Chemical-vapor-deposited (CVD) ZnS is an example of a polycrystalline material that is difficult to polish smoothly via the magnetorheological finishing (MRF) technique. When MRF-polished, the internal infrastructure of the material tends to manifest on the surface as millimeter-sized "pebbles," and the surface roughness observed is considerably high. The fluid's parameters important to develop...

Acknowledgements Soli Deo Gloria. The work presented in this thesis has been done during my time as a research staff member at the Otto-von-Guericke-Universität Magdeburg. I am indebted to Prof. Albrecht Bertram, who was the advisor and the first referee of this thesis. He was a guide in finding the topic of the work and finally finishing it. His mentorship by teaching the theoretical foundatio...

We demonstrate the feasibility of polycrystalline nitride semiconductor light-emitting diodes ~LEDs!. Here, polycrystalline LEDs were deposited on quartz substrates, incorporating a layer structure identical to that used for epitaxially grown LEDs. The deposition exhibits a tendency to produce c-oriented crystallites. Violet-blue ~430 nm! operation of a polycrystalline LED is demonstrated, with...

Graphene, a single atomic layer of graphitic carbon, has attracted intense attention because of its extraordinary properties that make it a suitable material for a wide range of technological applications. Large-area graphene films, which are necessary for industrial applications, are typically polycrystalline - that is, composed of single-crystalline grains of varying orientation joined by gra...

Stress-dependent elastic moduli of polycrystalline materials are used in a statistically based model for the scattering of ultrasonic waves from randomly oriented grains that are members of a stressed polycrystal. The stress is assumed to be homogeneous and can be either residual or generated from external loads. The stress-dependent elastic properties are incorporated into the definition of th...

Understanding the grain size-dependent failure behavior of polycrystalline graphene is important for its applications both structurally and functionally. Here we perform molecular dynamics simulations to study the failure behavior of polycrystalline graphene by varying both grain size and distribution. We show that polycrystalline graphene fails in a brittle mode and grain boundary junctions se...

V-VI thermoelectric compounds like Bi2Te3-based alloys are well known for room temperature applications like Peltier coolers or thermogenerators. Their anisotropic physical properties and mechanical weakness are a problem for the manufacturing. To overcome the mechanical problem Spark Plasma Sintering (SPS) was used. 2 inch Wafers of polycrystalline bismuth telluride based n-type and p-type the...