Browsing by Subject "Interfaces (Physical sciences)"

Now showing 1 - 5 of 5

Dynamical phenomena in multicomponent polymers
(2006) Narayanan, Bharadwaj; Ganesan, Venkat
This research concerns with different aspects of dynamical phenomena in the context of multicomponent polymeric systems. The polymer melts under investigation include polymer blends of varying compositions of two homopolymers (A and B), polymer emulsions of homopolymers blended with block copolymers (AB) and pure block copolymer systems. A novel computation algorithm termed the Self-Consistent Brownian Dynamics (SCBD) was developed and employed to explore the flow effects encountered in the aforementioned polymeric systems. Our contributions in polymer blend systems include, quantification of the slip phenomena at the interface of phase separated symmetric and asymmetric blends. We have also quantified the slip suppression phenomena by the addition of copolymer compatibilizers to the polymer blend interfaces. We have also used the SCBD approach to study the effect of copolymer characteristics on the dynamics of an isolated polymer droplet embedded in a matrix of another polymer. In the case of ternary polymer blend systems, we have studied the flow-induced phase transitions in the microemulsion phases. We provide molecular viewpoint suggesting that the interplay between polymer chain conformations and their flow deformations can lead to novel flow effects upon the phase, structure and rheological behavior of ternary blend systems. In the case of pure copolymer systems, we have studied the effect of oscillatory shear on the lamellar orientation of phase separated multiblock copolymers.
Interface engineering and reliability characteristics of HfO₂ with poly Si gate and dual metal (Ru-Ta alloy, Ru) gate electrode for beyond 65nm technology
(2004) Kim, Young-Hee; Lee, Jack Chung-Yeung
Chip density and performance improvements have been driven by aggressive scaling of semiconductor devices. In both logic and memory applications, SiO2 gate dielectrics has reached its physical limit, direct tunneling resulting from scaling down of dielectrics thickness. Therefore high-k dielectrics have attracted a great deal of attention from industries as the replacement of conventional SiO2 gate dielectrics. So far, lots of candidate materials have been evaluated and Hf-based high-k dielectrics were chosen to the promising materials for gate dielectrics. However, lots of issues were identified and more thorough researches were carried out on Hf-based high-k dielectrics. For instances, mobility degradation, charge trapping, crystallization, Fermi level pinning, interface engineering, and reliability studies. In this research, reliability study of HfO2 were explored with poly gate and dual metal (Ru-Ta alloy, Ru) gate electrode as well as interface engineering. Hard breakdown and soft breakdown were compared and Weibull slope of soft breakdown was smaller than that of hard breakdown, which led to a potential high-k scaling issue. Dynamic reliability has been studied and the combination of trapping and detrapping contributed the enhancement of lifetime projection. Polarity dependence was shown that substrate injection might reduce lifetime projection as well as it increased soft breakdown behavior. Interface tunneling mechanism was suggested with dual metal gate technology. Soft breakdown (1st breakdown) was mainly due to one layer breakdown of bi-layer structure. Low weibull slope was in part attributed to low barrier height of HfO2 compared to interface layer. Interface layer engineering was thoroughly studied in terms of mobility, swing, and short channel effect using deep sub-micron MOSFET devices. In fact, Hf-based high-k dielectrics could be scaled down to below EOT of ~10Å and it successfully achieved the competitive performance goals. However, it is still necessary to understand what is intrinsic we can not change, or what is extrinsic one we can improve.
Interfacial instabilities and the glass transition in polymer thin films
(2006) Besancon, Brian Matthew; Green, Peter F. (Peter Fitzroy); Ganesan, Venkat
Lithography, lubrication and active components in organic electronic devices are diverse applications of polymer thin films. Confinement and interfacial interactions have a profound effect on the properties of thin films and are responsible for behavior that is often counterintuitive and difficult to predict. Phenomena ranging from interfacial instabilities to thickness-dependent properties such as the glass transition (Tg) and viscosity are challenges associated with the design, processing, fabrication and performance of polymer thin films. In this dissertation, we examined three basic problems: the first concerns the morphology of interfacial instabilities, the second is the film thickness dependence of the viscosity, and the third is the thickness dependence of the Tg of thin film polymer-polymer mixtures. Thin liquid films in the nanometer thickness range often succumb to interfacial instabilities leading to break-up and droplet formation. While the destabilization process is well understood, the mechanisms by which the instability proceeds are not. One viii mechanism by which the dewetting process begins is with the formation and subsequent growth of circular holes. We show that fingering instabilities can develop at the periphery of these holes and that the morphology of the instability depends on chain length and the nature of the substrate-polymer interactions. The details of this secondary instability are examined and compared to fingering instabilities observed in macroscopic liquid fronts. A related issue in these systems is that the dynamics can be film thickness dependent. Since the viscosity and capillary forces determine the dynamics of interfacial instabilities, the time dependence of the hole size provides a method to measure the viscosity of the film. We used this approach to examine the influence of carbon nanotubes on the dewetting dynamics and determine the thickness dependence of the viscosity, which was found to depend on the thickness dependent Tg of the system. For the third problem, we examined the thickness dependence of the Tg of miscible thin film polymer-polymer mixtures. Using incoherent neutron scattering, and ellipsometry, we showed that effects associated with chain connectivity and dynamics of the individual blend components, together with interfacial interactions, determine the effective Tg of miscible polymer-polymer thin film mixtures
Polymer behavior under the influence of interfacial interactions
(2008-05) Kropka, Jamie Michael, 1976-; Green, Peter F. (Peter Fitzroy); Ganesan, Venkat
The properties of polymers, thin films or bulk, are profoundly influenced by interactions at interfaces with dissimilar materials. Thin, supported, polymer films are subject to interfacial instabilities, due largely to competing intermolecular forces, that cause them to rupture and dewet the substrate. The addition of nanoparticles (such as clay sheets, metallic or semiconductor nanocrystals, carbon nanotubes, etc.) to polymers can substantially affect bulk properties, such as the glass transition and viscosity, and influence the processability of the material. In this dissertation, we contribute to a fundamental understanding of the role of interfacial interactions on both the instabilities exhibited by polymer thin films and the properties displayed by polymer-nanoparticle mixtures. While conditions under which the destabilization of compositionally homogeneous thin films occurs are relatively well understood, the mechanisms of film stabilization in many two-component thin film systems are still unresolved. We demonstrate that the addition of a miscible component to an unstable film can provide an effective means of stabilization. The details of the stabilization mechanism are understood in terms of the compositional dependence of both the macroscopic wetting parameters and the effective interface potential for the system. We find that the suppression of dewetting in the system is not an equilibrium stabilization process and propose a mechanism by which the increased resistance to dewetting may occur. There is also significant interest in understanding the extraordinary property enhancement of polymers that are enabled by the addition of only small concentrations of nanoparticles. If these effects could be distilled down to a few simple rules, they could be exploited in the design of materials for specific applications. In this work, the influence of C60 nanoparticles on the bulk dynamical properties of three polymers is examined. Based on the findings from a range of measurement techniques, including differential scanning calorimetry, dynamic mechanical analysis, dynamic rheology and neutron scattering, we propose that the changes in the glass transition temperature for the polymer-C₆₀ mixtures can be understood in terms of a percolation interpretation of the glass transition. The proposed mechanism is also characterized computationally.
Transient charging processes at liquid-solid and vacuum-solid interfaces
(2006) Kenney, Jason Andrew; Hwang, Gyeong
The behavior of transient charging processes at interfaces has become increasingly important in the manufacture of materials on the micron-scale and below. Herein, the modeling and simulation of processes occurring at liquid-solid and vacuum-solid interfaces are considered. For the liquid-solid interface, an electrochemical machining system is modeled using equivalent circuits. Comparisons are then made between experimental and model results for transient current response and machining resolution. Predictions are given regarding the use of complex electrode shapes. For the vacuum-solid interface, surface charging of dielectric under plasma bombardment is considered. A high aspect ratio structure with varying absolute dimension is used with a bimodal ion energy distribution, and the resulting fluxes and energies of ions investigated.