This study is on thermodynamics of crystalline nanoparticles of materials. It provides measurements of the equilibrium melting point of nanocrystals of zinc in a size distribution of 30 - 120 nm, as observed by using Philips CM 12 TEM and JEOL 2010F TEM/STEM, and of the heat capacity, and melting enthalpy by using Perkin-Elmer Pyris-Diamond and TA Q100 Calorimeters. The observed melting point of zinc nanoparticles is lower than that of the bulk zinc, but their heat capacity increases and enthalpy of melting decreases. During heating, the nanoparticles oxidizes and forms zinc oxide surface layer reducing the amount and size of zinc nanocrystals. Calculations based upon the Debye theory for heat capacity show that the surface atoms on the zinc nanoparticles have ~ 55 % larger vibrational amplitude and therefore increase the entropy of the surface layer over that of the interior of the particles. During cooling, the crystallization of zinc oxide encaged zinc nanodroplets occurs in two stages, which are heterogeneous and homogeneous nucleations. As the amount of zinc nanocrystals decreases and the liquid-zinc oxide interface increases, homogeneous nucleation becomes less dominant and the two-stage crystallization merges. Nano-pharmaceuticals were produced by incorporating them in a nanoporous amorphous polymer matrix by using a technique based on diffusion method. The presence of embedded nano-pharmaceuticals is shown by their lower melting point relative to the bulk pharmaceuticals and by peak-broadening of x-ray diffraction, which shows that their size lies in 70 - 100 nm range. Although no phase inversion between allotropic forms of the pharmaceutical was observed, a sample calculation for polymorphs of tin shows that such phase inversion should occur at a smaller particle size at a lower temperature. In general, these findings show the effects of the increase in the surface energy relative to bulk energy of nanoparticles, and the consequent differences between the properties of their surface atoms relative to the interior atoms. / Thesis / Master of Applied Science (MASc)

Nanostructured ZnO films were obtained via thermal oxidation of thin films formed with metallic Zn-nanoparticle dispersions. Commercial zinc nanoparticles used for this work were characterized by microscopic and thermal analysis methods to analyze the Zn-ZnO core shell structure, surface morphology and oxidation characteristics. These dispersions were spin-coated on SiO₂/Si substrates and then annealed in air between 100 and 600 °C. Significant nanostructural changes were observed for the resulting films, particularly those from larger Zn nanoparticles. These nanostructures, including nanoneedles and nanorods, were likely formed due to fracturing of ZnO outer shell due to differential thermal expansion between the Zn core and the ZnO shell. At temperatures above 227 °C, the metallic Zn has a high vapor pressure leading to high mass transport through these defects. Ultimately the Zn vapor rapidly oxidizes in air to form the ZnO nanostructures. We have found that the resulting films annealed above 400 °C had high electrical resistivity. The zinc nanoparticles were incorporated into zinc indium oxide solution and spin-coated to form thin film transistor (TFT) test structures to evaluate the potential of forming nanostructured field effect sensors using simple solution processing. The functionalization of zinc tin oxide (ZTO) films with self-assembled monolayers (SAMs) of n-hexylphosphonic acid (n-HPA) was investigated. The n-HPA modified ZTO surfaces were characterized using contact angle measurement, x-ray photoelectron spectroscopy (XPS) and electrical measurements. High contact angles were obtained suggesting high surface coverage of n-HPA on the ZTO films, which was also confirmed using XPS. The impact of n-HPA functionalization on the stability of ZTO TFTs was investigated. The n-HPA functionalized ZTO TFTs were either measured directly after drying or after post-annealing at 140 °C for 48 hours in flowing nitrogen. Their electrical characteristics were compared with that of non-functionalized ZTO reference TFTs fabricated using identical conditions. We found that the non-functionalized devices had a significant turn-on voltage (V[subscript ON]) shift of ~0.9 V and ~1.5 V for the non-annealed and the post-annealed conditions under positive gate bias stress for 10,000 seconds. The n-HPA modified devices showed very minimal shift in V[subscript ON] (0.1 V), regardless of post-thermal treatment. The VON instabilities were attributed to the interaction of species from the ambient atmosphere with the exposed ZTO back channel during gate voltage stress. These species can either accept or donate electrons resulting in changes in the channel conductance with respect to the applied stress. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from Jan. 6, 2012 - Jan. 6, 2013