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Showing 1 to 20 of 84 for “"bandgaps"”.
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Photoacoustic measurement of bandgaps of thermoelectric materials
… defect states within the bandgap. Furthermore, bandgaps of heavily doped materials are difficult to observe optically, due to significant amounts of carriers in defects states within the bandgap. Conventional optical measurement techniques relying on transmittance change require extremely thin …
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Topology optimization of manufacturable photonic crystals with complete bandgaps
Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2022-04-06 without embargo terms
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Size-binary Zincblende: A Colloidal Approach to Omnidirectional Photonic Bandgaps
… the size and location of complete photonic bandgaps as a function of the structural and materials parameters. We examine both single and binary compositions, in which the dielectric constants of the constituent spheres are equal or unequal, respectively. Bandgap sizes are found up to 31.9% …
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Tunable mechanical bandgaps in elastic metamaterials: Patterning, straining, and spatiotemporal modulation
Metamaterials are novel engineered composites with special microstructural patterns that lead to uncommon macro properties compared to natural material systems. In this work, we first present a novel mechanism for evolving the elastic band gap structure in a bio-inspired composite through tension …
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Theoretical and Experimental Studies of Manipulation of Elastic Waves in Helix Metamaterials
… strategies for low-frequency elastic wave bandgaps remain limited, making large-range tunability within the low-frequency domain difficult. Therefore, widening the low-frequency bandgap, enhancing elastic wave attenuation, and achieving tunable control are critical for the practical …
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Modeling and characterization of elastic wave propagation in micro-scale photonic crystals
… structure. Such devices exhibit elastic bandgaps, which are very useful in many commercial applications. Filtering, guiding and mirroring of elastic waves are a few applications in which phononic crystals can be used. In this manuscript, the physical origins of phononic bandgaps were …
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Development of multifunctional software for evaluating the photonic properties of new dielectric composite geometries
… square array and it was discovered that sizeable bandgaps for 2D and 3D geometries appear along the principle axes for different polarizations of the structure. Furthermore, bandgaps in different directions and polarizations could be made to overlap for reasonably large frequency ranges. The …
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Towards High-Performance Multi-Junction Perovskite Solar Cells: Fabrication, Interlayer Design, and Characterisation
… long carrier diffusion lengths, and tuneable bandgaps, have driven remarkable progress, particularly in the field of photovoltaics. Metal halide perovskites are particularly attractive for multi-junction photovoltaics because their bandgaps can be finely tuned. By stacking materials with …
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Modeling and Characterization of Heterojunction Bipolar Transistors
… in the emitter and base with different bandgaps. These advantages include high current gain, large cut-off frequency and short gate delay in digital logic circuits. This thesis selects a few important and critical issues connected with the operation of HBTs with a view to provide a clear …
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Dynamic plasma photonic crystals: multidimensional electromagnetically active artificial structures in the mm-wave and thz regimes
… manipulate the flow of light, and form photonic bandgaps. As such, photonic crystals are useful in numerous applications that require the precise control of photons including, but not limited to, waveguides, microcavity lasers, sensors, communication systems, and quantum photonics. This thesis …
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Ion Beam Synthesis and Irradiation for Si-Based Photonic Materials and Nuclear Waste Management
… optical materials (group IV alloys) with tunable bandgaps, and for strategies to overcome fabrication challenges. Ion implantation and annealing were used to incorporate Ge and Sn into Si (2.5 – 10 × 10¹⁶ Ge/cm²; 5 ×10¹⁴ – 4 × 10¹⁶ Sn/cm², 0 – 800 °C annealing temperatures), producing …
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THEORY, FABRICATION, AND EXPERIMENTATION OF PHONONIC CRYSTALS IN MEMS AT MICRO/NANO SCALE: ENGINEERING OF THERMAL AND RF PHONONS TO APPLICATIONS IN THERMOELECTRICS AND MICRORESONATORS
… This periodic arrangement creates phononic bandgaps, and modifies phononic bandstructures of a material. Such a property offers promising applications at the micro and nano scales to engineer acoustic filters, high Q-factor resonators, and thermoelectric properties of materials. Studying …
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Synthesis and characterization of metal oxide semiconductors for photoelectrochemical hydrogen production
… mixture ambient, and ZnO:N films with various bandgaps were realized by varying N concentration, which was controlled successfully by varying the RF powers. Nitrogen incorporation narrows the bandgap of ZnO and shifts the optical absorption into the visible-light region. As a result, the ZnO:N …
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High-throughput Bandgap Mapping for Perovskite-inspired Materials
… a novel high-throughput technique to map local bandgaps with pixel-level resolution. This characterization technique utilizes spatially-resolved reflectance spectra and automated data analysis. I collected approximately a million optical bandgap measurements from the compositional space of …
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Analyzing Electronic Correlation Effects in Molecules and Semiconductor Point Defects from First Principles Beyond Density Functional Theory
… electronic and magnetic properties, such as bandgaps in semiconductors or magnetic ordering in defects, to name a few. This dissertation focuses on two areas in which traditional DFT methods are likely to produce inaccurate predictions. The first area is connected to an error that is …
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LARGE AREA 3D PHOTONIC CRYSTALS WITH EMBEDDED WAVEGUIDES
… periodic potentials that are responsible for the bandgaps for electrons and holes. For electrons and holes, the periodic potential effectively determines how the charged particles propagate through the crystal under applied fields. Similarly, for photons in a photonic crystal, the periodic …
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Dynamic Behavior of Sandwich Beams With Internal Resonators
… The effect of resonator parameters on these bandgaps was analyzed and the relationship between the bounding frequencies and the unit cell mode shapes was obtained. The interaction between the local resonance bandgap and the periodicity induced bandgaps was studied. It was shown that a wider …
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Fabrication and photonics properties of III-V semiconductor nanowire structures
… nanowire solar cell devices with different bandgaps were also investigated with a focus on optical absorption. Although traditional conductive oxide materials, such as indium tin oxide (ITO) and aluminum zinc oxide (AZO), have been successfully used in solar cell thin film devices, those …
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Growth and properties of hydrogenated amorphous silicon carbon alloys by DC reactive magnetron sputtering
… (Ar + H$\rm\sb2$ + CH$\sb4).$ Films with optical bandgaps of 1.8-2.0 eV and x $\le$ 0.2 have a compact microstructure; no CH$\rm\sb{x}$ groups are detected by their stretching mode infrared absorption, and small angle X-ray scattering indicates a microvoid volume of $\le$2.5% for x $\le$ 0.3. The …
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Controlling structure and composition in double-heterojunction nanorods for high quantum yield and tunable color
… of lengths from 10 – 50 nm and quantum-confined bandgaps between 2.62 – 2.78 eV. Variously sized CdS seeds are then used to investigate the effects of the rate of Zn-Oleate etching and of the rate and amount of ZnSe growth on DHNR morphology and optical properties. Structure and composition are …
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