Browsing by Author "Owuor, Peter Samora"

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    High-K dielectric sulfur-selenium alloys
    (AAAS, 2019) Susarla, Sandhya; Tsafack, Thierry; Owuor, Peter Samora; Puthirath, Anand B.; Hachtel, Jordan A.; Babu, Ganguli; Apte, Amey; Jawdat, BenMaan I.; Hilario, Martin S.; Lerma, Albert; Calderon, Hector A.; Hernandez, Francisco C. Robles; Tam, David W.; Li, Tong; Lupini, Andrew R.; Idrobo, Juan Carlos; Lou, Jun; Wei, Bingqing; Dai, Pengcheng; Tiwary, Chandra Sekhar; Ajayan, Pulickel M.
    Upcoming advancements in flexible technology require mechanically compliant dielectric materials. Current dielectrics have either high dielectric constant, K (e.g., metal oxides) or good flexibility (e.g., polymers). Here, we achieve a golden mean of these properties and obtain a lightweight, viscoelastic, high-K dielectric material by combining two nonpolar, brittle constituents, namely, sulfur (S) and selenium (Se). This S-Se alloy retains polymer-like mechanical flexibility along with a dielectric strength (40 kV/mm) and a high dielectric constant (K = 74 at 1 MHz) similar to those of established metal oxides. Our theoretical model suggests that the principal reason is the strong dipole moment generated due to the unique structural orientation between S and Se atoms. The S-Se alloys can bridge the chasm between mechanically soft and high-K dielectric materials toward several flexible device applications.
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    Interface Driven and Bio-mimetic Design of 3D Hybrid Materials
    (2018-10-19) Owuor, Peter Samora; Ajayan, Pulickel M.; Lou, Jun
    The discovery of Graphene, carbon nanotubes and subsequent other nano-materials led to an explosion in research geared towards utilizing their intriguing mechanical, physical and chemical properties. While the physical properties of nanomaterials have been extensively explored, the assembly in a bottom-up approach to design hybrid 3D nanostructures by taking advantage of their interfacial properties still needs a deeper inquiry. This thesis scope is to answer four key questions;  What role does the interfacial region plays in macro-scale materials properties?  Is the same effect of interfacial region at macro-scale applies to the nano-scale materials?  Is there a means to modify the interface region to assemble 3D hybrid structures?  What are the resulting applications of such design in materials? To address the aforementioned questions, novel synthetic and biomimetic strategies were employed. The first detour of the thesis delves into the chemical process where functionalization and freeze-drying methods are used to fabricate porous carbon nanotubes (CNT) with self-stiffening behavior. The chemical approach is then applied to zero-dimensional SiO2 nanoparticles to fabricate three-dimensional nanostructures with improved fire-retardant capability. Next, the thesis explores the physical methods in assembling 3D structures where graphene oxide foam is chemically and physically reinforced with polymer molecule to fabricate an oil absorption and electrical resistant foam. The thesis further develops a new method to functionalize hexagonal boron nitride (h-BN) to enable their networking forming property resulting in high porous foam for CO2 absorption. The above solutions all relates to what is referred to as ‘hard interface’ therefore there was a need to explore ‘mobile interface’ like those found in nature. In this regard, a new area of study was developed; solid-liquid composite in macro-scale materials. Here, the thesis presents two new approaches; high damping composite by addition of liquid metal in a polymer matrix and optical and stiffness switching of a phase change composite. Finally, the thesis attempts to combine the two interfaces in hybrid materials. The most important contribution of this thesis is the new techniques which can be used to design advanced composites. Furthermore, a new subset of solid-liquid composites which have never been looked at in terms of mechanical properties is brought-forth. Finally, the peer-reviewed papers published should form a basis for future scientists with plans to pursue this field.