: This problem in lieu of thesis report presents a study on gate electrode materials on high K dielectrics, including poly-SiGe and Ru. The stability of poly-SiGe in direct contact with Hf silicon-oxynitride (HfSiON) is studied by rapid thermal annealing (RTA), Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). By performing a series of RTA treatments we found that as RTA thermal budgets reach 1050 C for 30s, the poly-SiGe layer begins to intermix with the HfSiON film, as observed by TEM. The maximum annealing condition for the Hf0.14Si0.23O0.46N0.17 film to remain stable in contact with poly-SiGe is 1050 C for 20s in high purity N2(99.9%) ambient. We also found that after 1000 C annealing for 60s in a nitrogen ambient, the poly-SiGe crystal phase structure was changed from a columnar structure to a large grain structure. For a metal gate, Ru was studied to determine N2annealing effects on sheet resistance of Ru sample electrodes and electrical characterization of Ru/HfSiOx/Si stack. Results show that a pure Ru metal gate is not a good choice for high k materials since it is hard to etch off, and different annealing conditions can cause large changes in the electrical behavior.
Date: August 2003
Creator: Yao, Chun