SOVLENT REACTIVITY AND INTERFACE EVOLUTION AT MODEL ELECTRODES FOR ENERGY APPLICATIONS

The Li-ion rechargeable battery (LIB) is widely used as an energy storage device, but has significant limitations in battery cycle life and safety. During initial charging, decomposition of the ethylene carbonate (EC)-based electrolytes of the LIB leads to the formation of a passivating layer on the anode known as the solid electrolyte interphase (SEI). The formation of an SEI has great impact on the cycle life and safety of LIB, yet mechanistic aspects of SEI formation are not fully understood. In this dissertation, two surface science model systems have been created under ultra-high vacuum (UHV) to probe the very initial stage of SEI formation at the model carbon anode surfaces of LIB. The first model system, Model System I, is an lithium-carbonate electrolyte/graphite C(0001) system. I have developed a temperature programmed desorption/temperature programmed reaction spectroscopy (TPD/TPRS) instrument as part of my dissertation to study Model System I in quantitative detail. The binding strengths and film growth mechanisms of key electrolyte molecules on model carbon anode surfaces with varying extents of lithiation were measured by TPD. TPRS was further used to track the gases evolved from different reduction products in the early-stage SEI formation. The branching ratio of multiple reaction pathways was quantified for the first time and determined to be 70.% organolithium products vs. 30% inorganic lithium product. The obtained branching ratio provides important information on the distribution of lithium salts that form at the very onset of SEI formation. One of the key reduction products formed from EC in early-stage SEI formation is lithium ethylene dicarbonate (LEDC). Despite intensive studies, the LEDC structure in either the bulk or thin-film (SEI) form is unknown. To enable structural study, pure LEDC was synthesized and subject to synchrotron X-ray diffraction measurements (bulk material) and STM measurements (deposited films). To enable studies of LEDC thin films, Model System II, a lithium ethylene dicarbonate (LEDC)-dimethylformamide (DMF)/Ag(111) system was created by a solution microaerosol deposition technique. Produced films were then imaged by ultra-high vacuum scanning tunneling microscopy (UHV-STM). As a control, the dimethylformamide (DMF)-Ag(111) system was first prepared and its complex 2D phase behavior was mapped out as a function of coverage. The evolution of three distinct monolayer phases of DMF was observed with increasing surface pressure — a 2D gas phase, an ordered DMF phase, and an ordered Ag(DMF)2 complex phase. The addition of LEDC to this mixture, seeded the nucleation of the ordered DMF islands at lower surface pressures (DMF coverages), and was interpreted through nucleation theory. A structural model of the nucleation seed was proposed, and the implication of ionic SEI products, such as LEDC, in early-stage SEI formation was discussed.

Using landscape metrics to predict hydrologic connectivity patterns between forested wetlands and streams in a coastal plain watershed

Geographically isolated wetlands, those entirely surrounded by uplands, provide numerous ecological functions, some of which are dependent on the degree to which they are hydrologically connected to nearby waters. There is a growing need for field-validated, landscape-scale approaches for classifying wetlands based on their expected degree of connectivity with stream networks. During the 2015 water year, flow duration was recorded in non-perennial streams (n = 23) connecting forested wetlands and nearby perennial streams on the Delmarva Peninsula (Maryland, USA). Field and GIS-derived landscape metrics (indicators of catchment, wetland, non-perennial stream, and soil characteristics) were assessed as predictors of wetland-stream connectivity (duration, seasonal onset and offset dates). Connection duration was most strongly correlated with non-perennial stream geomorphology and wetland characteristics. A final GIS-based stepwise regression model (adj-R2 = 0.74, p < 0.0001) described wetland-stream connection duration as a function of catchment area, wetland area and number, and soil available water storage.

Landscape and Architecture: A Balance for Fellowship and Contemplation at Dumbarton Oaks

This thesis will explore ideas relating to the engagement of man and nature by promoting the experiences of contemplation and fellowship. The focus will be an urban academic retreat facility to provide an escape from distraction of typical modern urban life. Set within the historic Washington D.C. neighborhood of Georgetown, Dumbarton Oaks is an active academic research institution The Institute is holistically designed; architecture integrated with its surrounding landscape The Institute selects diverse scholars to think, live, and commune within the facility and landscape for up to two years. This thesis will use the existing site, themes, and history of Dumbarton Oaks as a launching point to explore the relationship between architecture, man, and landscape. A proposal to relocate the Fellow’s residences and reorganize the western edge of the site will help reactivate this forgotten piece of the site realize its potential.

TRADITION AND INNOVATION: ANALYSIS AND PERFORMANCE OF SELECTED COMPOSITIONS FOR VIOLONCELLO BY HEITOR VILLA-LOBOS

Brazilian composer Heitor Villa-Lobos (1887-1959) began his musical career as a cellist. When he was only twelve years old, it became imperativeupon the sudden and untimely death of his fatherthat the young Villa-Lobos earn money as a cellist to provide financial support for his mother and sisters. Villa-Lobos's intimate relationship with the cello eventually inspired him to compose great music for this instrument. This dissertation explores both the diversity of compositional technique and the evolution of style found in the music for cello written by Villa-Lobos. The project consists of two recorded recital performances and a written document exploring and analyzing those pieces. In the study of the music of Villa-Lobos, it is of great interest to consider the music's traditional European elements in combination (or even juxtaposition) with its imaginative and sometimes wildly innovative Brazilian character. His early works were greatly influenced by European Romantic composers such as Robert Schumann, Frédéric Chopin, and the virtuoso cellist/composer David Popper (whom Villa-Lobos idolized). Later, Villa-Lobos flourished in a newfound compositional independence and moved away from Euro-romanticism and toward the folk music of his Brazilian homeland. It is intriguing to experience this transition through an exploration of his cello compositions. The works examined and performed in this dissertation project are chosen from among the extensive number of Villa-Lobos's cello compositions and are his most important works for cello with piano, cello with another instrument, and cello with orchestra. The chosen works demonstrate the evolving range and combination of characteristic elements found in Villa-Lobos's compositional repertoire.