A New efficient and stable 3D Conformal FDTD

A novel conformal technique for the FDTD method, here referred to as Conformal Relaxed Dey-Mittra method, is proposed and assessed in this letter. This technique helps avoid local time-step restrictions caused by irregular cells, thereby im- proving the global stability criterion of the original Dey-Mittra method. The approach retains a second-order spatial convergence. A numerical experiment based on the NASA almond has been chosen to show the improvement in accuracy and computational performance of the proposed method.The work described in this letter and the research leading to these results has received support from the Projects TEC2013- 48414-C3-01 and TEC2015-68766-REDC (MINECO, Spain), P12-TIC-1442 (Junta de Andalucia, Spain), Alhambra-UGRFDTD (AIRBUS DS), and by the CSIRC alhambra.ugr.es supercomputing center

Micrometer-Thin Crystalline-Silicon Solar Cells Integrating Numerically Optimized 2-D Photonic Crystals

A 2-D photonic crystal was integrated experimentally into a thin-film crystalline-silicon solar cell of 1-{\mu}m thickness, after numerical optimization maximizing light absorption in the active material. The photonic crystal boosted the short-circuit current of the cell, but it also damaged its open-circuit voltage and fill factor, which led to an overall decrease in performances. Comparisons between modeled and actual optical behaviors of the cell, and between ideal and actual morphologies, show the global robustness of the nanostructure to experimental deviations, but its particular sensitivity to the conformality of the top coatings and the spread in pattern dimensions, which should not be neglected in the optical model. As for the electrical behavior, the measured internal quantum efficiency shows the strong parasitic absorptions from the transparent conductive oxide and from the back-reflector, as well as the negative impact of the nanopattern on surface passivation. Our exemplifying case, thus, illustrates and experimentally confirms two recommendations for future integration of surface nanostructures for light trapping purposes: 1) the necessity to optimize absorption not for the total stack but for the single active material, and 2) the necessity to avoid damage to the active material by pattern etching.Comment: Authors' postprint version - Editor's pdf published online on Nov.

Parametric Optimization of Visible Wavelength Gold Lattice Geometries for Improved Plasmon-Enhanced Fluorescence Spectroscopy

The exploitation of spectro-plasmonics will allow for innovations in optical instrumentation development and the realization of more efficient optical biodetection components. Biosensors have been shown to improve the overall quality of life through real-time detection of various antibody-antigen reactions, biomarkers, infectious diseases, pathogens, toxins, viruses, etc. has led to increased interest in the research and development of these devices. Further advancements in modern biosensor development will be realized through novel electrochemical, electromechanical, bioelectrical, and/or optical transduction methods aimed at reducing the size, cost, and limit of detection (LOD) of these sensor systems. One such method of optical transduction involves the exploitation of the plasmonic resonance of noble metal nanostructures. This thesis presents the optimization of the electric (E) field enhancement granted from localized surface plasmon resonance (LSPR) via parametric variation of periodic gold lattice geometries using finite difference time domain (FDTD) software. Comprehensive analyses of cylindrical, square, star, and triangular lattice feature geometries were performed to determine the largest surface E-field enhancement resulting from LSPR for reducing the LOD of plasmon-enhanced fluorescence (PEF). The design of an optical transducer engineered to yield peak E-field enhancement and, therefore, peak excitation enhancement of fluorescent labels would enable for improved emission enhancement of these labels. The methodology presented in this thesis details the optimization of plasmonic lattice geometries for improving current visible wavelength fluorescence spectroscopy

Modelling Curved and Non-Aligned Surfaces using the Finite-Difference Time-Domain Method

The finite-difference time-domain (FDTD) method is widely used for computational electromagnetic simulations due to its efficiency and ease of implementation. However, due to its reliance on an orthogonal grid, it is difficult to represent curved and non-aligned planar surfaces. A common method of dealing with this is to use stair-cased meshes that align with the stair-cased grid as close as possible to the surface being meshed. This work explores the errors that arise from using stair-cased meshes of cavities for shielding and scattering problems. It is determined that the increased surface area of a stair-cased mesh alters the transmission and reflection of incident waves. A method of altering the boundary properties is presented to counteract the errors in transmission and reflection. This method is shown to reduce the error in the magnitude of shielding effectiveness (SE) of stair-cased cavities. However, as this method does not change the geometry of the mesh itself, errors in resonant frequency and the presence of spurious resonances is not affected. A second method is proposed to locally deform FDTD cells to conform to a curved or non-aligned planar surface. This method incorporates a thin layer model to vastly increase the efficiency of the algorithm when compared to bulk material alternatives. The method is shown to improve errors in the magnitude of SE, resonant frequency and spurious resonances when compared to stair-cased models

Higher-order particle representation for particle-in-cell simulations

In this paper we present an alternative approach to the representation of simulation particles for unstructured electrostatic and electromagnetic PIC simulations. In our modified PIC algorithm we represent particles as having a smooth shape function limited by some specified finite radius, . A unique feature of our approach is the representation of this shape by surrounding simulation particles with a set of virtual particles with delta shape, with fixed offsets and weights derived from Gaussian quadrature rules and the value of . As the virtual particles are purely computational, they provide the additional benefit of increasing the arithmetic intensity of traditionally memory bound particle kernels. The modified algorithm is implemented within Sandia National Laboratories' unstructured EMPIRE-PIC code, for electrostatic and electromagnetic simulations, using periodic boundary conditions. We show results for a representative set of benchmark problems, including electron orbit, a transverse electromagnetic wave propagating through a plasma, numerical heating, and a plasma slab expansion. Good error reduction across all of the chosen problems is achieved as the particles are made progressively smoother, with the optimal particle radius appearing to be problem-dependent

Broadband solar energy harvesting enabled by micro and nanostructured materials

In der kommenden Ära des "Carbon Peak und der Kohlenstoffneutralität" ist es besonders wichtig, neue Energietechnologien zu entwickeln, die kostengünstig, umweltfreundlich und im industriellem Maßstab herstellbar sind, um die herkömmlichen fossilen Brennstoffe zu ersetzen, die weithin als Verursacher des Treibhauseffekts und häufiger extremer Wetterlagen gelten. Solarenergie ist sozusagen eine unerschöpfliche Energieform, die jedem Land der Erde kostenlos zur Verfügung steht. Daher ist sie im Vergleich zu Kernenergie, Windenergie und blauer Energie die vielversprechendste Alternative zu fossiler Energie. In dieser Arbeit werden breitbandige Materialien zur Gewinnung von Solarenergie als Lichtabsorber für Anwendungen zur Umwandlung von Solarenergie, wie Stromerzeugung, Wasserdampferzeugung und Wasserstofferzeugung, vorgestellt. Zunächst wird schwarzes Silizium (b-Si) mit einer Vielzahl von Mikro-Nanostrukturen durch reaktives Ionenätzen (RIE) hergestellt. Die so hergestellten b-Si-Proben mit ultra-breitbandiger Lichtabsorption können für die photo-thermoelektrische (P-TE) Stromerzeugung, die photothermische (PT) Wasserverdampfung und die photoelektrochemische (PEC) Wasserreduktion verwendet werden, was die Leistung der Solarenergieumwandlung aufgrund ihrer hervorragenden Lichtabsorption im gesamten Sonnenspektrum verbessert. Darüber hinaus wurde eine metastabile Atomlagenabscheidung (MS-ALD) mit Selbstorganisation zur Herstellung großflächiger plasmonischer 3D-Ag@SiO2 Hybrid-Nanostrukturen entwickelt. Diese zeigen auch eine ultrabreitbandige sehr hohe Absorption im gesamten Sonnenspektrum. Wenn sie für die P-TE- und PT-Wasserverdampfung verwendet werden, verbessert sich die Leistung der Solarenergieumwandlung im Vergleich zu b-Si-Proben.In the current era of "Carbon Peak and Carbon Neutrality", it is particularly important to develop low-cost, environmentally-friendly, and industrial-scale energy technologies to replace the traditional fossil fuels, which are widely considered to cause the greenhouse effect and frequent extreme weathers. Solar energy is a kind of energy that lasts forever and is freely available for all countries all over the world. Therefore, it is the most promising alternative to fossil energy compared to nuclear energy, wind energy, and blue energy (Energy that comes from ocean, such as tidal energy, salinity gradient energy). In this work, broadband solar energy harvesting materials are produced and demonstrated to serve as light absorbers for solar energy conversion applications, such as electric power generation, water steam generation and hydrogen generation. Firstly, black silicon (b-Si) with micro-nanostructures is fabricated by reactive ion etching (RIE). The as-prepared b-Si samples with ultra-broadband light absorption can be used for photo-thermoelectric (P-TE) power generation, photothermal (PT) water evaporation and photoelectrochemical (PEC) water reduction, which enhances solar energy conversion performance due to their excellent broadband light absorption. In addition, a metastable atomic layer deposition (MS-ALD) self-assembly strategy for fabricating large area 3D Ag@SiO2 hybrid plasmonic nanostructures was developed. They also demonstrate an ultra-broadband super-high absorption over the whole solar spectrum. When they are further used for P-TE and PT water evaporation, the solar energy conversion performances are improved compared with b-Si samples