Fabrication and Characterization of Nanoscale Pillar Arrays With Engineered Phononic and Photonic Properties

This dissertation reports the results of the investigation of nanoscale pillar structures with engineered phononic and photonic properties. It has been proven that phonon states in semiconductors can be tuned by external boundaries, either as a result of phonon confinement effects in individual nanostructures or as a result of artificially induced external periodicity, e.g., phononic crystals. The possibility of engineering acoustic phonon spectrum is of ultimate importance from scientific and application perspectives since they are the main heat carriers in nonmagnetic semiconductor and insulator materials. The change in acoustic phonon dispersion would affect the heat transport properties, alter the electron-phonon interactions, and affect the optical properties of the material system. It has been recently suggested that periodic structures with properly tuned dimensions can act simultaneously as phononic and photonic crystals, strongly affecting the light-matter interactions. In this dissertation research, I prepared nanoscale pillar structure samples and investigated their properties. The “pillar with hat” structures were fabricated using electron beam lithography on silicon substrates followed by inductively-coupled plasma cryogenic dry etching. The hats of the pillars were created with a unique design to have exactly the same orientation plane as the substrate. The structures were inspected with scanning electron microscopy. I used Brillouin-Mandelstam spectroscopy to measure the dispersion of acoustic phonons with energies in the range from 2 GHz up to 20 GHz through the entire second and higher order Brillouin zones. I analyzed the spectral signatures resulting from the surface ripple mechanism which dominates the light scattering in these specific samples. I found clear signatures of the phonon spectrum modification in the appearance of localized phonon sub-bands at energies between 2˗20 GHz. The variable angle ellipsometry measurements indicated modification of light scattering due to nanostructuring. The experimental data confirmed the dual functionality of the structure with engineered phononic-photonic properties. The results obtained in this dissertation research have important implications for the next generation of photonic and optoelectronic device technologies

Thermal Properties of the Binary-Filler Composites with Few-Layer Graphene and Copper Nanoparticles

The thermal properties of an epoxy-based binary composites comprised of graphene and copper nanoparticles are reported. It is found that the "synergistic" filler effect, revealed as a strong enhancement of the thermal conductivity of composites with the size-dissimilar fillers, has a well-defined filler loading threshold. The thermal conductivity of composites with a moderate graphene concentration of ~15 wt% exhibits an abrupt increase as the loading of copper nanoparticles approaches ~40 wt%, followed by saturation. The effect is attributed to intercalation of spherical copper nanoparticles between the large graphene flakes, resulting in formation of the highly thermally conductive percolation network. In contrast, in composites with a high graphene concentration, ~40 wt%, the thermal conductivity increases linearly with addition of copper nanoparticles. The electrical percolation is observed at low graphene loading, less than 7 wt.%, owing to the large aspect ratio of graphene. At all concentrations of the fillers, below and above the electrical percolation threshold, the thermal transport is dominated by phonons. The obtained results shed light on the interaction between graphene fillers and copper nanoparticles in the composites and demonstrate potential of such hybrid epoxy composites for practical applications in thermal interface materials and adhesives.Comment: 25 pages, 4 figure

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Fabrication and Characterization of Nanoscale Pillar Arrays With Engineered Phononic and Photonic Properties

This dissertation reports the results of the investigation of nanoscale pillar structures with engineered phononic and photonic properties. It has been proven that phonon states in semiconductors can be tuned by external boundaries, either as a result of phonon confinement effects in individual nanostructures or as a result of artificially induced external periodicity, e.g., phononic crystals. The possibility of engineering acoustic phonon spectrum is of ultimate importance from scientific and application perspectives since they are the main heat carriers in nonmagnetic semiconductor and insulator materials. The change in acoustic phonon dispersion would affect the heat transport properties, alter the electron-phonon interactions, and affect the optical properties of the material system. It has been recently suggested that periodic structures with properly tuned dimensions can act simultaneously as phononic and photonic crystals, strongly affecting the light-matter interactions. In this dissertation research, I prepared nanoscale pillar structure samples and investigated their properties. The “pillar with hat” structures were fabricated using electron beam lithography on silicon substrates followed by inductively-coupled plasma cryogenic dry etching. The hats of the pillars were created with a unique design to have exactly the same orientation plane as the substrate. The structures were inspected with scanning electron microscopy. I used Brillouin-Mandelstam spectroscopy to measure the dispersion of acoustic phonons with energies in the range from 2 GHz up to 20 GHz through the entire second and higher order Brillouin zones. I analyzed the spectral signatures resulting from the surface ripple mechanism which dominates the light scattering in these specific samples. I found clear signatures of the phonon spectrum modification in the appearance of localized phonon sub-bands at energies between 2˗20 GHz. The variable angle ellipsometry measurements indicated modification of light scattering due to nanostructuring. The experimental data confirmed the dual functionality of the structure with engineered phononic-photonic properties. The results obtained in this dissertation research have important implications for the next generation of photonic and optoelectronic device technologies

DUNE Offline Computing Conceptual Design Report

This document describes Offline Software and Computing for the Deep Underground Neutrino Experiment (DUNE) experiment, in particular, the conceptual design of the offline computing needed to accomplish its physics goals. Our emphasis in this document is the development of the computing infrastructure needed to acquire, catalog, reconstruct, simulate and analyze the data from the DUNE experiment and its prototypes. In this effort, we concentrate on developing the tools and systems that facilitate the development and deployment of advanced algorithms. Rather than prescribing particular algorithms, our goal is to provide resources that are flexible and accessible enough to support creative software solutions as HEP computing evolves and to provide computing that achieves the physics goals of the DUNE experiment.This document describes the conceptual design for the Offline Software and Computing for the Deep Underground Neutrino Experiment (DUNE). The goals of the experiment include 1) studying neutrino oscillations using a beam of neutrinos sent from Fermilab in Illinois to the Sanford Underground Research Facility (SURF) in Lead, South Dakota, 2) studying astrophysical neutrino sources and rare processes and 3) understanding the physics of neutrino interactions in matter. We describe the development of the computing infrastructure needed to achieve the physics goals of the experiment by storing, cataloging, reconstructing, simulating, and analyzing $\sim$ 30 PB of data/year from DUNE and its prototypes. Rather than prescribing particular algorithms, our goal is to provide resources that are flexible and accessible enough to support creative software solutions and advanced algorithms as HEP computing evolves. We describe the physics objectives, organization, use cases, and proposed technical solutions

DUNE Offline Computing Conceptual Design Report

This document describes Offline Software and Computing for the Deep Underground Neutrino Experiment (DUNE) experiment, in particular, the conceptual design of the offline computing needed to accomplish its physics goals. Our emphasis in this document is the development of the computing infrastructure needed to acquire, catalog, reconstruct, simulate and analyze the data from the DUNE experiment and its prototypes. In this effort, we concentrate on developing the tools and systems thatfacilitate the development and deployment of advanced algorithms. Rather than prescribing particular algorithms, our goal is to provide resources that are flexible and accessible enough to support creative software solutions as HEP computing evolves and to provide computing that achieves the physics goals of the DUNE experiment

Highly-parallelized simulation of a pixelated LArTPC on a GPU

The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on $10^3$ pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype

Highly-parallelized simulation of a pixelated LArTPC on a GPU

The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on $10^3$ pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype

DUNE Offline Computing Conceptual Design Report

This document describes Offline Software and Computing for the Deep Underground Neutrino Experiment (DUNE) experiment, in particular, the conceptual design of the offline computing needed to accomplish its physics goals. Our emphasis in this document is the development of the computing infrastructure needed to acquire, catalog, reconstruct, simulate and analyze the data from the DUNE experiment and its prototypes. In this effort, we concentrate on developing the tools and systems thatfacilitate the development and deployment of advanced algorithms. Rather than prescribing particular algorithms, our goal is to provide resources that are flexible and accessible enough to support creative software solutions as HEP computing evolves and to provide computing that achieves the physics goals of the DUNE experiment