Thesis advisor: Dunwei Wang / When their electrodes are made of nanomaterials or materials with nanoscale features, devices for energy conversion and energy storage often exhibit new and improved properties. One of the main challenges in material science, however, is to synthesize these nanomaterials with designed functionality in a predictable way. This thesis presents our successes in synthesizing TiSi₂ nanostructures with various complexities using a chemical vapor deposition (CVD) method. Attention has been given to understanding the chemistry guiding the growth. The governing factor was found to be the surface energy differences between various crystal planes of orthorhombic TiSi₂ (C54 and C49). This understanding has allowed us to control the growth morphologies and to obtain one-dimensional (1D) nanowires, two-dimensional (2D) nanonets and three-dimensional (3D) complexes with rational designs by tuning the chemical reactions between precursors. Among all these morphologies, the 2D nanonet, which is micrometers wide and long but only approximately 15 nm thick, has attracted great interest because it is connected by simple nanostructures with single-crystalline junctions. It offers better mechanical strength and superior charge transport while preserving unique properties associated with the small-dimension nanostructure, which opens up the opportunity to use it for various energy related applications. In this thesis we focus on its applications in lithium ion batteries. With a unique heteronanostructure consisting of 2D TiSi₂ nanonets and active material coating, we demonstrate the performances of both anode and cathode of lithium ion batteries can be highly improved. For anode, Si nanoparticles are deposited as the coating and at a charge/discharge rate of 8400 mA/g, we measure specific capacities >1000 mAh/g with only an average of 0.1% decay per cycle over 100 cycles. For cathode, V₂O₅ is employed as an example. The TiSi₂/V₂O₅ nanostructures exhibit a specific capacityof 350 mAh/g, a power rate up to 14.5 kW/kg, and 78.7% capacity retention after 9800 cycles. In addition, TiSi₂ nanonet itself is found to be a good anode material due to the special layer-structure of C49 crystals. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Darbe atlikta literatūros analizė šių procesų: (i) vykstančių vandens garų plazmoje; (ii) titano dangų oksidacija vandens garų plazmoje ir (iii) titano dioksido fotokatalitinės ir hidrofilinės savybės. TiO2 dangos buvo gautos po titano dangų ekspozicijos H2O garų plazmoje. Tyrimai parodė, kad TiO2 danga vandens garų plazmos aplinkoje formuoja elektrocheminį elementą. Darbe tirtos plazma aktyvuotos vandens skaldymo reakcijos. Parodyta, kad susidarę protonai pernešami per kietą TiO2 elektrolitą, o elektronai migruoja per plazmoje susiformavusią išorinę grandinę. Proceso metu dangos paviršinis sluoksnis formuojasi į TiO2–SiO2 kompozitą. Nors procesai vyksta žemoje temperatūroje, gauti rezultatai parodė masės pernešimo reiškinius, būdingus aukštoms temperatūroms. Pateikti nagrinėtų procesų mechanizmai. Darbo metu bandinių eksperimentinė analizė atlikta elektroninės dispersinės spektroskopijos (EDS), rentgeno spindulių difrakcijos (RSD), Auger elektroninės spektroskopijos (AES), skenuojančio elektroninio mikroskopo (SEM), optinės mikroskopijos ir kontaktinio profilometro metodais. / Processes in water vapor plasma, titania film oxidation in water vapor plasma and titanium dioxide photocatalytic and hydrophilic properties are discussed in this paper. Titatium dioxide thin films were obtained after titanium thin film exposure in water vapor plasma. Specimen together with H2O plasma forms electrochemical cell. In plasma film surface is activated and photocatalytic water splitting reactions occurs. Generated hydrogen ions are transported through solid titanium electrolyte and electrons are conducted to an external circuit via plasma. Titanium dioxide films surfaces are converted into composited composed of TiO2 and SiO2. Although oxidation process occurs in room temperature results showed mass transfer processes which occurs in high temperature. Specimens were analysed by electron dispersion spectroscopy (EDS), (X-ray diffraction (XRD), Auger electron spectroscopy (AES), glow discharge optical emission spectroscopy (GDOES), scanning electron microscopy (SEM), optical microscopy and nanoprofilometer methods.